期刊
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
卷 459, 期 -, 页码 321-337出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.palaeo.2016.05.023
关键词
Sr isotope; Nd isotope; C-org/P; Sturtian glaciation; Marinoan glaciation; Yangtze Block
资金
- China Geological Survey (CGS) Geological and Metallogenic Background in the Southeastern Margin of the Upper Yangtze Block Project [12120114016701]
- Ministry of Land and Resources of the People's Republic of China Deep Prospecting and Metallogenic System in the Southeastern Margin of the Upper Yangtze Block Project [201411051]
- U.S. National Science Foundation (Sedimentary Geology and Paleobiology program)
- NASA Exobiology program
- China University of Geosciences-Wuhan (SKL-GPMR program) [GPMR201301]
- China University of Geosciences-Wuhan (SKL-BGEG program) [BGL201407]
The Neoproterozoic Datangpo Formation of the Nanhua Basin in South China records interglacial sedimentation between the similar to 720-660-Ma Sturtian and similar to 654-635-Ma Marinoan glaciations. The lower part (1st Member) of this formation contains manganese-rich deposits that represent a mixture of two main components, Mn-carbonates and Mn-bearing aluminosilicates (clay minerals). The Mn-carbonate component is characterized by high La/Sc ratios, high initial Sr-87/Sr-86 ratios, and low initial epsilon Nd(t) values, and the siliciclastic component by low La/Sc ratios, low initial Sr-87/Sr-86 ratios, and high initial epsilon Nd(t) values. The likely source of the non-radiogenic siliciclastic material is weathering of Neoproterozoic continental flood basalts on the Yangtze Block. Discriminant plots show that the Mn-ore samples have compositions consistent with at least partial derivation from hydrothermal sources. Mn-carbonate deposition was the result of reactions between aqueous Mn and sedimentary organic matter during early diagenesis that led to elevated Mn2+ concentrations and alkalinity in sediment porewaters. Based on these observations, we propose a new metallogenic model for the Datangpo Formation manganese deposits. During the Sturtian glaciation, the anoxic Nanhua Basin accumulated abundant dissolved Mn, a substantial fraction of which was derived from hydrothermal sources. When glaciation ended and a redox-stratified water column developed in the basin with an oxic surface layer and an anoxic deep layer, the accumulated dissolved Mn precipitated as Mn-oxides on the basin floor during episodic ventilation events. After co-burial with organic-rich sediments, these Mn-oxides were reduced during organic matter oxidation, which led to the formation of secondary Mn-carbonates (rhodochrosite) through increases in sediment porewater Mn2+ and in alkalinity via microbial sulfate reduction and microbially mediated Mn reduction. (C) 2016 Published by Elsevier B.V.
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