Geophysical Studies of the Serpent Mound Structure, Adams County, Ohio, U.S.A

El-Saiti, Belgasem M. B (1998) Geophysical Studies of the Serpent Mound Structure, Adams County, Ohio, U.S.A. PhD thesis, University of Glasgow.

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Abstract

Integrated geophysical study of the Serpent Mound Structure provides significant new findings and confirms the previously reported findings. These findings are based on newly processed and interpreted seismic reflection data, gravity, magnetic, palaeomagnetic, the availability of deep continuous cores and well data. The purpose of this investigation is to resolve the controversy regarding the origin of the Serpent Mound Structure and its age. The reprocessing of seismic data shows a significant improvement when compared to earlier processing carried out by industry. The processed seismic data indicate a highly faulted, structurally complex depression extending downward to about 700 feet into the Precambrian basement beneath the central uplift area of the structure. These findings are supported by the analysis of two deep cores. The seismic data as well as the core data indicate a decrease in structural complexity and intensity with depth, and away from the central uplift area of the structure. The relative degree of structure complexity is related to the structural zone within the disturbance, ranging from the most complex in the central uplift to least complex in the ring graben. Seismic data also indicate a ring anticline associated with the ring graben of the structure and the presence of an anomalous lens-shaped volume of chaotic reflections occurs within the depression beneath the central uplift. The microgravity survey of the Serpent Mound Structure reveals a residual negative gravity anomaly associated with the central uplift area of the structure. The gravity anomaly reflects the lower density, fractured and brecciated target rocks at the centre of the structure. The modelling of the structure indicates a central uplift composed of brecciated and fractured lens surrounded by less deformed country rock. The brecciated lens extends to the top of the Gull River, about 2000 feet (610 m) below surface and has a density contrast of -0.06 gm/cc. The position and the diameter of the low-density region mimic the depression seen on the seismic section. The ground magnetic survey of the Serpent Mound Structure shows a well- defined magnetic anomaly indicated by its trend, width, and high amplitude. Our magnetic survey shows a significant revision of the previous map of the area. The Serpent Mound Structure is located near a north-south regional anomaly trend. The modelling of the magnetic data shows it is possible that a volume of rocks beneath the structure was magnetised by the passage of shock waves caused by the impact. Palaeomagnetic analysis of some oriented samples collected from deep cores within and outside the structure revealed a secondary magnetisation in both cores. The analysis shows the magnetisation was probably acquired during Late Permian (250+/-15 my). Better data based on radiometric methods are unlikely, this represents the best constraint of the upper age of the Serpent Mound Structure to date. Core DGS3274 drilled in the central uplift area of the structure shows abundant macroscopic evidence for shock metamorphism in the form of intense deformation, brecciation, and shatter cones. Microscopic evidence for shock is found as a set of planar deformation features (PDFs) in quartz grains. Based on the findings of geophysical studies including seismic, gravity, magnetic, and palaeomagnetic and petrographic and geochemical studies of the cores, the interpretation of the origin of the Serpent Mound Structure is of an impact which occurred during the Late Palaeozoic.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Doyle Watts
Keywords: Geophysics, Geophysical engineering
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-75404
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 20:14
Last Modified: 19 Nov 2019 20:14
URI: http://theses.gla.ac.uk/id/eprint/75404

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