Quartz diagenetic cement

Later diagenetic processes include development of fault-parallel micro-stylolites (see Fig. 7 in Sverdrup and Prestholm, 1990) and extensive quartz cementation due to deep burial (ca. 3500 m) prior to later uplift and erosion. Some key observations from Kvalvagen are presented in Table la. 

In nodular cemented sandstones, the areas left uncemented often reveal evidence of later burial diagenetic modifications, such as compaction and quartz cementation (Morad et al., 1995). Burial cements are believed to be sourced from meteoric or dissolution of detrital carbonates and bioclasts (cf. Wilkinson, 1991). As the sandstone framework is expected to be stabilized due to early cementation, the burial dissolution of bioclasts may be recognized by oversized pores and mouldic pores filled with cement. 

Diagenetic carbonate cement in reservoir sandstones of the Oseberg Formation (Brent Group) in the Oseberg field, Norwegian North Sea, occurs as disseminated siderite and ankerite, and as massively calcite-cemented intervals. Other diagenetic features include extensive feldspar dissolution and K-feldspar, quartz, kaolinite and dickite cements. Conditions of carbonate cementation are constrained on the basis of textural, geochemical and fluid inclusion evidence. 

Early ferroan dolomite occurs in an 18m thick fine-grained unit of the Hibernia Sandstone in well B-27, where in thin zones (<1 m thick) it occluded all available pore space and replaced detrital quartz. The early diagenetic nature of this cement (crystal size 30-200 pm, average 50 pm) is indicated by a high minus-cement porosity (>30%) and the lack of quartz overgrowths or other cements. 

Haszeldine, R.S. Osborne, M. (1993) Fluid inclusion temperatures in diagenetic quartz reset by burial implications for oil field cementation. In Diagenesis and Basin Development (Eds Horbury, A.D. Robinson. A.G.). Am. Ass. Petrol. Geol. Studies in Geology, 36, 35-46. 

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