Interpretation of early diagenesis of carbonates: An approach from hydrogeochemistry

Abstract

Carbonate sediments and/or rocks are subjected to various diagenetic processes and change their properties easily because of their chemistry. Consequently, their properties become different from that of primary carbonate sediments. Especially, the carbonate rock properties as porosity and permeability, change drastically by dissolution, precipitation and stabilization of carbonate minerals during early diagenesis. It is, therefore, very important and indispensable to understand the early diagenesis of carbonates. To elucidate the early diagensis, the following methods have been applied; 1) sedimentary petrological approach, 2) experimental approach, and 3) hydrogeochemical approach. A hydrogeochemical approach has been performed since 1970's and actively in the last several years. The approach is on the basis of chemistry of groundwater and it estimates diagenetic processes by mass balance and mass movement in the groundwater of each diagenetic environment. An advantage of the approach is that it is relatively easy to estimate quantitatively the proceeding diagenetic process, such as porosity change, transformation rate of aragonite to calcite, and so on, whereas the direct detection of the recent diagenetic process by other methods is difficult because of the very slow rate of reaction. A hydrogeochemical approach collectively evaluate a entire diagentic process in each diagenetic environment and deals macroscopically. Therefore, hydrogeochemical approach coupled with microscopic petrological analyses of rock samples will elucidate the diagenetic process synthetically.