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Tidal bore Turnagain Arm, Cook Inlet Region, Alaska. The bore is moving from right to left, followed by the flood tide. Cook Inlet Region, Alaska. n.d. Portion published as Figure 1, in U.S. Geological Survey, Circular 1022. 1988.
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Replacement by calcite cement in sandstone from the Nanushuk Group, Calcite replacement of detrital grains, leaving a clay rim around original (calcareous?) grain. Sample 78ACh35, Krupa anticline; magnification, 6,3 x 10. Central North Slope, Alaska. Published as Figure 43A in U.S. Geological Survey. Bulletin 1614. 1985.
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Complex wavefront of the Turnagain Arm bore. The bore is moving from right to left and is followed by flood tide. Photograph taken from airplane at approximately 100 ft. altitude, n.d. Cook Inlet Region, Alaska. Portion published as Figure 6 in U.S. Geological Survey, Circular 1022. 1988.
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Quartz overgrowths on sandstone grains after clay Nanushuk Group. Framework quartz grain with vacuoles by diagenetic clay. Clear areas of quartz-overgrowth (Q) are probably initiated where clay rim is absent, porosity (P) may be created by leaching of siliceous no clay development is taking place in the secondary Sample 78ACh325 Kurupa anticline; magnifications 6.3 photomicrograph. Central North Slope, Alaska. Published as Figure 47B in U.S. Geological Survey, 1614. 1985.
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Possible presence of hydrocarbons (?) in Nanushuk Group rocks. Migration apparently occurred during or after compaction of the sandstones. Possible hydrocarbon (?) migration is facilitated along solution seams probably formed during compaction. Sample 78ACh34, Marmot syncline; magnification, 2.5 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 51A in U.S. Geological Survey. Bulletin 1614. 1985.
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Undular bore and whelps near the mouth of Araguari River, Brazil. View is oblique toward toward mouth from airplane at approximately 100 ft. altitude. n.d. Portion published as Figure 5 in U. S. Geological Survey. Circular 1022. 1988.
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Secondary porosity in Nanushuk Group sandstones. Irregular surface on quartz-overgrowth crystal indicates possible dissolution of siliceous cement. Sample 78AChl75 Kurupa anticline; magnification, XI220, SEM. Central North Slope, Alaska, Published as Figure 49B in U.S. Geological Survey. Bulletin 1614. 1985.
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Secondary porosity features in sandstone from the Nanushuk Group, Embayed grains give secondary pores rounded borders. Pores are oversize and may have resulted from complete dissolution of a framework grain or from dissolution of cement thaft replaced a framework grain. Sample 78ACh799 Kurupa anticline; magnification, 2.5 x 10, photomicrograph. Published as Figure 50C in U.S. Geological Survey. Bulletin 1614. 1985.
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Tightly appressed sandstone from the Nanushuk Group, showing squeezing and contortion of less competent framework grains around more resistant grains and into intergranular spaces. Some cracking of resistant grains has also taken place. Sample 77AAH21f Tuktu Bluff; magnification, 6.3 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 42 in U.S. Geological Survey, Bulletin 1614. 1985.
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Secondary porosity features in sandstone from the Nanushuk Group. Abundant partial dissolution of grains results in elongate and oversize pores and floating grains. Sample 78ACh72, anticline; magnification, 6.3 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 50B in U.S. Geological Survey. Bulletin 1614. 1985.
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Secondary porosity features in sandstone from the Nanushuk Group. Apparent partial dissolution of a rounded polycrystalline quartz grain creates secondary porosity in a highly compacted sandstone. Sample 78ACh72, Kurupa anticline; magnification, 6.3 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 50A in U.S. Geoloqical Survey. Bulletin 1614. 1985.
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Replacement by calcite cement in sandstone from the Nanushuk Group. Framework quartz grain appears to float in calcite cement after partial replacement, but relict grain boundary is still visible. Sample 78AChl6, Kurupa anticline; magnification, 16 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 43B in U.S. Geological Survey. Bulletin 1614. 1985.
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Kaolinite fills pore spaces created by dissolution and (or) replacement of framework grains, in sandstone from the Nanushuk Group. Books of Hexagonal kaolinite crystals growing in pore space. Sample 78ACh41, Marmot syncline; magnification, X1340, SEM. Central North Slope, Alaska. Published as Figure 44C in U.S. Geological Survey. Bulletin 1614. 1985.
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Intergrain boundaries in sandstone from the Nanushuk Group. Stylolitic interpretation of rounded quartzose pebbles, probably resulting from high compaction pressures at grain boundaries. Sample 78AAh47L, Tuktu Bluff, magnification 2.5 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 41B in U.S. Geological Survey. Bulletin 1614. 1985.
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Possible presence of hydrocarbons (?) in Nanushuk Group rocks. Migration apparently occurred during or after compaction of the sandstones. Possible hydrocarbon (?) migration into intergranular pore spaces and into a grain cracked by compaction. Dissolution pore (P) unfilled by hydrocarbon indicates that migration may have occurred prior to creation of dissolution porosity. Sample 78ACh25, Marmot syncline; magnification, 2.5 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 51B in U.S. Geoloqical Survey. Bulletin 1614. 1985.
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Original porosity is still retained in this sandstone sample from the Nanushuk Group, but some reduction in porosity probably took place during compaction. Quartzose grains were dissolved at grain contacts and welded. At some later stage, minor secondary porosity was created by dissolution of quartzose grains (arrow). Growth of chlorite in pore spaces completes diagenetic cycle. Sample 78ACh32, Kurupa anticline; magnification, 6.3 x 10, photomicrograph. Central North Slope, Alaska. Published as Figure 45 in U.S. Geological Survey. Bulletin 1614, 1985.
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Kaolinite fills pore spaces created by dissolution aind (or) replacement of framework grains, in sandstone from the Nanushuk Group. Sample 78ACh54, Kurupa anticline. Central North Slope, Alaska. Published as Figure 44A in U.S. Geological Survey. Bulletin 1614, 1985.
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Intergrain boundaries in sandstone from the Nanushuk. Displacement of pebble boundary and extensive cracking as a result of compaction pressure. Central North Slope, Alaska. Published as Figure 41A in U, S. Geological Survey. Bulletin 1614, 1985.
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Quartz overgrowths on sandstone grains after clay formation, Nanushup Group. Chlorite cement and quartz overgrowths clog intergranular pore spaces. Sample 78ACh32, Kurupa anticline; magnification,, X 234, SEM. Central North Slope, Alaska. Published as Figure 47C in U.S. Geological Survey. Bulletin 1614. 1985.
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Quartz-grain surfaces are coated with chlorite in sandstone from the Nanushuk Group, which may inhibit development of quartz overgrowths. Quartz overgrowth is surrounded by a halo in which no chlorite cement exists. It is uncertain which cement is inhibiting growth of the other. Sample 78ACh32, Kurupa anticline; magnification X319, SEM. Central North Slope, Alaska. Published as Figure 46B in U.S. Geological Survey. Bulletin 1614. 1985.