Abstract: Deposition and Resedimentation of Abyssal Tephra

T. C. Huang, N. D. Watkins

Ash layers and disseminated volcanic dust in more than 92 cores have been examined. The regions represented are the Antarctic sector of the South Pacific; east of New Zealand; east of the Azores; east and west of Costa Rica; and the eastern Mediterranean. Along suspected volcanic-cloud axes downwind from an eruptive source, the apparent accumulation rates of selected tephra follow log-normal distributions. The downwind-distribution function varies with ash type, reflecting contrasts in the respective parent eruptions. Oceanic circulation appears to effect the distribution of pumice fragments but not fine-glass shards.

Active volcanic islands spasmodically have supplied a large volume of ash into adjacent oceanic basins during eruptions. Postdepositional processes can lead to further redistribution. Five major resedimentation processes have been recognized: (1) turbidity currents (evidenced by partial Bouma sequences, graded bedding, and sharp-scour base of ash layers); (2) slumps (ash lumps and lenses); (3) debris flows (dispersed grain fabric of volcanic pebbles in matrices of ooze); (4) bottom currents (ash laminae with manganese micronodules); and (5) bioturbation (upward broadening peaks of ash accumulation rates with mottling structures). Less than 20% of the deep-sea ashes so far studied have been redeposited, and these are restricted overwhelmingly to regions within 300 km of volcanoes.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC