Permian Marine Sand Wave Complex in Central Arizona: ABSTRACT

Abstract

The Lower Permian Rancho Rojo Member of the Schnebly Hill Formation exhibits unusual large-scale compound or intraset cross-stratification near Sedona, Arizona. The very fine-grained, moderately sorted subfeldspathic to quartzarenite, is divided into four facies. The lowermost tabular-planar foreset facies comprises giant foresets that dip westward at 13-19°, with foreset bundles of planar, wavy, and minor intraset cross-strata separated by surfaces of erosion. The intraset cross-stratified facies consists of giant foresets arranged in bundles that contain compound cross-stratification including tabular-planar herringbone pattern and complex trough sets separated by planar and trough erosion surfaces. The westerly dipping master sets have superimposed intrasets that display widely varying current vectors. Both facies were deposited in a marine sand wave complex following rapid transgression across underlying fluvial-estuary deposits. The erosion surfaces that bound the master sets were likely formed during storms. The intraset planar and trough sets were formed by migrating tidally driven megaripples on the westerly dipping surfaces of the sand wave. Documentation is provided by close similarities with other reported ancient sand waves and the newly proposed Allen sand wave model. These two facies are overlain by the ripple-laminated and homogeneous sand facies that developed during the waning stages of sand wave deposition. The former was probably produced by shoaling waves and the latter by bioturbation. The well-exposed Rancho Rojo will help advance the study of these controversial sand bodies and aid in the paleogeographical interpretation of the Permian in central Arizona. End_of_Article - Last_Page 903------------