USGS CMG W-3-09-MB Metadata

Optically Stimulated Luminescence (OSL) studies to determine age of turbidite
deposits

Age of sediment by means of OSL and 14C techniques

(see excel file)

1). We will conduct a novel sampling effort for Optically Stimulated 
Luminescence (OSL) studies. Our goal is to learn how long it takes for sand to 
move through the canyon system out onto Monterey Fan. We have shown that the 
last major sand-carrying event to move quartz sand within the channel of 
Monterey Fan occurred about 100 years ago and that this sand is compositionally 
indistinguishable from beach sand at the canyon head. However, these 
observations do not distinguish whether the sand moves from near the shoreline 
out onto the fan in a single event or whether the sand moves incrementally 
down-canyon. We are going to apply luminescence-dating techniques to resolve 
this question.
OSL is an established technique for determining how long quartz sands have been 
buried (e.g., removed from sunlight). The principle is that natural gamma 
radiation damages quartz crystals 
(http://www.ndsu.nodak.edu/ndsu/klepper/BreifOSL.html) and these imperfections 
anneal only when the samples are exposed to sunlight. In the process of 
annealing a small, but measurable amount of photons are given off. If the amount 
of gamma radiation produced in the surrounding sediments is measured, the age 
(or time since last exposure to sunlight) can be calculated with some accuracy. 
This has never been done for deep-marine sand, but OSL has promise for 
determining when quartz sands left the nearshore environment. The critical step 
is to sub-sample cores in the dark without any exposure to stray ambient light. 
We have tested our techniques in a darkroom with a red safelight using beach 
sand and sand from Ventana-collected vibracores from the upper canyon and feel 
comfortable with the sub-sampling procedure. We propose to collect cores from 
the Monterey Fan Channel in areas where we already know appropriate 
stratigraphies exist. OSL measurements will be made by Dr. Thomas Stevens now at 
the University of London.
2). We will be recovering the battery powered instrument node from Shepard 
Meander. This was deployed on September 6, 2007 on Tiburon dive 1127.  It is 
marked with Homer #80 and caries ADCP3 (sn5997), Seacat 16+ (sn 4190) Wetlabs 
(sn 0310010) OBS (sn 10025), HS-2 (sn H2oo31007) and ACM 10.
3). We will continue sample for organic carbon, DDTr, and infauna as well as 
collecting video transects.
Operations plan:
We are going to work primarily in areas where we have dove before.  As many of 
the sites are well off-shore our schedule will be adjusted as by the weather. 
Getting the existing instruments back from Shepard Meander and getting the cores 
for ~3600 m are the highest priorities. June 15, 1600 - As this is a late start 
we will dive within the upper canyon to test the new vibracoring system on Doc 
Ricketts.