| Subsidence center (SC), accumulation center (AC) and depocenter (DC) are three fundamental concepts in terrestrial lacustrine basins, which are good indicators of basin tectonics, sequence stratigraphy, and sedimentation, respectively. SC is characterized by the fastest rate of tectonic sinking, and the deepest place of certain basin. AC means the site with thickest sediments accumulation within sequence stratigraphic framework and DC, which represents certain area depositing the finest-grained sediments. Thus, three centers (i. e, SC, AC, and DC) have difference and correlations considering their genetic mechanism as well as special-and-temporal coupling. In this study, we firstly explicit the SC, AC and DC of Wenchang and Enping formation of Huidong district by the methodology of EBM basin modeling system and sequence stratigraphy. Then, analyzing the characterization of three centers of Wenchang and Enping formation, and meanwhile, comparing the special and temporal coupling relationships between them. On the basis of previous research, we proposed new recognition in Huidong district that three centers in Wenchang formation are integrated in one site, whereas in Enping formation, they are separated independently. Besides that, we depict the distribution characters of source rock of the Enping formation as well as provide new ideas in oil and gas exploration in study area.Three centers (i. e, SC, AC, and DC) in Wenchang stage are integrated in one site which is located in respective sag center (i. e, HZ22, HZ24, HZ14, HZ08 and HZ10 sag). The provenance in Wenchang stage is from the local uplift area, characterizing under-compensation condition since the strong intensity of basin-controlling faults activity. The relative sea level maintains a higher condition, which consequently exert significant influence on sediments accumulation process. The coarse-grained siliciclastic deposits are observed near the foot of the hanging wall of the bounding fault, indicating a proximal rapid accumulation, while the finest part of sediments are transported till the sag center having sufficient accommodation. The middle-deep lacustrine source rocks are also developed in the integrated site where it characters the highest tectonic subsidence as well as the thickest deposits sedimentation. Source rocks shows great quality with high maturity and effective thickness. Seismic facies of source rock in southern district characters low frequency, weak-to-blank amplitude, high continuity, while in northern district, by contrast, is characterized by low frequency, high amplitude and high continuity.Three centers (i. e, SC, AC, and DC) are separated independently in Enping stage. The SC and AC are integrated in one site which is located in respective sag center (i. e, HZ22, HZ24, HZ14, HZ08 and HZ10 sag). While the DC is developed in the intersection of shallow braided river delta originated from southern and northern district, respectively, which is far from the SC and AC. In the Enping stage, the South China fold belts in the north acted as a regional provenance. The intensity of basin-controlling faults activity gradually decreased and the sedimentation is mainly controlled by the entire subsidence of basement of basin. The relative sea level keeps in a low standard and the sufficient provenance which results in a stronger fluvial impact than lacustrine to basin deposition enable the sedimentation area in an overcompensation sedimentary condition. Tectonic subsidence near the boundary faults which causes a steep slope of paleogeomorphologic architecture has fan-shaped deltas with coarse-grained sediments to be rapidly deposited at the foot of the bounding faults. While the fine-grained sediments are deposited at the sag center after long-distance transport. Thus, according to the definition of SC, AC and DC. The SC and AC are integrated in one site near the basin steep slope belts, whereas the DC is located at the sag center which is separated from the SC and AC. Hydrocarbon source rocks in this stage is characterized by dispersal pattern with relatively poor quality. Not only has it developed at the sag center characterizing weak amplitude seismic facies which is interpreted as shore-shallow lake facies, but it generated at the AC showing low frequency, weak-to-moderate amplitude seismic facies which is interpreted as marsh micro-facies in delta plain sub-facies.Spatial and temporal coupling of three centers (i. e, SC, AC, and DC) in Huidong district experienced from integrating in one site in Wenchang formation to separating in Enping formation, corresponding to the evolution stages of terrestrial lacustrine baisn from rifted period to depression period. Such transformation is influenced by factors like tectonic intensity, pal eo-water depth, sedimentary provenance, etc. The three centers are always integrated in one site when tectonic activity is intense and the relative sea level is in high condition. By contrast, when the tectonic activity is dominated by basement subsidence, and water body is relatively shallow, three centers are always separated.Spatial and temporal coupling of three centers (i. e, SC, AC, and DC) has also significant impact in oil and gas exploration. When the three centers are integrated in one site, the thickest strata always generates the finest deposits, namely, the hydrocarbon center. Exploration target can be concentrated since the centralized distribution of source rocks and clearly dominant hydrocarbon migration directions. If three centers are separated, however, distribution of source rocks are scattered and the thickest strata becomes the coarse-grained reservoir rather than fine-grained source rocks. Exploration target is no longer concentrated in one tectonic belt since the complex hydrocarbon migration patterns. |
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