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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The apparent confusion among geologists about the meaning of "diagenesis" probably arises from the fact that there is no universally accepted definition of the word. There seems to be agreement that "diagenesis" begins with, or immediately after, deposition of a sediment, but considerable disagreement arises as to when "diagenesis" ceases.
In this paper, diagenesis refers to the chemical and or physical processes that change the textural and mineralogical characteristics of a sediment. On the basis of a study of some of these characteristics, discernible mostly in thin sections, it is possible to establish reliable sequences of mineral deposition. For this paper, such sequences observed in some limestones and dolomites are shown by paragenetic diagrams, and textural relations on which the paragenetic diagrams are based are shown in photomicrographs.
From an established sequence of mineral deposition in a rock it should be possible to determine an orderly progression of the diagenetic reactions that have taken place. A simple illustration would be a crinoidal limestone in which calcite forms not only distinct overgrowths on the crinoid fragments but also a cement between the enlarged fragments. Basically, the paragenesis would be (1) calcite: crinoid and other fossil fragments, (2) calcite: overgrowths, and (3) calcite: cement. If the deposition of the three calcites is definitely successive (that is, if the deposition of one calcite is completed before the other begins), some geologists might consider that lithification was complete after deposition of calcite (2) and that diagenesis ceased at that time. However, if there is any verlap in time of deposition of the three calcites, especially of (2) and (3), it seems logical to assume that diagenesis and lithification both terminated at the end of deposition of calcite (3).
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