Strelley Pool Formation: Continental Sedimentation Between Paleoarchean LIPs

Abstract

The predominantly volcanic Warrawoona and Kelly Groups are separated by a regional unconformity overlain by the Strelley Pool Formation, a 20–1000 m thick, shallow-water succession of conglomerate, sandstone, silicified sedimentary carbonate rocks, evaporites, and volcaniclastic rocks. The formation was deposited during a 75-million-year break in volcanic activity between eruption of the Warrawoona and Kelly LIPs. A measure of the great lateral extent of the Strelley Pool Formation is that it is present in all greenstone belts of the Pilbara Craton that expose c. 3400 Ma stratigraphy. Prior to breakup of the Pilbara Craton, the formation might have been continuous with the Buck Reef Chert in the Onverwacht Group of South Africa. The formations are about the same age, and they separate very similar stratigraphic successions. The Strelley Pool Formation was deposited in shallow-water marine, stromatolite reef, beach, sabkha, estuarine, fluviatile, and lacustrine environments. Extensive silicification of its carbonate and fine-grained clastic components has transformed much of the formation to ‘chert’, and the formation was once referred to as the ‘Strelley Pool Chert’. The formation contains some of Earth’s oldest and best-preserved fossil evidence of early life, including stromatolites, microbial mats, microfossils, and trace fossils.