Eocene Sediments in the South China Sea, precursor deposits of the Oligocene expansion?

Abstract

The stratigraphic record of Eocene in the Malaysian waters of the South China Sea is scarce; the few deep petroleum exploration wells and outcrops are located on the fringes of the SCS. Yet, despite the paucity of data we observe a variety of sediments that cover the range from fluviatile to (at least) neritic marine deposits. Whilst fluvial deposits dominate the Western Rim (Penyu, Malay basins), the Southern Rim (Sarawak) is characterized by deposits of a narrow and rapidly deepening shelf, with fluviatile, shallow marine clastics and carbonates passing seawards to outer shelf and neritic deposits. The proven record of the Eocene to-date is located in relatively small and deep sub-basins. Possibly, the Eocene underlies additional areas of the SCS, but there is to-date no sufficient well data to offer further confirmation. The presence of Eocene strata on the margins of Sundaland is associated with an early phase of extensional and/or transpressional tectonism, probably acting as precursor movements related to the onset of rifting of the crust underlying the SCS.

A Discussion on the relationship between prominent unconformities on the SCS shelf margins and the end of seafloor spreading in the South China Sea

“…For discussion purpose, we subdivide areas surrounding the SCS as follows (Kessler and Jong, 2016;Kessler et al, 2021aKessler et al, , 2021b) (Figure 1): Eocene deposits in the area were described and discussed in Kessler et al (2021a).…”

“…Jong, 2015, 2016). The end-of- Kessler et al, 2021b). The areas of oceanic crust and strongly thinned continental crust flanks are potentially bounded by the red line Red River Fault System, and the West Baram Line (WBL) (Jong et al, 2014;Kessler and Jong, 2016).…”

“…The end-of- Kessler et al, 2021b). The areas of oceanic crust and strongly thinned continental crust flanks are potentially bounded by the red line Red River Fault System, and the West Baram Line (WBL) (Jong et al, 2014;Kessler and Jong, 2016). Note (Sandwell et al, 2014) and (b) complete Bouguer gravity anomaly computed from (a) with the distribution of the post-spreading seamounts.…”

Sedimentary Record of Paleogene Sequences in the Penyu and Malay Basins, Offshore Peninsular Malaysia

“…The SCS, in geological terms, is an area of thinned continental crust overlain by Oligocene to Recent clastic and carbonate sequences, overlying areas of uplifted basement, and whereas its margin is characterized by a complex interaction of basin subsidence, erosion and uplift of mountain ranges (e.g., Kessler and Jong, 2016). Data points on the deeper Eocene-Oligocene sedimentary section of SCS are rare and derived from only a few oil and gas exploration wells located predominantly nearshore.…”

“…The unconformity was picked in Janglau-1 at 2860 mMDRT (Figures 6 and 7). It is perhaps the most prominent (regional) unconformity in the basin (e.g., Kessler and Jong, 2016;Morley, 2016), and appears to mark the shift from a predominantly clay-prone section (M sequence) to the younger sand-prone interval (L sequence). The section from M down to basement appears to be unusually hot, with elevated temperatures seen in Janglau-1 (182 0 C calculated at TD).…”