Sandstone calcite cement

In the Gidgealpa Field the 8 C signatures of the Namur Sandstone calcite cement (-12.9 to -2.5%o) broadly overlap with the 8 character of CO2 gases... 

The amount of calcite cement in sandstones varies widely, as mentioned, but formations as a whole tend to contain 1-5% calcite. Some formations contain sufficient detrital carbonate to supply the formation of calcite cement (Milliken et al, 1998). Some formations, however, appear to require an import of calcium (and CO2) from external sources. The values of 6 C, and... 

Two difficulties beset the notion of a mudrock source for calcite cement in sandstones. First, the lack of a strong depth trend for calcite cement in sandstones is difficult to reconcile with the prominent depth-related trend for carbonate loss in mudrocks. Second, there is a tremendous volume imbalance between the large amounts of CaCOa that appear to be missing from shales compared to the observed amount of calcite cement in sandstone (Land and Macpherson, 1992b). Unfortunately, quantitative data for depth trends of calcite in associated shales and sandstones outside the Gulf of Mexico are few. 

Beckner J. R. and Mozley P. S. (1998) Origin and spatial distribution of early vadose and phreatic calcite cements in the Zia Formation, Albuquerque Basin, New Mexico, USA. In Carbonate Cementation in Sandstones. Distribution Patterns and Geochemical Evolution (ed. S. Morad). International Association of Sedimentologists, Oxford, vol. 26, pp. 27-52. 

Bj0rkum P. A. and Walderhaug O. (1990) Geometrical arrangement of calcite cementation within shallow marine sandstones. Earth Sci. Rev. 29, 145—161. 

Lynch F. L. and Land L. S. (1996) Diagenesis of calcite cement in Frio Formation sandstones and its relationship to formation water chemistry. J. Sedim. Res. A66, 439-446. 

McBride E. F., Milliken K. L., Cavazza W., Cibin U., Fontana D., Picard M. D., and Zuffa G. G. (1995) Inhomogenous distribution of calcite cement at the outcrop scale in Tertiary sandstones, northern Apennines, Italy. Am. Assoc. Petrol. Geologists Bull. 79, 1044-1063. 

Sandstones may, however, become calcite cemented due to aragonite and Mg-calcite dissolution at very shallow depth (even at the surface). When cemented, the sediments may obtain brittle properties and deform by cataclasis and brecciation. Another source for early cement within sandstones is biogenic silica which acts as a precursor for silica cements at relatively shallow depth (ca. 1500 m). Clean quartz sandstones, however, are usually not cemented until the sediment has reached a considerable depth (approx. 3 km). Brittle deformation, which may occur in cemented sandstones, prevents fault planes closing entirely and can augment a fault-parallel permeability which increases the potential for mineralization. 

Fig. 6. Fault structures cutting through a calcite cemented (lower part) and non-calcite cemented (upper part) sandstone. The calcite cemented sandstone displays calcite filled fault structures, while the non-calcite cemented sandstone displays phyllosilicate enrichment only.

At shallow depths carbonate cements may cause sands to become brittle and hard. Carbonate which precipitates on the sea floor may also form hard grounds in dominantly clastic sequences. Sandstones may become calcite cemented due to dissolution of biogenic aragonite at relatively shallow depth (less than a few hundred meters). Calcareous sediments flushed by meteoric water at shallow depth or exposed during regression may become rapidly ce-... 

The raffinate is to be released to compacted-clay-lined evaporation ponds constructed in local sandstone and silty-sand formations. These formations contain a few percent of clays such as kaolinite and smaller amounts of calcite cement. You are asked to evaluate the capacity of the rock to neutralize the raffinate acid-... 

Although abundant skeletal bioclastic fragments play an important part in the development of calcite-cemented sandstones, they should not be considered as the only source of such cements. Evidence for this is the common presence of calcite-cemented sandstones in Precambrian sequences. Additional evidence is the absence of bioclastic carbonates in Jurassic sandstones with strata-bound calcite cements (Bjorkum Walderhaug, 1993 Prosser et al., 1993). This suggests that other sources such as sea water and carbonate mud... 

Another potential mechanism responsible for the formation of laterally continuous, strata-bound calcite-cemented sandstones is the episodic up>-welling of anoxic seawater (see Kempe, 1990 Grot-zinger Knoll, 1995). The upwelling of such high alkalinity waters to shelf and coastal areas may occur subsequent to periods of sea water stratification accompanying sea-level rise. 

Such cements occur in weakly compacted sediments and are characterized by low 6 0 values and fluid inclusions with high homogenization temperatures. This mechanism imposes difficulties in recognizing these cements from those formed by recrystallization at increased temperatures, as both mechanisms preserve a high, pre-cement porosity. A few workers (Giroir et al., 1989 Souza et al., 1995) argued that the early emplacement of calcite cement in sandstones of rift basins may take place... 

Lundegard, P.d. (1994) Mixing zone origin of C-depleted calcite cement Osberg Formation sandstones (Middle Jurassic), Veslefrikk Field, Norway. Geochim. Cosmochim. Acta, 58, 2661-2675. 

Poikilotopic calcite eement reveals evidence of substantial dissolution and creation of secondary porosity. In well 34/4-1 ealeite dissolution was accompanied by the precipitation of kaolinite. Evidence for calcite dissolution includes (i) the seat-tered, patchy corroded remnants (ii) similarity of eorroded shapes of framework grains in areas where ealeite is no longer present to those in areas eemented by calcite and (iii) the presence of replaeive calcite cement within the framework grains but not in adjacent pores. Sandstones subjected to partial cement dissolution contain undeformed ductile grains such as micas. 

CiBiN, U., Cavazza, W., Fontana, D., Milliken, K.L. McBride, E.F. (1993) Comparison of composition and texture of calcite-cemented concretions and host sandstones, northern Apennines, Italy. J. sediment. Petrol., 63, 945-954. 

Dolomite and ankerite occur in sandstones of the distal domain (Caioba and Robalo areas Fig. 2 av. 5.2% up to 38%), and are associated with calcite cement in the middle domain (Japoata-Penedo and Feliz Deserto areas). As far as calcite, dolomite is... 

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