Abstract:

Hydrocarbon generating organism is an important object for the source rock research.The studies,so far,were focused on their hydrocarbon-generation potential via simulation experiments,and less attention was paid to the geological settings that affect development and distribution of hydrocarbon generating organisms.However,the development and distribution of hydrocarbon generating organisms is very important for predicting source rocks and guiding petroleum exploration.In this study,the Lower Cambrian Xishanbulake and Yuertus formations were selected from the Southern Yaerdangshan and Dongergou sections in Kuluketage and Keping districts,respectively.Researches on two formations demonstrate that the hydrocarbon generating organisms in the Xishanbulake Formation are dominated by benthic algae,and include some planktonic algae;whereas hydrocarbon generating organisms in the Yuertusi Formation are benthic algae.Anomaly of elements Ce and Eu and REE patterns of cherts in the two formations imply that the two sections were affected by hydrothermal fluid,and that the influence in the Southern Yaerdangshan section was stronger than that in the Dongergou section.Major and trace elements analyses of mudstones indicate that the Xishanbulake Formation have less reduction water,and more active volcano in the Kuluketage district which might be resulted in more undulating terrain than that in the Keping district during the Early Cambrian.Correlated with distribution of extant algae,it could be concluded that the difference in tectonic activity,water depth,and paleo-terrian may be the major cause for the difference in hydrocarbon generating organism assemblages between the Xishanbulake Formation in the Southern Yaerdangshan section and the Yuertus Formation the Dongergou section.

Key words: hydrocarbon generating organism assemblage, source rock, Yuertusi Formation, Xishanbulake Formation, Lower Cambrian, Tarim Basin