Time, Cratons, and Voyageurs NP

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GeologicTimeScale• Bythemid‐1800s,geologistshadcorrelatedtheworldwidepatternoffossilrangesinsufficientdetailtoestablishatimescalefortheentireplanet.Thisscaleremainsvalidaftermorethan150yearsofcontinuedfieldresearch.• Thetimescaleisbasedonthestratigraphicpositionsofmajorchanges(extinctions)inthefossilrecord.Itishierarchical:majortimeperiodsaresubdividedonthebasisofminorchanges.
DivisionsofTimeScale• Eons(largestdivision):– Phanerozoic(“obviouslife”),rockswithobviousfossils– Precambrian(earlierthanCambrian),nowsubdividedintoProterozoic(“firstlife”),Archean,andPriscian• Eras– Cenozoic(“newlife”),organismssimilartomodern– Mesozoic(“middlelife”),suchasdinosaurs– Paleozoic(“oldlife”)• Periods• Epochs
Page 2 and 3: Today’s Lecture• Geologic Time
Page 4 and 5: PrinciplesofStratigraphy• Origina
Page 6 and 7: Layered sedimentary rock is typical
Page 8 and 9: The Principle of Superposition stat
Page 10 and 11: The mudcracks shown above formed ov
Page 13 and 14: The Principle of Cross-Cutting Rela
Page 15 and 16: Complex sequences of events can be
Page 17 and 18: Unconformities• Nosinglelocationo
Page 19 and 20: Intrusive igneous rocks and metamor
Page 21 and 22: Note the abrupt interruption of the
Page 23: Both “sides” of this angular un
Page 26: The Grand Canyon has several unconf
Page 29 and 30: FaunalSuccessionandCorrelation• W
Page 31: Correlation of rock units over grea
Page 36 and 37: SpontaneousRadioactiveDecay• Some
Page 38 and 39: RadiometricDatingofRocks• Inorder
Page 40 and 41: Potassium-Argon dating can be used
Page 42 and 43: The steep front of this Hawaiian ba
Page 44 and 45: Organic samples are prepared for ra
Page 46 and 47: Radiocarbon dating is useful for as
Page 48 and 49: OtherAbsoluteMethods• Severalothe
Page 50 and 51: Varves: Lakes which freeze overduri
Page 52 and 53: Cosmogenic (surface) dating: If a r
Page 54 and 55: Formation of Continental CratonsMet
Page 56 and 57: Terrane AccretionMarshak, EARTH (No
Page 58 and 59: Pillow basaltscraped off theocean f
Page 60 and 61: NORTH AMERICAN CONTINENT~500 Millio
Page 62 and 63: Voyageurs National Park• Establis
Page 64 and 65: Voyageurs National ParkRecent Histo
Page 66 and 67: Voyageurs National ParkGeologic His
Page 68 and 69: Voyageurs National ParkAn example o
Page 70 and 71: Voyageurs National ParkGeologic His

Time, Cratons, and Voyageurs NP

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