Maestrichtian through Neogene benthic foraminifers of Maud Rise

Upper abyssal to lower bathyal benthic foraminifers from ODP Sites 689 (present water depth 2080 m) and 690 (present water depth 2941 m) on Maud Rise (eastern Weddell Sea, Antarctica) are reliable indicators of Maestrichtian through Neogene changes in the deep-water characteristics at high southern latitudes. Benthic foraminiferal faunas were divided into eight assemblages, with periods of faunal change at the early/late Maestrichtian boundary (69 Ma), at the early/late Paleocene boundary (62 Ma), in the latest Paleocene (57.5 Ma), in the middle early Eocene to late early Eocene (55-52 Ma), in the middle middle Eocene (46 Ma), in the late Eocene (38.5 Ma), and in the middle-late Miocene (14.9-11.5 Ma). These periods of faunal change may have occurred worldwide at the same time, although specific first and last appearances of deep-sea benthic foraminifers are commonly diachronous. There were minor faunal changes at the Cretaceous/Tertiary boundary (less than 14?7o of the species had last appearances at Site 689, less than 9% at Site 690). The most abrupt benthic foraminiferal faunal event occurred in the latest Paleocene, when the diversity dropped by 50% (more than 35% of species had last appearances) over a period of less than 25,000 years; after the extinction the diversity remained low for about 350,000 years.
The highest diversities of the post-Paleocene occurred during the middle Eocene; from that time on the diversity decreased steadily at both sites. Data on faunal composition (percentage of infaunal versus epifaunal species) suggest that the waters bathing Maud Rise were well ventilated during the Maestrichtian through early Paleocene as well as during the latest Eocene through Recent. The waters appeared to be less well ventilated during the late Paleocene as well as the late middle through early late Eocene, with the least degree of ventilation during the latest Paleocene through early Eocene. The globally recognized extinction of deep-sea benthic foraminifers in the latest Paleocene may have been caused by a change in formational processes of the deep to intermediate waters of the oceans: from formation of deep waters by sinking at high latitudes to formation of deep to intermediate water of the oceans by evaporation at low latitudes. Benthic foraminiferal data (supported by carbon and oxygen isotopic data) suggest that there was a short period of intense formation of warm, salty deep water at the end of the Paleocene (with a duration of about 0.35 m.y.), and that less intense, even shorter episodes might have occurred during the late Paleocene and early Eocene.
The faunal record from the Maud Rise sites agrees with published faunal and isotopic records, suggesting cooling of deep to intermediate waters in the middle through late Eocene.

采自南极威德尔海东部毛德海隆（Maud Rise）的大洋钻探计划（Ocean Drilling Program，ODP）689站位（现今水深2080米）与690站位（现今水深2941米）的上深海带-下半深海带底栖有孔虫（benthic foraminifers），是南极高纬度地区马斯特里赫特期（Maestrichtian）至新近纪（Neogene）深水环境特征变化的可靠指示物。底栖有孔虫动物群被划分为8个组合，其群落更替发生于以下时期：马斯特里赫特期早/晚分界（69 Ma）、古新世（Paleocene）早/晚分界（62 Ma）、古新世最晚期（57.5 Ma）、中始新世（Eocene）早期至晚始新世早期（55-52 Ma）、中始新世中期（46 Ma）、始新世晚期（38.5 Ma）以及中新世（Miocene）中晚期（14.9-11.5 Ma）。尽管深海底栖有孔虫的特定首现与末现事件通常具有穿时性，但上述群落更替时期或曾在全球范围内同步发生。白垩纪/第三纪界线处仅存在轻微的群落更替：689站位有不足14%的物种发生末现，690站位该比例不足9%。最为剧烈的底栖有孔虫群落更替事件发生于古新世最晚期：在不足2.5万年的时间内，物种多样性下降了50%（超过35%的物种发生末现）；灭绝事件后，多样性维持在较低水平长达约35万年。
古新世之后的最高物种多样性出现在中始新世；自此之后，两个站位的物种多样性均呈持续下降趋势。基于动物群组成（内栖型（infaunal）与表栖型（epifaunal）物种占比）的数据表明：毛德海隆海域在马斯特里赫特期至古新世早期，以及始新世最晚期至现代（Recent），均处于良好的水体通风状态。而在古新世晚期，以及中始新世晚期至晚始新世早期，水体通风状况相对较差；其中古新世最晚期至始新世早期的通风程度最低。全球范围内公认的古新世最晚期深海底栖有孔虫灭绝事件，或由大洋深层-中层水的形成过程改变所引发：即从高纬度下沉形成深层水，转变为低纬度蒸发作用形成深层-中层水。底栖有孔虫数据（辅以碳、氧同位素数据佐证）表明：古新世末期存在一段短暂且剧烈的暖盐深层水形成过程（持续时长约0.35百万年（m.y.））；在古新世晚期与始新世早期，或曾出现强度更低、历时更短的类似事件。
毛德海隆站位的动物群记录与已发表的动物群及同位素记录相吻合，表明中始新世至晚始新世期间，大洋深层-中层水发生了降温过程。