Monterey Bay Aquarium Research Institute

Mendocino Fracture Zone Cruise - 2001
August 20 - 30, 2001
Over 300 km off the California-Oregon Coast
Logbook

August 25, 2001: Day #6

Log Entry: Much of the dive today was spent cruising the sedimented slope of the Gorda Escarpment. We did not see anything out of ordinary or exciting. We saw a few sedimentary ledges, which were sampled for fossils, and to correlate with the seismic section. The dive path followed the seismic line shot in 1999. We also came across a few carbonate slabs sticking out from the sediment (see picture). We interpreted these as pathways for fluid seeping out and precipitating authigenic carbonate.

We spent some of the day discussing the importance of biomineralization. It is not really clear what proportion of the carbonate and sulfide minerals we see in rocks is produced by microbial activity, and how much is precipitated by fluids passing through the rock. Carbon, nitrogen and sulfur isotopes have been used to distinguish between the two, and it appears that bugs (our nickname for bacteria) play a more important role than previously thought.

We also cut some more rocks for geochemical analysis. We want to use the bulk rock chemistry and age dating to deduce the origin of the Gorda Escarpment. The escarpment is now part of the Pacific Plate, but we think that it was once part of the Gorda Plate, and has since been accreted on to the Pacific Plate.

On future dives, we hope to find more vent fauna and authigenic carbonates. We also hope to finish our collection of fresh igneous rocks to complete the geochemical analysis for the origin of the Escarpment.

Below is a series of frame grabs showing some of the variety of creatures that we have seen during the dives. You can see some of the octopuses that are pretty common here (but poorly known to scientists).














 

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