Scientific Drilling (Mar 2009)

Clues of Early Life: Dixon Island–Cleaverville Drilling Project (DXCL-DP) in the Pilbara Craton of Western Australia

  • Fumio Kitajima,
  • Minoru Ikehara,
  • Takashi Ito,
  • Shoichi Kiyokawa,
  • Kosei E. Yamaguchi,
  • Yusuke Suganuma

DOI
https://doi.org/10.2204/iodp.sd.7.04.2009
Journal volume & issue
no. 7
pp. 34 – 37

Abstract

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The Pilbara Craton in NW Australia (Fig. 1) exposes one of the well-preserved and least -metamorphosed greenstone belts in the Archean. Greenstone belts are normally composed of a complex amalgam of meta-basaltic and meta-sedimentary rocks. Sedimentary rocks of the greenstone belts are good targets to search for clues of early Earth's environment and life. In recent years, several scientific drilling programs (e.g.: Archean Biosphere Drilling Project (ABDP), Ohmoto et al., 2006; Deep Time Drilling Project (DTDP), Anbar et al., 2007, Kaufman et al., 2007; PDP: Pilbara Drilling Project, Philippot et al., 2007) were successfully completed in the western Pilbara area, where 3.5, 2.9, 2.7, and 2.5 Ga sedimentary units were drilled. However, there is a huge time gap in the samples drilled by ABDP and DTDP that represents middle Archean time , between 3.5 Ga and 2.9 Ga (i.e., ~600 Ma, equivalent to the duration of the entire Phanerozoic). The Cleaverville-Dixon Island area of the coastal Pilbara terrain (Fig. 1) is suited to filling in the missing record. It contains well-preserved volcanosedimentary sequences (Cleaverville Group dated at 3.2 Ga) where hydrothermal vein systems, organic-rich siliceoussedimentary rocks, and iron-rich sedimentary rocks are developed (Kiyokawa et al., 2006). Such geological materials may be used to reconstruct past submarine hydrothermal activity and its influence on biological activity. Indeed, some attempts have been made to answer the key questions. However, the surface outcrops in this area are generally weathered to variable degrees; thus they are apparently notsuitable for geo-biological and geochemical studies which require unaltered original chemical/isotopic compositions from the time of their formation in the middle Archean. Consequently, we carried out the “Dixon Island - Cleaverville Drilling Project (DXCL-DP)”, to obtain “fresh” samples from the sedimentary sequences in the Cleaverville—Dixon Island area.

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