羌塘盆地白垩系海相油页岩特征及其形成条件分析

Characteristic and Formation Condition of the Cretaceous Marine Oil Shale in the Qiangtang Basin

近年来，在羌塘盆地胜利河、长梁山、长蛇山、托纳木等地发现的油页岩为目前我国规模最大的海相油页岩矿床，具有重要的工业开采价值。海相油页岩的主要矿物成分为碳酸盐、粘土矿物和石英，并见有黄铁矿、石膏、菱镁矿等矿物。粘土矿物以伊利石为主，少量高岭石，不含蒙脱石。有机地球化学分析表明，这些油页岩的有机质丰度较高，有机质类型较好。胜利河油页岩TOC含量在4．31％～21．37％之间，均值为8．40％；托纳木油页岩的TOC含量也较高，最大值为25．68％，平均为9．32％；长梁山剖面油页岩的TOC含量在2．96％～23．47％之间，平均值为9．56％；长蛇山油页岩的TOC含量在4．53％～9．49％之间，平均值为7．74％。长蛇山油页岩干酪根类型主要为Ⅱ_1型，少数为Ⅱ_2和Ⅲ型;胜利河油页岩主要为Ⅱ，和Ⅱ：型干酪根，而托纳木油页岩的干酪根类型主要为Ⅱ_1型和Ⅰ型。白垩系海相油页岩的形成受多方面因素控制，包括缺氧富氧状态、古生产力、古气候、粘土矿物的混积作用、古地形条件以及海平面变化等。其中，油页岩的总有机碳含量（TOC）与古环境元素指标Mo、V存在较强的相关关系，相关系数分别为0．975和0．917，而与古生产力指标P／Ti、Ba／A1之间为弱相关或无相关关系，相关系数分别为0．481和-0．739。因此，本文认为海相油页岩的形成以“保存模式”为主，有机质沉积时的水体环境对高有机质含量的油页岩的形成起主导作用，并在此基础上建立了海相油页岩的形成演化模式。

Recent years, the largest marine oil shale deposit in China was found in the Shengli River, Changliang Mountain, Changshe Mountain and Tuonamu regions in the Qiangtang Basin, which shows favorable prospects for commercial exploitation. The major minerals in the marine oil shales are calcite, clay, and quartz, with minor quantites of pyrite, anhydrite, and magnesite. The component of the clay minerals is mainly illite and a small amount of kaolinite without smectite. The organic geochemistry results of the oil shales reveal a high value of the total organic content （TOC）. The TOC content of the Shengli River oil shale ranges from 4.31% to 21.37% , with an average of 8.40% ; the TOC content of the Tuonamu oil shale is also very high, and the maximum is 25. 68%, with an average of 9.32% ; the TOC content of the Changliang Mountain oil shale varies from 2.96% to 23. 47%, with an average of 9.56% ; and the TOC content of the Changshe Mountain is between 4.53% and 9.49%, with an average of 7.74%. The Changshe Mountain oil shale is mainly of type Ⅱ_1 and a few type Ⅱ_2 and Ⅲ kerogen ; the Shengli River oil shale is mainly type Ⅱ_1 and type Ⅰ kerogen, while the Tuonamu oil shale is mainly type Ⅱ_1 and type Ⅰ kerogen. The formation of the Cretaceous marine oil shales was controlled by many factors, including： the redox state, palaeo-productivity, paleoclimate, the mixed deposits with clay mineral, differential palaeotopography and the sea level change. There is a significant positive relationship between TOC and palaeoenvironment element index Mo （ r = 0. 975 ） and V （ r = 0. 917 ）, while TOC shows a weak and negative relationship between the palaeo-productivity index P/A1 （r = 0.481 ） and Ba/A1 （r = -0.739）. Therefore, this paper proposes that the formation of the Cretaceous marine shale is mainly of preservation mode. The water environment during the organic matter deposit played a leading role in the formation of high organic matter content in the oil shale. Based on the above, we establish the sedimentation model of the marine oil shale.