Paleozoic limestone of the Kinta Valley: Paleogeography and implications to the regional geology of Peninsular Malaysia

A number of isolated limestone hills showing prominent karstic feature cover an area of about 200km2, over a 1,200 km2 area in the Kinta Valley. It overlies extensive younger granite bodies, which have affected the texture and composition of the limestone through contact metamorphism at the time of granite emplacement. The limestone hills are the remnants of limestone beds, presumed to be Paleozoic (Ordovician to Permian) in age, that have been severely eroded and karstified. The distribution of diagnostic fossils suggests that the youngest lie to the southwest and the oldest to the northeast. Most of the limestone hills have a similar, tower-like morphology, with steep flanks and a rounded or flat top, which is the result of karstification (limestone dissolution by fresh water) in a wet and humid, tropical climate. Several of these hills are exposed to being deteriorated by exogenic processes or due to human activities, such as quarried out for cement and marble factories. Alluvium covered limestone is intermittently and temporarily exposed and reported in the workings of the hydraulic open-cast tin mines. Stratigraphically, the carbonaceous limestone, dolomite and black shale of Carboniferous age are interbedded with carbonaceous shale up to 3000m (?) thick, which has estimated by the previous researcher. However, the detail sequence and thickness will be studied in a later time. Again, the sequence is certainly strongly folded and faulted. Metamorphism is the most crucial geological phenomena and an initial observation reveals that the degree of metamorphism of the limestone varies from hill to hill, from low to high. The degree of metamorphism appears to be, in places, somewhat anomalous with some intact (non-metamorphosed) limestone outcrops rest directly on top of granite. The relative position of the granite intrusions will be investigated through geophysical methods (gravity and magnetic survey). These two steps will lead to modeling the structural setting of the Kinta Valley and investigating the anomaly in the distribution of degree of limestone metamorphism. From the sedimentary facies, paleogeography, structural history and regional correlation, Kinta Valley can be speculated to a new potential hydrocarbon play. In early 1970’s the pre-Tertiery carbonate play was tested at three localities on the off-shore of Peninsular Malaysia at Sotong and Bunga Raya structures. These dry wells penetrated between 8 to 492m of limestone formation. To date, the only new play type that proved to be successful was the fractured basement play after the discovery of Anding Utara in 2005. Based on onshore regional data, the shallow marine sequences (Lower Carboniferous to Upper Triassic) cover most of the Sunda Shelf area in Peninsular Malaysia, Thailand and Indochina. Deep burial diagenesis of the reservoirs and its proximity to basement mass is believed to enhance the reservoir secondary porosity through dolomitization and dissolution.