Deep seismic evidence of late Middle Proterozoic rifting beneath the Kalahari, Western Botswana

Hoffe, Brian H. (1996) Deep seismic evidence of late Middle Proterozoic rifting beneath the Kalahari, Western Botswana. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (19MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The full processing of seven reconnaissance, deep seismic reflection profiles recorded in western Botswana reveal the presence of a single, deep basin with a relatively uniform fill of 12 to 15 km of sedimentary rocks underlain by a mid to lower crust which shows considerable structure and reflectivity. Much of western Botswana falls within the broad physiographic region known as the Kalahari where much of the bedrock geology is concealed by Cretaceous to Recent Kalahari sands making regional tectonic interpretations difficult. Potential field data suggested the existence of deep sedimentary basins which prompted the Government of Botswana, with assistance from Petro-Canada International Assistance Corporation (PCIAC), to acquire approximately 1,000 km of 12 to 15 fold deep seismic reflection data in the western Kalahari region to evaluate its petroleum potential. A followup well drilled to a total depth of approximately 4 km along one of these profiles showed that a majority (> 2 km) of the rocks are sedimentary and of late Proterozoic (Ghanzi?) to early Cambrian (Nama) age. The stratigraphic break between the rocks of the Nama Group and those of the Permo-Carboniferous - Jurassic Karoo Supergroup is marked by a major unconformity and represents a considerable hiatus (≈ 200 - 300 Ma). The gross lithologic nature of "bright" mid to lower crustal reflectors is explored in a qualitative fashion by examining possible correlations between the potential field anomalies and these zones of increased reflectivity. These seismic data also indicate the possible presence of large-scale extensional structures suggestive of continental rifting. These extensional structures, along with an ⁴⁰Ar-³⁹Ar date of 1,071.7 ± 11.1 Ma from a gabbroic body forming part of the Kalahari Line, and a series of continental rift sequences exposed along the northern and western fringes of the Kalahari region, all provide evidence of a widespread late Middle Proterozoic rifting event affecting much of the Kalahari region. This rifting may have marked the disassembly of a proposed Proterozoic supercontinent.

Actions (login required)

View Item