Abstract

Many of the subaerially exposed Pleistocene reef tracts on Barbados (West Indies) are mantled by secondary caliche profiles which range from thin, vaguely laminated surficial crusts to horizons two to three metres thick. On a regional scale there is a gradual transition from relatively well developed, laterally continuous caliche profiles in the more arid areas to a more karst-like topography in the high-rainfall regions. Major components of the caliche profiles consist of sediment inherited from the substrate on which the caliche has been superimposed, grains and matrix of diagenetic origin; carbonate cement exhibiting four distinct morphologies (micrite, equant and bladed spar, and elongate needle-fibre crystals), and pores of various origins. Fabrics common to many of the profiles include a micritic, often pelleted matrix, microscopic and macroscopic laminations, geopetal features of diagenetic origin, and complex cementation textures. Taken together, the components and fabrics are diagnostic of caliche and hence serve as criteria for the recognition of subaerial-exposure surfaces. The nature and complexity of the caliche profiles indicate that the near--surface subaerial environment is a highly variable one in which a number of processes must operate closely in time and space. In point of fact, at or near the rock-soil-air interface the diagenetic processes range from local dissolution and reprecipitation to micritization, recrystallization and brecciation. On a broader perspective, it is apparent that the initiation, evolution and thickness of the caliche profiles is controlled by the factors of climate, soil cover, substrate and time.

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