Contractional deformation of porous sandstone: Insights from the Aztec Sandstone, SE Nevada, USA

Abstract

International audienceContractional deformation of highly porous sandstones is poorly explored, as compared to extensional deformation of such sedimentary rocks. In this work we explore the highly porous Aztec Sandstone in the footwall to the Muddy Mountain thrust in SE Nevada, which contains several types of deformation bands in the Buffington tectonic window: 1) Distributed centimeter-thick shear-enhanced compaction bands (SECBs) and 2) rare pure compaction bands (PCBs) in the most porous parts of the sandstone, cut by 3) thin cataclastic shear-dominated bands (CSBs) with local slip surfaces. Geometric and kinematic analysis of the SECBs, the PCBs and most of the CSBs shows that they formed during ∼E–W (∼100) shortening, consistent with thrusting related to the Cretaceous to early Paleogene Sevier orogeny of the North American Cordilleran thrust system. Based on stress path modeling, we suggest that the compactional bands (PCBs and SECBs) formed during contraction at relatively shallow burial depths, before or at early stages of emplacement of the Muddy Mountains thrust sheet. The younger cataclastic shear bands (CSBs, category 3), also related to E–W Sevier thrusting, are thinner and show larger shear offsets and thus more intense cataclasis, consistent with the initiation of cataclastic shear bands in somewhat less porous materials. Observations made in this work support earlier suggestions that contraction lead to more distributed band populations than what is commonly found in the extensional regime, and that shear-enhanced compaction bands are widespread only where porosity (and permeability) is high

Distribution, microphysical properties, and tectonic controls of deformation bands in the Miocene subduction wedge (Whakataki Formation) of the Hikurangi subduction zone

“…Outcrop and microstructural data demonstrate that D2 bands, associated with a normal-fault regime, are compactional shear bands (CSBs) with normal-sense shear offset. This is consistent with previous studies of deformation bands formed in extensional tectonic regimes (Soliva et al, 2013;Ballas et al, 2014;Fossen et al, 2015;Soliva et al, 2016;Fossen et al, 2018). Associated with the D3 thrust-fault regime are reverse-sense CSBs and shear-enhanced compaction bands (SECBs), consistent with observations from other contractional regimes (Ballas et al, 2013;Soliva et al, 2013;Ballas et al, 2014;Fossen et al, 2015Fossen et al, , 2018.…”

Numerical Simulation of Deformation Band Occurrence and the Associated Stress Field during the Growth of a Fault-Propagation Fold

“…The fact that high Q/P ratio values were found close to the surface (few hundreds of meters depth), decreasing with depth, does not mean that SECBs generally form before the PCBs. The numerical results suggest that it is not possible to create PCBs, or only in particular areas, which is not what we expected, as these structures were found in most of the sites analyzed in the Tremp basin by Robert et al [24] and also in other areas associated with contractional deformation [7,10,[72][73][74][75]. The numerical results based on LAM only highlight the onset of the deformation, directly linked with the thrust activity, but the method does not allow us to view the stress evolution related to the compression before the fault movement.…”

Tectonic regime controls clustering of deformation bands in porous sandstone

“…Band frequency data (number of bands per meter) were measured in Nevada in the fine to medium grained porous Jurassic Aztec Sandstone (Fossen et al, 2015). This unit has been involved in the Cretaceous Sevier orogeny, with the east to southeast transport of the Muddy Mountain thrust sheet.…”