Sequence architecture and depositional evolution of Dongying Formation in steep slope zone of northern Liaodong Bay and its responses to tectonism

Abstract

The sequence architecture and depositional evolution of Dongying Formation in the steep slope zone are mainly developed in response to tectonism. The comprehensive analysis of cores, wireline logs, and seismic volumes is employed to reveal the relationship among sequence architecture, depositional evolution, and tectonism. The results indicate that the whole Dongying Formation can be divided into three third‐order sequences based on regional unconformity along the basin margin and slope and its correlative conformity in the basin centre. In addition, seven fourth‐order sequences are further divided based on regression surfaces within third‐order sequences. The sequence architecture of different‐order sequences is discussed and revealed in terms of systems tracts, stratal thickness and distribution, and seismic reflections. Four genetic types of sedimentary facies including fan delta, sublacustrine fan, near‐shore subaqueous fan, and braided delta are identified according to core observations, stacking patterns of wireline logs, internal configuration, and external geometry of seismic reflections. The depositional evolution in Dongying Formation is related to tectonic intensity and tectonic evolution stage in the steep slope. The whole Dongying Formation is in the midst of a strike‐slip and rifting stage during its depositional period. When tectonic movements are intensively active, it is mainly characterized by fan delta and near‐shore subaqueous fan along the steep slopes and sublacustrine fan in the basin centre. However, the opposite case is dominated by fan delta and braided delta around and along the uplifts. In addition, the palaeogeomorphology and sediment supply also play an important role in controlling facies distributions in the steep slope zone. The subsidence rate resulted from tectonism controls the sequence architecture and depositional filling in terms of fault activities and accommodation space in the steep slope.

Variability of sequence architecture in a rift margin controlled by tectonic activity: The Eocene Dongying Depression, Bohai Bay Basin, China

“…The evolution of fault segments with different strike‐length scales significantly influences the variability of coeval syn‐rift succession and deposition (Carr et al., 2003; Colombera & Mountney, 2020; Davies & Gibling, 2003). Therefore, it is necessary to modify and summarize the sequence stratigraphic model applicable to lacustrine rift basins (Deng et al., 2020; Li et al., 2019; Martins‐Neto & Catuneanu, 2010; Shang et al., 2022) to analyse the distribution of sedimentary systems and predict the sand bodies dispersal in sequence stratigraphic frameworks, thereby improving the efficiency of hydrocarbon exploration.…”