Miocene deep-sea benthic foraminifera from ODP sites 752, 1139 and 1168 (Southern Indian Ocean).

Ridha, Dana Noory (2020). Miocene deep-sea benthic foraminifera from ODP sites 752, 1139 and 1168 (Southern Indian Ocean). University of Birmingham. Ph.D.

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Abstract

Miocene deep-sea benthic foraminifera from ODP Sites 752A (Broken Ridge), 1168A (Western Tasmanian Margin) and 1139A (Kerguelen Plateau) in the southern Indian Ocean, have been studied for their stratigraphic distribution, diversity, abundance and test-size changes during periods of global climate shifts. All sites yielded similar taxa though the exact assemblage composition varied at each site. No major faunal extinctions were noted with many taxa ranging through. Site 752A had a major foraminiferal assemblage shift at ~13 Ma. While those from 1168A and 1139A recorded a significant drop in the Shannon diversity index at about 14 Ma. These events may relate to the expansion of the East Antarctic Ice Sheet during this period of marked global cooling, indicating an impact in deep-sea ecosystems. Nuttalides umbonifera and Sphaeriodina bulloides are the most abundant species of the early to the mid-Miocene interval at these sites, with the former known to favour highly oligotrophic conditions. Abdetodentrix pseudothalmani and Trifarina angulosa had their peak abundance during the mid-late Miocene in association with global cooling. Test size variability measured in five separate taxa (Abdetodentrix pseudothalmani, Cibicidoides mundulus, Globocassidulina subglobosa, Nuttalides umbonifera and Sphaeroidina bulloides) demonstrated rapid size increase at around 12 Ma in all Sites. Studies of benthic foraminiferal stable isotopes \(\delta ^{18}\)O and \(\delta^{13}\)C at all sites accords well with global published records for this interval. All sites demonstrated increasing \(\delta^{13}\)C values from the late early Miocene to mid-Miocene, coinciding with the early to mid-Miocene Monterey carbon isotope excursion. Mid-late Miocene \(\delta ^{18}\)O values reflect global cooling during the expansion of the East Antarctic Ice Sheet (14-12 Ma).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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