Petrographic criteria for the recognition of marine, syntaxial overgrowths, and their distribution in geologic time

Abstract

Syntaxial calcite overgrowths on echinoderm grains are a common cement type in ancient carbonate rocks. Most workers have interpreted these to be of meteoric diagenetic origin. Many originated, however, in the marine realm. Even when an initial marine overgrowth zone is present, it is common for later meteoric stages to make up a greater volume of this cement. Because marine overgrowths are often so thin, it is frequently difficult to sample for geochemical analysis. None the less, the initial marine overgrowths provided significant amounts of initial cement. We provide twelve petrographic criteria by which the marine parts of overgrowths can be recognized.