Publication Date

2022

Document Type

Dissertation/Thesis

First Advisor

Fischer, Mark P.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Earth, Atmosphere and Environment

Abstract

This thesis utilizes detailed field studies and numerical simulations to characterize near- salt deformation patterns. Establishing possible deformation patterns and their evolution helps to constrain assumptions within geomechanical models and aids in the evaluation of prospects that rely on trapping at or near the salt-sediment interface. For the field studies, I use a combination of mesoscopic structural analysis, drone photogrammetry, and 3D modeling to analyze variation in deformation patterns at a scale of meters to hundreds of meters along transects moving horizontally away from the salt-sediment interface adjacent to the western end of the Onion Creek salt diapir (OCSD) in the Paradox Basin, Utah, and vertically away from the salt-sediment interface below two allochthonous salt sheets in the Flinders Ranges, South Australia. Along the transect at the OCSD, four structural domains were determined and deformation features vary as a function of stratigraphy and structural position. Using the deformation pattern established at the OCSD, I interpret the possible timing for fluid movement and fracture development. I use the deformation pattern established at the OCSD to create a conceptual model of near-diapir deformation during salt emplacement and later burial, dissolution collapse, and reactivation from regional stresses. I compare the deformation patterns below the allochthonous salt sheets to those predicted by numerical models of salt sheet emplacement and expand upon a previously established framework for determining the origin and timing of deformation features near salt sheets. Within 50 m of the salt-sediment interface at Arkaba, there are abundant bedding-perpendicular and oblique fractures and bedding-parallel and nonsystematic veins. Fractures and veins at Arkaroola are sparse, but where present, barren fractures are typically oblique to bedding, whereas veins are generally nonsystematic. Documented deformation patterns suggest current numerical models overestimate the amount and stratigraphic extent of strain accumulated in subsalt strata during salt sheet emplacement. For the numerical study, I use AbaqusTM to conduct a suite of models investigating stress perturbations near the salt-sediment interface during the tectonic reactivation of a simplified 2D allochthonous salt sheet. The aim of this study is to distinguish relative control of material property and geometric variables on the resulting stress perturbations and uniquely discriminating what constitutes a reactivation deformation pattern. From the resulting stress regime, I hypothesize the formation of oblique fractures near the salt-sediment interface localized to the ramp structure, extensional faulting near the lower flat-ramp transition, and reverse faults near the upper ramp-flat transition. I then compare this deformation pattern to those predicted by numerical models and find that similarly oriented deformation features are predicted to form during salt emplacement. Along the transect at the OCSD, four structural domains were determined and deformation features vary as a function of stratigraphy and structural position (i.e., domain). There is evidence that fluid migration was accommodated by matrix and fracture flow, but there are no constraints on the timing of fluid movement or number of flow events. Deformation may be largely syndepositional and caused by along-strike changes in diapir geometry or are related to Neogene extension, subsequent to salt emplacement. I found that deformation features below the salt sheets in the Flinders Ranges are most abundant within 50 m of the salt-sediment interface and are dominated by oblique fractures and nonsystematic veins, suggesting current numerical models overestimate the amount and stratigraphic extent of strain accumulated in subsalt strata during salt sheet emplacement. The numerical analysis revealed that reactivation does produce significant stress perturbations in the subsalt strata, particularly near the ramp, but the resulting deformation pattern is not unique to reactivation and therefore has limited applicability as a means to definitively establish the origin and timing of deformation features observed below salt sheets in the field.

Extent

185 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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