Middle Permian Mixed Siliciclastic-Carbonate System on the Northwestern Margin of the Indian Plate, Pakistan: Implications for Paleoclimate and Carbonate Platform Evolution,Acta Geologica Sinica-English Edition

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Middle Permian Mixed Siliciclastic-Carbonate System on the Northwestern Margin of the Indian Plate, Pakistan: Implications for Paleoclimate and Carbonate Platform Evolution
Acta Geologica Sinica-English Edition ( IF 3.5 ) Pub Date : 2021-05-31 , DOI: 10.1111/1755-6724.14737
Bilal WADOOD _{1,

2} , Suleman KHAN ₃ , Hong LI ₁

Affiliation

A mixed siliciclastic-carbonate system that responds to changes in Permian climate and subsequent carbonate platform evolution is investigated using microscopic details of the Middle Permian Amb Formation (Fm.), in Saiyiduwali section, Khisor Range, northern Pakistan. Thin sections were made from rocks throughout the stratigraphic section of the Amb Fm. and analyzed with an emphasis on carbonate and clastic microfacies, and the latter interpreted within the existing chronostratigraphic framework. Outcrop observations reveal that the units comprise coarse-grained, channelized, ripple-marked, and burrowed sandstone and sandy, fossiliferous limestone with minor marls and shale intercalations, suggesting deposition in a subaqueous tide-dominated delta to beach barrier. Based on the determined seven microfacies coupled with outcrop observation, the Amb Fm. was deposited in a tide-influenced subaqueous delta to middle shelf environment under fluctuating sea level. The deposition of compositionally mature sandstone in the lower part of the formation suggests reworking of detritus from the rift shoulders and an adjacent source area with an ambient warm and humid climate. The stratal mixing of carbonates and compositionally mature siliciclastic units in the middle part suggest deposition under tectonic and climate-induced terrigenous and carbonate fluxes to the basin. Thus the deposition shows a perfect transition from clastic-dominated deltaic to pure carbonate platform settings as a result of warm climate and tectonics. This Middle Permian warming is confirmed by sea-level rise and the presence of a temperature-sensitive fusulinid fauna in association with photozoan-based ooids. Deposition of the Amb Fm. and establishment of a carbonate platform are envisaged to be associated with major rifting of northern Gondwana, which subsequently resulted in the development of a rift basin at the passive margin of the NW Indian Plate then in northern Pakistan.

中文翻译：

巴基斯坦印度板块西北缘中二叠统硅质碎屑-碳酸盐混合系统：对古气候和碳酸盐台地演化的启示

使用巴基斯坦北部 Khisor 山脉 Saiyiduwali 剖面的中二叠纪 Amb 组 (Fm.) 的微观细节研究了响应二叠纪气候变化和随后碳酸盐台地演化的混合硅质碎屑碳酸盐系统。薄片是由整个 Amb Fm 地层剖面的岩石制成的。并重点分析了碳酸盐和碎屑微相，后者在现有的年代地层框架内进行了解释。露头观察表明，这些单元包括粗粒、通道化、波纹标记和洞穴砂岩和含少量泥灰岩和页岩夹层的砂质化石石灰岩，表明沉积在以潮汐为主的水下三角洲至海滩屏障中。根据确定的7个微相结合露头观测，安布调频。沉积在海平面波动下受潮汐影响的水下三角洲至中陆架环境中。地层下部成分成熟砂岩的沉积表明裂谷肩和邻近源区的碎屑重新加工，周围气候温暖潮湿。中部碳酸盐和成分成熟的硅质碎屑单元的地层混合表明在构造和气候引起的陆源和碳酸盐通量流向盆地的作用下沉积。因此，由于温暖的气候和构造，沉积显示出从以碎屑为主的三角洲到纯碳酸盐台地环境的完美过渡。这种中二叠纪变暖得到了海平面上升的证实，并且存在与基于光生动物的鲕鱼相关的对温度敏感的梭菌属动物群。Amb Fm 的沉积。预计碳酸盐台地的建立与冈瓦纳北部的主要裂谷有关，随后导致在巴基斯坦北部西北印度板块被动边缘的裂谷盆地的发展。

更新日期：2021-05-31

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