| Abstract: | Three typical vitrinite reflectance (R0) proriles from Pearl River Mouth, Qiongdongnan and Beibuwan basins on the nortbern condsental shelf or the South China Sea display two or more different sub-linear slope relationships between IgR0 and deptb. According to the reconstruction of sedimentary and burial histories for these wells, a relatively large R0 gradient corresponds to a high depositional rate, while a relatively small R0 gradieut represeuts a low depositional rate. In this study, a modiried thermal backstripping model for paleokeat fIow using vitrinite reflectance data has been used to reconstruct paleotbermal history by the linear-segmeut regression. Tke study results indicate that the gentle parts of a IgR0 profile rerlect abnormai periods or high paleoheat flow, in contrast, the steep parts of a IgR0 profile reflect periods of peleoheat flow decay.In order to have an alternative approach and correlative study, an improved two-layer extensional model for the formation and evolution or rifting basin iu pesive contiueutal margin bas been applied. The model simulates basin subsidence process due to stretcbing and thinuing of continental lithospbere and thermal effects by asthenospbere upwelling, and determines the relationship between subsidence and paleoheat flux through the geological time. The simulation results suggest that these basins have undergone two or three rirting and thermal events, and it is clear that the large R0 gradient segment reflects a response to high paleoheat flow during the early, rapid subsidence stage, while the low R. gradient segmeut is a result or the tbermal decay during the thermal subsidence because of thermal contraction of a cooling Iitbospbere. The results also suggest that the maturity profiles of these basins can be employed to visual understanding tke paleogeothermal characteristics of rifting basins. |
