174 Sediments, Clastic (Posters)

Tuesday, 2 November 2010
8:00 AM - 6:00 PM
Hall D

USE OF SEM MICROTEXTURAL ANALYSIS TO ASSESS GRANITOID WEATHERING IN MODERN AND ANCIENT SEDIMENTARY SYSTEMS

Paper number: 174-8
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

SEM analysis is an established technique to study microtextures imparted on quartz grains as a result of physical and chemical weathering in various depositional environments. Although many of the textures can form in all types of environments, recent work suggests that certain textures may be characteristic of specific environments. For example, high-stress fractures are particularly common in glacial and proglacial systems. If these textures are preserved in ancient strata, then microtextural analysis might provide insight to paleoclimate interpretations. We are testing this by studying microtextures on plutonic-derived quartz grains from modern sediments of the (temperate semi-arid) Wichita Mountains (Oklahoma), and from ancient strata of the Permo-Pennsylvanian Cutler Formation (Colorado). The approach involves documenting the occurrence of textures that reflect (1) high-stress fracturing (e.g. micro-troughs and grooves), (2) percussion-induced fracturing (e.g. V-shaped cracks), and (3) polygenetic fractures (e.g. conchoidal fractures), following Sweet and Soreghan (2010).

The proximal Cutler Formation accumulated adjacent to the ancient Uncompahgre uplift, and has been variously interpreted as the product of hot-arid or hot-humid alluvial fan sedimentation, or cold-humid outwash sedimentation. Distinguishing amongst these options using facies evidence alone is difficult. Preliminary results from the proximal Cutler Formation indicate a high incidence (26% to 56% of the microtextures observed) of high-stress fractures, with the most proximal samples showing the highest incidences of these fracture types. In contrast, preliminary data from the Wichita Mountains exhibit a low incidence of such fractures.

More data, from a wider variety of modern systems, are needed to draw robust conclusions. However, initial results show promise that this approach may ultimately provide a means to distinguish non-glacial and proglacial sediments, especially when combined with other sedimentologic and geochemical data.

Sweet, D.E., and Soreghan, G.S., 2010, Application of quartz sand microtextural analysis to infer cold-climate weathering for the equatorial Fountain Formation (Pennsylvanian-Permian, Colorado, U.S.A.): Journal of Sedimentary Research, v. 80, p. 666-677.