Evans, D. A. D. and Beukes, N. J. and Kirschvink, J. L.
(2002)
Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment.
Journal of Geophysical Research B, 107
(B12).
Art. No. 2326.
ISSN 0148-0227.
doi:10.1029/2001JB000432.
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Abstract
The Olifantshoek Group in southern Africa contains Paleoproterozoic red beds that are exceptionally well preserved, lying unconformably atop a regionally extensive lateritic paleoweathering profile. We studied the basal unit of this succession, known as the Gamagara or Mapedi Formation, and the lateritized substrate (so-called “Drakenstein” or “Wolhaarkop” paleosol) on which it developed. Two ancient magnetic components are observed. One (INT), usually with a distributed unblocking spectrum between 300° and 600°C but occasionally persisting to >675°C, is directed shallowly southward or northward. A mesoscale fold test at South Sishen Mine indicates that this component was acquired during deformation; similarity of the direction to previous results suggests that it was acquired at ∼1240 Ma, during early Namaqua orogenesis. Combining our INT results with existing data from the Namaqua eastern zone (NEZ), we calculate the NEZ pole at (44.9°N, 021.5°E, K = 23.2, A_95 = 12.8°, Q = 5). The most stable component from our data set (HIG), always persisting as a nonzero endpoint to demagnetization at >665°–680°C, is observed in 32 samples from South Sishen and Beeshoek Mines. Directed moderately east-downward (Sishen) or west-upward (Beeshoek), this component predates the mesoscale fold at Sishen. More importantly, a conglomerate test at Beeshoek indicates that HIG was acquired prior to Paleoproterozoic deposition of the Gamagara/Mapedi Formation. The concordance between directions from the paleoweathering zone and immediately overlying red beds indicates that HIG is a primary magnetic remanence for the basal Gamagara/Mapedi (BGM) Formation. The dual-polarity BGM paleomagnetic pole (02.2°N, 081.9°E, dp = 7.2°, dm = 11.5°, Q = 6) lies neatly between previous Kaapvaal poles with ages of ∼2220 (Ongeluk lavas) and 2060 Ma (Bushveld complex). Our data thus support recent correlations of the Gamagara/Mapedi Formation with pre-Bushveld sediments of the Pretoria Group. A pre-Bushveld age for BGM is also consistent with its substantial distance from a new, albeit less reliable, paleomagnetic pole from the ∼1930-Ma Hartley lavas, higher within the Olifantshoek succession (12.5°N, 332.8°E, K = 18.6, A95 = 16.0°, Q = 3). Our conglomerate test at Beeshoek confirms previous allegations that the intense hematitization observed in the Drakenstein-Wolhaarkop paleosol occurred during Paleoproterozoic weathering under a highly oxygenated atmosphere.
Item Type: | Article |
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Additional Information: | © 2002 American Geophysical Union.
Received 3 May 2000; revised 25 January 2002; accepted 30 January 2002; published 6 December 2002.
We thank H. Wiggering for field assistance, and the managements of Sishen, Rooinekke, and Beekshoek Mines for
permission to collect samples. The Department of Geology at RAU provided logistical support for field work. D.Y. Sumner and Tiekie Beukes helped with the sample analyses. This project was supported by NSF grant EAR94-18523 (USA) and the NRF Open Research Program (South Africa), and DADE was supported by NSF Graduate and ARC Postdoctoral Research Fellowships. Data reduction was aided by the Paleomag and
GMAP programs, respectively administered by Craig Jones and Trond Torsvik. Jens Gutzmer and Dai Jones provided insightful comments, and we thank Rob Hargraves and Pierrick Roperch for their constructive reviews. Tectonics Special Research Centre contribution 157. |
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Funders: | Funding Agency | Grant Number |
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NSF | EAR94-18523 | NRF Open Research Program | UNSPECIFIED | NSF Graduate Research Fellowship | UNSPECIFIED | ARC Postdoctoral Research Fellowship | UNSPECIFIED |
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Subject Keywords: | paleomagnetism;
Paleoproterozoic;
South Africa;
apparent polar wander paths;
paleoatmosphere;
lateritic paleosols
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Other Numbering System: | Other Numbering System Name | Other Numbering System ID |
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Tectonics Special Research Centre | 157 |
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Issue or Number: | B12 |
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DOI: | 10.1029/2001JB000432 |
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Record Number: | CaltechAUTHORS:20130514-103309854 |
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Persistent URL: | https://resolver.caltech.edu/CaltechAUTHORS:20130514-103309854 |
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Official Citation: | Evans, D. A. D., N. J. Beukes, and J. L. Kirschvink, Paleomagnetism of a lateritic paleoweathering horizon and overlying Paleoproterozoic red beds from South Africa: Implications for the Kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment, J. Geophys. Res., 107(B12), 2326, doi:10.1029/2001JB000432, 2002. |
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Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. |
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ID Code: | 38490 |
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Collection: | CaltechAUTHORS |
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Deposited By: |
Jason Perez
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Deposited On: | 14 May 2013 20:09 |
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Last Modified: | 09 Nov 2021 23:37 |
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