Abstract

"The diagenetic histories of some Mississippian calcilutites from England and Wales are considered in the light of fabric criteria. . . . It is concluded that calcite-mudstone was, at the time of its cementation, a mud of discrete calcite crystals, only slightly finer-grained than the present mosaic. Whether the crystals had earlier inverted from aragonite it is impossible at present to say. Calcite-siltstones seem to have had a similar history, and evidence for cementation of original calcite crystals is to be seen in some examples. Criteria are presented for the distinction of mudstone aggregates (Bahamite 'grains,' faecal pellets, etc.) from relics of calcite-mudstone remaining after grain growth. Distinction is based on a study in thin section of the shapes of the finer-grained areas and their distribution, and of the fabrics of the intervening coarser mosaics. The fabrics of pseudobreccia are described in detail and are shown to be the result of patchily developed grain growth."

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