Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern Mediterranean

Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern Mediterranean

Geobios 43 (2010) 333–347 Original article Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern...

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Geobios 43 (2010) 333–347

Original article

Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern Mediterranean§ Analyse des palynofaciès des sédiments de la plateforme continentale interne et du milieu de talus au large de l’Égypte, Méditerranée sud-orientale Suzan El Hasanein Kholeif a,*, Mohamed Ismail Ibrahim b b

a National Institute of Oceanography and Fisheries (NIOF), Alexandria, Egypt Department of Environmental Sciences, Faculty of Science, University of Alexandria, Moharam Bay, 21511 Alexandria, Egypt

Received 24 June 2009; accepted 9 October 2009 Available online 31 March 2010

Abstract Marine palynological studies of Quaternary sediments usually focus on dinoflagellate and pollen assemblages for paleoceanographic and paleohydrographic interpretations of past events. This paper focuses on the use of palynofacies analysis for paleohydrological reconstructions of deltaic and deep sea environments to evaluate transport of organic matter to the ocean. These palynodebris data are used to interpret palaeoenvironmental and paleohydrographic changes in two marine cores from the continental shelf (core-1, 27 m water depth) and middle slope (core-2, 1030 m) offshore Egypt, south-eastern Mediterranean Sea, during the latest Pleistocene and the Holocene. The relative abundances of various types of sedimentary organic matter such as phytoclasts, zooclasts, amorphous organic matter and palynomorphs are related to paleohydrographic changes of the overlying water column. Based on the total palynodebris and organic carbon content, sediments of the inner continental shelf core are characteristic of a prodelta environment proximal to a fluvio-deltaic source and moderately distal oxic environments with enhanced structured organic matter preservation potential. In contrast, the palynodebris of the middle slope core show that the basal sediments (105–140 cm depth) indicate suboxic to dysoxic bottom water conditions, followed by anoxic-suboxic bottom water conditions for the interval from 30–85 cm, which represents the S1 Sapropel. The top sediments of core-2 (0–25 cm) were deposited under oxic bottom water conditions, suggesting good ventilation in the water column. A quantitative approach was also used for interpreting the Holocene sea-level changes, based on the correlation between phytoclast and organic matter abundances. Sedimentation rate in the continental shelf is varied, being relatively very low (6.7 cm/kyr) in the basal part and increased upward to be 20 cm/kyr (depth 115–120 cm). In the upper Gray clayey silt layer the sedimentation rate was high (about 40–45 cm/kyr) due to the high discharge from El Manzala Lagoon and Damietta Nile branch. In the middle slope depth the sedimentation rate was relatively low and uniform, around 14 cm/kyr. # 2010 Elsevier Masson SAS. All rights reserved. Keywords: Dinoflagellate cysts; Palynofacies; Phytoclasts; Sedimentary organic matter; South-eastern Mediterranean; Nile Delta

Résumé Les études palynologiques marines de sédiments quaternaires s’intéressent classiquement aux assemblages de dinoflagellés et pollens à des fins d’interprétations paléocéanographiques et paléohydrographiques d’événements passés. Ici, nous nous intéressons à l’utilisation de l’analyse des palynofaciès pour la reconstruction paléohydrologique d’environnements deltaïques et de mer profonde, afin d’apprécier le transport de matière organique vers l’océan. Ces données de palynodébris sont utilisées afin d’interpréter les changements paléo-environnementaux et paléohydrographiques dans deux forages marins de la plateforme continentale (forage-1, 27 m de profondeur) et du milieu de talus (forage-2, 1030 m) au large de l’Égypte, Mer Méditerranée sud-orientale, durant le Pléistocène terminal et l’Holocène. Les abondances relatives de divers types de matière organique sédimentaire tels que les phytoclastes, les zooclastes, la matière organique amorphe et les palynomorphes sont reliées aux changements paléohydrographiques de la colonne d’eau. Sur la base de l’ensemble des palynodébris et du contenu en carbone organique, les sédiments du forage de la plateforme continentale interne sont caractéristiques d’un environnement prodeltaïque proche d’une source fluvio-deltaïque et

§

Corresponding editor: Marc Philippe. * Corresponding author. E-mail address: [email protected] (S.E.H. Kholeif).

0016-6995/$ – see front matter # 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2009.10.006

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d’environnements oxiques modérément distaux avec un potentiel élevé de préservation de matière organique structurée. Au contraire, les palynodébris du forage de milieu de talus montrent que les sédiments de la base (105–140 cm de profondeur) correspondent à des conditions d’eau de fond suboxiques à dysoxiques, suivies par des conditions anoxiques-dysoxiques dans l’intervalle 30–85 cm, représentant la Sapropèle S1. Les sédiments au sommet du forage-2 (0–25 cm) furent déposés dans des conditions d’eau de fond oxiques, suggérant une bonne ventilation de la colonne d’eau. Une approche quantitative a également été utilisée afin d’interpréter les variations du niveau marin holocène, sur la base de la corrélation entre les abondances en phytoclastes et en matière organique. Le taux de sédimentation sur la plateforme continentale est variable, relativement très faible (6,7 cm/kyr) dans la partie inférieure, puis augmentant jusqu’à 20 cm/kyr (110–125 cm). Dans la couche silto-argileuse grise supérieure, le taux de sédimentation est élevé (environ 41 cm/kyr), du fait de fortes décharges du lagon El Manzala et de la branche du Damietta-Nil. Sur le milieu de talus, le taux de sédimentation est relativement faible et uniforme, aux environs de 14 cm/kyr. # 2010 Elsevier Masson SAS. Tous droits réservés. Mots clés : Kystes de Dinoflagellés ; Palynofaciès ; Phytoclastes ; Matière organique sédimentaire ; Méditerranée sud-orientale ; Delta du Nil

1. Introduction The Mediterranean Sea is located in a transitional geographical zone between the European and the African continents (Brasseur et al., 1996). It has a deficient hydrological balance with loss through evaporation exceeding the input of water through run-off and precipitation. This deficiency is mainly compensated by the flow of Atlantic surface waters entering the basin through the strait of Gibraltar, moving eastward along the North African coast and being subjected to seasonal thermal variations (Bartzokas et al., 1991). Sea surface temperature of the eastern Mediterranean Sea may range between 12 and 32 8C; the lowest being in winter in the northwest basin and in the north Adriatic Sea, and the highest temperature being recorded in summer in the southeastern part of the Levantine Sea (Bartzokas et al., 1991). Deep sea water in the Mediterranean has a temperature between 12.5 8C and 13.5 8C in the west and between 13.5 8C and 15 8C in the east. Low salinity of the Atlantic Water (AW) that enters the upper layer of the Gibraltar Strait is transformed into saline Mediterranean water that subsequently exits into Atlantic via the lower layer (Lascaratos et al., 1999). Although the surface AW progressively loses its characteristics through mixing and evaporation during its travel to the east, salinity rising from 36.15 at Gibraltar strait, to 38.6 in the Eastern Levantine basin (Ozsoy et al., 1989). The intermediate layer of the Eastern Mediterranean basin (200–500 m depth) is occupied by high salinity water (LIW). This water mass is known to be formed in the permanent Rhodes cyclic gyres in the north-western part of the Levantine Basin (Pinardi and Mosetti, 2000). During the summer, the surface layer of the Levantine Sea is occupied by warm and salty water mass known as Levantine Surface Water (LSW). Winter cooling increases the density of this water and consequently it sinks and mixes with underlying water. The Eastern Mediterranean Deep Water (EMDW) is mostly formed in the southern part of the Adriatic Sea (Lascaratos et al., 1999). It has overall temperature and salinity ranges from 13–13.7 8C and 38.6–38%, respectively (Zavatarelli and Pinardi, 2003), changing gradually towards the Ionian and Levantine basins by mixing of Adriatic deep water with LIW and Cretan water. Classically, EMDW was thought to be formed mostly in the southern Adriatic Sea, with a small input from dense Northern Adriatic waters (Lascaratos et al., 1999).

Since 1987, however, drastic circulation changes have been observed (Tsimplis et al., 2006), including a northward deflection of AW in the Western Mediterranean, and outflow of new, highly saline, oxygen-rich water from the Cretan Basin that pushes the older EMDW upwards. This new circulation pattern is called the Eastern Mediterranean Transient (EMT; Fig. 1(A)), and its occurrence seems to be related to changes following the damming of the Nile and Ebro Rivers, as well as longer-term global warming (Béthoux and Pierre, 1999). 1.1. Major Eastern Mediterranean environmental and climatic perspective Although, the south-eastern Mediterranean region experiences particular climatic conditions due to its unique position (transition between humid climate in the north and arid climate in the south), Holocene paleoclimatic and paleoenvironmental conditions in this region have received little attention. The south-eastern Mediterranean climate conditions are clearly influenced by the inter-relationship between the European climate pattern and the Africa-monsoon climate. One of the most distinctive features of this area is the Nile River. The regular Nile flood periods have occurred during the Quaternary and have been correlated with periodic monsoon intensification called pluvial periods (Said, 1993; Gasse, 2006; Ducassou et al., 2008). The runoff from Nile River to the Mediterranean Sea is responsible for about 95% of suspended sediment load. These sediments cover about 50% of the Levantine Basin. The high-resolution depositional sequences, linked to Quaternary climate fluctuations, are exceptionally well preserved on the Nile continental margin and particularly in the Nile deep sea fan (NDSF). The NDSF is the largest deep-sea sedimentary basin of the eastern Mediterranean, and it differs from most other large sub sea fans as being developed in a relatively small, enclosed sea (Stanley and Maldonado, 1977). As a consequence, the NDSF sediments are expected to provide crucial data of African climate, Nile River flow, and corresponding changes in ocean circulation and stratification. The anti-estuarine circulation and low river runoff promote strong oligotrophic conditions in open waters, revealed by low primary productivity (Béthoux, 1989). The low surface productivity affects the sedimentary features of the basin. The recent sediments from open sea in the Levantine basin are

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Fig. 1. (A) Mediterranean Sea map, showing the circulation of water system after the Eastern Mediterranean Transient is recognized; Atlantic Water is deflected northwards and Levantine intermediate water is deflected into the Cretan Basin forming Eastern Mediterranean Deep Water (Tsimplis et al., 2006); small black arrows = Atlantic water; grey arrows = Levantine intermediate water, long black arrows = Levantine shelf current. (B) Location map of core-1 and core-2 in the inner continental shelf and middle slope offshore Egypt.

typically characterized by an average total organic carbon concentration of around 0.3%, and higher concentrations are thought to be indicative of different environmental conditions (Murat and Got, 2000). However, the paleoceanographic and paleoenvironmental records suggest that the Mediterranean circulation, ecosystem and deep sedimentary processes have not always been the same as they are today. 1.2. Overview of Levantine Sapropel S1 The Nile floods and enhanced rainfall over the eastern Mediterranean basin enhance productivity and increase the

stratification of the water column and organic matter preservation. These conditions led to sapropel formation (Rohling, 1994; Béthoux and Pierre, 1999; Cramp and O’Sullivan, 1999). The sapropels are episodic dark-colored, organic carbon-rich sediments that are unique and recurrent features of the Quaternary sediment record of the Mediterranean Sea. The hypothesis of sapropel deposition has been studied by many researchers to improve understanding of sapropel formation (Kidd et al., 1978; Cramp and O’Sullivan, 1999; Rohling, 1999; Meyers and Negri, 2003; Bianchi et al., 2006). However, the eastern Mediterranean deep ventilation hypoth-

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esis of Rohling et al. (2000) has received the greatest attention. They studied the modern deep-water ventilation to explain the main processes that are responsible for sapropels formation in the eastern Mediterranean basin. They recognized that the relationship between enhanced humidity/runoff and a change in deep-water oxygenation, in addition to modern deep water ventilation, are main factors responsible for sapropel phenomena in the eastern Mediterranean basin. The eastern Mediterranean Holocene sapropel (S1) event extended for a period spanning the 6270–9500 years Before Present (yr BP). A 200-year interruption was found in Adriatic and Aegean sediment cores. This interruption corresponds to a cooler period that occurred between 7100 and 6900 yr B.P. (Rohling et al., 1997; De Rijk et al., 1999), during which less organic matter was deposited. In the eastern Mediterranean, the sapropelic sediment layers with extremely high organic matter content (2–13% dry wt) are a distinctive feature in the Levantine Basin, and they have often been interpreted as indicating very large Nile flood intervals during the Late Pleistocene–Holocene (Rossignol-Strick, 1983, 1985). The sapropel layers and flood intervals that supposedly led to their formation have often been correlated with climate cycles and periodic African monsoon intensification (RossignolStrick, 1985; Gasse, 2000; Scrivner et al., 2004; Kholeif and Mudie, 2009). At times of sapropel formation, the strong humidity/runoff increase affecting the basin caused a serious reduction in the net evaporation that is so critical in the first stage of deep ventilation. Conceptual reconstructions, supported by Ocean General Circulation Models suggest that the salty intermediate water would consequently have collapsed (Rohling et al., 2002). Without its salt-supply, the deep ventilation from the Adriatic Sea could penetrate only to shallow intermediate depths, reaching about 400 m. Below that level, there was very limited or no ventilation and ongoing oxygen consumption rendered the stagnant ‘‘old’’ deep water virtually anoxic within a matter of centuries. Organic matter that rapidly sank to the sea floor was no longer subject to oxidation in this old deep water mass, and it consequently became preserved and buried in the sediments–a sapropel was being deposited. Productivity during these events was also enhanced relative to the present, so the organic flux was increased, which augmented its concentration in the sediments. The scope of the present study is to investigate the palynofacies characteristics in relation to environmental changes and bottom water oxygenation in the southeastern Mediterranean over the past 16,000 years using two strategically located marine sediment cores from offshore Egypt. We do this by comparing the temporal and spatial variation of palynofacies parameters in marine cores taken from the continental shelf and middle slope, about 50 km north of the Nile Delta in the pathway of the Nile River discharge plume. In the south-eastern Mediterranean region, however, there have been few previous palynological studies in pre- and postQuaternary sediments on the continental shelves and upper slope (Zonneveld et al., 2001; Kholeif and Mudie, 2009) among

these, only two palynofacies studies have been published on the pre-Quaternary subsurface sediments of Egypt (Ibrahim et al., 1997, 2002). The present study is the first attempt to describe and interpret the frequent occurrence of phytoclasts, amorphous organic matter (AOM), palynomorphs and opaques as proxy-data derived from the total palynofacies content to infer the paleoenvironmental and paleoceanographic conditions which prevailed during the latest Quaternary. The use of palynofacies for pre-Quaternary environmental interpretation allows determination of depositional environments in terms of salinity, oxygenation, and water column stability (Tyson, 1993, 1995; Batten, 1996; Ibrahim et al., 1997, 2002). In modern marine sediments, changes in the relative abundance of sedimentary organic matter (SOM) are related to changes in environmental parameters such as distance from shoreline, hydrodynamic energy in the water column (i.e., vertical mixing rate and wave energy), sea-surface temperature (SST), salinity, nutrient availability and oxygen regime (Tyson, 1995; De Vernal et al., 1997; Harland and Pudsey, 1999; Lowe et al., 2001; Roncalgia, 2004). 2. Material and techniques Two gravity cores of about 140 cm (Core-1) and 170 cm (Core-2) long were taken from the inner continental shelf and middle slope offshore northeastern Egypt (Fig. 1(B)), at 27 and 1030 m water depth, respectively. The cores were obtained using a gravity corer from a Russian scientific cruise in 1988. The core sites are located at 318 400 000 N, 318 390 4800 E (Core-1) and 328 200 4200 N, 318 390 000 E (Core-2). Thirty-two sediment representative samples were chosen for palynological analysis, based on the variations in grain size and total organic carbon. (TOC wt%) values. Dry sediment samples were prepared for palynological study using standard palynological technique for marine samples, including hydrochloric and hydrofluoric acids digestion (without heating). After that, the residues were split into two parts; the first one was used to prepare the palynofacies slide, while the second portion was filtered using short ultrasonic cleaning with a 10 mm mesh sieve, and was used to prepare palynomorph slides. Finally, glycerin-jelly was used as a mounting medium. The use of acetolysis, oxidation, heavy liquid separation, staining and other chemical additions are not followed. The palynofacies parameters were counted to calculate relative abundances. 2.1. Palynofacies definition and classification The term ‘‘palynofacies’’ describes the quantitative and qualitative particulate organic matter in a sediment sample after removal of the sediment matrix by hydrochloric and hydrofluoric acids (Combaz, 1964). The palynofacies concept was an attempt to develop a holistic approach that dealt with all of organic matter observed in unoxidized palynological preparations. Since the work of Batten (1973) until now, the palynofacies classification established by Combaz (1964), who first

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introduced this term in palynology, is still used with some modification (see Robert, 1979; Batten, 1981,1982; Boulter and Riddick, 1986; Van Bergen et al., 1990). The first comprehensive review of palynodebris as sedimentary particles and tracers of hydrographic conditions was presented by Traverse (1994) along with proposal for standardization of palynodebris terminology (Boulter, 1994). The most recent overview on palynofacies classification was presented by Tyson (1995) in a first monographic work on SOM. The palynofacies classification terms used here follows Tyson (1995): phytoclasts, opaques (black debris), AOM and palynomorphs.  The term ‘‘phytoclasts’’ refers to all dispersed clay to fine sand-sized particles of plant-derived kerogen but excluding palynomorphs (pollen, plant spores, organic walled dinoflagellate cysts, algal spores and colonial algae). In the present study the term ‘‘phytoclasts’’ includes all structured terrestrial plant fragments such as cuticles and tracheids. Phytoclasts are mainly derived from terrestrial sources and they show high concentrations in places close to the parent flora, near the mouth of rivers and in oxidizing situations. A high percentage of cuticle debris derived from leaves characterizes the facies resulting from transport by flotation and suspension loads under low energy conditions (Fisher, 1980; Tyson, 1993). Relatively large pieces of cuticles characterize prodelta, delta top embayment and distributary facies (Gastaldo, 1994; Tyson, 1995). They are also abundant in the submarine fan system, especially in channel sandstones (Boulter and Riddick, 1986). The size of phytoclasts (tracheids and cuticles) decreases in offshore direction (Patterson et al., 1987);  The opaque phytoclasts (black debris) describes the oxidized or carbonized brownish-black to black woody tissues, including charcoal and opaque phytoclasts. Opaque fragments are produced as a result of oxidation of plant tissues. Charcoal is produced by natural pyrolysis of terrestrial macrophyte material, i.e. the action of high temperature under conditions of oxygen starvation. Pyrite is often distinctive but needs to be reliably differentiated from opaque organic matter; the shape of framboidal pyrite is clear, but the most reliable method is to look for the higher reflectance of pyrite using oblique incident illumination. Reworked and recycled opaque phytoclasts may be recognized by their more equidimensional and more rounded shape than in-situ clasts;  The AOM refers to all particulate organic components that appear structureless under the light microscope, including phytoplankton and bacterially-derived AOM, higher plant resins, and amorphous products of the diagenesis of macrophyte tissues (Tyson, 1993, 1995). In most aquatic sediments, the AOM is plankton-derived and is produced by benthic filamentous cyanobacteria and pelagic sulphur bacteria of oxygen deficient environments (Williams, 1984). AOM usually dominates sediments deposited in oxygen deficient conditions; generally, the increase of AOM indicates reducing conditions, distal dysoxic-anoxic shelf and

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high marine productivity (Batten, 1981; Tyson, 1995). Relative abundances of AOM in ancient sediments tend to be low in inner shelf facies but increases in offshore anoxic facies (Dow and Person, 1975; Bujak et al., 1977; Williams et al., 1985). Generally, palynofacies analysis provides a valuable contribution connecting particulate organic matter composition to depositional environments (Batten, 1996; Sebag et al., 2006);  Palynomorphs include all miospores (pollen, terrestrial and aquatic plant spores), dinoflagellate cysts, acritarchs, prasinophytes, colonial algae and other algal microfragments, microforaminiferal test linings and crustacean eggs. These palynomorphs are mostly abundant in fine-grained muds (Mudie, 1992), shales, clays, marls and sometimes in limestones and sandstones (Sarjeant, 1974). They have

Fig. 2. (A) Lithologic column and radiometric ages of the studied cores. (B) Simplified diagram showing the bathymetry and lithological differences between the two studied cores.

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been recorded from different kinds of terrestrial and aqueous environments such as estuarine, lacustrine, and open marine. 2.2. Data analysis In the present study, the observed organic particles are grouped into SOM and AOM. Four groups are recognized, based on the classification of Tyson (1993, 1995), as follows. The first three groups together are usually referred to as structured organic matter (SOM):  Palynomorphs include all spores, pollen, organic-walled dinocysts, acritarchs, prasinophytes, microforaminiferal linings, marine algae and crustacean eggs;  Phytoclasts include structured terrestrial plant fragments (greater than 15 mm size) such as cuticles, wood tracheid and cortex tissues;  Opaques (black debris) comprise oxidized or carbonized brownish black to black coloured woody tissues including charcoal;  AOM includes all particulate organic components that appear structureless at the scale of light microscopy, including bacterially-derived AOM, resinous and amorphous products of the diagenesis of macrophyte tissues. In order to compute the individual components as percentage of Total Sedimentary Organic Matter (TSOM), the operational diameter of counted clasts and AOM was established as greater than 15 mm according to Tyson (1995) and a minimum of 400 clasts was counted. The most common kind of data that is presented in palynofacies analysis is percentage data. However, ternary diagrams that are commonly used in geological studies are very effective for presenting palynofacies percentage data. The main advantage of the ternary plot is that data are displayed with spatial separation that is useful for grouping samples into

empirically-defined associations or assemblages. Tyson (1989,1993,1995) uses an AOM-Phytoclasts-Palynomorphs (APP) plot to pick out the status of the depositional environments and relative proximity to terrestrial organic matter sources. We have followed this method here. 3. Cores description The inner continental shelf core-1 shows two distinct sediment types. A basal calcareous neritic silty sand section of 40 cm thick (depth 110–140 cm) overlained by the upper clayey silt section 110 cm thick (depth 0–110 cm) (Fig. 2(A)), which represents the transgressive phase. The carbonate content (CaCO3 %) and TOC of the basal part are ranging from 4.03 to 12.62% and 0.33 to 0.76%, respectively, while in the upper part it is characterized by relatively lower carbonate (3.60–4.89%) and higher TOC values (0.93–1.41%; Table 1). Core-2 is taken from the middle slope of the Nile cone. Sediment of the lower part (120–168 cm) is calcareous silty clay with 15.55–29.94% carbonate content and 0.9– 0.98 wt% TOC (Table 2). The overlying silty clay layer (85– 120 cm) is distinguished by a higher organic carbon content (1.09–1.4 wt%) and lower carbonate content (13.27–16.46%). This layer is followed by an interval of organic carbon-rich sediments (sapropel: 30–85 cm), with TOC value ranging from 2.12 to 3.4 wt% and low carbonate content (10.31–14.09%). The Sapropel layer is overlained by a 25–30 cm-thick layer with lower TOC content (1.8 wt%) and carbonate content of about 30%. The top of this core is an oxidized layer with a minimum organic carbon content (0.1–0.7 wt%) and higher carbonate content (38.35–50.73%; Table 2). 3.1. Age assignment The age assignment is based primarily on three AMS radiocarbon ages for picked foraminiferal and mollusk shells of the shelf core-1 sediments and three AMS of Nile cone core-2

Table 1 Grain size percentages, carbonate content and total organic carbon (TOC) % in Core-1 samples. Sample number

Core depth cm

Sand %

Silt %

Clay %

Si/Cl ratio

CaCO3 %

TOC wt%

1 2 3 4 5 6 8 8 9 10 11 12 13 14 15 16

0–10 20–30 20–30 30–40 40–50 50–60 60–70 70–80 90–95 100–105 105–110 110–115 120–125 125–130 130–135 135–140

1 1 1 1 0 1 0 1 2 4 7 53 77 75 61 58

70 65 64 64 58 60 59 63 63 60 57 28 20 19 32 33

29 34 35 35 42 39 41 36 35 36 36 19 3 6 7 9

2.41 1.91 1.63 1.61 1.38 1.54 1.44 1.75 1.8 1.67 1.58 1.47 6.67 3.17 4.57 3.67

4.89 4.63 4.12 4.27 4.27 3.6 3.9 3.92 3.8 4.03 4.03 4.03 4.51 8.21 9.88 12.62

0.93 1.25 1.22 1.41 1.39 1.22 1.36 1.17 1.25 1.33 1.14 0.59 0.47 0.33 0.54 0.76

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Table 2 Grain size percentages, carbonate content and total organic carbon (TOC)% in core-2 samples. Sample number

Core depth cm

Sand %

Silt %

Clay %

Si/Cl ratio

CaCO3%

TOC wt%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0–10 15–20 25–30 30–45 50–55 60–65 70–75 80–85 85–95 100–110 110–120 120–130 130–140 140–150 150–160 160–168

5 3 3 2 2 2 1 2 1 2 1 2 2 4 3 2

37 40 20 27 17 15 18 11 19 24 20 15 21 43 36 30

58 57 77 71 81 83 81 87 80 74 79 83 77 53 61 68

0.64 0.7 0.26 0.38 0.21 0.18 0.22 0.13 0.24 0.32 0.25 0.18 0.27 0.81 0.59 0.44

50.73 38.35 29.57 26.28 12.38 10.31 12.14 14.09 14.33 13.72 16.46 15.55 16.04 29.94 19.33 18.96

0.54 0.1 1.83 2.71 3.01 2.52 3.4 2.12 1.4 1.87 1.09 0.98 0.88 0.62 0.88 0.9

Table 3 Radiometric age dating of selected core-1 and core-2 samples (after Kholeif and Mudie, 2009).

Core-1

Core-2

Interval (cm)

Sample Data

13

115–120 120–125 135–140 5–10 30–45 140–150

Beta-248090 Beta-248088 Beta-248089 Beta-248094 Beta-248093 Beta-248092

+1.3% +0.1% +1.3% 0.3% 1.52% 0.4%

sediments (Table 3). The ages used in this study are reported as uncalibrated 14C ages, in years (yr) BP. The detail lithostratigraphic description and correlation between core-2 sediment and the well-dated core of Stanley and Maldonado (1977) from the same area and similar water depth (1026 m), northeast of the Damietta Branch of the Nile Delta was recorded by Kholeif and Mudie (2009).

C/12C

Calendar Age yr BP 2680  40 3170  40 5380  40 2860  40 5880  40 13 160  40

BP BP BP BP BP BP

3.2. Sedimentation rate Sedimentation rate in the continental shelf (Core-1) is varied, being relatively very low (6.7 cm/kyr) in the basal part of the lower calcareous silty sand (120–135 cm) and increased upward to be 20 cm/kyr (depth 115–120 cm). For the upper Gray clayey silt layer (0–120 cm) the sedimentation rate was

Table 4 Relative abundances of palynofacies parameters based on Total Sedimentary Organic Matter in core-1 samples (following Tyson, 1995). Sample no.

Depth cm

Cuticles %

Brown wood %

Opaques %

Amorphous organic matter (AOM) %

Terrestrial palynomorphs %

Marine palynomorphs %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0–10 10–20 20–30 30–40 40–50 50–60 60–70 70–80 90–95 100–105 105–110 110–115 120–125 125–130 130–135 135–140

27 25 19 20 15 14 12 20 27 24 19 19 17 15 19 20

12 15 17 12 15 17 19 15 13 15 8 18 20 11 10 17

17 20 24 23 20 25 20 35 30 33 40 42 40 40 42 35

24 20 21 20 30 25 32 20 17 15 27 10 13 22 22 20

2 3 4 5 3 5 5 3 5 3 4 8 7 6 5 6

18 17 15 20 17 14 12 7 8 10 2 3 3 3 2 2

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Table 5 Relative abundances of palynofacies parameters based on Total Sedimentary Organic Matter in core-2 samples (following Tyson, 1995). Sample no.

Depth cm

Cuticles %

Brown wood %

Opaques %

Amorphous organic matter (AOM) %

Terrestrial palynomorphs %

Marine palynomorphs %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0–10 15–20 25–30 30–45 50–55 60–65 70–75 80–85 85–95 100–110 110–120 120–130 130–140 140–150 150–160 160–168

10 13 6 5 8 5 4 4 4 9 14 8 2 2 2 9

14 10 10 5 5 5 5 6 5 11 10 10 8 10 5 18

60 55 36 17 5 10 9 22 15 30 30 42 50 50 60 40

10 17 32 63 69 62 72 58 46 40 38 23 32 30 30 22

2 3 10 7 9 10 8 6 5 2 2 2 1 1 1 1

4 2 6 3 5 8 2 4 25 8 6 15 7 7 2 10

high (about 40–45 cm/kyr). As the climate became more humid and the rate of sediments influx from the Nile increased, the upper part of the core began to deposit. A high sedimentation rate is found in this part of the shelf, indicating high discharge from El Manzala Lagoon and Damietta Nile branch (Fig. 2(B)). In middle slope depth (Core-2) the sedimentation rate was relatively low and uniform (around 14 cm/kyr), but decreases at the top of the core where some sediment may be missing (Kholeif and Mudie, 2009).

4. Results The palynofacies composition and relative abundances in the core sediments (Tables 4 and 5; Figs. 3 and 4) and the AOMpalynomorphs-phytoclasts (APP) ternary plot (Fig. 5) show the

presence of four palynofacies types in the latest PleistoceneHolocene sediments of the study area (Figs. 6 and 7). 4.1. Palynofacies I: Opaque phytoclasts This palynofacies comprises core-1 depth 110–135 cm (samples 12–15; Fig. 5) and core-2 depth 0–20 cm (samples 12; Fig. 5). It is characterized by low TOC (mean 0.6 wt%), 10– 22% AOM and a predominance of opaque phytoclasts (up to 60% of the total particulate organic matter [POM]). The palynomorphs percentage is higher in core-1 (20%) than in core-2 (6%). The palynomorphs are dominated by marine elements, especially dinocysts (Fig. 6(2)). Opaque phytoclasts are mainly derived from the oxidation of translucent woody material either during prolonged transport or post-depositional alteration. In marine sediments, there is often an offshore

Fig. 3. Percentage diagram of core-1 palynofacies parameters (percentage calculated to Total Sedimentary Organic Matter; total organic carbon wt% and CaCO3).

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Fig. 4. Percentage diagram of core-2 palynofacies parameters (percentage calculated to Total Sedimentary Organic Matter; total organic carbon wt% and CaCO3).

increase in the ratio of opaque to well-preserved translucent woody material. The high values of opaque phytoclasts indicate oxidizing conditions and either proximity to terrestrial sources or redeposition of terrestrial OM from fluvio-deltaic sources (Tyson, 1989). 4.2. Palynofacies II: Structured phytoclasts, palynomorphs and amorphous organic matter This palynofacies occurs in Core-1 at depths 0–40, 50–60, 70–105 and 140 cm, respectively (samples 1–4, 6, 8–10, 16), and in core-2 at depth 120–168 cm (samples 12–16).

Contrasting with palynofacies I, this palynofacies is distinguished by the commonness (up to 27%) of well-preserved structured terrestrial plant fragments (mainly cuticles, tracheids, leaves and brown wood), common AOM (20–30%) and low frequency of opaques phytoclasts (Fig. 6(4, 5)). Palynomorphs are mostly of marine types with an average of 20%. TOC increases to the amount of 1–1.4 wt%. Relatively large pieces of cuticle as well as entire leaves are especially characteristic of prodelta facies and reflect active redeposition from a fluvio-deltaic source area, as in turbidites (Batten, 1974; Tyson, 1995; Ibrahim et al., 1997). High percentages of cuticle (15–40%) are characteristic of delta top embayment, prodelta and distributary facies. Boulter and Riddick (1986) observed that cuticle is relatively more abundant in the high energy parts of submarine fan systems, especially the channel sandstones. The phytoclast contents of this facies suggest the proximity to a fluvio-deltaic source and moderately distal oxic environments. 4.3. Palynofacies III: amorphous organic matter and phytoclasts

Fig. 5. Amorphous organic matter-Palynomorphs-Phytoclast ‘‘APP’’ ternary diagram of relative abundance of palynofacies parameters after Tyson (1995). The percentage of each parameter is calculated in relation to the total particulate organic matter counting. Empty circles: Core-1 samples; plain sandglasses: Core-2 samples.

This palynofacies occurs in core-1 depths 40–50 and 60– 67 cm (samples 5 and 7) and in core-2 depths 20–30 and 100– 120 cm (samples 3 and 10-11). This palynofacies is marked by an increase in AOM content (up to 35%) compared to palynofacies I and II, TOC up to 1.8%, and low frequency of black debris (opaques) (Fig. 6(6, 7)). The relative abundance of palynomorphs remains the same as in Palynofacies II, and is again dominated by marine taxa. The increase in AOM and TOC, and the decrease in opaques indicate a proximal dysoxicsuboxic environment (Tyson, 1995). The oscillation between dysoxic and suboxic conditions suggest changes in the oxygen content and energy levels of the bottom water, as reported by Roncalgia (2004) for the Faroe Islands.

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Fig. 6. Light microscope photographs of selected palynofacies types and main categories of particulate organic matter from the studied cores. 1. Palynofacies I, abundant opaque phytoclasts from core-1 sample #12, opaque phytoclasts (40% of total palynofacies parameters). 2. Palynofacies I, abundant opaque phytoclasts from core-2 sample #2, opaque phytoclasts (60% of total palynofacies parameters). The palynomorphs are dominated by dinocysts. 3. Palynofacies I, opaque biostructured phytoclasts, core 1 sample #13. Although, there is no definite biostructure, the shape of phytoclast reflects the good preservation of structured grain; the large particles often break up into smaller opaque particles during transportation. 4. Palynofacies II, abundant structured phytoclasts, common palynomorphs and amorphous organic matter (AOM) from core 1 sample #6, cuticles and brown wood (31%), AOM (25%), palynomorphs (20%). 5. Palynofacies II from core-1, sample #6. Note that in the upper right corner the translucent phytoclast may be derived from the gymnosperm xylem (Tyson, 1995); note in the left side of the figure the

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4.4. Palynofacies IV: amorphous organic matter and palynomorph This palynofacies is found only in core-2 at depth 30–85 (samples 4–8). This facies is characterized by high AOM (58– 72%), high TOC (up to 3.4 wt %) and common palynomorphs (10–30%). The AOM is fine to granulose, moderate to high relief and yellow to orange colour (Fig. 6(9, 10)). Resin is notable and pyrite is present as medium to fine crystals. Palynomorphs are dominated by terrestrial sporomorphs (5– 10%). High AOM preservation is due to reducing basin conditions (Tyson, 1995) in the Mediterranean; this is often in combination with increased stratification because of higher freshwater runoff (Aksu et al., 1995b; Aksu et al., 1999; Abrajano et al., 2002). Generally, the high percentage of AOM indicates reducing conditions, dysoxic-anoxic environment (Batten, 1983; Tyson, 1993). The AOM and palynomorph Palynofacies IV in Core-2 are characteristic and comparable with the eastern Mediterranean sapropel S1. The palynology of sapropel S1 was discussed in detail by Aksu et al. (1995a) and Zonneveld et al. (2001). 5. Discussion Generally, the shallow water core-1 sediments are dominated by phytoclasts (Fig. 3) while the middle slope core-2 sediments are dominated by AOM (Fig. 4). The relative abundance of palynofacies components was plotted in an AOM-phytoclasts-palynomorphs (APP) ternary diagram (Fig. 5) to compare the sediment samples in the two cores, in order to determine the oxygen content of the bottom water column and the quantity of terrestrial input (phytoclasts versus palynomorphs) in the marine sediments. Based on this ternary diagram and the defined palynofacies types I–IV, the core-1 sediments layer located at 110–130 cm depth (Fig. 3; samples 12, 13; age from 2860 to 3170 yr BP) is comparable with the upper 20 cm sediments of core -2 (Fig. 4; samples 1, 2). These sediments were deposited under oxic-dysoxic conditions, suggesting good bottom water ventilation. In core-1, the good to moderate bottom water ventilation, high energy level and well mixed water column (stable dysoxic condition) prevailed during the deposition of most of the continental shelf sediments and the basal interval of the middle slope core-2 from 130– 168 cm depth (Fig. 4; samples 13–16). Changes in oxygen content from dysoxic to suboxic, decreasing energy level and increased water mass stratification characterize the sediment intervals 40–70 cm (Fig. 3; samples 7-4) in core-1, and at 25– 30 cm (Fig. 4; samples 3-4) and 100–120 cm (Fig. 3; samples 10–12) in core-2.

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Most of the continental shelf sediments in core-1 are characterized by high values of cuticles, leaves, structured brown wood. Low amounts of opaques (Fig. 3) suggest low salinity due to close proximity to active fluvio-deltaic sources. The phytoclasts may also indicate a greater abundance of inland vegetation as a result of improved climatic conditions. On the other hand, high opaques phytoclasts, low AOM % (30%) and low TOC % in the basal sediments (130–168 cm) of the middle slope core-2 (Fig. 4) are characteristic of distal shelf sediments deposited during high sea levels. In the middle slope core-2, the organic matter-rich sediments (Sapropel layer, 6000–9500 yr BP) from 30–85 cm depth (Fig. 4; samples 4–8) is distinguished by a high organic carbon content of 2.1–3.4% dry weight and high AOM percentages ranging from 58 to 72. These sediments were deposited under conditions of strong stratification, with oxygen-deficient (dysoxic-anoxic) bottom water conditions allowing good preservation of autochthonous planktonic organic matter. High AOM percentage greater or equal to than 60% in organic matter rich sediments indicates reducing conditions and increased water column stability, resulting in dysoxic or anoxic bottom conditions (Tyson, 1995; Ibrahim et al., 2002). In addition, low phytoclasts, relatively low sporomorph concentrations (Table 4) and increased marine palynomorph concentrations may indicate enhanced inflow of Mediterranean Surface Water (MSW) of higher temperature and salinity relative to river discharge during the transgressive phases of Holocene sea level changes. Recent work on the palynology of Levantine Sapropel S1 (Cheddadi et al., 1991; Cheddadi and Rossignol-Strick, 1995; Zonneveld et al., 2001; Kholeif and Mudie, 2009) has shown that organic-walled dinoflagellate assemblage composition are differentially affected by changes in the redox potential of the sediments, with all palynomorph groups well represented in anaerobic Sapropel layers but with subsequent differential loss of oxidation-sensitive species during post-depositional oxidative diagenesis of the Sapropel. Moreover, Aksu et al. (1995a) confirmed that the S1 deposition (9600–6400 yr BP) is marked by increase in terrigenous sporomorphs and refractive humic compounds, with slight increase in dinocysts. Kholeif and Mudie (2009) mentioned that the sapropel S1 in the present core-2 sediments in the Nile cone is being deposited during a time of lower Monsoon index, moderate Nile flooding, warmer surface water and increased dinocysts production. They (op. cit) also observed that the dinocyst assemblages in the Nile Cone S1 differ from those of the deeper, more northern Levantine and Cretan basins in the near absence of heterotrophic protoperidinioid cysts, despite the uniformly high organic S1 carbon content.

gelified wood, structured phytoclast lacking clear internal structure, the internal structure of the particles has been infilled by gelification. 6. Palynofacies III common AOM and phytoclasts from core-1 sample #5, cuticles and brown wood (30%), AOM (30%) mainly resin (note the right corner of the figure), opaques (20%). 7. Palynofacies III, core-2 sample #10, cuticles and brown wood (20%), AOM (40%), opaques (30%). 8. Well preserved, diffuse edged AOM from core-1 sample #5. 9, 10. Palynofacies IV from sapropel sediments, core-2, samples #5 and 7. 11, 12. Moderately well preserved AOM, a flaky shape, a lumpy or granular texture, diffuse outlines and variable size, opacity and colour. Note the inclusion of some pyrite and tiny phytoclasts. The origin of the granules uncertain but the presence of dinocyst particles (Fig. 6(10)) indicates that the particles are not derived from phytoclats. Scale bar = 10 mm.

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6. Conclusion Based on the variations in sedimentary organic matter recovered from the studied sediments, the following conclusions are derived:  The continental shelf sediments, which deposited in the last 5380 yr BP are comparable with the upper 20 cm sediments of the Nile cone core-2. These were deposited under oxicdysoxic conditions suggesting good bottom water ventilation. Furthermore, good to moderate bottom water ventilation, high energy level and a well mixed water column (stable dysoxic condition) prevailed during the deposition of most of the continental shelf sediments and the lowest interval of the upper slope sediments. In contrast, the sapropel S1 layer in the middle slope sediments were deposited under conditions of strong stratification, with oxygen-deficient (dysoxicanoxic) bottom water conditions allowing good preservation of autochthonous planktonic organic matter. High percentage of AOM ( 60%) in organic matter rich sediments indicates reducing conditions and increased water column stability, resulting in dysoxic or anoxic bottom conditions;  Low phytoclast abundance, relatively low sporomorph concentrations and high marine palynomorph concentrations may indicate enhanced inflow of Mediterranean Surface Water of higher temperature and salinity relative to river discharge during the transgressive phases of Holocene sealevel change;  The Nile input appears to reach its lowest amount during the deposition of the lower sediment unit (115–150 cm) of the shelf core-1 and the topmost sediments (0–30 cm) of the Nile cone core-2, as indicated by the low percentages of AOM, sporomorphs and TOC. However, upward increase of TOC (1.4 wt%), AOM (27%) and increase of the fine grained silty-clay sediment percentages (90%) in the upper sediment unit (0–115 cm) of the shelf core-1 also provide some insight regarding the influence of the Nile River discharge in transporting fine-grained particulate organic matter across the Egyptian Shelf. This conclusion is in agreement with Pinardi and Zavatarelli (2005), regarding the presence of the Nile signal discharge on the Egyptian shelf. Acknowledgements The authors thank Prof. Peta Mudie (Geological Survey of Canada and Memorial University of Newfoundland) for her help in revising the palynofacies data and providing AMS 14C

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ages. We also thank the editor, associate editor and the two reviewers for their constructive remarks that improved the paper. References Abrajano, T., Aksu, A.E., Hiscott, R.N., Mudie, P.J., 2002. Aspects of carbon isotope biogeochemistry of Late Quaternary sediments from the Marmara Sea and Black Sea. Marine Geology 190, 151–164. Aksu, A.E., Abrajano, J., Mudie, P.J., Yasar, D., 1999. Organic geochemical and palynological evidence for terrigenous origin of the organic matter in Aegean Sea sapropel S1. Marine Geology 153, 303–318. Aksu, A.E., Yasar, D., Mudie, P.J., 1995a. Paleoclimatic and paleoceanographic circumstances leading to the development of sapropel layer S1 in the Aegean Sea Basins. Paleogeography, Paleoclimatology, Paleoecology 116, 71–101. Aksu, A.E., Yasar, D., Mudie, P.J., Gillespie, H., 1995b. Late glacial–Holocene paleoclimatological and paleoceanographic evolution of the Aegean Sea: micropaleontological and stable isotopic evidence. Marine Micropaleontology 25, 1–28. Bartzokas, A., Metaxas, D.A., Kateri, M., Exarchos, N., 1991. Sea surface temperature in the Mediterranean. Statistical properties. Rivista di Meteorologia Aeronautica 51, 47–64. Batten, D.J., 1973. Use of palynologic assemblage types in Wealden correlation. Palaeontology 16, 1–40. Batten, D.J., 1974. Wealden paleoecology from the distribution of plant fossils. In: Proceedings of the Geologic Association 85. pp. 433–458. Batten, D.J., 1981. Palynofacies, organic maturation and source potential for petroleum. In: Brooks, J. (Ed.), Organic maturation studies and fossil fuel exploration. Academic Press, London, pp. 201–223. Batten, D.J., 1982. Palynofacies, palaeoenvironments, and petroleum. Journal of Micropaleontology 1, 107–114. Batten, D.J., 1983. Identification of amorphous sedimentary organic matter by transmitted light microscopy. In: Brooks, J. (Ed.), Petroleum geochemistry and exploration of Europe. Geological Society Special Publication 12, Blackwell Scientific, Oxford, pp. 275–287. Batten, D.J., 1996. Chapter 26A. Palynofacies and paleoenvironmental interpretation. In: Jansonius, J., McGregor, D.C. (Eds.), Palynology: principles and applications. American Association of Stratigraphic Palynologists Foundation 3, Dallas, pp. 1011–64. Béthoux, J.P., 1989. Oxygen consumption, new production, vertical advection and environmental evolution in the Mediterranean Sea. Deep-Sea Research 36, 769–781. Béthoux, J.-P., Pierre, C., 1999. Mediterranean functioning and sapropel formation: respective influences of climate and hydrological changes in the Atlantic and the Mediterranean. Marine Geology 153, 29–39. Bianchi, D., Zavatarelli, M., Pinardi, N., Capozzi, R., Capotondi, L., Corselli, C., 2006. Simulations of ecosystem response during the sapropel S1 deposition event. Palaeogeography, Palaeoclimatology, Palaeoecology 235, 265–287. Boulter, M.C., 1994. An approach to a standard terminology for palynodebris. In: Traverse, A. (Ed.), Sedimentation of Organic Particles. Cambridge University Press, Cambridge, pp. 199–216. Boulter, M.C., Riddick, A., 1986. Classification and analysis of palynodebris from the Paleocene sediments of the Forties Field. Sedimentology 33, 871– 886.

Fig. 7. Light microscope photographs of the main categories of particulate organic matter distinguished by their morphological criteria from the studied cores. 1. Moderately well preserved amorphous organic matter (AOM) from core-2, sample #6. AOM of the freshwater alga (Botryococcus colony). Note the characteristic globular outline and lustrous yellow colour. 2. Resin particle showing some rounded angularity, from core-1, sample #5, lath-shape opaque phytoclasts from core-1, sample #4. 3. Resin particles showing different degrees of angularity and also severely cracking of the surface, core-2 sample #6. 4, 6. Well-preserved cuticles phytoclast from core-1, samples #5 and 16. Note that the distinct features of cuticle in immature sediments are the epidermal stomatas. 5. Well-preserved tracheid particles with visible pittings from core-1, sample #4. 7. Gelified wood particles present homogeneous texture, brown to amber colour, true outlines, with dulled angles from core. 8. Large pyrite particle from core-2, sample #5, indicates more anoxic environment. 9. Group of opaque lath-shaped phytoclasts from core-1, sample #16. The only evidence of structure is the sharp angular outlines and the elongated shape. 10. Large brown structured phytoclasts without visible internal structure and disseminated small opaques from core-1, sample #15. Scale bar = 10 mm.

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