39 Structural Geology (Posters)

Added due to amount of discipline abstracts submitted.

Wednesday, 11 March 2026
9:00 AM - 12:00 PM
RCC, Lower Level Hall

Clast Orientation and Aspect Ratio Anisotropy Inheritance as a Function of Grain Size: Comparison of Sedimentary Rocks from the Southeastern U.S. and Sangre de Cristo Mountains of New Mexico

Paper number: 39-4
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

A growing body of evidence from deformed and undeformed rocks suggests that sedimentary clasts may develop aspect ratio and orientation anisotropy as a function of grain size. Rf-phi (strain) analysis of deformed conglomerates and metaconglomerates from the southern Appalachians and Picuris Mountains of New Mexico showed significant differences in calculated bulk strain as a function of grain size. In those studies, Rf-phi analysis of clast populations with larger grain sizes (e.g., granules, pebbles) resulted in larger calculated bulk strain than analyses of clast populations with smaller grain sizes (e.g., sand) in the same rock. The observed grain size dependent strain “partitioning”, however, runs counter to mechanical studies of clasts, which suggest that smaller clasts should deform more rapidly than larger clasts during progressive deformation. Subsequent studies showed that clasts in undeformed and relatively undeformed conglomerates from the Gulf Coastal Plain and southern Appalachian Foreland were deposited with initial aspect ratio and grain orientation anisotropy as a function of grain size. In those studies, it was shown that larger grains were more likely to be preferentially aligned than smaller grains and were more likely to have larger aspect ratios than smaller grains. In this research, we compare results from a relatively undeformed conglomerate from the Pennsylvanian Flechado Formation in the Sangre de Cristo Mountains of New Mexico with similar rocks from the southeastern U.S. Interestingly, the conglomerate sample from the Flechado Formation showed far less grain size dependent anisotropy than similar rocks from the Cretaceous Tuscaloosa Formation (Georgia) and Ordovician Attalla Chert (Alabama). We explore the potential for differences in depositional environments and processes as an explanation for the differences in the magnitude of grain size dependent orientation and aspect ratio between the 3 samples.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411843

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