Abstract

Archean terrestrial-marine transitional strata provide insights in early-Earth coastal-zone dynamics and the onset of land colonization but are exceedingly rare. We here present results of detailed mapping, stratigraphic and petrographic analysis, and age dating of the Lomati Delta Complex, a morphologically prominent, wedge-shaped and dominantly arenaceous unit in the middle Moodies Group (~3.22 Ga) of the central Barberton Greenstone Belt (BGB). Subvertical regional bedding allows cross-sectional correlation within a prograding delta complex from proximal coarse-grained coastal-plain-facies sandstones to stratigraphically equivalent fine-grained and rhythmic prodelta siltstones over ca. 7 km strike length. Several reworked, subaerially exposed delta-top units mark sudden flooding events preceding progradational pulses. Microbial mats densely colonize shallow-marine facies. The provenance of detrital zircon grains and the feldspathic character of the sediments point to a proximal source comprising magmatic rocks formed mainly at 3.24, 3.28, 3.43 and 3.54 Ga within the BGB. The Lomati Delta Complex likely formed in a narrow, tide-dominated basin in which sedimentary systems quickly responded to changes in basin geometry, nearby source region uplift, and sediment supply.

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