BEDROCK GEOCHEMICAL MAPS COMPARED WITH SOIL GEOCHEMISTRY OF AGRICULTURAL REGIONS OF THE MIDWEST OF THE USA
The bedrock determines soil trace element chemistry only (anomalous)). Stream sediment maps (SSM) were used as a secondary documentation of regional geochemistry. Data was collected and used from the United States Geological Survey (USGS). Twelve elements were selected include As, Cd, Cr, Co, Cu, Pb, Mn , Hg, Ni, Se, V, Zn. The data was calculated according to TCI equation and incorporated into Geosoftware (Oasis montaj) to generate geochemical maps. USA geochemical maps were exported into ArcGIS software to clip three states. The chemical concentrations were normalized by maximum values of MAC for agricultural soil applications in USA according to the equation:
Total Geochemical Influence (TCI) = Σ Ci/Li
C: concentration of each element
n: number of chemicals considered (12)
L: Limit = MAC
i: sequence of the chemicals 1:12
MAC: Maximum Allowable Concentration
TCI: Total Chemical Influence
State maps can show chemicals as synthetic, lithologic bedrock, geochemical maps. That idea was tested through comparison of GMs with LGMs. the results showed that soils have been chemically impacted on a widespread scale. Iowa was the most effective region except four small circular areas in the east, center, and west side with lower concentration of chemicals. The reason probably might be that almost of Iowa are used for agricultural active areas.
The concentrations of elements In Northwest and Southwest of Nebraska were very low compare to Northeast & Southeast as anomalies areas. This big region where is investigated to be zero agricultural applications. In Kansas, all the higher concentrations located and completely cover the Northeast and Southeast that extend to middle north of the state.