Pressure solution, intergranular

Sibley, D. F. and H. Blatt, 1976, Intergranular pressure solution and cementation of the Tuscarora orthoquartzite. Journal of Sedimentary Petrology 46, 881-896. 

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.

Norphlet sandstones examined in this study display clear evidence of mechanical compaction and intergranular pressure solution (Fig. 13). A high proportion of long grain-to-grain contacts are observed along with sutured and interpenetrating quartz-quartz and quartz-feldspar... 

Fig. 14. Intergranular volume (IGV) versus total cement for Norphlet sandstones from Mobile Bay. The diagonal lines represent intergranular porosity. The majority of samples plot in the shaded area representing IGV < 26%, indicating that intergranular pressure solution has played a significant role in reducing IGV.

Many mechanisms have been suggested to explain quartz cementation processes in sandstones. Amongst these, pressure solution has been the focus of considerable attention as a principal process for supplying silica for quartz cementation (e.g. Taylor 1950 Heald 1956 Thompson 1959 Weyl 1959 Houseknecht 1984,1988). These observations led to the elaboration of theoretical geochemical models of intergranular pressure solution and a limited number of experimental simulations (Ernst and Blatt 1964 Heald and Renton 1966 Renton et al. 1969). There is still no consensus as to the importance of pressure solution. Some researchers insist that pressure solution considerably reduces the porosity of sandstone (e.g. Houseknecht 1984,1988) whereas others conclude it is of limited importance (e.g. Sibley and Blatt 1976 Blatt 1979). 

Quartz intergranular pressure solution and quartz overgrowths... 

Fig. 4.4a. General diagenetic effects within Saharan sandstones quartz intergranular pressure solution, quartz overgrowths, and mineral transformation and textural development...

Decompaction-Compaction by Intergranular Pressure Solution (of Quartz Grains) and Removal of Si02 by Alkaline Solutions... 

Fig. 4.11. Quartz intergranular pressure solution and quartz overgrowths, a Sequences of stages in the development of quartz pressure solution (modified after Siever 1962). b Schematic illustration defining detrital quartz (D.Q.), quartz cement (Q.C.) and overlap quartz (O.Q.). c Schematic diagram of major features of quartz overgrowths...

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... 

Influence of "Early" Cement. The presence of calcite, dolomite and anhydrite in the form of early cement strongly hinders pressure solution and thereby contributes to the preservation of intergranular space. This observation may also be made for early quartzose cement. The latter contributes to the formation of a solid framework in the sandstones which obstructs their later compaction by equalizing tension along the boundaries of the quartz grains of the framework. 

Fig. 4.13. Intergranular pressure solution, a Cambrian Oued el-Mya, b Devonian Ghadames, c Carboniferous Illizi, d Ordovician Ahnet-Mouydir...

As the distribution of samples of a certain succession is more or less even over the export and import fields we may assume that silica has migrated locally from the exporters , i.e. fine-grained sandstones, towards importers , i.e. coarser-grained sandstones, and in this way on the local scale an approximate mass balance was maintained. Nevertheless, the overall data show that an important transfer of silica has taken place on a much wider scale and that this is closely related to temperature as the controlling factor for intergranular pressure solution. In zones of higher thermal maturity pressure solution probably was so efficient that it could act simultaneously as the source and driving force for the mass transfer of silica. In zones of low thermal maturity pressure solution was not particularly effective for the mass transfer of silica and the reduction of the primary porosity. 

The calculation of the hydrological parameters necessary for establishing the above-mentioned silica balance appears to be a rather complicated problem as intergranular pressure solution leads to a dynamic reduction in rock mass and volume and frequently also to a lowering of the porosity. These parameters have been simulated for different petrophysical and geochemical conditions. The first results show that for the large amount of secondary silica observed to become exported, 0.5 x io -o.5 x lo cm of water is required for every cm of the Cambrian sandstones of the Oued el-Mya Basin. If we assume, on the other hand, that the quartz cement in the Ordovician sandstones from Ahnet Mouy-dir resulted within the rocks themselves from pressure solution then the water flux necessary was small or virtually nil and this formation approached an isochemical system. 

We shall now propose an approach for the evaluation, in the Saharan reservoirs, of the relative importance of the process of compaction and cementation in the reduction of porosity by presenting correlation plots of intergranular volume (VIG) vs. cement (Fig. 4.16). It is generally held that under the conditions of sediment accumulation on surface the VIG of well-graded sandstones is about 40%. This VIG or porosity can only be reduced by compaction, a mechanical process reducing VIG to 30%. Any further reduction by chemical compaction or pressure solution is a specially important process. The intergranular porosity of a sandstone is a function of the volume preserved after compaction and of its (the VIG s) portion filled by cement (Fig. 4.16). The inter-... 

Houseknecht DW (1984) Influence of grain size and temperature on intergranular pressure solution, quartz cementation and porosity in a quartzose sandstone. J Sed Pet 54(2) 384-36i Houseknecht DW (1988) Intergranular pressure solution in four quartzose sandstones. J Sed Pet 58(2) 228-246... 

Houseknecht DW (1988) Intergranular pressure solution in four quartzose sandstones. J Sediment Pet 58 228-246... 

Houseknecht DW, Hathon LA (1987) Petrographic constraints on models of intergranular pressure solution in quartose sandstones. Appl Geochem 2 507-521 Hower J, Eslinger E, Hower M (1976) Mechanisms of burial metamorphism of argillaceous sediments. 1. Mineralogical and chemical evidence. Geol Soc Am Bull 87 725-737... 

---