Figure 1 Rock to Duck–shows the Selenium Cycle for Kesterson
National Wildlife Refuge: How trace elements make their way from rock
outcrops into ground and surface water and eventually were concentrated
in standing bodies of water.
Contents–[this
page; see also the Site Map].
Issues
and Research–How did selenium first come to public attention
in the United States? How are rocks related to selenium enrichment in
surface water, ground water, plant, and soil? This web page provides background
and research results on certain sedimentary rocks that are enriched in
trace elements, including selenium.
Figure
2 Map of Petroleum source rocks and sedimentary basins in California–shows
sedimentary basins, onshore oil and gas fields, and principal areas of
California where trace element enrichment may occur.
Figure
3 Selenium Study Areas in the Arid and Semi-Arid Western United States–shows
the relationship of Cretaceous and Tertiary marine mudstone outcrops to
selenium contamination at study sites investigated by the Department of
the Interior (DOI) National Irrigation Water Quality Program.
Trace
Elements in the Monterey Formation–The Monterey Formation
is the principal petroleum source rock of California. It also contains
abundant trace elements, including selenium and uranium.
Figure
4 Stratigraphy of the Monterey Formation in the Santa Maria Basin, central
coast California–shows age and stratigraphic relationships
of rocks, including the Monterey Formation, in the Santa Maria Basin.
Figure
5 Chart of Trace Element Enrichment in the Monterey Formation–shows
that trace elements in the Monterey Formation are enriched compared to
the world shale average (WSA).
Figure
6 Correlation Diagram of Selenium and Organic Carbon in the Monterey Formation–shows
the strongly positive correlation between organic carbon and selenium.
Figure
7 Uranium and Selenium Content of Arco Bixby #1–shows the
relationship between uranium, selenium, and the gamma-ray well-log signature
of the Monterey Formation.
Depositional
Model for Trace Element Enrichment of the Monterey Formation–Marine
mudstones may become enriched in trace elements during deposition.
Using
Gamma-Ray Logs to Estimate Selenium Content of Rocks–In
the Monterey Formation, where uranium and selenium are highly correlated,
gamma-ray logs provide a proxy indication of selenium content.
Figure
8 Block Diagram–shows well log and outcrop gamma-ray methods
for detecting uranium-rich marine mudstones.
Figure
9 Average Annual Precipitation in the Western United States–shows
the high aridity of the western U.S., a region where selenium becomes
concentrated in soils due to evapo-transpiration processes.
Recent
Studies: Trace Elements in the Moreno Shale–Samples of the
Cretaceous Moreno Formation are enriched in selenium. Analyses show correlation
with organic-carbon-rich intervals in the formation, however, the correlation
is not as strongly positive as in the Monterey Formation.
Figure
10 Exxon Cheney Ranch #1 and Magnet Fearon #2–shows the location
of two wells where the Moreno Formation was sampled in the Cheney Ranch
and Coalinga oil fields.
Figure
11 Stratigraphy of the Moreno Formation in the western San Joaquin Basin,
central California–shows the age and stratigraphic relationships
of the Moreno Formation in the San Joaquin Basin.
Figure
12 Trace Element Content in Moreno Formation-shows that trace elements
are somewhat enriched in this formation.
Figure
13 Correlation Diagram of Selenium and Organic Carbon in the Moreno Formation-shows
the positive correlation between organic carbon and selenium, much like
the relationship between these components in the Monterey Formation.
Related
Studies–current USGS studies in the Minerals Program are
addressing trace element contamination issues associated with phosphate
mining in Idaho. Further studies are needed to refine our understanding
of other means by which selenium and other trace elements can pose a hazard
to health.
Frequently
Asked Questions (FAQ) about Selenium– Answers to questions
about the uses of selenium and the toxicity of selenium to humans and
wildlife.
Links–Trace
elements on the world-wide web.
Further
Readings–A short list of USGS and other literature about
selenium and a more comprehensive list of references mentioned in this
web site.
Site
Map–The graphics-rich equivalent of this site and an additional
navigational tool.
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http://geology.wr.usgs.gov/wreg/env/content.html
Contact: Margaret A. Keller (mkeller@usgs.gov)
Western Region Energy Group–Environmental Studies
Modified: November 15, 2002 |
