Carbonate-siliciclastic Facies Transition and Reef Growth on the Northeast Coast of Barbados, West Indies

Abstract

ABSTRACT On most of the insular shelf around Barbados, carbonate sediments are now accumulating from the growth of reefs, the contributions of the skeletons of carbonate-secreting organisms, and the erosion of the Pleistocene coral cap that covers six-sevenths of the island. However, after heavy rains, water laden with siliciclastic sediment eroded from the Scotland district (where the coral cap is breached) is discharged from four main rivers onto the northeast coast insular shelf. The coarse-grained material is transported as bedload onto an offshore sand ramp, over the shelf break into deeper water, or is incorporated into adjacent beaches. The fine-grained sediment is directed northward along the shore within a sediment plume by the equatorial current. Fine sediment settling out of the plu e is deposited on a spur and groove system and reefs growing on a deeper-water platform north of the sand ramp. Nearshore, the transition from the siliciclastic sediments to carbonate sediments is located on a submerged barrier reef at the seaward margin of a shallow-water platform. The facies transition on the deeper-water platform is gradual near the southern edge of the deeper-water reefs. Distribution of benthic biota and the growth of reefs are controlled by a combination of siliciclastic influx and shelf floor topography. The deeper-water reefs grow despite the periodic blanketing by fine siliciclastic sediment settling from the sediment plume that accumulates around them.