Historical Geology - Chapters 10 & 11

The Paleozoic Era. Six continental landmasses are believed to have existed.

Cratons and Mobile Belts. Craton = shields and platform. During the Phanerozoic Eon epeiric seas periodically transgressed and regressed over the continents, leaving behind deposits of chemical and detrital sediment covering the platforms and perhaps the shield areas.

Mobile Belts. Elongated areas of mountain building activity located along margins of continents. During plate convergence, sediments deposited along former passive continental margins are intensively deformed, intruded by magma and metamorphosed. Four mobile belts formed around the margin of the Morth American craton during the Paleozoic: Franklin, Cordilleran, Ouachita and Appalachian.

Cratonic Sequence. Proposed by Lawrence Sloss in 1963. Sedimentary record of NA is divided into six sequences (greater than a supergroup lithostratigraphic sequence representing a major transgressive regressive cycle bounded by cratonic-wide unconformities). Salk, Tippecanoe, Kaskaskia, Absaraka, Zuni, Tejas.

Sequence Stratigraphy. The study of rock relationships within a time stratigraphic framework of related facies bounded by erosional or non depositional surfaces. Basic unit is the sequence. Sequence boundaries form as a result of a relative drop in sea level.

Salk Sequence (Late Proterozoic to Upper Cambrian). In the Grand Canyon - Tapeats Sandstone, Bright Angel Shale and Mauv Limestone forms a typical transgressive sequence. Similar sequence is present in Michigan. By late Cambrian, Salk Sea reaches MI and the Chapel Rock sandstone is deposited in the Munising area (Picture Rocks). As the sea regressed, it exposed primarily limestones which were deeply eroded (continent still located near equator, which resulted in rapid weathering) producing a craton-wide unconformity.

Tippecanoe Sequence (Middle Ordovician-Early Devonian). Second major transgression on to craton. Reef-building and evaporite forming episode in the Great Lakes area. Barrier reefs are long linear features composed of reef-building organisms that separate deep marine waters from shallow lagoon. Pinnacle reefs are tall spindly structures up to 100 m high. Michigan basin forming at this time. Surrounded by barrier and pinnacle reefs, carbonate and evaporite deposits (particularly salt and anhydrite in center during Silurian). Salt forming sequence a function of solubility - CaCO₃, CaSO₄ then NaCl. Confusing - pinnacle reefs associated with evaporites. How could this happen?

Appalachian Mobile Belt and the Taconic Orogeny. First Phanerozoic orogeny (Middle Ordovician). Part of a global tectonic episode that began to suture together Pangea. During Salk time the Appalachian area was a passive continental margin, the Iapetus ocean was widening. Convergent plate boundary develops in middle Ordovician. Carbonate shelf deposition pattern replaced by deep water deposited - black, thinly bedded shales, graded beds, coarse sandstones, graywacke and volcanics. This latter suite of rocks marks the onset of Taconic Orogeny. Regional metamorphic event dated at between 440 and 480 m.y. ago. The Caledonian Orogeny was essentially a mirror image to the Taconic on the eastern side of the Iapetus.

The Acadian Orogeny. Whicle the Taconic and Caledonian Orogenies marked the closing of the northern Iapetus Ocean and the formation of Laurasia (suturing of Laurentia and Baltica). The Acadian Orogeny (Devonian) marked the beginning of the closure of the southern Iapetus Ocean and the forming of Pangea (suturing of Laurasia and Godwana) . This orogenic activity was stronger and more intense than the Taconic. This culminated in the Pennsyvanian-Permian Ouachita, Hercynian-Alleghenian orogeny.

Antler and Ellesmere Orogenies. Other tectonic events include the Cordilleran antler orgeny and the Ellesmere orogeny located along the northern margin of Laurasia (probably the collision of Laurasia with Siberia). Antler: West coast of Laurasia was a passive continental margin during Salk. An island arc developed off the west coast during the Devonian. The eventual collision of the arc with Laurasia caused the Antler orogeny in the Late Devonian, early Mississippian. Roberts Mtn. Thrust in Nevada marks the suture that closed the narrow ocean basin between the arc and the continent.

Ancestral Rockies. Cratons are generally stable areas. Mild deformation is occasionally expected, but the Pennsyvanian Period was a time of unusually severe deformation resulting in uplift of PreC. Basement and the downwarping of adjacent basins. Mostly associated with the collision of Laurasia with Gondwana. Crustal stresses developed in the SW due to the Ouachita Orogeny. Uplift and erosion produced volumes of coarse red arkose which filled adjacent basins. These are seen today such as Red rocks Amphitheater near Morrison Colorado.

Kaskaskia Sequence (Middle Devonian-Middle Mississippian). Produced clean, well-sorted sandstones. The source was probably the eroding highlands of the Appalachian Mobile belt, the Canadian Shield and basal sandstones from the Salk and Tippecanoe sequences. Majority of Kaskaskian rocks however are carbonates. Reef development in western Canada. Extensive potash development in the Devonian basins. Black shales common in the late Devonian to early missisppian, such as the Antrim Shale in Michigan. Produced in highly organic undisturbed bottom waters not far from a source of detrital sediment. Organic material used up O₂ leading to anaerobic conditions.

Absaroka Sequence. The erosional unconformity between the Kaskaskia and Absaroka sequences is what is used to divide the Carboniferous into the Mississippian and Pennsylvannian Periods in N.Am. Referred to as lower and upper Carboniferous in Europe. Lowermost sediments restricted to margins of craton. Deposits thickest in east and southeast near emerging highlands associated with the Appalachian and Ouachita mobile belts.

Cyclothems. Cyclical pattern of alternating marine and nonmarine strata. Resulting from repeated alternations of marine and nonmarine environments in areas of low relief, reflecting an interplay between nonmarine deltaic and shallow marine interdeltaic and shelf environments. Fluvial deltaic deposit - coals - detrital shallow water marine sediments - limestones.

Mineral Deposits of the Paleozoic. Silica sand from "clean" sandstones such as the upper Cambrian Jordan SS, the middle Ord. St. Peter SS, the basal SS of the Tippecanoe sequence. Used for glass, refractory brick for furnaces. Evaporite deposits, oil and gas deposits in Silurian reefs as well as Dev.-Permian, in MI. Il, Tx. and Williston Basin of Canada. Pb & Zn in Cambrian Dolomites in SE Missouri, Miss & Penn coal.