Topset-to-forest rollover trajectories as reliable predictors of sediment-volume partitioning into deep-lake areas

• 作者: Xian-Zheng Zhao Cheng-Lin Gong Li-Hong Zhou Dong-Wei Li Xiu-Gang Pu Guo-Meng Han Feng-Ming Jin Yi-Xin Yu Wen-Ya Jiang Xiong-Ying Dong
• 来源期刊: 石油科学（英文版）
• 年，卷（期）: 2021,（3）
• 所属期刊栏目: PETROLEUM GEOLOGY & GEOPHYSICS
• 页码范围: 712-727
• 页数: 16页
• 语种: 英文

摘要

Topset-to-forest rollover trajectories and their relation to sediment-and sand-budget partitioning into deep-lake areas are far from being well understood,as compared with their marine counterparts of shelf edges.Two quantitatively distinctive topset-to-forest rollover trajectories and clinothem-stacking patterns were recognized in the Oligocene Qikou Sag of the Bohai Bay Basin and are quantified in terms of trajectory angles(Tse),topset thickness(Tt),forest thickness(Tf),bottomset thickness(Tb),and clinothem-set relief(Rc).Rising topset-to-forest trajectories have positive Tse of 0.15°-0.51°(averaging 0.35°).Ranges in Tt,Tf,Tb,and Rc of their associated progradational and aggradational clinothem sets are,respectively,32.4-58.7 m(averaging 42.7 m),76.9-176.2 m(averaging 148.3 m),0 m,and 167.8-320.8 m(averaging 272.9 m).Falling topset-to-forest rollover trajectories,in contrast,have negative Tse of-0.12° to-0.02°(averaging-0.06°).Ranges in Tt,Tf,Tb,and Rc of their associated progradational and downstepping clinothem sets are,respectively,0 m,266.0-395.7 m(averaging 333.4 m),441.1-542.5 m(averaging 464.1),and 874.9-922.6 m(averaging 892.5 m).These two topset-to-forest rollover trajectories and clinothem-stacking patterns are closely linked to two distinctive patterns of sediment-and sand-volume partitioning into deep-lake areas,which are quantified in terms of Tt,Tb,and differential sediment aggradation of topset segments and forest-to-bottomset compartments(As/Ad).Rising topset-to-forest rollover trajectories and associated progradational and aggradational clinothem sets are characterized by aggradational topsets(reported as Tt of 32.4-58.7 m),a lack of time-equivalent bottomsets,and As/Ad of 0.22-0.87(averaging 0.33),and are fronted by mud-dominated deposi-tional deposits,with sporadic occurrence of thinner and regionally localized forest sands.They are,therefore,inefficient at delivering terrestrial sediments or sands into deep-lake settings.Falling topset-to-forest rollover trajectories and associated progradational and downstepping clinothem sets,in contrast,are characterized by toplap,erosional terminations but aggra-dational bottomsets(reported as Tb of 266.0-473.4 m),and As/Ad of 0,and are fronted by sand-rich depositional deposits,with widespread occurrence of thicker and regionally extensive time-equivalent deep-lake bottomset sands.They are,thus,efficient at delivering terrestrial sediments or sands into deep-lake settings.Topset-to-forest rollover trajectories and associ-ated clinothem-stacking patterns are thus reliable predictors of sediment-and sand-volume partitioning into deep-lake areas,assisting greatly in developing a more dynamic stratigraphy.