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Primary and Secondary Salt Welds in the Late Paleozoic Antigonish Sub-basin of Nova Scotia
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- Author / Creator
- Thomas, Alison
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The Antigonish sub-basin in the late Paleozoic Maritimes Basin stretches from the Nova Scotian Antigonish Highlands into western Cape Breton Island, Canada. The sub-basin is structural in origin and is bounded by faults that developed late in the history of the Appalachian orogen. The Late Devonian to Pennsylvanian basin-fill consists primarily of clastic sedimentary rocks with the exception of a marine succession of carbonates and evaporites, the Viséan Windsor Group. The evaporites include the halite-dominated Hartshorn Formation of the Lower Windsor Group and a Middle Windsor Salt unit (MWS) first identified by this study. Previous work located a discordant surface within the Hartshorn Formation that extends through much of the sub-basin. The surface was initially named the Antigonish Thrust, and then reinterpreted as a low-angle extensional fault, the Ainslie Detachment. The presence of salt walls in St Georges Bay and several onshore salt diapir exposures suggests that this surface is a primary salt weld, marking the expulsion of the Hartshorn Formation salt.
A combination of core, outcrop, remotely piloted aircraft photography, 3D modelling and seismic data was used to examine the sub-basin. Salt movement in the Hartshorn Formation began in the Viséan during Middle Windsor Group deposition, causing lateral thickness variations in the Middle Windsor Group. Poorly preserved salt diapirs are present around the margins of the Antigonish sub-basin and these prevented the local deposition of the Middle and Upper Windsor Group. A coastal section of outcrop at Lakevale on Cape George is interpreted to expose a primary salt weld.
Local salt expulsion from the Middle Windsor Salt began in the late Viséan during the deposition of the Hood Island Formation of the Upper Windsor Group. However, the majority of Middle Windsor Salt movement occurred later in the depositional history of the sub-basin after the deposition of Bashkirian strata (Mabou Group) that overlie the Windsor Group. Several structures in the sub-basin that were previously mapped as faults are re-interpreted by this study as surficial expressions of MWS diapirs.
At Little Judique Harbour on Cape Breton Island, steeply dipping strata of different ages have opposing younging directions juxtaposed across a breccia zone that represents a secondary salt weld. This weld originated as a previously unrecognized salt wall with the same orientation as the offshore salt walls in St Georges Bay identified by earlier work. Lateral variations in salt expulsion rates or different initial salt thicknesses are possible reasons for the juxtaposition of strata from different units across the secondary weld.
The Antigonish sub-basin contains exposures of both primary and secondary salt welds. Salt movement has shaped the basin-fill and created numerous salt structures. The results of this thesis and other work on evaporites in the nearby Cumberland sub-basin suggest that future geological studies of the Maritimes Basin need to consider the potential impact of regional salt movement. -
- Subjects / Keywords
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- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.