气候变化领域集成服务门户(CCPortal): Middle Jurassic ooidal ironstones (southern Tibet): Formation processes and implications for the paleoceanography of eastern Neo-Tethys

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DOI	10.3389/feart.2022.1055957
	Middle Jurassic ooidal ironstones (southern Tibet): Formation processes and implications for the paleoceanography of eastern Neo-Tethys
	Han, Kaibo; Han, Zhongpeng; Garzanti, Eduardo; Zhu, Shuaipeng; Yao, Hanwei; Guo, Huifang; Liu, Xuan; Wang, Chengshan
发表日期	2023
EISSN	2296-6463
卷号	10
英文摘要	The major facies changes documented in shallow-marine sediments of the northern Indian passive margin of Neo-Tethys throughout the Jurassic, from widespread platform carbonates in the Early Jurassic to organic-rich black shales in the Late Jurassic, imply a substantial turnover in oceanic conditions. All along the Tethys (Tibetan) Himalaya, from the Zanskar Range to southern Tibet, a peculiar interval characterized by ooidal ironstones of Dingjie Formation (Ferruginous Oolite Formation, FOF) marks the base of the organic-rich Spiti Shale. This laterally-extensive ooidal ironstone interval is a fundamental testimony of the mechanisms that led to major paleoceanographic changes that occurred in the eastern Neo-Tethys during the Middle Jurassic. In this article, we illustrate in detail the petrology, mineralogy, and geochemistry of ooidal ironstones and the major element contents of the entire Lanongla section. The FOF is characterized by significantly high contents of Fe2O3 (56.80% +/- 9.07%, n = 7) and P2O5 (1.72% +/- 1.19%, n = 7). In contrast, the Fe2O3 and P2O5 contents average 3.58% and 0.15% in the overlain carbonates of Lanongla Fm., and 5.55% and 0.16% in the overlying Spiti Shale. The ooidal ironstones are mainly composed of iron ooids with a few quartz grains and bioclasts cemented by sparry calcite. The iron ooids consist of concentric dark layers of francolite (carbonate fluorapatite), hence enriched in Ca, P, and F, and bright layers of chamosite, enriched in Fe, Si, Al, and Mg. Precipitation of francolite ensued from oversaturation of phosphorous ascribed to intensified upwelling, high biogenous productivity, and degradation of organic matter, whereas the formation of chamosite reflects enhanced continental weathering and erosion leading to increased Fe input to the ocean during transgressive stages characterized by low sedimentation rate and scarce oxygenation at the seafloor. Modern upwelling zones in outer shelf or slope areas perform similar geochemical characteristics to those as observed in this study. Under the Mesozoic greenhouse background, fluctuating redox conditions induced the alternate growth of francolite under anoxic conditions and of chamosite under suboxic conditions. Ooids were thus formed on the seafloor during continued resuspension and vertical oscillations of the chemocline rather than from interstitial waters after burial. The mineralogy of iron ooids indicates mainly reducing conditions in the water column, suggesting that extensive upwelling along the continental margin of eastern Neo-Tethys contributed significantly to the transition from carbonate deposits to organic-rich black shales during the Jurassic, as testified by the transition from well-oxygenated in Lanongla Fm. To a reduceing condition in Spiti Shale indicated by the Mn/Al ratios compared to PAAS.
关键词	ooidal ironstone facies changes fluctuating redox conditions upwelling southern Tibet
英文关键词	OCEANIC ANOXIC EVENT; OXYGEN MINIMUM ZONE; SEA-LEVEL CHANGES; SEQUENCE STRATIGRAPHY; CARBON-ISOTOPE; SEDIMENTARY HISTORY; APATITE FORMATION; PHOSPHORUS; ORDOVICIAN; EVOLUTION
WOS研究方向	Geosciences, Multidisciplinary
WOS记录号	WOS:000923262500001
来源期刊	FRONTIERS IN EARTH SCIENCE
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/282864
作者单位	China University of Geosciences - Beijing; China University of Geosciences - Beijing; China University of Geosciences - Beijing; University of Milano-Bicocca
推荐引用方式 GB/T 7714	Han, Kaibo,Han, Zhongpeng,Garzanti, Eduardo,et al. Middle Jurassic ooidal ironstones (southern Tibet): Formation processes and implications for the paleoceanography of eastern Neo-Tethys[J],2023,10.
APA	Han, Kaibo.,Han, Zhongpeng.,Garzanti, Eduardo.,Zhu, Shuaipeng.,Yao, Hanwei.,...&Wang, Chengshan.(2023).Middle Jurassic ooidal ironstones (southern Tibet): Formation processes and implications for the paleoceanography of eastern Neo-Tethys.FRONTIERS IN EARTH SCIENCE,10.
MLA	Han, Kaibo,et al."Middle Jurassic ooidal ironstones (southern Tibet): Formation processes and implications for the paleoceanography of eastern Neo-Tethys".FRONTIERS IN EARTH SCIENCE 10(2023).