Fischer, Mark P.
M.S. (Master of Science)
Department of Earth, Atmosphere and Environment
Halokinetic structures have been proven to serve as both structural and stratigraphic traps for petroleum and mineralizing ore fluids, making them critical to the energy and technology needs of society. Although modern exploration for these resources uses often uses 3-D seismic imagery, these data often cannot resolve the complexity of the strata within 300 meters of the salt sediment interface, an area that is critical to the trapping or migration of fluids. Because of this lack of constraint, drilling near salt risks encountering unexpected overturned strata, repeated units, overpressure, or abrupt changes in stress state, making it imperative to understand the nature of deformation within 300 meters of the salt-sediment interface by supplementing seismic imaging with field-based studies.This thesis uses a combination of geological field mapping, detailed field studies of deformation, drone photogrammetry, and 3-D modeling to establish the map-scale structural geometry and mesoscopic deformation patterns within 300 meters of an allochthonous salt sheet at the Tourmaline Hill area near Umberatana Station in the northern Flinders Ranges of South Australia. Using the stratal relationships near the salt and the geometry of the salt body itself, I interpret the linked structural and stratigraphic evolution of the area. I then analyze the spatial variability of deformational patterns and compare these patterns with those predicted by numerical models of salt body evolution. A combination of field mapping and structural data reveal two salt feeders present at the Tourmaline Hill salt sheet, as well as distinct halokinetic structures: a halokinetic sequence, subsalt halokinetic folds, a tertiary weld, and ramps and flats in the base of salt. I use these features to determine the salt was diapiric during the time of the Skillogalee Dolomite through the Yankaninna Formation at the southwestern feeder and through the Tapley Hill Formation at the central feeder before advancing as an allochthonous salt sheet. I used the subsalt folds to calculate that the salt sheet was advancing from a direction of approximately 283°. Subsalt stratal relationships reveal two ramps northeast of the central feeder that migrate upsection of the Tapley Hill Formation towards one another, forming a suture between two different salt sheets that were later evacuated and a tertiary weld in the approximate location of the suture. Detailed deformation studies in the suprasalt and subsalt strata reveal a common trend of deformation around the salt body. Within 80 meters of the salt-sediment interface the country rock hosts abundant, chaotic fractures with calcite mineralization and scapolite laths in the country rock. Farther than 80 meters away, the fractures become more systematic, with fewer veins present, and those veins are predominantly filled with quartz. One exception to this pattern is found in the subsalt Bolla Bollanna Tillite to the northeast of the central feeder that includes large veins of siderite, calcite, and quartz. Observed fracture patterns predominantly relate to a salt-emplacement phase, although one set striking approximately 200° is interpreted to relate to an evacuation and welding phase and its orientation may have been controlled by the regional folding of the Yankaninna Anticline.
Lueck, Lillian Ruth, "Structure, evolution, and mesoscopic deformation patterns near the tourmaline Hill salt sheet, Umberatana Station, South Australia" (2020). Graduate Research Theses & Dissertations. 7381.
Northern Illinois University
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