Stratigraphy and Palaeoichnology of “Black Shale” Facies: Chert Unit of the Semanggol Formation, Perak

Abstract

The exposed area of Bukit Putus, one of the Semanggol abandoned quarries in Bukit Merah (NNW of Taiping, Perak, Peninsular Malaysia) has allowed us to start a detailed study of the “black shales” of the chert unit of the Semanggol Formation. Presently, no integrated palaeoichnological-stratigraphical studies have ever been performed in the Semanggol Formation. The chert unit in particular is claimed to have been deposited in a deep oceanic basin under the influence of different regimes of transportation (Basir Jasin and Zaiton Harun [2]). The analysis conducted herein aims to reconstruct the palaeoenvironmental evolution, contrasting with previous interpretations. Description of sedimentary facies and facies associations was done at the main outcrop. Samples collected have been studied through thin sections, total organic content (TOC) analysis, scanning electron microscope (SEM)–EDX, and photography and image enhancement. As a result, palaeontological and sedimentological data indicate that as far as the “black shale” facies is concerned, the basin evolved from mid-distal continental shelf settings into shallower sublittoral conditions. The general evolution is compatible with the dynamics of a deltaic apparatus prograding seawards (prodelta facies evolving into lower delta front ones). At the outcrop of the Bukit Putus quarry, several levels bearing abundant specimens of Claraia sp.—an Early Triassic pectinid bivalve—have been found. Questionable brachiopods of the order Lingulida also seem to be present. In short, results from the integration of stratigraphical and paleoichnological data support the palaeoenvironmental conclusions obtained in this study.