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The Talang Akar Formation is a middle Eocene to early Miocene, orerall transgressivc succession of interbedded sandstones, siltstone, shales, coals, and limestones. It is the second leading productive interval in ARCOs Offshore Northwest Java (ONWJ) Production Sharing Contract (PSC) area. The total thickness of the Talang Akar ranges from 500 ft. to 5000 ft. with an average thickness of 2000 ft. A total of nine, regionally correlative, fine-grained, transgressive intervals were recognized on well logs, cores, biostratigraphic, and seismic data within the Talang Akar Formation in the Ardjuna Basin. These surfaces form the basis for a nex, chronostratigraphicbased, stratigraphic framework developed by using integrated scquence stratigraphic techniques. This paper focuses on the nature of the surfaces defined by sequence stratigraphic analysis of over 3400 ft. of conventional cores from 37 wells, tied to w d l logs, and correlated basin-wide on seismic data.The Talang Akar Formation is subdivided into two members: the predominantl\- non-marine Lower Talang Akar, and the fiuvialideltaiclmarine Upper Talang Akar. Two regional markers are defined within the Lower Talang Akar, five within the Upper Talang Akar, and one each define the boundary between the Lolyer and Upper Talang Akar and between the Upper TalaIig Akar and the overlying Batu Raja Formation. Within the middle Eocene to early Oligocene syn-rift Lower Talang Akar section: the t\vo transgressi-ie intervals are comprised of thick (50 ft.) lacustrine mudstones xvithin massive alluvial plain/fluvial sandstones ih siltstones and paleosols. These fine-grained intehals are interpreted to have been deposited within structural lows on a relatively flat and marshy coastal plain. Palynology data show the presence of black-mangrove taxa, and the presence of minor dinoflagelattes suggest minor marine influence. These are easily identified on well logs by their low sonic velocity, hence the names “Low Sonic Zones.Of the seven remaining transgressive intervals, the lowennost are typically comprised of a 50-100 ft thick interval of interbedded paleosols, lacustrine siltstones and shales, and backswamp coals. This interval denotes a change in overall basin style with the first introduction of true rooted coals. These environments might represent the continental expression of a rapid marine transgression: freshwater ponds may have developed as rising sea level rapidly raised the “baselevel of the fluvial system.The transgressive intervals within the Upper Talang Akar all have evidence of marine influence with the relative amount of marineness increasing upward in the stratigraphic section. In a basinward position, the transgressive intervals are comprised of argillaceous carbonate stringers (foraminifera1 pack-wackestone) within a 50-100 ft. thick marine shale. In a landward position, these intervals are typically comprised of rooted (insitu) delta plain coal beds and carbonaceous shales and siltstones.The lower intervals, within the rift-related Lower Talang Akar member, are likely tectonic related, formed during times of active fault movement. However, a possible eustatic origin or eustatic influence of these events cannot be dismissed. The transgressive intervals identified within the post-rift Upper Talang Akar are likely related to relative sealcvel fluctuations, possibly eustatic in origin, but due to the active nature of faults within this rift system, thcy may also have a tectonic component.