Uniform Mud (Unifite) Deposition in the Hellenic Trench, Eastern Mediterranean. Smithsonian Contributions to the Marine Sciences, Number 13

摘要

Unifites are nearly structureless, often thick, layers of clayey silt and silty clay that appear compositionally homogeneous and generally show a subtle fining-upward trend. Formed by uniform and faintly laminated muds, unifites are deposited from rapidly emplaced single gravity-flow events. Along the Hellenic Arc, unifites are restricted to small trench basins and interpreted as an end-member gravity-emplaced facies. Unifites are not truly homogeneous and the petrological distinctions observed are closely related with the trench basin depositional site relative to steep margins bounding the trench plain. The faintly laminated portions of unifites contain a higher silt content; the uniform mud portions are slightly better sorted and display an upward increase of planktonic tests. The sand fraction is dominated by clastic aggregates eroded from older margin sediments; unifites also comprise a large silt-size nannofossil content (including reworked forms). The increased uniformity basinward of unifites records deposition from turbidity current-related flows of diminished concentration that spread over large areas of a flat trench floor.