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T. D. Hamilton

Publications and source records attributed to T. D. Hamilton.

At least 37 records · Page 2Linked to original sources
USGS1983

Late Holocene ice wedges near Fairbanks, Alaska, USA: Environmental setting and history of growth

Test trenches excavated into muskeg near Fairbanks in 1969 exposed a polygonal network of active ice wedges. The wedges occur in peat that has accumulated since about 3500 yr BP and have grown episodically as the permafrost table fluctuated in response to fires, other local site conditions and perhaps regional climatic changes. Radiocarbon dates suggest one or two episodes of ice-wedge growth between about 3500 and 2000 yr BP as woody peat accumulated at the site. Subsequent wedge truncation evidently followed a fire that charred the peat. Younger peat exhibits facies changes between sedge-rich components that filled troughs over the ice wedges and woody bryophytic deposits that formed beyond the troughs. A final episode of wedge development took place within the past few hundred years. Pollen data from the site indicate that boreal forest was present throughout the past 6000 yr, but that it underwent a gradual transition from a predominantly deciduous to a spruce-dominated assemblage. This change may reflect either local site conditions or a more general climatic shift to cooler, moister summers in late Holocene time. The history of ice-wedge growth shows that wedges can form and grow to more than 1 m apparent width under mean annual temperatures that probably are close to those of the Fairbanks area today (-3.5°C) and under vegetation cover similar to that of the interior Alaskan boreal forest. The commonly held belief that ice wedges develop only below mean annual air temperatures of -6 to -8°C in the zone of continuous permafrost is invalid.

Alaska↗
USGS1983

The Alaska Mineral Resource Assessment Program: Guide to information contained in folio of geologic and mineral resource maps of the Philip Smith Mountains quadrangle, Alaska

The geology and mineral resources of the Philip Smith Mountains quadrangle were virtually unexplored until the investigations for oil began in northern Alaska. Construction of the Trans-Alaskan Pipeline System has now made the quadrangle accessible by road. In 1975 and 1976 a team of geologists, geochemists, and geophysicists investigated the quadrangle in order to assess its mineral resource potential. This report is a guide to the resulting folio of twelve maps that describe the geology, stream sediment geochemistry, aeromagnetic features, Landsat imagery, and mineral resources of the area. The bedrock geology and aeromagnetic surveys show that mineral deposits associated with intrusive rocks are probably absent. However, the geology and geochemical anomalies do indicate the possibility of vein and strata-bound deposits of copper, lead, and zinc in the Paleozoic shale and carbonate rocks in the southern part of the quadrangle and of stratabound deposits of zinc and copper in the Permian and Mesozoic shales along the mountain front. The northwestern part of the quadrangle has a low to moderate potential for oil or gas; Mississippian carbonate rocks are the most likely reservoir. The only minerals produced to date have been construction materials.

Alaska↗
USGS1982

A late Pleistocene glacial chronology for the southern Brooks Range: Stratigraphic record and regional significance

Radiocarbon dates from 11 measured sections in the Koyukuk region provide a chronology of the last Pleistocene glaciation. Glaciers were advancing strongly by 24,000 yr ago; they built moraines near the south flank of the Brooks Range, retreated briefly about 22,000 to 20,000 yr B.P., then readvanced at least one more time into their terminal zones. Glaciation was accompanied by alluviation of the Koyukuk and Kobuk drainage systems and by periglacial processes that resemble those taking place today farther north and at higher altitudes. Moraines near the south flank of the range were being revegetated by 13,500 yr B.P. A strong final readvance into end-moraine belts of some northern valleys occurred about 13,000 to 12,500 yr ago, and this event may be synchronous with less extensive glacier readvances in upper valleys of the Koyukuk region. Upper valleys were largely deglaciated by 11,800 yr B.P. Dated Stratigraphic sections from the northern Alaska Range show similar ages for initiation and close of glaciation and also suggest a possible interstadial episode about 20,000 yr ago. Scanty records of fluctuations during ice wastage probably reflect the general scarcity of datable wood, peat, and organic soils between about 19,500 and 13,500 yr ago. The Brooks Range and Alaska Range chronologies closely approximate glacial successions determined else-where in eastern Beringia and in Siberia. Advance and retreat of glaciers throughout this region evidently were associated with widespread climatic changes that also controlled the late Wisconsin history of the Laurentide ice sheet. The Itkillik II and late Itkillik phases of former usage are part of a single glaciation that was entirely separate from the preceding Itkillik I ice advance. For this reason, the local term "Walker Lake Glaciation" is here extended to the last major glaciation of the entire southern Brooks Range, and use of Itkillik phases should be discontinued. The term "Itkillik Glaciation" is hereby restricted to the next older ice advance, in accord with its original definition. Cold and dry conditions during the last glaciation of eastern Beringia are indicated by (1) relatively small mountain glaciers, (2) slight (200-m) depression of glaciation limits below modern values, (3) periglacial features indicating severe frost action on slopes with little protective plant cover, (4) widespread accretion of eolian sand, (5) low pollen influx rates, (6) scarcity of radiocarbon-datable organic remains, and (7) general absence of carbonaceous paleosols. Plant growth may have been much more restricted than generally believed, with relatively low capacity to support grazing animals and human hunting bands.

Alaska↗
USGS1982

Pingos in the Brooks Range, northern Alaska, U.S.A.

Some 70 pingos occur at 27 separate localities within and near the Brooks Range. The pingos are distributed through mountain valleys at altitudes up to 725 m and in terrain glaciated as recently as late Wisconsinan time. Most are open-system forms; possible closed-system pingos are present at only a single locality in a northern valley. Some pingos occur on thick alluvial or lacustrine sediments, but many seem to be localized above near-surface bedrock and possibly are related to northeast-trending fracture systems. Pingos are particularly abundant in the Koyukuk and Chandalar drainage systems of the south-central Brooks Range, where they may be associated with structural features of regional extent.

Alaska↗
USGS1979

The Alaskan Mineral Resource Assessment Program: Guide to information contained in the folio of geologic and mineral resource maps of the Chandalar quadrangle, Alaska

The Chandalar quadrangle in east-central Alaska was investigated by a multidisciplinary research group to assess the mineral resource potential of the quadrangle. This circular serves as a guide to and integrates with a folio of 10 miscellaneous field study (MF) maps and 2 open-file (OF) reports (table 1) concerned with the geology, geophysics, geochemistry, Landsat imagery, and mineral resources of the area. Revisions to the previously published Chandalar quadrangle geologic map, a new radiometric age determination, and a bibliography are also included.

Alaska↗