2. Early Paleozoic Earth History Chapter 10

3. William Smith, –a canal builder, published the first geologic map –on August 1, 1815 The First Geologic Map

4. The Paleozoic history of continents: – major mountain-building activity along continental margins –numerous shallow-water marine transgressions and regressions over their interiors These transgressions and regressions –were caused by global changes in sea level –that most probably were related –to plate activity and glaciation Paleozoic History

8. Cratons are the relatively stable –and immobile parts of continents –and form the foundation upon which –Phanerozoic sediments were deposited Cratons typically consist of two parts –a shield –and a platform Continental Architecture

9. The transgressing and regressing shallow seas –called epeiric seas –were a common feature of Paleozoic Continental glaciation –as well as plate movement –caused changes in sea level –and were responsible for the advance and retreat –of the seas in which the sediments were deposited Epeiric Seas

10. Mobile belts are elongated areas of mountain building activity – “orogenic activity” along the margins of continents –where sediments are deposited in the relatively shallow waters of the continental shelf –and the deeper waters at the base of the continental slope During plate convergence along these margins, –the sediments are deformed –and intruded by magma –creating mountain ranges Mobile Belts

11. Geologists use –paleoclimatic data –paleomagnetic data –paleontologic data –sedimentologic data –stratigraphic data –tectonic data Paleogeographic Maps

12. At the beginning of the Paleozoic, six major continents were present including : –Baltica - Russia west of the Ural Mountains and the major part of northern Europe –Gondwana - Africa, Antarctica, Australia, Florida, India, Madagascar, and parts of the Middle East and southern Europe –Laurentia - most of present North America, Greenland, northwestern Ireland, and Scotland Six Major Paleozoic Continents

13. –China - a complex area consisting of at least three Paleozoic continents that were not widely separated and are here considered to include China, Indochina, and the Malay Peninsula –Kazakhstan - a triangular continent centered on Kazakhstan, but considered by some to be an extension of the Paleozoic Siberian continent –and Siberia - Russia east of the Ural Mountains and Asia north of Kazakhstan and south Mongolia Besides these large landmasses, geologists have also identified –numerous small microcontinents –and island arcs associated with various microplates Six Major Paleozoic Continents (others)

14. For the Late Cambrian Period Paleogeography of the World

15. For the Late Ordovician Period Paleogeography of the World

16. For the Middle Silurian Period Paleogeography of the World

17. The geologic history of the North American craton may be divide into two parts –stable continental interior over which epeiric seas transgressed and regressed –mobile belts where mountain building occurred Early Paleozoic Evolution of North America

18. White areas represent sequences of rocks That are separated by large-scale unconformities shown in brown Cratonic Sequences of N. America Cordillera orogenies Appalachian oro- genies

19. A cratonic sequence is –a large-scale lithostratigraphic unit –representing a major transgressive- regressive cycle –bounded by cratonwide unconformities Cratonic Sequence

20. Rocks of the Sauk Sequence –during the Neoproterozoic-Early Ordovician –record the first major transgression onto the North American craton Deposition of marine sediments –was limited to the passive shelf areas of the –Appalachian and Cordilleran borders of the craton The craton itself was above sea level –and experiencing extensive weathering and erosion The Sauk Sequence

21. White areas = sequences of rocks Sauk sequenc e

22. North America was located in a tropical climate at this time –there is no evidence of any terrestrial vegetation, NO plants! –Rapid weathering and erosion of the exposed Precambrian basement rocks –the transgressive phase of the Sauk –began with epeiric seas encroaching over the craton The Sauk Sequence: Middle Cambrian Period

23. By the Late Cambrian, –the epeiric seas had covered most of North America, –leaving above sea level only a portion of the Canadian Shield and a few large islands These islands, –collectively named the Transcontinental Arch, –extended from New Mexico –to Minnesota and the Lake Superior region Transcontinental Arch

24. During this time North America straddled the equator Trans- continental Arch Cambrian Paleogeography of North America

25. Many of the Sauk carbonates (limestones) are –bioclastic composed of fragments of organic remains –contain stromatolites, –or have oolitic textures contain small, spherical calcium carbonate grains Such sedimentary structures and textures –indicate shallow-water deposition Sauk Carbonates

26. Sediments become finer away from land –coarse detrital sediments are typically deposited in the nearshore environment, –and finer-grained sediments are deposited in the offshore environment –Carbonates form farthest from land in the marine environment beyond the reach of detrital sediments A Transgressive Facies Model

27. Recall that facies are sediments –that represent a particular environment During a transgression, the coarse (sandstone), –fine (shale) and carbonate (limestone) facies –migrate in a landward direction A Transgressive Facies Model

28. This region provides an excellent example –of sedimentation patterns of a transgressing sea The region of the Grand Canyon occupied –the western margin of the craton during Sauk time, a passive shelf During Neoproterozoic and Early Cambrian time, –most of the craton was above sea level –deposition of marine sediments was mainly restricted to the margins of the craton on continental shelves and slopes The Cambrian of the Grand Canyon Region

29. A transgression covered –the Grand Canyon region. –The Tapeats Sandstone represents the shoreline deposits are clean, well-sorted sands –of the type one would find on a beach today As the transgression continued into the Middle Cambrian, –muds of the Bright Angle Shale –were deposited over the Tapeats Sandstone – Transgression

30. The Sauk Sea had transgressed so far onto the craton –by the Late Cambrian that in the Grand Canyon region –carbonates of the Muav Limestone were being deposited over the Bright Angel Shale This vertical succession of sandstone (Tapeats) shale (Bright Angel) and limestone (Muav) –forms a typical transgressive sequence Continued Transgression

31. Cambrian strata exposed in the Grand Canyon Cambrian Transgression The three formations exposed –along the Bright Angel Trail, Grand Canyon Arizona

32. Cambrian strata exposed in the Grand Canyon –Observe the time transgressive nature of the three formations Cambrian Transgression The three formations exposed –along the Bright Angel Trail, Grand Canyon Arizona

33. Outcrop of cross-bedded Upper Cambrian sandstone in the Dells area of Wisconsin Upper Cambrian Sandstone

34. As the Sauk Sea regressed –from the craton during the Early Ordovician, –it revealed a landscape of low relief The rocks exposed were predominately –limestones and dolostones –that experienced deep and extensive erosion –because North America was still located in a tropical environment The resulting cratonwide unconformity –marks the boundary between the Sauk –and Tippecanoe sequences Regression and Unconformity

35. White areas = sequences of rocks Cratonic Sequences of N. America brown areas = large- scale uncon- formities Regression Tippecanoe sequence

36. A transgressing sea deposited the Tippecanoe sequence over most of the craton –Middle Ordovician-Early Devonian –Like the Sauk sequence, this major transgression deposited clean, well-sorted quartz sands The Tippecanoe basal rock is the St. Peter Sandstone, –an almost pure quartz sandstone used in manufacturing glass The Tippecanoe Sequence

37. Paleo- geography of North America –showing change in the position of the the equator The continent –was rotating counter- clockwise Ordovician Period

38. Resulted in deposition of the St. Peter Sandstone –Middle Ordovician over a large area of the craton Transgression of the Tippecanoe Sea

39. Outcrop of St. Peter Sandstone in Governor Dodge State Park, Wisconsin St. Peter Sandstone

40. The Tippecanoe basal sandstones were followed by widespread carbonate deposition The limestones were generally the result of deposition –by calcium carbonate- secreting organisms such as corals, brachiopods, stromatoporoids, and bryozoans The Tippecanoe Sequence

41. Organic reefs are limestone structures –constructed by living organisms, –some of which contribute skeletal materials to the reef framework Today, corals, and calcareous algae –are the most prominent reef builders, –but in the geologic past other organisms –played a major role in reef building Reefs appear to have occupied –the same ecological niche in the geological past as today Tippecanoe Reefs and Evaporites

42. present-day reefs are confined –To between 30 degrees north and south of the equator Corals, the major reef-building organisms today, –require warm, clear, shallow water –of normal salinity for optimal growth Modern Reef Requirements

43. with reef-building organisms Present-Day Reef Community

44. Block diagram of a reef showing the various environments within the reef complex Reef Environments

45. The Middle Silurian rocks of the present-day Great Lakes region Tippecanoe sequence are reef and evaporite deposits The most significant structure in the region –the Michigan Basin –is a broad, circular basin surrounded by large barrier reefs These reefs contributed to increasingly restricted circulation –and the precipitation of Upper Silurian evaporites within the basin Michigan Basin Evaporites

46. Paleogeography of North America during the Silurian Period Reefs developed in the Michigan, Ohio, and Indiana-Illinois- Kentucky areas Silurian Period

47. As the Tippecanoe Sea gradually regressed –from the craton during the Late Silurian, –precipitation of evaporite minerals occurred in the Michigan Basin –approximately 1500 m of sediments were deposited, –nearly half of which are halite and anhydrite (gypsum) Tippecanoe Regression and Evaporites

48. How did such thick sequences of evaporites accumulate? 1. When sea level dropped, the tops of the barrier reefs were as high as or above sea level, –thus preventing the influx of new seawater into the basin –Evaporation of the basinal seawater would result in the precipitation of salts 2. Alternatively, the reefs grew upward so close to sea level –that they formed a sill or barrier that eliminated interior circulation Origin of Thick Evaporites (Gypsum, Halite)

49. Silled Basin Model for evaporite sedimentatio n by direct precipitation from seawater –Vertical scale is greatly exaggerate d Silled Basin Model

50. Because North America was still near the equator during the Silurian Period, –temperatures were probably high Basin Brines

51. Organisms constructing reefs could not have lived in such a highly saline environ- ment Reefs in a Highly Saline Environ-ment?

52. How then, can such contradictory features be explained? –Numerous models have been proposed, ranging from cessation of reef growth followed by evaporite deposition, to alternation of reef growth and evaporite deposition –no model yet proposed completely explains various reef, carbonate, and evaporite facies No Model Is Perfect

53. –where the first Phanerozoic orogeny –began during the Middle Ordovician –How would a mountain range influence –the climate and sedimentary history of the craton? The Appalachian Mobile Belt

54. Global tectonic regime –that sutured the continents together, forming Pangaea by the end of the Paleozoic The Appalachian region –throughout Sauk time, –was a broad, passive, continental margin –Sandstone – shale - carbonate Mountain Building

55. Iapetus Ocean was widening –as a result of movement –along a divergent plate boundary Beginning with the subduction of the Iapetus plate beneath Laurentia –which was an oceanic-continent convergent plate boundary the Appalachian mobile belt was born Iapetus Ocean

56. Evolution of the Appalachian mobile belt opening of Iapetus Ocean Appalachian Mobile Belt –with passive continental margins –and large carbonate platforms

57. The resulting Taconic orogeny, –named after present-day Taconic Mountains of eastern New York, central Massachusetts, and Vermont –was the first of several orogenies –to affect the Appalachian region The Taconic Orogeny

58. The subduction of the Iapetus plate beneath Laurentia –resulted in volcanism –and downwarping of the carbonate platform Throughout the Appalachian mobile belt, –indications that these deposits were derived from the east, come from facies patterns, paleocurrents, and sedimentary structures The sediment originated where –the Taconic Highlands –and associated volcanoes were rising Eastern Sediment Source

59. Middle Ordovician transition to convergence resulted in orogenic activity Appalachian Mobile Belt

60. The final piece of evidence –for the Taconic orogeny is –the development of a large clastic wedge, an extensive accumulation of mostly detrital sediments were deposited adjacent to an uplifted area and become thinner and finer grained away from the source area, eventually grading into the carbonate cratonic facies The clastic wedge resulting from the erosion –of the Taconic Highlands is referred –to as the Queenston Delta Queenston Delta Clastic Wedge

61. Queenston Delta clastic wedge Queenston Delta Clastic Wedge Taconic Highland s –coarse- grained detrital sediments near the highlands –thins laterally into finer- grained sediments on the craton

62. The Taconic orogeny –marked the first pulse of mountain building in the Appalachian mobile belt –and was a response to the subduction taking place beneath the east coast of Laurentia As the Iapetus Ocean narrowed and closed, –another orogeny occurred in Europe during the Silurian A European Orogeny

63. The Caledonian orogeny was essentially a mirror image of –the Taconic orogeny and the Acadian orogeny –and was part of the global mountain-building episode –that occurred during the Paleozoic Era Even though the Caledonian orogeny –occurred during Tippecanoe time, –we will discuss it with the Acadian orogeny – because the two are intimately related Caledonian Orogeny

64. The transition to convergence resulted in orogenic activity in North America and Europe Caledonian Orogeny –Caledonian Orogeny –was a mirror image of the Taconic Orogeny