Abstract
In this study, based on seismic profiles, complemented with boreholes and well logs, two types of deltas are recognized in the Paleogene Qiongdongnan Basin, namely fan deltas and braided river deltas, and their temporal–spatial evolution characteristics and associated controlling factors are studied. The results show the following: (1) The base-level cycle and episodic rifting lead that the characteristics of the basin-marginal deltas vary among different system tracts, third-order sequences, and second-order sequences or rifting stages, i.e. the temporal evolution of the basin-marginal deltas. Among the different system tracts in each third-order sequences, the deltas in the lowstand system tracts are vertically thick with small horizontal extension, while those in the transgressive system tracts present retrogradation with limited vertical thickness and horizontal extension, and those in the highstand system tracts turn to present large extension and develop toplap points. Among the different third-order sequences in each rifting stage, the extension of the deltas presents a pattern “small-medium-large” from bottom to top. Among different rifting stages, the deltas also exhibit different characteristics in terms of extension and thickness, and even the type may change. (2) The paleogeomorphology controls the characteristics of the deltas in lateral space, which is mainly reflected by the fact that the gradient of the paleogeomorphology influences the scale and type of the deltas. This study will enhance our understanding of the relative influence of the controlling factors exerted on fan or braided river deltas, and aid in the exploration of the coal-measure source rocks in the Qiongdongnan Basin, which is a typical basin lacking boreholes, located in the South China Sea.
Highlights
As the comprehensive manifestation of sedimentation, the development of basinmarginal deltas is affected by many factors, including syndepositional faults, base-level change, tectonism, sediment supply, etc. (Hoy and Ridgway, 2003; Li et al, 2015a; LopezBlanco et al, 2000; Lv et al, 2014; Muto and Steel, 2002; Pondrelli et al, 2008; Yang et al, 2017a)
With the successful exploration on the Gulf of Mexico, Columbus Basin, and coast of Africa, basin-marginal deltas have gradually received increasing attention from petroleum geologists and have become an area of interest for hydrocarbon prospecting. The reason for this is that basin-marginal deltas may serve as important reservoirs and show great significance for coal-bearing successions, they could act as critical hydrocarbon source rocks (Lv and Chen, 2014; Lv et al, 2011; Sun et al, 2005, 2006; Wang et al, 2016)
With consideration to the above two points, this paper aims to discuss the characteristics and main controlling factors of the temporal–spatial evolution of basin-marginal deltas found in the Paleogene QDN Basin
Summary
As the comprehensive manifestation of sedimentation, the development of basinmarginal deltas is affected by many factors, including syndepositional faults, base-level change, tectonism, sediment supply, etc. (Hoy and Ridgway, 2003; Li et al, 2015a; LopezBlanco et al, 2000; Lv et al, 2014; Muto and Steel, 2002; Pondrelli et al, 2008; Yang et al, 2017a). With the successful exploration on the Gulf of Mexico, Columbus Basin, and coast of Africa, basin-marginal deltas have gradually received increasing attention from petroleum geologists and have become an area of interest for hydrocarbon prospecting. Unlike onshore basins, there is a lack of boreholes revealing the buried strata and potential reservoirs, in the deepwater areas, which has led to high risk for hydrocarbon exploration in the South China Sea. determining how to use the existing geologic and seismic profiles to enhance the analysis of basin-marginal deltas, and thereby further analyze their temporal– spatial evolution for seeking reservoirs and coal-bearing successions, will be of great importance
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