Sedimentologic characteristics and paleogeographic implications of Tertiary sedimentary rocks in the upper plate of the Harcuvar metamorphic core complex, northern Rawhide and Artillery Mountains, Arizona

Geologic mapping and analysis of Oligocene-Miocene sedimentary rocks in the upper plate of the Buckskin-Rawhide detachment fault system (west-central Arizona) reveal a complex paleogeographic history during fault displacement, involving shifting sediment-source areas and multiple drainage reversals. Within the study area, four upper-plate fault blocks are capped by homoclinal sedimentary sections that display fanning dip relationships indicating concurrent tilting and sedimentation. Four sedimentary assemblages can be correlated between fault blocks on the basis of lithologic similarity, stratal position, provenance, paleocurrent data, and sparse geochronologic constraints. Detritus within the basal assemblage was derived from the granitic terrane surrounding the northern part of the study area. The overlying lower assemblage contains voluminous quantities of sedimentary breccia that were derived from source areas consisting mainly of Mesozoic and Paleozoic rocks exposed to the south of the study area. Middle-assemblage sediments were deposited by an extensive south-directed stream system that probably flowed off undistended parts of the hanging wall. Upper-assemblage sediments were deposited by a northeast-directed system of broad, shallow streams; these deposits display a variety of clast types, including Tertiary mylonitic rocks that were eroded from the upwarped footwall of the metamorphic core complex. During deposition of these sedimentary rocks, upper-plate sedimentation was intermittently confined to separate half-graben, while at other times rapid rates of aggradation relative to fault-displacement resulted in burial of ridges separating sub-basins.; Evaluation of sedimentary breccia bodies contained within the lower assemblage in the Artillery Peak area indicates that many are of rock-avalanche origin. Some are sufficiently large to have represented large rock avalanches (that is, sturzstroms) at the time of emplacement and display features consistent with descriptions of such lobes. Some rock-avalanche deposits interbedded with lacustrine sediments represent initially subaerial lobes that flowed into lakes. These bodies locally are intruded by substrate-derived injection structures and contaminated by lakebed mud; mud contamination was initially concentrated along the bases of lobes, but affected a progressively greater proportion of the flows with increasing subaqueous runout. Contaminated portions of rock-avalanche lobes exhibit features consistent with decreased shear strength, and thoroughly contaminated lobes appear to have transformed into slow-moving, slurry-like flows that experienced internal cycling of debris.