THE FIFTH INTERNATIONAL CONFERENCE ON THE GEOLOGY OF AFRICA Vol. (1), P-P.VII-33 – VII-51 (OCT. 2007) ASSIUT-EGYPT

UPPER PALEOCENE-LOWER EOCENE CALCAREOUS NANNOFOSSIL BOISTRATIGRAPHY AND PALEOECOLOGY OF GEBEL MATULLA SECTION, SOUTHWESTERN SINAI, EGYPT

Abu Shama, A. M.1, Faris, M.2 and Al-Wosabi, Kh. A.3 [1] Biological and Geological Sciences Department, Faculty of Education at Kafr El Sheikh University, Egypt, E-mail: [email protected] [2] Geology Department, Faculty of Science, Tanta University, Egypt, E-mail: [email protected] [3] Taiz University, Yemen, e-mail: [email protected]

ABSTRACT The calcareous nannofossil biozones NP7/8 through NP12 were identified from the Tarawan, Esna and base of the Thebes formations at Gebel Matulla, west central Sinai. The Subzone NP9a spans the Tarawan/Esna contact indicating a conformable relationship between the two formations, which in further emphasized by a gradational lithologic characters in the field. The Zone NP10 is easily differentiated into 4 subzones (a-d). The NP9/NP10 zonal boundary can be identified at the level of increase frequency of Neochiastozygus junctus. Zone NP11 occupies the topmost part of the Esna Formation and the base of the Thebes Formation indicating conformable relation between them. The Paleocene/Eocene boundary is traced between the NP9a/NP9b subzonal boundary which is marked by the first appearances of Rhomboaster spp. It is located at the basal part of the Esna Formation and conforms lithologic change from blackish calcareous shale to brown calcarenite. Kaolinite peak and abrupt increase in calcium carbonate content is also observed. On the basis of nannofossils, the Paleocene Eocene Thermal maximum (PETM) interval can be divided into two parts (lower and upper). The major assemblage shift across the P/E boundary suggests a change from colder, more productive surface waters to warmer, more oligotrophic conditions. Above the PETM interval, the niche of Fasciculithus spp. was filled by Neochiastozygus juncts and Rhabdolithus solus, the cooler and more eutrophic taxa.

INTRODUCTION

The late Paleocene/early Eocene interval is characterized by major global climatic and environmental changes that reflect various paleontological, sedimentological, mineralogical and isotopic variations. In Egypt, the Paleogene rocks are widely distributed in the Eastern Desert, Western Desert, Nile Valley and Sinai. These rocks offer a good chance to studying the P/E boundary events. In the central Nile Valley, the Paleocene-Eocene succession reaches up to 2km thick and attracted the attention of many geologists since many decades. A Global Standard Stratotype- section and Point (GSSP) for the Paleocene/Eocene has been proposed recently in the lowermost part of the Esna Shale at the Dababiya section in central Egypt (Aubry et al. 2002). In Sinai, the Paleocene-Eocene succession is greatly reduced in thickness. Calcareous nannofossils of some Paleocene-Eocene rocks in Sinai were studied before and after the determination of the late Paleocene/early Eocene GSSP such as that of El-Dawoody, 1992; Bolle et al., 2000; Faris et al., 2000; Faris and Zahran, 2002; Abu Shama, 2002; Ayaad et al., 2003 and Faris and Abu Shama, 2007). The previous studies on the calcareous nannofossils of the Paleocene-Eocene rocks should be correlated with the Dababiya section. The main purpose of this work is: 1) to present a study of the calcareous nannofossil biozonation for the Tarawan, Esna and the base of the Thebes formations at G. Matulla section. VII-34 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

2) definition of the Paleocene-Eocene boundary according to the last reports of the International Subcommission on Paleogene Stratigraphy (ISPS). 3) to investigate the calcareous nannofossil events related to paleoecologic conditions at this boundary.

MATERIAL AND METHODS At Gebel Matulla, Abu Zenima area, west central Sinai (Fig. 1), 55 samples are collected from the upper Paleocene-lower Eocene rocks at intervals between 30-70 cm. Smear slides were prepared from well-mixed and unsettled sediment of 1gm suspension. No ultrasonic cleaning or centrifuge concentration was applied in order to maintain the original nannofossil composition. Nannofossils were observed in the light microscope at 1250X magnification and identified following the taxonomic schemes of Perch-Nielsen (1985). For statistical analyses across the Paleocene/Eocene boundary, 50 views of smear slides were counted and analyzed (Table 1). Carbonate content and clay mineralogy of the carbonate free fraction are studied around the P/E boundary.

Fig. 1: Location and stratigraphy of Gebel Matulla.

LITHOSTRATIGRAPHY In Central Egypt, the Paleocene-Eocene sequence is generally subdivided into Dakhla, Tarawan, Esna and Thebes formations respectively from base to top. In west central Sinai, this sequence is recorded in many exposures but not as thick as in central Nile Valley. In Sinai, because of this many authors dealt with Dakhla Formation, Tarawan Chalk and Esna Shale as one unit termed Esna Shale (Formation). However, in Abu Zenima area, Anan (1992) dealt with these units as recognizable formations. In the present work, the base of Gebel Matulla is composed of Sudr Formation that overlain by Dakhla, Tarawan, Esna and Thebes formations, respectively (Fig. 1).

The Tarawan Formation (Awad and Ghobrial, 1965) At Gebel Matulla, the total thickness of the Tarawan Formation is about 4.1 m. It is composed of 2.5m of cliff forming yellowish limestone that grades upwards and downwards into marly limestone. The cliff forming yellowish limestone is dissected by two thin (about 3- Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-35

5cm) disconnected chert bands in its middle part. The carbonate contents range from about 70 to 84%. In the present study, the contact between the Tarawan Formation and the overlain Esna Formation is arbitrary put below sample no. 74, where the carbonate content decreases to about 60%. However, the lithologic boundary between the Tarawan and the Esna formations at the Dababiya section was arbitrary put by Dupuis et al. (2003) at level where the carbonate content falls bellow 50%.

Table 1 : Changes in the abundance of species across the Paleocene/Eocene boundary, G. Matulla section, Egypt.

VII-36 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

The Esna Formation (Beadnell, 1905) At Gebel Matulla, the Esna Formation consists of about 20m of gray to greenish calcareous shale and marls. It conformably overlays the Tarawan Formation and underlies the Thebes Formation. It is disconnected by brown calcarenite bed (at ~2.1m above the base) and three beds of very hard marlstone to limestone all form four conspicuous ledges (stringers) due to differential weathering (Fig.1). The lower part of the Esna Formation is mostly composed of calcareous shale where the upper part consists of nodular marls. At the Dababyia section, the Esna Shale is divided by Dupuis el al. (2003) into three informal rock units: a lower unit (Unit Esna1); a middle unit (Unit Esna 2); and an upper unit (Unit Esna 3).

The Thebes Formation (Said, 1960) The basal part of this Formation at G. Matulla consists of chalky limestone. A gradational contact between the Esna and Thebes formations is present in studied section. The lithologic boundary between them is arbitrary put at the limestone stringer which lies about 2m below the cliff forming chalky limestone.

Calcareous nannofossil Biozones: The standard zonation scheme of Martini (1971), complemented by Aubry (1996) and Aubry et al. (1999) was followed in this work (Fig. 2). At Gebel Matulla, the calcareous nannofossils are generally abundant and well to moderately preserved. The stratigraphic distribution of the calcareous nannofossil species and biozones are presented in Figures 3. Some of calcareous nannofossils are illustrated (Plates 1, 2).

Fig. 2: Proposed latest Paleocene-earliest Eocene nannofossil magneto-biochronology correlated with the present work.

Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-37

1-Discoaster mohleri Zone (=NP7/8): Hay (1964) emend. Romein (1979). Zones NP7 and NP8 are difficult to be differentiated in case of the absence of the marker species Heliolithus riedelii at the top of Zone NP7 (Romein, 1979). The base of this interval is defined at the lowest occurrence (LO) of Discoaster mohleri where its top is defined at the LO of Discoaster multiradiatus. It occupies the Tarawan Formation and is represented by Samples 67-72 with total thickness of about 3.6m. Samples 68-71 are composed of cliff forming yellowish cherty chalky limestone (~ 2.6m thick.) whereas Samples 67 and 72 (~ 1.0m) compose of white gray marly limestone (Fig. 1).

Fig. 3: Stratigraphic distribution of the calcareous nannofossil species at Gebel Matulla section, west central Sinai, Egypt. VII-38 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

Fig. 3: Continued

In east central Sinai, Zone NP7/8 was recorded by Faris and Abu Shama (2007) from the hard yellowish brown limestone stringer (1m) intercalating the Esna Formation at Gebel Mishiti. According to these authors, this limestone stringer is equivalent to the Tarawan Formation in the present study. The calcareous nannofossil assemblages are well to moderately preserved and they are abundant. Discoaster okadi, Ericsonia robusta and Discoaster nobilis are recorded from the top of this zone. The upper part of this zone displays common abundance of genera Fasciculithus; Sphenolithus and Ericsonia (Fig. 3). These taxa reflect relatively warm and, probably oligotrophic surface water.

2- Discoaster multiradiatus Zone (=NP9): Bramlette & Sullivan (1961), emend. Martini (1971) and Bukry & Bramlette (1970).

The base of this zone is well defined by the LO of Discoaster multiradiatus where its top is marked by the LO of Tribrachiatus bramlettei. In the absence of the primary index species for NP10, the top of this zone is provisionally placed at the highest occurrence (HO) of Fasciculithus involutus following Perch-Nielsen (1985). However, in the present study few reworked specimens of F. involutus and other Fasciculithus spp. are recorded from the base of Zone NP10 in association with Tribrachiatus bramlettei. Zone NP9 is represented here by one sample (Sample 73) from the Tarawan Formation and eight samples (Samples 74-81) from the lower part of the Esna Formation (4.55 m thick).Therefore, a conformable relation between the Tarawan and Esna formations is suggested. Perch-Nielsen (1985) suggested that Paleocene diversity reached a maximum in Zone NP9. The present study agrees with this statement because of 21 incoming species characteristic of the Paleocene have their LOs in this zone (Fig.3). Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-39

In Zone NP9, Rhomboaster evolved and radiated and Discoaster araneus had a short range within NP9 and the basal part of NP10. Aubry et al. (1999) subdivided the Discoaster multiradiatus Zone (NP9) into two subzones (NP9a and NP9b) based on the LOs of Rhomboaster and/or Discoaster araneus. This level was adopted by the ISPS as one of the most important events which characterize the Paleocene/Eocene boundary interval. In the present study, the lower boundary of the Subzone NP9b is put below Sample 79 (brownish calcarenite) which reveal the LOs of Rhomboaster spp. and D. araneus. The acme of Ericsonia Subpertusa is recorded in the middle part of Subzone NP9b whereas LO of Rhabdosphaera solus and the increase abundance of Neochiastozygus junctus characterize its topmost part. The HO of Fasciculithus alanii is coincided with the NP9a/NP9b subzonal boundary. However, Fasciculithus alanii is recorded slightly above the NP9a/NP9b subzonal boundary in the Dababiya section, Nile Valley (Aubry et al., 1999), and in Gebel Mishiti, west central Sinai (Faris and Abu Shama, 2007).

3- Tribrachiatus contortus Zone (=NP10): Hay (1964) and Bukry (1973). This zone includes the biostratigraphic interval from the LO of Tribrachiatus bramlettei to HO of Tribrachiatus contortus. It covers large portion of the Esna Formation of about 12.4 m thick. In this study the base of NP10 is delineated by the LO of T. bramlettei and D. diastypus. Other taxa were introduced throughout this zone such as Zygrhablithus bijugatus, Chiasmolithus bidens, Chiasmolithus consuetus, Discoaster barbadiensis, Tribrachiatus digitalis, Pontosphaera multipora, Campylosphaera dela and T. cf. contortus and T. contortus. The LO of Tribrachiatus orthosrylus is recorded in the topmost part of Zone NP10. It overlaps with T. contortus and their arms have slight bifurcation (Type A). It seems that the early forms of this species is a morphotype transitional between T. contortus and T. orthostylus. The basal part of Zone NP10 is characterized by high abundance of Neochiastozygus junctus and Rhabdosphaera solus. This event can be used to delineate the base of Zone NP10 in case of absence of T. bramlettei. The short-lived Rhomboaster spp. that generally occurs in Subzone NP9b is recognized here overlaps 0.6m with T. contortus. Similar overlap between the R. cuspis group and the T. contortus is recorded at ODP Site 1215 (Fig. 6 of Raffi et al., 2005). According to Aubry (1996), Zone NP10 is divided into four subzones based on sequential appearances of the different species of Tribrachiatus: 1) Subzone NP10a (T. bramlettei-T. digitali Subzone) is defined as the interval between the LO of T. bramlettei and the LO of T. digitalis; 2) Subzone NP10b (T. digitalis Subzone) is defined by the total range of the T. digitalis; 3) Subzone NP10c (T. digitalis-T. contortus Subzone) is the interval between the HO of T. digitalis and the LO of T. contortus; 4) Subzone NP10d (T. contortus Subzone) is defined by the total range of T. contortus. In Gebel Matulla section, the four subzones NP10a to NP10d are recorded. The total thickness of these Subzones are 6.8m, 1.2m, 0.7m and 3.7m, respectively. Subzones NP10b and NP10c are to lesser thicknesses compared with NP10a and NP10d. This may be interpreted if a small hiatus between the subzones NP10b and NP10c might had occurred. A minor hiatus was recorded in Gebel Mishiti section, west central Sinai slightly after the beginning of the early Eocene due to the missing of subzones NP10b and NP10c (Faris and Abu Shama, 2007). However, the reduced thickness of subzones NP10b and NP10c in the G. Matulla may be a normal thing because, 1) The T. digitalis morphotype (its total range = Subzone NP10b) is often reported from only a few samples in each section investigated (e. g. Aubry, 1996; Aubry et al., 1996, Cramer et al., 2003 and Dupuis et al., 2003), 2) The recorded thickness of NP10b (1.2m), about one sixth of the thickness of NP10a (6.8m), is large if compared with thickness of NP10b at the proposed P/E GSSP section of Dababiya in Egypt. In the latter, the thickness of Subzone NP10b (3.75m) (DBH 41.75- DBH 45.5) is about one tenth of the thickness of Subzone NP10a (31.25 m) (DBH 10.5- DBH 41.75) (Fig. 9 of Dupuis et al., 2003), 3) This thickness is more correspondence with the time duration of this zone that estimated to be an average of 80 k.y. (Raffi et al., 2005), and 4) the stratigraphic overlaps accompanied by the occurrence of morphtypes between T. bramlettei and T. contortus on the one hand, and between the T. contortus and T. orthostylus on the other hand indicate VII-40 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

stratigraphic completeness. Similar stratigraphic overlaps are recorded by Aubry et al. (1996) and Dupuis et al. (2003). Subzone NP10b (T. digitalis Subzone) is defined by the total range of the T. digitalis. However, in the upper part (sample 105) of Subzone NP10d, forms of. T. cf. digitalis as well as rare of T. digitalis similar forms are abnormally recorded overlaps the early forms of T. orthostylus. T. digitalis morphotype and its ranges (Aubry, 1996) are subjected to criticisms from Raffi et al. (2005). At G. Matulla section, it is noted that the arms of the morphotype T. cf. digitalis seems rounded whereas the proper morphotype T. digitalis is flattened in plane light. More investigations are need by SEM for discrimination between these forms.

4- Discoaster binodosus Zone (=NP11): Mohler & Hay in Hay et al. (1967). The HO of Tribrachiatus contortus defines the base of this zone where its top is defined by the LO of Discoaster lodoensis. The thickness of this zone covers about 6.6m in the studied section. It is represented by Samples 107-113 of grey nodular marlstone which consist the uppermost 4.8m of the Esna Formation and Samples 114-115 of marly limestone that represent the lowermost 1.8m of the Thebes Formation. Calcareous nannofossils are here abundant but moderately preserved. Sphenolithus editus, S. radians, S. conspicuous and Toweius spp. are the incoming early Paleocene taxa in this zone. T. orthostylus is common and two forms of this taxon are recorded; rare of form A (have three arms with slight bifurcation) and frequent abundance of form B (no bifurcation in the arms).

5- Tribrachiatus orthostylus Zone (=NP12): Brönnimann & Stradner (1960). This zone includes the biostratigraphic interval between the LO of Discoaster lodoensis and the HO of Tribrachiatus orthostylus. It is defined at Sample 116 by badly preserved Discoaster lodoensis specimens. Despite of a diligent search for samples across the low part of NP12, only very rare specimens were sparsely recorded because of D. lodoensis is affected by heavy overgrowth and thus will be there difficulty to identify. Sphenolithus radians and S. conspicuous appear close to the top of Zone NP11 respectively and can be used as provisional marker to trace the NP11/NP12 zonal boundary. On the other hand, Neococcolithes dubius that generally appears in the basal part of Zone NP12 is recorded in Sample 118 whereas LO of Sphenolithus conspicuous, that generally appears in the uppermost part of Zone NP11, occurs in Sample 113. Consequently, the lower boundary of Zone NP12 must be found between these two events (between samples 113 and 118). Therefore, the poorly preserved Discoaster lodoensis specimens in Sample 116 can delineate the base of Zone NP12.

The P/E stage boundary According to Dupuis et al. (2003) the P/E boundary GSSP is located between Subzones NP9a and NP9b at the base of a thin dark gray clayey layer which is considered as a part of the Esna Formation. The lithological and mineralogical changes can approximate the place of the boundary which is confirmed by nannofossils. a- Definition by Nannofossils At Gebel Matulla and Abu Zenima sections, Bolle et al. (2000) did not differentiate subzones of NP9 and they placed the P/E boundary in the basal part of the Esna Formation between the Zone NP9 and the Subzone NP10a. In east central Sinai, the P/E boundary was delineated by Faris and Abu Shama (2007) at Gebel El Mishiti between Subzones NP9a and NP9b based on the LOs of Rhomboaster calcitrapa, R. cuspis, R. bitrifida and Discoaster araneus. In the present work at Gebel Matulla, this boundary is also placed at the NP9a/NP9b subzonal boundary which corresponds to a brownish calcarenite bed, sample 79. This sample reveals the LOs of Rhomboaster spp. and D. araneus. b- Definition by lithology and mineralogy At the proposed P/E GSSP section of Dababiya, the P/E boundary was put at the base of a thin dark gray clayey horizon (~5.7 m above the top of the Tarawan Formation). In the present study, the P/E boundary is placed at the base of brownish calcarenite bed (Sample 79) that Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-41

locates ~ 3.8 m above the top of the Tarawan Formation. A lithological changes in the composition of the Esna Formation across the P/E interval is recognized. The calcarenite bed (Sample 79) is underlain by black marly shale (Sample 78) whereas the parts of the Esna Formation directly above and below the P/E interval compose of gray calcareous shale (Table 2). It seems that sample 79 is equivalent to bed 5 of the DBH that represent the last phase of the CIE interval (Berggreen and Ouda, 2003).

Table 2: Carbonate contents and clay mineralogy of the late Paleocene/early Eocene rocks at Gebel Matulla section.

n.d = not determined

Some mineralogical changes are also present across the P/E interval at G. Matulla (Table 2). Carbonate contents decreases from about 60% in the basal part of the Esna Formation to about 47% directly below the boundary (Sample 78). This may be related to carbonate dissolution due to the decreasing in dissolved oxygen during this interval time. On the other hand, a sharp increase of carbonate content to about 82% (the highest value in this interval) presents at Sample 79 which was followed by gradual decreases to about 52% in the basal part of Subzone NP10a. Bralower (2002) recognized that intervals of higher CaCO3 content at Site 690 correspond to lower fertility and suggested one or a combination of the following mechanisms: (1) higher runoff increased clastic supply to sediments, reduced CaCO3, and increased nutrient supply to the surface ocean or 2) decreased fertility led to increased productivity of generally oligotrophic calcareous microplankton groups (nannoplankton and foraminifers), causing an increase in CaCO3 content. Clay mineralogy is studied in the carbonate-free fraction from the top of the Tarawan Formation and the base of the Esna Formation across the P/E interval (Samples 71-82). Smectite (with average abundance ~ 98%) is the main constituent of the Esna Formation below the P/E boundary. It decreases to ~ 90% directly above the boundary in coincidence with the maximum carbonate content. Above the calcarenite bed smectite content increases again to reach percentage ~ 95% and then decreases progressively from the top of Subzone NP9b through Subzone NP10a. Illite increases in abundance from percentage ~ 1.3% below the boundary to about 8% in calcarenite bed and again decreases above it. Kaolinite peak appears directly above the boundary with progressive increase from ~ 1.8% in calcarenite bed to ~ 15.5% in the base of Subzone NP10a. Barite peak is recorded in Sample 79 suggesting increase of barium content. Schmitz (1987) suggested that barium concentration is high in the sediments of high biological productivity. The increases in the accumulation rates of biogenic Ba from across the P/E transition at a number of open ocean sites has been interpreted to signify increasing primary productivity during the event (Bains et al., 2000). However, Bralower (2002) suggested that the VII-42 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

nannofossil assemblages results at the site 690 shed doubt on the interpretations of high productivity based on Ba accumulation rates. He judged that the Ba peak could have resulted from enrichment of this element as large quantities of methane were derived from hydrate dissociation. The high anomalies of Ba, Cr, Ni, V and REEs around the P/E boundary at Gabal el-Qreiya, Nile Valley, were interpreted as the results of their incorporation in phosphatic components as well as organic matter (Soliman, 2003).

Calcareous nannofossil assemblages and Paleoecology at the P/E transition

The Paleocene/Eocene (P/E) transition is often referred to as the Paleocene Eocene Thermal Maximum (PETM; ~55 Ma). This interval is associated with a major turnover in benthic and planktonic marine communities (e.g., Thomas and Shackleton, 1996; Kelly et al., 1996, 1998; Bralower, 2002). About of the response of the calcareous nannoplankton to the PETM event, there have been some investigations (e.g., Aubry, 1998; Bralower, 2002; Tremolda and Bralower, 2004 and Raffi et al. 2005). In the studied section, quantitative investigations of calcareous nannofossil assemblages were performed on the interval from NP7/8 to the basal part of NP10 across the PETM. The later at G. Matulla section can be subdivided into a lower part and an upper part on the basis of the nannofossil assemblages. The lower part is represented by two samples (79 and 80) where as the upper part is represented by one sample (81). The abrupt changes in the nannofossil assemblages in the lower and upper parts of the PETM (Fig. 4) suggest that nannoplankton communities were not stable and that surface water conditions changed over the course of the event. The changes in the abundance of the calcareous nannofossil assemblages can be interpreted as a response to palaeocologic conditions such as paleotemperature and paleofertility. It was suggested that taxa were adapted to eutrophic upwelling environments should be common in cold-water assemblages; likewise, oligotrophic taxa are likely to be more common in warm-water assemblages that thrived in a stable water column (Haq et al., 1977; Wei and Wise, 1990 and Aubry, 1992, 1998). Ericsonia subpertusa (Coccolithus subpertusus) which is common in the basal part of Subzone NP9b becomes acme slightly above (10cm) the brownish calcarenite bed. Although, slight drop in the abundance of this species is present in the topmost part of Subzone NP9b, it again becomes acme in the base of NP10a. Ericsonia is thought to be a warm-water indicator (e.g., Wei and Wise, 1990; Kelly et al., 1996). Its absence at high latitudes and its common association with Discoaster indicate a similar affinity for warm oligotrophic environments (Bralower, 2002). The acme of E. subpertusa (C. subpertusus) was recorded at the Dababyia section by Dupuis et al. (2003) in the bed DBH 2.3 with the LOs of D. anartios and the long- armed species of Rhomboaster (the base of NP9b) and coincide with the minimum (negative) δ13C value of the CIE. They correlated this acme with that of this species at the Equatorial Pacific Ocean Drilling Site 865 (Kelly et al. 1996) in which case this is a global acme possibly is response in global warming. At Gebel Matulla section, common abundance of the Paleocene genus Fasciculithus that mainly represented by Fasciculithus tympaniformis characterizes the Zone NP7/8. In the higher Subzone NP9a, genus Fasciculithus diversified and other Fasciculthus species of low abundance are displayed with F. tympaniformis. However, the relative abundance of genus Fasciculithus gradually decreases from about 38% in the lower part of Subzone NP9a to about 12% at its top part. The relative abundance of genus Fasciculithus reached to about 10% in the lower part of the PETM and became extinct close to its upper part where the relative abundance of the Facsiculithus sharply decreased to <2%. The sharp decrease of Fasciculithus across the PETM interval was accompanied by decreases in its diversity.

Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-43

Fig. 4: Relative abundance of nannofossil assemblage across the Paleocene/Eocene boundary.

The final decline in Fasciculithus corresponding to an abrupt increase in the abundance of the genus Zygrhablithus as well as the abundance cross-over between the two genus has been observed to occur within the CIE-PETM interval in several deep-sea sections (e.g., ODP Site 690, DSDP Site 401and DSDP Site 213: Bralower, 2002; Tremolada and Bralower, 2004). Data from G. Matulla section in this study do not show any Z. bijugatus across the PETM interval. The sudden evolution and influx of Z. bijugatus and the linked abundance cross-over with Fasciculithus spp. is not observed in the proposed P/E GSSP section of Dababiya in Egypt (Dupuis et al., 2003). Therefore, lack of the holococcolith genus Zygrhablithus across the PETM interval is a conspicuous character in the Tethys realm. The early Eocene substitution of Fasciculithus by Zygrhablithus is also absent in equatorial regions (Raffi et al., 2005). VII-44 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-45

Although, the ecological affinities of Fasciculithus is not well known, Haq and Lohmann (1976) found an inverse correlation of this genus with Prinsius martinii, a species that was concentrated in high latitude, more eutrophic environments. Bralower (2002) interpret Fasciculithus as K mode specialist that was adapted to warmer, more oligotrophic environments. Zygrhablithus bijugatus was interpreted as an oligotrophic deep-dwelling species by Aubry (1998). However, the Fasciculithus spp./Z. bijugatus abundance cross-over was interpreted as a change from oligotrophic to cooler and more eutrophic conditions (Tremolada and Bralower, 2004). In the lower part of the PETM of the present work, a secondary sharp decrease of Fasciculithus spp. was in conjunction with increase of Rhomboaster spp. Raffi et al. (2005) recognized that the demise of Fasciculiths occurs concomitantly with the initial rise or marked abundance increase of the non-spined rhomboasters, i.e., R. cuspis. It is suggested that the Rhomboaster–D. araneus association showed strong provincialism, being geographically restricted to the Tethys seaway, the North and South Atlantic oceans, and the westernmost Indian Ocean (Aubry, 2001; Kahn and Aubry, 2004). Our data and observations on G. Matulla section reveal that increase in the abundance of the cool water taxa Neochiastozygus juncts and Rhabdolithus solus is concomitant with the final elimination of Fasciculithus spp. (Fig. 4). Then the niche of Fasciculithus spp. was filled by the cooler and more eutrophic taxa in the upper part of the PETM interval due to the environmental changes.

Plate (1) 1) Chiasmolithus spp. Sample 89, NP10a, Esna Formation. 2) Fasciculithus bobii Perch-Nielsen. Sample 83, NP10a, Esna Formation. 3) Fasciculithus stonehengi Haq and Aubry. Sample 73, NP9a, Tarawan Formation. 4) Ericsonia cf. E. robusta. Sample 83, NP10a, Esna Formation. 5) Bomolithus elegans Roth. Sample 73, NP9a, Tarawan Formation. 6) Campylosphaera dela (Bramlette and Sullivan) Hay & Mohler. Sample 120, NP12, Thebes Formation. 7) Sphenolithus moriformis (Bronnimann & Stradner). Sample119, NP12, Thebes Formation. 8) Sphenolithus radians Deflandre. Sample 119, NP12, Thebes Formation. 9) Discoaster nobilis Martini. Sample78, NP9a, Esna Formation. 10) Rhomboaster cf. spineus. Sample79, NP9b, Esna Formation. 11) Rhomboaster spineus (Shafik & Stradner). Sample79, NP9b, Esna Formation. 12) Rhomboaster spp. Sample 83, NP10a, Esna Formation. 13) Discoaster falcatus Bramlette & Sullivan. Sample79, NP9b, Esna Formation. 14) Rhomboaster bitrifida Romein. Sample79, NP9b, Esna Formation. 15, 17-18) Discoaster araneus Bukry. 15- Sample 80,17- Sample 79, 18- Sample 81, NP9b, Esna Formation. 16) Discoaster cf. araneus. Sample 79, NP9b, Esna Formation. 19) Rhomboaster calcitrapa Gartner. Sample79, NP9b, Esna Formation.

VII-46 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-47

The abundance of Discoaster spp. sharply increases during the Subzone NP9a but was followed by slight decrease at the top of this subzone. However the onset of Discoaster spp. in the lower part of the PETM interval was followed by sharp decrease in its upper part. The Discoaster spp reflect relatively warm water (Wei and Wise,1990) and, probably, oligotrophic surface waters (Aubry, 1992). Abundance of the genus Chiasmolithus – an indicator of relatively cool and eutrophic water- decreased dramatically across the P/E boundary. On the other hand, the ratio of Discoaster/Chiasmolithus sharply increased in the lower part of the PETM interval (Fig. 4) indicating prevalence warm oligotrophic conditions. Chiasmolithus increases again than the Discoaster since the upper part of the PETM interval. Sphenolithus are abundant throughout the combined Zone NP7/8 and their abundance are steady common in Subzone NP9a. The sharp increase in the abundances of Sphenolithus in the calcareinte bed was followed by pronounced decrease in its abundance in the upper part of the PETM interval up to Zone NP10. The ecological affinities of Sphenolithus is not well known. However, Bralower (2002) interpret Sphenolithus as K mode specialists that was adapted to warmer, more oligotrophic environments.

Plate (2) 1-2) Discoaster multiradiatus Bramlette & Reidel. Sample78, NP9a, Esna Formation. 3) Discoaster lenticularis Bramlette & Sullivan. Sample78, NP9a, Esna Formation. 4) Discoaster okadi Bukry. Sample 72, NP9a, Tarawan Formation. 5) Neochiastozygus junctus (Bramlette & Sullivan) Perch-Nielsen. Sample 81, NP9b, Esna Formation. 6-8) Discoaster mahmoudii Perch-Nielsen. 6- Sample 79, 7- Sample 81, NP9b, Esna Formation.8- Sample 83, NP10a, Esna Formation. 9- Neococcolithus dubius (Deflandre) Black. Sample 118, NP12, Thebes Formation. 10) Rhabdolithus solus Perch-Nielsen. Sample 81, NP9b, Esna Formation. 11) Discoaster diastypus Bramlette & Sullivan. Sample 86, NP10a, Esna Formation. 12-14) Tribrachiatus bramlettei (Bronnimann & Stradner). 12, 13- Sample 89 (12- Short arm, 13- Long arm), 14- Sample 93 (Short arm), NP10a, Esna Formation. 15-16) Tribrachiatus digitalis Aubry. Sample 97, NP10b, Esna Formation. 17-18)Tribrachiatus contortus (Stradner). Sample 105, NP10d, Esna Formation. 19-20) Tribrachiatus orthostylus Shamrai. Sample 107, NP11, Esna Formation.

VII-48 Abu Shama, A. M., Faris, M. and Al-Wosabi, Kh. A

SUMMARY AND CONCLUSIONS

Calcareous nannofossils are studied in the Tarawan, Esna and the base of the Thebes formations at G. Matulla section. Six nannofossil zones are recorded, NP7/8, NP9, NP10, NP11 and NP12, respectively from the base to top. Zone NP9 can be subdivided into two subzones and the four subzones of NP10 are recognized. The basal part of Zone NP10 is characterized by high abundance of Neochiastozygus junctus and Rhabdosphaera solus. This event can be used to delineate the base of Zone NP10 if T. bramlettei is absent. Nannofossil data indicates that the Esna Formation conformably overlies and underlies the Tarawan and the Thebes formations, respectively. At Gebel Matulla, the P/E boundary is placed at the NP9a/NP9b subzonal boundary at which the LOs of Rhomboaster spp. and D. araneus corresponds a brownish calcarenite bed (sample 79). Lithological and mineralogical changes are recorded at the P/E boundary in G. Matulla. The sharp increase of carbonate contents directly above the boundary (~ 82%) could be resulted from decreased fertility that led to increased productivity of generally oligotrophic calcareous microplankton groups (nannoplankton and foraminifers). Smectite decreases from ~ 98% to ~ 90% directly above the boundary. Illite increases in abundance from percentage ~ 1.3% below the boundary to about 8% in calcarenite bed. Kaolinite peak appears and progressively increases from ~ 1.8% directly above the boundary to ~ 15.5% in the base of Subzone NP10a. Although, some authors (e.g. Bralower, 2002) shed doubt on the interpretations of high productivity based on Ba accumulation rates, the recorded barite peak at the P/E boundary in G. Matulla are in agreement with increase productivity of the oligotrophic calcareous nannoplanktons. The nannofossil assemblage data can be used to provide information on temperature, productivity, and the thermal structure of the upper water column through the PETM interval. This interval can be subdivided into a lower part and an upper part on the basis of the nannofossil assemblages. The lower part is represented by two samples (79 and 80) where as the upper part is represented by one sample (81). The abrupt changes in the nannofossil assemblages in the lower and upper parts of the PETM suggest that nannoplankton communities were not stable and that surface water conditions changed over the course of the event. Ericsonia is thought to be a warm-water indicator and indicates for oligotrophic environments.The acme of Ericsonia subpertusa (Coccolithus subpertusus) was recorded in the lower part of PETM interval in concomitant with Rhomboaster. The niche of Fasciculithus spp. was filled by Neochiastozygus juncts and Rhabdolithus solus-the cooler and more eutrophic taxa- in the upper part of the PETM interval due to the environmental changes. The lack of the holococcolith genus Zygrhablithus across the PETM interval is a conspicuous character in the studied section as well as in the Tethys realm. The Discoaster spp. reflect relatively warm water and, probably, oligotrophic surface waters. The onset of Discoaster spp. in the lower part of the PETM interval was followed by sharp decrease in its upper part. The abundance of the genus Chiasmolithus –an indicator of relatively cool and eutrophic water- decreased dramatically across the P/E boundary. On the other hand, the ratio of Discoaster/Chiasmolithus sharply increases in the lower part of the PETM interval indicating prevalence warm oligotrophic conditions. Chiasmolithus increases again than the Discoaster since the upper part of the PETM interval. The fluctuations in the relative abundance between warm-water and cool-water species can be adopted to infer the climatic fluctuations during the PETM event. The major assemblage shift across the P/E boundary suggests a change from colder, more productive surface waters to warmer, more oligotrophic conditions.

ACKNOWLEDGMENTS

The authours are grateful to Prof. N. Obaidalla and Prof. M. S. Mahmoud, Assiut University, for their simulating review.

Upper Paleocene-Lower Eocene Calcareous Nannofossil Boistratigraphy ,…. VII-49

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