Analysis Of Sequence Stratigraphy And Predication Of Lithological Traps, The Third Section Of Shahejie Formation, Linnan Sub-depression

Sequence stratigraphy can contribute directly to the exploration of subtle stratigraphic traps. High-resolution stratigraphic correlation approaches used in this paper based on the principle of stratigraphic base-level cycles developed by T. A. Cross are well tested in shallow marine and adjacent coastal plain strata. This paper focuses on recognizing the stratigraphic cycles caused by multi-order base-level cycles, establishing the stratigraphic correlation framework and predicting the lithological traps of the third section of Shahejie Formation ,Linnan sub-depression.Linnan sub-depression which is Mesozoic and Cenozoic faulted lacustrine basin is located in the southwestern part of Huimin sag, depression of Jiyang. It is dominated by lacustrine-fill sub-depression.Based on well logs, three -dimension seismic profiles, cores and other basic data, 10 horizons including 6 turnaround surfaces and 4 maximum flooding surfaces are defined from Es3 to the lower part of Es2 formation, and 1 long-term and 5 intermediate-term base-level cycles which are named from C5 to C1 could be identified, and then the chronostratigraphic framework of the sub-depression is built. The third section of Shahejie formation is mainly comprised of C4, C3 and C2. There are 5 depositional systems in the region. They are Panne and Jishan delta systems coming from Chengning heave near the northwest border of the region, Shuangfeng delta located in southwest part of the region coming from Luxi dome, Qudi fan-delta located in the southeast of the studying area and the sub-fan near fault or fan-delta of the southern part of the region.Based on the study of sedimentary facies and depositional systems, 11 lithological traps are predicted. The strata formed during the base level falling period is the favorable zone to find excellent lithological traps.These traps are mainly in the C2 and C3 cycles. Every trap is related to relevant depositional system. The lithological traps related to JiShan delta ?turbidite fan depositional system inherently developed during the base level falling period of C3 cycle and the base level rising period; the lithological traps related to the underwater fan depositional system near XiaKou fault developed during C2 cycle; the lithological traps related to QuDi fan delta developed during the base level falling period of C2 cycle; and there are a few lithological traps related to Shangfeng delta. These predicted traps are mainly distributed in the deeply low-lying areas.Then this paper discusses the main control factors of Lithological Traps. The types, features and the distributional area of theses depositional systems are dominated by macro paleo-geomorphic units. And the exact position of these lithological traps are determined by local paleo-geomorphic units.