Anhydrite diagenetic

Fig. 11. Paragenetic sequence for the Upper Angel Formation, Angel Field. Dolomite cementation was a relatively late, pore-filling diagenetic event that occurred, at least in part, synchronously with microfracturing and hydrocarbon migration (see Fig. IOC). Later-stage anhydrite cement precipitated in some Angel Formation sandstones at Angel-2 and, to a lesser extent, at Angel-4.

Several lines of evidence suggest the involvement of TSR. Partially dissolved remnants of early diagenetic anhydrite cement are found embedded in quartz cement (Fig. 12). Fluid inclusion data indicate that nodular quartz cement with anhydrite inclusions (Fig. 15) formed at elevated temperatures, suggesting that anhydrite dissolution may have coincided with high temperature TSR. Post-pyrobitumen carbonate and pyrite cements and nodules are also present in the Norphlet and may represent late diagenetic precipitates associated with TSR. Pyrite cement from the Norphlet has sulphur isotope ratios that are identical to those of the Pine Hill Anhydrite (Table 3) and within the range reported for Jurassic seawater (Hoefs... 

The sulphates - mainly the products of the hypergenic processes - very easily undergo the diagenetic processes, in which the dominant role is played by hydration (gypsification) of anhydrite and dehydration (anhydritization) of gypsum both processes are reversible and the reaction takes place as follows ... 

The analysis of the primary minerals remains constituting the impurities in the secondary crystals enables determination of the diagenetic processes taking place in the evaporite deposits (including the mineral precursor for the secondary crystal), and the direction and cause of diagenetic transformations (e.g. anhydrite gypsification piitnaiy mineral -anhydrite, cause - presence of fresh or low-mineralized water in the deposit, e.g. as a result of tectonic uplift and exposition to the activity of shallow underground water). 

Kasprzyk A., 2003 - Sedimentological and diagenetic patterns of anhydrite deposits in the Badenian evaporite basin of the Carpathian Foredeep, southern Poland. Sedimentary Geology, 158 (3-4) 167-194. 

Shearman, D. J. (1985). Syndepositional and late diagenetic alteration of primary gypsum to anhydrite. 6th Int. Symp. Salt, The Salt Institute, 7,41-55. 

Diagenetic — Halite Gypsum Anhydrite Aragonite Magnesite... 

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