The Late Paleozoic World

Transcription

1 Chapter 15 Notes 1 of 6 The Late Paleozoic World I. Introduction A. The Late Paleozoic includes the Carboniferous with extensive coal deposits and the Permian which is best known for Mass extinction B. Climates were also varied which recorded warm waters and glaciation and ended with extreme aridity C. The final chapter of the Appalachian mountain building occurred during the late Paleozoic II. Life The marine life of the early Carboniferous was similar to that of the late Devonian. The exception was that new reef builders evolved following the mass extinction at the end of the Devonian. However, the terrestrial environment changed dramatically. Insects with modern characteristic evolved. Trees with seeds evolved during the Permian. Finally, the Reptiles evolved. A. New forms of Marine Life 1. The tabulate corals and the stromatoporid sponges did not recover 2. Ammonoids rediversified and assumed a prominent ecologic role. Heavy shelled nautiloids declined in favor of the more mobile ammonoids. 3. Bony fishes a. Armored fish declined at the expense of more agile fish. 4. Brachiopods rebounded and were important in the shallow water communities. 5. Crinoids reached their greatest diversity during the early Carboniferous. a. They were so productive that they deposited large quantifies of limestone during the Mississippian. 6. Lacy bryozoans filtered food from the water column (Fig. 15-4). 7. Fusulinids were large foraminifera that lived on shallow seafloors (Fig. 15-5). Enormous diversity during Carboniferous and became a guide fossil for strata through the Permian. B. Reefs and Aragonitic Seas 1. The tabulate strome reefs of the Silurian and Devonian did not recover during the Carboniferous. They made shells out of calcite. The Early Carboniferous seas had a high Mg to Ca ratio compared to the Silurian-Devonian seas. As such, aragonite precipitation was favored over calcite. It was not until much later that aragonitic formed evolved and rebuilt the reefs. C. Plant Life on Land 1. Plants, in particular, land plants, give the Carboniferous its name. Extensive coal deposits of Carboniferous age were formed. a. The Carboniferous was a time of extensive low land swamps. This is where coal deposits were formed from the fallen tree trunks and leaves. b. Lipidodendron and Sigillaria were the most dominant genera of the coal swamps (Fig 15 7). They are lycopod trees. They reproduced by spores which require water. c. Underneath the trees were the ferns and fern like plants (Fig 15-8). Some were spore plants, but others were seed bearing fern. Glossopteris is a seed fern in Gondwanaland (Fig 8-3).

2 Chapter 15 Notes 2 of 6 2. While the lycopods dominated the lowland swamps, Sphenopsids, moved to higher ground (Fig. 15-9). a. These are spores and seed bearing plants. b. Accumulated on levees, floodplains rather than the swamps. 3. Cordaites also occupied higher ground (Fig ). These plants are gymnosperms. a. Gymnosperms are naked seed plants such as conifers (pines, spruces, firs, redwoods) (Fig 15-11). b. During the Permian, the gymnosperms took over the terrestrial environments (Fig 15-12). D. Freshwater and Terrestrial Animals 1. Amphibians - Continued to return to water to lay their fishlike naked eggs a. Changes to the shift to land dwelling 1. Amphibians first evolved the so-called amniotic egg which protected the developing young from predation and desiccation 2. 3-chambered heart to route the blood more efficiently to and from the more efficient lungs. 3. limb and girdle bones were modified to overcome the constant drag of gravity, also to hold the body above the ground 4. spinal column was transformed into a sturdy but flexible bridge of interlocking elements b. Fossil record 1. ichthyostegids, retained many features of their fish ancestors 2. labyrinthodonts, name from the labyrinthic wrinkling and folding of tooth enamel 3. Eryop, a bulky, inelegant creature with flattish skull and bony nodules in skin for protection; declined during the Permian 2. The Rise of Reptiles a. Reptiles Earliest known remains are Early Pennsylvanian swamp deposits of Nova Scotia i. Developed a way to reproduce without returning to the water evolving enclosed eggs ii. embryonic animal was allowed to pass through the larval and other developmental iii. stages before being hatched in an essentially adult form iv. liberated the tetrapods from their reliance on water bodies v. hailed as a major milestone in the history of vertebrates 3. A new Level of Metabolism a. Therapsids - Displayed the beginnings of several mammalian traits i. widely dispersed during Permian and Triassic time ii. became extinct early in the Jurassic and gave origin to the early mammals predominantly small to moderate-sized animals iii. limbs were swung more directly into vertical alignment beneath the body iv. ribs were reduced in the neck and lumbar region for greater overall flexibility III. Paleogeography of the Late Paleozoic World A. The Early Carboniferous: Limestones and Glaciers Blanket of carbonates

3 Chapter 15 Notes 3 of 6 referred to as the great Mississippian lime bank record the last great Paleozoic flooding of the North American craton Late Mississippian time Kaskaskia seas began their final withdrawal w/ deposition of detrital sediments and thin, scattered limestones sandstone units suggest old stream valleys developed on the former sea floor derived from the northern Appalachians B. Events at the Mid- Carboniferous Boundary C. The Later Carboniferous Period: Continental Collision and Temperature Contrasts D. Permian Period: Climate Complexity\ IV. Atmospheric Carbon Dioxide and Carboniferous-Permian Climate V. The Mass Extinction Late Ordovician Extinctions Extinctions near the end of the Ordovician occurred in two phases. during the first phase planktic organisms as well as benthic creatures were the principal victims during the second phase trilobites became extinct, corals, conodonts, and bryozoans were severely reduced in numbers and diversity Both phases appear to be related to global cooling associated with the growth of Gondwana ice caps. an extensive ice sheet covered part of what is now northern Africa during the Ordovician the fossil record reveals that zones of many groups were shifted and compressed toward the equator in responses to cooling at higher latitudes ice accumulated, sea level was lowered causing the loss of shallow epeiric sea and shallow marginal shelf environments Cooler conditions can be inferred from the absence of significant limestone deposition - calcium carbonate is not readily precipitated in cold water Late Devonian Extinctions Environmental stress is reflected in the decimation of once extensive Devonian reef communities reef-building tabulate corals and stromatoporoids are rarely seen in rocks deposited during the remainder of the Paleozoic Late Devonian extinctions occurred over an interval of several million years a catastrophic sudden event is unlikely to have been the cause the basic cause was probably terrestrial and environmental appears to be related to continental glaciation in Gondwana Late Permian Extinctions "The mother of mass extinctions." the loss of biological diversity exceeded that of all other extinctions >90% of all preexisting marine species disappeared or were severely reduced on land, spore-bearing ferns and other plants gave way to conifers, cycads, ginkgoes and other gymnosperms of all groups, tropical marine invertebrates experienced the most extensive losses Factors that may have contributed to the mass extinction

4 Chapter 15 Notes 4 of 6 the supercontinent Pangaea had completed its development more rigorous climatic conditions existed across the great continent epeiric seas had been drained or were very limited frigid polar regions existed at both the north and south ends of Pangaea Pangaea blocked equatorial circulation in the ocean also a time of extraordinary volcanic activity VI. Regional Examples A. The Alleghenian Orogeny and the Appalachian Mountains The Allegheny Orogeny - aka the Appalachian orogeny Began during the Pennsylvanian Period continued throughout the remainder of the Paleozoic affected a belt that extended for over 1600 km from southern New York to central Alabama the result of closure of the Iapetus Ocean and the convergence of continents North Africa came into contact with southeastern North America B. Results of the Allegheny orogeny included Permian compression of early continental shelf and rise sediments as well as strata deposited along the bordering tract of the craton development of the Valley and Ridge Province enormous thrust faults formed along the east side of the southern Appalachians the entire region was moved forcibly against the central craton Erosion of the rising mountains produced another great clastic blanket of nonmarine sediments continental reddish sandstones and gritty shales C. The Ouachita Deformation Caused by the collision of the northern margin of Gondwanaland with the southeastern margin of the N. Am. craton northern South America and perhaps part of northwestern Africa began rather late in the Paleozoic carbonates predominated in the more northerly shelf zone Novaculites accumulated in the deeper marine areas hard, even-textured, siliceous rocks composed mostly of microcrystalline quartz formed from bedded cherts that have been subjected to heat and pressure used as a whetstone in sharpening steel tools Pace of sedimentation increased dramatically toward the end of the Mississippian over 8000 m of graywackes and shales was spread into the depositional basin deposition continued into the Pennsylvanian forming a great clastic wedge of sediment thickened and became coarser toward the south Radiometric dating of Gulf Coast basement rocks metamorphosed during the late Paleozoic likely source for the Pennsylvanian clastics documents several pulses of orogenesis that ultimately produced mountains along entire southern border of NAmer.

5 Chapter 15 Notes 5 of 6 strata of the continental rise were thrust northward onto the rocks of the shelf stability returned by Permian time Evidence of Ouachita orogeny Ouachita Mountains of Arkansas and Oklahoma Marathon Mountains of southwest Texas Ouachita belt is traced over a distance of nearly 2000 k, but only about 400 km are exposed B. Earth Movements in the Southwestern United States 1. Devonian subduction of oceanic lithosphere beneath the western margin of the continent was initiated beginning of the Antler orogeny volcanic island arc converged on the continent crushing sediment in the intervening basin accompanied by thrust faulting on a massive scale effects are clearly seen in Nevada into Idaho continental rise and slope deposits have been thrust as much as 80 km over shallow water sediments of the former continental shelf Antler orogeny continued actively into the Mississippian and Pennsylvanian highlands created provided detrital sediment that was transported into adjacent basins thick accumulations of Pennsylvanian and Permian shelf sediments Wasatch and Oquirrh mountains Oquirrh Formation, over 9000 m thick Mississippian and Pennsylvanian deposits west of the Antler highlands include a great volume of coarse detritus and volcanic rocks swept eastward from a volcanic arc source area lay along the western side of North America over 2000 m of sandstones, shales, lavas, and ash beds are found in the Klamath Mountains of northern California Volcanic rocks in western Idaho and British Columbia attest to a continuation of vigorous volcanism from Mississippian through the Permian Crustal deformation is indicated by areally extensive angular unconformities between Permian and Triassic sequences Cassiar orogeny - British Columbia Sonoma orogeny - southwestern US.was caused by the collision of an eastwardmoving island arc against North American continental margin in west-central Nevada oceanic rocks and remnants of the arc were thrust into the edge of the continent and became part of North America C. Coal with Cyclothems Cyclothems are most notable aspects of Pennsylvanian sedimentation repetitive alternation of marine and nonmarine strata

6 Chapter 15 Notes 6 of 6 a group of strata that records the variations in depositional environments caused by a single advance and retreat of the sea Typical cyclothem contains 10 units units 1-5 are continental deposits with a coal bed as the uppermost unit strata above the coal bed represent an advance of the seas over an old forested area correlated over great distances the result of repetitive and widespread advance and retreat of seas Cause periodic regional subsidence of the land re-establishment of dry lands may have resulted from temporary regional uplifts worldwide or eustatic changes in sea level continental glaciation 1. Shifting Environments and the Origin of Cyclothems 2. Glaciers and Sea Level