10:00 AM - 10:15 AM
[MIS22-11] Drilling proposal of 3.2 Ga Moodies Group in Barberton Greenstone Belt: high resolution reconstruction of surface envirnment and biosphere of middle Archean Earth
Keywords:Archean, Barberton, Moodies Group
Chritoph Huebeck and international collaborators are now proposing new ICDP drilling of Moodies Group in Barberton, South Africa. Scientific objectives for this drilling proposal are introduced in this presentation. Sedimentary rocks of the Moodies Group are about 3.22 Ga old and represent some of the world’s oldest, well-preserved, shallow-water strata. The metamorphic grade is lower greenschist facies. They thus represent a very clear window of Archean surface conditions and processes. Their coastal and fluvial-alluvial facies is ideal to investigate shallow surface environments of the early Earth, and Moodies Group may be the only group to investigate “surface” environmental processes of middle Archean Earth.
For instance, the oxidation state of 3.2 Ga surface environments has been vigorously debated in past literatures. Banded iron formations in Moodies Group are unique among other Archean BIFs, because of their shallow water deposition features. U and Cr enrichments are found in those shallow BIFs by our research group. This suggests that appreciable amounts of U and Cr were dissolved in 3.2 Ga Moodies shallow ocean, indirectly suggesting surface ocean water was oxygenic. However, those enrichments were found in surface rocks and it is highly desired to confirm the same enrichment in un-weathered drilled rocks. Microbial mat-like layers are also recognized in Moodies sedimentary rocks. But it is still uncertain if such microbial mats are ubiquitous in Moodies rocks and if they represent some consortia (mixture of photoautotrophs and heterotrophs, etc.) of different microorganisms, etc. Drilled samples from fresh Moodies rocks may give us a chance to answer those top-ranked scientific questions.
For instance, the oxidation state of 3.2 Ga surface environments has been vigorously debated in past literatures. Banded iron formations in Moodies Group are unique among other Archean BIFs, because of their shallow water deposition features. U and Cr enrichments are found in those shallow BIFs by our research group. This suggests that appreciable amounts of U and Cr were dissolved in 3.2 Ga Moodies shallow ocean, indirectly suggesting surface ocean water was oxygenic. However, those enrichments were found in surface rocks and it is highly desired to confirm the same enrichment in un-weathered drilled rocks. Microbial mat-like layers are also recognized in Moodies sedimentary rocks. But it is still uncertain if such microbial mats are ubiquitous in Moodies rocks and if they represent some consortia (mixture of photoautotrophs and heterotrophs, etc.) of different microorganisms, etc. Drilled samples from fresh Moodies rocks may give us a chance to answer those top-ranked scientific questions.