Presentation on theme: "Late Paleozoic Events CHAPTER 9. Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and Permian (in North America) Late Paleozoic = Devonian, Carboniferous,"— Presentation transcript:
North America (Laurentia) Transgressive Deposits Kaskaskia Sequence Oriskany Sandstone (eastern U.S.) initial deposit of transgression over unconformity clean sand (important for glass-making) transgressive deposits deposits become younger in craton-ward (inland) direction heavy mineral suites: stable and unstable
Figure 9-5 (p. 303) E xtent of the Oriskany Sandstone.
Kaskaskia Sequence Upper Devonian clastics: shed off rising Appalachians spread west, becoming finer grained and more marine influenced Chattanooga shale--muds from clastic wedge off Eastern North America mountains Uppermost Devonian and Mississippian strata massive marine limestones (= less clastic input) Crinoids, ooids, etc.
Cyclothems of Absaroka Sequence Cyclothems consist of 10 beds with minor disconformities at top and bottom of cyclothem shale (marine): youngest layer limestone (marine) shale (marine) limestone (marine) shale (near-shore) coal (swamp) grey underclay (lake) fresh-water limestone (lake) sand shale/siltstone (lake) sandstone (river deposits): oldest layer
Figure 9-11 (p. 308) An ideal coal-bearing cyclothem, showing the typical sequence of layers.
Formation theories of these rhythmically repetitive sequences Origin of cyclothems: 1.Temporary local subsidence 2.Temporary regional uplift 3.Eustatic (global) sea level change related to glaciation
The initial units represent deltaic deposits and fluvial deposits Above them is an underclay that frequently contains roots from the plants and trees that comprise the overlying coal The coal bed results from accumulations of plant material and is overlain by marine units Nonmarine Units of a Cyclothem
Columnar section of a complete cyclothem Cyclothem
During the Late Absaroka (Pennsylvanian), the southwestern part of the North American craton became deformed and formed the Ancestral Rockies Uplift of these mountains, Up to 2 km along near-vertical faults Resulted in the erosion of the overlying Paleozoic sediments Exposed basement rocks (Precambrian igneous and metamorphic rocks) Ancestral Rockies
Boulder Flatirons Very steeply dipping beds Late Pennsylvanian and early Permian Fountain Formation. Created from the erosion of the ancestral Rocky Mountains to the west. The beds were tilted to their present positions during the orogeny that produced the modern Rocky Mountains.
Acadian Orogeny Responsible for building northern Appalachian Mountains Collision between Baltica and Laurentia Deformed rocks from Newfoundland to West Virginia
Acadian Orogeny (continued) Avalon terrain – micro-continent colliding in “pulses” along an irregular eastern margin St. Lawrence (Middle Devonian) Southern “pulses” (Late-Middle Devonian)
Catskill Delta Clastic Wedge The Catskill Delta clastic wedge and are derived from the Acadian and Caledonian Highlands
Pocono Group Pocono facies: younger mimic of Catskill black shale (anoxic sea): west shale sandstsone (shoreline) conglomerate (mountain front): east Example: Sideling Hill, Maryland (near Hancock on Rt 68)
Alleghenian Orogeny Pennsylvanian to end of Permian Northern Gondwanaland collides with Laurasia (N. Africa-eastern USA and S. America-Gulf Coast of USA) Builds southern Appalachians and Ouachita Mountains, over 1600 km collision zone Due to closure of Iapetus (proto-Atlantic) Transferred energy to deform southwestern USA
Figure 9-29 (p. 319) Plate tectonic model for late Paleozoic continental collisions. (Adapted from Sacks, P. E., and Secor. D. T., Jr. 1990. Science 250: 1702-1705.)
Figure 9-20 (p. 314) Simplified diagrammatic plate tectonic sequence involved in the evolution of the northern and southern Appalachians. (Adapted from Taylor, S. R. 1989, GSA Memoir 172.)
Western (Cordilleran) Belt Subduction began during Devonian Antler Orogeny (Late Devonian- Pennsylvanian) Island-arc collision with west coast of Laurentia Vast thrust faulting and folding of back-arc sediments with thick clastic wedges in basins Associated Volcanism from collision (Mississippian-Permian
Figure 9-36 (p. 323) An interpretation of conditions in the Cordilleran orogenic belt in Early Mississippian time, shortly after the Antler orogeny. (Based on diagrams by Poole, G. F. 1974. Society of Economic Paleontologists and Mineralogists Special Publication 22: 58-82.)
Western Cordilleran Orogeny (cont) Due to collision with second island arc (Permian- Early Triassic) second period of orogenesis on west coast Cassier (British Columbia) Sonoma (southwestern U.S.) East of Antler Highlands Quiet, shallow sea, Deposition of Grand Canyon area stratigraphy of Permian age: stability and transgression Kaibab Limestone (shallow marine): youngest unit Toroweap Formation (coastal mudflats) Coconino Sandstone (eolian sand dunes) Hermit Shale (fluvial and lake): oldest unit
Gondwanaland of Late Paleozoic Moved from South pole toward equator where it collided with Laurasia (Hercynian and Alleghenian orogenies) Glaciers dominated this region in Late Paleozoic Central ice accumulation regions: southwest Africa eastern Antarctica During interglacial stages (cool, damp climates) thick coals formed (swamps) Glossopteris flora flourished
Glacial Evidence (striated glacial “pavement”) from South Africa
Climate of Late Paleozoic Hot/ Cold zones of Earth today similar then, but continents were in different areas Reduced CO 2 in Atmosphere: Carbon (organic matter) buried before reaction with oxygen--less CO 2 therefore cooler climate
Coal Northern Hemisphere contains abundant coal from Late Carboniferous (Pennsylvanian)