Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)
Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)
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DOI：
10.1007/s13146-017-0360-7
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发表时间：
2019-06
影响因子：
1.4
通讯作者：
Michaela M. Kahsnitz;H. Willems
中科院分区：
文献类型：
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作者：
Michaela M. Kahsnitz;H. Willems
古新世-始新世界线的负碳同位素偏移位于浙纯山组的一个结节状灰岩层，厚度约为9 m，激发了这些结节状灰岩在何种条件下形成的问题。根据野外观测结果，定日和甘巴浅水结核灰岩可划分为5类结核灰岩（茎节岩ⅰ、茎节岩ⅰ、茎节岩ⅱ、茎层岩和茎层岩）和部分过渡段（茎层岩向茎层岩ⅱ过渡）。粘土的变化被认为是沉积物中这些不同类型的结节灰岩的原因。差异成岩作用使灰岩结核在早期因碳酸盐供应而选择性胶结，而泥灰岩虽未胶结，但为结核胶结提供了碳酸盐。此外，胶结和富含碳酸盐的结核耐化学压实，而未胶结和富含粘土的泥灰岩层则受沉积物覆盖层的压力溶解过程的影响。此外，还提出了一个模型，说明了这里描述的不同结节灰岩的起源。
This paper examines the genesis of the Paleocene to Lower Eocene shallow-water nodular limestones in South Tibet. The negative carbon isotope excursion representative for the Paleocene–Eocene boundary is located in one nodular limestone bed of the Zhepure Shan Formation showing an extraordinary thickness of about 9 m, inspiring the question under which conditions these nodular limestones were formed. Based on field appearance, the shallow-water nodular limestones of Tingri and Gamba can be classified into five nodular limestone categories (Stylonodular Rock I, Nodular Rock I, Nodular Rock II, stylobedded rock and stylomottled rock) and some transitional members (stylobedded rock transitional to Stylobedded Rock II). Clay variations are assumed to be responsible for these various types of nodular limestones within the sediments. Observations of nodular limestones in South Tibet suggest that those sediments were mostly formed due to autochthonous rather than allochthonous processes. Differential diagenesis resulted in an early selective cementation of limestone nodules due to carbonate supply, while the marls were not cemented but provide the carbonate for the nodule cementation. Additionally, cemented and carbonate-rich nodules are resistant to chemical compaction, while the uncemented and clay-rich marl layers are affected by pressure solution processes due to an overburden of sediments. Additionally, a model is presented, illustrating the origin of different nodular limestones described here.