Journal
AUSTRALIAN JOURNAL OF EARTH SCIENCES
Volume 67, Issue 6, Pages 815-832Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/08120099.2019.1588695
Keywords
Patawarta diapir; Flinders Ranges; South Australia; rim dolomite; lateral carbonate caprock; salt-sediment interface; salt tectonics
Categories
Funding
- Anadarko
- BHP
- BP
- Chevron
- ConocoPhillips
- Devon
- ExxonMobil
- Hess
- Kosmos
- Marathon
- Nexen
- Repsol
- Samson
- Shell
- Statoil
- Total
- American Association of Petroleum Geologists
- Society of Professional Earth Scientists Award
- University of Texas El Paso Geological Sciences Department Bruce Davidson Memorial Award
- West Texas Geological Society Award
- Roswell Geological Society Award
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The 'rim dolomite' of South Australia's Central Flinders Ranges is a prominent ridge-forming, layered dolomitic and siliceous unit. The rim dolomite is interpreted to be a lateral caprock found exclusively at the salt-sediment interface between the Patawarta diapir and the Ediacaran-aged Bunyeroo Formation. Lateral dolomite caprock is defined by the following field relationships: (1) the rugose dolomicrite base that parallels the contact of the diapiric matrix and the bedding in the overlying stratigraphy, (2) the exclusive presence of dolomite at the salt-sediment interface, (3) the lack of sedimentary structures or fossils (cyanobacterial laminites and stromatolites), (4) the lack of interbedded Bunyeroo lithofacies, and (5) the inability to trace the rim dolomite capstone away from the diapir margin into the outboard stratigraphy. In addition to the field relationships, the rim dolomite displays the following capstone fabrics: (1) massive-microcrystalline dolomite, (2) porphyritic-two distinct crystal sizes, one forming microcrystalline dolomite groundmass and the other forming rosettes of silica, (3) banded-microcrystalline dolomite forming pressure-dissolution layers of silica and authigenic hematite, and (4) brecciated-mosaic to disorganised, forming a microcrystalline dolomite groundmass, which locally contains remnant clasts of Callanna non-evaporite lithologies, such as quartz arenite to arkosic sandstones and basalts, surrounded by an anastomosing cement-filled vein network. All capstone fabrics contain various amounts of anhydrite, quartz, feldspar and non-evaporite grains that represent the insoluble residue during halite dissolution and caprock accretion. Three different genetic models for the lateral caprock are described and tested, and that of these, only the halokinetically rotated caprock model fits the data. The field relationships and capstone fabrics of the rim dolomite match other lateral caprocks in salt basins such as the Paradox Basin and Gulf Coast, USA.
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