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Thinly laminated siltstoneand sandy siltstone are major components of the Upper Permian Brushy CanyonFormation, west Texas and south New Mexico. These rocks have been variouslyinterpreted as the deposits of low-density turbidity currents or as windblownsediment deposited over water. Nevertheless, all models agreed that thislithology was deposited without subsequent reworking by bottom currents orburrowing organisms. These siltstones, thus, are ideal test units for quantitativelyestimating hydraulic properties of the flows that formed them. In particular,the Zr-Ti ratio was tested as a geochemical proxy for flow size and transportdistance. In situ geochemical abundance and grain sizeof particles with contrasting susceptibility to erosion—Zr- and Ti-richparticles—were mapped and measured by X-ray fluorescence analytical microscopy,μXRF. Lamination thickness was measured from Fe fluorescence intensity, whichincreased sharply at the top of each layer. Within the same sample, zircongrains were systematically finer than rutilated quartz grains. Zr-Tifluorescence ratio positively correlated with lamination thickness, notparticle sizes. In other words, Zr-Ti fluorescence ratio fluctuations resultedfrom variations in mineral abundance. Therefore, variations of Zr-Tifluorescence ratio in these siltstones are likely caused by fluctuations in theintensity of erosional events rather than transport distance. High Zr-Ti ratiosand thick laminations reflect periods of enhanced erosion. The average windvelocity during typical events was estimated to be at least 150 km?hr?1,or the equivalent of a Category 1 hurricane. The method used here could beapplied to both outcrop and subsurface strata correlation.

KEYWORDS

Windblown Dust, Laminated Siltstones, Geochemical Mapping, Upper Permian Brushy Canyon Formation

Cite this paper

Motanated, K. and Tice, M. 2016 Siltstone Geochemical Compositions: Applications for Event Size and Correlation. International Journal of Geosciences, 7, 189-199. doi: 10.4236-ijg.2016.72015.





Autor: Kannipa Motanated1*, Michael M. Tice2

Fuente: http://www.scirp.org/



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