|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Article |
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany AEON-Africa Earth Observatory Network and Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa., e-mail: tbranch{at}geology.uct.ac.za
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany, e-mail: oritter{at}gfz-pozsdam.de (corresponding author)
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Universität Potsdam, Institut für Geowissenschaften, Karl-Liebknecht-Strasse 24, 14476 Potsdam, Germany, e-mail: uweck{at}gfz-pozsdam.de
Geologie und Lagerstättenlehre am Department Angewandte Geowissenschaften und Geophysik, Montanuniversität, A-8700 Leoben, Austria, e-mail: reinhard.sachsenhofer{at}mu-leoben.at
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany, e-mail: fsch{at}gfz-pozsdam.de
Within the Inkaba yeAfrica project, magnetotelluric (MT) data were acquired along three profiles across the Karoo Basin in South Africa. The entire Karoo Basin and its sedimentary sequences are intersected by a number of deep boreholes, which were drilled during exploration for coal, oil and uranium. One of the most consistent and prominent features in the electrical conductivity images is a shallow, regionally continuous, sub-horizontal band of high conductivity that seems to correlate with the Whitehill Formation. The Whitehill Formation in particular is known to be regionally persistent in composition and thickness and can be traced throughout the entire Karoo Basin. In the region of our experiments, the Whitehill Formation varies in thickness between 50 to 70 m and consists of pyritic black shales with up to 14 weight % carbonaceous matter. Rocks can exhibit high electrical conductivity if electronically conducting minerals, such as graphite, are interconnected. To study physical properties and the maturity of the carbon present in the Whitehill Formation, impedance spectroscopy and vitrinite reflectance were applied to core samples from the SA1/66 borehole, taken from this formation at a depth range between 2750 m and 2800 m. Vitrinite reflectance analysis of the pseudo-coal and oil shale rocks indicates that most of the carbon is in the meta-anthracite maturity field, approaching, in one sample, the "graphite window". Impedance spectroscopy reveals that the highest electrical conductivities are associated with the pyrite rich portion of one sample, showing conductivities well above 1 S/m. Recordings on pyrite-poor samples are less conclusive, with observed conductivities varying in the range of a few S/m to mS/m. Measurements on samples from the Whilehill Formation, on the other hand, show consistently low resistivities in the range between 4 to 6 
m. This result suggests strongly that the sub-horizontal conductivity anomaly in the MT models is linked with the carbon-rich sequences of the Whitehill Formation
This article has been cited by other articles:
|
|
 |
|
  E. J. Milani and M. J. De Wit Correlations between the classic Parana and Cape-Karoo sequences of South America and southern Africa and their basin infills flanking the Gondwanides: du Toit revisited Geological Society, London, Special Publications, January 1, 2008; 294(1): 319 - 342. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. Weckmann, A. Jung, T. Branch, and O. Ritter Comparison of electrical conductivity structures and 2D magnetic modelling along two profiles crossing the Beattie Magnetic Anomaly, South Africa South African Journal of Geology, September 1, 2007; 110(2-3): 449 - 464. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
