Geomorphological controls on the distribution of placer deposits

Abstract

The objective of this paper is to show that the global distribution of placer deposits is largely a product of variation (both at present and in the recent geological past) in geomorphological processes acting at the earth's surface, given suitable primary mineral sources. The distribution of known placers of diamonds and gold as well as certain littoral placers is considered in relation to the occurrence and tectonic setting of the primary sources of the various minerals. Climatic controls of the many variables that are relevant to placer formation (e.g. weathering, rate of erosion, nature of sediment supply, opportunities for sediment reworking) are discussed in terms of broad morphogenetic regions. Five such regions are identified on the basis of distinctive combinations of the geomorphological processes responsible for placer formation. Global changes in climate and accompanying changes in the surface processes responsible for placer formation during both the Tertiary and, more particularly, the Quaternary have been important in producing the alternation between erosional and depositional conditions that is especially suitable to placer formation. Primary source tectonic setting and morphogenetic processes all interact to allow the identification of regions in which placer formation is favoured.

Novel Techniques to Study Ancient Micro Amber from Tropical Beach Sand Reveal a Treasurehouse of Exceptionally Well Preserved Fossilized Microfungi

“…The present studies showed that dimensions of Indian Large pieces of amber can be easily disintegrated due to natural forces such as abrasion, friction, erosion, action of turbulent currents (Poinar, 1992;Sutherland, 1985). In natural sandy strata abrasion due to shifting sand particles which have sharp edges may also cause disintegration over period of time.…”

Zirconium and hafnium

“…Microtidal coasts-that is, those with tidal ranges of less than 2 m, such as those in southwestern Australia-have long been considered to be the most favorable for coastal placer development (Sutherland, 1985). In these systems, placers of beach (foreshore environment) and eolian (backshore or dune environment) origin are common (figs.…”

Novel Techniques to Study Ancient Micro Amber from Tropical Beach Sand Reveal a Treasurehouse of Exceptionally Well Preserved Fossilized Microfungi

“…Disintegration of original large pieces of amber may take place because of demanding hot, humid, turbulent and erosive tropical conditions in India. Large pieces of amber can be easily disintegrated due to natural forces such as abrasion, friction, erosion, action of turbulent currents [12,21]. In natural sandy strata abrasion due to shifting sand particles which have sharp edges may also cause disintegration over period of time.…”