Unravelling the internal structures of salt, by applying anisotropy of magnetic susceptibility to the Carboniferous evaporite deposits of Nova Scotia, Canada

Richardson, Jack C. (2021). Unravelling the internal structures of salt, by applying anisotropy of magnetic susceptibility to the Carboniferous evaporite deposits of Nova Scotia, Canada. University of Birmingham. Ph.D.

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Abstract

The mobilisation and intrusion of salt plays a major role in the evolution of basins. Although the geometry and distribution of salt structures can be easily examined, the internal dynamics of salt intrusion are only partially understood. Collecting detailed structural data from outcrop is difficult due to limited exposure, inaccessibility, and poorly preserved visible fabrics. To overcome this crucial impasse in salt tectonics, detailed and high-quality strain data is required from salt outcrops. To obtain structural strain data we have used anisotropy of magnetic susceptibility (AMS) measurements on oriented samples collected from mine and coastal exposures of Carboniferous evaporites in Nova Scotia, Canada. With any AMS study it is important to have a grasp of the magnetic components of the rock. Further magnetic techniques, along with chemical analyses, have been used to better constrain these magnetic properties. Out-of-Phase AMS was also applied for the first time on diamagnetic rocks and rock with very small ferromagnetic fractions to untangle the ferromagnetic fabric from the whole rock.

It is unusual to find diapiric structures so well exposed as they are on the west coast of Cape Breton, Nova Scotia. These evaporites overlay a predominantly halite diapir core and are surrounded by Carboniferous sediments. Deformation within the gypsum deposits reflect deformation of the underlying halite core of the diapir and the overall structure. Both brittle and ductile deformation fabrics have been recorded within the surrounding sediments and we have observed them imprinted within the evaporite facies. To understand the magnetic fabrics these are detailed and assessed in relation to AMS. 3D Models have been created using aerial drones and photogrammetry to help understand the scalar relationships between fabrics and geological structures related to halokinesis.

Pugwash mine offers a perfect opportunity to study diapiric growth structures at a much larger scale. Using 5 maps and 3D photogrammetric models at different depths we can better understand the deformation of the deposit and the 3D geometries formed. Similar experimental methods to those described above have been used to ascertain the strain recorded by the detrital material within the halite samples. This study provides evidence for AMS being a fast, quantitative approach to studying deformed evaporitic deposits.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):