滇东北地区晚奥陶世碳酸盐岩台地消亡的古环境因素【“深时碳酸盐生产工厂与资源环境效应”专辑】
- 收稿日期:
2023-07-06
- 网络出版日期:
2023-10-23
摘要: 【目的】滇东北地区晚奥陶世碳酸盐岩台地的萎缩消亡存在多种认识。为了深入探讨其成因，本文拟通过滇东北地区晚奥陶世古环境演化研究，分析古环境因素对滇东北地区晚奥陶世碳酸盐岩台地消亡的影响。【方法】选取滇东北地区万和剖面为研究对象，利用室内矿物学、岩石学、沉积地球化学等分析方法为主要手段，系统开展滇东北地区奥陶系临湘组—志留系龙马溪组的微相特征研究、此期间的古环境演变分析，探讨滇东北地区晚奥陶世碳酸盐岩台地萎缩消亡中的古环境影响。【结果】通过对万和剖面临湘组—龙马溪组岩石学特征、镜下矿物组成以及古生物特征等进行分析，共识别出六个沉积微相：含泥瘤状灰岩相、纹层状微晶灰岩相、微晶生屑灰岩相、纹层状钙质泥岩相、砂质泥岩和泥质砂岩相以及含钙质泥页岩和含钙质碳质泥岩相。并进一步划分出3个沉积亚相：浅缓坡、深缓坡和局限滞留陆棚；利用沉积地球化学方法，分析其古海洋地球化学特征，并建立地球化学剖面发现：在奥陶系大渡河组—志留系龙马溪组之间，古海洋环境指标如古生产力、古氧化还原条件、陆源碎屑输入量和古海平面变化在这一时期发生了显著变化，波动频繁。【结论】通过分析滇东北地区晚奥陶世碳酸盐岩台地周围的古海洋环境变化，认为滇东北晚奥陶世碳酸盐岩台地消亡成因为：海洋环境缺氧导致光合生物衰退，从而抑制了碳酸盐生产，使得碳酸盐岩台地的萎缩直至消亡。除此之外，海平面变化、气候变化、陆源碎屑输入量增加以及奥陶纪末生物大灭绝在碳酸盐岩台地消亡过程中发挥了重要作用。
Paleoenvironmental factors of Late Ordovician carbonate platforms extinction in northeastern Yunnan province
- Received Date:
2023-07-06
- Available Online:
2023-10-23
Abstract: [Objective] The shrinkage and demise of the Late Ordovician carbonate platform in northeastern Yunnan have been subject to various interpretations. To delve deeper into its origins, this paper intends to investigate the Late Ordovician paleoenvironmental evolution in northeastern Yunnan and analyze the influence of paleoenvironmental factors on the demise of the Late Ordovician carbonate platform in this region. [Methods] The Wanhe section in the northeast of Yunnan Province was selected as the research object. Using methods such as indoor mineralogy, petrology, and sedimentary geochemistry analysis, a systematic study was conducted on the microfacies characteristics of the Ordovician Linxiang-Silurian Longmaxi formations in northeastern Yunnan Province. During this period, an analysis of paleoenvironmental changes was conducted to explore the paleoenvironmental impacts during the contraction and extinction of carbonate platforms in the Late Ordovician in northeastern Yunnan Province. [Results] Through the analysis of lithological characteristics, microscopic mineral composition, and paleontological features within the Linxiang-Longmaxi formations at the Wanhe section, six sedimentary microfacies were identified: nodular limestone, laminated microcrystalline limestone, microcrystalline fossiliferous limestone, laminated calcareous mudstone, sandy mudstone and silty sandstone, and calcareous shale and calcareous carbonaceous mudstone. These were further divided into three sedimentary subfacies: shallow carbonate ramp, deep carbonate ramp, and restricted retention shelf. By utilizing sedimentary geochemical methods, we analyzed the paleoceanographic geochemical characteristics and established a geochemical profile. This analysis revealed frequent and significant changes in the paleoceanographic indicators, including paleoproductivity, paleoredox conditions, terrestrial detrital input, and paleosea level fluctuations, between the Ordovician Daduhe and Silurian Longmaxi formations. [Conclusions] Through the analysis of paleoceanographic changes around the Late Ordovician carbonate platform in Northeastern Yunnan Province, the extinction of the Late Ordovician carbonate platform in this region can be attributed to oceanic hypoxia. This hypoxia led to the decline of photosynthetic organisms and subsequently inhibited carbonate production, resulting in the contraction and eventual extinction of the carbonate platform. Additionally, sea-level changes, climate fluctuations, increased input of terrigenous debris, and the Late Ordovician mass extinction event played crucial roles in the process of the carbonate platform disappearance.
点击查看大图
下载:
