Elevated physical weathering exceeds chemical weathering of clays during the Paleocene-Eocene Thermal Maximum in the continental Bighorn Basin (Wyoming, USA)
Elevated physical weathering exceeds chemical weathering of clays during the Paleocene-Eocene Thermal Maximum in the continental Bighorn Basin (Wyoming, USA)
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DOI：
10.1016/j.palaeo.2023.111445
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发表时间：
2023-02
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通讯作者：
Kaipeng Ji;Chaowen Wang;H. Hong;K. Yin;Chen Zhao;Yanxiao Xu;B. Song;M. Prins;L. Lourens;P. Gingerich;H. Abels
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作者：
Kaipeng Ji;Chaowen Wang;H. Hong;K. Yin;Chen Zhao;Yanxiao Xu;B. Song;M. Prins;L. Lourens;P. Gingerich;H. Abels
距今5600万年前的∼古新世-始新世全球变暖事件改变了集水区的风化和侵蚀。硅酸盐矿物的化学风化增加被认为是从大气中去除二氧化碳的一个重要过程。然而，粘土矿物学的变化通常可以解释为在事件期间集水区红土的侵蚀加剧。在这里，我们研究了怀俄明州Bighorn盆地的化学和物理风化和侵蚀通量的变化，Bighorn盆地是一个拉拉米德前陆盆地，处于近岸大陆-内陆冲积环境。这表明碎屑蒙皂石的增加，其滞后时间为20KYR，主要发生在PETM之后。蒙脱石的增长在事件发生后至少持续了50-KYR。就地，沉积后成土粘土矿物的形成在PETM之前和PETM土壤剖面之间是相似的，尽管在事件之前和期间形成的土壤在宏观上有很大的差异。PETM期间更干燥、更炎热的夏季可能导致植被覆盖率下降，同时伴随着更频繁和更大的暴雨，加剧了集水区边缘富含蒙脱石的白垩纪膨润土的侵蚀，超过了集水区内化学风化的变化。在达到完整的PETM粘土矿物值方面的滞后反应可以用上游沉积物到达集水盆地泛滥平原所需的时间来解释。PETM事件后蒙皂石增强的延长性质可能再次与现在由于河流再循环率降低而导致的信号传播时间更长有关。我们的结果表明，在这个大陆-内陆研究区，化学风化变化可能被加强的物理风化和来自盆地边缘的粘土-矿物运移所取代。
The Paleocene-Eocene Thermal Maximum (PETM) global warming event at ∼56 million years before present changed catchment weathering and erosion. Increased chemical weathering of silicate minerals is thought to be an important process removing CO2from the atmosphere. However, changes in clay mineralogy can often be explained by enhanced erosion of catchment laterites during the event. Here, we investigate chemical and physical weathering and erosive flux changes through the PETM interval in the Bighorn Basin, Wyoming, a Laramide foreland basin, in a proximal continental-interior alluvial setting. These show an increase of detrital smectite with a lag time of 20-kyr after the main onset the PETM. The smectite increase continued for at least 50-kyr after the event. In-situ, post-depositional pedogenic clay mineral formation is similar between pre-PETM and PETM soil profiles, despite large macroscopic differences between soils that formed before and during the event. Drier, hotter summers during the PETM probably caused decreased vegetation cover that, in concert with more frequent and heavier rainstorms, intensified the erosion of smectite-rich Cretaceous bentonites on the margins of the catchment, which exceeded changes in chemical weathering within the catchment. The lagged response in reaching full PETM clay mineral values can be explained by the time required for upstream sediment to reach the catchment basin floodplain. The prolonged nature of smectite enhancement after the PETM event may again relate to signal propagation times that are now even longer due to lower fluvial recycling rates. Our results indicate that chemical weathering changes were probably superceded by enhanced physical weathering and clay-mineral transport from basin margins at this continental-interior study site.