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Bulk organic geochemical and palynofacies analyses of the Hettangian Datta Formation (Potwar Basin, Pakistan): Regional comparison with the time equivalent Lathi Formation (Jaisalmer Basin, India)
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-07-30 , DOI: 10.1007/s12040-021-01649-4
Nasar Khan 1, 2, 3 , Rudy Swennen 1 , Hafiz S Hussain 2, 4 , Irfan U Jan 3, 5 , Shahid Iqbal 6, 7 , Osman Salad Hersi 5
Affiliation  

Abstract

A detailed lithostratigraphic, bulk organic geochemical and palynofacies analyses were performed on organic-rich shale and coal samples from the Hettangian Datta Formation in the western Salt Range, southern Potwar Basin, Pakistan, to evaluate its hydrocarbon generation potential. Organic matter (OM) in the formation is mainly dominated by gas-prone Type III kerogen and oil- and gas-prone Type II kerogen. The coal and OM-rich shale intervals are thermally mature, while grey shale intervals are thermally immature. Palynofacies studies showed that the Datta Formation is rich in inertinite, vitrinite and amorphinite with minor liptinite. The OM is mainly of terrigenous origin with minor marine contribution and is interpreted to have been deposited under suboxic to anoxic conditions in a fluvio-deltaic depositional setting. The thermal maturity estimated from Spore Colour Index (SCI) and Thermal Alteration Index (TAI) was entirely consistent with estimates based on bulk organic geochemical data. Variations in thermal maturity are interpreted to be due to change in kerogen types as well as burial depth. Overall, the organic geochemical and palynofacies studies showed that the coal and OM-rich shale intervals in the Datta Formation have good-to-excellent source rock potential in the study area, whereas the grey shale intervals have poor potential as source rocks. The Datta Formation has tentatively been correlated with the stratigraphically equivalent Lathi Formation in the Jaisalmer Basin, India, which was deposited in a similar palaeo-depositional setting on the NW margin of the Indian Plate affected by Neo-Tethys realms.

Research Highlights

  • Organic matter within the Datta Formation is dominated by Type III and Type II kerogens.

  • The Lower Jurassic Datta Formation is enriched in inertinite, vitrinite and amorphinite with minor liptinite.

  • The Datta Formation was deposited in a fluvio-deltaic setting influenced by both terrigenous and marine organic influx.

  • The suboxic to anoxic conditions during shales deposition promoted organic matter preservation.

  • Datta Formation correlates with the Lathi Formation of Jaisalmer Basin of India.



中文翻译:

Hettangian Datta 组(巴基斯坦 Potwar 盆地)的大量有机地球化学和孢粉相分析:与时间等效的 Lathi 组(印度贾沙梅尔盆地)的区域比较

摘要

对来自巴基斯坦 Potwar 盆地南部盐岭西部 Hettangian Datta 组的富含有机质页岩和煤样进行了详细的岩石地层学、大块有机地球化学和孢粉相分析,以评估其生烃潜力。地层有机质主要以易产气的Ⅲ型干酪根和易产油气的Ⅱ型干酪根为主。煤层和富含有机质的页岩层段热成熟,而灰色页岩层层热不成熟。孢粉相研究表明,Datta 组富含惰性岩、镜质岩和无定质岩,并含有少量的 liptinite。OM 主要来源于陆源,有少量海洋贡献,被解释为在河流-三角洲沉积环境中的低氧至缺氧条件下沉积。根据孢子颜色指数 (SCI) 和热变化指数 (TAI) 估计的热成熟度与基于大量有机地球化学数据的估计完全一致。热成熟度的变化被解释为干酪根类型和埋藏深度的变化。总体而言,有机地球化学和孢粉相研究表明,研究区达塔组富含煤和有机质的页岩层段具有较好的烃源岩潜力,而灰色页岩层段作为烃源岩的潜力较差。Datta 组暂时与印度 Jaisalmer 盆地中地层等效的 Lathi 组相关联,后者沉积在受新特提斯界影响的印度板块西北边缘类似的古沉积环境中。

研究亮点

  • Datta 组内的有机质以 III 型和 II 型干酪根为主。

  • 下侏罗统 Datta 组富含惰性岩、镜质岩和无定质岩,并含有少量 liptinite。

  • Datta 组沉积在受陆源和海洋有机流入影响的河流-三角洲环境中。

  • 页岩沉积过程中的低氧到缺氧条件促进了有机质的保存。

  • Datta 组与印度 Jaisalmer 盆地的 Lathi 组相关。

更新日期:2021-07-30
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