Investigating the Influence of Parent Rock and Sedimentation on the Diagenesis of Tuffaceous Clastic Rock: An Example from the Lower Cretaceous Junggar Basin, China

This study focuses on tuffaceous clastic rocks of the Lower Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin. It aims to explore the influence of sedimentation and parent rock on this kind of reservoir development. The results show that the tuffaceous components formed by the denudation of ultramafic and mafic rocks can transform into chlorite coating or hematite, while those from intermediate rock denudation can be dissolved or transformed into illite. Sedimentary facies and lithofacies are essential in controlling the evolutionary result of tuffaceous components. Matrix-supported medium conglomerate and grain-supported medium-fine conglomerate that developed in the fan delta plain, with a closed original geochemical systems, have been in the oxidizing environment for a long time. The tuffaceous matrices mainly transforms into hematite or illite. These minerals occupy the primary pores and are difficult to dissolve by felsic fluids, which inhibits the development of high-quality reservoirs. The grain-supported sandy fine conglomerate developed in the fan delta front was in the underwater reductive environment with an open original geochemical system. The tuffaceous matrices not only can transform into chlorite coating to strengthen the particle's compaction resistance, but also can be fully dissolved, which promotes the formation of high-quality reservoirs.