North Sound, Grand Cayman, contains up to 4 m of sediments that accumulated under the influence of the Holocene rise in sea level. Originally, North Sound was a dish-shaped depression formed by the erosion of the Miocene dolostone and Pleistocene limestone bedrock. At that time, a sill along the northern margin isolated the area from the open ocean. Sedimentation from ∼ 5,000 to 3,800 yr B.P., which took place in a fresh-water to brackish-water regime, resulted in deposition of the Composite Grain, Gastropod, and Bivalve facies. As sea level rose above the sill, no later than ∼ 2,500 yr B.P., marine waters began to invade North Sound and open connections with the Caribbean Sea were established. Peats, which developed in mangrove swamps, were deposited during this transitional phase. Fully marine sedimentation, ongoing for at least the last 2,500 years, resulted in the deposition of the Halimeda, Halimeda-Benthic Foraminifera-Bivalve, and Bivalve-Halimeda facies. Sediment, which accumulated at an average of ∼ 85 cm/1000 years, did not keep pace with sea level, which rose at an average of ∼ 160 cm/1000 years. As a result, accommodation space in North Sound has progressively increased.
A sea-level curve, derived from basal peats and bivalves found in the sediments of North Sound, is comparable to sea-level curves derived for Barbados reefs. For the last 2,500 years, however, the North Sound curve is ∼ 3 m lower than a sea-level curve that was derived from peats on Barkers Peninsula, which forms the northwest boundary of North Sound. This discrepancy, attributed to original differences in elevations of the samples, highlights some of the problems associated with the construction and interpretation of sea-level curves.
The sedimentary succession in North Sound, which is similar to that found in the Bight of Abaco in the Bahamas, is a record of transient depositional environments that evolved in response to the Holocene rise in sea level.