Physical characteristics and distribution of bottom sediments from the Kelantan River Delta towards the South China Sea continental shelf, Malaysia

Abstract

The preponderance of sedimentological studies in the Kelantan River Delta onwards South China Sea shelf has led to a relatively good understanding on the sediments distribution and characteristics. The sediments of the area vary from very poorly sorted to very well sorted mixtures of sand, silt and clay and can be divided into three groups. Textural analysis of 65 surficial sediment samples showed that group 1 (silty) has a silt percentage of 65% to 85%, group 2 (silty sand) is dominated by sand ranging from 64% to 88% with the silt size varying between 12% to 23% and group 3 (sandy) is made up of 78% to 100% sand and 0% to 22% silt. Mineralogical analyses showed that the samples are dominated by polycrystalline sutured and straight boundary quartz as well as monocrystalline quartz. Small amounts of feldspar, mica and lithic fragments are present, while organic material is abundant. A semi-quantitative analysis of quartz grains surface texture and morphology was used to interpret the history of the grains. Six types of grains have been recognized; (a) irregular shape with various angles; (b) irregular surfaces with fractured plate and elongated fragments; (c) well rounded, with V marks, oriented etched pits on surface and protruding edges; (d) irregular breakage with rough texture on planar surface, adhering particles with uneven grooves and V marks with dimensions of <2μm; (e) irregular shape with rounded protruding edges, rough surface with oriented etched pits and V marks with dimensions of <2μm and adhering particles with trail of abrasion; and (f) very rough surface with irregular shape and protruding edges, abundant cracks and detachment of small particles and etching holes, V marks > 2μm dimension. In terms of distribution it can be divided into two sedimentological provinces according to the interrelationship between grain size, mineralogy, textural and morphology of sediment. Province A covers the shallower parts of the study area, which accumulated a large amount of silt and clay that possibly originated from the nearby land areas brought down by the Kelantan River and deposited as Recent sediments. Province B which covers most of the outer part of the shelf area, contains Recent and relict sediments with lesser amounts of inland sediment input. The relict sediments consist of oceanic sub-arkosic sand, which was deposited circa 5000 yr. BP during the mid Holocene relative sea-level low stand.