GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 280-1
Presentation Time: 9:00 AM-6:30 PM


HEUBECK, Christoph and BASE, Team, Jena University, Department of Geosciences, Burgweg 11, Jena, 07749, Germany

We target sedimentary rocks of the Paleoarchean Moodies Group (~3.22 Ga, up to 3.7 km thick) in the Barberton Greenstone Belt, South Africa. Its sedimentary (and minor volcanic) units were deposited within ~1-14 Ma and thus record Archean surface processes in fluvial to prodeltaic depositional environments at very high resolution. Despite tight regional folding, metamorphic grade is only lower greenschist-facies; widespread early-diagenetic silicification preserved abundant micro- and macrotextures, in many places virtually without strain. Moodies strata record numerous bio-geo-atmo-hydrosphere interactions and are ideal to investigate Archean terrestrial-marine transitions, particularly those related to diverse and well-documented microbial life. The “earth system” and “global environmental change” topics complement the themes of the UNESCO world heritage site declared 2018 in the Barberton Mountain Land.

In order to avoid the effects of oxidative weathering (a particular problem in fine-grained strata) and to obtain continuous sections suitable for geochemical and time-series analyses, we will drill five key sections. Nine inclined drillholes, each of 350-600 m length (MD), will investigate (1) conformable terrestrial-marine transitions for environmental proxies, (2) diagnostic lithologies (such as various paleosols, nearshore BIFs, evaporites and basaltic lavas) for their environmental significance, (3) the compositional, facies and morphological variability of thick and laterally extensive microbial mats, and (4) sedimentary and mineralogical responses to surface variables, such as tides, climate, potential meteorite impacts, and radiation, in particular in deep-water strata. Principal questions address the ecology, 3-D morphology and metabolism(s) of the abundant (oxygenic photosynthetic ?) microbial mats, stratigraphic rhythmicity, the redox state (sulfate, redox-sensitive metal isotopes), temperature and composition of ocean water and of early diagenetic fluids, and the relevance and processes of weathering and early diagenesis.