Packstone
“Grain-supported limestone with a muddy matrix”
Packstone is a carbonate rock where the grains — shells, ooids, peloids — are touching and supporting each other, but lime mud (micrite) fills the remaining spaces between them. This texture indicates moderate energy environments where grains accumulated faster than mud could be winnowed away.
calcite grains (bioclasts, ooids, peloids), micrite matrix, sparry calcite cement (partial), foraminifera, dolomite (if altered)
Persian Gulf (modern), Bahamas platform margins, Permian Basin (Texas, USA), North Sea subsurface, Jurassic platforms (Europe)
3-4
Packstone reservoirs in the Middle East hold enormous oil and gas reserves — the combination of grain-supported framework and partially muddy matrix creates moderate porosity and permeability ideal for hydrocarbon accumulation.
Test Your Knowledge
In the Dunham classification of carbonate rocks, what distinguishes packstone from wackestone?
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