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Open Access Thesis
Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
The biostratigraphy and isotope stratigraphy of the upper Aptian to lower Cenomanian interval including oceanic anoxic events OAE1b, 1c and 1d are investigated in ODP Site 763, drilled on the Exmouth Plateau offshore northwest Australia. Benthic foraminifera suggest that Site 763 was situated in outer neritic to upper bathyal water depths (~150-600 m). OAEs of the Atlantic basin and Tethys are typically associated with organic carbon-rich black shales and δ13C excursions. However, OAEs at this high latitude site correlate with ocean acidification and/or pyrite formation under anoxic conditions rather than black shales. Ocean acidification maybe responsible for sporadic low abundances of planktic foraminifera compared to radiolarians and benthic foraminifera associated with increased volcanogenic CO2 production during the formation of the Southern and Central Kerguelen Plateaus. Sea surface temperature may have cooled to 11°C in the late Aptian but increased gradually during the Albian. The Aptian/Albian boundary is placed at a negative carbon isotope excursion associated with the lowest occurrence of Microhedbergella renilaevis, typically found within the Niveau Kilian black shale of OAE1b. Third-order sea level cycles, particularly in the middle Albian, produced cyclic changes in the abundance of inoceramid prisms that increased during inferred times of falling sea level. The late Albian OAE1c and OAE1d coincide with horizons of intense pyritization and the absence of all biocomponents suggesting the development of euxinia. Warm Tethyan waters reached the Exmouth Plateau during the latest Albian based on the presence of thermocline dwelling keeled planktic foraminifera including Planomalina buxtorfi.
Robert Mark Leckie
Robert M DeConto
Alibrahim, Ali, "Micropaleontology and Isotope Stratigraphy of the Upper Aptian to Lower Cenomanian (~114-98 Ma) In ODP Site 763, Exmouth Plateau, NW Australia" (2016). Masters Theses. 361.