Benthic foraminiferal faunal changes during the Eocene-Oligocene climate transition at ODP sites 1209 A and 1211A at the Shatsky Rise, Pacific Ocean

Author(s): Julian, M.; Raymond, A.; Thomas, D.; Alvarez-Zarikian, C. A.
Author Affiliation(s): Primary:
Texas A&M University, Department of Geology and Geophysics, College Station, TX, United States
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English
Summary: This study focuses on benthic foraminiferal faunal changes at Shatsky Rise during the Eocene-Oligocene climate transition. The transition from the hothouse climate of the Eocene to the icehouse climate of the Oligocene is one of the most pivotal transitions in Earth's history, marked by the initial build-up of continental glaciers during the Cenozoic and possibly a significant component of global deep-water cooling. Oxygen isotope and Mg/Ca data from benthic foraminifera have been used to constrain the relative roles of ice buildup versus cooling, but the studies reach different conclusions about the contributions of each. A large marine biotic turnover began to occur in the middle Eocene and continued into the early Oligocene; both microfossils and marine invertebrates suffered a large decline in diversity. In the Weddell Sea (ODP Sites 689 and 690), benthic foraminiferal communities gradually changed from Bulimina dominated assemblages to Nuttallides dominated assemblages. We analyzed benthic foraminiferal assemblages from 100 core samples, taken at 50 cm intervals, across the Eocene-Oligocene transition at ODP Sites 1209A and 1211A. At site 1209A, the Eocene-Oligocene transition corresponds to depths of 113.83 to 138.18 mbsf and ages of 29.66 to 36.16 Ma, whereas at Site 1211A, it corresponds to depths of 69.78 to 93.96 mbsf and ages of 28.8 to 38.0 Ma for site 1211A). Analyses of upper Eocene sediment indicate that the benthic foraminiferal assemblage is dominated by the genera Cibicidoides (20% relative abundance) and Nuttallides (18%), with relatively lower abundances of Bulimina (17%) and Nodosaria (10%). At the Eocene-Oligocene transition, the sediment contains Cibicidoides (17%) and Nuttallides (14%) as the most prominent taxa, with Pleurostomella (10%) and Bulimina (8%) as common secondary components. In the lower Oligocene sediment, Cibicidoides (20%) and Nuttallides (17%) are also dominant, with Bulimina, Pleurostomella, and Nodosaria each comprising 10% of the assemblage. These results are similar to those of the Weddell Sea sediments in that the general abundance of Bulimina decreases and Nuttallides is dominant throughout the transition. Because the assemblages are similar at Shatsky Rise and the Weddell Sea, it suggests that the deep waters must have had common characteristics, such as low nutrient availability and colder temperatures, to influence the community structure.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Assemblages; Benthic taxa; Cenozoic; Climate change; Eocene; Faunal studies; Foraminifera; Glacial environment; Icehouse effect; Invertebrata; Leg 198; Microfossils; North Pacific; Northwest Pacific; ODP Site 1209; ODP Site 1211; Ocean Drilling Program; Oligocene; Pacific Ocean; Paleoclimatology; Paleogene; Protista; Shatsky Rise; Tertiary; West Pacific
Coordinates: N323900 N324000 E1583100 E1583000
N320000 N320000 E1575100 E1575100
Record ID: 2007070760
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