Mechanism of formation of wiggly compaction bands in porous sandstone: 1. Observations and conceptual model. Issue 12 (15th December 2015)

• Record Type: Journal Article
• Authors: Liu, Chun; Pollard, David D.; Deng, Shang; Aydin, Atilla
• Is Part Of: Journal of geophysical research. Volume 120:Issue 12(2015:Dec.)
• Page Start: 8138
• Page End: 8152
• Publication Date: 2015-12-15
• Subjects: wiggly compaction band -- formation mechanism -- sandstone deformation -- porosity -- grain sorting; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2015JB012372
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Field observations are combined with microscopic analyses to investigate the mechanism of formation of wiggly compaction bands (CBs) in the porous Jurassic aeolian Aztec Sandstone exposed at Valley of Fire State Park, Nevada. Among the three types of CBs (T1, T2, and T3), we focused on the wiggly CBs (T3), which show a chevron (T31 ) or wavy (T32 ) pattern with typical corner angles of approximately 90° or 130°, respectively. Where corner angles of wiggly CBs increase to 180°, they become straight CBs (T33 ). Image analyses of thin sections using an optical microscope show host rock porosity increases downslope in this dune, and the predominant type of wiggly CBs also varies from chevron to straight CBs. Specifically, band type varies continuously from chevron to wavy to straight where the porosity and grain sorting of the host rock increase systematically. Based on the crack and anticrack models, we infer that the change from chevron to straight CBs is due to increasing failure angle of the sandstone and this may correlate with increasing grain sorting. Wavy CBs with intermediate failure angle and host rock porosity are an intermediate stage between chevron and straight CBs. Previous sedimentological studies also have suggested that grain size and sorting degree increase downslope on the downwind side of sand dunes due to a sieving process of the wind‐blown grains. Therefore, the transition of wiggly CB types in this regard correlates with increasing sorting and perhaps with increasing porosity downslope. Key Points: Wiggly compaction bands formed in porous sandstone have different patterns Host rock porosity and sorting increase from chevron to wavy to straight CBs The change of CB shapes may due to increasing failure angle of sandstone