DOI: 10.1016/j.palaeo.2014.10.023
论文题名: Deep-sea benthic foraminiferal turnover during the early-middle Eocene transition at Walvis Ridge (SE Atlantic)
作者: Ortiz S. ; Thomas E.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2015
卷: 417 起始页码: 126
结束页码: 136
语种: 英语
英文关键词: Benthic foraminifera
; Cenozoic cooling
; Early-middle Eocene transition
; Ocean stratification
; ODP Leg 208
; Stable isotopes
; Walvis Ridge
英文摘要: The early-middle Eocene transition (EMET, ~51-47Ma) was a pivotal time in Cenozoic global climate development, encompassing the end of the Early Eocene Climate Optimum (EECO) and the start of high-latitude cooling, culminating in the early Oligocene Glacial Maximum (34-33Ma). We studied benthic foraminiferal assemblages and stable isotopes at upper abyssal Site 1263 (paleodepth ~1800m) and lower abyssal Site 1267 (paleodepth ~3500m) on Walvis Ridge (SE Atlantic) across the EMET. Benthic δ18O values at both sites rose from ~49.7Ma on, becoming slightly higher at the shallower site than at the deeper site from ~44Ma on. Benthic δ13C values show a broad maximum at ~49-48Ma. Benthic foraminiferal assemblages at both sites are dominated by calcareous taxa, particularly Nuttallides truempyi, indicative of oligotrophic conditions. Large species of Bulimina, indicative of more food-rich conditions, were less rare at the shallower site, where benthic foraminiferal accumulation rates were generally higher. Specimens intermediate in morphology between N. truempyi (a cosmopolitan warm-water species which died out in the latest Eocene) and its extant, also cosmopolitan, cold-water descendant Nuttallides umbonifera (indicative of corrosive bottom waters), are present, as well as various Epistominella species, indicative of seasonal delivery of phytodetritus to the sea floor, and globally more common after the Eocene-Oligocene transition. These assemblages indicate that deep water environments started a gradual evolution from conditions typical for the warm early Eocene greenhouse to those typical for icehouse conditions by the end of the early Eocene. Characteristic early Eocene species such as Aragonia aragonensis and Quadrimorphina profunda persisted at least until 48Ma (the end of the studied interval) at the deeper site, whereas at the shallower site, they had their last appearances at ~49.7Ma, the time of increase in δ18O values, i.e., high latitude and deep-water cooling. The benthic foraminiferal transition towards assemblages typical for a glaciated world thus started close to the end of the early Eocene in the SE Atlantic, with the middle Eocene already representing a transitional world. The faunal changes in the SE Atlantic began earlier at upper abyssal than at lower abyssal depths. This suggests that a more stratified ocean started to develop in the SE Atlantic at the end of the EECO, possibly due to changes in source regions of intermediate water masses due to polar cooling and/or circulation changes around the Antarctic continent. © 2014 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/69107
Appears in Collections: 过去全球变化的重建
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作者单位: Dpto. Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Leioa, Spain; PetroStrat Ltd., Tan-y-Graig, Parc Caer Seion, Conwy, Wales, United Kingdom; Department of Geology and Geophysics, Yale University, New Haven, CT, United States; Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, United States
Recommended Citation:
Ortiz S.,Thomas E.. Deep-sea benthic foraminiferal turnover during the early-middle Eocene transition at Walvis Ridge (SE Atlantic)[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2015-01-01,417