Evaluation of physical and chemical proxies used to interpret past glaciations with a focus on the late Paleozoic Ice Age
Evaluation of physical and chemical proxies used to interpret past glaciations with a focus on the late Paleozoic Ice Age
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DOI：
10.1016/j.earscirev.2021.103756
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发表时间：
2021-10
影响因子：
12.1
通讯作者：
J. Isbell;F. Vesely;Eduardo L.M. Rosa;K. Pauls;Nicholas D. Fedorchuk;Libby R. W. Ives;Natalie Mcnall;Scott A. Litwin;M. K. Borucki;J. Malone;Allison R. Kusick
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作者：
J. Isbell;F. Vesely;Eduardo L.M. Rosa;K. Pauls;Nicholas D. Fedorchuk;Libby R. W. Ives;Natalie Mcnall;Scott A. Litwin;M. K. Borucki;J. Malone;Allison R. Kusick
晚古生代冰期（LPIA）是地球上最重要的古生代气候事件之一，持续时间超过100 Mys。尽管它的重要性，它的历史是有争议的两个假设，描绘冰川作用不同（图1）。传统观点认为LPIA是一个持续的冰川事件，从中密西西比世一直持续到晚二叠世，在这段时间里，冈瓦纳大陆被巨大的冰盖覆盖。这种方法通常只使用一个或两个代理来定义冰川作用。另一个新出现的假说表明，许多冰盖发生在冈瓦纳与个别冰川事件持续长达10 Mys交替与冰川极小期/非冰川间隔相似的持续时间。这两种观点仍然很普遍。近场和远场代理都被用来定义冰河时代。近场代用指标包括杂岩、冰川构造沉积物/地貌、条纹碎屑和碎屑铺面、超大碎屑（坠石）、韵律岩、含杂岩的周期性继承、Glendonite、沟槽和条纹表面、流线地貌和U形古河谷的出现/缺失。碎屑锆石和化学蚀变指数（CIA）的研究有助于描绘冰川作用的发生，范围和位置。由于不同的非冰川过程和驱动因素可以产生类似的特征或结果，使用这些替代物会产生多种复杂性。远场代理侧重于确定海平面的变化。这些包括周期性演替的发生，由交替的非海相和海相地层（cyclothems），深切的山谷，paleotopographic救济，磷酸盐黑色页岩的深度，和不断变化的氧同位素比值。像近场记录一样，远场代理是复杂的指标，具有各种细微差别，使其应用具有挑战性。在这里，我们讨论了这些代理的局限性和使用，并促进多代理的方法来调查地球的冰期。我们建议，研究将多个代理加上详细的环境，古水流和古地理分析，以更好地约束冰川的发生，时间和范围及其对全球系统的影响。这种方法将提供一个强大的LPIA视图。我们还考虑的幅度和性质的海平面变化的冰量的响应，通过讨论冰量的波动，盆地沉降的修改glacioeustacy，和海平面的全球均衡调整（GIA）的响应。考虑到这些特征，很明显，冰川海平面变化比以前设想的要复杂得多。
The late Paleozoic Ice Age (LPIA) was one of Earth's most important Phanerozoic climatic events lasting for over 100 Mys. Despite its importance, its history is controversial with two hypotheses that portray glaciation differently (Fig. 1). Traditional views characterize the LPIA as a continuous glacial event that lasted from the Middle Mississippian until the Late Permian with a massive ice sheet that covered Gondwana throughout this interval. This approach often uses only one or two proxies to define the glaciation. The other emerging hypothesis suggests that numerous ice sheets occurred in Gondwana with individual glacial events lasting up to 10 Mys alternating with glacial minima/non-glacial intervals of similar duration. Both views are still prevalent. Both near- and far-field proxies are used to define the ice age. Near-field proxies include the occurrence/absence of diamictites, glaciotectonic deposits/landforms, striated clasts and clast pavements, outsized clasts (dropstones), rhythmites, cyclic diamictite-bearing successions, glendonites, grooved and striated surfaces, streamline landforms, and U-shaped paleovalleys. Detrital zircons and chemical index of alteration (CIA) studies help to delineate the occurrence, extent, and location of glaciation. Multiple complexities occur with the use of these proxies as different non-glacial processes and driving factors can produce similar features or results. Far-field proxies focus on identifying changes in eustacy. These include the occurrence of cyclic successions composed of alternating nonmarine and marine strata (cyclothems), depth of incised valleys, paleotopographic relief, phosphatic black shales, and changing oxygen isotope ratios. Like the near-field record, far-field proxies are complex indicators with varied nuances that make their application challenging. Here we discuss the limitations and use of these proxies and promote a multiproxy approach to investigating Earth's glacial intervals. We suggest that studies incorporate multiple proxies coupled with detailed environmental, paleoflow, and paleogeographic analyses to better constrain the occurrence, timing, and extent of glaciation and its influence on global systems. This approach will provide a robust view of the LPIA. We also consider the magnitude and nature of sea-level response to changing ice volumes by discussing ice-volume fluctuations, basin subsidence's modification of glacioeustacy, and sea-level's response to global isostatic adjustment (GIA). In considering these features, it becomes apparent that glacioeustacy is more complex than previously envisioned.