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Sedimentation Rates, Basin Analysis and Regional Correlations of Three Neoarchaean and Palaeoproterozoic Sub-Basins of the Kaapv

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Sedimentation Rates, Basin Analysis and Regional Correlations of Three Neoarchaean and Palaeoproterozoic Sub-Basins of the Kaapv ELSEVIER Sedimentary Geology 120 (1998) 225–256 Sedimentation rates, basin analysis and regional correlations of three Neoarchaean and Palaeoproterozoic sub-basins of the Kaapvaal craton as inferred from precise U–Pb zircon ages from volcaniclastic sediments a, b Wladyslaw Altermann Ł, David R. Nelson a Institut fu¨r Allgemeine und Angewandte Geologie, Ludwig-Maximilians-Universita¨t, Luisenstraße 37, D-80333 Mu¨nchen, Germany b Geological Survey of Western Australia, Department of Mines, 100 Plain Street, Perth, W.A., Australia Received 29 April 1997; accepted 26 June 1997 Abstract Calculation of sedimentation rates of Neoarchaean and Palaeoproterozoic siliciclastic and chemical sediments covering the Kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents. Zircons from tuff beds in carbonate facies of the Campbellrand Subgroup in the Ghaap Plateau region of the Griqualand West basin, Transvaal Supergroup, South Africa were dated using the Perth Consortium Sensitive High Resolution Ion Microprobe II (SHRIMP II). Dates of 2588 6 Ma and 2549 7 Ma for the middle and the upper part of the Nauga Formation indicate that the decompacted sešdimentation rate fšor the peritidal flat to subtidal below-wave-base Stratifera and clastic carbonate facies, southwest of the Ghaap Plateau at Prieska, was of up to 10 m=Ma, when not corrected for times of erosion and non-deposition. Dates of 2516 4 Ma for the upper Gamohaan Formation and 2555 19 for the upper Monteville Formation, indicate that some š2000 m of carbonate and subordinate shale sedimentatišon occurred during 16 Ma to 62 Ma on the Ghaap Plateau. For these predominantly peritidal stromatolitic carbonates, decompacted sedimentation rates were of 40 m=Ma to over 150 m=Ma (Bubnoff units). The mixed siliciclastic and carbonate shelf facies of the Schmidtsdrif Subgroup and Monteville Formation accumulated with decompacted sedimentation rates of around 20 B. For the Kuruman Banded Iron Formation a decompacted sedimentation rate of up to 60 B can be calculated. Thus, for the entire examined deep shelf to tidal facies range, Archaean and Phanerozoic chemical and clastic sedimentation rates are comparable. Four major transgressive phases over the Kaapvaal craton, followed by shallowing-upward sedimentation, can be recognized in the Prieska and Ghaap Plateau sub-basins, in Griqualand West, and partly also in the Transvaal basin, and are attributed to second-order cycles of crustal evolution. First-order cycles of duration longer than 50 Ma can also be identified. The calculated sedimentation rates reflect the rate of subsidence of a rift-related basin and can be ascribed to tectonic and thermal subsidence. Comparison of the calculated sedimentation rates to published data from other Archaean and Proterozoic basins allows discussion of general Precambrian basin development. Siliciclastic and carbonate sedimentation rates of Archaean and Palaeoproterozoic basins equivalent to those of younger systems suggest that similar mechanical, chemical and biological processes were active in the Precambrian as found for the Phanerozoic. Particularly for stromatolitic carbonates, matching modern and Neoarchaean sedimentation rates are interpreted as a strong hint of a similar evolutionary stage of stromatolite-building microbiota. The new data also allow for improved regional correlations across the Griqualand West basin and with the Malmani Subgroup carbonates in the Transvaal basin. The Nauga Formation Ł Corresponding author. E-mail: [email protected] 0037-0738/98/$ – see front matter 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 3 7 - 0 7 3 8 ( 9 8 ) 0 0 0 3 4 - 7 226 W. Altermann, D.R. Nelson / Sedimentary Geology 120 (1998) 225–256 carbonates in the southwest of the Griqualand West basin are significantly older than the Gamohaan Formation in the Ghaap Plateau region of this basin, but are in part, correlatives of the Oaktree Formation in the Transvaal and of parts of the Monteville Formation on the Ghaap Plateau. 1998 Elsevier Science B.V. All rights reserved. Keywords: basin analysis; sedimentation rates; Archaean; Proterozoic; Kaapvaal craton; SHRIMP 1. Introduction volcanic indolence. These two conditions are basic prerequisites for chemical or bio-chemical precipi- In the absence of biostratigraphic markers, high- tation. In the presence of clastic detritus, microbial precision isotopic data on the age and duration of organisms that facilitate carbonate precipitation can sedimentation are essential aspects of the study of be buried or swept away from the sediment surface Archaean and Proterozoic sedimentary basins. Pre- and from the water column, and inorganic precipita- cambrian siliciclastic basins containing thousands tion is hindered by the attachment of metal ions like of metres of sedimentary fill are often bracketed Ca and Fe to mineral grains. The scarcity of clastic by rare and imprecise stratigraphic data, and lat- detritus thus also allows purely chemical precipi- eral lithostratigraphic correlations lack arguments tates like Banded Iron Formations (BIF) to develop. other than similar facies development. As a conse- It is certainly not coincidental, that large Precam- quence, poorly constrained basin models and equiv- brian BIF provinces are often underlain by carbonate ocal tectonic interpretations are commonly presented platforms. Hence, the conspicuous carbonate (shale) for Precambrian sediments. Precambrian carbonate and BIF association must be explained not only in basin-fills are equally vulnerable. More particularly, terms of palaeoenvironmental atmospheric and hy- the carbonate sedimentary processes and the mech- drospheric evolution (Eriksson et al., 1998), but also anism of carbonate precipitation are generally not as a function of basin development (Simonson and well understood for the Archaean (see discussions Hassler, 1997). Comparisons of sedimentation and by Grotzinger, 1989, 1990; Sumner and Grotzinger, subsidence rates of clastic and chemical sedimen- 1996). Although stromatolites and microbial remains tary basins of the Precambrian and Phanerozoic, as are known from older deposits, the earliest large car- attempted here, may reveal important aspects of tec- bonate platforms apparently developed in intracra- tonic history, rates of erosion and sediment transport, tonic basins, following cratonic stabilization. This genesis of mineral deposits and the evolution of was until recently ascribed to the Palaeoprotero- carbonate precipitating microbiota. zoic, around 2.5–2.0 Ma ago (Grotzinger, 1989). The Kaapvaal craton of southern Africa hosts With the development of new dating techniques, three major Archaean to Palaeoproterozoic sub- it has now become apparent that the earliest large basins, in which clastic and chemical sediments carbonate platforms developed during the Neoar- and igneous rocks accumulated. The Transvaal basin chaean, between 2700 Ma and 2500 Ma (Jahn et in the Transvaal geographic region, the Griqualand al., 1990; Arndt et al., 1991; Hassler, 1993; Barton West basin in the Northern Cape Province of South et al., 1994). Consequently, the time span between Africa and the Kanye basin of Botswana share cratonization and subsequent carbonate basin devel- lithostratigraphically similar deposits which uncon- opment is now believed to be shorter, with less than formably cover the 2.7 Ga old volcanic Ventersdorp 1.0 billion years separating the formation of granite– Supergroup (Armstrong et al., 1991). In this con- greenstone terranes at around 3.5 Ga to 3.0 Ga from tribution the Kanye basin is not discussed and the the formation of huge stromatolitic platforms in the Griqualand West basin is subdivided into the Prieska Neoarchaean (Beukes, 1986; Altermann and Her- sub-basin and Ghaap Plateau sub-basin, because of big, 1991; Jahn and Simonson, 1995; Altermann and their different development. Carbonates are volumet- Siegfried, 1997). The rise of these platforms was rically dominant rocks in the Prieska, Ghaap Plateau made possible by the widespread absence of clas- and Transvaal sub-basins and, together with thin, tic input during periods of tectonic quiescence and lowermost siliciclastic rocks, form the base of the W. Altermann, D.R. Nelson / Sedimentary Geology 120 (1998) 225–256 227 Transvaal Supergroup, being overlain by BIF de- and Wotherspoon (1995) and in Altermann (1997). posits. The iron-rich chemical precipitates are in turn General stratigraphy is shown in Figs. 1–3 and 7. overlain by a thick sequence of predominantly clastic sediments. Similar volcano-sedimentary basin devel- 2. Regional geology and stratigraphy of opment can be deduced in other Archaean cratonic Griqualand West terranes, but especially well on the Pilbara craton of Western Australia, where the lithostratigraphic suc- The Vryburg Formation of the Schmidtsdrif Sub- cession is strikingly similar to that of the Kaapvaal group (Beukes, 1979) of the Ghaap Group (Fig. 1) craton (Cheney, 1996). is the lowest stratigraphic unit above the unconfor- At first glance, the three sub-basins discussed mity cutting into the 2709 Ma (Armstrong et al., here host mainly chemical sediments, and thus might 1991) Ventersdorp Supergroup lavas in Griqualand appear unsuitable for a special volume on Precam- West. This formation consists of shales, quartzites, brian clastic depositional systems. Nevertheless, we siltstones and lava. According to the South African feel that the sediments discussed herein impressively Committee for Stratigraphy
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