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Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA

Sedimentology

By:
and
DOI: 10.1111/j.1365-3091.2006.00809.x

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Abstract

Episodic, large-volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground-penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment-rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet-like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat-lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice- and charcoal-rich sand overlie one of the buried surfaces. Organic-rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time-correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel-fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand-filled dikes and sills indicate liquefaction caused by post-depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal-current reworking, which redistributes sediment into large fields of ebb- and flood-oriented bedforms.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA
Series title:
Sedimentology
DOI:
10.1111/j.1365-3091.2006.00809.x
Volume
53
Issue:
6
Year Published:
2006
Language:
English
Publisher:
Wiley
Contributing office(s):
Coastal and Marine Geology Program
Description:
18 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Sedimentology
First page:
1211
Last page:
1228
Number of Pages:
18
Country:
United States
State:
Washington
Other Geospatial:
Puget Sound