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)