Table T6. Summary of volcaniclastic components at Site 1138.
Unit/Subunit | Core,
section, interval |
Depth
to top of unit (mbsf) |
Thickness (m) |
Age | Lithologies
with volcanic components |
Volcanic components |
Authigenic
and secondary minerals |
---|---|---|---|---|---|---|---|
Lithologic: | |||||||
I | 1R-1, 0 cm, to 13R, 0 cm | 112.00 | late Miocene to late Pleistocene | Foraminifer-bearing diatom clay and ooze | Mixed disseminated volcanic ash with feldspar crystals, pumice lapilli, broken pumice (forming shards), brown (basaltic) glass, and lithic fragments. | Green clay (nontronite?) forming on basaltic glass rims, brown volcanic clay. | |
I, II, and IIIA | 1R-1, 0 cm, to 53R, 0 cm | 496.40 | late Maastrichtian to late Pleistocene | Foraminifer-bearing diatom clay and ooze; foraminifer-bearing nannofossil clay, ooze, and chalk | Discrete pyroclastic fall deposits forming cm thick tephra layers. Some are dominated by brown (basaltic) glass ± lithic fragments, and others by pumice ± feldspar crystals (see Table T10). | Green clay (nontronite?) forming on basaltic glass rims, brown clay in matrix of glassy intervals. Glauconite in lowermost discrete basaltic ashes. | |
Basement: | |||||||
1 | 74R-1, 0 cm, to 76R-1, 0 cm | 19.30 | Cretaceous | Aphyric dacite | Abraded, flow-banded, aphyric, dacite cobbles with spherulitic texture. | Spherulitic alteration (silicification) and pale brown clay minerals along flow banding. | |
2 | 76R-1, 0 cm, to 79R-4, 87 cm | 24.49 | Cretaceous | Trachytic pumice lithic breccias and ash deposits | Pumice lithic breccia, lithic breccia with pumice, ash-fall deposits with accretionary lapilli, highly altered pumice-rich clays, massive volcanic clays (see Figure F13). | A wide variety of alteration from red to pale green, abundant smectite, and minor kaolinite clay minerals. |