Correlation of borehole and seismic data in the Gulf of Alaska at Sites U1417, U1418, U1420 and U142
DESCRIPTION: During IODP Exp. 341, a transect of sites was drilled in the Gulf of Alaska across the shelf and slope, continuing as far as the distal Surveyor Fan, in order to investigate the sedimentary record from a period of changing climate during the Pliocene-Pleistocene that led to the glaciation of the southern Alaskan margin. A major objective of this expedition was to drill through a series of seismically- resolved sedimentary sequences and use the resulting record to study provenance, paleoclimate and glacimarine indicators, and ultimately to link the record to the tectonic and climatic history of the region. Wireline logging data are important for making borehole to seismic correlations, by providing a time-depth relationship for each logged site and geophysical characterization of the drilled sequences.
OUTCOMES: Preliminary shipboard integration of core, log, and seismic data indicate that distinct changes in lithology and logging data often coincide with significant seismic reflections or boundaries between primary seismic units. These results suggest that prominent seismic reflections may be associated with the presence of cemented sediments and increased clast abundance/size, among other things, that are observed in this glacially influenced sedimentary environment. Using synthetic seismograms and VSPs to determine time-depth relationships, detailed records from cores and logs can be accurately related to seismic stratigraphic features, and interpretation can be extended from individual boreholes into the large number of seismic profiles of different resolutions that have been collected throughout the Gulf of Alaska.