Mesozoic sediments

Approximately 70% of the samples re-investigated contain OSC (Table I). In Cenozoic samples they are more common and more diverse than in Mesozoic sediments (Table II). Most of the Cenozoic samples were collected from areas of present-day high surface-water bioproductivity, which presumably prevailed already when these sediments were deposited (18). The samples of Mesozoic age are predominantly so-called black shales, for which the exact paleodepositional environment (oxygen depletion due to restricted water circulation or due to high productivity) is still a matter of debate (19). 

The Lixian Depression, some 500 km south of Xi an, is filled by about 10,000 m of Palaeozoic and Mesozoic sediments. Mature source rocks occur throughout the stratigraphic sequence, but the complicated geological structure has impeded exploration and there are as yet no commercial discoveries of oil or gas. Located in southern China, the region has a very wet climate and is largely covered by rice fields, so that soils in the region are invariably moist. 

I. 0). The isotopic composition of alkanes and of other classes of compounds can also be used as a general source input indicator. Isotopic fractionation resulting from the metabolic pathways involved in the synthesis of biologically produced compounds, when preserved in a dlagenetlc product, is frequently used to differentiate between terrestrial and aquatic sources. Hydrogen and carbon isotopic compositions of biogenic methanes from shallow aquatic environments is discussed in a later chapter of this volume (R. A. Burke and W. M. Sackett). The applicability of carbon isotopic data to tracing the source of deep-sea Mesozoic sediments is discussed by R.M. Joyce and E. S. Van Vleet. 

Fig. 5. Geohistory plot for Eromanga basin sediments (Gidgealpa-7). Note that the Upper Jurassic Namur Sandstone and younger Mesozoic sediments underwent rapid initial burial, the same as in the Angel Field area (Fig. 4).

Dypvik, H. (1983) Clay mineral transformations in Tertiary and Mesozoic sediments from the North Sea. Bull. Am. Ass. Petrol. Geol., 67, 160-165. 

Kopf et al. (1981) found a correlation between the susceptibility and clay-mineral content Fciay (in volume percentage according X-ray analysis) for clay-, silt-, and sandstones (Cenozoic and Mesozoic sediments from the North German-Polish Basin) and derived an empirical equation (converted to SI units) ... 

Sanchez JA, Coloma P, Perez A (1999) Sedimentary processes related to the groundwater flows from the Mesozoic Carbonate Aquifer of the Iberian Chain in the Tertiary Ebro Basin, northeast Spain. Sediment Geol 129 201-213... 

Mesozoic volcanic rocks and coeval intrusive complexes within the Quesnel geotectonic terrain of central British Columbia host several major porphyry copper-gold mines. Exploration for new deposits in this region has been met with limited success, because prospective bedrock is mantled by Late Pleistocene glacial sediment (e.g.,till) and Late Olig-ocene to Pleistocene plateau basalt. 

The large sedimentary basins trend NW and contain extensive deposits. Sedimentation occurred from the Neo-Proterozoic to Mesozoic. The Dos Parecis Basin (Siqueira 1989 Pedreira Bahia 2000) is comprised of marine and... 

Distribution of Organic Sulfur Compounds in Mesozoic and Cenozoic Sediments from the Atlantic and Pacific Oceans and the Gulf of California... 

Figure 4.2 An example from the G-BASE project of a gridded image for arsenic in stream sediments (top) and stream waters (bottom) from eastern England. Note The maps show how stream water and stream sediment maps can be used in combination to explain the distribution and behaviour of elements in the surface environment. The Mesozoic sedimentary ironstone referred to in the text is shown by the white outline.

If the accretion of extraterrestrial He-containing IDPs can be determined to have been constant through time, or if variability in the accretion rate can be constrained within known limits, then normalization to the concentration of extraterrestrial He in marine sediments could be used to evaluate the preserved fluxes of other sedimentary constituents (similar to the approach used with °Th Equation (26)). Because He is a stable isotope, and it is retained within IDPs over timescales of at least the past 10 yr (Farley, 1995 Patterson et al., 1998), it holds potential for application as a CFP to paleoceanographic studies well back into the Mesozoic. 

In the two Mesozoic examples shown in Figure 4, the light and uniform values that typify water-column pyrite formation under euxinic conditions, and are further favored by the comparatively slow rates of sediment accumulation, are well expressed. The Cretaceous data of Gauher (1986,... 

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