The dynamics and interaction of compaction bands in Valley of Fire State Park, Nevada (USA): Implications for their growth, evolution, and geostatistical property

摘要

Geometry, geostatistics and microstructures of two sets of high-angle compaction bands within Aztec Sandstone are investigated for the purpose of characterizing their dimensions, distributions, and growth dynamics. Both sets generally terminate at the dune boundaries. The first set of compaction bands is longer than the second set, which is thought to be controlled by the depositional architecture. The macroscopic thickness of single compaction bands varies from zero at their tips to maximum values, 3 to 10 mm commonly within the central parts. The compaction bands often cluster into zones, the thickness of which increases by addition of a new band subparallel to the previously formed bands. The average thickness of a given zone does not change significantly except for a limited number of places along their lengths and a high thickness/distance gradient at their ends. The high thickness anomalies in the thickness distribution plots along the zones correspond to local complexities such as eye structures, steps, and intersections of converging or diverging bands and may reach to about 35 cm. Microstructural analysis of single compaction bands highlights the presence of two typical portions, a thin portion and a thick portion. The thin portion of the band contains pockets of tightly packed grains surrounded by large pores in the band. The thick portion is characterized by an almost homogeneously distributed compaction throughout the band. The thin portions are found close to the tips, whereas the thick portions occur primarily in the central parts of the bands. Two other characteristics of both single bands and zones of bands in high resolution images are that their thicknesses appear to be smaller and that their lateral boundaries are unexpectedly rough with respect to their appearance in outcrops and hand samples, the latter of which may play an important role in their lateral growth. (C) 2015 Elsevier B.V. All rights reserved.