Organic Geochemical Characteristics Of Lower Cretaceous Sedimentary In The Offshore Area Of Shandong

Offshore Area of Shandong is located in the middle section of Sulu Orogenic Belt on both sides of Jiaozhou Bay.This area can be divided by the fault of Wurong-Muji into two parts, which are the south, partial region of Jiaolai Basin, and the north part on which different people have different opinions. We think that it is a large scale trending northeast rift basin during Late Mesozoic in offshore area of Shandong. Furthermore, we consider that this basin is a extended part of Jiaolai Basin in ancient seawater and propose for the first time the definition of “rift basin during Late Mesozoic in the offshore area of Shandong ”.This research is focused on the Lingshan Island and Jiaolai Basin where we carry out the field investigation and systematically sample sedimentary rocks. By applying the methods of organic carbon, chloroform bitumen ”A” extraction, rock pyrolysis, total rock maceral, gas chromatography of saturated hydrocarbon and GC-MS of biomarkers, we analysis the organic geochemical characteristics and comprehensively evaluate the abundance, types, maturity of organic matters and biomarkers of the lower cretaceous sedimentary rocks in the offshore area of Shandong which provide references for predicting the potential resources.The results indicate that the rock in Lingshan Island has the good organic abundance and the sedimentary environment is brackish water to salt water. The two main types of organic matters are sapropel and humus and maturity of organic matters are in the stage of high mature-mature stage. The organic abundance in Jiaolai Basin are lower than Lingshan Island totally and the Shuinan section in Laiyang sag has the best abundance and type of organic matters, which suggests the strongest capacity of hydrocarbon generation. Most sedimentary samples in Jiaolai Basin of which vitrinite reflectance(Ro) is >0.7% and lower than that in Lingshan Island are in the stage of high mature-mature. According to the slightly degraded normal paraffin hydrocarbons, single peaked gas chromatography of saturated hydrocarbons and advantage of phytane, the matrix in the offshore area of Shandong forms in the reductive condition. Samples in Lingshan Island have the the content of C27 is higher than C28. The GC-MS shows “V” type which indicates the matrix resources is mixed type. Whereas samples in Jiaolai basin have the content of C29 is higher than C27, showing reverse “L” type in the GC-MS which suggest the main source of organic matrix is higher plant.