Geochemistry and depositional environment of black shale beds of the Belata Formation, Peninsular Malaysia.

Shale deposits from Belata Formation outcrops were examined geochemically and mineralogically to establish their paragenesis and, subsequently, to identify factors that govern their depositional environment. Fifty representative samples were examined through SEM/EDX, XRD and XRF. The findings show the mineralogical composition was abundant in quartz, with pyrite and calcite in trace amount. Zr–TiO2 bivariate diagram showed predominantly felsic and intermediate igneous rocks, suggesting that the shales may be coming from the hidden basement rocks of Peninsular Malaysia. The diagenetic controls on the geochemistry are suggested by the changes in compositional trends. The samples exhibit CIA values ranging from 62.2 to 80.2, and PIA values ranging from 65 to 100. According to the V/Ni, Ni/Co, and V/Cr ratios, these black shales were formed in a suboxic environment. Additionally, the high V/Ni ratios (1.47) point to a marine source for the organic content that gives the shales their dark color. The paleoclimate during deposition was interpreted to be semiarid to warm. The black shale samples are inferred to have originated from a passive margin tectonic setting that followed continental collision and rifting stages of the foreland basin development phase of Peninsular Malaysia based on geochemical proxies and associated diagrams. Highlights: A detailed mineralogical and geochemical composition study of the black shales reveal variations in the mineralogy and a common and local source rock (provenance). The source rock of the Belata black shales is inferred to be from igneous rocks with contribution from subordinate intermediate igneous rocks. Dimensionless parameters such as CIA, PIA and ICV calculations infers the black shales to be formed in a humid and warm environment. The tectonic settings of the Belata black shales are revealed to be of passive continental margin as compared to other shales in the Peninsular. Black shales are deposited in a suboxic to anoxic marine environment. [ABSTRACT FROM AUTHOR]