Regional geochemistry of cryptic geology: variations in trace element distribution across the Southern Uplands terrane, Scotland

Abstract

Stream-sediment geochemistry is commonly used to provide a regionally averaged, background composition against which may be judged the anomalies caused by unusual geology, mineralisation or pollution. Its interpretation may be based on assumptions of relative compositional uniformity within broad categories of bedrock lithology. This approach is undermined by the dramatic variations in stream-sediment chemistry that occur over some large areas of superficially homogeneous geology. In these cases, regional geochemistry may pickout subtle compositional variations in bedrock that are not otherwise apparent. Thick greywacke sequences present a particular problem of geological interpretation by virtue of their general uniformity, with a good example provided by the Southern Uplands terrane. There, some stratigraphical variations in greywacke composition, reflecting changes in sedimentary provenance, are known from petrographic and analytical work but are not visible macroscopically. However, contoured stream sediment geochemistry maps, supplemented by cross-strike element abundance profiles, reveal a remarkable level of detailed variation pertinent to stratigraphical sub-division and a much-improved provenance interpretation. Of particular value are the transition metals Cr-Ni-Mg-V and the feldspar-related elements Sr-Rb-K-Ba, the latter defining a major structural break within the terrane. An important corollary to the improved geological understanding arising from regional geochemical survey is the parallel improvement in understanding of the surface processes influencing element distribution in the stream-sediment environment.

Arsenic and presumed resistate trace element geochemistry of the Lincolnshire (UK) sedimentary ironstones, as revealed by a regional geochemical survey using soil, water and stream sediment sampling

“…In addition to presenting results in a series of geochemical atlases, G-BASE samples and data are utilised in a wide range of applications and reported in peer-reviewed publications. Recent publications have shown how these regional geochemical data can be used: to interpret subtle geological changes (Stone et al, 2004); to demonstrate the relationships between soils, heavymetal pollution and parent material (Breward, 2003;Rawlins et al, 2002Rawlins et al, , 2003; in bioacessibility studies (Palumbo-Roe et al, 2005), in archaeology (Chenery et al, 2001); and surface water research (Hutchins et al, 1999). The geochemical maps shown here display a subset of the regional geochemical data used in the Humber-Trent Regional Geochemical Atlas (British Geological Survey, 2007), re-gridded at a suitable scale (100 m per pixel).…”

Geological controls on radon potential in Scotland

“…Group units (Stone et al, 2004) implying an evolved granitic sediment sourcedisplays a provisional moderate radon potential of 3.9 %>AL (Table 5), although more measurements would be required to confirm this.…”

Editorial

“…Stream sediment sampling and analysis is a standard method of exploration and pollution monitoring, but may not always provide solutions in 'homogenous' regions. Stone et al 10 have implemented a method of contouring and profiling to maximise contrasts in bedrock chemistry. Their example is the Southern Upland terrane of Southern Scotland.…”