Evidence of early C4 grasses, habitat heterogeneity, and faunal response during the Miocene Climatic Optimum in the Mojave Region
Evidence of early C4 grasses, habitat heterogeneity, and faunal response during the Miocene Climatic Optimum in the Mojave Region
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莫哈韦地区中新世气候最佳时期早期 C4 草、生境异质性和动物群反应的证据
DOI：
10.1016/j.palaeo.2017.11.020
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Reynolds, Robert E.
中科院分区：
文献类型：
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作者：
Smiley, Tara M.;Hyland, Ethan G.;Cotton, Jennifer M.;Reynolds, Robert E.
在大约 17 至 14 Ma 的中新世气候最适宜期 (MCO) 期间，北美西部的区域范围内的地貌、气候和哺乳动物区系发生了重大变化，但很少有研究关注 MCO 如何影响盆地规模的环境。古环境重建加上加利福尼亚州莫哈韦沙漠克劳德和卡洪谷地层的哺乳动物化石组合，有助于深入了解海明福德阶和巴斯托阶北美陆地哺乳动物时代局部规模（数十公里）对变暖的反应。通过整合岩性描述、植硅体分析、保存的土壤有机质的碳同位素组成 (δ13CSOM) 和古土壤的元素地球化学，我们通过 MCO 提供沉积环境、植被和降水的重建。植硅体和 δ13CSO 证据表明，古环境主要是 C3 草原，在大约 17 Ma 的克劳德地层内发现了该地区最早可能存在的 C4 草。根据古土壤的元素地球化学，克劳德地层的年平均降水量估计为 807 (±182) mm yr−1 (17 Ma)，卡洪谷地层的年平均降水量为 740–800 (±182) mm yr−1 (16 至 15 Ma)。我们的多代理方法表明，克劳德和卡洪谷盆地是稳定的、大规模的辫状河和洪泛区系统，具有间歇性的古土壤发育以及空间尺度上植被和水分条件的异质性。总体而言，我们发现MCO期间当地古环境稳定的信号；然而，克劳德地层的显着干燥趋势确实与动物群更替和存在的类群数量减少相对应。动物群落内的物种多样性很高，尤其是小型哺乳动物，而且克劳德和卡洪谷群落之间的共享物种比基于引导分析的预期要少，这表明在北美西部持续的构造活动和 MCO 期间，局部和区域尺度上的哺乳动物多样性达到峰值。
Major changes to landscapes, climate, and mammalian faunas occurred at the regional scale in western North America during the Miocene Climatic Optimum (MCO) between ~17 and 14 Ma, but few studies have looked at how the MCO affected basin-scale environments. Paleoenvironmental reconstructions coupled with mammalian fossil assemblages from the Crowder and Cajon Valley formations in the Mojave Desert, California, contribute insights into local-scale (10s of kilometers) responses to warming during the Hemingfordian and Barstovian North American Land Mammal Ages. By integrating lithological descriptions, phytolith analyses, carbon isotope composition of preserved soil organic matter (δ13CSOM), and elemental geochemistry of paleosols, we provide reconstructions of depositional environments, vegetation, and precipitation through the MCO. Phytolith and δ13CSOMevidence suggest that paleoenvironments were predominately C3grasslands, with the earliest potential presence of C4grasses in the region found within the Crowder Formation at ~17 Ma. Based on elemental geochemistry of paleosols, mean annual precipitation estimates are 807 (±182) mm yr− 1at 17 Ma in the Crowder Formation and 740–800 (±182) mm yr− 1from 16 to 15 Ma in the Cajon Valley Formation. Our multiproxy approach indicates that the Crowder and Cajon Valley basins were stable, large-scale braided stream and floodplain systems with intermittent paleosol development and heterogeneity in vegetation and moisture conditions across spatial scales. Overall, we find a signal of local paleoenvironmental stability during the MCO; however, a significant drying trend in the Crowder Formation does correspond with faunal turnover and reduction in the number of taxa present. High species diversity within faunal assemblages, especially among small mammals, and fewer shared species between the Crowder and Cajon Valley assemblages than expected based on bootstrap analysis indicate that peak mammal diversity was accommodated at both local and regional scales during sustained tectonic activity and the MCO in western North America.