Silica budget

Within the limits of each group of samples in the diagrams the relative position of the individual sample points is controlled by the grain dimensions. Sandstones with smaller grains are located in the lower portion of the exporter field whereas coarser-grained sandstones are found in the upper part of the importer field. The relative positions of these groups of data are also controlled by thermal maturity. Samples from zones of low thermal maturity fall farther into the direction of the upper part of the importers compared to samples from zones of higher thermal maturity. 

When carrying out the same evaluation on the results from other successions we may conclude that for the Devonian of the Ghadames Basin, 4.92% silica has been 

Chapter 4 Reservoir Decompaction and Formation of Accumulation Capacity 

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. 

Within each stratigraphic entity studied samples of fine-grained sandstones and those containing well-developed illitic clay films plot in the lower right of the respective diagram whereas those of coarser grain size and with few illitic films or none at all plot in the upper left. 

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Because diatoms play such a large role in the biogeochemistry of silicon, changes in their productivity are thought to have the potential to affect other aspects of the crustal-ocean-atmosphere factory. To consider this future, we first look at the marine silica budget. 

SIEVER (R.), 1957. The silica budget in the sedimentary cycle. Amer. 

Conley, D.J. (1997) Riverine contribution of biogenic silica to the oceanic silica budget. Limnol. Oceanogr. 42, 774—777. 

If any of the above minerals were to be the only mineral injected into the bulk of ocean waters, could it measurably affect the overall silica budget If so, to what extent ... 

Is there any simple way to relate mineral structure to solubilities and release rates Will this ranking allow us to suggest the order of importance of these minerals with respect to input or removal of silica to the silica budget ... 

Hurd, D. C., The effect of glacial weathering on the silica budget of Antarctic waters, Geochim. 

Cathodoluminescence was greatly used for studying quartz diagenesis and for estimating the silica budget. It covered some 400 sandstone samples. 

Silica concentrations in pore waters particularly and also in other subsurface and surface waters were determined in dozens of samples as part of this study, using atomic absorption spectrophotometry as well as inductive coupled plasma. This was essential for silica budget estimations. Present-day and paleothermal profiles were obtained from measured temperatures in boreholes, vitrinite reflectance (Rq) in interlayered-with-sandstones shales and from basins thermal modeling. 

Table 4.7. Silica budgets of quartzose sandstones in Saharan basins (Si flux expressed as a percentage of current rock volume negative values indicates volume of silica exported and positive values indicates volume of silica imported)...

Demaster, D. J., The marine silica and 32Si budgets, PhD Thesis, Yale University, New Haven, Connecticut, 260 (1979). 

A box model fiar the marine silica cycle is presented in Figure 6.11 with respect to the processes that control DSi and BSi. An oceanic budget is provided in Table 16.3 in which site-specific contributions to oceanic outputs are given. This table illustrates that considerable uncertainty still exists in estimating the burial rate of BSi. Regardless, burial of BSi is responsible for most of the removal of the oceanic inputs of DSi, with the latter being predominantly delivered via river runoff. This demonstrates the importance of the biological silica pump in the crustal-ocean-atmosphere factory. 

SIC Standard Industrial Code. Prepared by the United States Office of Management and Budget. Silica Gel A regenerative absorbent consisting of the amorphous silica. Used in dehydrating and in drying and as a catalyst carrier. 

The offshore advective flux for Si shown in Fig. 17.3 (30 X 10 mol d l) was calculated by difference, based on the total flux of dissolved Si supplied to the shelf system (32 X 10 mol Si d-1), the estimated deltaic burial rate (1-3 x 10 mol Si d ), and the nearshore particulate flux (0.1-0.7 x 10 mol Si d ). This advective flux is in good agreement with the results of Daley (1997), who estimated that 30 x 10 mol d of Si leave the shelf, based on seasonal field data and a multibox model for the shelf. Most of the silicate (94%) supplied to the shelf by external sources appears to be transported to the open ocean in either dissolved or particulate form. Approximately 36% of the Si leaving the outer shelf is in particulate form according to these calculations. Biogenic silica export may have contributed to the lack of closure in the Edmond et al. (1981) silicate budget for the shelf, although deltaic burial also remains as a potentially important sink. 

The imbalance in the K+ budget and small imbalances in other budgets may be nullified by a number of processes. One possibility is the concept of reverse weathering reactions . In reverse weathering, highly degraded clay minerals react with cations, HCOf and silica in seawater to form complex clay mineral-like silicates. An example reaction addressing the K+ problem would be ... 

In this chapter, we encounter questions that focus instead on chemical reactions. These questions ask us to convert from amount of one substance in a given chemical reaction to amount of another substance participating in the same reaction. For example, a business manager, budgeting for the production of silicon-based computer chips, wants to know how much silicon can be produced from 16 kg of carbon and 32 kg of silica, Si02, in the reaction... 

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