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 quantifed in terms of trajectory angles(T_(se)),topset thickness(T_(t)),forest thickness(T_(f)),bottomset thickness(T_(b)),and clinothem-set relief(R_(c)).Rising topset-to-forest trajectories have positive T_(se) of 0.15°-0.51°(averaging 0.35°).Ranges in T_(t),T_(f),T_(b),and R_(c) 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 T_(se) of−0.12°to−0.02°(averaging−0.06°).Ranges in T_(t),T_(f),T_(b),and R_(c) 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 sandvolume partitioning into deep-lake areas,which are quantifed in terms of T_(t),T_(b),and diferential 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 T_(t) 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 depositional deposits,with sporadic occurrence of thinner and regionally localized forest sands.They are,therefore,inefcient 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 aggradational bottomsets(reported as T_(b) 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,efcient at delivering terrestrial sediments or sands into deep-lake settings.Topset-to-forest rollover trajectories and associated 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.
基金
This research was jointly funded by the Science Foundation of China University of Petroleum,Beijing(Nos.2462017YJRC061 and 2462020YXZZ020).
