Nodular cementation

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. 

Nodular cementation indicates an initial stage of cementation. In addition to its nodular distribu-... 

Nodular Term synonymous with glaebular and refers to soft to highly indurated concretions of carbonate, or carbonate cemented host material. The margins may be gradational to sharp, and internally the nodules may be uniform, showing concentric laminae or septarian cracks or veins. The nodules can range in shape from spherical to elongate. The nodules typically consist of micrite or less commonly microsparite. Nodular calcrete develops primarily in siliciclastic host material... 

Fig. 6. Stratigraphical column showing details of the relationships between grain size, lithology, sorting and degree of cementation in sediments from the Chamisa Mesa and Canada Pillares Members. Note correlation between coarser and better sorted channel (CH) associations and good cementation. Nodular, platy and rod-shaped concretions are associated with crevasse splay (CS), paleosol (P), interdune facies (ID) and overbank fine (OF) sediments. Scattered ovoid to elongate concretions dominate in the cross-stratified aeolian facies (EC). Note that the coarser portions of aeolian sandsheets (ES) are preferentially cemented.

Nodular white patches observed in core represent a somewhat unusual mode of quartz cement occurrence. These millimetre-scale, globular bodies occur both in the tight-zone and within... 

For primary inclusions in quartz cement the Jh values obtained range from 85 to 225 °C (Fig. 15). The conspicuous majority of values fall above 150°C with the greatest number clustering between 190 and 225 °C. There is no distinction between the range of Tj, values measured in quartz cements of the tight-zone and the reservoir interval. In addition, no difference was observed in Tj, between nodular quartz cement attributed to anhydrite replacement and the more common post-pyrobitumen... 

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... 

Lateral variations in the eogenetic association may be related to changes in sedimentary conditions or to the starting mineral composition. The development of nitrates was probably controlled in part by sedimentary rhythms. In the border zones of the Triassic Basin of the Sahara where the source of supply (Hoggar Massif) was probably closer by, calcretes were formed and the deposits were cemented by calcite with a heterogeneous structure. In the case of farther removed source areas and a more stable sedimentation the sandstones are characterized by a poikilitic nodular dolomite cement. Variations in the composition of the sandstone cements between calcite and dolomite may be explained by the ionic composition of the solutions in the... 

The black, nodular clinker is stored on site in silos or clinker domes until needed for cement production. Clinker, gypsmn and other process additions... 

It is recommended to use ductile (nodular) cast iron instead of gray cast iron (brittle). Ductile iron pipe with a cement mortar lining has given excellent performance. 

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