المنشورات
فرضية
2003
Micropaleontological and stratigraphical analyses of the Late Cretaceous/Early Tertiary succession of the Southern Nile Valley (Egypt).
Ali, Dr. Mohamed Youssef . 2003
The marine Late Campanian to Early Eocene sedimentary sequence of the Southern Nile Valley (Egypt) is recorded and described in five land sections in the area between Sinn El Kaddab in the south and Wadi Abu Ghurra in the north. A total of 210 samples was investigated with respect to quantitative and qualitative analyses of the calcareous nannofossils, planktonic and benthonic foraminiferal assemblages.
The biostratigraphical zonation of the sediments is achieved by using calcareous nannofossils and planktonic foraminifera, seven biozones of calcareous nannofossils and nine biozones of planktonic foraminifera were distingushed. A major hiatus was recorded between the Maastrichtian and the Paleocene covering the A. mayaroensis Zone, (Zones P0 and P alpha)
and (subzones P1a,b), another minor hiatus includes the (Zone P2), upper part of (Zone P3a), the (Zone P3b), and the lower part of (Zone P6a). Due to their composition the benthonic foraminiferal assemblages are assigned to three different ecological groups: 1) mixohaline shallow water assemblages, 2) Tethyan carbonate faunal assemblages (TCF) and 3) euhaline deeper shelf assemblages: Midway-type fauna (MF) and Velasco-type fauna (VF). These three assemblages suggest lagoonal environments with considerably reduced salinity in warm climates and high runoff for the Late Campanian-Maastrichtian interval. Middle-outer neritic conditions (50-200 m) are indicated for the Paleocene and inner-middle shelf carbonate platforms (<50-75 m) for the Early Eocene sequence. The investigated sedimentary sequence generally reflects a continuous deepening of the marine sedimentary system from Campanian/Maastrichtian to Paleocene times for this part of the so-called “Stable Shelf” of Egypt. This transgressive development was interrupted by several
short-lived regressions of varying intensity. After the climax of the transgression during Late Paleocene time which caused open marine deposits (Garra Formation), a fall in the sea level was recorded in Early Eocene time. This caused the development of a shallow-shelf facies and the replacement of an outer neritic benthonic assemblages by an inner neritic assemblages containing larger foraminifera. The impact of the Paleocene Eocene Thermal Maximum event on three microfossil groups (calcareous nannofossils, planktonic foraminifera and calcareous benthonic foraminifera) was investigated. A conspicuous generic and family turnover of calcareous nannoplankton fossils, major turnover in the diversity and abundance of the planktonic foraminifera and an extinction of some calcareous benthonic foraminiferal species were recorded. The study of benthonic foraminiferal turnover suggests that the benthonic extinction event is not only a deep-sea phenomenon. Neritic environments are, according to my findings, also perturbed, with a decrease of taxa becoming extinct from the deep sea towards shallower neritic depths. Restricted environments prevailed during Late Campanian and Maastrichtian times. Low-food, high oxygen conditions prevailed during planktonic foraminifera biochrons
P1c (NP3) and P3a-P4 (NP6-NP9), when assemblages were mostly dominated by Cibicidoides spp. Assemblages dominated by buliminids, Lenticulina spp., Stainforthia spp., Valvulineria scrobiculata and Anomalinoides aegyptiacus mark increased trophic levels and dysoxic conditions. These were established after the benthonic extinction event (=BEE), during biochrons P6a,b-P7 and P8 (NP10, NP11). Thin walled and small taxa (e.g. Ammobaculites spp., Haplophragmoides spp. and Trochammina spp.) were recorded in the dark shale sequence above the BEE. Warm humid climates with high rainfall and high runoff prevailed during the Late Campanian-Early Paleocene, while arid climatic conditions persisted during the Late Paleocene and Early Eocene.
The biostratigraphical zonation of the sediments is achieved by using calcareous nannofossils and planktonic foraminifera, seven biozones of calcareous nannofossils and nine biozones of planktonic foraminifera were distingushed. A major hiatus was recorded between the Maastrichtian and the Paleocene covering the A. mayaroensis Zone, (Zones P0 and P alpha)
and (subzones P1a,b), another minor hiatus includes the (Zone P2), upper part of (Zone P3a), the (Zone P3b), and the lower part of (Zone P6a). Due to their composition the benthonic foraminiferal assemblages are assigned to three different ecological groups: 1) mixohaline shallow water assemblages, 2) Tethyan carbonate faunal assemblages (TCF) and 3) euhaline deeper shelf assemblages: Midway-type fauna (MF) and Velasco-type fauna (VF). These three assemblages suggest lagoonal environments with considerably reduced salinity in warm climates and high runoff for the Late Campanian-Maastrichtian interval. Middle-outer neritic conditions (50-200 m) are indicated for the Paleocene and inner-middle shelf carbonate platforms (<50-75 m) for the Early Eocene sequence. The investigated sedimentary sequence generally reflects a continuous deepening of the marine sedimentary system from Campanian/Maastrichtian to Paleocene times for this part of the so-called “Stable Shelf” of Egypt. This transgressive development was interrupted by several
short-lived regressions of varying intensity. After the climax of the transgression during Late Paleocene time which caused open marine deposits (Garra Formation), a fall in the sea level was recorded in Early Eocene time. This caused the development of a shallow-shelf facies and the replacement of an outer neritic benthonic assemblages by an inner neritic assemblages containing larger foraminifera. The impact of the Paleocene Eocene Thermal Maximum event on three microfossil groups (calcareous nannofossils, planktonic foraminifera and calcareous benthonic foraminifera) was investigated. A conspicuous generic and family turnover of calcareous nannoplankton fossils, major turnover in the diversity and abundance of the planktonic foraminifera and an extinction of some calcareous benthonic foraminiferal species were recorded. The study of benthonic foraminiferal turnover suggests that the benthonic extinction event is not only a deep-sea phenomenon. Neritic environments are, according to my findings, also perturbed, with a decrease of taxa becoming extinct from the deep sea towards shallower neritic depths. Restricted environments prevailed during Late Campanian and Maastrichtian times. Low-food, high oxygen conditions prevailed during planktonic foraminifera biochrons
P1c (NP3) and P3a-P4 (NP6-NP9), when assemblages were mostly dominated by Cibicidoides spp. Assemblages dominated by buliminids, Lenticulina spp., Stainforthia spp., Valvulineria scrobiculata and Anomalinoides aegyptiacus mark increased trophic levels and dysoxic conditions. These were established after the benthonic extinction event (=BEE), during biochrons P6a,b-P7 and P8 (NP10, NP11). Thin walled and small taxa (e.g. Ammobaculites spp., Haplophragmoides spp. and Trochammina spp.) were recorded in the dark shale sequence above the BEE. Warm humid climates with high rainfall and high runoff prevailed during the Late Campanian-Early Paleocene, while arid climatic conditions persisted during the Late Paleocene and Early Eocene.
نوع عمل المنشور
Ph. D
اسم الناشر
LAP LAMBERT Academic Publishing AG & Co. KG
مدينة النشر
Bochum
نوع الفرضية
Ph. D
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