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312 Cards in this Set
- Front
- Back
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Geologic time is also known as?
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Deep time
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What is catastrophism?
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All things on Earth connected to a catastrophe. (Noah's Flood or "Great Flood")
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Catastrophism also says...
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Landscape was developed by catastrophes.
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In the mid 1600's _________ concluded Earth was only a few thousand years old.
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James Ussher
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James Ussher said that the Earth was made?
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October 26 at 9 a.m. in 4004 B.C.
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What is uniformitarianism?
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(Fundamental principle of geology) Look at processes that occurred today will help you explain the features in the past.
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James Hutton published?
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Theory of the Earth in the late 1700's. (Scottish)
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What is relative dating?
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Placing rocks and events in sequence
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Who came up with relative dating?
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Nicolaus Steno 1636-1686
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What are the five rules on relative dating?
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1.) Law of superposition
2.) Principle of original horizontality 3.) Principle of cross-cutting relationships 4.) Inclusions 5.) Principle of fossil succession |
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What is the law of superposition?
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Oldest rocks are on the bottom
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What is the principle of original horizontality?
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Sediment is deposited horizontally
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What is the principle of cross-cutting relationships?
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Younger features cut through older features
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What are inclusions?
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One rock contained within another (Rock containing the inclusions is younger)
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What is the principle of fossil succession?
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Fossils succeed one another in a definite and determinable order.
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What are unconformities?
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Any break in the rock record. (Time and erosion)
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What are the three main types of unconformity?
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1.) Angular unconformity
2.) Disconformity 3.) Nonconformity |
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What is an angular unconformity?
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Tilted rocks are overlain by flat-lying rocks
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What is a disconformity?
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Strata on either side are parallel. (Like sandstone on top of sandstone but one is older than another which at that point is a disconformity.)
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What is a nonconformity?
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Metamorphic or igneous rocks below, younger sedimentary above.
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What is a correlation of rock layers?
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Matching rocks of similar age in different regions.
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What does the correlation of rock layers usually rely upon?
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Fossils (Ex. National Parks in West)
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Fossils are?
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Evidence of past life
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What are some conditions favoring preservation?
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1.) Rapid burial
2.) Possession of hard pats |
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Fossils and correlation usually ties in to?
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The principle of fossil succession
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Who proposed the principle of fossil succession?
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William Smith in the late 1700's and early 1800's
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Determining the age of rock using fossils...
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Can determine around what age by seeing where one ends and another one starts.
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What is an index fossil?
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Fossils that show up only a little in history at a certain time. (So can use them to date and age.)
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What is radioactivity?
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Spontaneous breaking apart of atomic nuclei.
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A lot of archeologists use ____ to radioactive date?
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Carbon-14
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In radioactive decay a _______ and _________ are left.
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A parent and daughter products
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What is a parent?
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An unstable isotope
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What are the daughter products?
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Isotopes formed from the decay of a parent.
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What forms of radioactive decay are there?
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Alpha, Beta, and electron.
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Radiometric dating...(3)
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1.) Uses half-lives (Half life)
2.) Requires a closed system 3.) Yields numerical date |
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For radiometric dating, sedimentary rocks are?
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Not very good for age dating but they are where the fossils lie.
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For radiometric dating, igneous rocks are?
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Good for age date because they capture the isotopes and atoms, so both the parent and daughter is there.
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Carbon-14 has a half-life of?
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5,730 years
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Based on it's half-life, Carbon-14 is only used to date?
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Very recent events
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Carbon-14 is produced?
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In the upper atmosphere
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As soon as an animal dies it stops taking in Carbon-14. T or F?
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True
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Carbon-14 is also...
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Incorporated into CO2 and absorbed by living matter
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Carbon-14 dating is a useful tool for?
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Anthropologists, archeologists, historians, and geologists.
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To about how many years can you use Carbon-14 dating?
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50,000 years
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What is the geologic time scale?
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Divides geologic time into units.
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How was the geologic time scale originally developed?
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It was originally developed using relative dates.
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The first subdivision of the geological time scale is?
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Eon
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What is an eon?
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The greatest expanse of time.
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How many eons are there on Earth?
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4
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Name the eons. (4)
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1.) Phanerozoic - "Visible life," most recent eon that we know the most about, started 540 mya.
2.) Proterozioc (These 3 make up the Precambrian) 3.) Archean 4.) Hadean - Oldest eon |
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What is the subdivision of an eon?
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Era
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What is the eras of the Phanerozoic eon?
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1.) Cenozoic - "Recent life"
2.) Mesozoic - "Middle life" 3.) Palezoic - "Ancient life" |
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Eras are divided into?
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Periods
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Name the periods.
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1.) Cambrian
2.) Ordovician 3.) Silurian 4.) Devonian 5.) Mississippian (Part of Carboniferous) 6.) Pennsylvanian (Part of Carboniferous) 7.) Permian (Paleozoic) 8.) Triassic 9.) Jurassic 10.) Cretaceous (Mesozoic) 11.) Tertiary 12.) Quaternary (Cenozoic) |
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Periods are divided into?
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Epochs
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We live in which epoch?
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Holocene epoch
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What are the difficulties in dating for the time scale?
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1.) Not all rocks are datable
2.) Materials are often used to bracket events and arrive at ages |
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Which rocks are not datable?
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Sedimentary rocks are rarely reliable
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When was the Precambrian Era?
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4.5 bya (Beginning of Earth) to 540 mya
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The Hadean eon was?
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4.5 - 3.8 bya
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The Archean eon was?
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3.8 - 2.5 bya
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The Proterozoic eon was?
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2.5 bya - 540 mya
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The Precambrian era makes up?
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88% of Earth's history
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Why do we only have "sketchy" knowledge about the Precambrian Era?
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Most Precambrian rocks are devoid of fossils.
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3.5 bya the first...
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Early bacteria
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What are the most common Precambrian fossils?
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Stromatolites
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What is a stromatolite?
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Sediments trapped by algae that formed limestone deposits.
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What was this algae?
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Cyanobacteria were the early photosynthesizers
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Because there was so much cyanobacteria this began the...
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Oxygen Crisis
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Oxygen came into the atmosphere when?
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About 2 billion years ago when Fe oxidized
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Precambrian rocks...(4)
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1.) Each continent has a "core area" of Preacmbrain rocks called a shield
2.) Extensive iron ore deposits 3.) No fossil fuels 4.) Oldest rocks on Earth ~3.8 billion years old |
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Where are the oldest rocks on Earth found?
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Isua, Greenland
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Rodinia is?
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The first super continent
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The breakup of Rodinia...
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Lasted from 650-630 mya
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The breakup of Rodinia also created?
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The Iapetus Ocean
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The Iapetus ocean...
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Is often called the proto-atlantic and is where the North Atlantic is today.
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During the breakup of Rodinia...
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Flooding of shallow continental shelves allowed for rapid evolution of organisms.
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This rapid evolution of organisms is called the?
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Cambrian Explosion
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The Paleozoic Era was from?
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542 - 248 mya
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The Paleozoic era also held the first...
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First life with hard parts
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There are abundant Paleozoic fossils. T or F?
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True
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During Paleozoic history...
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A southern continent called Gondwanaland exists.
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North America during the Paleozoic era?
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Was a tectonic orogeny that effected Eastern North America (Ordovician)
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What is an orogeny?
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A mountain building event.
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What makes an orogeny?
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Two masses pushing against another.
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During the late Paleozoic history...
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The super continent Pangea formed
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When Pangea formed, the ___________ also formed.
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The super ocean Panthalassa
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During the movement of the continents many ________ formed.
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Mountain belts or orogenies
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These orogenies that formed during Pangea were?
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1.) Acadian/Antler (Devonian)
2.) Ovachita (Mississippian/ Pennsylvanian) 3.) Appalachian (Pennsylvanian/ Permian) |
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The breakup of Pangea occurs?
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During the Mesozoic era
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The Mesozoic era was from?
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248 - 65 mya
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The Mesozoic history goes from...(5)
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1.) Begins with much of the world's land above sea level
2.) Seas invade western North America 3.) Breakup of Pangea begins forming the Atlantic ocean 4.) The North American plate began to override the Pacific plate 5.) Mountains of western North America begin to form |
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There were no _______ when Pangea was present.
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Glaciers
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What are the mountains that formed during the Mesozoic era? (3)
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1.) Sonoman Orogeny (Triassic) (Professor's dog named after)
2.) Nevaden Orogeny (Jurassic) 3.) Sevier Orogeny (Cretaceous) |
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The Cenozoic era goes from?
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65 mya to present
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The Cenozoic era is the?
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Smallest fraction of geologic time than either the Paleozoic or Mesozoic.
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During the Cenozoic Era, North America was?
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Mostly above sea level
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During the Cenozoic era, eastern North America...
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1.) Stable with abundant marine sedimentation
2.) Eroded Appalachians were raised isostatic adjustments |
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What are isostatic adjustments?
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Block in water floats to density that matches, as it erodes it goes high and higher as it's mass decreases
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During the Cenozoic Era, western North America...
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1.) Building of the Rocky Mountains were coming to an end
2.) Laramide orogeny formed (Paleogene - Epoch) |
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During the Cenozoic Era, large regions uplifted...
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1.) Basin and range province form
2.) Rivers erode and form gorges |
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What is an example of these?
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Grand Canyon and Black canyon
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Evolution of early organisms began with?
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Life during the Proterozoic, 2.5 bya - 540 mya
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Complex prokaryote fossils can be found in?
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Gunflint chert superior in Canada these date back to 1.9 bya
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The first eukaryote fossils were probably around?
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1.6 - 1.4 bya
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What are acritarchs?
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Spherical microfossils with thick, complex organic walls, they may have been considered the first phytoplankton, they went extinct 700 mya.
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The Ediacaran fauna held...
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First large, multicelluled fossil animals, most soft-bodied
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These fossils were from?
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The Vendian period of 610 - 540 mya
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The fossils in the Ediacaran fauna include?
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Tracks and burrows as well as shallow marine environment
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Most of the soft bodied organisms probably were?
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Jellyfish and sea anemones
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The Ediacaran fauna was?
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Flat with large surface which are probably grazed extensively algae mats and bacteria.
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What happened in the Cambrian explosion?
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Rapid apperance and diversity of "body plans", also adaptive radiation.
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What is adaptive radiation?
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Organisms evolved to fill niches
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Lower Cambrian fossils can be found in?
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Chengjiang fauna
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Middle Cambrian fossils can be found in?
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Burgess Shale fauna
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All but ________ appeared in the Cambrian Explosion.
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Bryozoans
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Why did the Cambrian explosion happen?
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1.) End of an ice age
2.) Sea level rise covering continental shelves 3.) Increasing oxygen levels 4.) Increasing upwelling, nutrient rich sediments, and burrowing. |
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In the early Paleozoic life...
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Vertebrates had not evolved yet
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During the Paleozoic Era life consisted of?
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Several invertebrate groups
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Name a few to the invertebrates. (3)
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1.) Trilobites
2.) Brachiopods 3.) Cephalopods |
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When did the first fishes evolve?
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During the Ordovician period
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When did the first plants evolve?
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During the Silurian period
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During the late Paleozoic...
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1.) Organisms diversified dramatically
2.) Fishes evolve into 2 groups of bony fish (Lung fish and lobe finned fish) 3.) Insects invade the land (Devonian period) 4.) Amphibians diversify rapidly 5.) Extensive coral swamps develop |
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What are the 2 groups of fish that evolved in the late Paleozoic?
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The lung fish and the lobe finned fish.
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These fish became?
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The first amphibians in the Devonian period
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During the late Paleozoic era, what happened at the Permian period?
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A mass extinction
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Why did a mass extinction occur?
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Volcanism and plate tectonics
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Explain the occurrence of the mass extinction.
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1.) Warm oceans means that less and less oxygen can be found in the ocean.
2.) The water make hydrogen sulfide which is toxic and kills both land and water animals 3.) A meteor may have also aided in this |
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Mesozoic life starts with...
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The survivors of the great Permian extinction
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During the Mesozoic era...
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Dinosaurs dominate
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During the Mesozoic era, when did the first mammals come into being?
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Triassic period
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These mammals were most likely?
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Little things like rats, voles, and moles.
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One group of reptiles lead to the birds in which period?
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The Jurassic period
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The first angiosperm was in?
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The Cretaceous period
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By the close of the Mesozoic...
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Many reptile groups along with many animal groups become extinct
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Why did this extinction occur?
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1.) One hypothesis states that a large asteroid or comet struck the Earth.
2.) Another possibility could be extensive volcanism |
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Why is it believed a asteroid or comet struck the Earth?
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There is the Chicxulub crater in Yucatan, as well as a crater in the Chesapeake Bay that are typed to be Triassic
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With the start of Cenozoic life...
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1.) Mammals replace reptiles as the dominant land animals.
2.) Angiosperms dominate the plant world |
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What are angiosperms?
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Flowering plants with covered seeds
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Angiosperms strongly influenced?
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The evolution of both birds and mammals because it was a food source.
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After the mass extinction of the reptiles two groups of mammals evolve which are?
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Marsupials and placentas
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Marsupials are?
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Animals that are born and taken care of in a pouch
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Placentas are?
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Develop inside mother before born.
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Since mammals diversified rapidly some groups became quite large...
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Such as the Hornless rhinoceros which stood 16 feet high
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Many of these large animals went extinct, some believe this is from?
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Another extinction event
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The extinction event is proposed to be the?
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Evolution of humans
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Continental drift was a first proposed hypothesis by?
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Alfred Wegener in 1915
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Wegener published?
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The Origin of Continents and Oceans
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Wegner's hypothesis on continental drift...
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1.) Super continent Pangea began breaking apart about 200 mya
2.) Continents drift to present position 3.) Continents "broke" through oceanic crust |
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What evidence did Wegener provide? (5)
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1.) Fit of South America and Africa
2.) Fit of North America and Europe 3.) Fossils match across sea 4.) Rock types and structures match 5.) Ancient climates |
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What was the main objection to Wegener's proposal?
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The inability to provide a mechanism
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A debate came forth based on the continental drift hypothesis, which was?
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Drifters vs. Nondrifters this debate carried on until the 1960's
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Wegener's ideas were dismissed by some of the most prominent scientists in the U.S.. T or F?
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True
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One of those scientists was?
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R. T. Chamberlin
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What happened after this?
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1.) Development of paleomagnetic techniques
2.) Radioactive dating techniques 3.) Extensive sea floor mapping |
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Based on these new developments of technology...
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Evidence for a new model based on continental drift
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Paleomagnetism came out to be?
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The most persuasive evidence
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Paleomagnetism shows that?
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Ancient magnetism preserved in rocks
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Paleomagnetism records two important dates which are?
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1.) Polar wandering
2.) Earth's magnetic field reversals |
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What is polar wandering?
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Continents move
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Where is it recorded that Earth's magnetic field reverse?
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At ocean ridges
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Polar wandering paths of North American and Eurasia don't point to the same direction for north but...
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When put together into "Pangea" the north pole is showed to be in the same direction
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How were magnetic reversals through time found?
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By combining radioactive dating techniques with the polarity of minerals in igneous rocks, a magnetic polarity scale was developed.
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How do rocks record magnetism?
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Magma cooling below the Curie point (~600 degrees C) is magnetized in prevailing polarity of the Earth
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Are polarity reversals normal through time?
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Yes
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Do the basalts on the sea floor also record polarity?
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Yes
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What did Harry Hess do?
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Mapped large continuous mountain ridges in center of oceans
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Harry Hess developed the ideas of?
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Sea floor spreading which was called geopoetry
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The major driving point of sea floor spreading was?
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Convection cells within mantle
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Do magnetic anomalies mirror each other on each side of a sea floor rift?
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Yes
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What are anomalies?
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Added or subtracted to normal magnetic field
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Do the rocks on either side of a rift get older the further away from the rift they are?
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Yes
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When was this discovered?
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1968/1969
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Vine and Matthews wrote a book about magnetic anomalies that...
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Tied magnetic anomalies on sea floor to polarity reversals of Earth's magnetic field. (Based on ideas of Hess and Dietz)
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In 1965 continental drift and sea floor spreading...
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Combined into plate tectonics
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Who combined this two ideas?
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J. Tuzo Wilson a canadian geophysicist
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In oceans where are the old rocks?
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There are no "old" rocks, denser rocks move out from ridge then get pressed onto continents
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The ocean ridge itself is?
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The youngest
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When was the oldest sea floor from?
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Mesozoic age
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The younger the ocean crust...
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The shallower the ocean is there.
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What is the general equation for age vs. depth?
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D = 2500 + 350t^1/2
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D is what in the equation?
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Depth
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T is what in the equation?
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Age in millions of years.
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The crust sinks...
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About 1000 m in first 10 million years, sinks next 1000 meters in 26 million years.
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What makes the general equation of depth and time so useful?
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It is simple and quantitative.
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What evidence is there for plate tectonics model?
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Earthquake patterns and volcanoes
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Earthquakes are...
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Associated with plate boundaries.
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Deep-focus earthquakes...
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Along trenches provide a methods for tracing the plates descent.
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The structure of Earth is composed of?
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Crust, mantle, outer core, and inner core.
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The crust is...
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The thin skin on the outer surface.
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What are the two types of crust?
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Oceanic and continental
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Oceanic crust...
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Is 5-7 km thick, mostly basalt, and 3.0 g/cm^3 density.
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Continental crust...
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20-50 km thick, granitic composition and 2.7 g/cm^3 density.
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The crust is...
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1.) Mostly O, Al, and Si.
2.) It is separated from mantle by "mojo discontinuity" |
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The mantle is? (5)
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1.) Base of crust down to 2,900 km
2.) 84% of Earth's volume 3.) 68% of mass 4.) Average density is 4.5 g/cm^3 (But less dense) 5.) Mostly O, Mg, and Si |
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The core is?
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1.) 2,900 km to center of Earth
2.) Average density of 13 g/cm^3 3.) 16% volume of Earth 4.) 31% mass 5.) Mostly Fe (~90%) and Ni |
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The outer core is?
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Liquid, from 2,900 km - 5,100 km
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The inner core is?
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Solid, from 5,100 km - 6,371 km
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The Earth's structure in the rheological point of view is? (5)
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1.) Lithosphere
2.) Asthenosphere 3.) Mesosphere 4.) Outer core 5.) Inner core |
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The lithosphere is? (3)
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1.) About 100 km thick
2.) Grabs some of the upper mantle 3.) Brittle behavior |
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The asthenosphere is? (3)
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1.) Form base of lithosphere to 350 km -700 km
2.) Driving force of plates (Convection cells) 3.) Relatively plastic behavior |
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The mesosphere is? (3)
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1.) Base of asthenosphere to core
2.) Lower mantle 3.) Rigid mantle |
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The outer core is? (2)
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1.) Viscous liquid
2.) 11.8 g/cm^3 density |
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The inner core is?
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1.) Solid
2.) 16 g/cm^3 3.) Spins faster than rest of the Earth creating magnetic field |
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How do we know all of the components as well as what the components of Earth are made up of? (4)
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1.) Indirect methods
2.) Gravity measurements 3.) Earthquakes 4.) The field of seismology |
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What is seismology?
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The study of earthquakes
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Earthquakes have?
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P waves and S waves
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P waves are? (3)
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1.) Horizontal
2.) Compressional 3.) Can travel through everything including liquids |
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S waves are? (3)
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1.) Snake-like
2.) Vertical 3.) Can't go through liquids |
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Based on Earth's structure oceanic crust...
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Oceanic crust is denser than continental crust
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Oceanic crust lies...
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Below sea level
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Continental crust lies...
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Above sea level
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Due to isostasy...
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The Earth's outer layer tends toward gravitational equilibrium by height adjustments between areas of different relative buoyancy
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According to plate tectonics...
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Surface of Earth is made up of 7 lithosphere plates
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Which plate is the largest?
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The Pacific plate
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Plates can be made up of?
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Both oceanic and continental crust
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There are ____ types of boundaries separating the plates.
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Three
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What are three types of boundaries?
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1.) Divergent
2.) Convergent 3.) Transform |
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A divergent plate boundary is?
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Plates move apart
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A convergent plate boundary is?
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Plates move together or towards each other
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What is a transform boundary?
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Plates move past each other (Ex. St. Andreas boundary)
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A divergent plate boundary...(4)
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1.) Constructive margins
2.) Two plates move apart 3.) Mantle material upwells to create new seafloor 4.) Ocean ridges and sea floor spreading |
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What is the Wilson's cycle?
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Building up of mountains, then the breakdown of materials
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Name the structure of the oceanic lithosphere. (5, but 4 layers)
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1.) Layer 1 - Deep sea sediment
2.) Layer 2A - Basaltic pillow lavas, broken down and fractured (.5 km thick) 3.) Layer 2B - Basaltic dikes (1.5 km thick) 4.) Layer 3 - Gabbro (5 km thick) 5.) Layer 4 - Peridotite ("True mantle material") |
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What makes up most of the oceanic crust?
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Olivine tholeiites
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What are olivine tholeiites?
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Type of basalt that contains plagioclase feldspar, pyroxene, and olivine.
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How do we know how the oceanic lithosphere is layered?
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1.) Geophysical techniques (Sounds waves off sea floor)
2.) Dredged material 3.) Submersibles observation 4.) Ophiolites |
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What are ophiolites?
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Preserved piece of ocean floor has been emplaced onto continental material, usually during collision events
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What are ophiolites made of?
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May contain chert, pillow basalts, serpentinite (Greenschists) and gabbro, and peridotite.
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Convergent plate boundaries...
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1.) Destructive boundaries
2.) Plates move together 3.) Oceanic - continental convergence --- Denser oceanic slab sinks into the asthenosphere 4.) Pockets of magma develop and rise 5.) Continental volcanic arcs form (Ex. Andes, Cascades, and the Sierra Nevadan system) |
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What are the processes of the boundaries?
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1.) Subduction
2.) Accretion 3.) Accretionary wedge or prism |
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What is subduction?
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One segment of lithosphere inserted partially or wholly beneath another
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What is accretion?
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Process of offscraping material from outer plate and trench, and adding it to continental margin
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What is an accretionary wedge of prism?
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The material that is scraped onto continental margin
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What is the basic model?
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1.) Subduction begins with development of accretionary wedge (Blueschist facies) (Accretionary wedge may become subaerial Ex.) Barbados)
2.) Development of magmatic arc (Rocks formed include andesite, diorite, and granites 3.) Sometimes development of back arc basin |
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Oceanic - oceanic convergence? (3)
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1.) Two oceanic slabs converge and one descends beneath the other
2.) Often formed volcanoes on the sea floor 3.) Volcanic island arcs forming are volcanoes emerge from sea (Ex. Aleutian, Marian, and Tonga islands) |
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Island arc systems? (6)
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1.) Arc line of islands
2.) Prominent volcanic activity, high heat flow on continental side of arc 3.) Deep trench on ocean side 4.) Shallow trench on continental side 5.) Active tectonism (earthquakes) from 60-700 km 6.) These are subduction zones |
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Continental - continental convergence? (2)
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1.) When subducting plates contain continental material two continents collide
2.) Can produce new mountain ranges (Ex. Himalayas) |
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What is a suture?
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Contact of plates
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Transform fault boundaries?
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Plates slide past one another
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In a transform fault boundary...
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No new crust is created and no crust is destroyed
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Transform faults...(3)
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1.) Most join two segments of a mid-ocean ridge
2.) At the time of formation, they are roughly parallel to the direction of plate movement 3.) Aid in the movement of ocean crust material |
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Hot spots are...
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Thought to originate in lower mantle
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Hot spot basalts are?
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Basalts from hot spots are enriched in certain rare Earth elements, different than MOR (Mid-ocean ridge) basalts.
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Hot spots are thought to be?
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Believed to be stationary
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Hot spot tracks in Indian Ocean from Reunion Island and Kerguelen trace...
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Trace out path of India subcontinent
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The hot spot beneath Yellowstone...
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Is responsible for Columbia river flood basalts
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Hot spots can be used...
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To track plate movement, "hot spot reference"
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What are some examples of island chains?
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Marshall islands, Hawaiian islands, several others in the Pacific.
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The Hawaiian islands...
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Age progression from oldest in west to youngest in east
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Seamounts were described by?
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Harry Hess in the 1940's
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Flat topped seamounts are called?
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Guyots
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Hess proposed that?
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Seamounts formed similar to Darwin's atoll hypothesis
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What is an atoll?
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Circular rings of coral with lagoon in center
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What is Darwin's atoll hypothesis?
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Atoll formed from islands sinking and middle falling away leaving the fringing coral
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Seamounts...
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Are greater than 1000 m elevation off sea floor and a 5 - 15 degree slopes
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There are about _______ seamounts in the Pacific.
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10,000
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Some seamounts occur as?
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Linear chains (Ex. Emperor seamount chain)
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A barrier reef is?
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A space between coral fringe and island
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How fast is the ocean spreading?
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About as fast as your fingernail grows, so about 2 cm a year
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How do we find continental margins and basins?
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With bathymetry
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What is bathymetry?
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The depth and the contours of the ocean floor.
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How do we study bathymetry? (4)
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1.) Weighted line soundings
2.) Echo sounding (More recently) 3.) Satellite altimetry 4.) Sea surface changes because of gravity from undersea objects (Mapping these sea surface differences allows for bathymetric maps to be created) |
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What are some examples of echo sounding?
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1.) Pingers and fish finders
2.) Multibeam echo sounders (Gloria - older form) |
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What are multibeam echo sounders?
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Sends out a range of sound and can see contours at a larger range
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What satellite altimetry?
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Measures accurate distance from sea surface to satellite
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What is velocity of sound in water?
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1,500 m/s
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What is the equation for finding depth with velocity as a factor?
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D = V x T/2
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What are the two major marine provinces?
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Continental margins and ocean basins
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What is the equation for vertical exaggeration?
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Vertical Exaggeration = Horizontal scale / Vertical scale
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What are the two types of continental margins?
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1.) Passive (Tectonically - no earthquakes) or Atlantic-type margins
2.) Active (Tectonically active) or Pacific-type margins (Coincide with plate boundaries are tectonically active) |
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What are the three components of a continental margin?
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1.) Continental shelf
2.) Continental slope 3.) Continental rise |
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The continental shelf...(6)
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1.) Submerged portion of continental crust
2.) May be narrow or wide depending on setting 3.) Low gradient (Fairly flat) (.1 degrees, or 1-2 m/km of ocean depth for how far out) 4.) Less than 150 m deep 5.) Covered with sediments derived from continent 6.) Sea level a important component in continental shelf evolution |
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What are the processes controlling shelf evolution? (5)
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1.) Sea level
2.) Climate 3.) High rainfall, high weathering, terrigenous sediments delivered to shelf 4.) High latitude, glacial process create moraines and fjords 5.) Sediment supply |
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Why is sea level an important process for controlling shelf evolution? (3)
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1.) The modern shelf is still a product of last sea level lowstand
2.) Not in equilibrium, coarse sands at shelf break 3.) Sea level fluctuated throughout geologic time altering sedimentation |
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How does climate help control shelf evolution?
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Low latitudes, reefs
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What are moraines?
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Linear features of glaciers that dropped sediment making linear hills
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What are fjords?
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Glacially carved "U" shaped valley
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How does sediment supply help control shelf evolution? (2)
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1.) High terrigenous sediment supply creates deltas (Ex. Mississippian Nile)
2.) Low supply allows for reef growth in low latitudes |
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Is the shelf represented today or in the past?
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Relic sediments and palimpsest show that the modern shelf was reworked into how it is presently
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What are relic sediments?
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Sediments reworked from lowstands of sea level
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What is palimpsest?
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Shelf is reworked over and over like an ancient scroll
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What is a shelf break?
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It is defined at point where slope begins to increase; prominent feature
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About where is the shelf break?
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100-150 m depth about where most of the recent level lowstands have been
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What are the features of the continental slope? (5)
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1.) 10's of km wide, ~4 degree slop or 70 m/km (Can be variable)
2.) Deposition is combination of sediments from shelf and herripelagic deposits 3.) High sedimentation rate may lead to mass wasting events (Underwater landslide) may be triggers by earthquake 4.) Contour currents may move sediments (Gulf stream, Bahamain contourites (Deposits of sediment)) 5.) Cut by submarine canyons important for transport of sediments on slope made into features to the ocean basins |
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Submarine canyons...(4)
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1.) Major feature on continental slope
2.) Similar to canyons on land 3.) Steep sides (~20 - 45 degrees) 4.) May even have over hangs |
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What are the characteristics of a submarine canyon? (3)
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1.) Some occur as extensions off shore valleys
2.) Abundant on sea slopes, absent on others 3.) May cross the rise and continue |
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What is a hypothesis for the origins of a submarine canyon?
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River cutting during low sea level stands
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Why is this incorrect?
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Some canyons are clearly too deep for rivers to cut, must be a way to cut underwater
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So what is the actual origin of a submarine canyon?
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Turbidity currents weather away shelf and slope
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What is a turbidity current?
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A slurry of sediment and water, that deposits sediments in a grain size pattern
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What is a alluvial fan?
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Delta of deposited sediments down mountain
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Turbidity currents...(3)
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1.) Highly erosional
2.) Move up to 80 km/hr 3.) Deposit is called turbidite |
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A turbidite is?
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Deposit of a turbidity current that consists of graded bedded (Coarse to fine), called Bouma sequence
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Name the Bouma sequence. (5)
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1.) A - massive graded
2.) B - plane, parallel laminae 3.) C - ripple laminae 4.) D - upper plane laminae 5.) E - normal pelagic |
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Turbidites...
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1.) Can be up to 30 m thick
2.) Recognized in the Alps as Flysch deposits |
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Continental rise...(5)
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1.) Begins where the slope begins to flatten
2.) Much of sediment gets moved onto the rise by slides, slumps, and turbidity currents 3.) Moves sediment out into ocean basins from terrigenous sources 4.) Apron of sediments at base of continental slope 5.) Rise may stretch from 100 to 1000 km into ocean basin |
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Ocean Basins...
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1.) Thick layer of sediment overlying oceanic crust (Basaltic)
2.) Make up 1/2 of Earth's surface area |
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The features of the ocean basins include? (4)
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1.) Oceanic ridges
2.) Abyssal plains and hills 3.) Seamounts and guyouts 4.) Deep sea trenches |
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Why are there more seamounts and guyouts in the Pacific?
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Sediment that comes down slope in the Pacific goes into a trench leaving the sea floor unmarred.
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Oceanic ridges...(4)
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1.) Continuous submerged mountain chain 65,000 km
2.) Ridges occur at active sea floor spreading centers (Volcanism, earthquakes, and rift valley) 3.) Offset by transform faults and fracture zones 4.) Contain hydrothermal vents |
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Ridge topography...(9)
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1.) 30 -50 km wide rift valley, less on East Pacific rise
2.) 1 km + deep 3.) Very rugged complex bathymetry, steep flanks in Atlantic, low angle flanks in Pacific 4.) Shallow earthquakes (<60 km) 5.) Active volcanism, patchy in Atlantic, more continuous in Pacific 6.) High heat flow 7.) Spreading between 1 -3 cm layer in Atlantic, between 6 -8 cm/year in Pacific 8.) New crust less dense die to thermal expansion 9.) Depth of 2,500 - 3,000 m |
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When a mid-ocean ridge is offset...
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1.) The area between ridge segements is an active transform fault
2.) This area has shallow earthquakes |
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What is an inactive fracture zone?
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The area beyond the ridge segments
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How is the inactive fracture zone recognized?
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It is recognized on the sea floor by dramatic relief (Different age crust on each side of fracture zone)
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There is no ______ along the inactive fracture zone.
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Earthquakes
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What is a fracture zone?
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After transform fault and earthquakes are done then the "chunks" of ridges move together
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What are hydrothermal vents?
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Along ridges, sea water leaks into, which starts to become part of the convection
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Abyssal plains and hills...(5)
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1.) Cover 1/4th of Earth
2.) Abyssal plains are the flattest areas of Earth 3.) 3,500 and 5,500 m deep 4.) Mostly in the Atlantic, less in Pacific 5.) Abyssal hills are low, (Less than 1 km) volcanic hills partially covered by sediments |
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Trenches...(6)
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1.) ~100 km wide; hundreds to 1000 km long
2.) V-shaped, although may have flat bottom because sediment fills in 3.) Slopes between 8 - 15 degrees; some steeper 4.) Depths 7,000 - 10,000 m; deepest off island arcs 5.) Accretionary prism of sediment on continental side 6.) Trenches associated with magmatic arcs |
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Why are the deepest trenches off island arcs?
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Island arcs do not have a lot of sediment to dump into trenches, so they are sediment starved (Marianna trench)
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What are some magmatic arcs trenches are associated with?
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1.) Islands arcs: Aleutians, Marianna, and Tonga
2.) Continental arcs: Indonesia and Western South America |
