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

biostratigraphic unit A biostratigraphic unit is a body of rock that is defined or characterized by its fossil content. fossil zone (or biozone) 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) Biostratigraphy

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

Index Fossils and Sedimentary Facies Facies- dependent Facies- independent

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)

Biozones – Formations of Biostratigraphy

Regional Time Markers Volcanic Ash Eruptions Long Valley Caldera 700,000 yr Mt Mazama Eruption 6,500 yr

Global Time Markers Meteor Impacts K-T impact site K-T Boundary mudstone-impact layer (Ir anomaly)

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

CALCULATED ARRIVAL TIMES FOR EFFECTS AT GUNFLINT LAKE (480 miles from Sudbury Impact) And you thought you were having a bad day… 1) ~13 seconds—Fireball (thermal radiation=3 rd 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—Airborne ejecta 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?) Meteorite.org, Pangea International, Inc 6) Post-impact environmental changes (duration and magnitude? Global?)

Global Time Markers Magnetic Reversals ODP site 1149

Global Time Markers Climate Change A typical deep sea sediment core record of ∂18O in foraminifera shells

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

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

Angular Unconformity Disconformity Nonconformity Grand Canyon Stratigraphy Creating Unconformities

Unconformities related to Regression - Transgression Disconformity

Paleozoic Formations of the Upper Midwest

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

Gaps in the Minnesota Timescale

Global Unconformities Ordovician

Global Unconformities at the Edges of the Continents

Reading Time in Strata

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