The end-Triassic bivalve extinction event
The end-Triassic bivalve extinction event
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DOI：
10.1016/0031-0182(81)90092-4
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发表时间：
1981
期刊：
影响因子：
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通讯作者：
A. Hallam
中科院分区：
文献类型：
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作者：
A. Hallam
整个中生代动物群大规模灭绝的最重要事件之一发生在三叠纪后期，但脊椎动物的主要动物群更替时间比海洋无脊椎动物早几百万年。如菊石，腕足类和牙形石，下降从卡尼早期诺利多样性的高峰，其次是一个显着的灭绝事件结束时的时期。双壳类软体动物可能是最丰富和最多样化的大型无脊椎动物群，在属和亚属水平上证实了这种模式。本文对双壳类进行了详细的分析，并试图从晚三叠世相记录的环境变化中寻找双壳类灭绝事件的关系。根据最近的建议，Rhaetian阶段被删除，上Norian（Sevatian）细分为三个新的菊石区。这表明，经典的西北欧“雷蒂克”与阿尔卑斯山的Kössen层和Zeliach层相关，至少大致对应于这两个带的上部。据估计，近一半的现有双壳类属和几乎所有的物种都未能在三叠纪末的灭绝事件中幸存下来。trigonioid，uniodium和hippuritoid订单特别强烈的影响，但大多数pholadomyoid属幸存下来。三个主要的生态类别区分：浅浅海组，其中大多数类群属于，广盐组，可以容忍边缘海洋和泻湖条件，和深浅海组，显着Halobia和Monotis。所有群体都受到了强烈的影响，但物种的深海浅海组显然是最容易受到影响。为了分析的目的，区分了七个地理区域，并表明省性是轻微的，但一些重要的分类群是特提斯和太平洋地区特有的。特有属被证明比世界分布属更容易灭绝。世界上很少有地方在三叠纪-侏罗纪界线上有或多或少连续的海相沉积序列。详细介绍了在阿尔卑斯山，西北欧和内华达州的部分，并简要提及其他部分。关于晚三叠世的古地理变化，那些涉及气候是可忽略的，但有一个或多或少的进步海退的陆表海后，拉丁早期卡尼海侵最大，相应的变浅，在更连续的海洋特提斯地区。这种一级效应是由于海平面的升降而引起的，这是相当确定的，但对于二级海进-海退旋回，情况就不那么清楚了。然而，晚诺利期（“雷期”）旋回的晚期可能是一次轻微的海平面升降事件的结果。到三叠纪末，海洋已经大幅度后退，大规模灭绝事件被认为部分与这一现象有关，部分与随后的Hettangian海侵期间发生的广泛缺氧阶段有关。
One of the most important episodes of mass extinction of animal groups in the whole of the Phanerozoic took place in the latter part of the Triassic, but the time of major faunal turnover of the vertebrates preceded that of marine invertebrates by several million years. As shown by ammonites, brachiopods and conodonts, decline from a Carnian—early Norian diversity peak was followed by a significant extinction episode at the end of the period. This pattern is confirmed at generic and subgeneric level by the bivalve molluscs, probably the most abundant and diverse macroinvertebrate group. This paper analyses the bivalves in detail and attempts to seek a relationship of the extinction event to environmental changes as recorded by late Triassic facies.Stratigraphy of the youngest Triassic is briefly discussed. Following a recent recommendation, the Rhaetian stage is dropped and the Upper Norian (Sevatian) subdivided into three new ammonite zones. It is suggested that the classic northwest European “Rhaetic” correlates with the Kössen and Zlambach Beds of the Alps and corresponds at least approximately with the upper two of these zones.It is estimated that nearly half the existing bivalve genera and nearly all the species failed to survive the end-Triassic extinction event. The trigonioid, unionoid and hippuritoid orders were especially strongly affected but most of the pholadomyoid genera survived. Three major ecological categories are distinguished: a shallow neritic group, to which most taxa belong, a euryhaline group that could tolerate marginal marine and lagoonal conditions, and a deep neritic group, notablyHalobiaandMonotis. All groups were strongly affected by the extinction but species of the deep neritic group were apparently the most susceptible. Seven biogeographic regions are distinguished for the purpose of analysis and it is shown that provinciality is slight, but some important taxa are endemic to the Tethyan and Pacific regions. Endemic genera prove to have been much more subject to extinction than cosmopolitans.There are very few places in the world with a more or less continuous marine sequence of deposits across the Triassic-Jurassic boundary. Details are given of sections in the Alps, northwest Europe and Nevada and briefer mention made of others. With regard to late Triassic palaeogeographic changes, those involving climate were neglibible, but there was a more or less progressive regression of epicontinental seas following a Ladinian—early Carnian transgressive maximum, with a corresponding shallowing in the more continuously marine Tethyan region. That this first-order effect was due to a eustatic lowering of sea level is fairly certain, but the situation is less clear for second-order transgressive-regressive cycles. The late late Norian (“Rhaetian”) cycle is probably, however, the results of a minor eustatic event. By the end of the Triassic the sea had regressed substantially and the mass extinction event is though to be bound up partly with this phenomenon and partly with the phase of widespread anoxicity that occurred during the succeeding Hettangian transgression.