Research about Southern Brooks Range

USGS2008

Preliminary integrated geologic map databases for the United States. Digital data for the geology of the southern Brooks Range, Alaska

The growth in the use of Geographic Information Systems (GIS) has highlighted the need for digital geologic maps that have been attributed with information about age and lithology. Such maps can be conveniently used to generate derivative maps for manifold special purposes such as mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This report is part of a series of integrated geologic map databases that cover the entire United States. Three national-scale geologic maps that portray most or all of the United States already exist; for the conterminous U.S., King and Beikman (1974a,b) compiled a map at a scale of 1:2,500,000, Beikman (1980) compiled a map for Alaska at 1:2,500,000 scale, and for the entire U.S., Reed and others (2005a,b) compiled a map at a scale of 1:5,000,000. A digital version of the King and Beikman map was published by Schruben and others (1994). Reed and Bush (2004) produced a digital version of the Reed and others (2005a) map for the conterminous U.S. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis of this product. The digital geologic maps presented here are in a standardized format as ARC/INFO export files and as ArcView shape files. The files named __geol contain geologic polygons and line (contact) attributes; files named __fold contain fold axes; files named __lin contain lineaments; and files named __dike contain dikes as lines. Data tables that relate the map units to detailed lithologic and age information accompany these GIS files. The map is delivered as a set 1:250,000-scale quadrangle files. To the best of our ability, these quadrangle files are edge-matched with respect to geology. When the maps are merged, the combined attribute tables can be used directly with the merged maps to make derivative maps.

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↗