96-11 Breakout and Advance at Beltana: Allochthonous Salt Emplacement in the Flinders Ranges of South Australia

Session: Twenty-Seven Years of Advances in Understanding Salt-Sediment Interaction: A Legacy of Katherine A. Giles

Presenting Author:

C. Evelyn Gannaway Dalton

Authors:

Gannaway Dalton, C. Evelyn¹, Giles, Katherine A.², Brunner, Benjamin³, Fiduk, J. Carl⁴, Giles, Sarah M.⁵, Rowan, Mark G.⁶, Lankford-Bravo, David F.⁷, Langford, Richard P.⁸

(1) Department of Geosciences, Utah State University, Price, UT, USA, (2) Department of Earth, Environmental and Resource Sciences, University of Texas El Paso, El Paso, TX, USA, (3) Department of Earth, Environmental and Resource Sciences, University of Texas at El Paso, El Paso, TX, USA, (4) Fiduk Consulting, LLC, Houston, TX, USA, (5) Lamont-Doherty Earth Observatory, Columbia University, Houston, TX, USA, (6) Rowan Consulting, Inc., Boulder, CO, USA, (7) BP Exploration, House, TX, USA, (8) Department of Earth, Environmental and Resource Sciences, University of Texas at El Paso, El Paso, TX, USA,

Abstract:

The initial breakout and subsequent advance of allochthonous salt involves the dynamic interplay between salt body growth, sedimentation patterns, and accommodation rates. Oblique cross-sectional exposures of the Beltana diapir in the Flinders Ranges of South Australia capture the transition from feeder diapir to allochthonous salt sheet. We use new field mapping, along with sedimentologic, stratigraphic, structural, and geochemical analyses to decipher a complex sequence of allochthonous salt emplacement during the late Neoproterozoic, adding to the inventory of styles by which salt breaks out and advances laterally.

 

In a subsalt position, a partially to completely overturned syncline is preserved beneath a base-salt flat. The folding occurs over a lateral distance of <200 m, indicative of a hook halokinetic sequence. Additionally, various diapir-proximal conglomerates and breccias occur that are atypical of regional sedimentation. Tabular and lenticular intervals of roof- and diapir-derived pebble conglomerates are involved in the aforementioned drape fold. Upsection towards the base-salt and along strike away from the feeder, these are replaced by more chaotic horizons, transitioning to boulder breccias containing diapir-derived clasts and recycled blocks of roof- and diapir-derived conglomerates. Collectively, this suggests the abrupt transition from feeder diapir to allochthonous sheet occurred initially by slump breakout, and continued lateral advance occurred by pinned inflation. Roof strata were halokinetically drape-folded until oversteepening led to slope failure, allowing for lateral breakout. Roof- and diapir-derived material were thus progressively shed into the minibasin by gravity-driven transport processes and subsequently overridden by the advancing sheet, supporting interpretations invoking slumping, rather than shear, to produce rubble zones beneath salt.

 

In a suprasalt position, discontinuous outcrops of unique dolomitic facies sit stratigraphically just above the inclined top of the salt sheet and are interpreted to form in locally shallow-water settings above the inflated sheet, passing quickly upsection into deeper-water regional facies. Above these suprasalt strata are klippen of diapiric material above a subhorizontal contact, representing the base-salt of a second, shallower sheet with a low-angle ramp. We postulate that as allochthonous advance progressed over time, it stepped back from the tip of the original sheet, with further extrusive advance emanating from a position of inflated salt with minimal to no roof. This suggests an apparent change in style of lateral salt advance over time in response to variable sedimentation patterns.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4728

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