5:15 PM - 6:30 PM
[BCG04-P04] Analysis and Observation result in the Cleaverville Formation, Pilbara, Western Australia
★Invited Papers
Keywords:Banded Iron Formation, Archean
The Cleaverville Formation was well identified as Mesoarchean banded iron formation (CL BIF 31Ga) in the coastal Pilbara terrane in Western Australia (eg. Kiyokawa et al., 2019). The CL BIF was a key formation to know correlation with east and west sedimentary sequence in Pilbara Craton (eg. Hickman, 2012). In this study, we reconstructed stratigraphy of the CL 3 core of DXCL drilling project.In this study,we didvery detail stratigraphic reconstruction and organized lithological characteristics by observation by thin section and FE-SEM. Very detail geochemical analysis byESD, XRD and REE.
Thickness of the Cleaverville Formation is about 370m, and it is composed of the Black Shale Member (about 150m) and BIF Member (about 220m) to top. We collected 210m long core from 60 m below surface. The Black Shale Member contains organic rich black shale with few cm thick volcanic very fine sandstone, which contains cross lamination. The BIF Member composed of siderite/greenish shale (SG unit), magnetite/greenish shale (MG unit) and siderite/black shale (SB unit). The BIF Member formed five units from SG, MG , SG, MG, SG and SB units from bottom to top.
black shale member is composed of homogeneous black shale and black silt rock with cross lamination. They are composed of quartz, chlorite, muscovite and pyrite. Moreover, they include fine grain of quartz and feldspar(50~100μm).
The SG unit form stratify laminated siderite/chert layer and massive greenish shale layer (about 10cm thickness). Laminated siderite/chert is composed very fine clay layer with siderite courted[ks1] quartz grain (10-30μm). White chert layer formed fine quartz and recristallized siderite. The massive greenish shale is composed siderite and chlorite, and have homogeneous structure.
The MG unit become stratify magnetite/chert layer and massive greenish layer alternately (about 10cm thickness). Moreover, stratify magnetite layers become magnetite lamination and quartz lamination alternately (1mm-1cm). Magnetite lamination is formed idiomorphic cubic magnetites. The idiomorphic magnetite crystals formed only clay layers. Quartz layer and the massive greenish shale are similar to that of SG unit.
The SB unit become stratify siderite/chert layer and black shale (about 10cm thickness).There are organic carbon rich waveylamination in this sequence.
Most sequence of the BIF Member contains recrystallized idiomorphic siderite and is very difficult identified original sedimentary condition. Only the SB unit might be preserved original sedimentary structure to form BIF sequence.
The REE date normalization by PAAS indicate positive anomaly of Eu in the all type rocks and high HREE.
The date of Fe/Ti-Al/(Al+Fe+Mn+Na+K+Ca) indicates monotonic decrease. Moreover, the date of Fe/Ti in magnetite/chert layer is highest, and that in black shale is lowest. Therefore, the effect of hydrothermal water is highest when magnetite/chert layer is indicipated, and the effect of detritus is highest when black shale is indicipated.
Thickness of the Cleaverville Formation is about 370m, and it is composed of the Black Shale Member (about 150m) and BIF Member (about 220m) to top. We collected 210m long core from 60 m below surface. The Black Shale Member contains organic rich black shale with few cm thick volcanic very fine sandstone, which contains cross lamination. The BIF Member composed of siderite/greenish shale (SG unit), magnetite/greenish shale (MG unit) and siderite/black shale (SB unit). The BIF Member formed five units from SG, MG , SG, MG, SG and SB units from bottom to top.
black shale member is composed of homogeneous black shale and black silt rock with cross lamination. They are composed of quartz, chlorite, muscovite and pyrite. Moreover, they include fine grain of quartz and feldspar(50~100μm).
The SG unit form stratify laminated siderite/chert layer and massive greenish shale layer (about 10cm thickness). Laminated siderite/chert is composed very fine clay layer with siderite courted[ks1] quartz grain (10-30μm). White chert layer formed fine quartz and recristallized siderite. The massive greenish shale is composed siderite and chlorite, and have homogeneous structure.
The MG unit become stratify magnetite/chert layer and massive greenish layer alternately (about 10cm thickness). Moreover, stratify magnetite layers become magnetite lamination and quartz lamination alternately (1mm-1cm). Magnetite lamination is formed idiomorphic cubic magnetites. The idiomorphic magnetite crystals formed only clay layers. Quartz layer and the massive greenish shale are similar to that of SG unit.
The SB unit become stratify siderite/chert layer and black shale (about 10cm thickness).There are organic carbon rich waveylamination in this sequence.
Most sequence of the BIF Member contains recrystallized idiomorphic siderite and is very difficult identified original sedimentary condition. Only the SB unit might be preserved original sedimentary structure to form BIF sequence.
The REE date normalization by PAAS indicate positive anomaly of Eu in the all type rocks and high HREE.
The date of Fe/Ti-Al/(Al+Fe+Mn+Na+K+Ca) indicates monotonic decrease. Moreover, the date of Fe/Ti in magnetite/chert layer is highest, and that in black shale is lowest. Therefore, the effect of hydrothermal water is highest when magnetite/chert layer is indicipated, and the effect of detritus is highest when black shale is indicipated.