Sequence Stratigraphy:Problems and Discussion
Li Shaohu;Li Shupeng;Hu Yanye;Wu Wei;Liu Biao;Li Zunting;Faculty of Earth Resources,China University of Geosciences;Key Laboratory of Tectonics and Petroleum Resources,Ministry of Education;Earthquake Administration of Shandong Province;
This article reviews contributions and influences of seismic stratigraphy to sequence stratigraphy,and theoretical accumulations of sequence stratigraphy;and points four problems as followings:sequence boundaries(subaerial unconformities and their correlative conformies)spanning boundaries of Erathem,System,Series and Stage;"transgressive-regressive"cycles as base of original sequence stratigraphic models inducing to adjust sequence boundaries at least three times,base-level curve delaying transgressive-regressive(T-R)curve,and the purely geometric correlative conformity(c.c)obstructing theoretically sequence stratigraphy.Meanwhile this paper points four aspects as followings.(1)Stillstand normal regression(SNR)replacing highstand normal regression is used to avoid the non-periodicity hiding in sequence stratigraphy due to the unreasonable design of highstand normal regression.(2)Based on the character of remnant maximum flooding surfaces potentially closed to or in accord with the boundaries of chronostratigraphic units or even the lower boundaries of stage(GSSP),sequence stratigraphy is necessary to establish compound sequence boundary composed of remnant maximum flooding surfaces(RMFS)and their correlative unconformities(CSU),and to use the RMFS component to solve the problem that current sequence boundaries have been spanning the boundaries of chronostratigraphic units.(3)It may be applied the one-to-one tracing style(one RMFR to oneCSU)from basin to land in compound sequence boundary to the problem that current sequence boundaries have been adjusted many times,i.e.,they were placed to base of T-R,base of lowstand systems tract in three-divided model or base surface of forced regression,and top of forced regressive wedge systems tract,due to one-to-many tracing style(one subarial unconformity to many potential correlative conformities)from basin to land in existing sequence stratigraphic models.(4)The term "correlative unconformity"should be reduced to a lower rank as boundary of systems tract so as to solve the problem about"doubly defined correlative conformities"in existing sequence stratigraphic models.Respectively,Hunt and Tucker(1992)'s correlative conformity is replaced by extension of subarial unconformity(ESU)from correlative subaerial unconformity component of compound sequence boundary,and is as base of lowstand systems tract and partially as subarial unconformable base of transgressive systems tract;whereas,Posamentier and Allen(1999)'s correlative conformity is replaced by the resumed term basal surface of forced regression(BSFR)above compound sequence boundary,and is as base of falling stage systems tract.Moreover,regressive surface of marine erosion(RSME)as the synonymous term for basal surface of forced regression does not completely represent marine and nonmarine settings.