Geological and trace element evidence for a marine sedimentary environment of deposition and biogenicity of 3.45 Ga stromatolitic carbonates in the Pilbara Craton, and support for a reducing Archaean ocean

• DOI: 10.1046/j.1472-4669.2003.00014.x
• Publication Date: 2003-10-17T16:30:25Z
• Authors: Martin J. Van Kra...; Gregory E. Webb; Balz S. Kamber
• Keywords: Stromatolite; Ankerite; Banded iron formation; Terrigenous sediment; Rare-earth element; Microbial mat

ABSTRACT Bedded carbonate rocks from the 3.45 Ga Warrawoona Group, Pilbara Craton, contain structures that have been regarded either as oldest known stromatolites or abiotic hydrothermal deposits. We present new field and petrological observations high‐precision REE + Y data carbonates in order to test origin of Trace element geochemistry a number laminated stromatolitic dolomite samples c . 3.40 Strelley Pool Chert conclusively shows they precipitated anoxic seawater, probably very shallow environment consistent with previous sedimentological observations. Edge‐wise conglomerates troughs between widespread cross‐stratification provide additional evidence stromatolite construction, at least partly, layers particulate sediment, rather than solely rigid crusts. Accumulation sediment on steep sides high‐energy suggests organic binding surface. Relative absolute contents are exactly comparable Late Archaean microbial widely agreed biological origin. Ankerite unit bedded ankerite–chert couplets near top stratigraphically older (3.49 Ga) Dresser Formation, which immediately underlies wrinkly small, broad, low‐amplitude domes, also seawater. The Formation contrast strongly those siderite jasper–siderite–Fe‐chlorite banded iron‐formation base Panorama (3.45 Ga), is clearly geochemical results, together data, support: (1) deposition part sediment; (2) biogenicity carbonates; (3) reducing atmosphere; (4) ongoing extensive terrestrial erosion prior ∼3.45 Ga.