Diagenetic Fabrics in Biosparites from the Pleistocene of Barbados, West Indies

Abstract

ABSTRACT In recent years much attention has been given to the study of Recent depositional environments of carbonate sediments. If we are to truly understand the origin of carbonate rocks it is equally important that we study diagenetic environments, for many carbonate rocks are as much the product of diagenesis, as they are the product of deposition This paper presents some preliminary results coming out of a continuing study of diagenesis and diagenetic environments in the coral cap of Barbados, West Indies. The purpose of the paper is to call attention to the diagenetic fabrics observed in these samples whose diagenetic history is well known, to point out the possible environments in which these modifications may have occurred, and to suggest the possibility of distinguishing the environmen in which various fabrics developed on the basis of petrographic inference. Cementation fabrics observed in these rocks include monocrystal syntaxial overgrowths on echinoderm foundations; polycrystalline syntaxial overgrowths on radial hyaline Formainifera; and crusts on porcelaneous Foraminifera, coralline algae, fine-grain carbonate rock fragments, and on grains and secondary voids possessing well developed micrite envelopes. Three types of secondary porosity observed are as follows: moldic after grains with well developed micrite envelopes, moldic after grains lacking micrite envelopes, and larger scale solution vugs. Petrographic evidence exists for post-depositional mechanical rearrangement of particles in some samples. All diagenetic modifications noted occurred in the marine environment, in the fresh water vadose zone, or in some environment intermediate between these two. Petrographic criteria may allow more specific inference as to which modification occurred in which environment.