marine geology

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School

Cornell University *

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Course

1540

Subject

Geography

Date

Oct 30, 2023

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docx

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Uploaded by UltraSeaLion3766

Measuring ocean bathymetry (depth) with ships and sonars (that were initially created for WW2 to search for the enemy underwater) ● Single-beam sonar ( trackline - a single line ) ● Multi-beam ( swath - like a line) ● Towe multi-beam (a high-resolution swath) It is also possible to conduct with satellites (which also figures out the topography as well as currents) Plate tectonic theory - he system of ideas behind plate tectonics theory suggests that Earth's outer shell (lithosphere) is divided into several plates that glide over the Earth's rocky inner layer above the soft core (mantle). The plates act like a hard and rigid shell compared to Earth's mantle. There is oceanic and continental crust Oceanic: ✦ thin (~5 km) ✦ relatively higher density

✦ relatively young ✦ consists mostly of basalt ✦ Less dense and floats lower Continental: ✦ thick (~70 km) ✦ relatively lower density ✦ relatively old ✦ consists mostly of granite ✦ Denser and floats higher Evidence of continental drift: - Continents “fit” next to each other (bacon and snider-Pelligrini) - Paleobiogeography ( Alfred Wegener noted that the distribution of fossil and mineral belts made sense if continents were joined together in the past - mineral and fossil belts) Evidence of Seafloor Spreading - Mid-ocean ridges (Marie tharp) - Extensional Faulting ( Some indication of seafloor spreading at mid-ocean ridges was inferred based purely on observed morphology of the faulting* patterns along the ridge axis) extensional faulting - Movement which produces relative displacement of adjacent rock masses along a fracture in the rock 1. The earth’s outer crust is composed of many individual crustal plates called tectonic plates that move relative to one another 2. Tectonic Plates can be composed of both ocean crust and continental crust Three Possible Convergent Boundaries 1. Oceanic Crust & Continental Crust • Because ocean crust is more dense than continent crust, this is the plate that is subducted under the continent crust and pushed back down into the mantle 2. Oceanic Crust & Oceanic Crust

• The plate that gets subducted is often the one that is furthest from its respective spreading center and thus older, colder, and more dense than the newer plate 3. Continental Crust & Continental Crust • This is a battle of titans because neither wants to subduct under the other. • Mountain-building is a common result Sediments get their name by the dominant material ● Biological (usually mid-ocean, especially if there is a lot of bio activity ● (coastal) Terrigenous ● Red clay (dust basically) ● One of the components dominates, but all 3 are present Summary of Sediment Accumulation 1. Wide range of material raining down

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- river-born sediments, continental dust, biological material 2. Sediment thickness is high near coast - due to river runoff of Terrigenous sediment , and high productivity that leads to high rain rate of biological material 3. Red Clays found in open ocean: • Slow rain of continental dust (and very low biological addition) creates red clays 4. Calcareous or Siliceous Sediments found In high biological productivity regions (and in the absence of river outflows containing terrigenous material): - downward rain of biological material causes red clays to be flooded/diluted by biologically-derived calcareous or siliceous material 5. The rate of sediment accumulation is very slow and a 10-meter sediment core can represent a record of up to a million years of Earth history Indirect ( proxy ) estimates of the temperature of seawater can be obtained from calcite fossils using the isotope ratio 18O:16O preserved in the oxygen atoms of their shells . This ratio is temperature dependent 1. Deep-Sea Sediments Accumulate at Very Slow Rates • On the order of centimeters per thousand years 2. Deep-Sea Sediment Cores Provide a Time Series of Ocean Events Dating Back Nearly 200 Million Years 3. Sediment Cores Can Record the Past Conditions of Ocean Primary Production and Ocean Temperatures 4. Sediment Cores Can Also Record Past Extinction Events in the Ocean 5. Humanity is now the cause of a 6th Mass Extinction Event