Diagenesis and Geochemistry of Sediments in Marine Environment: ABSTRACT

Abstract

Diagenetic alterations were induced in sediments in a model representing a shallow-marine shelf by injecting synthetic sea water under partial pressure of carbon dioxide. The sediments from the model were then removed and studied under the petrographic microscope. The study included (1) the interrelation of the chemistry of the interstitial fluid and the mineralogy of sediments, (2) the factors controlling the formation of silica and calcite cements, (3) the processes responsible for transforming sediments into hard rocks, and (4) the sequence of these processes. The precipitation of silica and calcium carbonate as cements in the model sediments was detected under the petrographic microscope and is shown on photomicrographs. The petrographic analyses indicate that during early diagenesis cements formed in intergranular space only. The calcite cement crystallizes as small fibrous crystals around the grains extending into the pore space and subsequently results in rim cement. Silica cement is formed simultaneously both as overgrowths and in optical continuity around sand grains. The silica and calcite precipitated as cements in the model seem to be derived from the interaction of clays and sea water. Geochemical environments for such reactions and environments which enhance the cementation of sediments were interpreted from the studies. End_of_Article - Last_Page 634------------