Geochemical landscapes of the conterminous United States: New map presentations for 22 elements

Shacklette and Boerngen (1984) collected soil and other regolith samples from 1,323 sites in the conterminous United States (7,840,000 km 2 ) and prepared single-element point-symbol geochemical maps in black and white for7 major and 39 trace elements. We have reprocessed these data, using weighted-median and Bootstrap procedures for interpolation and smoothing, and produced full-color maps for seven major elements (Al, Ca, Fe, K, Mg, Na, and Ti) and 15 trace elements (As, Ba, Cr, Cu, Hg, Li, Mn, Ni, Pb, Se, Sr, V, Y, Zn, and Zr). Comparison of the K map produced in this manner with a corresponding map obtained from airborne radiometric measurements of 4 0 K indicates that the reliability of the soil maps is good even with this ultra low sample density. Many broad geochemical dispersion patterns for both major and trace elements have been delineated. Some of these agree with known geologic and physiographic features, whereas others seem to reflect variations in natural parameters such as soil type and climate. Certain patterns may be due to pollution, and others are difficult to interpret in view of the present knowledge. It is concluded that geochemical maps based on ultra low density sample distributions, such as those presented in this publication, should have potential use in various fields. This type of map may be used to (1) establish general baselines against which more specific natural geochemical variations and human-induced perturbations can be appraised, (2) reflect large underlying geologic features and therefore delineate geochemical provinces of interest in exploration for mineral resources, (3) show how geochemical patterns in the regolith are influenced by natural features such as soil type, climate, and vegetation, (4) provide a basis for research within the field of geomedicine (environmental geochemistry and health), and (5) show large geochemical contrasts between continents.