conodont biostratigraphy of the late devonian—early carboniferous ...
Late Paleozoic Events CHAPTER 9. Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and...
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Transcript of Late Paleozoic Events CHAPTER 9. Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and...
Late Paleozoic Events
CHAPTER 9
Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and Permian (in North America)
Late Paleozoic = Devonian, Carboniferous, and Permian (outside of N. America)
1.By end of Early Paleozoic, Iapetus closed
2.Orogeny continued--Laurasia formed in Devonian
3.Pennsylvanian--Gondwanaland and Laurasia
4.By Late Permian, Pangaea has completely formed
North America (Laurentia) Transgressive Deposits
Kaskaskia SequenceOriskany Sandstone (eastern U.S.) initial deposit of transgression over unconformityclean sand (important for glass-making)
transgressive depositsdeposits become younger in craton-ward (inland) direction
heavy mineral suites: stable and unstable
Figure 9-5 (p. 303) Extent 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 stratamassive marine limestones (= less clastic input)
Crinoids, ooids, etc.
North America during the Devonian Period.
North America during the Mississippian Period.
The Following Transgressive Deposit…
Absaroka SequenceProgressive facies change in initial depositsthin marine limestones, shales (western sea)
mixed near-shore sandstones, shalesthick clastic wedges (eastern mountain slopes)
North America during the Pennsylvanian Period.
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 depositsand 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 faultsResulted in the erosion of the overlying Paleozoic sediments
Exposed basement rocks (Precambrian igneous and metamorphic rocks)
Ancestral Rockies
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.)
Ouachita Deformation: southern margin
Northern Gondwanaland hits southeastern North America
Orogenic mountains todayOuachita Mountains (AR, OK)Marathon Mountains (TX)subsurface folded structures (U.S. Gulf Coast)
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 coastCassier (British Columbia)Sonoma (southwestern U.S.)
East of Antler HighlandsQuiet, shallow sea, Deposition of Grand Canyon area stratigraphy of Permian age: stability and transgressionKaibab 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 CO2 in Atmosphere:
Carbon (organic matter) buried before reaction with oxygen--less
CO2 therefore cooler climate
Coal
Northern Hemisphere contains abundant coal from Late Carboniferous (Pennsylvanian)