Eogenetic and telogenetic cementation of sandstones

Abstract

The present study concentrates on a major problem in many sedimentological studies, the prediction of Dorosity and permeability properties of sandstone unit in the subsurface: i.e., the destruction, preservation, and enhancement of porosity and permeability in subsequent diagenetic stages. Porosity and permeability properties of a sandstone, are, above all, related to cementation and thus to the factors controlling cementation. In addition, compaction is an important, usually complementary, process. It is governed by the clastic composition of the sediment and by the timing of cementation. Cementation usually retards or even stops compaction. Cementation is the main cause of porosity reduction in sandstones, especially in sandstones composed of rigid grains. Calcite and quartz commonly are the most important cementing minerals (Blatt, 1979). Calcite frequently constitutes the main or exclusive cement mineral in marine sandstones. In addition, quartz can be important in continental and mixed marine-continental settings. For any substantial cementation, many volumes of interstitial water have to percolate through the sediment in order to supply the materials needed (e.g., Blatt, 1979). With increasing burial depth, the permeability of most sandstones decreases through compaction, through authigenesis or replacement and, of course, also by cementation. Unless dissolution occurs, the flow of interstitial solutions thus becomes progressively inhibited, and the time needed for cementation by chemicals introduced from outside the pertinent sand body increases to a geologically unacceptable length (Blatt, 1979). Therefore, bulk cementation during deep burial is strongly conflicting. A main problem in understanding cementation is thus the way in which the cementing minerals are brought into the sandstones (Land, 1984).