Isotopes to ice: Constraining provenance of glacial deposits and ice centers in west-central Gondwana
Isotopes to ice: Constraining provenance of glacial deposits and ice centers in west-central Gondwana
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DOI：
10.1130/abs/2017am-304461
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发表时间：
2019-10
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通讯作者：
N. Griffis;I. Montañez;Nicholas D. Fedorchuk;J. Isbell;R. Mundil;F. Vesely;Luiz Weinshultz;R. Iannuzzi;E. Gulbranson;A. Taboada;Alejandra Pagani;M. Sanborn;M. Huyskens;J. Wimpenny;B. Linol;Q. Yin
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作者：
N. Griffis;I. Montañez;Nicholas D. Fedorchuk;J. Isbell;R. Mundil;F. Vesely;Luiz Weinshultz;R. Iannuzzi;E. Gulbranson;A. Taboada;Alejandra Pagani;M. Sanborn;M. Huyskens;J. Wimpenny;B. Linol;Q. Yin
摘要晚古生代冰期高纬度冈瓦那南部冰川的时间和地理分布仍然受到限制，最终使我们无法估计地球倒数第二个冰库期间的冰量和相关的气候遥相关和反馈。目前的冰川航拍范围受到沉积流动方向的限制，几乎完全推断古冰川作用是由高地驱动的，并可能低估了可能形成冰盖的大陆地区的潜在冰源。在这里，我们报道了从两个关键的中高纬度贡德瓦南盆地(巴西巴拉那和阿根廷巴塔哥尼亚特普埃尔)的硅质岩中恢复的碎屑锆石的U-Pb年龄和Hf同位素组成。结果表明，这两个盆地在晚古生代冰川早期的区域性物源在冈瓦那南部和西部的末次冰川消融期间演化为更远的物源。类似时代的沉积物来自刚果盆地的透辉岩，这需要在东非建立一个冰中心，这表明在靠近石炭-二叠纪边界的这一非洲地区可能存在巨大的冰盖，这可能是巴拉那盆地的沉积物来源。特普尔盆地冰川沉积物的南方远端来源认为，在巴塔哥尼亚冰川历史接近尾声时，南极洲埃尔斯沃斯地块存在冰盖(S)。这些发现表明，在晚古生代冰期期间，从近端到盆外来源的沉积物演变，反映了大陆规模的冰川作用，以及随后从温得和克高地、埃尔斯沃斯地块和冈瓦那中西部的东非来源的排水。与宾夕法尼亚纪大气二氧化碳长期下降到石炭-二叠纪界线上的最低值以及随后在早二叠世上升的巧合表明，巴拉那盆地冰川消融的主要二氧化碳驱动因素。额外的边界条件，包括水分和古地理的可用性，可能进一步促进了这些冈德瓦南冰川成核、生长和消亡的时间。
Abstract The timing and geographic distribution of glaciers in high-latitude southern Gondwana during the Late Paleozoic Ice Age remain poorly constrained, ultimately precluding our ability to estimate ice volume and associated climate teleconnections and feedbacks during Earth's penultimate icehouse. Current aerial extents of glaciers, constrained by sedimentary flow directions, near exclusively infer paleo-glaciation to be highland-driven and may underestimate potential ice sources in continental regions from which ice sheets may have emanated. Here, we report new U-Pb ages and Hf isotope compositions of detrital zircons recovered from diamictites in two key mid- to high-latitude Gondwanan basins (Parana, Brazil and Tepuel, Argentine Patagonia). The results indicate regional sediment sources for both basins during the early period of late Paleozoic glaciation evolving into more distal sources during the final deglaciation along southern and western Gondwana. Similar age sediment sourced from diamictites in the Congo Basin, that require an ice center in eastern Africa suggest the possibility of a large ice sheet in this area of Africa proximal to the Carboniferous-Permian boundary, which may have sourced sediments to the Parana Basin. An inferred distal southern source of glacial sediment for the Tepuel Basin argues for the presence of an ice sheet(s) in the Ellsworth Block of Antarctica towards the end of the glaciation history in Patagonia. These findings indicate an evolution during the Late Paleozoic Ice Age from proximally to extrabasinally sourced sediment reflecting continental-scale glaciation and subsequent drainage from the Windhoek Highlands, Ellsworth Block and an east African source in west-central Gondwana. Coincidence with a long-term fall in atmospheric pCO2 during the Pennsylvanian to a minimum across the Carboniferous-Permian boundary and a subsequent rise in the early Permian suggests a primary CO2-driver for deglaciation in the Parana Basin. Additional boundary conditions including availability of moisture and paleogeography likely further contributed to the timing of nucleation, growth and demise of these Gondwanan glaciers.