Introduction
The 14 papers that follows continue the series
of U.S. Geological Survey (USGS)
reports on investigations in the geologic sciences in Alaska. The series presents new and
sometimes preliminary findings that are of interest to earth scientists in academia, government,
and industry; to land and resource managers; and to the general public. Reports presented
in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the
State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation’s
needs for earth-science information in Alaska.
The papers in this volume are organized under the topics Geologic Framework,
Environment and Climate, and Resources. Such an organization is intended to reflect the
scope and objectives of USGS programs currently active in Alaska. Geologic framework
studies provide background information that is the scientific basis for present and future
studies of the environment, mineral and energy resources, paleoclimate, and hazards in
Alaska. One paper presents ages of numerous igneous intrusive rocks in southern Alaska
(Bradley and others). The authors demonstrate a systematic, along-strike diachronous age
trend of near-trench magmatism in this region during the early Tertiary. Hildreth and others
provide a map, rock descriptions, and chemical compositions of a geologically young
volcanic center in Katmai National Park. Another paper describes the results of sedimentologic
and paleontologic comparisons of lower Paleozoic, deep-water-facies rock units in
central Alaska (Dumoulin and others). The authors show which of these scattered occurrences
are likely to correlate with one another, suggest likely source regions, and provide a
structural restoration of occurrences that have been fragmented by large fault motions. The
paper by Bradley and Wilson provides the reconnaissance geology of the southeast part of
the Kenai quadrangle. Another paper discusses the character, origin, and deformation of the
major bedrock units within the Fourmile River area in east-central Alaska (Day and others).
Further understanding the bedrock geology of this area is important for the assessment of
potential environmental effects of placer-gold mining operations. The last Geologic Framework
paper presents stratigraphic variations in composition within sandstones of the
Nanushuk Group in the North Slope (Johnsson and Sokol). Studying the variations in the
compositions of fluvial/deltaic sandstones of the Nanushuk Group is important in assessing
climate change in northern Alaska during the Cretaceous.
Environmental studies are the emphasis of five papers. One study focuses on the
environmental effects of gold-placer mining operations on the Fortymile River area of eastern
Alaska (Wanty and others). The authors conclude that there is relatively little effect on
metal content or turbidity of waters downstream from suction-dredge operations in this
region. A second study presents an interesting synthesis and discussion of onshore geology,
regional gravity and magnetic data, information about mineral deposits, and natural processes that disperse metals in the Bering Strait region (Hudson and Saltus). The source
and dispersion of metals in this region is significant because elevated metal concentrations
have been noted in tissues of some Pacific walrus in the Bering Sea. Two papers deal with
climatic conditions during the Quaternary. Muhs and others present morphological and
chemical criteria for identifying buried soils that developed in loess under a variety of different
vegetation types. Loess sequences contain detailed records of Quaternary environmental
conditions. The second paper presents the results of pollen analyses of two late Quaternary
deposits in the southern Cook Inlet region (Ager). These results present the first dated postglacial
vegetation histories for southern Cook Inlet in south-central Alaska and present useful
examples of postglacial vegetation development under the partial influence of maritime
climates. The fifth environmental paper presents major- and trace-element abundances, and
Sr and Pb isotopic compositions of ground waters near Fairbanks (Farmer and others). The
geochemical and isotopic compositions can be used to characterize these waters and assess
the factors controlling variations in dissolved arsenic concentrations.
Resource papers include one that presents recently obtained ages of gold-mineralized
dikes from the Stuyahok area in the Holy Cross quadrangle (Miller and others). The results
suggest that the Stuyahok dikes are part of the Late Cretaceous and early Tertiay belt of
gold-bearing deposits such as Donlin Creek and the Marshall-Kako Creek area in the
Kuskokwim mineral belt. The last two resource papers focus on Ag-Pb-Zn (with or without
Ba) occurrences and deposits in the Brooks Range of Alaska. Kelley and others present
stable-isotope data that supports a genetic relationship between vein-breccia occurrences in
clastic rocks and overlying shale-hosted massive sulfide deposits, such as the Red Dog
deposit in northwestern Alaska. Soil and stream-sediment geochemical analyses and detailed
descriptions of the vein-breccia occurrence at Whoopee Creek make up the subject matter of
the last Resource paper (Schmidt).
Two bibliographies at the end of the volume present reports about Alaskan earth
sciences in USGS publications during 1998, and reports about Alaska by USGS authors in
non-USGS publications during the same period.