Transverse infilling of the central Aleutian Trench by unconfined turbidity currents

Abstract

Holocene sand layers cored from the central Aleutian Trench are dominated by volcaniclastic debris, and the only likely source is the central Aleutian volcanic arc. This creates something of an enigma because bathymetric obstructions seemingly prevent direct delivery of sediment via transverse canyons or channels. Turbidity Currents are funneled through submarine canyons on the upper trench slope, but the flows become unconfined as they cross the midslope Aleutian Terrace. Evidently, the turbid flows maintain high enough velocities to climb over the trench-slope break; acceleration down the lower trench slope then allows forearc bypassing to occur without the aid of through-going channels.

Source to sink: A review of three decades of progress in the understanding of volcaniclastic processes, deposits, and hazards

“…Trenches that are isolated from the arc by an uplifting accretionary prism may receive volcaniclastic material only as distal tephra fall and volcaniclastic turbidites (Ballance et al, 2000;Stewart, 1978;Underwood, 1986;Underwood and Karig, 1980;Underwood and Moore, 1995). Elsewhere high sediment-supply rates produce immense submarine fan complexes, such as that infilling the Cascadia trench, carrying variable contributions of volcanic materials from the associated arc.…”

Clay-Mineral Provenance, Sediment Dispersal Patterns, and Mudrock Diagenesis in the Nankai Accretionary Prism, Southwest Japan

“…However, the background fallout of suspended sediment does not always follow the same pattern of regional-scale sediment dispersal as transport by turbidity currents (Underwood 1986(Underwood , 1991Hathon and Underwood 1991). Repeated episodes of mud resuspension and mineral homogenization are common within the near-bottom nepheloid layer in response to bioturbation, thermohaline bottom currents and turbidity currents (Gorsline 1984(Gorsline , 1985.…”

Provenance and dispersal of muds south of the Aleutian arc, north Pacific Ocean

“…These relatively low smectite contents agree with the results of Johnson (1986), who examined a more limited suite of cores from the trench and insular slope. Underwood (1986b) demonstrated that most of the turbidite sands in the central trench segment are volcanogenic and, hence, were likely derived from the arc and transported to the trench via transverse flows. Turbidite sands cored at DSDP Site 186 in Atka Basin require a similar, and seemingly unequivocal, volcanic-arc provenance (Stewart 1978).…”

“…As suggested by Hathon (1988), the westward protrusion of smectite-depleted mud in the abyssal Gulf of Alaska is probably a consequence of turbidity currents flowing down the trench. More importantly, petrographic analyses of turbidite sands from as far west as the central trench segment show that some axial-flow deposits (probably derived from the Alaska Peninsula) are interstratified with volcanogenic sands transported from the arc via transverse flows (Underwood 1986b). The limit of this westerly transport of sand and mud is uncertain, but it seems unlikely that turbidity currents could continue for appreciable distances beyond longitude 180 ~ .…”