Deciphering condensed sequences: A case study from the Oxfordian (Upper Jurassic) Dhosa Oolite member of the Kachchh Basin, western India
Deciphering condensed sequences: A case study from the Oxfordian (Upper Jurassic) Dhosa Oolite member of the Kachchh Basin, western India
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破译压缩序列：印度西部卡奇盆地牛津阶（上侏罗统）多萨鲕粒岩成员的案例研究
DOI：
10.1111/j.1365-3091.2012.01351.x
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发表时间：
2013
期刊：
影响因子：
3.5
通讯作者：
Pandey
中科院分区：
文献类型：
--
作者：
Alberti;Fürsich;Pandey
位于印度西部的中生代裂谷盆地Kachchh盆地的大部分地区，Oxfordian序列的特点是强烈凝聚和几个沉积空隙。早、中牛津期dhosa橄榄岩段的顶层是一个很好的标志层，提出了dhosa砾岩层的概念。尽管厚度大多不到1 m，但这个单元可以在整个卡其赫大陆被跟踪超过100 公里。详细的沉积学分析为其形成提供了一个复杂的模型。空中风化的迹象，包括古岩溶特征，表明该地区至少有两个阶段的重现。漂浮在细粒基质中的米大小的凝固板，以及同沉积构造的迹象，表明了一个高度活跃的断裂系统，导致盆地反复发生地震。该模型考虑了Kachchh大陆以外露头的信息，从而极大地完善了目前对晚侏罗世盆地历史的认识。大型断裂系统和可能的所谓中高隆起将盆地分成几个子盆地。牛津期序列中凝结的主要原因是逆温作用，切断了沉积物的供应，影响了盆地的大部分地区。多沙砾岩层是一个很好的例子，展示了凝聚单元在重建非沉积阶段发生的沉积环境和事件方面的潜力。虽然凝聚层序在整个沉积记录中经常出现，但它们在卡洛夫期到牛津期的过渡期间尤其常见。已经提出了一系列模型来解释这些几乎在世界范围内发生的现象，范围从海平面高位到与海退有关的冰川阶段。Kachchh盆地的演替在这一界线上显示出几乎稳定的条件，但相对海平面仅略有下降，不是在牛津纪晚期之前达到最低水平。
In large parts of the Kachchh Basin, a Mesozoic rift basin situated in western India, the Oxfordian succession is characterized by strong condensation and several depositional gaps. The top layer of the Early to Middle Oxfordian Dhosa Oolite member, for which the term ‘Dhosa Conglomerate Bed’ is proposed, is an excellent marker horizon. Despite being mostly less than 1 m thick, this unit can be followed for more than 100 km throughout the Kachchh Mainland. A detailed sedimentological analysis has led to a complex model for its formation. Signs of subaerial weathering, including palaeokarst features, suggest at least two phases of emersion of the area. Metre‐sized concretionary slabs floating in a fine‐grained matrix, together with signs of synsedimentary tectonics, point to a highly active fault system causing recurrent earthquakes in the basin. The model takes into account information from outcrops outside the Kachchh Mainland and thereby considerably refines the current understanding of the basin history during the Late Jurassic. Large fault systems and possibly the so‐called Median High uplift separated the basin into several sub‐basins. The main reason for condensation in the Oxfordian succession is an inversion that affected large parts of the basin by cutting them off from the sediment supply. The Dhosa Conglomerate Bed is an excellent example, demonstrating the potential of condensed units in reconstructing depositional environments and events that took place during phases of non‐deposition. Although condensed sequences occur frequently throughout the sedimentary record, they are particularly common around the Callovian to Oxfordian transition. A series of models has been proposed to explain these almost worldwide occurrences, ranging from eustatic sea‐level highstands to glacial phases connected with regressions. The succession of the Kachchh Basin shows almost stable conditions across this boundary with only a slight fall in relative sea‐level, reaching its minimum not before the late Early Oxfordian.
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