Structural and palynomorph evidence for Early Palaeogene‐Neogene conglomerate series in Peninsular Malaysia: Implication for basin development and tectonic history

Abstract

Rifting initiation and development in Western Sundaland is spectacularly synchronous and diffuse spatially, with only one exception, the Malay Peninsula that appears as a large crustal horst, weakly deformed and thus isolated from the presently offshore stretched crust. Cenozoic stratigraphic records are limited onshore, with only isolated conglomeratic series that are keys to integrating the Malay Peninsula in the regional chronology of events. This study focuses on the Lawin and Chenderoh conglomeratic series, located in the Perak Valley, Peninsular Malaysia, that were previously interpreted as Late Tertiary to Quaternary in age, albeit without proper basin analysis and/or geochronological data. Through a GIS-based kinematic analysis, we investigate the deformation affecting the basement rocks, while a field-based study and palynomorph analysis were used to constrain the tectonic framework at the time of deposition of each conglomeratic series. Our findings reveal that the Lawin alluvial fan was deposited during an episode of E-W extension controlled by a N-S normal fault. The fan evolved from debris flow to sheet flooding depositional stages. The palynomorph study suggests a burial from the Pliocene onwards (<5 Ma) but older series are suspected at depth. From the Oligocene Chenderoh shale unit, a Miocene age of the conglomeratic series is inferred. Chenderoh conglomerate is believed to have developed within pre-existing isolated depressions formed during regional transtensional events. Our study reveals that the Malay Peninsula was indeed affected by extension in the Late Palaeogene-Early Neogene, but with low rates of subsidence as compared to rapidly subsiding offshore basins.