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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >The Whitehill Formation - a high conductivity marker horizon in the Karoo Basin
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The Whitehill Formation - a high conductivity marker horizon in the Karoo Basin

机译：Whitehill组-Karoo盆地的高电导率标记层

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摘要

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 he traced throughout the entire Karoo Basin. In the region of our experiments, the Whitehill Formation varies in thickness between 50 to 70 in and consists of pyritic black shales with tip 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 in 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 Omega 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
机译：在Inkaba yeAfrica项目中，沿南非Karoo盆地的三个剖面采集了大地电磁（MT）数据。整个Karoo盆地及其沉积层序被许多深孔相交，这些深孔是在勘探煤，石油和铀的过程中钻出的。电导率图像中最一致和最突出的特征之一是高电导率的浅，区域连续，水平下带，似乎与怀特希尔组相关。尤其是怀特希尔山地层的成分和厚度在区域上是持久的，可以在整个Karoo盆地中追踪到。在我们的实验区域中，白山地层的厚度在50到70英寸之间变化，由黄铁矿黑页岩组成，顶端含碳量为14％（重量）。如果将导电的矿物（例如石墨）相互连接，则岩石可以表现出高电导率。为了研究Whitehill地层中碳的物理性质和成熟度，将阻抗谱和镜质体反射率应用于SA1 / 66井眼的岩心样品，该深度取自SA1 / 66井眼，深度在2750 in和2800 m之间。假煤和油页岩的玻璃体反射率分析表明，大部分碳都在亚无烟煤成熟度场中，其中一个样品接近“石墨窗”。阻抗谱显示最高的电导率与一个样品的富黄铁矿部分有关，显示出远高于1 S / m的电导率。黄铁矿贫乏样品的记录结论性较差，观察到的电导率在几S / m至mS / m的范围内变化。另一方面，对Whilehill地层样品的测量结果显示，其电阻率始终较低，范围为4至6Ωm。这一结果强烈表明，MT模型中的亚水平电导率异常与怀特希尔组的富碳序列有关。

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