Sequence stratigraphy of mixed clastic-carbonate systems – a case example from the Eocene of Jamaica Ravidya Maharaj and Simon F. Mitchell Department of Geography and Geology, University of the West Indies, Mona, Kingston 7, Jamaica This paper was prepared for presentation at the GSTT 2000 SPE Conference held in Port of Spain, Trinidad 10-13 July 2000. This paper was selected for presentation by a Technical Committee following review of the information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by this Technical Committee and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Technical Committee, Geological Society of Trinidad & Tobago, Society of Petroleum Engineers, its officers, or members. Copies of papers should contain conspicuous acknowledgment of where and by whom the paper was presented. Abstract The Yellow Limestone Group (Eocene) in the Central Inlier of central Jamaica consists of two sedimentary cycles, each represented by a lower clastic division and an upper carbonate division. The lower cycle has a more restricted distribution than the upper cycle, erosion having locally removed it particularly in the south. Only the upper cycle is considered in detail here. The upper cycle can be divided into a lower clastic division (Guys Hill Formation) characterised by fluvial conglomerates and sandstones and restricted marine sandstones, heterolithics and mudrocks, and an upper carbonate division (Chapelton Formation) characterised by more open marine foraminiferal and molluscan wackestones, packstones and grainstones. Detailed mapping and logging have constrained the basin architecture, and four parasequences have been recognized within the Guys Hill Formation. Parasequences show a transition from fluvial dominated facies in the east to more open marine dominated facies in the west. Towards the western part of the basin, the marine flooding surface at the base of each parasequence is represented by thin shallow water limestones or fossiliferous lignitic shales, the latter having potential source rock characteristics. In this region, the upper part of the parasequences is represented by thick, clean-washed cross-bedded, ?tidally influenced arenites. Parasequences are stacked into a retrogradational parasequence set, which is attributed to the TST. To date, lowstand deposits have not been unequivocally recognized. The late TST and HST are characterised by carbonate deposition, and correspond to times of clastic starvation, related to relative sea level rise. The Yellow Limestone Group of central Jamaica can be used as a model for mixed carbonate-clastic depositional systems where clastics are restricted to the TST and carbonates to the HST. Introduction In the Central Inlier of Jamaica (Fig. 1), an Eocene sedimentary succession was deposited comprising two major cycles of mixed clastic-carbonate sediments, each represented by a lower clastic division and an upper carbonate division. The clastic division of the upper cycle is significantly thicker and better developed than in the lower cycle. This unit, although predominantly comprising clastic facies, also shows complex stacking associations with carbonate facies, and has therefore been selected as a case example to demonstrate the complex evolution of a mixed clastic-carbonate depositional system. Geological background The Central Inlier is the second largest inlier of Cretaceous rocks in Jamaica. Around the Cretaceous rocks the Eocene clastics and carbonate of the Yellow Limestone Group are extensively developed (Fig. 1). The Yellow Limestone Group in the Central Inlier has been recently discussed by Robinson and Mitchell (1999) and their terminology is used here. The Yellow Limestone Group (Robinson and Mitchell, 1999) of the Central Inlier (Fig. 1) comprises a early-middle to middle-Eocene sedimentary succession immediately overlying a succession of Cretaceous to ?late Paleocene volcaniclastic sediments. The sedimentary facies comprising the Yellow Limestone Group represent two major cycles of mixed clastic- carbonate deposition, and range from fluvial clastics to shallow marine impure carbonates. Each cycle is characterised by a lower clastic unit which grades into an upper carbonate division. The lower cycle has a more restricted distribution than the upper cycle, erosion having locally removed it particularly in the south and east of the inlier. The lower clastic unit (the Freemans Hall beds of Robinson, 1996) of the lower cycle is generally thin (estimated maximum thickness of 10 to 12 m). It is represented by a lower unit of fluvial conglomerates overlain by shelf sandstones and mudrocks. The succession is interpreted as an incised valley fill. The upper carbonate portion of the lower cycle is represented by the Stettin Formation (Robinson and Mitchell, 1999), which grades from thinly bedded silty foraminiferal marlstones through clean- washed cross-bedded carbonate grainstones, and finally into thickly bedded micritic mudstones and wackestones. The maximum thickness of the Stettin Formation is ~100 m in the north-western part of the inlier. The lower clastic division of the upper cycle consists of the Guys Hill Formation, which unconformably overlies the hard micrites of the Stettin Formation. The Guys Hill Formation is characterised by fluvial conglomerates and sandstones in the east and south, and a mixed a clastic- carbonate shelf succession in the west and north. The mixed clastic-carbonate succession comprises shallow