Facies architecture of a continental, below-wave-base volcaniclastic basin: the Ohanapecosh Formation, Ancestral Cascades arc (Washington, USA)
Facies architecture of a continental, below-wave-base volcaniclastic basin: the Ohanapecosh Formation, Ancestral Cascades arc (Washington, USA)
The >800-m-thick, Oligocene Ohanapecosh Formation records voluminous sedimentation of volcanic clasts in the Ancestral Cascades arc (Washington State, USA). Most volcaniclastic beds are dominated by angular pumice clasts and fiamme of andesitic composition, now entirely devitrified and altered. All beds are laterally continuous and have uniform thickness; fine sandstone and mudstone beds have features typical of deposits from low-density turbidity currents and suspension settling. Erosion surfaces, cross-beds, and evidence of bi-directional oscillatory currents (i.e., wave ripples and swaley and hummocky cross-stratification) are almost entirely absent. We infer that the setting was subaqueous and below wave base.
The abundance of angular pumice clasts, crystals and dense volcanic clasts, and the extreme thickness of several facies, suggest they were derived from magmatic volatile-driven explosive eruptions. The extremely thick beds are ungraded or weakly graded, and lack evidence of hot emplacement, suggesting deposition from subaqueous, water-supported, high-concentration volcaniclastic density currents. Some of the thickest beds contain coarse, rounded, dense clasts at their base and are interbedded with accretionary lapilli–bearing mudstone; these beds are interpreted to be deposits from subaqueous density currents fed by subaerial pyroclastic flows that crossed the shoreline. Shallow basaltic intrusions and mafic volcanic breccia composed of scoria lapilli indicate the presence of intra-basinal scoria cones that may have been partly subaerial.
The range in facies in the Ohanapecosh Formation is typical of below-wave-base, continental (lacustrine) basins that form in proximity to active volcanic arcs, and includes eruption-fed and resedimented facies. Extreme instantaneous aggradation rates are related directly to explosive eruptions, and sediment pathways reflect the locations of active volcanoes, in contrast to conventional sedimentation processes acting in non-volcanic environments.
352-376
Jutzeler, M.
fbaf10c4-6597-4eb5-96cc-fc9d466aae86
McPhie, J.
902a7abf-9499-48e4-a5c2-fdf688e347f8
Allen, S.R.
6f8def59-b7a8-4b0a-8ed1-45359d864e81
March 2014
Jutzeler, M.
fbaf10c4-6597-4eb5-96cc-fc9d466aae86
McPhie, J.
902a7abf-9499-48e4-a5c2-fdf688e347f8
Allen, S.R.
6f8def59-b7a8-4b0a-8ed1-45359d864e81
Jutzeler, M., McPhie, J. and Allen, S.R.
(2014)
Facies architecture of a continental, below-wave-base volcaniclastic basin: the Ohanapecosh Formation, Ancestral Cascades arc (Washington, USA).
Geological Society of America Bulletin, 126 (3-4), .
(doi:10.1130/B30763.1).
Abstract
The >800-m-thick, Oligocene Ohanapecosh Formation records voluminous sedimentation of volcanic clasts in the Ancestral Cascades arc (Washington State, USA). Most volcaniclastic beds are dominated by angular pumice clasts and fiamme of andesitic composition, now entirely devitrified and altered. All beds are laterally continuous and have uniform thickness; fine sandstone and mudstone beds have features typical of deposits from low-density turbidity currents and suspension settling. Erosion surfaces, cross-beds, and evidence of bi-directional oscillatory currents (i.e., wave ripples and swaley and hummocky cross-stratification) are almost entirely absent. We infer that the setting was subaqueous and below wave base.
The abundance of angular pumice clasts, crystals and dense volcanic clasts, and the extreme thickness of several facies, suggest they were derived from magmatic volatile-driven explosive eruptions. The extremely thick beds are ungraded or weakly graded, and lack evidence of hot emplacement, suggesting deposition from subaqueous, water-supported, high-concentration volcaniclastic density currents. Some of the thickest beds contain coarse, rounded, dense clasts at their base and are interbedded with accretionary lapilli–bearing mudstone; these beds are interpreted to be deposits from subaqueous density currents fed by subaerial pyroclastic flows that crossed the shoreline. Shallow basaltic intrusions and mafic volcanic breccia composed of scoria lapilli indicate the presence of intra-basinal scoria cones that may have been partly subaerial.
The range in facies in the Ohanapecosh Formation is typical of below-wave-base, continental (lacustrine) basins that form in proximity to active volcanic arcs, and includes eruption-fed and resedimented facies. Extreme instantaneous aggradation rates are related directly to explosive eruptions, and sediment pathways reflect the locations of active volcanoes, in contrast to conventional sedimentation processes acting in non-volcanic environments.
Text
Ohanapecosh JUTZELER - accepted version without links.pdf
- Accepted Manuscript
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e-pub ahead of print date: 3 February 2014
Published date: March 2014
Organisations:
Marine Geoscience
Identifiers
Local EPrints ID: 363465
URI: http://eprints.soton.ac.uk/id/eprint/363465
ISSN: 0016-7606
PURE UUID: 0f87c2fd-11d7-4ae4-a088-454650aa6547
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Date deposited: 25 Mar 2014 10:50
Last modified: 14 Mar 2024 16:24
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Author:
M. Jutzeler
Author:
J. McPhie
Author:
S.R. Allen
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