Holocene and Pleistocene Subaerial Crusts and Pisolites, Northern Barbados, West Indies: ABSTRACT

Abstract

Laminated calcareous crusts are present on most surface outcrops of Pleistocene limestone on northern Barbados and are similar to the caliche so common in areas with semiarid climate and a source of CaCO3. Crust development is most intense at the surface of relatively young, poorly lithified, commonly little diagenetically altered carbonates. The complete zone of alteration (irregular, hard calcareous bands alternating with soft, chalky carbonate) may extend to depths of 6 ft or more. Large amounts of salt spray, either wind blown or direct splash, also contribute CaCO3 to the system, resulting in the formation of thick crusts. When developed on poorly indurated carbonates, crusts are usually interbedded with pisolites. These pisolites are either laminated microcrystalline grains, formed in the process of limestone alteration or, where salt spray is heavy, coated skeletal grains. The Pleistocene section on northern Barbados includes a succession of transgressive reef complexes, unlike the generally regressive sequence on the rest of the island. Each episode of reef building is considered to represent a separate high stand of sea level during the late Pleistocene. Occurrence of fossil calcareous crusts and pisolites (similar to those forming on the surface today) between overlapping reef complexes in the transgressive sequence suggests a period of subaerial exposure and diagenesis between the formation of each successive reef complex. The presence of comparable calcareous crusts and pisolites, both Holocene and fossil, in other Pleistocene and some Paleozoic limestone successions indicates they are useful criteria for subaerial exposure. End_of_Article - Last_Page 345------------