Volcanic degassing, hydrothermal circulation and the flourishing of early life on Earth: A review of the evidence from c. 3490-3240 Ma rocks of the Pilbara Supergroup, Pilbara Craton, Western Australia

A deep subaqueous fan depositional model for the Palaeoarchaean (3.46 Ga) Marble Bar Cherts, Warrawoona Group, Western Australia

“…The Marble Bar Chert Member is a well-preserved unit of centimetre-scale layered red, white and dark-blue chert up to 200 m thick (Hickman, 1983;Van Kranendonk, 2006). This Member displays important thickness variations that repeat at regular intervals over the 30 km long band along which it crops out (Hoashi et al 2009).…”

“…This Group consists of ultramafic, tholeiitic, felsic lavas and volcaniclastic rocks with subordinate cherts. The Marble Bar Chert Member occurs at the top of the 3.472-3.465 Ga Duffer Formation and is overlain by the Apex Basalt Formation (Van Kranendonk, 2006). This Member is best exposed at the Marble Bar Pool and Chinaman Pool localities (Fig.…”

“…Previous studies on the sedimentary rocks of the Marble Bar Chert Member focused on the chemical and thermal conditions associated with the precipitation of these cherts (Sugitani, 1992;Minami et al 1995;Kojima et al 1998;Orberger et al 2006;van den Boorn et al 2007van den Boorn et al , 2010. However, the depositional environment and the mode of formation of the Marble Bar Cherts remain subject to debate, and both hydrothermal †Author for correspondence: Nicolas.Olivier@univ-lyon1.fr environments on a mid-oceanic ridge and large submarine caldera settings have been proposed (Oliver & Cawood, 2001;Kato & Nakamura, 2003;Van Kranendonk, 2006;Hoashi et al 2009;van den Boorn et al 2010). Hoashi et al (2009) argued that the haematite grains in the Marble Bar Cherts precipitated directly when hydrothermal fluids of temperature greater than 60 • C and rich in reduced iron mixed rapidly with seawater containing oxygen in a submarine volcanic depression at depths between 200 m and 1000 m. Supporting evidence for such a deep environment for the Marble Bar Chert Member is at best indirect, based on the absence of sedimentological or volcanic features characteristic of shallow water settings (Hoashi et al 2009).…”

“…Sedimentary deposits of the Palaeoarchaean greenstones of the East Pilbara Craton, Western Australia, are of particular geological significance for hosting the oldest putative microfossils (Schopf, 1993;Schopf et al 2002), the oldest stromatolites (Allwood et al 2006;Van Kranendonk, 2006) and preserving evidence of the environmental conditions of the Early Earth (Robert & Chaussidon, 2006;Hoashi et al 2009;van den Boorn et al 2010). Among these rocks, the c. 3460 Ma Marble Bar Chert Member of the Duffer Formation (Warrawoona Group) is a typical Archaean red-white-grey banded chert remarkably exposed at the Marble Bar Pool and Chinaman Pool localities ( Fig.…”

“…Among these rocks, the c. 3460 Ma Marble Bar Chert Member of the Duffer Formation (Warrawoona Group) is a typical Archaean red-white-grey banded chert remarkably exposed at the Marble Bar Pool and Chinaman Pool localities ( Fig. 1; Buick & Barns, 1984;Van Kranendonk, 2006). Previous studies on the sedimentary rocks of the Marble Bar Chert Member focused on the chemical and thermal conditions associated with the precipitation of these cherts (Sugitani, 1992;Minami et al 1995;Kojima et al 1998;Orberger et al 2006;van den Boorn et al 2007van den Boorn et al , 2010.…”