Craton Pilbara

Coonteninah and Warrawoona Groups Pilbara Craton, Austraha 3.5 Green et al. (2000)... 

Some of the oldest preserved oceanic plateau sequences are those found in —3.5 Ga Barberton and Pietersberg belts of the Kaapvaal Shield of southern Africa (De Wit et aL, 1987 Smith and Erlank, 1982). These belts contain pillow basalts and komatiites, with chemical signatures (Lahaye et aL, 1995) suggesting a likely origin as part of an oceanic plateau. The Pilbara craton of Australia appears to possess some of the oldest oceanic plateau material so far identified (Green et aL, 2000) in the —3.5 Ga Coonterunah and Warrawoona Groups. 

Green M. G., Sylvester P. I., and Buick R. (2000) Growth and recycling of early Archaean continental crust geochemical evidence from the Coonterunah and Warrawoona Groups, Pilbara Craton, Australia. Tectonophysics 322, 69-88. 

Buick R., Thronetree J. R., McNaughton N. J., Smith J. B., Barley M. E., and Savage M. (1995) Record of emergent continental crust 3.5 billion years ago in the Pilbara Craton of Australia. Nature 375, 574-576. 

Rather interestingly, the oldest usable biomarkers in carbonaceous shales date from the Neoarchean. Molecular fossils extracted from 2.5 Ga to 2.7 Ga shales of the Fortescue and Hamersley groups in the Pilbara Craton, Western Australia, indicate that the photic zone of the water column in the areas where these shales were deposited was probably weakly oxygenated, and that cyanobacteria were part of the microbial biota (Brocks et al., 1999, 2002 Summons et al., 1999). The similarity of the timing of the rise in the range of in sediments and the earliest evidence for the presence of cyanobacteria may, however, be coincidental, because to date no sediments older than 2.7 Ga have been found that contain usable biomarker molecules (Brocks, personal communication, 2002). 

Ohmoto H. (1999) Redox state of the Archean atmosphere evidence from detrital heavy minerals in ca. 3,250-2, 750 Ma sandstones from the Pilbara Craton, Australia Comment. Geology 27, 1151 — 1152. 

Martin D. McB., Clendenin C. V., Krapez B., and McNaughton N. J. (1998) Tectonic and geochronological constraints on Late Archean and Paleoproterozoic statigraphic correlation within and between the Kaapvaal and Pilbara Cratons. 

Morris R. C. (1993) Genetic modeling for banded iron-formation of the Hamersley Group, Pilbara Craton, Western Australia. Precamb. Res. 60, 243 -286. 

Several lines of geochemical evidence support low to negligible concentrations of atmospheric O2 during the Archean and earliest Proterozoic, when oxygenic photosynthesis may have evolved. The presence of pyrite and uraninite in detrital Archean sediments reveals that the atmosphere in the earliest Archean contained no free O2 (Cloud, 1972). Although Archean-age detrital pyrites from South Africa may be hydrothermal in origin, Australian sediments of the Pilbara craton (3.25-2.75 Ga) contain rounded grains of... 

Thick, stacked, flood basall-komatiite-rhyolite sequences, e.g. Pilbara craton... 

Collins, W. J., van Kranendonk, M. J. Teyssier, C. 1998. Partial convective overturn of Archaean crust in the East Pilbara Craton, Western Austra-... 

Thorpe, R. I., Hickman, A. H., Davis, D. W., Mortensen, J. K. Trendall, a. F. 1992. U-Pb zircon geochronology of Archaean felsic units in the Marble Bar region, Pilbara Craton, Western Australia. Precambrian Research, 56, 169-189. 

Van Kranendonk, M. J. Collins, W. J. 1998. Timing and tectonic significance of late Archaean, sinistral strike-slip deformation in the central Pilbara structural corridor, Pilbara Craton, Western Australia. Precambrian Research, 88, 207-232. 

Van Kranendonk, M. J., Hickman, A. H., Smithies, R. H., Nelson, D. R. Pike, G. 2002. Geolo and tectonic evolution of the Archaean North Pilbara Terrain, Pilbara Craton, Western Australia. Economic Geology, in press. 

Wellman, P. 2000. Upper crust of the Pilbara Craton, Australia 3D geometry of a granite/greenstone terrain. Precambrian Research, 104, 175-186. 

Wingate, M. T. D. 1999. Ion microprobe baddeleyite and zircon ages for Late Archaean mafic dykes of the Pilbara Craton, Western Australia. Australian Journal of Earth Sciences, 46, 493-500. 

The relatively small number of late Archaean basins may reflect a low preservation potential, but may also indicate that relatively few cratonic nuclei had stabilized before the end of the Archaean. Examples of late Archaean basins include the (3.1-2.7 Ga) Witwatersrand basin in South Africa (Robb Meyer, 1995), and its correlative the 3.0-2.67 Ga Pongola Supergroup in Swaziland (Walraven. Pape, 1994 Gold von Veh, 1995), both unconformable upon the Kaapvaal Craton. In western Australia the 2.77-2.71 Ga Fortescue Group is unconformable upon older Archaean rocks of the Pilbara Craton (Blake et al., 2004). 

Kerogenous filaments in cherts from within the Apex basalt sequence in the Pilbara Craton, western Australia, became famous in the late 1980s as the world s oldest microfossils. They were described by Schopf and Packer (1987) and Schopf (1993) and have, until recently, been widely accepted as authentic, because of their supposed good preservation state. The kerogenous filaments are divided into cell-like compartments and have carbon isotope signatures as low as (S13C = —30%o) -all the hallmarks of microfossils (Schopf, 1993 Schopf et al., 2002). 

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