Bedrock assemblages of the Bering Strait region: Implications for offshore metal sources in the marine environment: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

Professional Paper 1615
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Abstract

The Bering Strait region is important habitat for Pacific walrus (Odobenus rosmarus divergens). Elevated metal levels in tissues of some walrus have raised concerns about the sources of these metals. This study synthesizes and integrates onshore geology, regional gravity and magnetic data, and information about mineral deposits and the natural processes that weather, erode, and disperse metals in the Bering Strait region. In this region (Seward Peninsula, St. Lawrence Island, Chukotsk Peninsula, and intervening areas of the Bering Sea shelf), six bedrock assemblages can be defined and extended from onshore to offshore areas. These assemblages include (1) Paleozoic sedimentary and low-grade metasedimentary rocks, (2) upper Paleozoic to Triassic sedimentary and related mafic igneous rocks, (3) Mesozoic high-pressure, low-temperature metamorphic rocks, (4) Cretaceous amphibolite-facies metamorphic rocks, (5) Cretaceous volcanic and related intrusive rocks, and (6) Tertiary sedimentary and volcanic rocks. Cretaceous plutonic rocks are widely scattered and locally intrude all of the pre-Tertiary bedrock assemblages. The distribution and thickness of Tertiary sedimentary rocks can be approximated in offshore areas using satellite gravity data. The resulting new map shows that about 40 percent of the offshore Bering Strait region may have bedrock at or near the sea floor. Some mineral deposits and rock units with high background metal contents are associated with specific bedrock assemblages whereas other mineral deposits are more regionally distributed. The mineral deposits of the region are mostly types that contain Cu, Pb, Zn, Ag, Mo, Sn, or Au (or certain combinations of these metals) and elevated concentrations of associated elements, such as As, Bi, Be, B, Sb, and F. The mineral deposits have been physically and chemically weathered and eroded by both subaerial and marine processes. Marine processes have been particularly important as the region has experienced several sea-level fluctuations that have alternately exposed and submerged the Bering Sea shelf. The marine transgressions and regressions that accompanied sea-level fluctuations have eroded mineral deposits and reworked and redistributed metals and associated element suites derived from them. The distribution of natural metal sources and the natural processes responsible for dispersal of metals from them to the environment have existed in the Bering Strait region throughout a large part of the Quaternary. As a consequence, the nearshore and offshore areas have served as an accumulation region for metals for at least many hundreds of thousands of years.

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Bedrock assemblages of the Bering Strait region: Implications for offshore metal sources in the marine environment: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998
Series title Professional Paper
Series number 1615
DOI 10.3133/70180648
Year Published 2000
Language English
Publisher U.S. Geological Survey
Publisher location Denver, CO
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 15 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Geologic studies in Alaska by the U.S. Geological Survey, 1998 (Professional Paper 1615)
First page 111
Last page 125
Country United States
State Alaska
Other Geospatial Bering Strait
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