Organic petrology and geochemistry data reveal depositional and thermal history of coal in the Guaduas formation, Colombian Eastern Cordillera

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
L. Camacho-Aristizabal , L. Burnaz , L. Castro-Vera , L. Mojica Silva , R. Littke
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Abstract

Colombia is a country rich in coal deposits; however, there are few published studies characterizing these coals in detail from a scientific perspective. This study investigates the thermal maturity and depositional environment of a coal seam from the Guaduas formation (Maastrichtian-Paleocene) of the Eastern Colombian Cordillera Basin, providing insight into burial and temperature history and changes in the depositional environment over time. This three-meter-thick hard coal seam reflects about 20 m of former peat deposition, representing a period of roughly 10.000 years.

Five large, fresh samples (A to E) were collected from the seam every thirty centimeters and divided into seventeen sub-samples analyzed using organic petrological methods, Rock-Eval pyrolysis and organic geochemistry. Different thermal maturity- and depositional environment-related parameters have been determined. Results reveal a maturity of approximately 0.9% vitrinite reflectance, and relatively high HI values (kerogen type II-III). Correspondingly, high values of νCHx over γCH indicate a high relative abundance of aromatic rings over aliphatic groups. Moreover, high CH2/CH3 ratios suggest long and simple aliphatic chain structures. Molecular data indicate a balanced odd- over even n-alkane distribution and a high amount of long-chain n-alkanes. High Pr/Ph ratios and hopanoid biomarkers reveal an oxidizing depositional environment. The coal seam investigated in this study is characterized by low ash yields and low sulfur contents particularly in the central part of the seam, while percentages of inertinite are high (up to 54 Vol.-%). This data supports a low water table and oligotrophic, raised bog conditions during deposition in a humid, tropical climate which is consistent with the almost equatorial position of the study area during deposition of the Guaduas Formation. Water was mainly supplied via rainfall leading to overall low ash yields. In contrast, the top of the coal seam is strongly enriched in sulfur revealing that rapid marine flooding ultimately ceased peat accumulation leading to authigenic pyrite formation.

有机岩石学和地球化学数据揭示哥伦比亚东科迪勒拉山系瓜杜阿斯地层煤炭的沉积和热历史
哥伦比亚是一个煤炭储量丰富的国家;然而,从科学角度详细描述这些煤炭特征的公开研究却寥寥无几。本研究调查了哥伦比亚科迪勒拉盆地东部瓜杜阿斯地层(马斯特里赫特-古新世)煤层的热成熟度和沉积环境,为了解埋藏和温度历史以及沉积环境随时间的变化提供了见解。从煤层中每隔三十厘米采集了五个大型新鲜样本(A 至 E),并将其分成十七个子样本,使用有机岩石学方法、Rock-Eval 高温分解法和有机地球化学方法进行分析。测定了不同的热成熟度和沉积环境相关参数。结果显示,成熟度约为 0.9%,玻璃光泽反射率约为 0.9%,HI 值相对较高(角质类型 II-III)。相应地,νCHx 值比 γCH 值高,表明芳香环比脂肪族相对丰富。此外,高 CH2/CH3 比率表明脂肪族链结构长而简单。分子数据表明,正构烷烃的奇偶分布均衡,长链正构烷烃的数量较多。高Pr/Ph比率和hopanoid生物标志物揭示了氧化沉积环境。本研究调查的煤层具有灰分产量低、硫含量低的特点,尤其是在煤层中部,而惰性物质的比例较高(高达 54 Vol.-%)。这些数据表明,在瓜杜阿斯地层沉积过程中,地下水位较低,沼泽条件较差,属于湿润的热带气候,这与研究地区在瓜杜阿斯地层沉积过程中几乎位于赤道的位置相吻合。水主要通过降雨提供,因此灰分产量总体较低。与此相反,煤层顶部的硫含量却很高,这表明快速的海洋洪水最终停止了泥炭的堆积,导致了自生黄铁矿的形成。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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