LITHOSTRATIGRAPHY AND PALAEONTOLOGY OF THE ‘BLACK SHALE’ FACIES OF THE SEMANGGOL FORMATION (CHERT UNIT) AT BUKIT MERAH (PERAK, PENINSULAR MALAYSIA)

Abstract

In the Semanggol formation cropping out in Northern Perak, a ‘black shale’ facies was identified at the lowermost level of the chert unit at Bukit Merah, containing trace and body fossils. Despite some recent contributions made in Northern Perak outcrops, some questions about the origin of the ‘black shale’ facies remain open, particularly its depositional palaeoenvironment, palaeo-oxygenation history and biochronological age. Moreover, the presence of trace and body fossils in the facies contradicts ‘classical’ views of the ‘black shales’ of the Semanggol formation. Therefore, this study aims to describe the lithostratigraphic and palaeontological contents of the facies, as well as to apply sedimentological, palaeoichnological, petrographical and geochemical analyses for ascertaining the origin of it. The results revealed a shallow marine, sublittoral setting based on the identification of the Cruziana ichnofacies. The coarsening- and the thickening-upward trend observed in the studied stratigraphic section is compatible with a prograding, distal deltaic sequence. Two sources of additional oxygen are identifying as the episodic storm events and the presence of microbial mats, which frequently replenished the oxygen levels at the seafloor. Hence, the deposition occurred under relatively well-oxygenated conditions. Finally, the age of the succession is Early Triassic based on the presence of the bivalve genus Claraia.

Keywords

• cruziana ichnofacies
• palaeo-oxygenation
• body fossils
• sedimentological
• petrographical
• microbial mats