Migrated Sequence Stratigraphic Architecture And Its Geological Significance In Continental Lacustrine Rift Basin

Continental lacustrine rift basin is featured by tectonic activity of multi-stage and multiple depositional center. Because the control of sedimentary pattern is complex, there are many different kinds of sequence configurations. But so far the domestic researchers didn’t set up a unified system of sequence configurations for continental lacustrine rift basin. The classification of the various definitions, characteristics and main control factors are unknown. Migrated sequence stratigraphic architecture is one non-normal type in the evolution of continental lacustrine rift basin, which is rare documented. Based on the sequence stratigraphic units analysis of Paleogene Wenchang Formation of Huizhou and Enping depressions, Zhu I Depression, Pearl River Mouth Basin, this paper aims at describing the denifitation and fearures of migrated sequences and analyzing the controls of different sequence migration,which will inrich the unified system of sequence configurations for continental lacustrine rift basin. Based on the recovery of Wenchang formation’s stripped thickness, analyzing the deposition thickness and original structures, this paper explored the tectonic response to the configuration of migrated sequences.Based on the bore-drilling and seismic data, this paper deeply observed Wenchang formation of Huizhou and Enping depression and analyzed the evolution and migration of sequence units. Seven sequences was divided in the Wenchang formation, which are PSQ1, PSQ2、PSQ3, PSQ4, PSQ5, PSQ6, PSQ7. Using the para-second sequence boundary of SB5, Wenchang formation can be divided into lower Wenchang formation and upper Wenchang formation. The lower Wenchang formation concludes PSQ1, PSQ2, PSQ3, PSQ4 and the upper Wenchang formation includes PSQ5, PSQ6, PSQ7.Moreover,this paper defined the concept of migrated sequence stratigraphic architecture and divided into autogenic and allogenic migration. Autogenic migrated sequences are mainly controlled by horizontal displacement of low-angle syndepositional normal fault, whereas allogenic migrated sequences are controlled by the different tectonic activation episodes of boundary fault on both sides of the basin. As for Enping depression, controlled by the low angle normal fault Fl,lower wenchang group sequence (PSQ1-PSQ4) are mainly distributed in the central parts of the EP17 depression. But with the difference of F1 fault activities, after SB5 interface, these sequence units gradually migrate to the northwest side of depression. But in Huizhou depression, with the episodic tectonic activity in two different sides, the sequence units in XJ24 depression migrated to HZ26 depression, which shows as "seesaw" type.In order to reveal the controls of characteristics and evolution of migrated sequence, this paper ultilize the quantitative characterization migrated sequence and quantitative simulation sequence. The results shows that (1) in Enping depression, the sequence configuration evoluted from type L to Type T in the initial stage of basin evolution, and finally turned into type H due to the migration settlement of sedimentary center; (2) In Huizhou depression, tectonic activities of southern depression strengthen largely and sequence configuration show as Type T. But when it came to rifted stage IB, sequence configuration show as Type H, which mainly develops upper Wenchang Formation.In other words, autogenic and allogenic migrated sequences are controlled by one and two syndepositional boundary fault, respectively. Moreover, lateral migration of sequences leads that reservoirs and source rocks also migrate and stack laterally.This generates multi-block reservoirs along the direction of migration and multiple hydrocarbon accumulation, which are all with great potential exploration.