Ancient coastal–shallow marine sedimentary rocks preserve a fragmented history of competing tidal, wave, storm and fluvial processes and changes in sedimentary environments, including the influence of variations in sea level, tectonics, climate and ocean circulation. To unravel these records, this study integrates detailed sedimentary analysis of outcrop and sub-surface data, palaeogeographic and palaeotectonic reconstructions, palaeo-ocean modelling and process-based analysis of modern depositional systems.
This approach was applied to the Miocene–Modern Baram Delta Province (BDP), which is one of several peripheral basins around the South China Sea (SCS). Here, the ancient and modern systems are intimately linked through close similarities in climate (humid-tropical), tectonic setting (active margin) and sedimentary environments. The main focus was on shoreline environments, which comprise two main groups: (1) mixed-process, wave-dominated, fluvial- and tide-influenced shelf to shelf-edge deltas/shorelines, and (2) coastal embayments with similar mixed-process bayhead deltas, shorelines and estuaries. The principal controls on ancient stratigraphic preservation and architecture along this active tectonic margin were (1) drainage basin switching, (2) high rates of sedimentation and accommodation space, and (3) a coastal-deltaic plain with multiple fluvial entry points.
The controls on tidal processes and preservation of tidal deposits, including ancient mangroves, are investigated for the Oligocene–Miocene around the SCS. Palaeotidal modelling results indicate that a regional-scale decrease in tidal energy during the Oligocene to present-day was a major control on coastal geomorphology, sediment dispersal, deposition, mangrove habitat and organic carbon (OC) burial during this period. Lithospheric storage of organic carbon (OC) in peripheral SCS basins during this period potentially exceeded 4000 Gt; this is equivalent to 2000 ppm of atmospheric CO2.