Situated at tropical latitudes with a humid paleoclimate, the area of the present-day Indonesian archipelago was very suitable for production and accumulation of carbonate sediment during much of the Cenozoic. Following early Paleogene rifting that resulted in development of horst and graben structures, the peak of carbonate production occurred from the late Oligocene to Mio–Pliocene. This paper summarizes several Indonesian isolated carbonate platforms that formed on marine horsts. Of these examples, Banyu Urip in Java, Kerendan in Kalimantan, and Arun Field in Sumatra have provided important contributions to Indonesian oil and gas production for the last few decades, whereas Natuna D-Alpha in the Natuna Sea will become a giant gas field in the future. To achieve the objective of characterizing Cenozoic carbonate platform reservoirs of Indonesia, this study reviews the Cenozoic carbonates in the East Java Basin, Kutei Basin, North Sumatra Basin, and Natuna area and places them in the context of the regional geology of Sundaland. Insights from previously published work are supplemented by new descriptions of cores, well-log analyses, and interpretations of two- and three-dimensional seismic facies analysis, well-log correlation, and sequence stratigraphy. These geological and geophysical data have been integrated with dynamic reservoir data to validate the geological and geophysical interpretations. The results reveal that the Indonesian carbonates of Banyu Urip, Kerendan, Arun, and Natuna D-Alpha are classic isolated carbonate platforms and can serve as examples to recognize reservoir character. Those platforms developed in the same general regional geologic setting relative to the Sundaland continent and share certain similarities, but local geologic variations and distinct processes gave each platform particular characteristics. Reservoir quality of the carbonate platforms is influenced by relative changes in sea level, the position relative to the shoreline or fully open-marine settings, and the influences of both regional and local tectonic events. The fields thus illustrate several conceptual models of carbonate reservoirs in isolated platforms. Understanding the character and variety of Indonesian reservoirs as related to their depositional processes and regional position provides insights for exploration and reservoir management of analogs elsewhere.

Abstract Recent work has applied microtextural and heavy mineral analyses to sandy storm and tsunami deposits from Portugal, Scotland, Indonesia and the USA. We looked at the interpretation of microtextural imagery (scanning electron microscopy) of quartz grains and heavy mineral compositions. We consider inundation events of different chronologies and sources (the AD 1755 Lisbon and 2004 Indian Ocean tsunamis, the Great Storm of 11 January 2005 in Scotland, and Hurricane Sandy in 2012) that affected contrasting coastal and hinterland settings with different regional oceanographic conditions. Storm and tsunami deposits were examined along with potential source sediments (alluvial, beach, dune and nearshore sediments) to determine provenance. Results suggest that tsunami deposits typically exhibit a significant spatial variation in grain sizes, microtextures and heavy minerals. Storm deposits show less variability, especially in vertical profiles. Tsunami and storm quartz grains had more percussion marks and fresh surfaces compared to potential source material. Moreover, in the studied cases, tsunami samples had fewer fresh surfaces than storm deposits. Heavy mineral assemblages are typically site-specific. The concentration of heavy minerals decreases upwards in tsunamigenic units, whereas storm sediments show cyclic concentrations of heavy minerals, reflected in the laminations observed macroscopically in the deposits.

Abstract: The rift basins of Thailand exhibit remarkable diversity of fault displacement patterns, fault length–displacement characteristics and mapped fault patterns during late rift, and post-rift, stages. These patterns reflect influences by: (1) zones of strength anisotropy in the pre-rift basement; (2) syn-rift fault patterns on post-rift faults; (3) spatial stress deflection, commonly related to irregularities in major fault profiles, and the basement–sediment interface; (4) temporal stress rotation, usually related to changes in the regional plate setting; and (5) varying strength properties (strain hardening or softening) of fault zones during their life. These influences created strongly segmented boundary faults, and long, low-displacement post-rift fault trends. The former are commonly strongly over-displaced, while the latter can be strongly under-displaced with respect to their length compared with typical length:displacement distributions. Seismic interpretation of multi-rift fault patterns requires 3D data to identify the complexities, otherwise the linkage pattern between deeper and shallower faults, and the changing fault strike-directions with depth, may be incorrectly mapped. Incorrect identification of fault patterns as breached relay structures may also arise. Oblique extension, the influence of pre-existing trends and stress rotation in multi-phase rifts provides a more comprehensive explanation for the observed features than the strike-slip interpretation of previous studies.

Abstract The Andaman Sea is proposed to have developed from a margin where Palaeogene back-arc collapse closed a mid-Cretaceous back-arc oceanic basin, and resulted in the collision between island arc crust to the west and the western margin of Sundaland. Subsequent east–west to WNW–ESE extension during the Late Eocene–Oligocene resulted in highly extended continental crust underlying the Alcock and Sewell rises, and the East Andaman Basin, and moderately extended crust in the Megui–North Sumatra Basin. As India coupled with western Myanmar, the margin became dominated by dextral strike-slip and NNW–SSE transtensional deformation during the Miocene. The narrow belt of NNW–SSE-directed extension is proposed to have focused on the region where ductile middle crust remained following Late Eocene–Oligocene extension, whereas strike-slip faults are located in the regions of necking where ductile middle crust was considerably thinned by Late Eocene–Oligocene extension. The last phase of NNW–SSE-extension switched between probable Late Miocene–Early Pliocene seafloor spreading, and extension (by dyke intrusion and faulting) in the Alcock and Sewell rises, and then recently back to the spreading centre.