High-Resolution Sediment Records of Seismicity and Seasonal Sedimentation from Prince William Sound, Alaska, using XRF Core Scanning
The southern coast of Alaska is a climatically sensitive and tectonically active region, however due to its remoteness and harsh climate there are limited long-term historical records of environmental conditions such as storm frequency, river discharge, and earthquakes. In order to determine the pot...
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| Format: | Others |
| Language: | English |
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W&M ScholarWorks
2014
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| Online Access: | https://scholarworks.wm.edu/etd/1539617947 https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=3077&context=etd |
| Summary: | The southern coast of Alaska is a climatically sensitive and tectonically active region, however due to its remoteness and harsh climate there are limited long-term historical records of environmental conditions such as storm frequency, river discharge, and earthquakes. In order to determine the potential for Prince William Sound sediments to contain high-resolution paleorecords of these conditions, a suite of 11 gravity cores was collected within the Sound in order to determine the modern day sediment depositional trends and to develop elemental proxies for earthquakes and seasonal sedimentation. 210Pb/137Cs-derived sedimentation rates and grain size trends indicate that there are two distinct sediment sources to the Sound; an allochthonous source of sediment that is advected into the Sound through Hinchinbrook Entrance, and an autochthonous source of sediment from the Columbia Glacier region of the northern Sound. Cyclic variations in grain size were identified in Hinchinbrook Entrance sediments using the XRF Sr/Pb ratio and were interpreted to be the result of seasonal sedimentation; with coarse-grained sediments deposited during the winter when storm-driven wave and currents in the nearshore region are high, and fine-grained sediments deposited during the summer when costal conditions are less energetic and when the discharge and transport of sediments from the Copper River is high. Additionally, light and dark colored laminations in northern Hinchinbrook Entrance sediments were interpreted to be the result of seasonal variations in the supply and preservation of organic matter; with high concentrations of organic matter preserved in the summer when primary production, the flux of terrestrial organic matter from rivers, and costal upwelling of potentially low oxygenated waters is high, and low organic matter concentrations preserved in the winter when primary production and river discharge are low, and when downwelling conditions likely introduce highly oxygenated waters. The use of the XRF Br/Cl ratio as a proxy for marine organic matter suggested that at least a portion of the dark, organic-rich, summer deposits had a marine origin, and may therefore be a potential proxy for seasonal sedimentation under certain conditions. Gravity flow deposits from the northern Sound were identified as having a source from the Columbia Glacier region using the XRF K/Ca ratio. The gravity flows that caused these deposits were identified as being triggered by historically recorded earthquakes, which likely remobilized sediment on the steep slopes of the northern channel and which then flowed downslope to the south. The results of this study indicate that the rapidly accumulating sediments in Hinchinbrook Entrance potentially contain high resolution records of Copper River discharge, storm activity and primary production, whereas sediments in the northern Sound may contain a regional seismic record. |
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