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Earth History GEOL 2110

Earth History GEOL 2110. Lecture 8 Fundamentals of Stratigraphy II Biostratigraphy , Time Markers, and Unconformities. Biostratigraphy. A biostratigraphic unit is a body of rock that is defined or characterized by its fossil content .

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Earth History GEOL 2110

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  1. Earth History GEOL 2110 Lecture 8 Fundamentals of Stratigraphy II Biostratigraphy, Time Markers, and Unconformities

  2. Biostratigraphy A biostratigraphic unit is a body of rock that is defined or characterized by its fossil content. A fossil zone (or biozone) is an interval of strata characterized by a particular index fossil. The best index fossils are those that evolve rapidly and were not sensitive to the sedimentary environment (flyers and floaters)

  3. Index Fossils and Sedimentary Facies Good Index Fossil Cephlapods – Rapid evolving Floaters Poor Index Fossil Brachiopods – Slow evolving Sand burrowers

  4. Index Fossils and Sedimentary Facies Facies-dependent Facies- independent

  5. Best Ever! Index Fossils Conodonts Eel-like creatures with hard “teeth and jaw” parts; Existed Late Cambrian (495 Ma) to Late Triassic (200 Ma) Graptolites Planktonic colonial zooids that floated in the oceans (“ocean beehives”) Existed from Ordovician (490 Ma) to Devonian (419 Ma)

  6. Biozones – Formations of Biostratigraphy

  7. Regional Time MarkersVolcanic Ash Eruptions Long Valley Caldera 700,000 yr Mt Mazama Eruption 6,500 yr

  8. Global Time MarkersMeteor Impacts K-T Boundary mudstone-impact layer (Ir anomaly) K-T impact site

  9. The 1.85 Ga Sudbury Impact The First Major Extinction Event ?? Iron Formation Breccia Accretionary Lapilli

  10. And you thought you were having a bad day… CALCULATED ARRIVAL TIMES FOR EFFECTS AT GUNFLINT LAKE (480 miles from Sudbury Impact) Meteorite.org, Pangea International, Inc 1) ~13 seconds—Fireball (thermal radiation=3rd degree burns; 50 minutes) 2) ~2-3 minutes—Earthquake (magnitude >10 at Sudbury, 1000X Haiti) (New data estimates magnitude 13 at Chicxulub) 3) ~5-10 minutes—Airborneejecta arrives (~1-3 m thick , fragments < 1 cm) 4) ~40 minutes—Air blast (compression wave, wind speeds >1400 mph) 5) ~1-2 hours—Tsunami(the first of several?) 6) Post-impact environmental changes (duration and magnitude? Global?) www.lpl.arizona.edu/impacteffects

  11. Global Time MarkersMagnetic Reversals ODP site 1149

  12. Global Time MarkersClimate Change A typical deep sea sediment core record of ∂18O in foraminifera shells

  13. Unconformities Gaps in the Geological Record Siccar Point, Scotland Utah

  14. Types of Unconformities Nonconformity – Sedimentary/volcanic strata resting on intrusive or metamorphic rocks Angular Unconformity – Relatively flat-lying strata resting on steeply-dipping strata Disconformity – Strata resting conformably on other strata across a significant time gap

  15. Creating Unconformities Grand Canyon Stratigraphy Nonconformity Angular Unconformity Disconformity

  16. Unconformities related to Regression - Transgression Disconformity

  17. Paleozoic Formations of the Upper Midwest

  18. The Jordan Sandstone Disconformity Oneota Dolomite Ordovician Jordan Sandstone Cambrian Missing Fossils

  19. Gaps in the Minnesota Timescale

  20. Global Unconformities Ordovician

  21. Global Unconformities at the Edges of the Continents

  22. Reading Time in Strata

  23. Next Lecture Absolute Dating of the Earth Quiz – Chapters 4 & 5

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