Carbonate cements mesogenetic

PATTERNS OF FLUID FLOW CLUES TO THE ORIGIN AND MECHANISMS OF MESOGENETIC CARBONATE CEMENTATION... 

In the Furado area there was no interruption in burial conditions caused by post-rift uplift, and the reservoirs remained at similar depths during this phase. Therefore, it is uncertain whether or not the mesogenetic constituents were precipitated during syn-rift or post-rift phases. Some C2 calcite, which engulfed and thus post-dated albite, chlorite, illite, quartz and trace amounts of pyrite, barite and sphalerite, is interpreted to have precipitated during this time interval. This C2 calcite is characterized by a chemical and isotopic composition similar to the carbonate cements formed during the syn-rift subsidence phase. 

In many cases mesogenetic carbonatization has taken place even in compact quartz sandstones. Fissures and lamellar porosity assure sufficient penetration for leaching solutions to start the process of decarbonatization. As secondary porosity is formed it favours the continued access of acid waters to the sandstones. The secondary porosity that may form during intense decarbonatization is limited by the content of carbonate cement and by the mechanical stability of the non-carbonate portion of the matrix. 

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