Post-burial sideritisation of calcite in Eocene beds from the Maracaibo Basin, Venezuela

Summary

Core material from carbonate cemented sandstones of Eocene age from the Maracaibo Basin, Venezuela, exhibits evidence of post-burial sideritisation of calcite. the process being identical in its essentials with dolomitisation. and resulting in a marked increase in porosity and permeability of the cemented sandstones. As a result of this increase, sub-surface waters have been able to leach out much of the sideritc cement, and subsequent mechanical compaction of the sandstones has produced a characteristic “bead”-like arrangement of remnant sideritc granules around the sand grains. The whole process can be reconstructed from thin-sections, and these are used to illustrate the text.