| 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. ?? Journal compilation 2006 International Association of Sedimentologists No claim to original US government works. |
| Genre: | Article |
| ProdID: | 70028973 |
| Citation Author: | Barnhardt, W. A.; Sherrod, B. L. |
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| Citation End Page: | 1228 |
| Citation Issue: | 6 |
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| Citation Language: | English |
| Citation Larger Work Title: | Sedimentology |
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| Citation Number Of Pages: | 18 |
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| Citation Search Results Text: | Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA; 2006; Article; Journal; Sedimentology; Barnhardt, W. A.; Sherrod, B. L. |
| Citation Start Page: | 1211 |
| Citation Volume: | 53 |
| Citation Year: | 2006 |
| Type: | citation/reference |
| Text: | Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA; 2006; Article; Journal; Sedimentology; Barnhardt, W. A.; Sherrod, B. L. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1111/j.1365-3091.2006.00809.x |
| Date Other: | Sun, 1 Jan 2006 00:00 -0600 |
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