关键词: 古地温梯度, 辽河断陷, 油气资源, 早第三纪, 沙河街组, 西部凹陷, 地温恢复, 东部凹陷, 镜质体反射率, 生油区

Abstract: Based on vitrinite reflectance and other index, an attempt in reconstructing paleogeotemperature pattern of Liaohe graben district has recently been conducted for evaluating the oil-generation processes. Results showed that the paleogeothermal gradient and, hence, the paleo-heat flow had been higher during earJy Eogene compared with present-day's ones and experienced a decline by the end of Eogene and rise again since Neogene. The averaged paleotemperature throughout Cz time was similar to that observed at present. Some conclusions can be made as follows: 1. The relatively high paleogeotemperature during Eogene is of great importance to the oil generation of lower strata of Sahejie group in depressions. 2. Sahejie group has been considered to be the key oil-genetic series of Cz sediments in North China Basin. In Liaohe graben district, oil-genetic epoch for Sahejie group in some deep depressions started as early as late Eogene, continuing till present day and leading to higher degree of petroleum maturation. Oil-genetic process of Dongying group is limited to the southern part of Liaohe graben. Epoch of large-scale petroleum occurrence for Dongying group must be traced back to late Neogene, the magnitude and potential of oil generation of Dongying group, however, is much more smaller than that of Sahejie group. Petroleum occurrence in Neogene strata is expected in Liaohe Gulf and seems to be impossible on land. 3. An isobath map of temperature threshold for large-scale petroleum maturation is given and its implications for predication and assessment of oil resouces are discussed.