Burial, depth

It has been determined that, with burial depths greater than two thirds the radius of the pipe, this equation provides a means of determining the required pipe stiffness for critical buckling. To make the equation easier to use, it can be rewritten by substituting certain values and solving for the required stiffness for buckling. Suppose that this Luscher Hoeg equation says we will require a pipe stiffness of 0.123 x 106 lb-in2/lineal in. to... 

It is this increase in scattering that is detected, and this approach has been the basis for a number of devices designed to detect buried mines. However, soil penetration is relatively poor for the 60—100 keV yrays required in these devices, thus limiting their utility to shallow burial depths... 

The evolution of sedimentary organic matter (OM) under the influence of increasing burial depth and related temperature rise is termed maturation and this process is commonly subdivided into three stages, i.e., diagenegisis, catagenesis, and metagenesis (Figure 1). 

Geologists often refer to an oil window , which is the temperature range between 60 and 150 °C that oil forms in -below the minimum temperature, oil remains trapped in the form of kerogen above the maximum temperature, the oil is converted to natural gas through the process of thermal cracking. This temperature corresponds to a burial depth of at least 2 km. 

COl, and graphite C, at low P and T conditions, several organic complexes form metastably, mainly as the result of bacterial activity, and persist at P and T conditions that may exceed those achieved at a burial depth on the order of 5 km, which is generally considered the limit of complete degradation. 

Govett Atherden (1987) show Pb and Zn shallow soil geochemical data collected over the Thalanga Pb-Zn-Cu deposit. Four lines were sampled that represent burial depths of 0, 1, 30 and 50 m. The anomalies display a rabbit-ear pattern centred on the deposit regardless of overburden thickness. The magnitude of the anomalies diminishes with increasing cover and Pb diminishes more rapidly than Zn. 

In weathering situations, saturation of fluids with SiC relative to any species of pure silica is probably only rarely achieved. In continental and shallow sea deposits, silica is precipitated in some initially amorphous form, opaline or chert when lithified or extracted by living organisms. Authigenically formed silicates are probably not in equilibrium with quartz when they are formed. As compaction increases in sediments, silica concentrations in solution are again above those of quartz saturation (15 ppm) and again it must be assumed that the diagenetic minerals formed are not in equilibrium with a silica polymorph except where amorphous silica is present. It is possible that burial depths of one or two kilometers are necessary to effectively stabilize that quartz form. It must be anticipated that the minerals formed under conditions of silica saturation near the earth s surface will be a minority of the examples found in natural rock systems. 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

Figure 12. Apparent growth temperatures for various Altiplano carbonates based on clumped isotope thermometry, plotted as a function of estimated maximum burial depth. Symbols discriminate among soil carbonates from sections near Callapa, Corque and Salla and lacustrine carbonates from near Tambo Tambillo, as indicated by the legend. The heavy solid line indicates an estimated burial geotherm, assuming a surface temperature of 20 °C and a gradient of 30 °C per km. The dashed lines define a 10° offset from this trend, which we consider a reasonable estimate of its uncertainty. Carbonates deposited within the last 28.5 Ma and buried to 5000 meters or less exhibit no systematic relationship between apparent temperature and burial depth, and show no evidence for pervasive resetting of deeply buried samples. Error bars are la (when not visible, these are approximately the size of the plotted symbol).

Rapid increases in the interstitial water concentrations of dissolved strontium with increasing burial depth of deep-sea carbonate sediments have been interpreted as evidence of the recrystallization reaction (Baker et al., 1982 Elderfield et al., 1982 Gieskes, 1983). Figure 8.17 shows an example of interstitial-water profiles of dissolved alkaline-earth species from a carbonate nanno-fossil ooze from the Ontong Java Plateau (DSDP site 288 5°58 S, 161°50 E). At this site calcium and magnesium concentrations are linearly correlated, and their gradients are governed by chemical reactions deep in the sediment column. 

Figure 8.20. Generalized relationship between Sr and Na in CaC03 for periplatform carbonate sediments at ODP site 716, Maldives Archipelago, Indian Ocean. In general, Sr and Na concentrations in the carbonate phase decrease with increasing burial depth at this site. (After Malone et al., 1990.)...

Table I lists the results of this experiment. A metallic calcium sample was prepared from limestone from an 11-m depth and was not preenriched. The sample was assumed to contain no cosmogenic 41Ca at the instrumental detection limit of the AMS system used, because of its geological age (Mesozoic) and burial depth. No counts were observed for a time approximately three times longer than that for the bone sample. From the measurement...

Phillipsite is the most abundant zeolite in the surface sediments of the Pacific (Boles, 1977 Kastner and Stonecipher, 1978). Although it may be locally abundant (>50 wt.% on a carbonate-free basis, Bonatti (1963)), its etched surface, and the pattern of its decreasing abundance with the burial depth, suggest that it is a metastable phase under deep-sea conditions (Kastner, 1979). The primary mechanism of formation is thought to be alteration of basaltic glass, but it may also form by reaction of biogenic silica and dissolved AP+ (Arrhenius, 1963). Phillipsite is commonly found in association with authigenic smectite, and the combined formation of the two minerals may be represented as... 

The transformation of opal-A to opal-CT generally begins at 35-50 °C, corresponding to burial depths of hundred of meters. In some environments this temperature may be as low as 17-21 °C (Matheney and Knauth, 1993 Monterey Formation) or even 0-4 °C (Botz and Bohrmann, 1991 Antarctic deep sea). The acoustic properties of the sediment are altered during the transformation to opal-CT, typically providing an acoustic reflector of the diagenetic front (Calvert, 1983 Tribble et al., 1992). Opal-CT, also known as porcelanite, exhibits X-ray characteristics of low cristobalite and tridymite (Figure 4). This mineral exists as... 

Cavazza W. and Gandolfi G. (1992) Diagenetic processes along a basin-wide marker bed as a function of burial depth. J. Sedim. Petrol. 62, 261-272. 

Reconsider Prob. 3-124. Using EES (or other) software, plot the rate of heat loss from the pipe as a function of the burial depth in the range of 20 cm to 2.0 m. Discuss the results. 

EXAMPLE4-6 Minimum Burial Depth of Water Pipes to Avoid Freezing... 

The ground at a particular location is covered with snow pack at -lOX for a continuous period of three months, and the average soil properties at that location arc k = 0.4 W/m °C and a = 0.15X 10 m /s (Fig. 4-31). Assuming an initial uniform temperature of 15°C for the ground, determine the minimum burial depth to prevent the water pipes from freezing. 

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