Beschreibung
Two facing, each ca. 1000 m-long, subvertically dipping sections of the Moodies Group are exposed in a ca. 2900 m long water tunnel which traverses the Saddleback Syncline in the Barberton Greenstone Belt (BGB), South Africa. The siliciclastic sediments and minor volcanics of this unit, deposited ca. 3224 - 3218 Ma ago, represent the world’s oldest well-preserved shallow-water and terrestrial strata. They are currently targeted by an ICDP full proposal (currently in revision; to be resubmitted Jan. 15, 2019) because they uniquely constrain multiple Paleoarchean environmental conditions. The section(s) exposed in the tunnel overlap only partially with the stratigraphy of the six boreholes of ca. 400m each proposed to be drilled in the ICDP project; they rather extend their range significantly. Sandstone petrography and geochemistry of BIF, tuffs and minor jaspilites from the tunnel section will extend and complement insights to be gained from the cores; they will also greatly improve previous, low-resolution findings from surface outcrops. Traversing the nearly unstrained strata despite a nearly isoclinal hinge (a well-known phenomena in the BGB) will allow to test several hypotheses related
to structural geology of greenstone belts and its syndepositional deformation. Data acquisition in the tunnel offers an uniquely low-risk, repeatable, detailed and highly cost-effective access to samples unaffected by prolonged oxic weathering. In a global context, our findings will shed light on the tectonic and stratigraphic understanding of syndepositional deformation in non-actualistic, highly mobile, nonplate-tectonic greenstone belts, on our knowledge of Early Earth surface conditions and early life adaptation.