Unravelling the paleoecology of flat clams: New insights from an Upper Triassic halobiid bivalve
Unravelling the paleoecology of flat clams: New insights from an Upper Triassic halobiid bivalve
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DOI：
10.1016/j.gloplacha.2020.103195
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发表时间：
2020-07
影响因子：
3.9
通讯作者：
Nicolo Del Piero;S. Rigaud;S. Takahashi;S. Poulton;R. Martini
中科院分区：
文献类型：
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作者：
Nicolo Del Piero;S. Rigaud;S. Takahashi;S. Poulton;R. Martini
扁蛤普遍存在于海洋三叠纪和侏罗纪深水环境中，在那里它们通常被发现为单一或少数特定的组合。它们在缺氧条件下沉积的深水相中的丰度表明了潜在的独特性，但仍有争议，古生态学。在加拿大温哥华岛Tsiko湖上三叠统半远洋演替露头中的海葵（Halobia cordilleranin）的分布是一个具有启发性的案例研究。在那里，深水矿床进行了调查，使用多学科的方法，包括相描述（矿物学，化石和有机物含量），埋藏，形态测量，显微镜（阴极发光，扫描电子显微镜）和独立的古氧化还原代理约束（framboidal黄铁矿分布，铁形态）。总的来说，Tsiko湖的盐生生物埋藏学表明原位积累很少或没有改造。在半远洋沉积物中，确定了三个主要的岩石生物相（BFC 1，2，3）;古氧化还原指标表明，这些岩石生物相沉积在不同的氧条件下，从极端dysopolysis（BFC 1）占主导地位的缺氧（BFC 3）。H. Cordilleranais被证明直接受到底层水氧化作用的影响，在极端缺氧条件下（即BFC 1和2），这种生物的丰度和尺寸都达到峰值。相反，在普遍的低氧条件下（即BFC 3），H. cordilleranais以幼虫或后幼虫阶段的形式为主，这些形式可能被水柱euxinia杀死。因此，虽然这里的物种是生活在最有可能作为一个epibenthic躺椅，一个早期（幼虫）浮游/游泳阶段是必要的，以解释它的发生模式，在占主导地位的euxinic条件（即BFC 3），其广泛的分布和快速扩张。最后，本研究强调了在恢复氧气条件下的嗜盐生物的定殖能力，强调了扁蛤在古环境重建中的潜在意义。
Flat clams are ubiquitous in marine Triassic and Jurassic deep-water environments, where they are often recovered as mono- or pauci-specific assemblages. Their abundance in deep-water facies deposited under oxygen-depleted conditions suggests a potentially unique, but nevertheless debated, paleoecology. The distribution ofHalobia cordilleranain an Upper Triassic hemipelagic succession outcropping at Tsiko Lake, Vancouver Island, Canada, serves as a revealing case study. There, deep-water deposits were investigated using a multi-disciplinary approach including facies description (mineralogical, fossil and organic content), taphonomy, morphometry, microscopy (cathodoluminescence, scanning-electron microscope) and independent paleo-redox proxy constraints (framboidal pyrite distributions, Fe speciation). Overall, halobiids' taphonomy at Tsiko Lake is indicative of in situ accumulations with little or no reworking. Among the hemipelagic deposits, three major litho-biofacies (BFC 1, 2, 3) were identified; paleo-redox proxies indicate that these litho-biofacies were deposited under different oxygen conditions ranging from extreme dysoxic (BFC 1) to dominantly euxinic (BFC 3). The distribution ofH. cordilleranais shown to be directly influenced by bottom water oxygenation with this organism peaking both in abundance and dimensions under extreme dysoxic to anoxic conditions (i.e. BFC 1 & 2). Conversely, under prevailing euxinic conditions (i.e. BFC 3), the population ofH. cordilleranais dominated by forms at larval or post-larval stage which were presumably killed by water-column euxinia. Thus, although the species is here shown to have lived most likely as an epibenthic recliner, an early (larval) planktonic/nektonic stage is needed to explain its mode of occurrence during dominantly euxinic conditions (i.e. BFC 3), and its wide distribution and rapid expansion. Finally, this study highlights the colonizing capacity of halobiids in case of restored oxygen conditions, stressing the potential significance of flat clams for paleoenvironmental reconstruction.