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Figure 5. The Monterey Formation is enriched in trace elements compared to the world shale average (WSA). Among these, uranium and selenium are strongly correlated with organic-carbon-rich intervals (see Figures 6, 7). Monterey Formation data are from outcrop samples reported by Piper and Isaacs (1995a).

Trace Elements in the Monterey Formation Comparted to
World Shale Average (WSA)
Element Average
Shale (WSA)*		 Organic-
carbon-rich
Monterey
Formation*		 Relative
Enrichment
Factor
Silver 0.07 2.1 30
Bromine 4 75 19
Cadmium 0.3 16.5 55
Chromium 90 310 3
Copper 45 103 2
Molybdenum 2.6 38.5 15
Nickel 68 267 4
Antimony 1.5 10.3 7
Selenium 0.6 30.5 51
Uranium 3.7 20.8 6
Vanadium 130 564 4
Zinc 95 335 4

*Parts per million (PPM)

Sources: Turekian & Wedepohl (1961), Piper & Issacs (1995a)

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http://geology.wr.usgs.gov/wreg/env/wsa_chart.html
Contact: Margaret A. Keller (mkeller@usgs.gov)
Western Region Energy Group–Environmental Studies
Modified: July 31, 2002

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