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Research - Determine the amount of hydrocarbons that exist in the 1002 Area Research - Summary: Thermal Maturity of Sedimentary Basin in
Alaska Thermal maturity is the level of alteration the of the organic matter in a given sedimentary rock due to high temperatures. It gives the absolute maximum temperature to which the rock has been exposed. When there is no igneous source of heat, the maximum temperature measured is just a product of burial heating. Therefore, the thermal maturity of a rock can be used to determine the uplift it has suffered, and this can show broad patterns of geologic structure in a studied region. The tectonic makeup of Alaska is very complex and there is little stratigraphic correlation between areas. There, thermal maturity is used to determine the structure of basins and the deformations they have. Thermal maturity indicators: The most common available data for Alaska comes from vitrinite reflectance and conodon color alteration. Vitrinite is organic matter composed of remains of woody plants that is found in clastic sedimentary rocks. It originated in terrestrial environments. During burial heating, vitrinite loses volatile compounds and the carbon turns into graphite, increasing its reflectivity. This reflectivity is proportional to the temperature reached, is not influenced by pressure or common chemical reactions, and doesn't return to the original state after it has reached a given level. For heating periods greater than 1,000 years, the reflectance of vitrinite depends only on the maximum temperature reached and not in the time. Conodons are teeth-like fossils of primitive fish that existed from the Cambrian to the Triassic. They were deposited in marine environments, and are found in carbonates and loose clastic sedimentary rocks. Conodons are composed of layers of apatite (calcium fluoride phosphate Ca5F(PO4)3) and organic matter. When conodons are buried and the temperature rises, the organic matter is carbonized and its color changes from light yellow to black, then to white and finally to clear. There are established standards between the color of conodons and the temperature they were subject to. Regional thermal maturity patterns: Tertiary basins of interior Alaska: The low thermal maturity of surface rocks show that the basins are at their maximum burial depth and they have suffered no uplift. Aleutian Arc: The rocks mature with depth, being undermature at the surface. This shows that the basins are near their maximum burial depth. Colville basin (North Slope): At the surface, the thermal maturity of rocks increases from the coast at the north to the Brooks Range orogen at the south. Yukon-Koyukuk basin, Kuskokwin flysh (sandstone+schist) belt: There is a nearly concentric thermal maturity pattern, showing greater uplift at the basin margins. The basin as a whole suffered uplifting and deformation. Kandik basin (east-central Alaska): The basin shows uplifts and a fold and thrust belt, placing younger mature rocks over older immature rocks. |
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