Earth History GEOL 2110

1. Earth History GEOL 2110 Lecture 7 Fundamentals of Stratigraphy I Geologic Time Scale, Stratigraphic Units, Sedimentary Facies

2. Major Concepts • In the early 1800’s, the geologic rock record and time scale was deciphered from careful mapping and observations of fossil assemblages throughout Europe • In studying modern sedimentary environments it became obvious that different types of sediment were deposited in transitional geological enviornments simultaneously – this gave rise to the idea of sedimentary facies • As a correlary to the recognition of sedimentary facies, it is clear that rock units (formations) are not perfectly time equivalent along their lateral extent • Although time is evident in a vertical succession of strata, one must use fossil correlation to establish time equivalence laterally

3. Early Mapping and Correlation of Strata Armed with the principles of superposition, original horizontality, cross cutting relationships, correlation of faunal assemblages, and index fossils, the relative ages of rocks throughout Europe were mapped out in the early 1800’s

4. Relative Geologic Time

5. The Modern (relative) Geologic Time Scale

6. Stratigraphy The study of layered sequences of sedimentary and/or volcanic rock that conform to the principles of superposition A geologic rock unit is a naturally occurring body of rock or rock material distinguished from adjoining bodies of rock on the basis of some stated property or properties. Commonly used properties include composition, texture, included fossils, magnetic signature, radioactivity, seismic velocity, and age. A lithostratigraphic unit is a geologic rock unit that conform to the principles of superposition. Biostratigraphy is the branch of stratigraphy that deals with the distribution of fossils in the stratigraphic record and the classification of bodies of rock or rock material into biostratigraphic units based on their contained fossils.

7. The Birth of Stratigraphy Great Britain Rock Units vs. Time Units From A. Hallam Great Geological Controversies Oxford Press, 1989

8. Categories of Stratigraphic Units Units based on content or physical limits Lithostratigraphic Lithodemic Magnetopolarity Biostratigraphic Pedostratigraphic Allostratigraphic A lithodemicunitis a defined body of predominantly intrusive, highly deformed, and/or highly metamorphosed rock, distinguished and delimited on the basis of rock characteristics. In contrast to lithostratigraphic units, a lithodemic unit generally does not conform to the Law of Superposition.

9. Categories of Stratigraphic Units Lithostratigraphic Lithodemic Magnetopolarity -alternating normal and reversed polarity Biostratigraphic Pedostratigraphic Allostratigraphic A magnetostratigraphic unit is a body of rock unified by specified remanent-magnetic properties and is distinct from underlying and overlying magnetostratigraphic units having different magnetic properties.

10. Categories of Stratigraphic Units Lithostratigraphic Lithodemic Magnetopolarity Biostratigraphic – based on the principles of faunal succession and superposition Pedostratigraphic Allostratigraphic A biostratigraphic unit is a body of rock that is defined or characterized by its fossil content.

11. Categories of Stratigraphic Units Lithostratigraphic Lithodemic Magnetopolarity Biostratigraphic Pedostratigraphic – Soil horizons (regolith) Allostratigraphic A pedostratigraphic unit is a body of rock that consists of one or more pedologic horizons

12. Categories of Stratigraphic Units Lithostratigraphic Lithodemic Magnetopolarity Biostratigraphic Pedostratigraphic Allostratigraphic An allostratigraphic unit is a mappable body of rock that is defined and identified on the basis of its bounding discontinuities

13. Heirarchy of LithostratigraphicUnits A lithostratigraphic unit is a defined body of sedimentary, extrusive igneous, metasedimentary, or metavolcanic strata which is distinguished and delimited on the basis of lithology and stratigraphic position. It generally conforms to the Law of Superposition and commonly is stratified and tabular in form. Supergroup- a formal assemblage of related or superposed groups, or of groups and formations. Such units have proved useful in regional and provincial syntheses. Supergroups should be named only where their recognition serves a clear purpose. Group- the lithostratigraphic unit next higher in rank to formation; a group may consist entirely of named formations, or alternatively, need not be composed entirely of named formations. Formation- the fundamental unit in lithostratigraphic classification. A formation is a body of rock identified by lithic characteristics and stratigraphic position; it is prevailingly but not necessarily tabular and is mappable at the Earth's surface or traceable in the subsurface. Member- formal lithostratigraphic unit next in rank below a formation and is always a part of some formation. It is recognized as a named entity within a formation because it possesses characteristics distinguishing it from adjacent parts of the formation. A formation need not be divided into members unless a useful purpose is served by doing so. Some formations may be divided completely into members; others may have only certain parts designated as members; still others may have no members. Bed(s) - the smallest formal lithostratigraphic unit of sedimentary rocks. Flow- the smallest formal lithostratigraphic unit of volcanic flow rocks. A flow is a discrete, extrusive, volcanic body distinguishable by texture, composition, order of superposition, paleomagnetism, or other objective criteria. From NASC, 2005

14. Categories of Geologic Time Units A geochronologic unitis a division of time distinguished on the basis of the rock and fossil record preserved in a chrono-stratigraphicunit. Example: Devonian Period. A chronostratigraphic unitis a body of rock established to serve as the material reference for all rocks formed during the same span of time. Example: Devonian System

15. Subdivisions of Geologic Units Fundamental Units From NASC, 2005

16. Boundaries between Lithostratigraphic Units Boundaries of lithostratigraphic units are placedat positions of lithologicchange. Boundaries are placed at distinct contacts or may be selected at some arbitrary level within zones of gradation. Both vertical and lateral boundaries are based on the lithic criteria that provide the greatest unity and utility. i.e. lithostratigraphic boundaries are rarely time equivalent. From NASC, 2005

17. Depositional Environments and Sedimentary Facies

18. Depositional Environments and Sedimentary Facies

19. Depositional Environments and Sedimentary Facies

20. Transgression/Regression

21. Walther’s Law The vertical progression of facies will be the same as the corresponding lateral facies changes

22. Transgression/Regression in the Midcontinent during the Early Paleozoic Tran

23. Advanced Transgression Regression

24. Paleozoic Formations of the Upper Midwest

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

26. 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)

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

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

29. 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)

30. Biozones – Formations of Biostratigraphy

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

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

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

34. 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

35. Global Time MarkersMagnetic Reversals ODP site 1149

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

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

38. 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

39. Creating Unconformities Grand Canyon Stratigraphy Nonconformity Angular Unconformity Disconformity

40. Unconformities related to Regression - Transgression Disconformity

41. Paleozoic Formations of the Upper Midwest

42. The Jordan Sandstone Disconformity Missing Fossils

43. Gaps in the Minnesota Timescale

44. Global Unconformities Ordovician

45. Global Unconformities at the Edges of the Continents

46. Reading Time in Strata

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