Calcareous nannoplankton changes during the Paleocene-Eocene Thermal Maximum in West Central Sinai, Egypt


Abstract: Abstract: The Upper Paleocene-Lower Eocene Hanadi and Dababiya Quarry members in West Central Sinai, Egypt, contain nannofossil taxa assigned to the NP9 and NP10 zones. The Hanadi Member displays lateral variation in thickness and is sharply overlain by a dark gray clay layer that defines the base of the Dababiya Quarry Member. The strata immediately overlying this layer contain nannofossil species assigned to the earliest Eocene. The lateral variation in thickness of the Hanadi Member and the abrupt lithological changes between the Hanadi and the Dababiya members probably suggest active syndepositional tectonism and possibly discontinuous sedimentation. The onset of the Eocene brought oceanic anoxic to dysoxic bottom water conditions as revealed by the dark gray and probably organic rich clay and the common occurrence of Chondrites trace fossils. The earliest Eocene calcareous nannofossil NP9b subzone is missing in the area of study and therefore the incoming of the Eocene is placed at the base of the NP10 zone at the first occurrences of Tribrachiatus bramlettei. The dominant nannofossil taxa around this boundary (Rhomboaster intermedia, R. bitrifida, and R. calcitrapa) in addition to Ericsonia subpertusa are interpreted as proxies for warm surface water. The abundance and diversity of Fasciculithus spp. decreased abruptly in the uppermost part of the NP9a subzone and they became fully extinct shortly above the Paleocene/Eocene interval (base of NP10 zone).

Keywords: Paleocene-Eocene boundary, Sinai, Rhomboaster-Discoaster taxa, calcareous nannofossils turnover, paleoecology, Dababiya Quarry Bed

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