Chlorite cement authigenic

Kaolinite and chlorite occur both in sandstones and shales. It is clear that in sandstones these minerals are primarily authigenic. They form largely as cements, but also as grain replacements. While these minerals may constitute a few percent locally, they usually amount to less than a percent... 

Authigenic clay minerals identified by SEM/EDS include minor amounts of kaolinite, chlorite, illite and mixed-layer illite/smectite, which form grain coatings, platelets or fibrous cements. 

Authigenic chlorite occurs as thin grain coatings and as fibrous cements, in both the Avalon/Ben Nevis and Catalina Sandstones, but rarely in the deeper reservoirs of Hibernia Field. It is one of the earliest cements in Hibernia Field, preceding early quartz cement. 

Authigenic illite forms characteristic grainbridging cements, as seen by SEM. In very few samples, rims of illite of uniform thickness were found lining the pores (Fig. 14D) and contributing substantial amounts (2-5%) of cement, but in general illite cement, like chlorite, is negligible in Hibernia Field. 

Analcime is specific in Zone IV. Under the microscope, it occurs commonly as the pseudomorphs of clinoptilolite and mordenite which replaced glass shards or cemented the interstitial pores of tuffs. Mordenite and Ca-clinoptilolite frequently coexist with analcime, however. Authigenic quartz appears as microcrystalline aggregates in the cement and is associated with montmorillonite, corrensite, or chlorite. Mont-... 

Fig. 9. General paragenesis for the Norphlet Formation at Fairway Field and surrounding areas. The timing of compaction, intergranular pressure solution and authigenic cements are plotted relative to the occurrence of grain-coating chlorite and pyrobitumen.

Fig. 3. 13d. Impact of diagenetic mineral cement transformation on reservoir quality, Saharan Basins. A Diagram illustrating the impact of the chloritization on reservoir quality. B Porosity and C permeability plots against authigenic chlorite content in clay cement in reservoir rocks from Oued el-Mya ( ) and Illizi-Ghadames (o) basins. Reservoir rocks involved in the correlations were selected a manner, that their other petrographic features are similar or very near, e.g. average grain size M.D. = 0.2-0.4 mm, clay cement content = 10-15% (°f total mass of the rock), with very little or no carbonate cement...

Further conversion of mixed-fay-er clays towards illite authigenesis. Authigenic kaolinite precipitation. Authigenic chlorite development. Mixed-layer s ordering corrensite,allevardite. Feldspar dissolution.Significant quartz overgrowths development, chert dissolution. Carbonate cement dissolution/predpi-tation. Some secondary porosity development. 

Plate 13. Intergranular pressure solution of quartz. The contact zones between the quartz grains are clearly discernible. The silica dissolved in the contact zones appears to be exported . Despite the obvious dissolution of quartz the amount of quartz cement is negligible. Photo h clearly shows dissolution features on quartz. The films enveloping the quartz grains are made up of authigenic chlorite... 

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