Geology Reports⌕ Search

Geology topics

D.R. Thor

Publications and source records attributed to D.R. Thor.

6 recordsLinked to original sources
USGS1981

Depositional and erosional features of the inner shelf, northeastern Bering Sea.

Sonographs and bathymetric profiles from water depths less than 15m in the Nome-Solomon, Port Clarence, and Yukon Delta areas of the Alaskan Bering Sea coast show features generated by waves, currents, and drifting ice. The surficial sediments in the Nome-Solomon and Port Clarence areas range in grain size from sand to boulder gravel and have many surface features visible on sonographs, whereas the sediments off the Yukon Delta are fine sands and silts that have few such features. Materials in the Nome-Solomon and Port Clarence areas have been seggregated by grain size into ribbons and irregular, elongate, and lobate patches. Coarse sand and fine gravel patches and ribbons are characterized by symmetrical ripples generated by storm waves. Ice-gouged furrows occur in all the nearshore areas studied.-from Authors

Geologie en Mijnbouw↗
USGS1979

Biogenic and thermogenic gas in gas-charged sediment of Norton Sound, Alaska

Chemical and isotopic compositions of sediment gas from Norton Sound have been determined for near-surface, gas-charged sediments at two sites identified in acoustic profiles and bottom observations. At one site air-driven vibracorer penetrated sediment saturated with methane. The isotopic value suggests that the methane originated from active biological processes operating on peat in the top 4 m of sediment. At the other site, characterized by a large subsurface acoustic anomaly , smaller near-surface acoustic anomalies and active seepage of gas, the vibracorer obtained sediment saturated with gas composed of 98% CO2. Associated with the CO2 are minor concentrations of petroleum-like light hydrocarbons. The carbon isotopic compositions of CO2 and methane along with the chemical distribution of gaseous hydrocarbons indicate that at this site these gases are derived from thermal processes operating at depth in Norton Basin. Apparently CO2 from the decarbonation of marine limestone acts as a carrier for hydrocarbon gases that have been generated from organic matter buried in the basin. The gases reach the surface by faults and escape at the seafloor as a submarine seep. The presence of near-surface gas-charged sediment in Norton Sound reduces the stability of the seafloor. Areas where sediments are charged with gas may pose potential hazards for engineering developments.

Alaska↗
USGS1979

Geologic implications and potential hazards of scour depressions on bering shelf, Alaska

Flat-bottomed depression 50-150 m in diameter and 60-80 cm deep occur in the floor of Norton Sound, Bering Sea. These large erosional bedforms and associated current ripples are found in areas where sediment grain size is 0.063-0.044 mm (4-4.5 ??), speeds of bottom currents are greatest (20-30 cm/s mean speeds under nonstorm conditions, 70 cm/s during typical storms), circulation of water is constricted by major topographic shoals (kilometers in scale), and small-scale topographic disruptions, such as ice gouges, occur locally on slopes of shoals. These local obstructions on shoals appear to disrupt currents, causing separation of flow and generating eddies that produce large-scale scour. Offshore artificial structures also may disrupt bottom currents in these same areas and have the potential to generate turbulence and induce extensive scour in the area of disrupted flow. The size and character of natural scour depressions in areas of ice gouging suggest that large-scale regions of scour may develop from enlargement of local scour sites around pilings, platforms, or pipelines. Consequently, loss of substrate support for pipelines and gravity structures is possible during frequent autumn storms. ?? 1979 Springer-Verlag New York Inc.

Environmental Geology↗
USGS1979

Modern biogenic gas-generated craters (sea-floor “pockmarks”) on the Bering Shelf, Alaska

As many as 1,340 small craters per square kilometre cover the sea floor of Norton Sound in the northeastern Bering Sea. The craters are circular pits, 1 to 10 m in diameter and less than 1 m deep, observed on sonographs over 20,000 km 2 of northern Norton Sound sea floor. Craters typically are associated with acoustic anomalies, near-surface peaty mud, and gas-charged sediment. The peaty mud is a thick (>1.5 m), nonmarine pre-Holocene deposit that is now covered by a 1- to 3-m-thick layer of Holocene marine mud in the area of the craters. The peaty mud (2% to 8% organic carbon) contains abundant biogenic methane [C 1 /(C 2 + C 3 ) = 256 to 7,669] with carbon isotope (δ 13 C) values of −69‰ to −75‰- Decomposition of organic debris in the peaty mud apparently charges the mud with gas. The peaty and gassy zones attenuate sound waves and cause acoustic anomalies on high-resolution seismic profiles in the area with craters. The craters are forming now, as shown by the disruption of modern ice gouges by the craters. In the absence of storms, the gas apparently is trapped in the peaty mud in a saturated state by the cover of Holocene mud. Periodically, possibly during storms, the gas escapes through the thin Holocene cover and forms craters.

Alaska↗
USGS1979

Resource report for proposed OCS lease sale 57: Norton Basin, Alaska

This report is a summary of information about an area of the northern Bering Sea continental shelf that is bounded by the Seward Peninsula on the north, by the line of the United States-Russia Convention of 1867 on the west, and by St. Lawrence Island and the coastline that rims Norton Sound on the south and east. Scholl and Hopkins (1969) report that a sedimentary basin underlies the offshore area. More recent data, which form the basis of part of this report, show the basin is deepest beneath Norton Sound; also, the basin has sufficient depth and areal extent that the basin may be a target for development of hydrocarbon resources after Outer Continental Shelf (OCS) Lease Sale 57. The informal, but widely used, name for the basin is Norton Basin. The following discussion includes regional geology, geologic history, and offshore structure and stratigraphy as background data to discussion of the hydrocarbon potential and resource appraisal of the offshore area. Sections on environmental geology and on the technology and manpower needed and available for development of offshore resources are also included.

Alaska↗