Collaborative Research: New Chemo- and Biostratigraphic Framework for the Lower Triassic of the Western U.S.: Towards a high-resolution understanding of Early Triassic events

该奖项由2009年《美国复苏与再投资法案》(公法111-5)资助。合作研究：美国西部下三叠统新的化学和生物地层学框架：寻求对早期三叠纪事件的高分辨率理解加州大学河滨分校Pedro Marenco，EAR-0921127玛格丽特·弗里泽，大学。威斯康星州，密尔沃基，EAR-0920894加州大学圣克鲁斯分校，马修·克拉彭，EAR-0918184摘要二叠纪末期物种大灭绝的原因仍然存在争议。然而，由西伯利亚圈闭喷发引发或催化的二氧化碳或硫化氢毒性和/或气候变化的某种组合似乎是最有可能的致死机制。二叠纪末期生物大灭绝的生物恢复受到的关注较少，尽管早三叠世的恢复时间异常长(~5英里。年。)？时代相的出现？(例如，海底沉淀晶体、潮下叠层石生物礁和褶皱构造)、碳同位素多次漂移和下三叠统海水硫酸盐硫同位素值的升高表明，在可能推迟了生物恢复的大规模灭绝之后，异常环境条件延长了。多条证据表明，早三叠世是大气二氧化碳升高的时期，很可能是西伯利亚圈闭极端火山作用的结果。与此同时，直到中三叠世，后生动物珊瑚礁从化石记录中消失了，而钙化的海洋无脊椎动物往往较小。这些对生物体的观察和实验工作引起了人们对海洋酸化的生态后果的关注，特别是在珊瑚礁生态系统中。实验室对现存珊瑚的实验表明，随着pH值的下降，珊瑚会以没有骨骼的息肉的形式存活，直到pH值恢复到合适的水平。有人提出，早三叠世类似的海洋酸化作用抑制了大型钙质贝壳的生长，有利于小型生物，并阻止珊瑚形成骨骼。因此，如果旷日持久的恢复反映了由于二氧化碳水平升高而受到抑制的生态系统，那么早三叠世群落可能代表了温室气体强迫的海洋酸化对地球生态系统S生态系统影响的古代类比。考虑到珊瑚骨架在支持现代珊瑚礁生态系统生物多样性方面的极端重要性，珊瑚不能产生骨架很可能会对渔业和依赖它们的经济产生严重的负面影响。因此，异常的早三叠世沉积可能提供了在大气二氧化碳增加和海洋二氧化碳减少的条件下的海洋生态系统的预览。美国西部的下三叠统沉积在盘古陆西海岸的两个盆地中，这两个盆地加在一起构成了整个早三叠世的几乎完整的记录。对美国西部生物恢复的研究主要集中在化石丰度和多样性模式以及不合时相的出现上。这些研究表明，海底沉淀型文石扇和大型潮下叠层石生物礁等时代相仅存在于较深的水环境中，低于晴朗天气的波基(除了直接的P-T边界区间)。结晶扇仅见于斜坡或盆地剖面，而叠层石生物礁则出现在更接近环境的准层序底部的泛滥表面上。海底水晶扇和叠层石生物礁都是在厌氧条件下形成的。时代相的相依分布导致了早三叠世缺氧是深海现象的结论，而浅层环境是大灭绝后缺氧的避难所。早三叠世缺乏浅水缺氧的证据表明，浅海生物恢复可能不是受到缺氧的阻碍，而是由于大气中二氧化碳含量高而导致的高二氧化碳和海洋酸化。为了了解恢复的性质，需要更详细地研究深水缺氧和浅水酸化对海洋生态系统的独立和协同影响。由于每个应力的环境范围不同，这两种现象的证据很少在一个单独的剖面中找到；因此，目前缺乏一个强有力的地层格架来精确对比两个下三叠统序列内和两个下三叠统之间的近端和远端沉积环境，这阻碍了研究。PIS将通过创建美国西部高分辨率的生物和化学地层格架来解决这个问题，然后利用这些研究结果来检验与生物恢复性质有关的两个假说：1)牙形刺磷酸盐和腕足碳酸盐的氧同位素组成表明，由于西伯利亚圈闭火山作用导致大气中二氧化碳含量增加，早三叠世曾多次发生气候变暖和海洋酸化；2)时空多变的环境条件促成了古生代动物群的生态变化，这种变化可以在物种灭绝后立即进行追踪，并贯穿了漫长的早三叠世生物危机。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Collaborative Research: New Chemo- and Biostratigraphic Framework forthe Lower Triassic of the Western U.S.: Towards a high-resolutionunderstanding of Early Triassic eventsPedro Marenco, UC Riverside, EAR-0921127Margaret Fraiser, Univ. Wisconsin, Milwaukee, EAR-0920894Matthew Clapham, UC Santa Cruz, Ear-0918184 ABSTRACTThe cause of the end-Permian mass extinction remains controversial. However, some combination of CO2 or H2S toxicity and/or climate change, triggered or catalyzed by the eruption of the Siberian Traps, appears to be the most likely kill mechanism. The biotic recovery from the end-Permian mass extinction has received less attention, despite the fact that the Early Triassic recovery was unusually long (~5m.y.) The occurrence of ?anachronistic facies? (e.g., seafloor precipitated crystals, subtidal stromatolite bioherms, and wrinkle structures), multiple carbon isotopic excursions, and elevated seawater sulfate sulfur isotopic values in Lower Triassic strata suggest a prolonged period of anomalous environmental conditions following the mass extinction that may have delayed the biotic recovery.Multiple lines of evidence imply that the Early Triassic was a time of elevated atmospheric CO2 most likely resulting from the extreme volcanism of the Siberian Traps. At the same time, metazoan reefs disappeared from the fossil record until the Middle Triassic, while calcifying marine invertebrates tended to be small. These observations and experimental work on living organisms have raised concerns about the ecological consequences of ocean acidification, in reef ecosystems in particular. Laboratory experiments with extant corals have demonstrated that as pH drops, corals survive as polyps without skeletons until pH returns to favorable levels. It has been suggested that similar ocean acidification during the Early Triassic inhibited growth of large calcareous shells, favoring small organisms, and prevented corals from forming skeletons. Thus, if the protracted recovery reflects a suppressed ecosystem due to elevated CO2 levels, Early Triassic communities may represent an ancient analog for the effects of greenhouse gas-forced ocean acidification on Earth?s ecosystems. Considering the extreme importance of coral skeletal frameworks in supporting the biodiversity of modern reef ecosystems, the inability of corals to produce skeletons will most likely have severe and negative effects on fisheries and the economies that depend on them. Thus, unusual Early Triassic deposits may provide a preview of marine ecosystems under conditions of increased atmospheric pCO2 and reduced ocean pH.The Lower Triassic of the western U.S. was deposited in two basins on the western coast of Pangaea, which together comprise a nearly complete record of the entire Early Triassic. Studies of the biotic recovery in the western U.S. have largely focused on fossil abundance and diversity patterns and the occurrence of anachronistic facies. These studies have demonstrated that anachronistic facies such as seafloor-precipitated aragonite fans and large subtidal stromatolite bioherms are found exclusively in deeper water settings, below fair-weather wave base (except for the immediate P-T boundary interval). Crystal fans have been reported only from slope or basinal sections while stromatolite bioherms occur on flooding surfaces at the bases of parasequences in more proximal environments. Both seafloor crystal fans and stromatolite bioherms are interpreted to have formed under anaerobic conditions. The facies-dependent occurrence of anachronistic facies has led to the conclusion that anoxia was a deep-ocean phenomenon during the Early Triassic, and that shallower settings were a refuge from anoxia in the aftermath of the mass extinction. The lack of evidence for shallow-water anoxia during the Early Triassic suggests that the biotic recovery in the shallow realm may have been hindered not by anoxia, but by hypercapnia and ocean-acidification due to high atmospheric carbon dioxide.The impact of atmospheric carbon dioxide and ocean acidification during the Early Triassic has received little study. In order to understand the nature of the recovery, the independent and synergistic effects of deep-water anoxia and shallow-water acidification on marine ecosystems need to be examined in greater detail. Because of the different environmental range of each stress, evidence for the two phenomena is rarely found in a single section; thus studies are currently hindered by the lack of a robust stratigraphic framework for the precise correlation of proximal to distal depositional settings both within and between the two Lower Triassic successions. PIs will address this issue by creating a high-resolution bio- and chemostratigraphic framework for the western U.S. and then use those results to test two hypotheses related to the nature of the biotic recovery: 1) The oxygen isotopic composition of conodont phosphate and brachiopod carbonate indicates that the Early Triassic was a time of recurrent climate warming and ocean acidification resulting from increased atmospheric carbon dioxide from Siberian Trap volcanism, and 2) spatially and temporally variable environmental conditions facilitated ecologic change in the Paleozoic Fauna that can be tracked in the immediate extinction aftermath and through the prolonged Early Triassic biotic crisis.