Sedimentology zyxwvutsrqpo (1983) zyxwvutsr 30, 235-247 zyxwvutsrq Eocene fan delta-submarine fan deposition in the Wagwater Trough, east-central Jamaica WILLIAM A. WESCOTT* and FRANK G. ETHRIDGEt *Amoco Production Company P.O. Box 3092, Houston, Texas 77253 and ?Department zyxwvu of Earth Resources, Colorado State University, Fort Collins, Colorado 80523, U.S.A. ABSTRACT The Wagwater Trough is a fault-bounded basin which cuts across east-central Jamaica. The basin formed during the late Palaeocene or early Eocene and the earliest sediments deposited in the trough were the Wagwater and Richmond formations of the Wagwater Group. These formations are composed of up to 7000 rn of conglomerates, sandstones, and shales. Six facies have been recognized in the Wagwater Group: Facies I-unfossiliferous massive conglomerates; Facies IILchannelized, non-marine conglomerates, sandstones, and shales; Facies 111-interbedded, fossiliferous conglomerates and sandstones; Facies IV- fossiliferous muddy conglomerates; Facies V-channelized, marine conglomerates, sandstones, and shales; and Facies VI-thin-bedded sheet sandstones and shales. The Wagwater and Richmond formations are interpreted as fan delta-submarine fan deposits. Facies associations suggest that humid-region fan deltas prograded into the basin from the adjacent highlands and discharged very coarse sediments on to a steep submarine slope. At the coast waves reworked the braided-fluvial deposits of the subaerial fan delta into coarse sand and gravel beaches. Sediments deposited on the delta-front slope were frequently remobilized and moved downslope as slumps, debris flows, and turbidity currents. At the slope-basin break submarine fans were deposited. The submarine fans are characterized by coarse inner and mid-fan deposits which grade laterally into thin bedded turbidites of the outer fan and basin floor. INTRODUCTION The Wagwater Trough is a fault-bounded basin containing lower Tertiary sedimentary and volcanic rocks which cuts across east-central Jamaica (Fig. 1). The lowermost Tertiary rocks in the basin are the lower Eocene (possibly Palaeocene?) Wagwater and Richmond formations. The Wagwater Formation is a sequence of red conglomerates, sandstones, and shales and the Richmond Formation is predominantly a flysch sequence of grey-brown sandstones and shales with conglomerates and minor amounts of limestones. Robinson et af. (1970) suggested that the depositional environment of the Wagwater Formation may be analogous to the modern Yallahs fan delta in south- 003770746/83/0400-0235 $02.00 zyxwvuts 0 1983 International Association of Sedimentologists eastern Jamaica. The Richmond Formation is gener- ally interpreted as a turbidite sequence with its conglomeratic facies deposited as submarine slides associated with a shelf edge (Matley, 1951 zy ; Burke & Robinson, 1965; Robinson, Lewis & Cant, 1970; Burke & Mann, 1980). Recent studies of modern fan-delta systems (McGowen, 1970; Boothroyd & Ashley, 1975; Booth- royd, 1976; Galloway, 1976; Ward, Stephen & Nummedal, 1976; Wescott & Ethridge, 1980, 1982) have resulted in criteria for recognition and interpre- tation of these previously little-studied depositional environments. Two major types of fan-deltas were recognized by Wescott & Ethridge (1980), those that prograde directly on to submarine slopes and those that are deposited on the margins of marine shelves. 235