Neoproterozoic Allochthonous Salt-Body Geometry, Minibasins and Salt-Influenced Sedimentation in the Willouran Ranges, South Australia

Thomas E. Hearon IV¹, Patrick T. Hannah¹, Timothy F. Lawton¹, Mark G. Rowan², and Katherine A. Giles^1
1Institute of Tectonic Studies, New Mexico State University, Las Cruces, NM
²Rowan Consulting, Inc., Boulder, CO

Current research and understanding of allochthonous salt-body geometry and structure are mostly based on seismic data and conceptual models because few global onshore basins contain exposed outcrops available for study. An exception is the Willouran Ranges, a northwestern extension of the Flinders Ranges near Marree, South Australia, where outcrop-scale evidence for evaporite formation, subsequent evacuation and diapirism is well exposed in Neoproterozoic strata. Cross-sectional geometries of complex allochthonous salt structures and associated sub- and suprasalt minibasins are displayed in plan view. The Callanna Group (900-850 Ma), the original source of diapiric salt, is an assemblage of brecciated, highly disrupted carbonate, siliciclastic and mafic volcanic rocks that were originally interbedded with evaporites that are no longer present. Salt movement began shortly after deposition of the Callanna and continued during loading by the suprajacent Burra Group strata and younger Sturtian glacial deposits. On the basis of detailed mapping (1:10,000), restored balanced structure sections, eight measured sections and thin-section analysis, we recognize the following allochthonous salt geometries, structures and related stratigraphy: (1) A primary minibasin with a half-turtle structure containing the lower part of the Burra Group, bounded by two primary diapirs with flanking halokinetic deformation; (2) a multi-level, mostly welded canopy with associated debris flows, folded strata and omitted stratigraphic section; and (3) two suprasalt minibasins of different ages, one with basal conglomeratic debris, containing the upper part of the Burra Group and overlying the welded canopy. Our field data and interpretations contribute to a better understanding of salt systems, allowing us to test models of allochthonous salt emplacement and associated salt-sediment interaction.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas