Outcrop Sections

Figure 5. Mass chromatogram of m/z 217 of the desulfurised polar fraction of the bitumen of an outcrop section at Naples Beach (California, U.S.A.) of the Monterey Formation.

Confined aquifers (section 2.8) are rare in tectonically undisturbed regions with horizontal rock beds (Fig. 3.5). Tilting of the aquifer and aquiclude sandwich makes room for the formation of confined aquifers. It provides each case with a recharge outcrop section, forming a phreatic aquifer (section 2.8) and a confined section fed by the former (Fig. 3.6). 

To derive a reservoir geological model various methods and techniques are employed mainly the analysis of core material, wireline logs, high resolution seismic and outcrop studies. These data gathering techniques are further discussed in Sections 5.3 and 2.2. 

Geologic maps constitute a familiar class of models. To map a sedimentary section, a geologist collects data at certain outcrops. He casts his observations in terms of the local stratigraphy, which is itself a model that simplifies reality by allowing groups of sediments to be lumped together into formations. He then interpolates among his data points (and projects beneath them) to infer positions for formation contacts, faults, and so on across his field area. 

To track the sources of the geochemical anomalies of heavy metals in suspended matters along the Shun an River basin (one of the main tributary basins of the Anhui section of the Yangtze River basin), a rock survey was conducted on typical ore deposits and outcrops of main strata and geological bodies along the Shun an River basin. The results shown in Table 3 indicate the largest source of Cd in suspended matters on the Shun an River basin is endogenetic deposits, especially Pb-Zn deposits. 

Petrographic observations were made on polished thin sections, for 313 outcrop samples. Average sample spacing was one sample per 1 km within a radius of 15 km or less from the known porphyry Cu-Mo deposits, and one sample per 2 km outside this area. Five rock types are distinguished in the district andesites, diorites, granodiorites, dacites, rhyolites and sandstones. Rhyolites and dacites dominate in the zone of known porphyry Cu-Mo deposits. Sandstones are much less common and were not studied. 

Most of the analyses of Antarctic coal were based on blocks of transportable size taken from surface outcrops. In earlier work, sections of purer coal were cut from the blocks and submitted for analysis. In later work, selected blocks were crushed, and a float fraction of purer coal was submitted to provide analytic data from each deposit. These samples, while not useful for determining coal grade, may be adequate for indicating rank. Practically all of the Antarctic coal, with the exception of that at Amery (which may represent high volatile bituminous coal), corresponds to medium volatile bituminous or higher rank. The high apparent rank Antarctic coal may be classified according to conventional ASTM standards of rank based on proximate analysis, but it seems clear that these results serve only as a first approximation. 

Two general areao in Colorado exhibit extensive alteration of coalo by igneouo intrusives. The first locality it near Somerset in the west central part of the state, and the second area is the Spanish Peaks region near Trinidad and Walsenburg. Drill core samples, outcrop samples, materials from active mines, and thin sections of the intrusive rocks were studied. The results show that mean maximum reflectance of the altered coal or natural coke increases as the distance from an intrusive body decreases. Carbon and ash values increase as the distance from intrusive decreases whereas volatile matter values decrease. Sulfur data are variable. Hydrogen values increase as the distance from an intrusive increases. Hydrogen and reflectance are considered the most sensitive and reliable indicators of degree of alteration. 

Cover illustration The cover art shows an eroding ancient Martian shoreline with sedimentary rock outcrops and ice remnants of a former lake, including rock deposits similar to those now being explored by the Mars Opportunity rover. The ancient lake is shown in the cutaway cross section at bottom right as it once may have been, with an ice-covered liquid brine lake and bubbles associated with gas hydrates and/or life. 

Fig. 2.6 Components of a confined aquifer with through-flow tilted, or folded, water-bearing rock strata, sealed at the top and the base by aquicludes. Each active confined system also has a phreatic section at outcrops of the aquifer rocks. The level of the water table in the phreatic section defines the piezometric head in the confined section. Water ascends in boreholes drilled into confined aquifers. Water reaches the surface in artesian flow in boreholes that are drilled at altitudes lower than the piezometric head.

Fig. 3.6 Tectonic tilting of rock strata provides the necessary condition for the formation of a partially confined aquifer. A phreatic section, located at the outcrop of the rock bed, serves as recharge intake area feeding the confined section in cases where the inclined rock bed has a drainage outlet at its lower end enabling through-flow (which is a rare case).

Regional aquifers consist, in certain cases, of a recharged outcrop of a conductive rock layer that dips below other rocks and is thus partially confined (section 2.8). Occasionally, wells tap only the confined section of such an aquifer, but in other cases wells also exist in the recharge area. In such systems carbon isotope studies are relevant for... 

Fig. 11.21 Suggested geological cross-section of the Bunter sandstone aquifer. The researchers suggested that water recharged in the western outcrops flows eastward down-gradient into the confined section. (Following Bath et al., 1979.)...

This system has been studied by Geyh and Wirth (1980). Figure 11.28 depicts the outcrop areas and the suggested groundwater flow direction. The 14C data reveal a sharp discontinuity of waters, with 32-70 pmc near the outcrops (A) and 2-7 pmc in the downflow section of the confined aquifer (B)—another example of lack of hydraulic communication between adjacent phreatic and confined systems. 

Fig. 11.28 14C values (pmc) in wells of the Sokoto basin, northern Nigeria. The arrow denotes the orginally suggested groundwater flow direction. The phreatic aquifer (A) coincides with the rock outcrops (stippled) and has high 14C values. An abrupt drop in 14C values is observed in the adjacent confined section of the system (B). (Data from Geyh and Wirth, 1980.)... 

Values discussed in the previous section represent an oceanic average and individual regions and parts of the water column may behave differendy. For example, Abell et al. (2000, 2005) found that the DOM reminerahzed along isopycnals outcropping in the subtropical North Pacific Ocean is C-rich (C N 30) based on this C N ratio these authors concluded that DOM contributes between 70 and 90% of the total organic matter remineralized in the upper thermocHne. As more data are collected, other sites in the ocean may show similar variabiHty. 

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