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.

The first deposits overlying an unconformity may give important insights on the tectonic vertical motions and erosion processes that erased previous records. The Early Cenozoic Deposits in Peninsular Malaysia are reported to be isolated and lie unconformably on Paleozoic basement rocks. Denudation pulses from the Late Cretaceous to Eocene left the Cenozoic deposits in scarce. Stratigraphic and sedimentology studies were restricted to the availability of the resources. This study aims at providing information on the development of the early deposits from a structural perspective with the emphasis on source to sink dynamics. We interpreted the structural settings of Lawin using Digital Elevation Model (DEM) data and satellite images. Structural interpretations were cross-checked with published studies. Field observations were conducted and have been assessed through chemical and petrographic analyses. Evidence of compression and shearing are found to support interpretation. We learned that Lawin had experienced a compression and stages of extensions in its history and developed during extension. Lawin is associated to a major fault that reactivated several times, and from XRD analysis, we have illite-mica which has a close-relationship to a frequent tectonic activities and kaolinite is due to weathering. Petrography analysis were performed from SEM images and thin sections to support minerals found. Evidence of mineral fragments, iron-rich sedimentation and clay fillings were common with few kaolinite pouches. Sedimentology studies were modelled as alluvial fans. Based on DEM analysis, two different lobes are observed and on outcrop, two different angles of tilted bedding between the two lobes were measured, thus we modelled them as incised alluvial fans where the recent fan we see on DEM has extended further from abandoned lobe. Due to its tilting towards the west, we modelled them following an extensional regime.