Geochemical characterization of beach sediments of the NW Borneo, SE Asia: Implications on provenance, weathering intensity and assessment of coastal environmental status

Abstract

The bulk chemistry of coastal sediments is governed by the geochemical nature of the river basin, the physical and chemical processes involved during weathering, and transportation of these sediments to the coastal zone and the post-depositional diagenetic alterations. The geochemical study of coastal sediments helps to assess heavy metal contamination and risk of toxicity to coastal ecosystems, and thus, is often considered important in coastal zone management. The hydrocarbon-rich, thickly populated and industrialized city of Miri and its coastal region are among the rapidly developing urban-economic-industrial, yet ecologically fragile regions of Sarawak State in Malaysia. The coastal regions of Miri consist of sandy and rocky beaches with natural erosional features such as cliffs, sea caves, arches, sea stacks, and so forth. Three major rivers confluence into the South China Sea near Miri: (1) the Baram River (NE part), (2) the Miri River (SW part), and (3) the Sibuti River (further SW from the SW part). The study described in this chapter reports on the bulk geochemistry (major, trace, and rare earth elements) of the beach sediments to interpret source rock weathering, provenance, and the environmental significance of selected trace elements. The beach sediments are medium to fine grained sand in the NE part, and very fine sand-mud in the SW part. The bulk chemistry of the sediments is controlled by the source rock lithology (via. rivers), with additional input of selected elements by the geological processes and anthropogenic input. The beach sediments show Chemical Index of Alteration (CIA) values of 68 and 67 for SW and NE, respectively, suggestive of moderate intensity of weathering. The domination of recycling effects, more so than weathering intensity over the geochemistry of studied samples, as shown explicitly in the CIA/WIP ratio and Zr enrichment, is observed. However, selected samples from the NE part show a higher content of Zr concentration due to the addition of zircon minerals by the sorting process. Localized enrichments of a few elements, namely, Zr, Hf, Cu, and Zn, due to natural processes and anthropogenic input (Pb), are also observed. The SW part sediments are moderately to highly contaminated by Cu, Zn, and As; whereas NE part sediments are low to moderately contaminated by Cu, Zn, Cr, and Sn. The biological effect of trace metals linked to Cu and possibly to As are interpreted. These inferences are also supported by morphological deformities of microorganisms, such as foraminifera and ostracoda.