Marine Geology

how to track sound in the sea

1. single-beam sonar: creates a trackline of bottom depth as the ship moves forward

2. multi-beam sonar: creates a swath of bottom depth as the ship moves forward so you get a 2d image of the sea floor as your move along

3. towed multi-beam sonar: creates a high-resolution swath of bottom depth as the ship moves forward

main seafloor features

• continental shelf

• deep sea trench

• mid-ocean

• ridge

• abyssal plain seamounts

proof for plate tectonic theory

• sea floor subduction → at mid-ocean mountain ranges, there is a drop on the ride (extensional faulting) ->

• magnetic anomaly patterns: earth magnetic field is moving 35 miles per years and has gone through many reversals (seen through how minerals lined up opposite)

parts of the earth

• rigid outer crust

  • thin and rigid and floats on the higher density mantle below

• plastic upper mantle

  • although solid, the high temperatures cause the material to be sufficiently ductile to flow on very long timescales

• molten outer core

• solid inner core

different crusts of the earth

• oceanic

  • thin (~5km), higher density, younger, mainly made of basalt

• continental

  • thick (~70km), lower density, older, mainly granite

what is the driving mechanism of plate tectonic movements

• hot molten rock rises to divergent boundaries via convection and solidifies to form new oceanic crust

• oceanic crust spreads laterally, cools over time and gets more dense, sinks and is pulled by gravity back into the mantle at subduction

what does a tectonic plate consist of

a lithosphere (solid ridge upper mantle that is topped by either an oceanic, continental crust or both)

what happens when a tectonic plate moves

continent that is part of the plate also moves

what really sealed the deal that the continents were once pangaea

discovery of deep sea trenches and associated seismic activity helped to explain the eventual loss of ocean crust that was initially formed at mid-ocean ridges

types of boundaries

divergent, convergent and transform

what crusts are involved at a divergent boundary

• continent-continent

• ocean-ocean

what crusts are involved at a convergent boundary

• ocean-continent

• ocean-ocean

• continent-continent

what is the rate of sediment accumulation

• very slow and a 10-meter sediment core can represent a record of up to a million years of earth history

divergent plate boundaries

• two plates moving apart

• most are mid-ocean ridges

• less commonly they are also continental rift zones → east africa rift zone

  examples: cocos plate and nazca plate, eurasion and caribbean and african plate

what is the process that caused pangaea to break up

wilson rock cycle

convergent plate boundaries - oceanic and continental crust

• since ocean crust is more dense than continent crust, it subducts under continent and is pushed into the mantle

• generates deep ocean trench and forms very explosive volcanoes → it is SiO2 rich and very viscous, rich in H2O → water is derived from subducting oceanic crust

example: north cascade mountains mountains in washington and andes mountains in chile; mount saint helens (explosive volcano caused from o-c colliding)

convergent plate boundaries - ocean and ocean

• plate subducted is often furthest from its respective spreading and thus older, colder and denser

• creates deep oceanic trench (sometimes filled with sediments)

• chain of volcanoes an “island arc”

• examples: aleutian islands in japan and idnonesia

convergent plate boundaries - continental and continental

• neither want to subduct so mountain building often happens because both plate boundaries are largely equal density

• forms large mountain ranges

• example: india’s collision with asia to form mt everest

transform plate boundaries

plates slide laterally relative to one another

example: san andreas fault

example of stationary mantle plume underlying a moving tectonic plate

hawaii

what is the range of material raining down in sediment accumulation

wide-range: river-born sediments, continental dust, biological material

what are the biological marine sediment types

calcareous and siliceous ooze that sink to the bottom of the ocean

what is the sediment thickness near the coast

high due to river runoff of terrigenous sediment and high productivity that leads to high rain rate of biological material

where is red clay ooze found in

open ocean due to the slow rain of continental dust (and very low biological addition) which creates red clay

where are calcareous/siliceous sediments usually found in

high biological productivity regions (and absence of river outflows containing terrigenous material)

how can sediments tell us the ocean’s temperature in the past

• many microorganisms’ shells found in sediment cores are constructed of calcite

• all oxygen atoms have 8 protons → most have 8 neutrons but some have 10

• 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 shell

how many mass extinction events have there been

5, a 6th one caused by humans may happen

are the oceanic and continental crusts denser or less dense than the underlying mantle material

less dense

how did alfred wegener theorize that the continents used to make up pangaea

• apparent good fit of continental boundaries 

• distribution of fossil and mineral belts made sense if the continents were joined together in the past

how did naturalists first theorize about pangaea (before alfred wegener)

the apparent fit of continents

age of ocean crust at ridges and off-axis

• ocean crust at ridges are younger and symmetrically older off-axis

what can the remains of planktonic organisms be a proxy measurement for

• reveal information about growth conditions of the overlying ocean

• such as: surface water temperatures level of biological productivity

what is an example of reconstructing earth history using sediment core analysis

mass extinction event