Palynology, palynofacies and organic geochemistry analysis of the late Eocene shale from Meghalaya, Northeast India,Journal of Earth System Science

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Palynology, palynofacies and organic geochemistry analysis of the late Eocene shale from Meghalaya, Northeast India
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-03-29 , DOI: 10.1007/s12040-021-01562-w
N Reshma Devi , Y Raghumani Singh , Mark B Abbott , A Bijayalaxmi Devi

Abstract

Here the depositional environment and hydrocarbon source rock potential of the Kopili Formation is investigated using palynological analysis and Rock-Eval pyrolysis on samples from a borehole section (Borehole BUM14) collected at Umphyrluh area in the Jaintia Hills, Meghalaya. In these Kopili shales, amorphous organic matter is often associated with structural terrestrial organic matter, biodegraded organic matter, charcoal, black carbon debris, dinoflagellate cysts, and spores. The palynotaxa are mainly composed of dinoflagellate cysts comprising eight genera and twelve referable species. Based on the palynological data, the sediments of the study area were deposited in a shallow marine setting under oxygen deficient conditions in an environment that received a continuous terrestrial influx throughout the succession. Rock-Eval pyrolysis and Total Organic Carbon (TOC) analysis determine the quantity, type, and thermal maturity of the associated organic matter. TOC values range from 0.03 to 0.45 wt.% (averaging 0.28 wt.%) and the Genetic Potential (GP) and Hydrogen Index (HI) values vary from 0.04 to 0.24 mg HC/g rock and 22–100 mg HC/g TOC, respectively. These values imply that all the shale samples have very low TOC values (< 0.5%), S1, S2, and Hydrogen Index (HI) values. Although most of the samples are in a mature stage as the average T_max value is 428.16°C and the Production Index (average 0.16) indicates a potential for oil generation, low Genetic Potential (S1 + S2) and TOC concentrations suggest there is limited potential for oil generation. The HI vs. OI plot and HI vs. T_max plot show that most of the shale samples fall in the predominantly gas prone domain (mostly Type III and Type IV), because the organic matter is generally derived from a terrestrial source. Thus, the source rock potential for the Kopili shales of the Umphyrluh area is considered to be poor for gaseous hydrocarbons.

Research Highlights

1.
Depositional environment and hydrocarbon source rock potential for the late Eocene Kopili shales of the Umphyrluh area, Jaintia Hills, Meghalaya were investigated.
2.
Palynofacies were recovered by using palynological analysis indicating the status of the depositional environment of the Kopili Formation as a shallow marine environment by influx of terrestrial matter under a proximal dysoxic-anoxic condition.
3.
Rock-Eval pyrolysis and Total Organic Carbon (TOC) analysis suggested the quantity, type, and thermal maturity of the associated organic matter.
4.
The studied samples are predominantly gas prone (mostly Type III and Type IV) indicating their potentially for gaseous hydrocarbon.

中文翻译：

印度东北梅加拉亚邦晚始新世页岩的孢粉学，孢粉相和有机地球化学分析

摘要

在这里，通过孢粉分析和岩石-热解热解法，对在梅加拉亚邦Jaintia Hills的Umphyrluh地区采集的井段（钻孔BUM14）的样品进行了孢粉分析和岩石热解研究，研究了科皮里组的沉积环境和烃源岩潜力。在这些科皮利页岩中，无定形有机物通常与结构性陆生有机物，生物降解有机物，木炭，黑碳碎片，鞭毛藻囊肿和孢子有关。紫杉类主要由鞭毛囊肿组成，囊肿包括八个属和十二个可参考物种。根据古生物学数据，研究区域的沉积物在缺氧条件下在浅海环境中沉积，该环境在整个演替过程中都受到连续陆生涌入的影响。岩石评估热解和总有机碳（TOC）分析确定相关有机物的数量，类型和热成熟度。TOC值范围为0.03至0.45 wt。％（平均0.28 wt。％），遗传潜能值（GP）和氢指数（HI）值范围从0.04至0.24 mg HC / g岩石和22–100 mg HC / g TOC ，分别。这些值意味着所有页岩样品的TOC值（<0.5％），S1，S2和氢指数（HI）值都非常低。尽管大多数样本均处于成熟阶段这些值意味着所有页岩样品的TOC值（<0.5％），S1，S2和氢指数（HI）值都非常低。尽管大多数样本均处于成熟阶段这些值意味着所有页岩样品的TOC值（<0.5％），S1，S2和氢指数（HI）值都非常低。尽管大多数样本均处于成熟阶段T _max值为428.16°C，生产指数（平均0.16）表示有产油的潜力，低遗传潜力（S1 + S2）和TOC浓度表明有潜在的产油潜力。HI vs. OI图和HI vs. T _max图表明，大多数页岩样品都属于天然气易发地区（主要是III型和IV型），因为有机质通常来自陆源。因此，Umphyrluh地区Kopili页岩的烃源岩潜力被认为对气态碳氢化合物不利。