The paleogeography of the juxtaposed Southeast Asian terranes, derived from the northeastern margins of Gondwana during the Carboniferous to Triassic, resulted in complex basin evolution with massive carbonate deposition on the margins of the Paleo-Tethys. Due to the inherited structural and tectonothermal complexities, discovery of diagnostic microfossils from these carbonates has been problematic. This is particularly the case for the Kinta Limestone, a massive Paleozoic carbonate succession that covers most of the Kinta Valley in the central part of the Western Belt of Peninsular Malaysia. Owing to the complex structural and igneous events, as well as extensive diagenetic alterations, establishing precise age constraints for these carbonates has been challenging. Furthermore, the sedimentation history of these deposits has been masked. Three boreholes, totaling 360 m thickness of core, were drilled at either end of the Kinta Valley on a north-south transect through sections with minimal thermal alteration. The sections are composed chiefly of carbonaceous carbonate mudstone with shale and siltstones beds, in which the carbonates were sampled for microfossils. Five hundred conodont elements were extracted. Nine diagnostic conodont genera and 28 age diagnostic conodont species were identified. The identification of Pseudopolygnathus triangulus triangulus and Declinognathodus noduliferus noduliferus indicated that the successions ranged from Upper Devonian to upper Carboniferous. Further analysis and establishment of stage-level datum that range from the Famennian to Bashkirian (Late Carboniferous) enabled detection of continuous sedimentation and improved age constraints in undated sections of the Kinta Limestone. This higher-resolution conodont biostratigraphy suggests a prevalence of continuous carbonate deposition during the Early Devonian to Late Carboniferous in the Paleo-Tethys. Thus, the identification of diagnostic conodont species for the first time from subsurface data in the area has helped improve the biostratigraphic resolution and establishes depositional continuity of the Kinta Limestone. These data could provide clues to the Paleo-Tethys paleogeographic reconstruction and paleodepositional conditions, and could establish higher temporal resolution correlation than previously attempted.

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Higher-resolution biostratigraphy for the Kinta Limestone and an implication for continuous sedimentation in the Paleo-Tethys, Western Belt of Peninsular Malaysia

Following the successful production from fractured basement in similar Tertiary basins, the basement play was pursued in the Malay Basin, particularly during the 2000-2010 period but, unfortunately, that effort fell short of expectations. The only oil discovery in fractured basement reservoir was Anding in the southwestern part of the basin. Despite its development being delayed due to economic reasons, the Anding discovery had been the basis for the basement play concept: namely, a fractured reservoir formed of pre-Tertiary metamorphic rock, charged from overlying Tertiary lacustrine source rocks in an adjacent half-graben and sealed by a transgressive shale unit. This paper examines seismic, gravity and well evidences on the pre-Tertiary basement geology, with the aim of assessing further the hydrocarbon potential of pre-Tertiary basement. The pre-Tertiary basement subcrops beneath the Malay and Penyu basins represent a continuation of the onshore geology of Sundaland Mesozoic terrane. Wells that penetrate the Base-Tertiary Unconformity (BTU) indicate a variety of rock types including igneous, metamorphic and sedimentary. Seismic data show the widespread presence of layered rocks beneath the BTU which could include potential new plays. Gravity modelling was carried out to help distinguish between pre-Tertiary layered rocks and Tertiary synrift sediments. Fractured reservoirs, like those discovered at Anding, seem to be associated with major strike-slip fault zones which are identifiable on high-quality seismic. Carbonate structures such as paleokarsts and buried hills are also recognisable and could potentially be mapped with seismic. These pre-Tertiary plays also rely on hydrocarbon charge mainly from the overlying Tertiary source rocks. Although Palaeozoic-Mesozoic source rocks may have passed their hydrocarbon generation stage, their gas potential cannot be ruled out.

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Pre-Tertiary Basement Subcrops Beneath The Malay And Penyu Basins, Offshore Peninsular Malaysia: Their Recognition And Hydrocarbon Potential

Abstract Study of secondary dolomitization and documentation of the evolution of basinal fluids and host rock, especially that of fine-grained deepwater carbonate mudstone are of interest toward of reservoir characterization. From this perspective, field characteristics in relation to mineralogy, petrography and geochemistry of the Paleaozoic carbonates of the Kinta Valley, Peninsular Malaysia, were investigated and documented. A total of 33 samples were collected across the various degree of dolomitization and analyzed for their petrographic properties ( n = 55), while mineralogical and geochemical compositions ( n = 33) were analyzed using XRD, ICP and ICPMS analysis, respectively. These analyses were performed to elucidate the diagenetic events, episodic dolomitization and development of fluid evolution as a function of regional tectono-thermal events during the Permian to Cenozoic. It is interpreted that the host calcareous mudstones (HCMs) were deposited in oxygenated, open marine seawaters. The studied samples retain the original seawater characteristics despite negligible, minor alterations of REE characteristics due to diagenesis and detrital input. Though the concentrations and trends of REEs of the dolomitic facies are modified to a certain extent, their affinities with HCMs are preserved. Enrichments of Mg, Mn, Na and depletion of Sr are linked to the effect of dolomitization under the open system of diagenesis. The redox conditions fluctuated to show distinct, recognizable variations between different dolomite phases. The MREE enrichments with other trace elements such as Mn, Fe and low Sr content indicate the association of diagenetic fluids with deep-circulating crustal hydrothermal fluids. Hydrothermal influence has been recorded along the fractures, which might have originated from the sub-surface litho units and facilitated episodic dolomitization, especially during significant tectono-thermal events. This study affirms that the occurrence, geochemical and mineralogical evolution of the dolomites of the Kinta Valley were controlled by magmatic events, whereas the intensity of replacement dolomitization was controlled by host rock texture, varied bulk chemistry of host rock, circulating fluid and temperature. 

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Geochemical evolution of structure-bedding controlled hydrothermal dolomites of the Kinta Valley, Western Malaysia

Slump structures may be created by submarine sediment slides with a rotational mode of failure. The limestone hills in Sg. Siput display impressive slump structures, especially in the upper section of a sequence exposed in an abandoned quarry, near Bt. Kemuning, NW of the town of Sg Siput. The sequence is mainly dominated by thinly laminated dark grey mudstone to wackestone with occasional turbidite beds and is part of the Kinta Valley limestones which are relicts of thick Paleozoic carbonate
deposits, mainly Carboniferous to Permian in age. Intense slumping is mainly observed in the upper part of the section, where it is enhanced by thin beds of light grey chert and of dark grey to black shaley limestone, interbedded with medium-grey micritic limestone.

Impressive Slump Structures in Permo-Carboniferous Limestone at Sg. Siput, Perak, Malaysia

To define reservoir geometry, scale, pore networks, and spatial complexities for purposes of exploration and development, near-surface histories of karst features and their later burial modifications must be understood (Loucks, 1999).

Mapping the Kinta Valley Karst System, Peninsular Malaysia: Implications for Better Insight of Subsurface Karst Features

The limestone hills of the Kinta Valley are remnants of extensive limestone beds, which are part of a Paleozoic carbonate complex that covered large parts of South-East Asia and south China. The original limestone beds of the Kinta Valley, presumed to be Carboniferous (Ingham & Bradford, 1960; Hutchison, 2007) or possibly Permian in age (Fontaine, 1995), have been severely eroded and karstified (Figure 1).

W. S. Chow

Papers

Impressive Slump Structures in Permo-Carboniferous Limestone at Sg. Siput, Perak, Malaysia

Mapping the Kinta Valley Karst System, Peninsular Malaysia: Implications for Better Insight of Subsurface Karst Features

Sedimentology of the Palaeozoic Limestone of the Kinta Valley, Malaysia