Dr Tony Dickson

Micrograph of stained thin section, echinoderm stereom - pink, ferroan calcite cement - blue, Pennsylvanian, Dry Canyon, New Mexico, USA.

Diagenesis of modem biogenic carbonates can start while the parent organism that produced the carbonate is still alive and may persist for many millions of years! The increasing use of carbonates as proxies for reconstructing ancient conditions of precipitation requires that all diagenetic changes to have affected these proxies are accounted for. The change from unconsolidated lime sediment to hard limestone is often accompanied by the elimination of pore space with obvious consequences for the oil, gas and water industries. Fluids are the vehicle of diagenesis; their initial seawater composition changes as they are buried in sedimentary basins or on exhumation with the introduction of meteoric waters. Fluids are also introduced into sediments by human activities, such as mining, waste disposal sites, and during oil field production; these fluids often cause very rapid diagenetic changes.