Mendocino Fracture Zone Cruise
August 24 - 31, 2000
Over 300 km off the California-Oregon Coast
August 26, 2000: Day #3
Log Entry: Today's dive was a search of sediment-covered slopes for occasional rocky outcrops, and ended early with high seas and a precarious recovery. The dive track was located on the westernmost end of the Gorda Escarpment, where the seismic data suggested that we might find outcroppings of basement rock capped by old folded and uplifted layers of sediment. The foot of the hill was all unconsolidated sediment with the monotony broken only by the visit of an octopus or a red jellyfish. There was no evidence of active tectonics. Climbing the wall of the escarpment we saw mostly brittle stars and small angular rock fragments. We had to use the vehicle sonar to guide us to the rare patches of exposed rock. Many of these were layered deposits of broken volcanic rocks. We don't know whether these are sedimentary accumulations that are related to the uplift or primary volcanic breccias.
We cored into one site but recovered only a small fragment of rock-the rest must have washed out. Pillow basalt outcrops are always more crumbly and more difficult to sample either by drilling or by grab sample, suggesting that the outcrop was a pillow basalt. The next outcrop for rock coring was much more coherent as well as decorated by the Octopus Garden. The core from here is of excellent quality. The new Tiburon rock coring sled is working very well in spite of the loss of output from many of the sensors (e.g. rpm, torque) due to problems with the data manager.
Unusual anemones that we called "Venus flytrap anemones" are abundant in this area (see frame grab of close up). We also found a piece of wood that was penetrated by wormholes and covered with brittle stars. Unfortunately our prized biological sample was washed away during the dramatic recovery, characterized by water splashing up and through the moonpool. The recovery took careful timing (and good nerves) by the Western Flyer crew to get the vehicle back on board in one piece and with only one sample lost. We were all very impressed. Unfortunately, the early recovery meant that we never made it to the top of the ridge to find the contact between basement and the overlying sediments. After a long night of gravity coring, we will return to follow a track line up an adjacent ridge and hopefully find this critical geological contact tomorrow.
Oatmeal w/ raisins and brown sugar
Eggs to order
Omelets: ham, mushroom, bell pepper, cheese, onion
Broccoli cheddar soup
Corned beef & cabbage
Roasted red pepper pesto penne pasta prepared perfectly
Broccoli cheddar soup
Roast turkey breast & gravy
Steamed vegetable medley