In situ porosity and permeability of selected carbonate sediment: Great Bahama bank Part 2: Microfabric

Abstract Selected oolitic sediments from the Great Bahama Bank were studied to assess (1) the role of microfabric in determining porosity and permeability, and (2) particle packing relationships, i. e., grain support versus matrix support. Scanning electron microscopy and light microscopy revealed that the sediment consists of ooids, which are the major constituents of the sand‐size fraction, supported by a matrix composed predominantly of aragonite needles. The supporting matrix of aragonite needle clusters, which constitutes only about 10–20% of the total sediment dry weight, is the microstructural characteristic that increases the porosity and lowers the wet bulk density compared to a grain‐supported microfabric characteristic of clean sands. The presence of a fine‐grained matrix reduces the permeability of these sediments relative to clean sands. The influence of the microfabric is clearly reflected in the mass physical and depositional (particle packing) properties of the sediment. Laboratory values ...