Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

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• 作者：Daniel R. Muhs^a ; ^{dmuhs@usgs.gov} ; Kathleen R. Simmons^a ; R. Randall Schumann^a ; Lindsey T. Groves^b ; Jerry X. Mitrovica^c ; DeAnna Laurel^d
• 关键词：Marine terraces ; Sea levels ; Last Interglacial period ; Uranium-series dating ; Corals ; Paleozoogeography ; Uplift ; Glacial isostatic adjustment ; San Nicolas Island ; California
• 刊名：Quaternary Science Reviews
• 出版年：2012
• 期刊代码：78_02773791
• 类别：ear
• 出版时间：22 March, 2012
• 卷：37
• 期：Complete
• 页码：1-25
• 文件大小：3013 K

摘要

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of 鈭?70聽m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38-36聽m (terrace 2a), 33-28聽m (terrace 2b), and 13-8聽m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: 鈭?20聽ka on terrace 2a (marine isotope stage [MIS] 5.5), 鈭?20 and 鈭?00聽ka on terrace 2b (MIS 5.5 and 5.3), and 鈭?0聽ka (MIS 5.1) on terrace 1. We conclude that corals on terrace 2b that date to 鈭?20聽ka were reworked from a formerly broader terrace 2a during the 鈭?00聽ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the 鈭?20聽ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the 鈭?00聽ka sea stand. The聽abundant extralimital northern species on terrace 1 indicate cooler than present waters at 鈭?0聽ka.

Using the highest elevations of the 鈭?20聽ka platform of terrace 2a, and assuming a paleo-sea level of聽+6聽m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of 鈭?.25-0.27聽m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (鈭?00聽ka) and terrace 1 (鈭?0聽ka) yield relative (local) paleo-sea level elevations of聽+2 to聽+6聽m for the 鈭?00聽ka sea stand and聽鈭?1 to聽鈭?2聽m for the 鈭?0聽ka sea stand. These estimates are significantly higher than those reported for the 鈭?00聽ka and 鈭?0聽ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.