Petrology and Chemistry of Modern Big River Sands

Abstract

The sands of many of the world's modern big rivers were studied to provide a worldwide baseline of their petrology and chemistry, the ultimate objective being to advance our understanding of the tectonic and climatic significance of ancient sandstones, which extend backward in time almost 3.7 b.y. The sands of 36 rivers, rivers that represent 45% of the earth's land surface draining to the world ocean, are dominantly moderately to well sorted, angular to subangular lithic arenites, notably deficient in clay and silt and have an average feldspar content of 11%, some sands from tropical rivers with low relief watersheds being notable exceptions. Additionally, rivers draining Atlantic or trailing edge continental borders have a composition of , are subangular and have a ratio of 2.04, whereas rivers debouching on the collision coasts of leading or Andean continental margins have a framework averaging , are angular and a ratio of 1.0. Using the foregoing and other data, some of the interrelationships between sandstone maturity, tectonics, climate and earth history are explored. Key Idea: Worldwide baseline of modern river sand composition and its implications for ancient sandstones.