Introduction Exploring sediments and rocks of the seafloor is one of the themes of our first weekend field trip. As we travel from stop to stop imagine yourself traveling around on the seafloor. Through the combination of this field trip and the Pt Lobos field trips, we’ll be able to visit many of the seafloor areas we’ve talked about in class, including the submarine canyon like the Monterey Canyon, a submarine fan, a mid-ocean ridge, and the deep sea floor of the abyssal plain. Some of the other themes are the deposition of river gravels, and the contrasts between the rocky emergent coastline of Big Sur and the smooth, sandy coastline of a more stable environment like Marina and Ft Ord. Field Trip stops Monterey Formation on Olmstead Road. The main thing to notice here is the Monterey Formation Diatomaceous Shale. To the naked eye, this rock looks like mudstone. But if we had powerful microscopes, we could see all of the diatoms that comprise this rock. Since there is very little terrigeneous material in the rock, we know that it was formed far from continents. It was probably formed in the deep oceans of the abyssal plains. What is the evidence that tectonics moved these rocks up to this spot and higher on the hill rather than the sea level dropping to expose these rocks? How did the rocks move from the seafloor to the North American continent? Through tectonic processes. When plates or blocks of rocks converge, the rocks in the middle deform in such a way that they get thicker. Getting thicker means creating mountains and mountain ranges. Imagine continents colliding and mountain ranges forming. Mountaineers at the top of Mt Everest in the Himalayas have found fossils of creatures that lived in the oceans (If the gate’s not closed we will visit the) Vista Point on Jack’s Peak and/or Laureles Grade. Overview of the low lying areas north of MPC from Ft. Ord to the mouth of the Salinas River and beyond. The coast line in this area is smooth and sandy with a large dune system. Clearly, this area has been an area of sand accumulation for a long time. This sand is taken out of the coastal system and does not go down submarine canyons. Carmel Valley Overlook. (Because of the big bus, we may not be able to get to this stop) At this stop we can see down into Carmel Valley. Note the geomorphic features associated with the Carmel River. Note the river terraces and the wide river valley. Garland Park. We’ll take a look at the sediments in the river bed and at the flood plain. What kind of sediments occur in the river bed? What kind of rocks occur? What is the size of the clasts? How is the sorting? In the visitor center, when did the last major flood occur in the Carmel River drainage system? What information can you gleam from the hydrograph on the bridge over the Carmel River? Carmel Valley Road Outcrop There are two types of sediments or rocks exposed here. One of them is the Monterey Formation. What process formed the other deposit? What is the geologic history of this place? Monastery Beach A nearby canyon causes deep water to occur very close to shore here. Also, good views of marine terraces. What differences can you see in grain size of the beach? What is distinctive about the slope angle of the beach as it reaches the water? Garrapata Beach Two main things to see here: the distal turbidites and the San Gregario Fault. The sedimentary rocks here are distal turbidites. That means that they are deposited by turbidity currents, but far out on the submarine fan. Remember these rocks and compare their grain size to the rocks that we’ll see at Pt Lobos later. What is the evidence that the turbidites here were deposited far from shore on the continental slope? Also at Garrapata Beach, we’ll see the San Gregario Fault. The San Gregario Fault is part of the San Andreas Fault system and is one of the faults that separates the Pacific plate from the North American Plate. It is the same kind of fault as the San Andreas Fault. What kind of fault is the San Gregario Fault? How were you able to locate the San Gregario Fault on Garrapata Beach? Where is it? Hurricane Point Excellent view of the Big Sur coastline, one of the worlds best examples of an emergent coastline. It just doesn’t get any better than this! The rock here is a marble, which is a metamorphosed limestone. Limestone is deposited in warm shallow seas where coral and tropical fish make it nice to snorkel. Then the limestone gets metamorphosed into marble. What is the difference between a marine terrace and a wave-cut platform? Andrew Molera State Park We’ll walk to the mouth of the Big Sur River here and see the results of volcanism and sedimentation at a mid-ocean ridge. Note the pillow basalts and chert. We’ll also note wave refraction as the waves move in towards the beach. Can you find any pink sand? If you can I think it is composed of the chert that crops out nearby. What is the evidence that this group of rocks were deposited near a mid-ocean ridge or on a seamount?
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