Abstract
More than fifteen bentonite beds have been identified in the Santonian/Campanian section of the Campos Basin, offshore Brazil. These range in thickness up to 1 m and are mainly composed of interstratified illite/smectite. Relict textural features can still be observed, identifying them as former volcanic ash layers. They also display gradational or sharp contacts with the associated lithologies. In the Carapeba Field, `pure' bentonite beds, formed mainly by expandable clay minerals, occur intercalated with pelitic rocks. Bentonite beds with up to 20% terrigenous silty material (micas, quartz and feldspars), here classified as `impure', are found directly overlying siliciclastic turbidite sandstones. These bentonite beds incorporate constituents of turbiditic dust and are interpreted as equivalent to the Bouma E division of the underlying turbidite layers. This fact suggests a contemporaneity of the turbidite and the volcaniclastic processes. Therefore, the volcanism and associated tectonic seismicity are considered a potential mechanism for the onset of turbidite sedimentation.
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