Sedimentological Characteristics And Hydrocarbon Source Rocks Development Regularity Of The Mesozoic In Fujian And Zhejiang Region

On the basis of the measured outcrops in Fujian and Zhejiang provinces, thisarticle built a sequence stratigraphic framework for Mesozoic and studied thesedimentary facies for the hydrocarbon source rock. Added with the laboratoryanalysis, we gain a clear view for the distribution of the source rock and thecharacteristics of organic matter. We analysed the control factors of the source rocksin the study areas. This article provided a basic research result for Fujian and Zhejiangprovinces, as well as the adjacent offshore areas in East China Sea. The main resultsare as follows.There are4large-scale regional tectonic movements in Mesozoic of Fujian andZhejiang provinces and they formed4regional unconformity surfaces. The Mesozoiccan be divided into4tectonic sequences by these surfaces. Namely, the UpperTriassic-Lower Jurassic tectonic sequence, Upper Jurassic-lower Lower Cretaceoustectonic sequence, upper Lower Cretaceous tectonic sequence and Cretaceous tectonicsequence.The main Mesozoic depositional systems developed in Fujian and Zhejiangregion include: alluvial, fluvial, lacustrine, delta and shore. The hydrocarbon sourcerocks are mainly developed in the lacustrine system and the shore system.There are two sets of Mesozoic source rocks developed in Fujian and Zhejiangregion. The first set is Late Triassic–Middle Jurassic source rock, which composedof carbonaceous mudstone and coalbed and its organic type is humic, tend to generategas. The other set if Lower Cretaceous source rock, which is composed ofdark mudstone and oil shale and its organic matter type is sapropel, tend to generateoil.The maturity of Mesozoic source rock in Fujian and Zhejiang region is generallyhigh. All of the maturity results of the samples reached mature or over-mature stage.The source rock maturity in the adjacent offshore areas in East China Sea, however, isrelatively low and just at the peak of oil phase. Therefore, offshore areas in East ChinaSea are favorable for oil generation zone.There are3factors controlling the development of the Mesozoic source rocks inFujian and Zhejiang region: The first is the regional transgressive event; the second is the development characteristics of the sedimentary sequence; the third is periodicvolcanic activities.There are two regional transgressive events which took place in the Mesozoicperiod in Fujian and Zhejiang region. The first transgression occurred in the LateTriassic–Early Jurassic and its direction is from the southwest direction. Anothertransgression is in the Early Cretaceous and its direction is from the southeastdirection.In a certain sequence stratigraphic framework, the low stand systems tract is notconducive to the development of hydrocarbon source rocks; the transgressive systemstract hosts the most favorable source rocks; and the high stand systems tract is easy toform humic source rocks which are prone to generate gas.