Echinoderms and Oligo‐Miocene Carbonate Systems: Potential Applications in Sedimentology and Environmental Reconstruction
Echinoderms and Oligo‐Miocene Carbonate Systems: Potential Applications in Sedimentology and Environmental Reconstruction
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棘皮动物和寡中新统碳酸盐系统：在沉积学和环境重建中的潜在应用
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发表时间：
2012
期刊：
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通讯作者：
J. Nebelsick
中科院分区：
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作者：
A. Kroh;J. Nebelsick
棘皮动物是一种主要的生态成分，对渐新世-中新世碳酸盐沉积具有重要的贡献，无论是作为大型化石还是作为骨骼颗粒。综述了现存的5个棘皮动物纲(棘皮纲、小行星纲、蛇形纲、海鞘纲、海鞘纲)的骨骼形态。除棘类外，脱节的骨骼成分是muchmorecommoninsedimentsthanarticulatedspecimensforallechinodermclasses；仅依靠完整标本的研究可能存在严重偏见。综述了棘皮动物的繁殖和生长、骨骼的组成以及棘皮动物听小骨的结晶学和成岩作用。棘皮动物骨骼由含3-18.5wt%镁的高镁方解石组成。骨架表现出微晶方解石与有机材料的强烈交织和晶体的非随机取向，实现了相当大的硬度和耐用性。棘皮动物的生物层位和脱节物质的鉴定被考虑。沉积物颗粒的棘皮起源通常可以通过它们的特征微结构来识别。由于高度的专业化，脱节的遗骸通常可以被识别到科或属的水平，导致更准确的空间和时间分布的棘皮动物的图像。棘皮动物的地球化学从骨骼中的镁含量作为古温度指标，以镁/钙比值作为古海水组成的监测指标，并考虑了锶/钙比值和碳、氧稳定同位素。棘皮动物骨骼在成岩作用过程中发生变化，并转化为低镁方解石。骨架的微观结构在很大程度上不受这一过程的影响，但同位素特征和微量/微量元素含量可能会发生变化。这些因素，加上同位素摄取的生理效应，阻碍了地球化学的应用。然而，棘皮动物已经成功地用于显生界海水chemistry:theMgandSrcontentsofechinodermskeletonsapparentlystronglycorrelate随温度的研究。小行星和蛇绿体可能最适合于古温度重建，因为骨架内缺乏已知的分馏作用，需要andbecausegeneticeffectsarelesspronouncedthaninechinoids.Controlledlaboratory实验来建立校准。棘皮动物残留物可能占特定渐新世和中新世碳酸盐相颗粒的5-30%。它们似乎在温带陆架碳酸盐中比在热带环境中更丰富。与棘皮动物听小骨相关的成岩变化强烈影响埋藏沉积物并促进岩化。放牧棘球类的生物侵蚀对珊瑚礁的碳酸盐收支是重要的，并通过生产碳酸盐泥浆影响沉积物的模式尺寸分布。穴居棘皮动物可能会引起强烈的生物扰动和沉积物的重新加工。棘皮动物为古环境重建提供了有价值的证据。生态信息既可以通过与现代棘皮动物的实际比较获得，也可以通过功能形态方法获得，从而能够详细评估一般生活习性、底物条件、养分可获得性和水动力状况。
Echinoderms represent a major ecological component and contribute considerably to Oligocene–Miocene carbonate sediments, both as macrofossils and as skeletal grains. The skeletal morphology of all five extant echinoderm classes (echinoids, asteroids, ophiuroids, crinoids, holothuroids) is reviewed. Disarticulated skeletal elements are muchmorecommoninsedimentsthanarticulatedspecimensforallechinodermclasses except for echinoids; studies relying on complete specimens alone may be severely biased. The reproduction and growth of echinoderms, the composition of the skeleton, and the crystallography and diagenesis of echinoderm ossicles are reviewed. The echinoderm skeleton consists of high-Mg calcite with 3–18.5 wt% Mg. The skeleton exhibits strong interlacing of microcrystalline calcite with organic material and nonrandom orientation of crystals, achieving considerable hardness and durability. Echinoderm biostratinomy and the identification of disarticulated material are considered. The echinoderm origin of sediment particles can usually be recognised by their characteristic microstructure. Due to the high degree of specialisation, disarticulated remains can often be identified to family or genus level, leading to a more accurate picture of spatial and temporal echinoderm distributions. Echinoderm geochemistry is reviewed with respect to the Mg-content of the skeleton as a palaeotemperature proxy, and the Mg/Ca ratio as a monitor of ancient seawater composition; Sr/Ca ratios and carbon and oxygen stable-isotopes are considered. The echinoderm skeleton is altered during diagenesis and is transformed to low-Mg calcite. The microstructure of the skeleton is largely unaffected by this process, but changes in the isotopic signature and minor/trace-element contents may occur. These factors, together with physiological effects of isotope intake, hamper geochemical applications. However, echinoderms have been used successfully in studies of Phanerozoic seawater chemistry:theMgandSrcontentsofechinodermskeletonsapparentlystronglycorrelate with temperature. Asteroids and ophiuroids are probably best suited for palaeotemperature reconstructions because of the lack of known fractionation within the skeleton andbecausegeneticeffectsarelesspronouncedthaninechinoids.Controlledlaboratory experiments are needed to establish calibrations. Echinoderm remains may account for 5–30% of the particles within specific Oligocene and Miocene carbonate facies. They seem to be more abundant in temperate shelf carbonates than in tropical settings. Diagenetic changes associated with echinoderm ossicles strongly affect the embedding sediment and promote lithification. Bioerosion by grazing echinoids is important for carbonate budgets in coralreefs and influencesthe modal size-distribution of sediments by the production of carbonate mud. Burrowing echinoderms may cause intensive bioturbation and reworking of sediments. Echinoderms provide valuable evidence for palaeoenvironmental reconstructions. Ecological information can both be gained by actualistic comparisons with modern echinoderms and by a functional morphological approach, allowing the detailed assessment of general life habits, substrate conditions, nutrient availability and hydrodynamic regimes.