Architecture of tectonic sequences, depositional systems, and tectonic controls of the sedimentary fills of the rift‐related Wenchang Formation in the Lufeng Depression, Pearl River Mouth Basin, China

Abstract

Different sequence types were formed in various stages associated with tectonic variations and changes of the sediment supply in the rift‐related Wenchang Formation. Based on cores, wire logging, and seismic data, the sequence stratigraphy, depositional systems, and controls on the depositional systems of the Wenchang Formation in the Lufeng Depression were studied. The Wenchang Formation developed braided‐delta, lacustrine, fan‐delta, and nearshore subaqueous fan deposits and represents one first‐order sequence and three second‐order sequences, indicating three stages of tectonostratigraphic evolution. (a) The early syn‐rift sequence (SSQ1) developed fan‐delta and shallow lacustrine deposits. (b) The rift climax sequence (SSQ2) contains the early rift climax systems tract and the middle‐late rift climax systems tract. The early rift climax systems tract formed primarily braided‐delta and shallow lacustrine deposits, whereas the middle‐late rift climax systems tract developed mostly semi‐deep to deep lacustrine deposits. (c) The late syn‐rift sequence (SSQ3) developed braided‐delta and shallow lacustrine deposits. In the SSQ3 transgressive systems tract, retrogradational parasequence sets developed along the southern dip slope because of the weak sediment supply from the Huilu low uplift, whereas westward aggradational–progradational parasequence sets developed along the long axis because of the stronger sediment supply from the Lufeng eastern low uplift. Tectonic activity primarily controlled the early syn‐rift and rift climax deposition; syn‐depositional faults formed the transfer zones and slope break zones. Three types of transfer zones for sedimentary transport into the basin were distinguished, including synthetic approaching transfer zones, strike ramps, and collateral transfer zones. Three types of slope break zones were also recognised, including fault scarp zones controlling fan deltas and nearshore subaqueous fans, fault terrace zones controlling low‐stand fan deltas, and antithetic fault terrace dip‐slope zones controlling braided deltas.

Impacts of Sedimentation and Diagenesis on Deeply Buried Reservoir Quality of a Rift Basin: A Case Study of Wenchang Formation in the Lufeng Depression, Pearl River Mouth Basin, China

“…According to the characteristics of well logs and seismic reflection of the interfaces within E 2 w, two first-order sequence boundaries (SB1 and SB4) and two second-order sequence boundaries (SSB2 and SSB3) were identified (Figures 2 and 3). Based on the identified sequence boundaries, the rift-related Wenchang Formation can be further divided into one first-order sequence (E 2 w) and three second-order sequences, including SSQ1, SSQ2, and SSQ3, which correspond to the early syn-rift phase (Ew 6 ), rift climax phase (Ew 5 -Ew 4 ), and late syn-rift phase (Ew 3 -Ew 1 ) [36]. SSQ1 is composed of transgressive systems tract (TST) and highstand systems tract (HST).…”

“…According to the core description, thin-section analysis, shape of logging curve, and seismic reflect patterns, as well as papers published about the study area [3,36], four main sedimentary facies were recognized in the study area: braided-delta facies, lacustrine facies, fan-delta facies, and nearshore subaqueous fan facies (Figures 4-6), which can be further divided into a variety of subfacies and microfacies. Three subfacies developed in braided-delta facies: braideddelta plain, braided-delta front, and predelta facies, and the sandbodies of braided-delta front are the main focus of this study.…”

“…For rift basins, the development of sequence units and sedimentary facies in the basin is complex and diverse due to the complexity of basin tectonic movements and the diversity of provenance systems [36][37][38]. For example, in the early stage of Paleogene rifting, the Qiongdongnan Basin mainly developed lowstand systems tract and deposited alluvial fans and braided rivers.…”

“…From the bottom up, the Wenchang Formation (E 2 w) and Enping Formation (E 2 e) correspond to the syn-rift phase and postrift phase, respectively [51]. Furthermore, based on the evidence of tectonic activities, unconformities, and sedimentary cycles, the syn-rift phase of the deposition of E 2 w can be further subdivided into three typical stages: the early syn-rift (Ew 6 ), the rift climax (from Ew 5 -Ew 4 ), and the late syn-rift (from Ew 3 -Ew 1 ) [36].…”

Analysis of the geometric characteristics of clinothems and the relationship with shelf‐edge trajectories of thePlio‐Pleistocenecontinental slope in the Qiongdongnan Basin, South China Sea

“…The sediment supply is another factor that affects the development of large fans, and even controls their development, which is also concluded in numerous other studies (e.g. Liu et al ., 2017, 2019; Jia et al ., 2019; Gao et al ., 2020; Patruno et al ., 2020). Earlier analyses of the source‐to‐sink system in the study area (Liu et al ., 2019) indicated that the sediment that came from Hainan Island (north of the QB) was probably transported by the Lingshui and Wanquan rivers (see the section Factors controlling clinothem development for details), and that there were consequently two independent source‐to‐sink systems.…”