Stratigraphic and environmental control on marine benthic community change through the early Toarcian extinction event (Iberian Range, Spain)
Stratigraphic and environmental control on marine benthic community change through the early Toarcian extinction event (Iberian Range, Spain)
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DOI：
10.1016/j.palaeo.2019.03.039
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发表时间：
2019-06-15
影响因子：
3
通讯作者：
Twitchett，Richard J.
中科院分区：
文献类型：
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作者：
Danise，Silvia;Clemence，Marie-Emilie;Twitchett，Richard J.
在侏罗纪早期(~183万 Ma以前)，全球变暖和与之相关的环境变化与海洋生物领域的一次灭绝事件(托阿尔西亚早期灭绝事件)相吻合。此前，缺氧被认为是物种灭绝的主要原因，但在整个事件过程中，仍保持充氧状态的地方也会发生物种灭绝，这表明温度等其他因素可能起到了重要作用。为了验证这一假设，我们将底栖大型无脊椎动物的定量分析与高分辨率地球化学指标相结合，在西班牙伊比利亚山脉没有黑色页岩沉积的两个剖面的散体岩石(TOC，δ13C，δ18O)以及贝壳和腕足类贝壳(δ13C，δ18O)上进行了定量分析。这些剖面沿着向北加深的陆上-近海梯度呈东南-西北方向。占主导地位的底栖生物群体，双壳类和腕足类，对物种灭绝表现出不同的反应：腕足类经历了一个完整的物种水平的更替，而许多双壳类物种在整个事件中范围广泛。在浅层，丰富度和均匀度的变化与总有机碳相关，这表明径流输入的营养物质的变化，以及可能局部开始的低氧化还原条件(总有机碳 >； 4 wt%)控制了动物多样性。相反，在更深的部分，群落变化与δ18O的变化相关，表明温度变化可能影响了动物群的变化。两地之间存在不同的灭绝地层模式，最后一次出现的物种聚集在浅部的最大泛滥面上，而在较深的海侵面上。观察到的两个地点之间的差异突出了当地沉积和地层过程在控制地球化学和化石记录形状方面的重要作用，以及需要研究沿陆上-近海梯度的多个剖面，以推断区域和全球格局。
In the Early Jurassic (~183 Ma ago) global warming and associated environmental changes coincided with an extinction event in the marine realm (early Toarcian extinction event). Anoxia was previously considered to have been the main cause of extinction, but extinctions also occur at localities that remained oxygenated throughout the event, suggesting that other factors, such as temperature, may have played a major role. To test this hypothesis, we integrated quantitative analyses of benthic macro-invertebrates with high-resolution geochemical proxies on the bulk rock (TOC, δ13C, δ18O) and on belemnites and brachiopod shells (δ13C, δ18O) from two sections from the Iberian Range, Spain, with no black shale deposition. The sections are orientated SE-NW along an onshore-offshore gradient deepening to the north. The dominant benthic groups, bivalves and brachiopods, show a different response to the extinction: brachiopods go through a complete species-level turnover, while many bivalve species range through the event. In the shallower section, changes in richness and evenness correlate with TOC (Total Organic Carbon), suggesting that variations in nutrient input from runoff, and the possible local onset of low-redox conditions (TOC > 4 wt%), controlled faunal diversity. In contrast, at the deeper section, community change correlates with changes in δ18O, indicating that temperature variations might have influenced faunal change. Different stratigraphic patterns of extinction occur between the two localities, with last-occurrences clustering at the maximum flooding surface in the shallower section, and at the transgressive surface in the deeper one. The observed differences between the two localities highlight the important role of local sedimentary and stratigraphic processes in controlling the shape of the geochemical and fossil record, and the need for studying multiple sections along onshore-offshore gradients in order to extrapolate regional and global patterns.