14:30 〜 14:45
[MGI31-09] Reports of BASE project by ICDP: New perspectives on surface environments and microbial activities at 3.2 Ga Earth
キーワード：ベース、ムーディーズ層群、ICDP
The BASE (Barberton Archean Surface Environments) scientific drilling project aimed at recovering unweathered continuous core from the Paleoarchean Moodies Group (ca. 3.2 Ga), central Barberton Greenstone Belt (BGB), South Africa. The Moodies Group samples have potentials to understand the early evolution of surface environments, life and continents.
Drilling activities, sampling parties and current scientific progresses will be introduced at this presentation. Eight boreholes between 280 and 495 m length, drilled November 2021 through July 2022. As a result, a total of 2903 m of curated cores were obtained. Boreholes encountered a variety of conglomerates, diverse and abundant, mostly tuffaceous sandstones, rhythmically laminated shale-siltstone and banded-iron formations, and several horizons of early-diagenetic silicified sulfate concretions. Some deposited within only a few million years in alluvial, fluvial, coastal-deltaic, tidal, and prodeltaic settings. They represent a very-high-resolution record of Paleoarchean surface conditions and processes.
Japanese PIs and teams at the BASE project are trying to constrain the evolution of cyanobacteria and origin of banded iron formation using the recovered cores. For example, fossilized microbial mats are found in drilled core samples with appreciable amounts of organic carbons. Those microbial mat community most likely included early cyanobacteria. Significant amounts of banded iron formations or jasper are also found in the coastal sedimentary rocks. They are accompanied by highly carbonaceous shales. Organic matter in those shales may represent the bloom of photosynthesizing bacteria. Those discoveries will contribute to our understanding of the early evolution of biosphere.
Drilling activities, sampling parties and current scientific progresses will be introduced at this presentation. Eight boreholes between 280 and 495 m length, drilled November 2021 through July 2022. As a result, a total of 2903 m of curated cores were obtained. Boreholes encountered a variety of conglomerates, diverse and abundant, mostly tuffaceous sandstones, rhythmically laminated shale-siltstone and banded-iron formations, and several horizons of early-diagenetic silicified sulfate concretions. Some deposited within only a few million years in alluvial, fluvial, coastal-deltaic, tidal, and prodeltaic settings. They represent a very-high-resolution record of Paleoarchean surface conditions and processes.
Japanese PIs and teams at the BASE project are trying to constrain the evolution of cyanobacteria and origin of banded iron formation using the recovered cores. For example, fossilized microbial mats are found in drilled core samples with appreciable amounts of organic carbons. Those microbial mat community most likely included early cyanobacteria. Significant amounts of banded iron formations or jasper are also found in the coastal sedimentary rocks. They are accompanied by highly carbonaceous shales. Organic matter in those shales may represent the bloom of photosynthesizing bacteria. Those discoveries will contribute to our understanding of the early evolution of biosphere.