Influence of Climate and Relief on Compositions of Sands Released at Source Areas

Abstract

Mass balance requires that any study of the relation between provenance and detrital sediments must take into account all the processes, such as climatic and biochemical, that contribute to any modification of the parent material at the beginning of a sedimentary cycle. In addition, exceptions to the relationship between tectonic setting and sandstone composition may be traced to climatic processes. Despite an enormous amount of research on atomic level dissolution phenomenon, little work has been done to characterize the sandy residue of weathering. Available modal data, albeit meagre, show that the mineralogic composition of the sand size fraction of soils is similar to that of first order stream sands. This indicates that pedogenic processes largely control the composition of first cycle sands derived from similar bedrocks. Further, the data also suggest that modal compositions of first cycle sands are broadly indicative of both parent rock type and climate. Recalculation of data from o n l y o n e available study indicates that steep hill slopes exceeding the angle of repose can obscure climatic effects on first cycle sand composition. One may infer that slope angle, which controls the duration of pedogenic processes, not relief, has more significance in overcoming climatic effects. Evaluation of the relative importance of dissolution and disintegration of minerals, especially polycrystalline quartz, is difficult because lattice dislocation increases solubility as well as brittle strength. Given the extreme paucity of data from controlled studies on the effects of climate and relief and the seemingly significant compositional diversity brought about by pedogenic processes, we must conclude that this is a potential area of much fruitful research.