Advance of Allochthonous Salt Sheets: Field Evidence from the Patawarta Diapir, Flinders Ranges, South Australia

Mark G. Rowan¹, Timothy F. Lawton², Katherine A. Giles², Patrick T. Hannah², and Thomas E. Hearon^2
1Rowan Consulting, Inc., Boulder, CO
²Institute for Tectonic Studies, New Mexico State University, Las Cruces, NM

The Patawarta diapir, located in the Central Flinders Ranges of South Australia, is an allochthonous salt sheet and equivalent weld with a ramp-flat geometry at its base. It provides a natural laboratory for testing models of allochthonous salt emplacement. We emphasize here three salient aspects of the observed relationships. First, the sheet is underlain by a continuous base-salt-parallel zone of disrupted strata up to 300m in thickness, similar to so-called gumbo or rubble zones in the Gulf of Mexico. However, there is no evidence that this is a basal shear zone. Instead, it is a debrite containing clasts of both diapir and overburden lithologies and is interpreted as a debris apron deposited at the toe of the topographic scarp at the front of the advancing sheet. Second, beneath the debris apron is a zone of folded strata that is narrower beneath the base-salt flat and more pronounced at the ramp, creating a triangle of apparently thickened strata at the base of the ramp. Stratigraphic thickness and facies variations show that this deformation was caused by halokinetic drape folding at the edge of the salt sheet rather than by thrusting or shearing beneath the sheet. Third, the ramp is a true ramp in the sense that it cuts up-section. It did not form by subsalt thrust imbrication and folding of an original base-salt flat. There is one minor thrusted fold in front of the ramp that may be related to either sheet advance or later orogenic shortening, but there is no evidence of an accretionary wedge geometry in the subsalt section and accretionary advance of the salt sheet.

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