| Provenance analysis is of great significance in basin analysis, and is also the important evidence in studying source area position, property and transport path of sediment, predicting Palaeocurrent stretching trend, determining the distribution of sedimentary facies and sand-body, and reconstructing tectonic evolution and ancient environment of sedimentary basins. It has developed into a comprehensive research field which is multi-method and multi-technology. Analysis of outcrop or drilling data, as the traditional method of provenance analysis, is unable to depict the whole provenance system well, including the provenance channel, transport model, deposit unloading area and the distribution of sand-body, although it often be used to restore sedimentary environment from a macroscopic angle. However, the provenance analysis method of seismic-based sedimentology makes up for the traditional method and makes provenance analysis be more systematic, continuous and microscopic.The study area is located on the western slope of Bozhong sag, which is the biggest sag in Bohai Bay area. It contacts with Shijiutuo Uplift by fault in north, and overlaps on the Shaleitian Uplift in south. The former sedimentary facies studies about Bohai Bay basin were mostly regional and macroscopic, and the discussions about the ancient provenance channel’differences between Shaleitian Uplift and Shijiutuo Uplift were less, problems such as the type of ancient provenance channel, the direction of sedimentary transposition, the capacity of sedimentary supplement, the contribution to sediment et al. Taking Dongying formation in western slope of Bozhong sag as the study object, based on the sequence stratigraphic framework, using the method of qualitative analysis of traditional sedimentology (including zircons tracer, clastic rock components, heavy minerals et al) and quantitative analysis of seismic sedimentology (seismic-basedsedimentology method), in the condition of sparse well data, this paper indentyfies the differences of provenance supplement between Shaleitian Uplift and Shijiutuo Uplift (type, derection, scale), summaries the sediment provenance system, and predicts the distribution of sand-bodies. The research result changes the traditional knowledge about sdudy area, in that opinion eastern Shaleitian Uplift mainly developed fan delta which was close to source rock and deposited in a quick time, and establishes the model for looking for favorable reservoir and potential oil and gas.The main achievement of this paper are follows:(1) Constructed the sequence stratigraphic framework and sedimentary filling pattern of Paleogene Dongying formation in western slope of Bozhong sag, Bohai Bay basin.The Paleogene can be subdivided into two fault-fault sag cycle:member III of Shahejie formation-member I of Shahejie formation and member III of Dongying formation-member I of Dongying formation. Dongying formation, as the objective zone of this paper, is a second-order sequence and can be subdivided into four third-order sequences:SQd3, SQd2L, SQd2u, SQdl。 During the Dongying formation rift cycle, the fan delta sand in the abrupt slope belt is largely distributed and the large-scale braided deltas are mainly developed on the southeast of Shaleitian Uplift in sequence SQd3.The braided deltas with large-scale progradational reflection are widely distributed in sequence SQd2.(2) Discussed the fault-uplift pattern in western slope of Bozhong sagEvolution of uplift and fault directly controls the deposit pattern and sand-body distribution. In the period of sequence SQd3, the abrupt slope belt in the north of Shijiutuo Uplift is favorable for the deposition of fan deltas, while braided deltas are mainly develop on the southeast of Shaleitian Uplift. For sequence SQd2, the slope belt of eastern margin of Shaleitian Uplift, which has a series of fault-trough being near vertical to uplift, is helpful to guide the coarse clastic from Shaleitian Uplift and regional palaeocurrent transfer to east. Due to regional faults, there is a long-term abrupt slope belt in southern Shijiutuo Uplift, and fan delta locates in the footwall of faults.(3) Confirmed three sedimentary provenance pathways and three sedimentary provenance systems in western slope of Bozhong sagThere are three sedimentary transport pathways in western slope of Bozhong sag: paleo-channel, fault-trough, and structural transfer zone. It is concluded that the local provenance can be divided into three systems, respectively: fault-trough sedimentary provenance system, the vertical sedimentary provenance system and transfer zone sedimentary provenance system. There are obviously differences among the three kinds of local sedimentary provenance systems, such as the type of ancient provenance channel, the direction of sedimentary transposition, the capacity of sedimentary supplement, the contribution to sediment et al. Fault-trough provenance sedimentary system, taking fault trough as the channel, is mainly distributed in the eastern Shaleitian Uplift and the corresponding sedimentary system is braided delta, and matchs with the source-channel (a sand conveying system)-fault trough channel (a sand conveying system)-Delta-lacustrine mode; the vertical sedimentary provenance system, characterized by the direction of sedimentary supplyment is vertical to fault strike and the corresponding sedimentary system is fan-shape fan delta, is mainly distributed in the south of Shijiutuo Uplift and matchs with the mode of source-channel (a sand conveying system)-(fan) Delta (gravity)-lacustrine; transfer zone sedimentary provenance system, taking fault transfer zone as the channel, is mainly distributed in the southeast of Shaleitian Uplift and composed by braided delta. (4) Identified the differences of source area between Shaleitian Uplift and Shijiutuo UpliftThe differences of source area can be identified between Shaleitian Uplift and Shijiutuo Uplift, such as the types of ancient provenance channel, the direction of sedimentary transposition, the capacity of sedimentary supplement, the contribution to sediment, et al. Study area is mainly controlled by fault-trough channel, which starts in eastern Shaleitian Uplift and extends in NEE linear; southern Shijiutuo Uplift is controlled by paleo-channel system; the local Shaleitian Uplift of southeast, is controlled by structural transfer zone system.The major innovations are follows:Under the conditions of sparse well data, using quantitative analysis of seismic sedimentology which makes up for the traditional method, this paper is mainly to identify the differences of provenance supplement between Shaleitian Uplift and Shijiutuo Uplift (types, direction, scale), confirm that the deposits of study area is mainly controlled by fault-trough channel that starts in eastern Shaleitian Uplift and extends in NEE linear, and describe sedimentary facies boundaries and types. The results had provided the new ideas and changed the traditional knowledge about the sediment provenance characteristics of the study area. |
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