Paleoecological Patterns in Molluscan Extinctions and Recoveries: Comparison of the Cretaceous–Paleogene and Eocene–Oligocene Extinctions in North America
Paleoecological Patterns in Molluscan Extinctions and Recoveries: Comparison of the Cretaceous–Paleogene and Eocene–Oligocene Extinctions in North America
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DOI：
10.1016/j.palaeo.2004.06.017
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发表时间：
2004-11
期刊：
影响因子：
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通讯作者：
T. Hansen;P. Kelley;D. Haasl
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文献类型：
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作者：
T. Hansen;P. Kelley;D. Haasl
在德克萨斯州和密西西比州的白垩纪-第三纪（K-T）和始新世-渐新世（E-O）界线上的暴露可能代表了世界上这些界线上最完整和保存最完好的软体动物化石序列。这两个边界的露头都含有原始文石和方解石的软体动物壳，它们沉积在开阔海洋环境的细颗粒沉积物中。K-T和E-O灭绝表现出非常不同的恢复模式，可能反映了非常不同的灭绝原因和程度。K-T序列包含一个软体动物化石记录，与K-T边界的突然灭绝事件和在恶劣海洋条件下的长期初始恢复相一致。上白垩纪最上层10米沉积物中有多种软体动物（约40种），以悬浮食性动物为主。海啸床上方最早的古新世沉积层包含了以沉积物食性动物为主的贫瘠动物群。古新世动物群的多样性缓慢上升，但在灭绝后的数十万年里仍然相对贫乏，并以沉积物捕食者为主，同时δ13C值异常表明海洋初级生产力长期受到抑制。随着初级生产的正常条件的恢复，以悬浮饲料为主的多种软体动物组合重新出现。从长远来看，古新世早期到中期的伽马多样性包括进化的“开花分类群”，这些科表现出不寻常的物种爆发，在始新世逐渐消退。墨西哥湾沿岸的总多样性直到始新世晚期才接近白垩纪的水平，这代表了近2500万年的总恢复间隔。虽然E-O事件也反映了墨西哥湾软体动物的灭绝率超过90%，但在恢复动物群中没有任何不利环境条件的迹象。早渐新世软体动物种类繁多，以正常海洋条件下的悬浮捕食动物为主。然而，东至西边界的中断可能掩盖了短期恢复的动物群。也没有迹象表明E-O大灭绝会造成长期扰动。在几百万年的时间里，没有开花类群，伽马多样性接近灭绝前的水平。E-O灭绝的总体模式与与长期冷却有关的灭绝（和/或迁移）是一致的。
Exposures across the Cretaceous–Tertiary (K–T) and Eocene–Oligocene (E–O) boundaries, in Texas and Mississippi, respectively, probably represent the most complete and best-preserved fossil molluscan sequences across these boundary intervals in the world. Outcrops from both boundaries contain pristine aragonitic and calcitic molluscan shells, which were deposited in fine-grained sediments from open marine environments. The K–T and the E–O extinctions exhibit very different recovery patterns, probably reflecting very different causes as well as magnitudes of extinction. The K–T sequence contains a molluscan fossil record that is consistent with an abrupt extinction event at the K–T boundary and a prolonged initial recovery in hostile oceanographic conditions. The uppermost 10 m of Upper Cretaceous sediments contain a diverse (approximately 40 species) molluscan fauna dominated by suspension feeders. The earliest Paleocene sediments immediately above the tsunami bed contain an impoverished fauna dominated by deposit feeders. The Paleocene fauna slowly climbs in diversity but remains relatively impoverished and dominated by deposit feeders for several hundred thousand years after the extinction in conjunction with anomalous δ13C values that suggest prolonged suppression of marine primary productivity. Diverse suspension-feeder dominated molluscan assemblages reappear with the resumption of normal conditions of primary production. In the long term, early to middle Paleocene gamma diversity includes evolutionary “bloom taxa,” families that exhibit unusual speciation bursts that subside in the Eocene. Total diversity for the Gulf Coast does not approach Cretaceous levels until the Late Eocene representing a total recovery interval of nearly 25 million years. While the E–O event also reflects a molluscan extinction rate of over 90% in the Gulf of Mexico, there are no signs of hostile environmental conditions in the recovery fauna. Early Oligocene molluscan assemblages are diverse and dominated by suspension feeders characteristic of normal marine conditions. The hiatus at the E–O boundary, however, could have obscured a short-term recovery fauna. There is also no sign of long-term perturbation by the E–O extinction. There are no bloom taxa and gamma diversity approaches pre-extinction levels within a few million years. The overall pattern of the E–O extinction is consistent with extinction (and/or migration) associated with long-term cooling.