Locke Island is located in the Columbia River in south-central Washington. The US Department of E... more Locke Island is located in the Columbia River in south-central Washington. The US Department of Energy (DOE) owns Locke Island as part of its Hanford Site. In the 1960s and 1970s, as a result of intensive irrigation developments on the inland shoreline to the east of the island, the White Bluffs, which form the eastern boundary of the Columbia River channel in this area, began to show geological failures as excess irrigation water seeped out along the bluffs. One of the largest such failures, known as the Locke Island Landslide, is located just east of Locke Island. By the early 1980s, this landslide mass had moved westward into the river channel toward the island and was diverting the current at the island`s eastern perimeter. Erosion of the bank in the center of the island accelerated, threatening the cultural resources. By the early 1990s, the erosion had exposed cultural features and artifacts along the bank, leading to the beginning of intermittent monitoring of the cutbank. In 1994, DOE initiated more scheduled, systematic monitoring of island erosion to better understand the physical processes involved as well as mitigate ongoing loss of the archaeological record.
Sediments overlying Miocene basalt record aggradation, degradation, and relative tectonic movemen... more Sediments overlying Miocene basalt record aggradation, degradation, and relative tectonic movements within the central Cold Creek syncline, a basin with a long history of subsidence. Seven lithofacies were found to correlate among 40 boreholes over an area of approx. 80 km/sup 2/; five belong to the Neogene fluvial-lacustrine Ringold Formation: (1) a quartzitic, conglomeratic sand overlain by (2) fine-grained fluvial facies capped by a well-developed paleosol, collectively referred to as the basal Ringold. Next, laminated mud (3) accumulated slowly in a low-energy environment. Quartzitic, braided stream gravels (4) of the middle Ringold were deposited next when the main channel of the ancestral Columbia reoccupied the study area. A sudden, regional transition from conglomerate to (5) fine-grained facies is interpreted to reflect upstream changes in either climate or tectonic activity. Other correlative units include: (6) locally derived Pleistocene(.) detritus that filled a paleochannel near the synclinal axis; pedogenic calcrete developed, coevally, adjacent to this channel and (7) late-Pleistocene cataclysmic flood deposits that blanket the study area. Subsurface lithostratigraphic correlations generally corroborate a model for long-term, low-average rate of tectonic deformation. Structure contour and isopach maps suggest syndepositional folding resulted in nearly continuous aggradation and preservation of sediments during Ringold time. Subsidencemore » may have accelerated temporarily during middle Ringold time, as indicated by the thick conglomeratic sequence which is significantly warped at the base but not on top.« less
Worldwide, loess-paleosol sequences are archives of terrestrial Quaternary paleoenvironment data.... more Worldwide, loess-paleosol sequences are archives of terrestrial Quaternary paleoenvironment data. The Rulo site is a newly described site in the Palouse loess of southeastern Washington State, USA. The site reveals a 19 m thick deposit of loess and flood sediment, preserving a total of 30 m of reconstructed stratigraphic section. Five unconformity-bound sequences of sediment are exposed at the site, the lowest two of which have yielded fossil remains, including the first reported occurrence of flat-headed peccary (Platygonus compressus) in northwestern North America. The unconformities, two diamicts bearing extrabasinal clasts, and a number of clastic dikes provide evidence for pre-Wisconsin glacial outburst floods in southeastern Washington. More than a dozen paleosols are preserved at the site. These soils are relatively unweathered and therefore primarily record periods of slow sedimentation accumulation in the Palouse, rather than changes in weathering rates. A paleosol near the base of the sequence is unusually weathered for Palouse paleosols, and records a period of increased weathering during the Middle Pleistocene. All units above the sand are normal paleomagnetic polarity; additional age control is provided by a tephra in the upper third of the sequence that matches a ca. 220 ka tephra from Newberry Volcano, and by stratigraphic correlation of later units to other sites in the Palouse. The Rulo site adds to the record of Irvingtonian fauna in North America, and supports accumulating evidence for pre-Late Wisconsin glacial outburst floods in the Pacific Northwest.
Locke Island is located in the Columbia River in south-central Washington. The US Department of E... more Locke Island is located in the Columbia River in south-central Washington. The US Department of Energy (DOE) owns Locke Island as part of its Hanford Site. In the 1960s and 1970s, as a result of intensive irrigation developments on the inland shoreline to the east of the island, the White Bluffs, which form the eastern boundary of the Columbia River channel in this area, began to show geological failures as excess irrigation water seeped out along the bluffs. One of the largest such failures, known as the Locke Island Landslide, is located just east of Locke Island. By the early 1980s, this landslide mass had moved westward into the river channel toward the island and was diverting the current at the island`s eastern perimeter. Erosion of the bank in the center of the island accelerated, threatening the cultural resources. By the early 1990s, the erosion had exposed cultural features and artifacts along the bank, leading to the beginning of intermittent monitoring of the cutbank. In 1994, DOE initiated more scheduled, systematic monitoring of island erosion to better understand the physical processes involved as well as mitigate ongoing loss of the archaeological record.
Sediments overlying Miocene basalt record aggradation, degradation, and relative tectonic movemen... more Sediments overlying Miocene basalt record aggradation, degradation, and relative tectonic movements within the central Cold Creek syncline, a basin with a long history of subsidence. Seven lithofacies were found to correlate among 40 boreholes over an area of approx. 80 km/sup 2/; five belong to the Neogene fluvial-lacustrine Ringold Formation: (1) a quartzitic, conglomeratic sand overlain by (2) fine-grained fluvial facies capped by a well-developed paleosol, collectively referred to as the basal Ringold. Next, laminated mud (3) accumulated slowly in a low-energy environment. Quartzitic, braided stream gravels (4) of the middle Ringold were deposited next when the main channel of the ancestral Columbia reoccupied the study area. A sudden, regional transition from conglomerate to (5) fine-grained facies is interpreted to reflect upstream changes in either climate or tectonic activity. Other correlative units include: (6) locally derived Pleistocene(.) detritus that filled a paleochannel near the synclinal axis; pedogenic calcrete developed, coevally, adjacent to this channel and (7) late-Pleistocene cataclysmic flood deposits that blanket the study area. Subsurface lithostratigraphic correlations generally corroborate a model for long-term, low-average rate of tectonic deformation. Structure contour and isopach maps suggest syndepositional folding resulted in nearly continuous aggradation and preservation of sediments during Ringold time. Subsidencemore » may have accelerated temporarily during middle Ringold time, as indicated by the thick conglomeratic sequence which is significantly warped at the base but not on top.« less
Worldwide, loess-paleosol sequences are archives of terrestrial Quaternary paleoenvironment data.... more Worldwide, loess-paleosol sequences are archives of terrestrial Quaternary paleoenvironment data. The Rulo site is a newly described site in the Palouse loess of southeastern Washington State, USA. The site reveals a 19 m thick deposit of loess and flood sediment, preserving a total of 30 m of reconstructed stratigraphic section. Five unconformity-bound sequences of sediment are exposed at the site, the lowest two of which have yielded fossil remains, including the first reported occurrence of flat-headed peccary (Platygonus compressus) in northwestern North America. The unconformities, two diamicts bearing extrabasinal clasts, and a number of clastic dikes provide evidence for pre-Wisconsin glacial outburst floods in southeastern Washington. More than a dozen paleosols are preserved at the site. These soils are relatively unweathered and therefore primarily record periods of slow sedimentation accumulation in the Palouse, rather than changes in weathering rates. A paleosol near the base of the sequence is unusually weathered for Palouse paleosols, and records a period of increased weathering during the Middle Pleistocene. All units above the sand are normal paleomagnetic polarity; additional age control is provided by a tephra in the upper third of the sequence that matches a ca. 220 ka tephra from Newberry Volcano, and by stratigraphic correlation of later units to other sites in the Palouse. The Rulo site adds to the record of Irvingtonian fauna in North America, and supports accumulating evidence for pre-Late Wisconsin glacial outburst floods in the Pacific Northwest.
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