Formation factor sediments

The presence of particles in the fluid medium complicates diffusion in a sediment due to the effects of porosity, represented by n, and tortuosity. Since tortuosity of natural sediments is seldom known it is more convenient to use the term "formation factor" or "lithological factor," denoted L, which takes into account everything but porosity. Tick s diffusion constant D is replaced by the whole sediment diffusion constant Ds, where < D. 

The second section groups chapters that are case studies of specific sedimentary environments and focus on environmental factors that influence the behavior of sulfur in the formation of sediments and fossil fuels. 

Fig. 2.7 Formation factor versus porosity for six gravity cores retrieved from different sedimentation provinces in the South Atlantic. Porosities were determined on discrete samples by wet and dry weights and volumes, formation factors by resistivity measurements. The dashed lines indicate Archie s law for a = 1 and cementation exponents (m) between 1 and 5. For a description of the sedimentation provinces, core numbers, coring locations, sediment compositions, water depths and constants (a) and (m) derived from linear least square fits please refer to Table 2.1. Unpublished data from M. Richter, University Bremen, Germany.

The influence of the sediment composition on the formation factor-porosity relation illustrates Figure 2.7 for six provinces in the South Atlantic. For each core porosities and formation factors were evaluated at the same core depths by wet and dry weights and volumes of discrete samples... 

Table 2.1 Geographical coordinates, water depth, core length, region and composition of the sediment cores considered in Figure 2.7. The cementation exponent (m) and the constant (a) are derived from the slope and intercept of a linear least square fit to the log-log display of formation factors versus porosities.

If porosities and wet bulk densities are determined by galvanic resistivity measurements (Sect. 2.2.3) varying sediment temperatures are considered by computation of the formation factor (F) (see Eq. 2.12). While the resistivity (R ) of the sediment is determined by the small hand-held probe (cf. Sect. 2.2.3) the resistivity (R. ) of the pore fluid is derived from a calibration curve which describes the temperature (T) - conductivity (c) relation by a fourth power law (Siedler and Peters 1986)... 

In sediment samples, methylmercury levels are typically only a few percent or less of the inorganic mercury level and even minor artificial methylmercury formation during sample preparation will result in significant overestimation of the actual methylmercury content. A correction can be carried out with a single measurement, when stable Hg isotopes are used, by measuring different isotopes to determine the artefact formation factor. 

The additional interface conductive component was also detected in unconsolidated porous rocks. For example, Repsold (1976) found a dependence of the formation factor on water conductivity in sand, particularly in fine sand. Studies by Rink and Schopper (1974), Pape and Worthington (1983), and Bomer and Schon (1991) of various consolidated and unconsolidated sediments leads to an explanation of the second conductive component of rocks based on the specific internal surface, pore wall morphology, and surface charge density. 

Emerson, S. and Widmer, G. (1978). Early diagenesis in anaerobic lake sediments II. Equilibrium and kinetic factors controlling the formation of iron phosphate. Geochim. Cosmochim. Acta 42,1307-1316. 

In echinoderms, zinc concentrations are usually higher in detrital feeders than in carnivores, higher in surface feeders than in sediment feeders, and higher in specimens collected inshore than those collected offshore in deeper waters (Eisler 1980). Sea cucumbers, Stichopus tremulus, accumulate radiozinc-65 from seawater by a factor of 1400 however, radiozinc accumulation data should be viewed with caution because addition of stable zinc can reduce zinc-65 accumulations in echinoderm viscera up to tenfold (Eisler 1981). Zinc inhibits the formation of the fertilization membrane in sea urchin eggs, possibly by interfering with cortical granule-derived proteases and proteins (Nakamura et al. 1989). 

The temperature dependency of the sulfate reduction rate for single sulfate-reducing bacteria is high, corresponding to a temperature coefficient, a, of about 1.13, i.e., a change in the rate with a factor Q10 = 3.4 per 10°C of temperature increase. Because diffusion of substrate into biofilms or sediments is typically limiting sulfide formation, the temperature coefficient is reduced to about... 

Minerals formed in natural waters and in sediments provide a record of the physical chemical processes operating during the period of their formation they also give us information on the environmental factors that regulate the composition of natural waters and on the processes by which elements are removed from the water. The memory record of the sediments allows us to reconstruct the environmental history of the processes that led to the deposition of minerals, in the past. 

---