Geochemistry of upper Permian siliceous rocks from the Lower Yangtze region

The Permian Chert Event is of great significance to understanding the geological evolution of the entire Permian however the origin of widespread chert formation is debated. We report new geochemical data from deep-marine siliceous rocks of the upper Permian Da-long Formation Lower Yangtze region so...

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Bibliographic Details
Published in:Petroleum Science
Main Authors: Liao, Zhi-Wei, Hu, Wen-Xuan, Fu, Xiu-Gen, Zhong-Ya
Format: Report
Language:English
Published: SPRINGEROPEN 2019
Subjects:
Lower Yangtze region
Da-long Formation
Siliceous rock
Biological chert
Volcanism
EARTH-ELEMENT GEOCHEMISTRY
TRIASSIC BOUNDARY
SOUTH CHINA
DALONG FORMATION
RARE-EARTH
DEPOSITIONAL-ENVIRONMENTS
SICHUAN BASIN
ACIDIFICATION
EXTINCTION
EVOLUTION
Energy & Fuels
Engineering
Petroleum
Ocean acidification
Online Access:http://ir.nigpas.ac.cn/handle/332004/15761
http://ir.nigpas.ac.cn/handle/332004/15762
https://doi.org/10.1007/s12182-018-0293-3
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Summary:The Permian Chert Event is of great significance to understanding the geological evolution of the entire Permian however the origin of widespread chert formation is debated. We report new geochemical data from deep-marine siliceous rocks of the upper Permian Da-long Formation Lower Yangtze region southeastern China. Their geochemical results show that these thin-bedded siliceous rocks have a clear biologic origin with rare to no evidence of hydrothermal influence. The values of Al/(Al+Fe+Mn) and Eu/Eu* are 0.60-0.84 (mean=0.72) and 0.45-1.08 (mean=0.77) respectively and Mn/Ti ratios are relatively low (mean=0.72). The correlations of La-N/Ce-N La-N/Yb-N and Fe2O3/TiO2 with Al2O3/(Al2O3+Fe2O3) along with the Ce anomaly indicate that the Da-long siliceous rocks were deposited at a transitional zone between a continental margin and the open ocean i.e. relatively close to terrestrial sediment input and far from hydrothermal activity. The accumulation of chert is related to its unique paleogeographic location in an equatorial setting with many submarine paleo-highlands. Intense upwelling and frequent local volcanism are the main factors that promoted the development of siliceous rocks in the studied area. Ocean acidification triggered by large-scale volcanism (Large Igneous Province) during the late Permian led to extensive silica precipitation and preservation.

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