Publication Date : 2016-01-01
Author : Collins, D. S., Johnson, H. D., Allison, P. A., Guilpain, P., & Damit, A. R.
Countries :
Disaster Management Theme :
Disaster Type : Flood
Document Type : Research Paper
Languange : en
Link : http://onlinelibrary.wiley.com/doi/10.1111/sed.12316/pdf
Abstact :
The Miocene to Modern Baram Delta Province is a highly ef?cient source to sink system that has accumulated 9 to 12 km of coastal–deltaic to shelf sediments over the past 15 Myr. Facies analysis based on ca 1 km of total vertical outcrop stratigraphy, combined with subsurface geology and sedimentary processes in the present-day Baram Delta Province, suggests a ‘storm-?ood’ depositional model comprising two distinct periods: (i) fair-weather periods are dominated by alongshore sediment reworking and coastal sand accumulation; and (ii) monsoon-driven storm periods are characterized by increased wave-energy and offshore-directed downwelling storm ?ow that occur simultaneously with peak ?uvial discharge caused by storm precipitation (‘storm-?oods’). The modern equivalent environment has the following characteristics: (i) humid-tropical monsoonal climate; (ii) narrow (ca <100 km) and steep (ca 1°), densely vegetated, coastal plain; (iii) deep tropical weathering of a mudstone-dominated hinterland; (iv) multiple independent, small to moderate-sized (102 to 105 km2) drainage basins; (v) predominance of river-mouth bypassing; and (vi) supply-dominated shelf. The ancient, proximal part of this system (the onshore Belait Formation) is dominated by strongly cyclical sandier-upward successions (metre to decametre-scale) comprising (from bottom to top): (i) ?nely laminated mudstone with millimetre-scale silty laminae; (ii) heterolithic sandstone–mudstone alternations (centimetre to metre-scale); and (iii) sharp-based, swaley cross-strati?ed sandstone beds and bedsets (metre to decimetre-scale). Gutter casts (decimetre to metre-scale) are widespread, they are ?lled with swaley cross-strati?ed sandstone and their long axes are oriented perpendicular to the palaeoshoreline. The gutter casts and other associated waning-?ow event beds suggest that erosion and deposition was controlled by high-energy, offshoredirected, oscillatory-dominated, sediment-laden combined ?ows within a shoreface to delta front setting. The presence of multiple river mouths and exceptionally high rates of accommodation creation (characteristic of the Neogene to Recent Baram Delta Province; up to 3000 m Ma1), in a ‘storm?ood’-dominated environment, resulted in a highly ef?cient and effective offshore-directed sediment transport system.
