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首页> 外文期刊>Current Science: A Fortnightly Journal of Research >Lakadong limestone: Paleocene-Eocene boundary carbonate sedimentation in Meghalaya, northeastern India
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Lakadong limestone: Paleocene-Eocene boundary carbonate sedimentation in Meghalaya, northeastern India

机译：Lakadong石灰岩：印度东北部梅加拉亚邦的古新世-始新世边界碳酸盐沉积

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摘要

The Lakadong Limestone comprises the lowermost unit of the Sylhet Limestone Group which represents a major marine transgression during the Paleocene in the South Shillong Plateau. The tidal flat sedimentation took place in carbonate ramp platform environment. The carbonate facies of the Lakadong Limestone are rich in algae and larger foraminifera, which indicate that it is of a Late Paleocene (Thanetian)-earliest Eocene (Ilerdian) age. The Lakadong Limestone has yielded several taxa of algal-foraminiferal assemblages known from western Tethyan-Mediterranean realm indicating extension of the Neotethys Sea in the Shillong Plateau area, northeastern India. Carbon and oxygen isotopic signatures of the Lakadong Limestone have been obtained for the first time and indicate shallow marine depositional environment. The stable C and O isotope data corresponds to the marine Paleocene carbonate sediments and provides chemostratigraphy of the Lakadong Limestone well exposed in the Mawmluh Quarry near Cherrapunji. Petrographic study reveals that Lakadong Limestone is composed mainly of calcite, dolomite and smaller and larger microfossils. The microfacies identified include micrite, intramicrite, sparite, oosparite and intrasparite. The calcareous algal-foraminiferal assemblage recognized in the Lakadong Limestone includes coralline algae (Lithophyllum, Dasycladaceae) and larger forams (Alveolina, Miscellania, Rotalia, Ranikothalia, miliolids, Dentaloides, Textularia, Discocyclina and Nummulites). Some microfish remains are also present. The sedimentary structures indicate tidal influence in carbonate reef environment.
机译：Lakadong石灰岩是Sylhet石灰岩群的最下部单元，代表了南西隆高原古新世期间的一次主要海侵。潮滩沉降发生在碳酸盐斜坡平台环境中。 Lakadong石灰岩的碳酸盐岩相富含藻类和较大的有孔虫，这表明它是晚新世（Thanetian）-始新世（Ilerdian）时代的。 Lakadong石灰石产生了几种藻类-有孔虫类群，从印度西部特提斯-地中海地区已知，表明新特提斯海在印度东北部西隆高原地区扩展。首次获得了Lakadong石灰岩的碳和氧同位素特征，表明海洋沉积环境较浅。稳定的C和O同位素数据对应于海相古新世的碳酸盐沉积物，并提供了在Cherrapunji附近的Mawmluh采石场裸露的Lakadong石灰岩井的化学地层学。岩石学研究表明，Lakadong石灰岩主要由方解石，白云石以及越来越小的微化石组成。鉴定出的微相包括微晶，微晶，滑石，卵石和微晶。 Lakadong石灰岩中公认的钙质藻-有孔虫组合包括珊瑚藻（Lithophyllum，Dasycladaceae）和较大的孔（Alveolina，Miscellania，Rotalia，Ranikothalia，miliolids，Dentaloides，Textularia，Discocyclina和Nummulites）。还存在一些小鱼。沉积结构表明在碳酸盐礁环境中存在潮汐影响。

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