羌塘盆地鄂尔托陇巴剖面上三叠统泥岩地球化学数据

上三叠统是羌塘盆地油气勘探的重要靶区，但目前认识还不充分。对鄂尔托陇巴剖面上三叠统泥岩的有机、无机地球化学特征进行了研究，以评价其含油气潜力，探讨其沉积环境。总有机碳和可萃取沥青含量分别为0.59 ~ 1.81%（平均1.20%）和460 ~ 1663 ppm（平均778 ppm）。它们被解释为良好的烃源岩。通过干酪根指数（TI）、氢指数（HI）、干酪根H/C和O/C原子比、C29-C28-C27甾烷等指标证明了陆生植物和浮游生物的混合有机质来源。其特征为ⅱ型干酪根，但接近于ⅲ型干酪根。中等修正的蚀变指数（CIAcorr = 67 ~ 82）表明，这些泥岩的物源受温暖湿润气候控制，风化条件温和。古氧化还原指数（U/Th、Ni/Co、Corg/ pto）表明这些泥岩沉积于缺氧-缺氧水柱中。研究泥岩Sr/Ba（0.25 ~ 1.28）、伽马蜡烷/C30 hopane（0.23 ~ 0.68）和Ts/Tm（0.68 ~ 1.54）比值范围较广，显示出低盐度至高盐度的层状水柱（海相半咸淡水）。分层水柱和缺氧条件可能适合有机质保存。镜质体反射率（Ro）、热解峰温度（Tmax）、生产指数（PI）、生物标志物等指标表明有机质热成熟。在有机质来源和有机质类型相似的情况下，鄂尔托陇巴剖面泥岩的油气丰度高，热成熟度适宜，具有较好的含油气潜力。本研究共采集了19块鄂尔托陇巴剖面的黑色泥岩样品。在中国石化无锡石油地质研究院进行了有机地球化学分析，测试中：（1）利用Leco C-S 200分析仪测定19件样品的TOC含量，分析精度优于10%；（2）利用Rock-Eval VI仪器进行的岩石热解的分析，符合国家标准 GB/T18602-2012；（3）应用Elementar vario MARCO立方元素分析仪进行干酪根元素分析；（4）镜质体反射率（Ro）的测试分析采用尼康入射光显微镜，依据国家标准GWB13401进行实验；（5）应用HP 6890色谱仪对8件岩石粉末样品进行气相色谱（GC）分析，气相色谱-质谱（GC-MS）的分析则使用Agilent 5973I仪器连接HP 6890色谱仪。此外，选取了11块新泥岩在中国北京铀地质研究所进行了主、微量元素分析，其中主量元素分析中应用Philips PW2404型X射线荧光（XRF）光谱仪；微量元素分析则应用HR-ICP-MS（Finnigan MAT）进行分析。主、微量元素的分析精密度均在5%以上。

The Upper Triassic is an important oil and gas exploration target in the Qiangtang Basin, but current understanding remains insufficient. This study investigated the organic and inorganic geochemical characteristics of Upper Triassic mudstones from the E’erduolongba section, aiming to evaluate their hydrocarbon generation potential and clarify their sedimentary environment. Total Organic Carbon (TOC) and extractable bitumen contents range from 0.59% to 1.81% (average 1.20%) and 460 to 1663 ppm (average 778 ppm), respectively, which are classified as good source rocks. Mixed organic matter sources derived from terrestrial plants and plankton were confirmed via indicators including Kerogen Index (TI), Hydrogen Index (HI), atomic H/C and O/C ratios of kerogen, and C29-C28-C27 steranes. These mudstones are characterized by Type II kerogen, but are close to Type III kerogen. Moderately corrected Chemical Index of Alteration (CIAcorr = 67–82) indicates that the provenance of these mudstones was controlled by warm and humid climates with moderate weathering conditions. Paleoredox indicators (U/Th, Ni/Co, Corg/pto) suggest that these mudstones were deposited in anoxic-suboxic water columns. Wide ranges of Sr/Ba (0.25–1.28), gammacerane/C30 hopane (0.23–0.68), and Ts/Tm (0.68–1.54) ratios in the mudstones indicate stratified water columns spanning from low to high salinity (marine brackish-fresh water). Stratified water columns and anoxic conditions are likely favorable for organic matter preservation. Indicators including vitrinite reflectance (Ro), pyrolysis peak temperature (Tmax), Production Index (PI), and biomarkers demonstrate that the organic matter is thermally mature. With similar organic matter sources and types, the mudstones from the E’erduolongba section have high hydrocarbon abundance and appropriate thermal maturity, showing favorable hydrocarbon generation potential. A total of 19 black mudstone samples were collected from the E’erduolongba section in this study. Organic geochemical analyses were conducted at the Wuxi Petroleum Geology Research Institute of Sinopec, with the following testing procedures: (1) TOC contents of the 19 samples were measured using a Leco C-S 200 analyzer, with analytical precision better than 10%; (2) Rock pyrolysis analyses were performed using a Rock-Eval VI instrument, which complies with the national standard GB/T 18602-2012; (3) Kerogen elemental analyses were carried out using an Elementar vario MACRO cube elemental analyzer; (4) Vitrinite reflectance (Ro) tests and analyses were conducted using a Nikon incident-light microscope, following the national standard GWB 13401; (5) Gas chromatography (GC) analyses of 8 rock powder samples were performed using an HP 6890 chromatograph, while gas chromatography-mass spectrometry (GC-MS) analyses were conducted using an Agilent 5973I instrument coupled to an HP 6890 chromatograph. Additionally, 11 additional mudstone samples were selected for major and trace element analyses at the Beijing Uranium Geology Research Institute in Beijing, China. Major element analyses were performed using a Philips PW2404 X-ray fluorescence (XRF) spectrometer, while trace element analyses were conducted using high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS, Finnigan MAT). The analytical precisions for both major and trace element analyses are greater than 5%.