Seismic stratigraphy of Discovery Bay, Jamaica

Abstract

High resolution seismic reflection profiling within Discovery Bay, Jamaica has revealed that this 54 m deep, subcircular, reef-protected coastal basin has over 100 m of relief. Partially buried reefal structures at a water depth of −40 m indicate a past sea-level stillstand. In addition, side scan sonar reveals that the slopes leading down into the basin from these upper reefs are nearly acoustically featureless indicating little downslope movement by reefal debris and no slope failure. The basin center is dominated by a 15 m thick upper sequence of mollusk-rich carbonate mud which has accumulated at a rate of 1600 mm 1000 yrs for the past 9000 yrs based upon 14C dates. The total 50 m of basinal infilling consists of two primary sequences both approximately of the same thickness. Without very long cores (> 15 m) we can only speculate on basin infilling history. The deepest subsurface portion of the basin lies on line with a fault-controlled, dry valley and a pronounced change in the seaward reef trend. The north coast of Jamaica consists of a terraced, limestone coastal plain. We propose that Discovery Bay initially formed by dissolution from calcite-undersaturated groundwaters focused along this fault. A reefal barrier rim developed and sealed off this depression from the open Caribbean Sea sometime during the Pleistocene. A similar coastal depression, Rio Bueno, lies just to the west of Discovery Bay, but remained open probably due to continued freshwater influx which retarded reef growth during lowstands throughout the late Neogene and Quaternary.