Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE China: A record of Late Mesozoic intraplate deformation in East Asia

Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE China: A record of Late Mesozoic intraplate deformation in East Asia

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Journal Pre-proof Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE China: A record of Late Mesozoic intraplate deformation in East Asia Zhi-Xin Guo, Yong-Tai Yang, Xian-Zheng Zhao, Wei-Ning Dan, Xin Wang, Lan Du PII:

S0264-8172(19)30353-8

DOI:

https://doi.org/10.1016/j.marpetgeo.2019.07.043

Reference:

JMPG 3962

To appear in:

Marine and Petroleum Geology

Received Date: 26 January 2019 Revised Date:

3 July 2019

Accepted Date: 27 July 2019

Please cite this article as: Guo, Z.-X., Yang, Y.-T., Zhao, X.-Z., Dan, W.-N., Wang, X., Du, L., Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE China: A record of Late Mesozoic intraplate deformation in East Asia, Marine and Petroleum Geology (2019), doi: https://doi.org/10.1016/ j.marpetgeo.2019.07.043. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Ind oc hin a

Collision of WPM with South China occurred during the late Early Cretaceous

(Guo et al., 2018b) (maximum age of sandstone)

Seismic surface

Lithology

Contraction

Extension

Aer24

Upper Tenggeer Formation

T3

Contraction

Extension

K 1 au

H37 H12 Tai14 (Sun et al., 2017)

J46 J31-1

Contraction

Extension

J74 HC1-1

J42-7 Ha35-2 HC1-2

A18-11 (Aershan Fm.; Guo et al., 2018a) H17-2 J55 H40-1 J45 J13-1 H33 HC1-3 J33

Lower Tenggeer Formation

T6

K 1 al

Bayanhua Group

J19 J9

140

gtang

ora BNT In m-L Z a nd u s - Y gbo arlu has Te t n g a hys

Aptian Valanginian

Okhotomorsk M

Qian rak

Evolution

T2

T8 Contraction Extension T10 Contraction Extension T11

s s s

lt

South China

Songpan-Ganzi

Ka

130

Qilian-Qaidam

Tarim

WP

Turan

Collision of Okhotomorsk with East Asian margin occurred at ca. 100 Ma

Ta nl u F au

North China

Zircon U-Pb ages provided by this and former studies

Saihan Formation

110

South Korea

Hauterivian Barremian

North Korea

Aershan Fm.

B

Berriasian

lian

Eer

asin

120

Mongolia

s ia Rus a C h in

Amuria

Central Asian Orogenic Belt

Early Cretaceous

Kazakhstan

Iza na gi

Closure of the eastern MongolOkhotsk Ocean occurred during the latest Jurassicearliest Cretaceous

Russia

Albian

Collision of Kolyma-Omolon with Siberia occurred during ca. 155-135 Ma

Mongol-Okhotsk Ocean

Strata

Hugejiletu Fm.

Siberia

Geologic Time (Ma)

Chukotka Collision of Chukotka with KolymaK Omolon occurred during the latest Barremian-early Aptian (ca. 126O mo l y m o l o a - 120 Ma) n

Earliest Cretaceous

Contraction

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Early Cretaceous tectonostratigraphic evolution of the Erlian Basin, NE

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China: A record of Late Mesozoic intraplate deformation in East Asia

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Zhi-Xin Guoa, Yong-Tai Yanga, *, Xian-Zheng Zhaob, Wei-Ning Danc, Xin Wangc, Lan Duc

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a

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Sciences, University of Science and Technology of China, Hefei, China.

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b

PetroChina Dagang Oilfield Company, Tianjin, China

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c

PetroChina Huabei Oilfield Company, Renqiu, China

*

Corresponding author: Yong-Tai Yang

CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space

10 11 12

Corresponding author Email: [email protected]

13

Postal address: School of Earth and Space Sciences, University of Science and Technology of

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China, NO. 96 Jinzhai Road, Hefei, Anhui Province, P. R. China.

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1

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Abstract

The Erlian Basin is one of the largest intracontinental Meso-Cenozoic basins in Northeast

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China. The basin is filled with extra-thick Cretaceous sediments and offers unique opportunities

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to untangle the Late Mesozoic intraplate deformation in East Asia. However, despite decades of

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petroleum exploration in the basin, the Early Cretaceous chronostratigraphy and structural

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evolution of the Erlian Basin have been poorly studied. Based on newly obtained zircon U-Pb

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geochronological data, well lithological logs, and seismic reflection profiles, the present study

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carries out a detailed analysis of the tectonostratigraphic evolution of the Erlian Basin during the

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Early Cretaceous. The depositional ages of the Lower Cretaceous strata in the basin are refined,

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and the Early Cretaceous evolution of the basin is reestablished. The Lower Aershan, Upper

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Aershan, Lower Tenggeer, Upper Tenggeer, and Saihan formations are constrained to the middle

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Valanginian (ca. 138–135 Ma), late Valanginian (ca. 135–133 Ma), Hauterivian–early Aptian (ca.

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133–121 Ma), middle Aptian (ca. 119–115 Ma), and latest Aptian–Albian (post ca. 115 Ma),

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respectively. The Early Cretaceous syn-rift subsidence of the basin was intermittent rather than

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continuous, and was punctuated by multiphase contractional deformation during the earliest

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Cretaceous (prior to ca. 138 Ma), middle Valanginian (ca. 135 Ma), latest Valanginian (ca. 133

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Ma), middle Aptian (ca. 120 Ma), late Aptian (ca. 115 Ma), and Early/Late Cretaceous boundary.

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We tentatively attribute the extensional and contractional deformation in the Erlian Basin to a

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series of continental collisions along Asian margins: Karakoram-Lhasa/Qiangtang collision,

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Kolyma-Omolon/Siberia collision, Siberia/Amuria collision, Chukotka/Kolyma-Omolon

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collision, West Philippines/South China collision, and Okhotomorsk/East Asia collision.

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Keywords

Erlian Basin; Northeast China; Early Cretaceous; U-Pb zircon chronostratigraphy; intraplate

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deformation; continental collision

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1 Introduction

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Numerous Late Mesozoic intracontinental petroliferous basins are distributed in Northeast

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China, East Mongolia and Southeast Russia (Graham et al., 2001; Meng et al., 2003; Zhang et al.,

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2017) (Fig. 1a–b). The Erlian Basin, located in the Inner Mongolia, Northeast China, with the

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Songliao Basin to the east, the Hailar-Tamsag Basin to the northeast, and the East Gobi Basin to

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the northwest, is one of the largest, covering a total area of ca. 109,000 km2 (Li and Lyu, 2002)

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(Fig. 1b–c). The basin is filled with 5-km-thick Jurassic–Cretaceous fluvio-lacustrine clastic

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rocks underlain by the Paleozoic metamorphosed basement, and is highly prospective for

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hydrocarbons (Gou et al., 1986; Lin et al., 2001; Guo et al., 2018a, b) (Fig. 2). Petroleum

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exploration and production have been active in the basin since the late 1950s (PGGHO, 1988; Li

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and Lyu, 2002; Chen et al., 2014). To date, 15 oil fields have been ascertained in the Erlian

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Basin, with annual oil production up to 8 million tons and proven oil reserves up to 240 million

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tons (Zhu et al., 2018).

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Despite decades of petroleum exploration, the depositional ages of the Lower Cretaceous

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strata in the Erlian Basin have remained poorly constrained. Customarily, the depositional ages

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of the Meso-Cenozoic strata in the basin are estimated on the ground of terrestrial fossil

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assemblages (such as charophytes, ostracods, spores, pollen, and bivalves) and stratigraphic

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correlations among the Erlian Basin, the Great Xing'an Range, the Songliao Basin, and the Yan

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Shan (Xu et al., 2003; Tao et al., 2013) (Figs. 1 and 2). Recently acquired isotope ages of the 3

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Late Mesozoic strata in the Great Xing'an Range, the Songliao Basin and the Yan Shan deviate

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from the generally accepted fossil-based ages (Chang et al., 2009; Zhang et al., 2008a, 2010;

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Huang et al., 2011; Xu et al., 2013; Wang et al., 2015), indicating that the fossil-based ages of

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the Late Mesozoic strata in Northeast China are questionable. The depositional ages of the

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Jurassic and Upper Cretaceous lithostratigraphic units of the Erlian Basin have been revised

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based on new zircon U-Pb ages obtained by our recent studies (Guo et al., 2018a, b) (Fig. 2).

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However, to date, strict constraints on the depositional ages of the Lower Cretaceous strata in the

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Erlian Basin have still been absent.

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Generally, the Jurassic–Cretaceous evolution of the Erlian Basin is divided into three

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episodes, including two episodes of syn-rift subsidence during the deposition of the Aqitu–

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Hugejiletu formations and during the deposition of the Aershan–Tenggeer formations, and one

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later episode of post-rift thermal subsidence during the deposition of the Saihan–Erlian

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formations (Lin et al., 2001; Chen et al., 2014) (Fig. 2). Recently, based on the analysis of

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seismic reflection profiles in the Erlian Basin, a series of Jurassic and Late Cretaceous

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contractional events have been recognized, suggesting that the extension and syn-rift subsidence

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in the basin during the Jurassic and Late Cretaceous, was intermittent rather than continuous

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(Guo et al., 2018a, b) (Fig. 2). However, so far, tectonostratigraphic evolution of the Erlian Basin

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during the Early Cretaceous has still remained speculative (Lin et al., 2001; Chen et al., 2014)

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(Fig. 2).

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The poor chronostratigraphic and structural constraints on the Early Cretaceous evolution of

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the Erlian Basin, have seriously hindered the understanding of the tectonic evolution of East Asia

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during the Late Mesozoic. It has long been suggested that a monotonous extension episode

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prevailed in Northeast China, East Mongolia, and Southeast Russia throughout the late Late

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Jurassic–Early Cretaceous (e.g., Graham et al., 2001, 2012; Johnson et al., 2001, 2004; Ren et al.,

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2002; Meng, 2003; Wang et al., 2011; Xu et al., 2013). The remarkable extension episode has

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been generally attributed to the subduction of the Paleo-Pacific Plate beneath the eastern

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Eurasian continent (e.g., Watson et al., 1987; Ren et al., 2002; Wu et al., 2011; Zhu et al., 2012,

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2017). However, this generally accepted assertion was questioned by recent reassessments of

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stratigraphic evolution of sedimentary basins and mountain belts in East Asia (e.g., Erlian Basin,

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Yan Shan, Hailar-Tamsag Basin, Mohe Basin, Songliao Basin, and Sanjiang-Middle Amur Basin

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in Fig. 1; Davis et al., 1998, 2001; Darby et al., 2001, 2007; Yang et al., 2015a; Guo et al., 2017,

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2018a and references therein), which argued that the Late Mesozoic extension in East Asia was

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punctuated by a significant contractional event during the latest Jurassic–earliest Cretaceous.

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Yang et al. (2015a) proposed that the latest Jurassic–earliest Cretaceous compressional event

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resulted from the closure of the eastern Mongol-Okhotsk Ocean along the Mongol-Okhotsk

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Suture (Fig. 1b), and the extensional regime in East Asia during the Early Cretaceous was

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induced by the postorogenic gravitational collapse. To further untangle the tectonic evolution of

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East Asia during the Early Cretaceous, a deep understanding of the Early Cretaceous

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tectonostratigraphic evolution of these intracontinental basins is imperative.

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Furthermore, an investigation of the tectonostratigraphic evolution of the Erlian Basin

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during the Early Cretaceous is critical to the assessment of undiscovered petroleum potential in

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the Erlian Basin. The Erlian Basin contains more than 50 NE-SW striking sags (sub-basins),

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which are separated by intrabasinal highlands (Lin et al., 2001; Qi et al., 2015) (Fig. 1c). So far,

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only a dozen of these sags have been well explored by means of seismic reflection surveys and

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cored boreholes. Outlining the tectonostratigraphic evolution of typical sags in the Erlian Basin

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is beneficial for establishing the stratigraphic and structural correlation among different sags, and

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predicting source rocks, reservoirs, and favorable traps within sags with a low degree of

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prospecting.

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The present study provides a detailed analysis of the tectonosedimentary evolution of the

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Erlian Basin during the Early Cretaceous, using new zircon U-Pb ages of intercalated volcanic

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rocks, well lithological logs, and seismic reflection profiles. Afterwards, potential drivers of the

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Early Cretaceous intraplate compressional and extensional deformation in the Erlian Basin are

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discussed.

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2 Material and method

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2.1 Seismic and well data

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Seismic reflection profiles and related well data were utilized to investigate the subsurface

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structure and stratigraphy of the Erlian Basin (Figs. 3–12). A total of 14 seismic reflection

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profiles were used in the present study (Figs. 3f–h, 5f–h, 7f–g, 9d–e, 11b–d, and 12c). Among

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them, the Fig. 5f was modified after Guo et al. (2018a), the Fig. 5h was modified after Guo et al.

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(2018a, b), the Fig. 9d was modified after Sun et al. (2017), and the other 11 were newly

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provided by the PetroChina Huabei Oilfield Company and had not been published before. A total

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of 28 wells were used (Figs. 4, 6, 8, 10, and 12b). Among them, the well A18 and Liancan1 were

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modified after Guo et al. (2018a), the well Tai28, Tai26 and Taican2 were modified after Sun et

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al. (2017), and the other 23 were obtained from unpublished reports of the PetroChina Huabei

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Oilfield Company.

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2.2 Zircon U-Pb dating

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Twenty core samples of volcanic and volcaniclastic rocks from the Lower Aershan, Upper

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Aershan, Lower Tenggeer, and Upper Tenggeer formations, were collected from eighteen wells

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(Figs. 4, 6, 8, and 12b) for zircon U-Pb dating. Details of the collected samples are presented in

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Table 1. Single zircon crystals, extracted from the collected volcanic and volcanoclastic rock

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samples, were mounted in epoxy resin, were polished to expose their internal structures, and

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were checked under cathodoluminescence (CL). Cathodoluminescence (CL) images of typical

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zircon crystals analyzed in the present study are presented in Supplementary Fig. S1. U-Pb

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dating and trace element analyses of the selected zircon crystals were performed at the CAS Key

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Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology

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of China, using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS).

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Analytical details have been described in Guo et al. (2018a, b). Analysis results of U-Pb ages of

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single zircon crystals that are ≤10% and ≥-5% discordant were accepted. Concordia diagrams

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and weighted mean U-Pb ages calculated for the analyzed samples are displayed in Fig. 13.

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3 Stratigraphy, sedimentology and structural geology

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3.1 Stratigraphic subdivision

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The Erlian Basin is composed of a group of small-sized sub-basins, filled with similar

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sedimentary successions (Lin et al., 2001; Qi et al., 2015) (Fig. 1c). Seismic sections and well

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logs unravel that these sub-basins are mainly filled with Jurassic–Cretaceous fluvio-lacustrine

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clastic rocks, which are underlain by the Paleozoic folded and metamorphosed basement (Lin et

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al., 2001; Qi et al., 2015) (Fig. 2). The Paleozoic basement is mainly made up of metamagmatite,

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metasedimentary and metacarbonate rocks (Zhu et al., 2000). The Jurassic–Cretaceous

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sedimentary infill of the basin contacts the underlying Paleozoic basement with an angular

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unconformity (named as Tg in seismic reflection sections), and is unevenly preserved in a series

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of irregular grabens and half-grabens, controlled by NE–SW, E–W, and NW–SE striking normal

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faults (Lin et al., 2001; Qi et al., 2015; Guo et al., 2018a, b).

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Traditionally, on the basis of lithological features, unconformities, and fossil assemblages,

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the sedimentary infill of the Erlian Basin is subdivided into the Aqitu Formation, the Gerile

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Formation, the Qiha Formation, the Xing’anling Group, the Hugejiletu Formation, the Bayanhua

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Group, and the Erlian Formation, in ascending order (Gou et al., 1986; Xu et al., 2003; Tao et al.,

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2013) (Fig. 2). The Aqitu, Gerile and Qiha formations and the Xing’anling Group, deposited

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during the Middle–early Late Jurassic, are syn-extensional successions locally preserved in

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grabens and half-grabens in a few sub-basins of the Erlian Basin (Gou et al., 1986; Xu et al.,

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2003; Guo et al., 2018a). The Hugejiletu Formation, a synorogenic conglomerate- and pebbly

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sandstone-dominated sedimentary succession, is sporadically discovered in the Erlian Basin, and

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is formed due to contemporary compressional deformation during the latest Jurassic–earliest

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Cretaceous (Xu et al., 2003; Guo et al., 2018a). The Bayanhua Group, consisting of the Aershan,

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Tenggeer, and Saihan formations in ascending order, was deposited during the Early Cretaceous,

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is widely preserved in the basin, and constitutes the chief part of the basin-fill deposits. The

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Erlian Formation was deposited during the Late Cretaceous, and is locally preserved in the

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northwestern basin (Tao, 2003; Guo et al., 2018b). The present study mainly focuses on the

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Bayanhua Group.

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Based on lithological characteristics, the Aershan Formation is further divided into two

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fining-upward successions, named as the Lower and the Upper Aershan formations (Fig. 2). The

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Lower Aershan Formation rests on the Jurassic strata with an angular unconformity (named as

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T11 in seismic reflection sections), and comprises two intervals (Figs. 2, 4, 6, and 8). The lower

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interval with a maximum thickness of ca. 433 m, is a succession of coarse-grained sediments,

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dominated by alluvial fan and braided channel conglomerate and pebbly sandstone (Tao, 2003;

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Wu, 2009). The upper interval with a maximum thickness of ca. 650 m, is mainly made up of

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thick lacustrine mudstone, interbedded with a few thin layers of siltstone, sandstone and

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intermediate-basic volcanic rocks (Tao, 2003; Wu, 2009). The Upper Aershan Formation, with a

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maximum thickness of ca. 680 m, overlies the Lower Aershan Formation with an angular

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unconformity (named as T10 in seismic reflection sections), and is characterized by coarse-

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grained sediments, mainly made up of alluvial fan and braided channel conglomerate, pebbly

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sandstone, and sandstone (Tao, 2003; Wu, 2009) (Figs. 2, 4, 6, and 8). Fine-grained sediments,

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dominated by fluvial and lacustrine alternating beds of sandstone, siltstone, and mudstone, are

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recognized in the upper part of the Upper Aershan Formation in the center of some sub-basins

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(Figs. 6 and 8).

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The Tenggeer Formation is also subdivided into two sub-stratigraphic units: the Lower and

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the Upper Tenggeer formations, in ascending order (Lin et al., 2001) (Fig. 2). The Lower

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Tenggeer Formation with a maximum thickness of ca. 1,250 m, contains the most important

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source rocks of the Erlian Basin. The formation contacts the Upper Aershan Formation with an

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angular unconformity (named as T8 in seismic reflection sections), and is characterized by thick-

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bedded lacustrine mudstone, interbedded with thin layers of carbonaceous mudstone, siltstone,

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sandstone and intermediate-basic volcanic rocks (Tao, 2003; Wu, 2009) (Figs. 2, 4, 6, 8, and 10).

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In some local areas, this formation is a typical fining-upward sequence, made up of

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conglomerate- and pebbly sandstone-dominated basal beds and mudstone- and sandstone-

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dominated upper beds (Figs. 4, 6, 8, and 10). The Upper Tenggeer Formation with a maximum

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thickness of ca. 1,350 m, contacts the Lower Tenggeer Formation with an angular unconformity

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(named as T6 in seismic reflection sections), and is a fining-upward sequence, containing a

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alluvial fan–fluvial pebbly sandstone- and sandstone-dominated lower succession and a

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lacustrine mudstone- and siltstone-dominated upper succession in most sub-basins of the Erlian

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Basin (Tao, 2003; Wu, 2009) (Figs. 2, 4, 6, and 10). In some sub-basins, such as the Abei-Anan

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Sag, the coarse-grained lower succession of the Upper Tenggeer Formation was absent, and the

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fine-grained upper succession rested on the Lower Tenggeer Formation directly (Fig. 8).

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The Saihan Formation rests on the Upper Tenggeer Formation with an angular unconformity

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(named as T3 in seismic reflection sections), and can be subdivided into three intervals with a

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total maximum thickness of ca. 1200 m (Fig. 2). The basal and top intervals are characterized by

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alluvial fan–fluvial conglomerate, pebbly sandstone and sandstone, while the middle interval is

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mainly made up of fluvial and lacustrine mudstone and siltstone, interbedded with medium- to

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fine-grained sandstone (Tao, 2003; Wu, 2009) (Figs. 4, 6, 8, and 10).

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After the deposition of the Saihan Formation, a significant sedimentary hiatus occurred in

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most regions of the Erlian Basin. The Upper Cretaceous Erlian Formation was locally deposited

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in a few sub-basins in the northwestern basin, and the Saihan Formation was rested by the Erlian

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Formation or the Cenozoic sediments with angular unconformities (Guo et al., 2018b). The

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unconformity between the Saihan and Erlian formations is named as T2 in seismic reflection

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sections, and the unconformity between the Saihan Formation and the Cenozoic strata is named

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as T0 (Fig. 2).

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3.2 Sedimentology and structural geology of typical sub-basins

To clarify the sedimentary and structural characteristics of the sub-stratigraphic units of the

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Bayanhua Group in the Erlian Basin, 5 typical sub-basins, consisting of the Honghaoershute,

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Jiergalangtu, Abei-Anan, Central Wuliyasitai, and Saihantala sags, are investigated (Fig. 1c).

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Using lithological columns of wells and seismic reflection profiles, new sketchy isopach maps of

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the Lower Aershan, Upper Aershan, Lower Tenggeer, Upper Tenggeer, and Saihan formations of

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the Honghaoershute, Jiergalangtu, Abei-Anan, and Central Wuliyasitai sags are established, and

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a detailed analysis of the sedimentary and structural features of these sub-basis are conducted

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(Figs. 3–10). In addition, on the basis of seismic reflection profiles, the unconformity T6 in the

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Saihantala Sag is particularly studied (Fig. 11).

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3.2.1 Honghaoershute Sag

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The Honghaoershute Sag, located in the eastern margin of the Erlian Basin, is a NE–SW-

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trending half-graben (Figs. 1c and 3a–e, f). The architecture and depocenter of the half-graben

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were controlled mainly by the NE-striking, NW-dipping southeastern boundary fault (Fig. 3f).

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In the Honghaoershute Sag, the Lower Aershan Formation is separated from the deformed

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and eroded Jurassic or Paleozoic basement by the unconformity T11 or Tg, and occupies the

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basal stratigraphic position of the basin fill (Fig. 3f–h), signaling the beginning of syn-rift

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subsidence in the sag. Isopach map, seismic profiles and well lithostratigraphic data show that

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the Lower Aershan Formation is extensively distributed in the sag, and shows a tendency of

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southeastward thickening from the northwestern margin of the sag to the master normal fault

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(Fig. 3a, f and Fig. 4), indicating that the deposition of the Lower Aershan Formation was

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controlled mainly by the southeastern boundary normal fault. 11

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The Lower and Upper Aershan formations are separated by the angular unconformity T10

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(Fig. 3f–g). Below the unconformity, the Lower Aershan Formation was tilted and eroded, and

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an obvious syncline is recognized in the south of the sag in seismic reflection profiles (Fig. 3f),

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indicating that contractional deformation occurred in the sag between the deposition of the

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Lower and Upper Aershan formations. During the deposition of the Upper Aershan Formation,

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the depositional area shrank, and depocenters migrated inward (Figs. 3b and 4). The Upper

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Aershan Formation onlapped the uplifted, eroded Lower Aershan Formation, and was controlled

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by normal faults (Fig. 3f–g), suggesting the resumption of extensional regime during this period.

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After the deposition of the Upper Aershan Formation, contractional deformation occurred in

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the sag. The Upper Aershan Formation was tilted, and was truncated by the angular

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unconformity T8 at the base of Lower Tenggeer Formation (Fig. 3f–h). During the deposition of

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the Lower Tenggeer Formation, the depositional area expanded, and depocenters migrated to the

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northeastern and southwestern parts of the sag (Figs. 3c and 4). The Lower Tenggeer Formation

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gradually onlapped the tilted and eroded Upper and Lower Aershan formations, and was

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controlled by the southeastern boundary normal fault and a series of secondary normal faults (Fig.

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3f–g). Thick-bedded mudstone and dolomitic mudstone of the Lower Tenggeer Formation occur

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in the wells H40, H37 and HC1, reflecting a lacustrine environment in depocenters of the sag

251

(Fig. 4).

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The Lower and Upper Tenggeer formations are separated by the angular unconformity T6

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(Fig. 3f–h). Below the unconformity, the Lower Tenggeer Formation was inhomogeneously

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tilted and eroded, and an obvious syncline, involving the Lower Tenggeer Formation and lower

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strata, was formed in the central part of the sag (Fig. 3h), indicating that the sag underwent

256

significant contractional deformation between the deposition of the Lower and Upper Tenggeer

12

257

formations. The axis of the syncline is traced in seismic refection sections by the present study,

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and is delineated in Fig. 3d. The axis strikes NW–SE, signaling that the maximum principal axis

259

of the contractional stress, that resulted in the formation of the syncline and the unconformity T6,

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was approximately oriented NE–SW. After the contractional deformation, the southeastern

261

boundary fault reactivated, a series of secondary normal faults were generated in the center of the

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sag, and the Upper Tenggeer Formation onlapped the tilted and truncated Lower Tenggeer

263

Formation (Fig. 3f–h). During the deposition of the Upper Tenggeer Formation, the depositional

264

area expanded, and the sedimentary thickness increased significantly (Fig. 3d, f–h and Fig. 4).

265

Thick-bedded mudstone was deposited in wells H40, H12, and H17 (Fig. 4), reflecting the

266

northwestward migration of lacustrine environment in the sag after the deposition of the Lower

267

Tenggeer Formation.

268

After the deposition of the Upper Tenggeer Formation, contractional deformation occurred

269

in the sag again. In seismic reflection sections, especially NW–SE striking sections, an obvious

270

angular unconformity T3 can be identified (Fig. 3f–h). The angular unconformity truncated the

271

underlying titled Upper Tenggeer Formation and was onlapped by the overlying Saihan

272

Formation. After the contraction deformation, normal-fault-controlled subsidence and

273

sedimentation continued. The sedimentary thickness further increased, and shows a tendency of

274

southeastward thickening to the boundary normal fault (Figs. 3e–f and 4). The Saihan Formation

275

contains a coarse-grained basal succession and thin layers of coal (Fig. 4).

276

3.2.2 Jiergalangtu Sag

277 278

The Jiergalangtu Sag, located to the northwest of the Honghaoershute Sag in the eastern part of the Erlian Basin, is a NE–SW-trending half-graben (Figs. 1c and 5a–e, g). The architecture

13

279

and depocenter of the Bayanhua Group in the half-graben were controlled mainly by the NE-

280

striking, SE-dipping northwestern boundary fault (Fig. 5g).

281

The Middle Jurassic Aqitu, Gerile and Qiha formations are locally distributed in the

282

southwestern margin of the Jiergalangtu Sag (Fig. 5f). The remained Aqitu, Gerile and Qiha

283

formations were strongly folded and eroded, and were directly onlapped by the mildly deformed

284

Lower Aershan Formation with an angular unconformity T11 (Fig. 5f), indicating that intense

285

contractional deformation occurred in the sag between the deposition of the Qiha and Lower

286

Aershan formations. In the central and southwestern parts of the sag, the Lower Aershan

287

Formation is widely encountered by wells and interpreted on seismic reflection profiles (Fig. 5a,

288

f–h and Fig. 6). Seismic profiles show that the Lower Aershan Formation in the southwestern

289

part of the sag was controlled mainly by the NE-striking northwestern boundary normal fault,

290

and displays a tendency of northwestward thickening from the sag center to the boundary fault

291

(Fig. 5a, f–g). In the central part of the sag, a southeastern boundary normal fault was also

292

generated, controlling the deposition of the Lower Aershan Formation (Fig. 5h).

293

In the southwestern and southeastern parts of the Jiergalangtu Sag, the Upper Aershan

294

Formation is absent, and the Lower Aershan Formation is directly covered by the Lower

295

Tenggeer or Saihan formations (Figs. 5b, f and 6). In the central part of the sag, the Lower

296

Aershan Formation is inhomogeneously tilted and uplifted, and is truncated by the angular

297

unconformity T10 at the base of the Upper Aershan Formation (Fig. 5g–h). It is suggested that an

298

episode of contractional deformation occurred in the sag between the deposition of the Lower

299

and Upper Aershan formations, resulting in the shrinkage of depositional area and the formation

300

of the unconformity T10. Following the contractional deformation, the southeastern boundary

301

normal fault in the central part of the sag and the northwestern boundary fault reactivated,

14

302

controlling the deposition of the Upper Aershan Formation (Fig. 5g–h). In the southwestern sag,

303

the Upper Aershan Formation thickened northwestward from the sag center to the boundary fault

304

(Figs. 5b, g and 6), implying that the deposition of the Upper Aershan Formation in the

305

southwestern sag was mainly controlled by the northwestern boundary fault.

306

Seismic profiles reveal that an unconformity T8 exists between the Upper Aershan and

307

Lower Tenggeer formations (Fig. 5g–h). The Upper Aershan Formation was tilted and was

308

truncated by the unconformity. The Lower Tenggeer Formation onlapped southeastward onto the

309

underlying Upper and Lower Aershan formations, and contains a coarse-grained basal succession

310

of pebbly sandstone (Figs. 5g–h and 6). These lines of evidence indicate that the extensional

311

regime in the sag during the deposition of the Upper Aershan and Lower Tenggeer formations

312

was discontinuous, and was punctuated by a contractional event. During the deposition of the

313

Lower Tenggeer Formation, the northwestern boundary normal fault was still active, while the

314

activation of the southeastern boundary normal fault in the central part of the sag ceased (Fig.

315

5g–h). The depositional area expanded and the depocenter migrated slightly northeastward (Figs.

316

5c and 6). As shown by the well lithostratigraphic cross sections, the sediments of the Lower

317

Tenggeer Formation in wells J45, J46, J19, J74, and J31 is dominated by proximal alluvial and

318

fluvial pebbly sandstone and sandstone, while the sediments of the Lower Tenggeer Formation in

319

wells J42, J33 and J55 contains abundant lacustrine dolomitic mudstone (Fig. 6). The tendency

320

of northwestward fining from the sag center to the boundary fault implies that a northwestward

321

deepening lake existed in the sag during this period.

322

The Lower Tenggeer Formation at the northwestern and southeastern margins of the sag was

323

truncated by a low-angle unconformity T6 at the base of the Upper Tenggeer Formation (Fig. 5f–

324

h). The Upper Tenggeer Formation onlapped the tilted and eroded Lower Tenggeer Formation

15

325

and lower strata with a pebbly sandstone-dominated coarse-grained basal succession (Fig. 6),

326

suggesting that an episode of contractional deformation and erosion occurred in the sag between

327

the deposition of the Lower and Upper Tenggeer formations. During the deposition of the Upper

328

Tenggeer Formation, depositional area further expanded (Fig. 5d). As shown by the well

329

lithostratigraphic cross sections, the Upper Tenggeer Formation thickens northwestward from

330

well J13, through well J9, to well J19, from well J46, through well J45, to well J42, and from

331

well J31, through wells J74 and J55, to well J33 (Fig. 6). The tendency of northwestward

332

thickening from the southeastern margin and center of the sag to the northwestern boundary

333

normal fault, suggesting that the deposition of the Upper Aershan Formation was mainly

334

controlled by the northwestern boundary normal fault.

335

An unconformity T3 can be observed at the southeastern margin of the sag between the

336

Upper Tenggeer and Saihan formations (Fig. 5h), indicating that the sag suffered another episode

337

of inhomogeneous erosion between the deposition of the Upper Tenggeer and Saihan formations.

338

After the erosional event, the northwestern boundary normal fault reactivated, and the Saihan

339

Formation was extensively deposited in the sag with a maximum thickness exceeded 700 m (Figs.

340

5e, g and 6). Unlike the underlying Upper and Lower Tenggeer formations, the Saihan

341

Formation in the sag lacks thick-bedded mudstone, and is characterized by interbedded layers of

342

coal (Fig. 6), reflecting fluvial and delta plain swamp environments.

343

After the deposition of the Saihan Formation, an intense contractional event occurred in the

344

sag, the Saihan Formation and lower strata were strongly folded, and were onlapped by the

345

barely deformed Cenozoic sediments (Fig. 5h).

16

346

347

3.2.3 Abei-Anan Sag

The Abei-Anan Sag, located in the northern part of the Erlian Basin, is a NE–SW-trending

348

asymmetric graben (Qi et al., 2015) (Figs. 1c and 7). The architecture of the sag is complex, and

349

is controlled mainly by a series of NE- and NEE-striking normal faults (Fig. 7f–g).

350

The Upper Jurassic Xing’anling Group is locally found in the Abei-Anan Sag (Fig. 7f). The

351

Xing’anling Group was strongly deformed and was overlaid by the Lower Aershan Formation

352

with a high-angle unconformity T11 (Fig. 7f), indicating that the sag underwent intense

353

deformation between the deposition of the Xing’anling Group and the Lower Aershan Formation.

354

After the deformational event, the sag entered into an episode of extension, and the normal-fault-

355

controlled Lower Aershan Formation was deposited in the southeastern sag (Fig. 7a, f–g). The

356

Lower Aershan Formation displays a tendency of southeastward thickening towards the

357

southeastern boundary normal fault (Figs.7a, f and 8), suggesting that the deposition of the

358

formation was mainly controlled by the southeastern boundary fault. The formation in the

359

depocenter of the sag is characterized by thick-bedded mudstone interbedded with thin layers of

360

siltstone (Fig. 8).

361

During the deposition of the Upper Aershan Formation, unlike the aforementioned

362

Honghaoershute and Jiergalangtu sags, the depositional area in the Abei-Anan Sag enlarged

363

significantly (Fig. 7b). Resting on the underlying Lower Aershan Formation and the Jurassic or

364

Paleozoic basement, the Upper Aershan Formation in the sag is characterized by thick-bedded

365

conglomerate and pebbly sandstone, and fine-grained sediments are identified only in the

366

southeastern depocenter (Figs. 7b, f–g and 8). Although intense normal faulting occurred

367

throughout the northwestern and southeastern parts of the sag during this period, the thickness of

368

the Upper Aershan Formation shows a clear southeastward thickening trend (Figs. 7b, f and 8), 17

369

suggesting that the deposition of the Upper Aershan Formation was mainly controlled by the

370

southeastern boundary normal fault. Seismic profiles show that the remained Lower Aershan

371

Formation was tilted and was truncated by the unconformity T10 at the base of the Upper

372

Aershan Formation (Fig. 7f). Combined with that the Upper Aershan Formation in the Abei-

373

Anan Sag is dominated by pebbly sandstone (Fig. 8), it is suggested that an episode of

374

compressional deformation occurred in the basin between the deposition of the Lower and Upper

375

Aershan formations, resulting in the formation of the unconformity T10, and the rapid uplift of

376

the circumferential highlands of the Abei-Anan Sag.

377

After the deposition of the Upper Aershan Formation, the Upper Aershan Formation was

378

inhomogeneously uplifted and folded, leading to the formation of a series of monoclines in the

379

northwestern part of the sag, which was onlapped by the Lower Tenggeer Formation (Fig. 7g).

380

During the deposition of the Lower Tenggeer Formation, the activation of the southeastern

381

boundary normal fault ceased, and the sediments gradually onlapped southeastward onto the

382

uplifted and eroded Upper Aershan Formation (Fig. 7f).

383

The Upper Tenggeer Formation is separated from the Lower Tenggeer Formation and Upper

384

Aershan Formation by the angular unconformity T6 (Fig. 7f–g). In the southeastern sag, the

385

Upper Tenggeer Formation was controlled by the northwestern boundary normal fault and a

386

series of secondary normal faults, and onlapped southeastward onto the tilted Lower Tenggeer

387

Formation (Fig. 7f). In the northwestern sag, the Lower Tenggeer Formation and the Upper

388

Aershan Formation were tilted, and were truncated by the unconformity T6 (Fig. 7g). During the

389

deposition of the Upper Tenggeer Formation, depositional area expended, and depocenters were

390

located in the southeastern and northwestern parts of the sag (Fig. 7d). Both the Lower and

391

Upper Tenggeer formations in the sag are dominated by thick mudstone, with several layers of

18

392

dolomitic mudstone occur at the base (Fig. 8). Therefore it is difficult to distinguish between the

393

two formations merely on the grounds of well sections.

394

The Saihan Formation was extensively deposited in the sag (Fig. 7e–f), and was separated

395

from the underlying Upper Tenggeer Formation by a typical conglomerate- or pebbly sandstone-

396

dominated basal succession (Fig. 8). During the deposition of the Saihan Formation, the

397

northwestern boundary normal fault in the southeastern sag and the northwestern boundary

398

normal fault in the northwestern sag were still active, and numerous secondary normal faults

399

were generated in the sag (Fig. 7f–g), signing an extensional setting.

400

3.2.4 Central Wuliyasitai Sag

401

The Central Wuliyasitai Sag, located in the northeastern margin of the Erlian Basin, is a

402

NE–SW-trending half-graben, bounded by the NE-striking, SE-dipping master normal fault to

403

the northwest and the basement highland to the southeast (Figs. 1c and 9).

404

Generally, it is suggested that the entire Erlian Basin entered into a syn-rift extension

405

episode during the deposition of the Aershan Formation, and the Aershan Formation was

406

deposited in almost all the sags of the basin. The infill of the Central Wuliyasitai Sag was

407

subdivided into the Xing’anling Group, the Aershan Formation, the Lower Tenggeer Formation,

408

the Upper Tenggeer Formation, and the Saihan Formation, in ascending order (Ren et al., 1999;

409

Lin et al., 2001; Deng et al., 2010). However, grounded on detailed stratigraphic correlations

410

using well, seismic, and isotope age data, a recent study conducted by our research team and

411

collaborators of the PetroChina Huabei Oilfield Company, unraveled that the Aershan Formation

412

was absent in the sag, and the Lower Tenggeer Formation rested directly on the Jurassic

413

Xing’anling Group and Paleozoic basement (Sun et al., 2017) (Figs. 9d–e and 10). This suggests

19

414

that after the Late Jurassic initial syn-rift deposition of the Xing’anling Group, a sedimentary

415

hiatus occurred in the Central Wuliyasitai Sag, and syn-rift subsidence resumed until the time

416

when the Low Tenggeer Formation was deposited. Therefore, the start time of Early Cretaceous

417

syn-rift deposition in the sags of the Erlian Basin was spatially asynchronous. Although most

418

sags, such as the Honghaoershute, Jiergalangtu and Abei-Anan sags, entered into a syn-rift

419

subsidence episode during the deposition of the Aershan Formation, some sags, such as the

420

Central Wuliyasitai Sag, entered into the Early Cretaceous syn-rift subsidence episode much

421

later, during the deposition of the Lower Tenggeer Formation.

422

In the Central Wuliyasitai Sag, conglomerate- or pebbly sandstone-dominated successions

423

are identified at the base of the Lower Tenggeer, Upper Tenggeer and Saihan formations (Fig.

424

10), signaling abrupt changes in depositional environment between the deposition of these

425

formations. Although the Lower Tenggeer Formation is mainly made up of mudstone,

426

conglomerate-dominated basal successions are recognized in some wells in the southern sag,

427

such as the well T8. As shown by the seismic sections (Fig. 9d–e), the Lower Tenggeer, Upper

428

Tenggeer and Saihan formations in the Central Wuliyasitai Sag, were mainly controlled by the

429

NE-striking, SE-dipping boundary normal fault to the northwest, and onlapped southeastward

430

onto the basement highland in the southeastern margin of the sag. An angular unconformity T6

431

between the Lower and Upper Tenggeer formations can be recognized in the central part of the

432

sag (Fig. 9d–e). The Lower Tenggeer Formation was tilted and eroded, and was onlapped by the

433

Upper Tenggeer Formation, indicating that an episode of contractional deformation affected the

434

sag between the deposition of the Lower and Upper Tenggeer formations.

20

435

3.2.5 Saihantala Sag

436

The Saihantala Sag, located in the southern part of the Erlian Basin, is a NE–SW-trending

437

half-graben (Figs. 1c and 11). In this sag, the angular unconformity T6 between the Lower and

438

Upper Tenggeer formations is much easier to be recognized in the NE–SW striking seismic

439

sections than in the NW–SE striking section (Fig. 11). In the NW–SE striking section (Fig. 11b),

440

the unconformity T6 resembles a simple bedding plane, and the super- and sub-unconformity

441

beds are parallel or subparallel. However, in the NE–SW striking sections (Fig. 11c–d), the beds

442

below the unconformity are tilted and eroded, and are truncated at the unconformity, while the

443

beds above the unconformity are sub-horizontal, and roughly parallel to the unconformity

444

surface. In the eastern part of the Saihantala Sag, an obvious syncline involving the Lower

445

Tenggeer Formation and lower strata can be recognized, and the syncline is onlapped by the sub-

446

horizontal to gently tilted Upper Tenggeer Formation (Fig. 11c–d). The axis of the syncline is

447

traced in seismic refection sections by the present study, and is delineated in Fig. 11a. The axis

448

runs NW–SE, signaling that the maximum principal axis of the contractional stress, that led to

449

the formation of the syncline and the unconformity T6, was roughly oriented NE–SW.

450

4 Chronostratigraphy

451

4.1 Previous work

452

Grounded on terrestrial fossil assemblages (such as charophytes, ostracods, spores, pollen,

453

and bivalves), depositional ages of sub-stratigraphic units of the Bayanhua Group have been

454

documented in numerous papers and reports (e.g., Gou et al., 1986; Song et al., 1986; Zhao,

455

1987; Tao, 2003; Tao et al., 2013; Wang et al., 2014) (Fig. 2). Generally, according to the

21

456

identification of the spore and pollen assemblage of Cicatricosisporites-Leiotriletes-

457

Protoconiferus-Psophosphaera, the age of the Lower Aershan Formation is estimated as

458

Berriasian–early Valanginian (Tao, 2003; Tao et al., 2013). According to the identification of the

459

spore and pollen assemblage of Aequitriradite-Concavissimisporites-Densoisporites, the age of

460

the Upper Aershan Formation is estimated as late Valanginian–early Hauterivian (Tao, 2003;

461

Tao et al., 2013). According to the identification of the spore and pollen assemblage of

462

Monosulcites-Protoconiferu, the age of the Lower Tenggeer Formation is estimated as early–

463

middle Hauterivian (Tao, 2003; Tao et al., 2013). According to the identification of the spore and

464

pollen assemblage of Classopollis-Cicatricosisporites-Pinuspollenites, the age of the Upper

465

Tenggeer Formation is estimated as late Hauterivian–Barremian (Tao, 2003; Tao et al., 2013).

466

According to the identification of the spore and pollen assemblage of Angiosperm-

467

Appendicisporites-Laevigatosporites, the age of the Saihan Formation is suggested as early

468

Aptian (Tao, 2003; Tao et al., 2013), while according to the identification of charophyte

469

assemblage of Aclistochara mundula-Atopochara restricta-A. caii-A. daerqiensis sp. nov.-A.

470

subquadrularia-Mesochara symmetrica-M. stipitata-Obtusochara maedleri (Yang et al., 2003),

471

and the identification of the spore and pollen assemblage of Classopollis-Cicatricosisporites-

472

Densoisporites-Disacciatrileti-Pilosisporites-Protoconiferus-Protopinus-Pseudopicea (Nie et al.,

473

2007; Fan et al., 2008; Liu and Dai, 2013), the age of the Saihan Formation is also suggested as

474

Aptian–Albian.

475

However, zircon U-Pb dating of a basalt from the well A18 at a depth of 2566 m in the

476

bottom of the Aershan Formation in the Abei-Anan Sag yielded an age of 138 ± 1 Ma (Guo et al.,

477

2018a) (Fig. 8). Zircon U-Pb dating of two andesites from the well T14 at a depth of 767 m and

478

the well T18 at a depth of 811 m in the upper part of the Lower Tenggeer Formation in the

22

479

Central Wuliyasitai Sag yielded ages of 121 ± 1 Ma and 124 ± 13 Ma, respectively (Sun et al.,

480

2017) (Fig. 10). Detrital zircon U-Pb dating of two sandstones of the Saihan Formation in the

481

Jiergalangtu Sag yielded a maximum depositional age of 115 ± 4 Ma (Guo et al., 2018b). These

482

recently published radiometric ages unravel that the absolute ages of the Aershan, Tenggeer, and

483

Saihan formations are inconsistent with those presently indicated by the fossils found in them.

484

Thus, it is necessary to systematically reassess the actual ages of the sub-stratigraphic units of the

485

Bayanhua Group.

486

4.2 New zircon U-Pb geochronological data

487

A total of 715 zircon crystals were analyzed in the present study, and the analysis results are

488

summarized in Supplementary Table S1, Supplementary Fig. S1, and Fig. 13. The 715 selected

489

zircons display well-developed oscillatory zoning (Supplementary Fig. S1), and yield high Th/U

490

ratios (Th/U ratios of 3 zircons range from 0.04 to 0.10; Th/U ratios of the remnant zircons range

491

from 0.11 to 2.60), indicating magmatic origin (Hoskin and Schaltegger, 2003). Among the 715

492

analyzed zircon crystals, 643 zircon crystals give ages with acceptable discordance, and are used

493

for geochronological interpretations.

494

Sample H40-1, an andesite from the Lower Aershan Formation, was collected from the well

495

H40 at a depth of 1057 m in the Honghaoershute Sag (Table 1; Fig. 4). A total of 28 analyses

496

were carried out, and 27 gave ages with acceptable discordance (≤10% and ≥-5% discordant).

497

Among the 27 acceptable ages, the youngest 4 constitute a tight cluster (overlap in age at 1σ),

498

range from 136 ± 6 to 139 ± 4 Ma, and give a weighted mean 206Pb/238U age of 138 ± 4 Ma

499

(MSWD = 0.08) (Fig. 13a) that is suggested as the eruption age of the andesite. The remnant 23

23

500

ages range from 176 ± 5 to 859 ± 12 Ma, and are suggested as the crystallization ages of

501

inherited zircon crystals.

502

Sample H17-2, a tuff from the Lower Aershan Formation, was collected from the well H17

503

at a depth of 1531 m (Table 1; Fig. 4). A total of 29 analyses were carried out, and all the

504

analyses gave ages with acceptable discordance. Among the 29 acceptable ages, the youngest 21

505

constitute a tight cluster, range from 135 ± 3 to 141 ± 3 Ma, and yield a weighted mean

506

206

507

the tuff. The remnant 8 ages range from 147 ± 4 to 277 ± 5 Ma, and are suggested as the

508

crystallization ages of inherited zircon crystals.

509

Pb/238U age of 138 ± 1 Ma (MSWD = 0.34) (Fig. 13b) that is suggested as the eruption age of

Sample HC1-3, a tuff from the Lower Aershan Formation, was collected from the well HC1

510

at a depth of 2749 m (Table 1; Figs. 3g and 4). A total of 28 analyses were carried out, and 26

511

gave ages with acceptable discordance. Among the 26 acceptable ages, the youngest 8 constitute

512

a tight cluster, range from 135 ± 4 to 145 ± 7 Ma, and yield a weighted mean 206Pb/238U age of

513

136 ± 3 Ma (MSWD = 0.25) (Fig. 13c) that is suggested as the eruption age of the tuff. The

514

remnant 18 ages range from 150 ± 4 to 1396 ± 66 Ma, and are suggested as the crystallization

515

ages of inherited zircon crystals.

516

Sample H33, a tuff from the Lower Aershan Formation, was collected from the well H33 at

517

a depth of 2246 m (Table 1; Figs. 3f and 4). A total of 32 analyses were carried out, and all these

518

analyses gave ages with acceptable discordance. Among the 32 acceptable ages, the youngest 31

519

constitute a tight cluster, range from 133 ± 3 to 139 ± 3 Ma, and give a weighted mean 206Pb/238U

520

age of 136 ± 1 Ma (MSWD = 0.30) (Fig. 13d) that is suggested as the eruption age of the tuff.

521

The remnant 1 age of 148 ± 3 Ma, is suggested as the crystallization age of an inherited zircon

522

crystal.

24

523

Sample HC1-2, an andesite from the top of the Upper Aershan Formation, was collected

524

from the well HC1 at a depth of 1905 m (Table 1; Figs. 3g and 4). A total of 28 analyses were

525

carried out, and 25 gave ages with acceptable discordance. Of the 25 acceptable ages, the

526

youngest 19 constitute a tight cluster, range from 131 ± 10 to 135 ± 4 Ma, and give a weighted

527

mean 206Pb/238U age of 134 ± 2 Ma (MSWD = 0.05) (Fig. 13e) that is suggested as the eruption

528

age of the andesite. The remnant 6 ages range from 154 ± 3 to 232 ± 5 Ma, and are suggested as

529

the crystallization ages of inherited zircon crystals.

530

Sample HC1-1, a tuff from the Lower Tenggeer Formation, was collected from the well

531

HC1 at a depth of 1706 m (Table 1; Figs. 3g and 4). A total of 60 analyses were carried out, and

532

54 gave ages with acceptable discordance. Among the 54 acceptable ages, the youngest 27

533

constitute a tight cluster, range from 129 ± 6 to 143 ± 8 Ma, and give a weighted mean 206Pb/238U

534

age of 132 ± 1 Ma (MSWD = 0.21) (Fig. 13f) that is suggested as the eruption age of the tuff.

535

The remnant 27 ages range from 146 ± 5 to 440 ± 7 Ma, and are suggested as the crystallization

536

ages of inherited zircon crystals.

537

Sample H37, an andesite from the Lower Tenggeer Formation, was collected from the well

538

H37 at a depth of 1728 m (Table 1; Fig. 4). A total of 28 analyses were carried out, and 25 gave

539

ages with acceptable discordance. Of the 25 acceptable ages, the youngest 20 constitute a tight

540

cluster, range from 120 ± 10 to 134 ± 7 Ma, and yield a weighted mean 206Pb/238U age of 128 ± 2

541

Ma (MSWD = 0.77) (Fig. 13g) that is suggested as the eruption age of the andesite. The remnant

542

5 ages range from 151 ±5 to 258 ± 6 Ma, and suggested as the crystallization ages of inherited

543

zircon crystals.

544 545

Sample H12, an andesite from the Lower Tenggeer Formation, was collected from the well H12 at a depth of 743 m (Table 1; Fig. 4). A total of 32 analyses were carried out, and 24 gave

25

546

ages with acceptable discordance. Of the 24 acceptable ages, the youngest 18 constitute a tight

547

cluster, range from 120 ± 4 to 128 ± 8 Ma, and yield a weighted mean 206Pb/238U age of 125 ± 2

548

Ma (MSWD = 0.38) (Fig. 13h) that is suggested as the eruption age of the andesite. The remnant

549

6 ages range from 138 ± 5 to 309 ± 5 Ma, and are suggested as the crystallization ages of

550

inherited zircon crystals.

551

Sample J55, an andesitic breccia from the bottom of the Lower Aershan Formation, was

552

collected from the well J55 at a depth of 1343 m in the Jiergalangtu Sag (Table 1; Fig. 6b). A

553

total of 28 analyses were carried out, and 25 gave ages with acceptable discordance. Of the 25

554

acceptable ages, the youngest 23 constitute a tight cluster, range from 135 ± 4 to 141 ± 3 Ma, and

555

yield a weighted mean 206Pb/238U age of 138 ± 1 Ma (MSWD = 0.31) (Fig. 13i) that is suggested

556

as the eruption age of the andesitic breccia. The remnant 2 ages of 158 ± 4 and 237 ± 5 Ma, are

557

suggested as the crystallization ages of inherited zircon crystals.

558

Sample J45, an andesite from the Lower Aershan Formation, was collected from the well

559

J45 at a depth of 1533 m (Table 1; Fig. 6a). A total of 32 analyses were carried out, and 22 gave

560

ages with acceptable discordance. Among the 22 acceptable ages, the youngest 7 constitute a

561

tight cluster, range from 136 ± 4 to 144 ± 5 Ma, and give a weighted mean 206Pb/238U age of 138

562

± 4 Ma (MSWD = 0.33) (Fig. 13j) that is suggested as the eruption age of the andesitic. The

563

remnant 15 ages range from 274 ± 6 to 1626 ± 60 Ma, and are suggested as the crystallization

564

ages of inherited zircon crystals.

565

Sample J13-1, a basaltic breccia from the Lower Aershan Formation, was collected from the

566

well J13 at a depth of 207 m (Table1; Fig. 6a). A total of 32 analyses were carried out, and 30

567

gave ages with acceptable discordance. Of the 30 acceptable ages, the youngest 25 constitute a

568

tight cluster, range from 135 ± 5 to 147 ± 8 Ma, and yield a weighted mean 206Pb/238U age of 137

26

569

± 2 Ma (MSWD = 0.23) (Fig. 13k) that is suggested as the eruption age of the basaltic breccia.

570

The remnant 5 ages ranges from 169 ± 10 to 339 ± 8 Ma, and are suggested as the crystallization

571

ages of inherited zircon crystals.

572

Sample J33, an andesite from the top of the Lower Aershan Formation, was collected from

573

the well J33 at a depth of 1663 m (Table 1; Fig. 6b). A total of 25 analyses were carried out, and

574

21 gave ages with acceptable discordance. Of the 21 acceptable ages, the youngest 5 constitute a

575

tight cluster, range from 134 ± 6 to 138 ± 7 Ma, and yield a weighted mean 206Pb/238U age of 135

576

± 3 Ma (MSWD = 0.08) (Fig. 13l) that is suggested as the eruption age of the andesite. The

577

remnant 16 ages range from 201 ± 3 to 816 ± 15 Ma, and are suggested as the crystallization

578

ages of inherited zircon crystals.

579

Sample J42-7, an andesite from the Upper Aershan Formation, was collected from the well

580

J42 at a depth of 1890 m (Table 1; Figs. 5h and 6a). A total of 11 analyses were carried out, and

581

8 gave ages with acceptable discordance. Of the 8 acceptable ages, the youngest 5 constitute a

582

tight cluster, range from 133 ± 8 to 136 ± 5 Ma, and yield a weighted mean 206Pb/238U age of 135

583

± 5 Ma (MSWD = 0.04) (Fig. 13m) that is suggested as the eruption age of the andesite. The

584

remnant 3 ages of 156 ± 9, 348 ± 13, 1267 ± 53 are considerably older than the calculated

585

weighted mean age of the sample, and are suggested as the crystallization ages of inherited

586

zircon crystals.

587

Sample J46, an andesitic breccia from the Upper Aershan Formation, was collected from the

588

well J46 at a depth of 1005 m (Table 1; Fig. 6a). A total of 44 analyses were carried out, and 41

589

gave ages with acceptable discordance. Of the 41 acceptable ages, the youngest 4 constitute a

590

tight cluster, range from 133 ± 5 to 135 ± 14 Ma, and yield a weighted mean 206Pb/238U age of

591

134 ± 6 Ma (MSWD = 0.01) (Fig. 13n) that is suggested as the eruption age of the andesitic

27

592

breccia. The remnant 37 ages range from 234 ± 4 to 1215 ± 65 Ma, and are suggested as the

593

crystallization ages of inherited zircon crystals.

594

Sample J31-1, a tuff from the top of the Upper Aershan Formation, was collected from the

595

well J31 at a depth of 620 m (Table 1; Fig. 6b). A total of 64 analyses were carried out, and all

596

the analyses gave ages with acceptable discordance. Of the 64 acceptable ages, the youngest 21

597

constitute a tight cluster, range from 132 ± 7 to 140 ± 3 Ma, and yield a weighted mean

598

206

599

the tuff. The remnant 43 ages range from 149 ± 4 to 447 ± 9 Ma, and are suggested as the

600

crystallization ages of inherited zircon crystals.

Pb/238U age of 133 ± 2 Ma (MSWD = 0.04) (Fig. 13o) that is suggested as the eruption age of

601

Sample J74, a tuff from the bottom of the Lower Tenggeer Formation, was collected from

602

the well J74 at a depth of 955 m (Table 1; Fig. 6b). A total of 72 analyses were carried out, and

603

70 gave ages with acceptable discordance. Among the 70 acceptable ages, the youngest 21

604

constitute a tight cluster, range from 130 ± 5 to 140 ± 7 Ma, and yield a weighted mean

605

206

606

the tuff. The remnant 49 ages range from 143 ± 4 to 362 ± 12 Ma, and are suggested as the

607

crystallization ages of inherited zircon crystals.

Pb/238U age of 133 ± 2 Ma (MSWD = 0.10) (Fig. 13p) that is suggested as the eruption age of

608

Sample J19, an andesite from the Upper Tenggeer Formation, was collected from the well

609

J19 at a depth of 452 m (Table 1; Fig. 6a). A total of 43 analyses were carried out, and 33 gave

610

ages with acceptable discordance. Of the 33 acceptable ages, the youngest 16 constitute a tight

611

cluster, range from 111 ± 9 to 123 ± 9 Ma, and yield a weighted mean 206Pb/238U age of 117 ± 4

612

Ma (MSWD = 0.10) (Fig. 13q) that is suggested as the eruption age of the andesite. The remnant

613

17 ages range from 154 ± 5 to 474 ± 9 Ma, and are suggested as the crystallization ages of

614

inherited zircon crystals.

28

615

Sample J9, a basalt from the Upper Tenggeer Formation, was collected from the well J9 at a

616

depth of 373 m (Table 1; Fig.6a). A total of 37 analyses were carried out, and 28 gave ages with

617

acceptable discordance. Among the 28 acceptable ages, the youngest 24 constitute a tight cluster,

618

range from 112 ± 6 to 120 ± 8 Ma, and yield a weighted mean 206Pb/238U age of 116 ± 3 Ma

619

(MSWD = 0.09) (Fig. 13r) that is suggested as the eruption age of the basalt. The remnant 4 ages

620

range from 134 ± 5 to 316 ± 10 Ma, and are suggested as the crystallization ages of inherited

621

zircon crystals.

622

Sample Ha35-2, an andesitic breccia from the top of the Upper Aershan Formation, was

623

collected from the well Ha35 at a depth of 1288 m in the southern Abei-Anan Sag (Table 1; Fig.

624

8). A total of 31 analyses were carried out, and 29 gave ages with acceptable discordance. Of the

625

29 acceptable ages, the youngest 22 constitute a tight cluster, range from 131 ± 4 to 135 ± 3 Ma,

626

and yield a weighted mean 206Pb/238U age of 134 ± 1 Ma (MSWD = 0.10) (Fig. 13s) that is

627

suggested as the eruption age of the andesitic breccia. The remnant 7 ages range from 155 ± 4 to

628

476 ± 7 Ma, and are suggested as the crystallization ages of inherited zircon crystals.

629

Sample Aer24, an andesite from the bottom of Upper Tenggeer Formation, was collected

630

from the well Aer24 at a depth of 1332 m in the Aer Sag (Table 1; Figs. 12b–c). A total of 31

631

analyses were carried out, and 30 gave ages with acceptable discordance. Of the 30 acceptable

632

ages, the youngest 10 constitute a tight cluster, range from 117 ± 3 to 121 ± 4 Ma, and yield a

633

weighted mean 206Pb/238U age of 119 ± 2 Ma (MSWD = 0.38) (Fig. 13t) that is suggested as the

634

eruption age of the andesite. The remnant 20 ages range from 133 ± 3 to 744 ± 15 Ma, and are

635

suggested as the crystallization ages of inherited zircon crystals.

29

636

637

4.3 Geochronological constraints on the Bayanhua Group

The newly obtained zircon U-Pb ages in the present study display a systematic upsection

638

decrease (Table 1; Figs. 4, 6, 8, and 14a), and are consistent with the previously published U-Pb

639

age data (Sun et al., 2017; Guo et al., 2018a, b) (Figs. 2 and 14a). Integrating the newly obtained

640

with the previously published (Sun et al., 2017; Guo et al., 2018a, b) zircon U-Pb ages, the age of

641

the Lower Aershan Formation is adjusted to the middle Valanginian (ca. 138–135 Ma), the age

642

of the Upper Aershan Formation is adjusted to the late Valanginian (ca. 135–133 Ma), the age of

643

the Lower Tenggeer Formation is adjusted to the Hauterivian–early Aptian (ca. 133–121 Ma),

644

the age of the Upper Tenggeer Formation is adjusted to the middle Aptian (ca. 119–115 Ma), and

645

the age of the Saihan Formation is adjusted to the latest Aptian–Albian (post ca. 115 Ma) (Figs. 2

646

and 14a).

647

To further confirm the refined depositional ages of the Bayanhua Group in the Erlian Basin,

648

a stratigraphic correlation between the Erlian Basin and the Yan Shan is conducted. The Yan

649

Shan, situated to the southeast of the Erlian Basin (Fig. 1b), is an E–W-striking fold-thrust belt,

650

and contains plenty of intermontane basins filled with Late Mesozoic sediments (Ren et al.,

651

2019). The uppermost Jurassic–Lower Cretaceous strata in the Yan Shan include the Tuchengzi,

652

Zhangjiakou, Dabeigou, Yixian, Jiufotang, and Fuxin formations, in ascending order (Fig. 14b).

653

The Tuchengzi Formation is a typical synorogenic succession dominated by conglomerate and

654

pebbly sandstone (Li et al., 2004; Cope et al., 2007; Sun et al., 2007; Kuang et al., 2013). The

655

Zhangjiakou Formation rests on the Tuchengzi Formation with a high angle unconformity (Yang

656

et al., 2005; Xu et al., 2011; Liu et al., 2016), and consists mainly of medium–acidic volcanic

657

rocks (BGMRHP, 1996; Ren et al., 2019). The Dabeigou Formation contacts the Zhangjiakou

658

Formation with a parallel unconformity (Deng et al., 2017), and is comprised of conglomerate, 30

659

various-grained sandstone, and intercalating volcanic and tuffaceous rocks (BGMRHP, 1996;

660

Ren et al., 2019). The Yixian Formation, overlying the Dabeigou Formation with a parallel

661

unconformity (Tian et al., 2008; Deng et al., 2017, Ren et al., 2019), is made up of conglomerate

662

and volcanic rocks, interbedded with lacustrine mudstone (Ren et al., 2019). The Jiufotang

663

Formation unconformably overlies the Yixian Formation (Wang et al., 2018), and consists

664

mainly of lacustrine shale and siltstone, interbedded with sandstone and coal beds (Ren et al.,

665

2019). The Fuxin Formation is characterized by coal-bearing siliciclastic rocks (Sha, 2007), and

666

is separated from the underlying Jiufotang Formation by an angular unconformity (Sha, 2007;

667

Qin et al., 2015; Wang et al., 2018).

668

Ar-Ar and U-Pb dating of volcanic rocks from the Tuchengzi, Zhangjiakou, Dabeigou,

669

Yixian, and the lower part of the Jiufotang formations has mainly yielded age ranges of 154–137

670

Ma (Zhang et al., 2005a, 2008b; Cope et al., 2007; Chang et al., 2009; Xu et al., 2012b ; Wang et

671

al., 2013), 138–135 Ma (Liu et al., 2003; Niu et al., 2003; Zhang et al., 2005a, b, c; Sun et al.,

672

2007), 134–130 Ma (Liu et al., 2003; He et al., 2006; Wang et al., 2015), 133–119 Ma (Swisher

673

et al., 2002; Peng et al., 2003; Zhang et al., 2005d, 2006; Meng et al., 2008; Zheng et al., 2011;

674

Xu et al., 2012a ; Zhang et al., 2016), and 122–120 Ma (He et al., 2004; Chang et al., 2009),

675

respectively. Although no radioisotope age is available for the uppermost Jiufotang Formation,

676

zircon U-Pb dating of a subvolcanic rock that was intruded into the Jiufotang Formation, yielded

677

an age of 116 Ma, providing an upper limit for the Jiufotang Formation (Xu et al., 2012a). By

678

virtue of paleomagnetic data, the age of the Fuxin Formation has been estimated as ca. 114–110

679

Ma (Ma et al., 2002). In combination with that K-Ar dating of a basalt from the top of the Fuxin

680

Formation yielded an age of 100 Ma (Zhang and Zheng, 2003), the Fuxin Formation was likely

681

deposited during the late Aptian–Albian (ca. 114–100 Ma).

31

682

The collected radiometric and paleomagnetic ages of the Lower Cretaceous strata in the Yan

683

Shan and unconformable contacts among them point to a good correlation of the Lower

684

Cretaceous strata between the Erlian Basin and the Yan Shan (Fig. 14a–b). It is suggested here

685

that the Lower Aershan Formation of the Erlian Basin is correlated with the Zhangjiakou

686

Formation in the Yan Shan. Both formations are unconformably underlain by the uppermost

687

Jurassic–lowermost Cretaceous synorogenic successions, and give identical radiometric age

688

range of volcanic rocks. For similar reasons given above, the Upper Aershan Formation is

689

matched roughly with the Dabeigou Formation, the Lower Tenggeer Formation is comparable

690

with the Yixian Formation, the Upper Tenggeer Formation is equivalent to the Jiufotang

691

Formation, and the Saihan Formation is corresponded with the Fuxin Formation. The established

692

correlation of the Lower Cretaceous strata between the Erlian Basin and the Yan Shan further

693

confirms that the newly refined ages of the Bayanhua Group in the Erlian Basin are reliable.

694

5 Early Cretaceous tectonostratigraphic evolution of the Erlian Basin

695

Grounded on the stratigraphic, sedimentary, and structural characteristics unraveled by

696

isopach maps, well logs and seismic sections (Figs. 3–11), and the newly acquired zircon U-Pb

697

geochronological data (Table 1; Fig. 13), the present study reestablishes the tectonosedimentary

698

evolution of the Erlian Basin during the Early Cretaceous, with primary characteristics shown in

699

Figs. 2 and 14a. The Early Cretaceous tectonosedimentary evolution of the Erlian Basin can be

700

split into eleven stages, each separated by a rapid transition in tectonic regime between extension

701

and contraction and marked by the formation of basin-wide unconformities (Fig. 14a).

702 703

Before the deposition of the Lower Aershan Formation, significant contractional deformation occurred in the Erlian Basin. A conspicuous angular unconformity (T11 or Tg)

32

704

separated the Lower Aershan Formation from the Paleozoic and Jurassic strata (Figs. 3f–h, 5f–g

705

and 7f). The Paleozoic basement, the Aqitu, Gerile and Qiha formations, and the Xing’anling

706

Group were strongly folded and eroded (Figs. 3f–h, 5f–g and 7f). However, the deformation of

707

the Lower Aershan Formation was relatively weak, indicating that intense compressional

708

deformation occurred in the basin between the deposition of the Xing’anling Group and the

709

Aershan Formation. Simultaneously with the contractional deformation, the Hugejiletu

710

Formation was sporadically deposited in the Erlian Basin. The Hugejiletu Formation is mainly

711

composed of synorogenic conglomerate, breccia, and pebbly sandstone (Xu et al., 2003; Guo et

712

al., 2018a) (Fig. 2). On the basis of zircon U-Pb ages and regional stratigraphic correlations, the

713

ages of the Hugejiletu Formation and the Xing’anling Group have been refined to the Tithonian–

714

early Valanginian (ca. 151–139 Ma) and the Oxfordian–early Kimmeridgian (ca. 163–153 Ma),

715

respectively (Guo et al., 2018a) (Fig. 2). Integrating with the middle Valanginian (ca. 138–135

716

Ma) age of the Lower Aershan Formation (Figs. 2 and 14a), the present study refines the

717

contractional event before the deposition of the Lower Aershan Formation to the late

718

Kimmeridgian–early Valanginian (ca. 153–138 Ma) (Figs. 2 and 14a).

719

During the middle Valanginian (ca. 138–135 Ma), the Erlian Basin entered into an

720

extensional stage (Figs. 2 and 14a). Numerous normal faults were generated in the basin,

721

controlling the deposition of the Lower Aershan Formation (Figs. 3f–h, 5g–h and 7f).

722

After the deposition of the Lower Aershan Formation (middle Valanginian, ca. 135 Ma), the

723

Erlian Basin underwent another episode of contractional deformation (Figs. 2 and 14a). In many

724

sags of the Erlian Basin, the Lower Aershan Formation was moderately folded and eroded, and

725

was truncated by the angular unconformity T10 at the base of the Upper Aershan Formation

726

(Figs. 3f–h, 5g–h and 7f).

33

727

During the late Valanginian (ca. 135–133 Ma), extension and syn-rift subsidence resumed in

728

the Erlian Basin (Figs. 2 and 14a). The Upper Aershan Formation was deposited in a series of

729

grabens and half-grabens, as revealed by seismic profiles (Figs. 3f–h, 5g–h and 7f–g).

730

After the deposition of the Upper Aershan Formation (latest Valanginian, ca. 133 Ma),

731

contractional tectonic regime sprung up again in the Erlian Basin (Figs. 2 and 14). The Upper

732

Aershan Formation was inhomogeneously folded and uplifted, and was truncated by the

733

unconformity T8 (Figs. 3f–h, 5g–h and 7f–g). The unconformity T8 is a typical angular

734

unconformity and is widely recognized in the Erlian Basin.

735

During the Hauterivian–early Aptian (ca. 133–121 Ma), extensional stress regime resumed

736

(Figs. 2 and 14a). Significant syn-rift subsidence occurred in the entire Erlian Basin, including

737

the sags where the Lower and Upper Aershan formations were not deposited, such as the Central

738

Wuliyasitai Sag (Figs. 3f–h, 5f–h, 7f–g, 9d–e, and 11). This long-term, monotonous extensional

739

stress regime resulted in the formation of long-lasting lakes in most sags of the Erlian Basin and

740

the accumulation of extra-thick-bedded lacustrine mudstone (Figs. 4, 6, 8, and 10). The organic-

741

rich deep lacustrine mudstone of the Lower Tenggeer Formation constitutes the prime petroleum

742

source rocks of the Erlian Basin (Chen et al., 2014; Zhu et al., 2018).

743

After the deposition of the Lower Tenggeer Formation (middle Aptian, ca. 120 Ma), a NE–

744

SW contractional event probably occurred in the basin (Figs. 2 and 14a). The Lower Tenggeer

745

Formation and underlying strata were tilted and eroded, and was truncated by the unconformity

746

T6 (Figs. 3f–h, 5f–h, 7f–g, 9, 11, and 12c). The unconformity T6 was widely developed in the

747

sags of the Erlian Basin, and has become one of the most obvious angular unconformities in the

748

basin. Numerous NW–SE striking folds involving the Lower Tenggeer Formation have been

34

749

recognized below the unconformity T6 in some sub-basins, such as the Honghaoershute and

750

Saihantala sags (Figs. 3h and 11c–d).

751

During the middle Aptian (ca. 119–115 Ma), extensional stress regime recovered in the

752

basin (Figs. 2 and 14a). New secondary normal faults were developed, and boundary master

753

normal faults were reactivated, controlling the deposition of the Upper Tenggeer Formation (Figs.

754

3f–h, 5f–h, 7f–g, 9, and 11).

755

After the deposition of the Upper Tenggeer Formation (late Aptian, ca. 115 Ma), a

756

contractional event probably occurred in the basin (Figs. 2 and 14a). The Upper Tenggeer

757

Formation and underlying strata were moderately or slightly tilted and eroded, and were

758

truncated by the unconformity T3 (Figs. 3f–h, 5h and 7f–g). The unconformity T3 is widely

759

observed in the Erlian Basin, and is another typical angular unconformity of the basin.

760

During the latest Aptian–Albian (post ca. 115 Ma), extensional tectonic stress regime

761

reactivated in the Erlian Basin (Figs. 2 and 14a). The Saihan Formation was deposited and was

762

controlled by the reactivated and newly-formed normal faults (Figs. 3g, 5g, 7f–g, 9, and 11),

763

suggesting that the Erlian Basin experienced another episode of syn-rift subsidence rather than

764

thermal subsidence during the latest Early Cretaceous as suggested by Lin et al. (2001) and Chen

765

et al. (2014) (Fig. 2).

766

After the deposition of the Saihan Formation, a significant NW–SE compressional inversion

767

occurred in the basin (Guo et al., 2018b) (Figs. 2 and 14a). The Saihan Formation and lower

768

strata were strongly folded, exhumed, and eroded, and the depocenter of the basin migrated to

769

the northwestern basin (Guo et al., 2018b). Basin-scale intense extension and syn-rift subsidence

770

during the Early Cretaceous finally ceased.

35

771

In summary, the Early Cretaceous tectonostratigraphic evolution of the Erlian Basin is

772

characterized by frequent transitions in tectonic stress regime between extension and contraction.

773

During the middle Valanginian–Albian (ca. 138–101 Ma), the basin underwent intense extension

774

and syn-rift subsidence. Thick clastic sediments of the Bayanhua Group were deposited in the

775

long-term syn-rift episode, providing a prerequisite for deposition and maturation of source rocks,

776

especially the lacustrine mudstone of the Lower Tenggeer Formation. The syn-rift subsidence

777

was interrupted by multiphase contractional events, that occurred during the middle Valanginian

778

(ca. 135 Ma), the latest Valanginian (ca. 133 Ma), the middle Aptian (ca. 120 Ma), and the late

779

Aptian (ca. 115 Ma). The multiphase short-lived compressional pulses formed many anticlines

780

and several important unconformities in the basin, providing favorable traps for accumulating

781

hydrocarbon. At the Early/Late Cretaceous boundary, a strong compressional inversion event

782

occurred, the Bayanhua Group was severely eroded, and the basin-scale extension and syn-rift

783

subsidence finally ceased. The erosion of the upper part of the Bayanhua Group likely resulted in

784

that the source rocks in some sags of the Erlian Basin exited the oil window, which reduced, to

785

some extent, the hydrocarbon potential of the Erlian Basin.

786

6 Tectonic implications

787

Generally, the tectonic mechanisms, that drove regional tectonic stress regime transitions in

788

East Asia during the Late Mesozoic, are interpreted as changes in subduction styles of the Paleo-

789

Pacific Plate beneath the eastern Eurasian continent. The Late Jurassic–Early Cretaceous

790

extensional regime in East Asia is attributed to the roll-back of the westward subducting Paleo-

791

Pacific slab (e.g., Watson et al., 1987; Traynor and Sladen, 1995; Liu et al., 2018), and the

792

sporadic compressional events are suggested to be caused by rapid low-angle subduction of the

36

793

Paleo-Pacific Plate (e.g., Liu et al., 2018). However, such an interpretation fails to account for

794

the fact that the transitions in tectonic stress regime between extension and contraction occurred

795

repeatedly and frequently in the Erlian Basin during the Early Cretaceous (Fig. 14). The model

796

of low-angle subduction of the Paleo-Pacific Plate also fails to explain the NE–SW direction of

797

the compressional deformation in the Erlian Basin during the middle Aptian (ca.120 Ma), that

798

was nearly perpendicular to the subduction direction. In addition, given that the subduction angle

799

of the Paleo-Pacific Plate during the Early Cretaceous has still been poorly constrained, and the

800

Erlian Basin was located over 2,000 km away from the Asia-Pacific boundary, the subduction of

801

the Paleo-Pacific Plate was probably not the first-order geodynamic mechanism for the

802

extensional and compressional deformation in the Erlian Basin during the Early Cretaceous.

803

It is suggested here that the contractional event in the Erlian Basin during the earliest

804

Cretaceous (prior to ca. 138 Ma) was likely induced by the combined effects of the collision

805

between the Kolyma-Omolon Block and the Siberia Craton, and the rapid closure of the Mongol-

806

Okhotsk Ocean, as suggested by Yang et al. (2015a, b) and Guo et al. (2018a) (Fig. 15). The

807

collision between the Kolyma-Omolon Block and the Siberia Craton occurred during the latest

808

Jurassic–earliest Cretaceous (ca. 155–135 Ma), led to severe folding and thrust faulting in the

809

northeastern margin of the Siberia (Oxman, 2003; Prokopiev and Oxman, 2009; Fridovsky,

810

2018), and enhanced the continental collision between the Siberia Craton and Amuria Block

811

along the eastern Mongol-Okhotsk Suture following the closure of the Mongol-Okhotsk Ocean

812

(Yang et al., 2015a). Far-field effects of these continental collision events likely resulted in the

813

compressional tectonic regime in the Erlian Basin prior to ca.138 Ma.

814

The intermittent extension and syn-rift subsidence in the Erlian Basin during the middle

815

Valanginian–Albian (ca. 138–101 Ma), probably resulted from the northeast- and east-ward

37

816

tectonic escape of East Asia, driven by the collision of the Karakoram-Lhasa Block with the

817

southern margin of Asia, as suggested by Yang et al. (2015a, 2017) (Fig. 15). The continuous

818

collision between the Karakoram-Lhasa Block and the southern margin of Asia during the Early

819

Cretaceous led to significant contractional deformation in the Tibet Plateau and the Northwest

820

China, and probably drove the left-lateral strike-slip faulting in Northeast China (Yang et al.,

821

2015a, 2017). Postorogenic gravitational collapse of the thickened continental crust was likely

822

activated by these strike-slip faults, resulting in the extension and syn-rift subsidence in the

823

Erlian Basin and other regions in East Asia. Several structural studies of the Erlian Basin (Qi et

824

al., 2015; Miao et al., 2017) have suggested that the Hegenshan Fault and Xar Moron Fault

825

underwent left-lateral strike-slip motion during the Early Cretaceous (Figs. 1b and 15), resulting

826

in vertical and horizontal extension of major border faults in the Erlian Basin.

827

The multiple episodes of short-lived compressional deformation in the Erlian Basin during

828

the middle Valanginian (ca. 135 Ma), latest Valanginian (ca. 133 Ma), middle Aptian (ca. 120

829

Ma), and late Aptian (ca. 115 Ma) were likely driven by several continental collision events

830

along Asian margins during the Early Cretaceous (Figs. 14 and 15). (1) During middle–late

831

Valanginian, the last stage of the collision between the Siberia Craton and the Amuria Block

832

following the final closure of the Mongol-Okhotsk Ocean occurred to the north and northeast of

833

the Mohe-Upper Amur Basin (Guo et al., 2017). The collision event resulted in the uplift of the

834

northern margin of the Mohe-Upper Amur Basin, and the formation of a regional sedimentary

835

hiatus in the Hailar-Tamsag, Songliao and Sanjiang-Middle Amur basins (Guo et al., 2017 and

836

references therein) (Fig. 1b), and likely shortly affected the Erlian Basin, leading to the

837

compressional deformation during the middle and latest Valanginian (ca. 135 Ma and ca. 133 Ma)

838

and the formation of the T10 and T8 angular unconformities.

38

839

(2) During the latest Barremian–early Aptian (ca. 126–120 Ma), the Chukotka Block

840

collided with the Kolyma-Omolon Block along the South Anyui Suture in Northeast Russia

841

(Miller et al., 2009; Shephard et al., 2013; Amato et al., 2015). The collision and indentation of

842

the Chukotka Block resulted in thrusting and folding along the South Anyui Suture (Sokolov et

843

al., 2002, 2009; Amato et al., 2015; Sokolov and Tuchkova, 2015). The far-field effects of this

844

collision likely led to the NE–SW contractional deformation and the formation of the significant

845

T6 unconformity in the Erlian Basin during the middle Aptian (ca. 120 Ma). The contractional

846

deformation was also recorded in the Yan Shan, the southern Great Xing’an Range, and the

847

Songliao Basin (Figs. 1b and 15). In the Yan Shan, the angular unconformity between the Yixian

848

and the Jiufotang formations is equivalent to the T6 unconformity in the Erlian Basin (Fig. 14a–

849

b). In the southern Great Xing’an Range, a coeval unconformity is preserved between the Murui

850

and the Baiyingaolao formations (Han et al., 2018). In the Songliao Basin, the Lower Cretaceous

851

Huoshiling–Shahezi formations were rested by the Yingcheng Formation with an angular

852

unconformably named T41 (Wang, 2017; Li et al., 2018). Zircon U-Pb dating of volcanic rocks

853

in the Huoshiling and Yingcheng formations gave age ranges of ca. 133–120 Ma and ca. 119–

854

106 Ma, respectively (Pei et al., 2008; Cao, 2010), revealing that the T41 unconformity in the

855

Songliao Basin is comparable with the T6 unconformity in the Erlian Basin.

856

(3) Determining the geodynamic origin of the contractional deformation in the Erlian Basin

857

during the late Aptian (ca. 115 Ma) is difficult, as no coeval continental collision events has been

858

precisely constrained along Asian margins. We tentatively suggested here that this contractional

859

deformation was possibly associated with the collision between a microcontinental block and the

860

South China Block. The microcontinental block might be the West Philippines microcontinent,

861

which is composed of the islands of Mindoro, Romblon, Panay, and Palawan, the eastern Borneo,

39

862

and the northern Sulawesi, in Southeast Asia (Faure et al., 1989; Faure and Natal'in, 1992;

863

Charvet et al., 1994). Suture zone between the West Philippines microcontinent and the South

864

China Block has been identified in the islands of Mindoro, Romblon, Sibuyan, Tablas, and

865

Palawan (Faure et al., 1989; Faure and Natal'in, 1992; Charvet et al., 1994; Lapierre et al., 1997).

866

Although the timing of the collision between the West Philippines microcontinent and the South

867

China Block has not been precisely dated, ductile sinistral shearing of faults and a magmatic

868

quiescence during ca. 117–108 Ma have been identified in South China (Tong and Tobisch, 1996;

869

Wang and Lu, 2000; Li et al., 2014). The timing of the collision event is generally compatible

870

with the contractional deformation in the Erlian Basin during the late Aptian (ca. 115 Ma),

871

indicating a possible causal relationship. The contractional deformation was also recorded in the

872

Yan Shan and the Jiaodong Peninsula to the southeast of the Erlian Basin (Figs. 1b and 15). In

873

the Yan Shan, the unconformity between the Jiufotang and Fuxin formations is equivalent to the

874

T3 unconformity in the Erlian Basin (Fig. 14a–b). In the Jiaodong Peninsula, multiple-

875

thermochronometer studies of Early Cretaceous granites revealed that these granites underwent a

876

rapid cooling event during ca. 117–110 Ma (Wu et al., 2018).

877

The contractional inversion event in the Erlian Basin after the deposition of the Saihan

878

Formation was likely induced by the continental collision between the Okhotomorsk Block and

879

the eastern margin of Asia (Yang, 2013; Guo et al., 2018b) (Fig. 15). The intense continental

880

collision led to a significant continental-scale orogenic event in East Asia (Yang, 2013), and

881

terminated the basin-scale extension and syn-rift subsidence in the Erlian Basin.

40

882

7 Conclusions

883

Based on the newly obtained zircon U-Pb geochronological data, well logs, and seismic

884

reflection profiles, the present study refines the ages of the Lower Cretaceous strata of the Erlian

885

Basin, and reestablishes the Early Cretaceous tectonosedimentary evolution of the basin. The age

886

of the Lower Aershan Formation is constrained to the middle Valanginian (ca. 138–135 Ma), the

887

age of the Upper Aershan Formation is constrained to the late Valanginian (ca. 135–133 Ma), the

888

age of the Lower Tenggeer Formation is constrained to the Hauterivian–early Aptian (ca. 133–

889

121 Ma), the age of the Upper Tenggeer Formation is constrained to the middle Aptian (ca. 119–

890

115 Ma), and the age of the Saihan Formation is constrained to the latest Aptian–Albian (post ca.

891

115 Ma). The Early Cretaceous evolution of the basin is characterized by intermittent extension

892

and syn-rift subsidence, and the Early Cretaceous syn-rift subsidence was interrupted by

893

multiphase contractional events, that occurred during the earliest Cretaceous (prior to ca. 138

894

Ma), middle Valanginian (ca. 135 Ma), latest Valanginian (ca. 133 Ma), middle Aptian (ca. 120

895

Ma), late Aptian (ca. 115 Ma), and Early/Late Cretaceous boundary.

896

The geodynamic mechanisms for the Early Cretaceous tectonostratigraphic evolution of the

897

Erlian Basin are discussed. The extensional and contractional deformation in the Erlian Basin

898

during the Early Cretaceous is tentatively attributed to a series of continental collisions along

899

Asian margins: Karakoram-Lhasa/Qiangtang collision, Kolyma-Omolon/Siberia collision,

900

Siberia/Amuria collision, Chukotka/Kolyma-Omolon collision, West Philippines/South China

901

collision, and Okhotomorsk/East Asia collision.

41

902

903

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No.

904

41372111). We sincerely thank the Editor Adam Bumby and two anonymous reviewers for their

905

very helpful comments and suggestions. We also thank Yi-Lin Xiao and Zhen-Hui Hou for their

906

support during U-Pb dating by LA-ICP-MS.

907

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Yang, Y.T., Song, C.C., He, S., 2015b. Jurassic tectonostratigraphic evolution of the Junggar

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significance of bottom and top Beds of Zhangjiakou Formation in Liaoning and Hebei

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1264

Craton in a backarc setting: Evidence from crustal deformation kinematics. Gondwana

1265

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1267

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2233-2257.

1269

Zhu, X., Zhang, R., Zhu, S., Wei, W., Shi, Y., Jiang, S., 2018. Characteristics and genetic

1270

mechanism of unusual reservoir rocks in the Cretaceous of Erlian Basin (in Chinese).

1271

Science Press, Beijing, 1-235.

1272

Zhu, Y.H., Zhang, W.C., Wang, H.S., Cui, Z.Q., Li, H.Y., Han, C.Y., Zhang, F., Liu, X., 2000.

1273

Sedimentary Facies and Hydrocarbon-bearing of Lower Cretaceous strata in Erlian Basin

1274

(in Chinese). Science Press, Beijing, 1-234.

58

1275

Fig. 1. (a) Tectonic map of Asia, modified after Sokolov et al. (2009), Jolivet (2015) and Yang et

1276

al. (2017). (b) Tectonic map of Northeast China and adjacent areas, showing the locations of the

1277

sedimentary basins, faults, sutures, and mountain belts involved in the text. (c) Geological map

1278

of the Erlian Basin, showing the locations of sub-basins mentioned in the text.

1279 1280

Fig. 2. Stratigraphic section of the Erlian Basin. Thickness, lithology and sedimentary facies are

1281

modified after Xu et al. (2003), Tao et al. (2013) and Guo et al. (2018a, b). Fossil-based ages are

1282

adapted from * Tao et al. (2013); ** Xing (2012); *** Van Itterbeeck et al. (2005) and Bonnetti

1283

et al. (2014). Basin evolution is adapted from ① Lin et al. (2001) and Chen et al. (2014); ② Guo

1284

et al. (2018b); ③ Guo et al. (2018a); ④ the present study.

1285 1286

Fig. 3. (a) Sketchy isopach map of the Lower Aershan Formation in the Honghaoershute Sag. (b)

1287

Sketchy isopach map of the Upper Aershan Formation. (c) Sketchy isopach map of the Lower

1288

Tenggeer Formation. (d) Sketchy isopach map of the Upper Tenggeer Formation. (e) Sketchy

1289

isopach map of the Saihan Formation. (f–h) Interpreted and uninterpreted seismic reflection

1290

profiles from the Honghaoershute Sag, with section locations shown in (a–e).

1291 1292

Fig. 4. Well sections of the Bayanhua Group in the Honghaoershute Sag, showing the locations

1293

and U-Pb ages of the analyzed samples. Well locations are shown in Fig. 3a–e.

1294 1295

Fig. 5. (a) Sketchy isopach map of the Lower Aershan Formation in the Jiergalangtu Sag. (b)

1296

Sketchy isopach map of the Upper Aershan Formation. (c) Sketchy isopach map of the Lower

59

1297

Tenggeer Formation. (d) Sketchy isopach map of the Upper Tenggeer Formation. (e) Sketchy

1298

isopach map of the Saihan Formation. (f–h) Interpreted and uninterpreted seismic reflection

1299

profiles from the Jiergalangtu Sag, with section locations shown in (a–e).

1300 1301

Fig. 6. Well sections of the Bayanhua Group in the Jiergalangtu Sag, showing the locations and

1302

U-Pb ages of the analyzed samples. Well locations are shown in Fig. 5a–e.

1303 1304

Fig. 7. (a) Sketchy isopach map of the Lower Aershan Formation in the Abei-Anan Sag. (b)

1305

Sketchy isopach map of the Upper Aershan Formation. (c) Sketchy isopach map of the Lower

1306

Tenggeer Formation. (d) Sketchy isopach map of the Upper Tenggeer Formation. (e) Sketchy

1307

isopach map of the Saihan Formation. (f–g) Interpreted and uninterpreted seismic reflection

1308

profiles from the Abei-Anan Sag, with section locations shown in (a–e). Note that the

1309

northeastern part of the sag is not involved in the isopach maps, due to a lack of seismic

1310

reflection profiles.

1311 1312

Fig. 8. Well sections of the Bayanhua Group in the Abei-Anan Sag, showing the locations and

1313

U-Pb ages of the analyzed samples. Well locations are shown in Fig. 7a–e.

1314 1315

Fig. 9. Sketchy isopach maps of the Lower Tenggeer Formation (a), Upper Tenggeer Formation

1316

(b), and Saihan Formation (c), and interpreted and uninterpreted seismic reflection profiles (d–e)

1317

of the Central Wuliyasitai Sag.

1318

60

1319

Fig. 10. Well sections of the Xing’anling Group, Lower Tenggeer, Upper Tenggeer, and Saihan

1320

formations in the Central Wuliyasitai Sag, showing the locations and U-Pb ages of samples

1321

analyzed by Sun et al. (2017) and Guo et al. (2018a). Well locations are shown in Fig. 9a–c.

1322 1323

Fig. 11. Interpreted and uninterpreted seismic reflection profiles (b–d) from the Saihantala Sag,

1324

with section locations shown in (a).

1325 1326

Fig. 12. Lithological section of the well Aer24 (b) and interpreted and uninterpreted seismic

1327

reflection profile (c) from the Aer Sag, with seismic section and well locations shown in (a).

1328 1329

Fig. 13. Zircon U-Pb age concordia diagrams and weighted mean ages of the analyzed samples.

1330 1331

Fig. 14. (a) A summary of zircon U-Pb ages of the Bayanhua Group, reported in this and

1332

previous studies, and the reestablished tectonostratigraphic evolution of the Erlian Basin during

1333

the latest Jurassic–Early Cretaceous. (b) Stratigraphic section of the Yan Shan. (c) Regional

1334

tectonic events that occurred along Asian margins. Timing of the collision between the Kolyma-

1335

Omolon and Siberia is from Oxman (2003). Timing of the closure of the eastern Mongol-

1336

Okhotsk Ocean is from Yang et al. (2015a) and Guo et al. (2017). Timing of the collision

1337

between the Karakoram-Lhasa and Qiangtang is from Zhu et al. (2013) and Yang et al. (2017).

1338

Timing of the collision between the Chukotka and Kolyma-Omolon is from Miller et al. (2009),

1339

Shephard et al. (2013), and Amato et al. (2015). Timing of the collision between West

1340

Philippines microcontinent and Southeast Asian margin is estimated from the magmatic hiatus in

1341

Southeast China (Li et al., 2014).

61

1342 1343

Fig. 15. Tectonic reconstruction of East Asia during the earliest Cretaceous, modified after Faure

1344

and Natal’in (1992), Golonka (2011), and Yang et al. (2013, 2015a, 2017). Abbreviation, BNT:

1345

Bangong-Nujiang Tethys; EB: Erlian Basin; DF: Derbugan Fault; GR: Great Xing’an Range; HF:

1346

Hegenshan Fault; HTB: Hailar-Tamsag Basin; MUB: Mohe-Upper Amur Basin; SLB: Songliao

1347

Basin; SMB: Sanjiang-Middle Amur Basin; XMF: Xar Moron Fault; YAN: Yan Shan.

1348

62

1349

Table 1 Details of samples collected for zircon U-Pb dating. Sample

Well

Depth (m)

Lithology

Stratigraphic division

U-Pb age (Ma)

andesite tuff tuff tuff andesite tuff andesite andesite

Lower Aershan Fm. Lower Aershan Fm. Lower Aershan Fm. Lower Aershan Fm. top of the Upper Aershan Fm. Lower Tenggeer Fm. Lower Tenggeer Fm. Lower Tenggeer Fm.

138 ± 4 138 ± 1 136 ± 3 136 ± 1 134 ± 2 132 ± 1 128 ± 2 125 ± 2

bottom of the Lower Aershan Fm.

138 ± 1

Lower Aershan Fm. Lower Aershan Fm. top of the Lower Aershan Fm. Upper Aershan Fm.

138 ± 4 137 ± 2 135 ± 3 135 ± 5

Upper Aershan Fm.

134 ± 6

top of the Upper Aershan Fm. bottom of the Lower Tenggeer Fm. Upper Tenggeer Fm. Upper Tenggeer Fm.

133 ± 2 133 ± 2 117 ± 4 116 ± 3

Honghaoershute Sag H40-1 H17-2 HC1-3 H33 HC1-2 HC1-1 H37 H12

H40 H17 HC1 H33 HC1 HC1 H37 H12

1057 1531 2749 2246 1905 1706 1728 743

Jiergalangtu Sag J55

J55

1343

J45 J13-1 J33 J42-7

J45 J13 J33 J42

1533 207 1663 1890

J46

J46

1005

J31-1 J74 J19 J9

J31 J74 J19 J9

620 955 452 373

andesitic breccia andesite basaltic breccia andesite andesite andesitic breccia tuff tuff andesite basalt

Abei-Anan Sag Ha35-2

Ha35

1288

andesitic breccia

top of the Upper Aershan Fm.

134 ± 1

Aer24

1332

andesite

bottom of the Upper Tenggeer Fm.

119 ± 2

Aer Sag Aer24 1350

63

lia

India

(c) 46°

110°

108°

112°

ult

lt

an

ton

Fa

ult

gF a

ult

Fau

ish

nh

pa

n

ihan Bal ng-

f Ja

Yan Shan

ao

n Fault

North China

Major sub-basins of the Erlian Basin

Du

ina Ch orea K

Se

Xar Moro

114°

Songliao Basin

Sanjiang Basin

Erlian Basin

Yi n Sh an 40˚

n

ult

ult

North China Jiaodong Q a id a m Peninsula Song p a n - Q in li n g -D a b ie Ganz i South China

Hege

Fa

Fa

Ja

ng

bi

n sha

lu

Lh as a H im a la y a

Q il ia n -

Go

n

Ta n

30°

Q ia n g ta

st Ea

n pa

lipp Sea ine

Karakoram

Tarim

Phil

Pamir

si Ba

Ne

Sea of Japan

Karakoram Fault

Middle Amur Basin

Rus s C h in ia a

njia

Belt

Great

Oro gen ic

Ha

As ian

50˚

ila B a r - Ta sin ms a

50°

ral

asin

Fa

b

- Yi

50˚

ns

g D e rb X i n g ’ a n R a n g e ugan

Tr a

on B

f Sea o k O k h o ts

-M

ke

ka

La

Sea of Okhotsk

ai

Siberia

(b)

Cent

Bok Mohe-Upper Amur Basin

Ba

E Eu ast rop e

Kolyma-Omolon

Siberia

an

t uth Anyui Su

130˚

120˚

Yi l

So

110˚

(b)

ua

Chukotka

l



ika

14

e

100°

°

ur

60

(a)

40˚

Beijing

116° Fig. 9 Central Wuliyasitai Sag

118°

120°

Fig.12 Aer Sag

46°

Seismic cross sections China/Mongolia border

Fig.7 Abei-Anan Sag

Basin boundary

Fig. 5 Jiergalangtu Sag 44°

44°

East Gobi Basin

Fig.3 Honghaoershute Sag

Erlian Basin Mo

Great Xing’an Range

lia ngo ina h C

42°

42°

Fig.11 Saihantala Sag

Yan Shan 108°

Yin Shan

Hohhot 112°

114°

116°

100 km

118°

s s s

2500

Xing’anling Gp.

2400

2300

2200

2100

2000

1800

1700

ss ss ss

1500

Pz

1400

Upper Tenggeer Fm.

1600

1300

1400

1200

Paleozoic

(Guo et al., 2018a)

154 Ma

J 3 x: Xing'anling Group s s

800

900

700

800

1100

1000

800

Lower Tenggeer Fm. 1200

s sssssssss s s s s s s s s s s s s s

1300

1000

124 Ma

s s

s s s

900

900

600

Saihan Fm.

700

500

900

700

800

600

400

700

600

200

300

300

500

300

Saihan Fm.

300

400

Upper Tenggeer Fm.

500

400

500

400

Saihan Fm. 500

Saihan Fm. 600

600

Xing’anling Gp. Lower Tenggeer Fm. Upper Tenggeer Fm.

1000

1000

(Sun et al., 2017)

s s

1400

1100

1100

Upper Tenggeer Fm. 1200

700

400

Saihan Fm.

200

100

200

200

(m)

(m)

(m)

(m)

(m)

T18

s s s

s s

1300

800

K 1 tu

TC2

s s

s s

1900

Lower Tenggeer Fm.

Paleozoic

155 Ma

2600

1500

Lower Tenggeer Fm.

900

T28

2700

(Guo et al., 2018a)

sssssss sssssss sssssss

1600

Paleozoic

J3x

1000

Lower Tenggeer Fm. 1100

T8 T14

(Sun et al., 2017)

121 Ma

stratigraphic subdivision

basalt

andesite

tuff

conglomerate

pebbly sandstone

sandstone

tuffaceous siltstone

siltstone

coal

dolomitic mudstone

mudstone/shale

sample locations

K 1 tu: Upper Tenggeer Formation

(b)

0.5

(a) Saihantala

0.5

Saihan Fm

Sag

N

1.0

1.5

1.5

T6

Lower Tenggeer Fm

T8 2.0

2.0

Aershan Fm T11/Tg

2.5

3.0

2.5

Jurassic or Paleozoic

T3

NW

T6

T8

T11/Tg

1 km

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

1 km

NW

Fig. 11b Fig. 11c Fig. 11d

Seismic cross sections Axis of the syncline innvolving the Lower Tenggeer Fm.

3.0

0.5

3.0

20 km

Two-way travel time (s)

Two-way travel time (s)

1.0

Upper Tenggeer Fm

Two-way travel time (s)

Two-way travel time (s)

T3

3.0

(c) 0.5

0.5

Saihan Fm

1.0

Upper Tenggeer Fm 1.5

onlap

T6 T8

Lo w er Te

2.0

ng ge er

1.5

Fm

2.0

T11/Tg

truncation

2.5

Two-way travel time (s)

Two-way travel time (s)

T3 1.0

2.5

Aershan Fm Jurassic or Paleozoic T3

SW

T6

T8

syncline

T11/Tg

1 km

3.0

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

3.0

1 km

SW

Two-way travel time (s)

Two-way travel time (s)

3.0

3.0

(d) 0.5

0.5

Saihan Fm T3 1.0

Upper Tenggeer Fm 1.5

onlap

T6

T8

1.5

Lower Tenggeer Fm T11/Tg

2.0

2.0

truncation Jur

2.5

Aershan Fm ass

ic o

rP

ale

ozo

ic

syncline

Ju

s ic ras

or P

a le

ozo

ic

2.5

truncation

3.0

3.0

SW

T3

T6

T8

T11/Tg

1 km

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

3.0

3.0

SW

1 km

Two-way travel time (s)

Two-way travel time (s)

Two-way travel time (s)

Two-way travel time (s)

1.0

10 km

Aer24

(c)

Two-way travel time (s)

1.0

1.5

1200

Upper Tenggeer Fm.

1300 1400

119 Ma (Aer24)

1500

N Aer24

1600

Fig. 12c

1100

(b) Aer24

Aer Sag

Lower TenggeerFm.

(a)

Aer24 truncation

Upper Tenggeer Fm

T6

2.0

Lower Tenggeer Fm

truncation

2.5

3.0

SW

T6

1 km

Two-way travel time (s)

1.0

1.5

2.0

2.5

3.0

SW

1 km

(a) H40-1 0.16

(b) H17-2 0.05

Mean age = 138 ± 4 Ma MSWD = 0.08; n = 4

(c) HC1-3

0.28

Mean age = 138 ± 1 Ma MSWD = 0.34; n = 21

900

0.24

0.025

(d) H33

0.024

Mean age = 136 ± 1 Ma MSWD = 0.30; n = 31

160

Mean age = 136 ± 3 Ma MSWD = 0.25; n = 8

300

1400 150

260

220

0.03

180

144

0.023

1000 0.16

100

0.04

132

130

0.4

0.8

207Pb/235U

1.2

0.1

0.2

0.3

0.4

207Pb/235U

550 260

(f) HC1-1

450

206Pb/238U

206Pb/238U

0.03

180

350

134

250

0.04

1

2

150

0.12

300 0.055

Mean age = 128 ± 2 Ma MSWD = 0.77; n = 20 260

0.2

0.4

0.03 180

132 124 60

116 0.2

0.4

0.6

0.8

207Pb/235U

1.0

1.2

1.4

1800

0.06

Mean age = 138 ± 4 Ma MSWD = 0.33; n = 7

0.3

0.1

0.2

0.3

0.005 0.0

0.4

207Pb/235U

(k) J13-1

380

Mean age = 137 ± 2 Ma MSWD = 0.23; n = 25

0.05

1400

0.28

340

0.24

1000

155 141

200

(m) J42-7 1300

0.16

142

700

0.20

Mean age = 134 ± 6 Ma MSWD = 0.01; n = 4

180

0.12

500

300

130 0.1

0.2

0.3

207Pb/235U

0.4

2

3

207Pb/235U

(p) J74

450 0.06

450

Mean age = 133 ± 2 Ma MSWD = 0.10; n = 21

250

0.04

139

250

0.04

142

150 150

0.02

133

134

0.04 140

1

100

100

126

0.00 0

2

Mean age = 117 ± 4 Ma MSWD = 0.10; n = 16

0.00 0

3

207Pb/235U

(q) J19

50

126 1

2

650

(r) J9

1300 0.09 1100

Mean age = 116 ± 3 Ma MSWD = 0.09; n = 24

50

127

0.00 0.0

3

207Pb/235U

0.18

0.2

126

0.4

0.6

207Pb/235U

(s) Ha35-2

550 0.08

0.00 0.0

0.14

550

Mean age = 134 ± 1 Ma MSWD = 0.10; n = 22

0.12

450

450

0.10

120

350 0.05 250

110 500

350

250

0.04

140

0.03

100

0.06

206Pb/238U

130 700

206Pb/238U

206Pb/238U

900 0.14

0.01

1.5

2.5

0.5

207Pb/235U

0.7

0.00 0.0

124

126

0.2

0.4

207Pb/235U

120

130 0.02

0.3

700

0.06 300

50

0.1

0.5

500

0.08

134 50

207Pb/235U

0.4

(t) Aer24

100

110

100 0.5

0.3

207Pb/235U

0.04

150 0.02

120

100

0.2

Mean age = 119 ± 2 Ma MSWD = 0.38; n = 10

142

150

300

0.1

0.10

0.07 206Pb/238U

1

350

0.02

134

150

128

120

142

300

120

0.06

140

0.00 0

0.5 550

Mean age = 133 ± 2 Ma MSWD = 0.04; n = 20

200

134

144 160

350

700

160

0.04 100

0.08

1300

900

0.08

500

0.08

0.24

0.01 0.0

5

4

3

207Pb/235U

0.06

900

0.12

700 500

136

(o) J31-1

0.16

0.12

0.04

1100

1100

900

100

(n) J46

1500

Mean age = 135 ± 5 Ma MSWD = 0.04; n = 5

2

1300

1100

0.16

300

138 100

1

1500

Mean age = 135 ± 3 Ma MSWD = 0.08; n = 5

140

135

100

0.0 0

0.4

206Pb/238U

206Pb/238U

0.3

0.4

(l) J33

0.08

206Pb/238U

207Pb/235U

0.20

154

115

0.2

0.3

207Pb/235U

180

150

200

133 0.1

220

0.03

0.02

0.018

0.014

0.04

146

137

120

260

250

600

0.1

0.022

0.02

0.2

300 206Pb/238U

160

0.2

206Pb/238U

0.026

206Pb/238U

206Pb/238U

206Pb/238U

0.030

0.22

0.1

0.20 200

0.24

100

115 0.01

0.034

0.28

180 140

0.015

(j) J45

Mean age = 138 ± 1 Ma 240 MSWD = 0.31; n = 23

340

300

0.025

125

126

(i) J55

0.20

220

140

134

0.00 0.0

0.6

207Pb/235U

0.18

(h) H12 Mean age = 125 ± 2 Ma MSWD = 0.38; n = 18

100

Mean age = 134 ± 2 Ma MSWD = 0.05; n = 19 0.01 0.0

207Pb/235U

260

0.02

0.02

0.16

0.035

142

150

(e) HC1-2

100

0.14

0.045

135

0.02

0.042

3

207Pb/235U

140

0.038

132 0.019

220 206Pb/238U

0.06

115

0.04

Mean age = 132 ± 1 Ma MSWD = 0.21; n = 27

220

136

0.020

140

(g) H37

0.08

135

130

120 0.00 0

155 0.04

142

200

132

0.01 0.0

1.6

160

206Pb/238U

100

140

0.021 0.08

138

0.02

136

140

0.00 0.0

150

600 140

150

140

0.022

0.12

140 300 0.04

206Pb/238U

500

0.08

0.20 206Pb/238U

0.04

700 206Pb/238U

206Pb/238U

0.12

0.6

0.8

0.00

0.2

116 0.4

0.6

0.8

207Pb/235U

1.0

1.2

siltstone conglomerate pebbly sandstone sandstone coal tuff mudstone unconformity K 1 al: Lower Aershan Formation K 1 au: Upper Aershan Formation K/C collision: Kolyma-Omolon/Chukotka collision sedimentary hiatus W/A collision: collision between West Philippines microcontinent and southeastern margin of Asia O/A collision: collision between Okhotomorsk and eastern margin of Asia

dolomitic mudstone

basalt

andesite

Saihan Fm.

Upper Tenggeer Fm.

Lower Tenggeer Fm.

Upper Aershan Fm.

Lower Aershan Fm.

Extension

Contraction

W/A collision

?

Fuxin Formation

O/A collision

Contraction

T11

Karakoram-Lhasa/Qiangtang collision

?

Jiufotang Fm

(Guo et al., 2018b) (maximum age of sandstone)

Lithology

Seismic surface

Strata

Gradual closure of the eastern Mongol-Okhotsk Ocean

Contraction

? K/C collision ?

Yixian Formation

J19 J9

Saihan Formation

(Ma)

(b) Yan Shan

Kolyma-Omolon/Siberia collision

Contraction Extension T10 Contraction s s s

Extension

K1d

T6

s s s

Extension

s s s

Aer24

T3

s s s

H37 H12 Tai14 (Sun et al., 2017)

J74 HC1-1

J46

Upper Tenggeer Formation

Albian

Extension

K1z

J42-7

J31-1

Ha35-2 HC1-2

Aptian Bayanhua Group

110

T2

Basin evolution and stress field

s s s

Lower Tenggeer Formation

A18-11 (Aershan Fm.; Guo et al., 2018a) H17-2 J55 H40-1 J45 J13-1 H33 HC1-3 J33

K 1 au

Hauterivian Barremian

Early Cretaceous

120

Zircon U-Pb ages provided by this and former studies

Tuchengzi Formation

s s s

K 1 al

Aershan Fm.

Valanginian

130

Strata

ss ss ss

Berriasian

140 Geologic Time

Hugejiletu Formation

Tithonian

150 Late Jurassic

(a) Erlian Basin (c) Regional tectonic events

Contraction

T8

Chukotka Collision of Chukotka with KolymaKo Omolon occurred during the latest Barremian-early Aptian (ca. 126Om lym o l o a - 120 Ma) n

Earliest Cretaceous Siberia

Collision of Kolyma-Omolon with Siberia occurred during ca. 155-135 Ma

Mongol-Okhotsk Ocean

MUB

EB X

Chin a

MF

GR HF

Jiaodong Peninsula

Collision of Okhotomorsk with East Asian margin occurred at ca. 100 Ma

Tarim South China

Songpan-Ganzi

Okhotomorsk

gtang M

oc hin a

rak ora BNT Ind m-L Zan us-Y gbo arlu has Te t n g a hys

WP

Qian

Ind

Ka

South Korea

Ta n lu F a u

Qilian-Qaidam

North Korea

YAN

North China Turan

SLB

Iz an ag i

Mongolia

continental-continental convergent boundary strike-slip fault motion direction of continental blocks continent ocean basin

HTB

lt

Central Asian Orogenic Belt

Am

uri

Kazakhstan

Closure of the eastern MongolOkhotsk Ocean occurred during the latest JurassicSMB earliest Cretaceous

DF

a

Russia

continental-oceanic convergent boundary

Collision of WPM with South China occurred during the late Early Cretaceous

Sedimentary facies

Seismic surface Source rock

Lithology

Maximum thickness

Stratigraphy

Basin evolution

Stratigraphic age Fossil-based age estimate

Radiometric age

① ② ③ ④

Saihan 1200 m Fm.

Braided channel Alluvial fan

late Valanginian–early Hauterivian

ca. 135–133 Ma (this study)

(Tao, 2003; Tao et al., 2013)

T10

Lake (Tao, 2003; Tao et al., 2013)

Lake

138 ± 1 Ma (Guo et al., 2018a) Oxfordian–Kimmeridgian

Tithonian–early Valanginian

(Tao et al., 2013)

(ca. 151–139 Ma, Guo et al., 2018a)

Tithonian–early Berriasian

Oxfordian–early Kimmeridgian

(Xu et al., 2003; Tao et al., 2013)

(ca. 163–153 Ma, Guo et al.,2018a)

Qiha Fm.

792 m

Lake

Gerile Fm.

363 m

Fluvial and swamp

Aqitu Fm.

456 m

Bajocian–Callovian (Tao et al., 2013)

Aalenian–early Bathonian Toarcian–Aalenian

Alluvial fan

(ca. 174–167 Ma, Guo et al., 2018a)

(Tao et al., 2013)

Fluvial and swamp

BI

Alluvial fan s s s s s s s s s s s s s s s

Xing’anling Gp. 800 m

T11

Syn-rift

Braided channel Alluvial fan

ca. 138–135 Ma (this study)

Syn-rift

Berriasian–early Valanginian

1083 m

s s s

Jurassic

Syn-rift

ca. 133–121 Ma (this study)

T8

Fluvial and lake 680 m

(Tao, 2003; Tao et al., 2013)

BI Syn-rift BI

early–middle Hauterivian

Lake

1250 m

Pliensbachian (Tao et al., 2013)

Tg

conglomerate pebbly sandstone sandstone dolomitic mudstone andesite coal tuff

siltstone unconformity

BI

ss ss ss

Paleozoic

mudstone/shale basin inversion

Syn-rift

121 ± 1 Ma (Sun et al., 2017) 124 ± 13 Ma (Sun et al., 2017)

Hugejiletu Fm. 355 m

Middle

BI

T6

BI

Alluvial fan

ca. 119–115 Ma (this study)

BI

(Tao, 2003; Tao et al., 2013)

Fluvial

Syn-rift

late Hauterivian–Barremian

1350 m

BI

Upper AersLowr Aershan Fm. han Fm.

T3

Lake

Fluvial

Aershan Fm.

latest Aptian–Albian (post ca. 115 Ma, Guo et al., 2018b)

Syn-rift

Upper Tenggeer Fm. Lowr Tenggeer Fm.

Tenggeer Fm.

Bayanhua Group

Cretaceous

Lower

early Aptian (Tao, 2003; Tao et al., 2013) or Aptian–Albian (Yang et al., 2003; Nie et al., 2007; Fan et al., 2008; Liu and Dai, 2013)

Delta Lake Alluvial fan

Upper

T2

BI Syn-rift

Fluvial

after early Cenomanian (≤ ca. 96 Ma, Guo et al., 2018b)

Syn-rift

Braided channel

Coniacian–early Campanian*, middle–late Campanian**, or post late Campanian***

Post-rift

500 m

Second syn-rift

Erlian Fm.

First syn-rift

Upper

T0 Overbank

BI Syn-rift

Cenozoic

(a) Lower Aershan Formation

(b) Upper Aershan Formation Fig. 4 H12

20 km

Fig. 3h

H37

HC1

HC1

Fig. 3f

(d) Upper Tenggeer Formation

HC1

N Fig. 4

H12

20 km

N H37

H33

Fig. 3g

(e) Saihan Formation

H40 Fig. 4

Fig. 3h

H17

H37

H40

H12

20 km

N

H33 Fig. 3f

Fig. 3g

Fig. 4

Fig. 3h

H17

N

H33

(c) Lower Tenggeer Formation

H12

20 km

H17

Fig. 3g

H40 Fig. 4

H40

Fig. 3f

20 km

H40

H12

≥ 400 m

200 ~ 400 m

0 ~ 200 m

Well locations Fig. 3h

H17 H37

HC1 Fig. 3g

H33

Fig. 3h

H17

N

Fig. 3f

Lithostratigraphic cross sections

H37

HC1

Boundary normal fault (arrow on the hanging wall)

H33

Fig. 3g

Axis of the syncline involving the Lower Tenggeer Fm. and underlying strata

Seismic cross sections

N

Fig. 3f

Axis of the syncline involving the Lower Tenggeer Formation and underlying strata H33

(f)

0.5

onlap

Saihan Fm T3

1.0

1.0

Upper Tenggeer Fm

T6

truncation

onlap 1.5

T8

Lower Tenggeer Fm

Upper Aershan Fm

H33

truncation

2.0

2.0

Lower Aershan Fm T3

NW

T6

T8

T10

T11/Tg

T11/Tg

truncation

syncline

Jurassic or Paleozoic

1 km

2.5

2.5

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

Two-way travel time (s)

Two-way travel time (s)

1.5

onlap

T10

Two-way travel time (s)

Two-way travel time (s)

0.5

1 km

NW 2.5

2.5

HC1

(g) 0.5

0.5

T3

1.0

HC1-1 HC1-2

Lower Tenggeer Fm 1.5

T8

1.5

Upper Aershan Fm T10

HC1-3

T11/Tg

2.0

truncation

T3

SW

T6

T8

T10

Lower Aershan Fm

Jurassic or Paleozoic

2.0

truncation 1 km

T11/Tg

2.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

1 km

SW

Two-way travel time (s)

0.5

2.5

2.5

H37

(h)

0.5

Upper Tenggeer Fm

H37

syncline

1.5

1.5

T6 T8 2.0

T 11

Lowe r Teng geer Fm 2.0

Aershan Fm

/Tg

Jurassic or Paleozoic 2.5

2.5

SW

T3

T6

T8

T11/Tg

1 km

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

SW

1 km

Two-way travel time (s)

1.0

T3

Two-way travel time (s)

Saihan Fm 1.0

Two-way travel time (s)

0.5

Two-way travel time (s)

1.0

Upper Tenggeer Fm T6

2.5

Two-way travel time (s)

Saihan Fm

Two-way travel time (s)

Two-way travel time (s)

onlap

s s s

Jurassic

136 Ma (HC1-3)

s s s

2300

1900

2200

2100

2000

Lower Tenggeer Fm.

2000

134 Ma (HC1-2)

2400

2100

1900

1800

1600

s s s

1700

1800

1700

1600

1400

1500

1600

1500

1300

1200

1300

1400

1300

1200

1200

1100

Upper Tenggeer Fm.

1400

Upper Tenggeer Fm.

Upper Tenggeer Fm.

1500

Lower Tenggeer Fm.

132 Ma (HC1-1)

2500

Lower Aershan Fm.

2200

1700

Lower Tenggeer Fm. 1800

1100

1000

900

900

K 1 tl

1000

1000

1000

1100

1100

700

600

500

900

800

900

800

800

700

800

600

500

700

600

600

Saihan Fm.

500

500

400

300

(m)

(m)

200 (m)

100 (m)

200

(m)

Saihan Fm.

200

200

200

300

300

300

(m)

Saihan Fm. 200

Saihan Fm.

300

300

400

400

400

400

500

500

Saihan Fm.

600

Saihan Fm.

600

Upper Tenggeer Fm.

700

700

700

400

Upper Tenggeer Fm.

HC1

s ss ss s s s s s s s s s s s s ss ss s s s s s s s s s s s s ss ss s s s s s s s s s s s

K 1 tl: Lower Tenggeer Formation

2600

K 1 al: Lower Aershan Formation

s s s s s s s s s

sample locations

2300

Upper Aershan Fm.

mudstone/shale

2400

dolomitic mudstone

2500

siltstone

2600

sandstone

1900

tuff

2700

basalt

2000

andesite 128 Ma (H33)

Lower Aershan Fm.

pebbly sandstone

H37

2800

conglomerate 138 Ma (H17-2)

2100

stratigraphic subdivision 1200

138 Ma (H40-1)

1300

Upper Aershan Fm.

Jurassic

s s s s s s

1400

800

125 Ma (H12)

1500

K 1 al

800

Lower Tenggeer Fm. Upper Tenggeer Fm.

900

Lower Tenggeer Fm.

H17

Aershan Fm.

Pz

1000

H12

2200

ss ss ss

s s s

1100

Lower Aershan Fm. 1200

H40 H33

136 Ma (H33)

(a) Lower Aershan Formation

(b) Upper Aershan Formation

Fig. 5h

Fig. 5h Fig. 5g Fig. 6b

J42

Fig. 5g Fig. 6b

J45

J33

(c) Lower Tenggeer Formation

J46 J55 J19 J74 J9 J13 Fig. 6a J31 Fig. 5f

J55

Fig. 5h Fig. 5g J42 Fig. 6b J45 J33 J19 J46 J55 J74 J9 J13 J31 Fig. 6a

J42 J33 J45 J46 J19 J74 J9 J13 Fig. 6a J31

Fig. 5f

(d) Upper Tenggeer Formation

Fig. 5f

N

(e) Saihan Formation

20 km

200 ~ 400 m

≥ 400 m

Fig. 5g Fig. 6b J55

Well locations

Fig. 5h Fig. 5g J42 Fig. 6b J45 J33 J19 J46 J55 J74 J9 J13 J31 Fig. 6a

Fig. 5h J42 J33 J45 J46 J19 J74 J9 J13 Fig. 6a J31

Fig. 5f

0 ~ 200 m

Seismic cross sections Lithostratigraphic cross sections

Fig. 5f

Boundary normal fault (arrow on the hanging wall)

0.5

Upper Tenggeer Fm

K 1 tl

Aqitu, Gerile and Qiha fms

truncation

T8

K 1 al

1.0

T11 Tg

Paleozoic

K 1 tl: Lower Tenggeer Fm. K 1 al: Lower Aershan Fm.

truncation T6

NW

T8

Tg

T11

1 km

0.5

onlap

1.0

r Te Uppe

T8

Low 1.5

T10

Upper

truncation

Low

A e rs h a

er A

e r Te

ngge

ngge

er Fm

er Fm

n Fm

ersh

an F

m

Paleozoic

Tg

truncation NW

T3

T6

T8

T10

Tg

1 km

1.0 0.5

1 km

NW

J42

(h)0.5 Cenozoic T0

onlap Saihan Fm

1.0

T3

Two-way travel time (s)

Saihan Fm

T3 T6

2.0

1.5

Up

1.5

per

Lo

we

g Te n

n r Te

g

T6

Fm

T8

gg

2.0

Up

Fm eer

pe

r

ee

r

r Ae

an

truncation

Fm

Paleozoic

T10

Tg

truncation NW

Lower Aershan Fm

T0

T3

T6

T8

T10

Tg

1 km

0.5

1.0

1.5

2.0

2.5

NW

1.5

NW

truncation

J42-7 sh

1.0

2.0

2.5

Two-way travel time (s)

Two-way travel time (s)

T6

1.5

Two-way travel time (s)

(g)

onlap

0.5

Two-way travel time (s)

Two-way travel time (s)

(f)

1 km

1 km

1700

mudstone/shale

basalt conglomerate

stratigraphic subdivision pebbly sandstone

dolomitic mudstone

tuff sandstone

siltstone andesite

K 1 al: Lower Aershan Formation K 1 au: Upper Aershan Formation

K 1 tl: Lower Tenggeer Formation K 1 tu: Upper Tenggeer Formation

sample locations

Paleozoic

1100

135 Ma (J33) 1200

1100

Jurassic

1000

138 Ma (J55)

700

600

800

700

600

s s s

800

600

500

500

500

500

400

200

300

300

400

K 1 tu

400

133 Ma (J74)

(m)

300

200

(m)

(m)

(m)

(m)

200 (m)

Saihan Fm.

200

300

Saihan Fm. 300

400

300

(m)

Saihan Fm.

200

200

Saihan Fm.

300

Saihan Fm.

500

400

(m)

(m)

200(m)

Saihan Fm.

200

Saihan Fm.

300

200

300

Lower Aershan Fm.

400

500

K 1 tu

600

500

600

500

300

Saihan Fm.

Upper Tenggeer Fm.

400

400

400

Saihan Fm.

400

Saihan Fm. 500

J74

s s s s s s s s s

K 1 au

700

K 1 tl

700

Lower Tenggeer Fm.

800

900

600

Upper Tenggeer Fm. 900

s s s s s s s s s s s s s s s s s s

900

600

Upper Tenggeer Fm.

700

Upper Tenggeer Fm.

1000

600

Upper Tenggeer Fm.

700

600

J55

1100

K 1 au

1000

Lower Tenggeer Fm.

1200

800

800

800

Upper Tenggeer Fm.

700

J33

1300

K 1 al

1300

Lower Tenggeer Fm.

Paleozoic

1400

900

K 1 tl

900

K 1 tl

900

800

Paleozoic

1500

Paleozoic

Upper Aershan Fm.

1000

K 1 au

1000

900

Upper Tenggeer Fm.

116 Ma (J9) 137 Ma (J13-1)

1600

1100

Lower Tenggeer Fm.

1000

117 Ma (J19)

J13

1700

1200

134 Ma (J46)

J9

1800

1300

1100

J19

ss ss ss

1400

1200

J46

1900

138 Ma (J45) Pz

1300

Lower Tenggeer Fm. 1400

Upper Aershan Fm.

1500

J45

Lower Aershan Fm.

135 Ma (J42-7) 1500

K 1 al

1600

J42

2000

1800

Upper Aershan Fm. 1900

(a) (b) J31

Jurassic

133 Ma (J31-1)

(a) Lower Aershan Formation

(b) Upper Aershan Formation

Fig. 7g

(c) Lower Tenggeer Formation

Fig. 7g

Fig. 7g A74

A74

A74 Fig. 8

Fig. 8

Fig. 8 A90

A90

A90

A20

A20

A20

Ha35 Fig. 7f

Ha35

Ha35

Fig.7f

Ha20

Fig. 7f Ha20

A18

(d) Upper Tenggeer Formation

(e) Saihan Formation N

Fig. 7g

20 km ≥ 400 m

A74

Fig. 7g

Fig. 8 A90

A74 Fig. 8

200 ~ 400 m

A90

A20

0 ~ 200 m

A20 Ha35

Well locations

Ha35

Seismic cross sections

Fig.7f Ha20

Ha20 A18

A18

Lithostratigraphic cross sections

Fig. 7f

Boundary normal fault (arrow on the hanging wall)

(f) 0.5

0.5

1.0

1.0

T3

Upper Tenggeer Fm T6 1.5

Lower Tenggeer Fm

T8

1.5

onlap truncation

2.0

2.0

T11

Xing’anling Group

Upper Aershan Fm

T10

Lower Aershan Fm

2.5

2.5

Tg

NW

T3

T6

T8

T10

T11

Tg

truncation

Paleozoic 3.0

1 km

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

2.5

3.0

3.0

1 km

NW

(g) T3 1.0

Low

1.0

er T eng

Upper Tenggeer Fm gee

r Fm T6

onlap

1.5

T8

1.5

Upper Aershan Fm T11/Tg

2.0

Jurassic or Paleozoic

2.5

NW

T3

T6

T8

T11/Tg

2.0

truncation

1 km

2.5

0.5

0.5

1.0

1.0

1.5

1.5

2.0

2.0

2.5

NW

1 km

2.5

Two-way travel time (s)

Two-way travel time (s)

0.5

Saihan Fm

Two-way travel time (s)

Two-way travel time (s)

0.5

Two-way travel time (s)

Two-way travel time (s)

onlap

Two-way travel time (s)

Two-way travel time (s)

Saihan Fm

3.0

Ha20

A18

A18

2400

2300

2200

2100

2000

1900

Upper Aershan Fm.

1800

1700

s sss s s s ss s s s sss s s s ss s s s sss s s s ss s s

2300

1600

2200

1900

1500

1400

1300

1200

1800

Lower Tenggeer Fm. 2000

Lower Tenggeer Fm.

2100

1100

1700

1600

1200

1000

1500

1100

900

900

1400

1000

1300

900

1100

1200

800

800

600

900

800

700

600

1100

600

1000

700

900

500

500

Upper Tenggeer Fm.

700

500

Lower Tenggeer Fm.

700

Upper Tenggeer Fm.

1000

Upper Tenggeer Fm.

1200

800

Upper Tenggeer Fm.

Upper Aershan Fm.

1000

Lower Tenggeer Fm.

1300

1100

500

300

300

400

800

400

600

400

600

200

300

Saihan Fm.

700

300

Saihan Fm.

500

200

200

(m)

(m)

200

(m)

(m)

Saihan Fm.

100 (m)

(m)

Saihan Fm.

Saihan Fm.

Upper Tenggeer Fm.

400

Saihan Fm.

400

Upper Tenggeer Fm. 600

Ha20

2500

s ss s s s s s s s s s s s s s s ss s s s s s s s s s s s s s s ss s s s s s s s s s s s s s

2400

andesite

Lower Aershan Fm.

K 1 au: Upper Aershan Formation

sample locations

siltstone

2600

stratigraphic subdivision

tuff

sandstone

2500

dolomitic mudstone 134 Ma (Ha35-2)

2600

pebbly sandstone

Upper Aershan Fm.

Jurassic

2700

conglomerate 1300

K 1 au

1200

Lower Tenggeer Fm.

Jurassic

Ha35

2800

1400

1300

700

A20

2900

mudstone/shale

ss ss ss

basalt 1400

Upper Aershan Fm.

Jurassic

1500

800

Lower Tenggeer Fm. 900

A90

Lower Aershan Fm.

Pz

K 1 au 1000

A74 A18

Paleozoic

(Guo et al., 2018a)

138 Ma

(a) Lower Aershan Fm

Fig. 10 T14

(b) Upper Aershan Fm

T18

T28

Fig. 9d

T18 Fig. 9d

T28

Fig. 9e

T8

T18

200 ~ 400 m

0 ~ 200 m

Well locations

TC2 T28

Fig. 9e

T8

T14

TC2

20 km ≥ 400 m

Fig. 10

Fig. 10 T14

TC2

N

(c) Saihan Fm

Fig. 9d

Fig. 9e

T8

Seismic cross sections Lithostratigraphic cross sections Boundary normal fault (arrow on the hanging wall)

TC2 1.0

Saihan Fm 1.5

Two-way travel time (s)

Two-way travel time (s)

(d)

onlap

T3

1.5

Upper Tenggeer Fm T6

2.0

2.0

Lower Tenggeer Fm

T11

2.5

2.5

Xing’anling Group Paleozoic

Tg

NW

T3

T6

T11

1 km

Tg

Two-way travel time (s)

Two-way travel time (s)

1.0

1.5

1.5

2.0

2.0

2.5

2.5 1 km

NW

(e)

1.0

Two-way travel time (s)

Two-way travel time (s)

1.0

Saihan Fm onlap

1.5

1.5 td4

T3

Upper Tenggeer Fm

2.0

2.0

T6

truncation

Lower Tenggeer Fm

2.5

NW

T11/Tg

2.5

Jurassic or Paleozoic T3

T6

T11/Tg

1 km

1.0

1.5

1.5

2.0

2.0

Two-way travel time (s)

1.0

2.5

2.5

NW

1 km

Highlights: 1. Depositional ages of the Lower Cretaceous strata of the Erlian Basin are refined. 2. Early Cretaceous tectonostratigraphic evolution of the Erlian Basin is established. 3. Early Cretaceous extension in Erlian Basin was intermittent rather than continuous. 4. Multiphase Early Cretaceous contractional deformation occurred in Erlian Basin. 5. Geodynamic origin of the extensional/contractional events in the basin is proposed.