Packstone

The Dunham classification system for carbonate sedimentary rocks was devised by Robert J. Dunham in 1962, and refined by Embry and Klovan in 1971 to include sediments that were organically bound during deposition.

Robert J. Dunham published his classification system for limestone in 1962. His scheme focuses on the depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are essentially for rock families. His efforts deal with the question of whether or not the grains were originally in mutual contact; and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk classification scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is more useful for hand samples because it is based on texture and not the grains in the sample.

The classification is a way of describing the composition of calcareous rocks in hand sample. For descriptions detailing the textural components of sediments and sedimentary rocks, as in thin section, the Folk classification is generally preferred - both are equally valid methods of classification with different emphases.

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