235 Paper 14 Stratigraphic framework and palaeoenvironment interpretation of PM303 and adjacent areas, North Malay Basin AzMI M. YAKZAN 1 , MAHANI MOHAMED 1 , M. RAPI M. SOM 1 , 001 CHIT MENG 2 AND.ANY! N GAU 2 1PETRONAS Research & Scientific Services Sdn. Bhd. (PRSS) Lots 3288 & 3289, Kawasan Institusi Bangi 43000 Kajang, Selangor 2Shell Exploration and Production Malaysia (SEPM) Sarawak Shell Berhad/Sabah Shell Petroleum Co. Ltd. 98100 Lutong, Sarawak, Malaysia The stratigraphic framework and depositional environments of PM303 and its adjacent areas were re-assessed using selected well and regional seismic data, as part of a PRSS-SEPM joint study of the North Malay Basin. This paper presents some of the preliminary results from the joint study. Seismic interpretation was made on multi-vintage 2D data acquired in 1993, 1996 and 1997. Biostratigraphic data were reviewed using multi-source data that were generated in the 1980s and 1990s. In addition, new biostratigraphic data from three wells were also included. The wells that were used in this study mostly penetrated the Groups AlB, D, E, F and H sediments in PM303. The older stratigraphic intervals were penetrated by several wells outside the block. Lower Group H sediments were deposited during late Early Miocene whilst the upper H was deposited during early Middle Miocene (Fig. 1). This is based on the occurrence of an intra-Group H, NN4INN5 nannofossil zone boundary, dated as 16.2 Ma. This conclusion has enabled the subdivision of Middle and Lower Miocene sections of Group H in the study area. The Group F sediments were deposited during Middle Miocene. This is based on the recognition of the NN5INN6 nannofossil zone boundary within upper Group F. The datum is dated as 13.5 Ma. Similarly, deposition of Group E sediments mostly occurred during the Middle Miocene, except for the uppermost part. Within upper Group E, the last consistent downhole occurrence ofthe regional palynological marker, Stenochlaenidites papuanus, which has been dated as 9.5 Ma elsewhere in this region, suggests that this interval and the overlying Group D sediments are within the Upper Miocene. The age of the overlying Group B ranges from late Upper Miocene to Pleistocene. The base of Group B is bounded by a tectonically-induced regional unconformity, which is estimated to be 7 Ma old. This conclusion is based on the occurrence of N17 planktonic foraminifera zone and NNll nannofossil zone, immediately above the unconformity. Within the study area, this unconformity represents about 1.5 Ma. These findings imply that the basal Group B Unconformity is an Upper Miocene event rather than Middle Miocene, as previously thought, and may be correlated to similar Late Miocene semi-regional unconformities in the West Natuna Basin, offshore Sabah and southern Vietnam. Depositional environments in the study area were interpreted using a model that was based on published materials and a modern analogue. By taking into account of the wide, ramp margin nature of the basin, a relatively broad and gently-sloping coastal plain was assumed. The coastal plain bears very distinctive vegetation belts and may be further differentiated on the basis of their microfossil content and lithologic characters. For example, the lower coastal Warta Geologi, Yolo 27, No.5, Sept-Oct 2001 Warta Geologi (Newsletter of the Geological Society of Malaysia), Vol. 27, No. 5, September-October 2001 Copyright © 2017 by Geological Society of Malaysia (GSM)