Transcript Ch 10 ppt
Chapter 10 Early Paleozoic Earth History New York State Most surface rocks are from the Paleozoic Paleozoic History of North America • Major mountain-building activity • Shallow-water marine transgressions and regressions over the interiors Causes: global changes in sea level • plate activity along continental margins • glaciation Continental Architecture • Cratons are stable and “immobile” a shield and a platform (granite-gneiss) form the foundation upon which Phanerozoic sediments were deposited Mobile Belts • Areas of mountain building activity – – “orogenic activity” along the margins of continents – sediment are deposits in shallow waters • continental shelf – and the deeper waters at the base of the continental slope During plate convergence along margins, the sediments are deformed – intruded by magma – mountain ranges are formed from subduction volcanoes • Or continental collision Epeiric Seas • The transgressing and regressing shallow seas – common feature of Paleozoic as evidenced by sediments deposited now forming the surface rock in New York State Marcellus Shale Devonian Age Conglomerate Mt. Marion Saugerties NY (exit 20 I-87 Oriskany Sandstone Near Utica NY How old are the Herkimer “diamond” source rocks? Paleogeographic Maps • Geologists use – paleoclimatic data: (glacial, rock types, coal) – paleomagnetic data: (preserved in igneous rocks) tells latitude and magnetic pole directions – paleontologic data: pollens, plants, animals – sedimentologic data: structures, environments – Stratigraphic: data rock relationships and age – tectonic data : evidence of plate boundaries Six Major Paleozoic Continents • At the beginning of the Paleozoic: – 1. Baltica - Russia west of the Ural Mountains and the major part of northern Europe – 2. Gondwana - Africa, Antarctica, Australia, Florida, India, Madagascar, and parts of the Middle East and southern Europe – 3. Laurentia - most of present North America, Greenland, northwestern Ireland, and Scotland Six Major Paleozoic Continents – 4. China - include China, Indochina, and the Malay Peninsula – 5. Kazakhstan - a triangular continent centered on Kazakhstan, – 6. Siberia - Russia east of the Ural Mountains and Asia north of Kazakhstan and south Mongolia • AND numerous small microcontinents • and island arcs associated with various microplates Paleogeography of the World • For the Late Cambrian Period Paleogeography of the World • For the Late Ordovician Period Paleogeography of the World • For the Middle Silurian Period Early Paleozoic Evolution of North America – epeiric seas transgressed and regressed Over the stable continental interior – mobile belts where mountain building occurred Cratonic Sequences of N. America • White areas represent sequences of rocks That are separated by large-scale unconformities shown in brown Cordillera orogenies Appalachia orogenies Cratonic Sequence • A cratonic sequence is – a large-scale lithostratigraphic unit representing a major transgressiveregressive cycle bounded by cratonwide unconformities Regressing Sea • White areas = sequences of rocks • Sauk sequence The Sauk Sequence • Rocks of the Sauk Sequence – Late Proterozoic-Early Ordovician (long, slow process) – first major transgression onto the North American craton • Deposition of marine sediments : • passive shelf areas of the East and West borders of craton • Many of the Sauk carbonates (limestones) contain fragments of organic remains – bioclastic rock • The craton was above sea level – and experiencing extensive weathering & erosion SHALLOW WATER DEPOISITION! The Sauk Sequence: Middle Cambrian Period • North America was located in a tropical climate at this time – there is no evidence of any terrestrial vegetation, NO plants! – Rapid weathering and erosion of the exposed Precambrian basement rocks = widespread unconformity Highlands: Transcontinental Arch • By the Late Cambrian, – the epeiric seas covered most of North America, • Above the sea: • a portion of the Canadian Shield • and a few large islands • “Transcontinental Arch” Cambrian Paleogeography of North America Sauk Transgression • During this time North America straddled the equator • Transcontinental Arch A Transgressive Facies Model • Facies are sediments that represent a particular environment • During a transgression: the coarse (sandstone), fine (shale) and carbonate (limestone) facies migrate in a landward direction The Cambrian of the Grand Canyon Region • Grand Canyon at western margin of the craton during Sauk time, a passive shelf – most of the craton was still above sea level – deposition of marine sediments • was at the margins of the craton • on continental shelves and slopes Evidence of Transgression – The Tapeats Sandstone represents the shoreline deposits are clean, well-sorted sands – of the type one would find on a beach today • By Middle Cambrian, – muds of the Bright Angle Shale – were deposited over the Tapeats Sandstone By Late Cambrian – carbonates of the Muav Limestone were being deposited over the Bright Angel Shale Cambrian Transgression • Cambrian strata in the Grand Canyon • The three formations exposed – along the Bright Angel Trail, Grand Canyon Arizona Cambrian Transgression – Observe the time transgressive nature of the three formations Regression and Unconformity • The Sauk Sea regressed • rocks exposed were predominately – Limestones: deep extensive erosion – North America was still located in a tropical environment – increased weathering • The resulting cratonwide unconformity – marks the boundary between the Sauk – and the NEXT Cratonic sequence Tippecanoe Cratonic Sequences of N. America • White areas = sequences of rocks Brown areas = large-scale” uncon-formities • Regression • Tippecanoe sequence Ordovician Period • Paleogeography of North America – showing change in the position of the the equator • The continent – was rotating counterclockwise Transgression of the Tippecanoe Sea Resulted in deposition of the St. Peter Sandstone – Middle Ordovician over a large area of the craton St. Peter Sandstone Outcrop of St. Peter Sandstone in Governor Dodge State Park, Wisconsin The Tippecanoe Sequence • The Tippecanoe basal sandstones were followed by widespread carbonate deposition • The limestones were generally the result of deposition – by calcium carbonatesecreting organisms such as • • • • corals, brachiopods, stromatoporoids, and bryozoans Tippecanoe Reefs and Evaporites • Organic reefs limestone structures constructed by living organisms, • Today, corals, and calcareous algae – are the most prominent reef builders, – but in the geologic past other organisms – played a major role in reef building • Reefs appear to have occupied – the same ecological niche in the geological past as today Present-day reefs are 30 degrees north and south of the equator • Corals require warm, clear, shallow water – of normal salinity for optimal growth Present-Day Reef Community • with reef-building organisms Reef Environments • Block diagram of a reef showing the various environments within the reef complex Michigan Basin Evaporites • significant structure in the region a broad, circular basin surrounded by large barrier reefs • reefs contributed to restricted circulation – and the precipitation of Upper Silurian evaporites within the basin – Evaporites form when water evaporates and leaves salts and brines behind halite, gypsum, sylvite Silurian Period • Paleogeography of North America Silurian Period • Reefs developed in the Michigan, Ohio, and Indiana-IllinoisKentucky areas Origin of Thick Evaporites – 1500 m (Gypsum, Halite) 1. When sea level dropped, the tops of the barrier reefs were as high as or above sea level, 2. Preventing influx of new seawater into the basin Evaporation of the basin seawater would result in the precipitation of salts 2. Alternatively, the reefs grew upward so close to sea level – that they formed a sill or barrier that eliminated interior circulation Silled Basin Model • Silled Basin Model for evaporite sedimentatio n by direct precipitation from seawater Basin Brines • Because North America was still near the equator during the Silurian Period, – temperatures were probably high The Appalachian Mobile Belt – Phanerozoic orogeny – mountain building Iapetus Ocean was widening as a divergent plate boundary caused movement • Beginning with the subduction of the Iapetus plate beneath Laurentia – which was an oceanic-continent convergent plate boundary • the Appalachian mobile belt was born The Taconic Orogeny • The resulting Taconic orogeny, – Today’s Taconic Mountains • eastern New York, • central Massachusetts, • and Vermont – First of 3 to form Appalachians Appalachian Mobile Belt • Transition to convergence resulted in orogenic activity Queenston Delta Clastic Wedge • Evidence for the Taconic orogeny • The remnants of the mountains The remains of a large clastic wedge, • detrital sediments adjacent to an uplifted area • thinner and finer grained away from the source area, • eventually grading into the carbonate cratonic facies • The clastic wedge resulting from the erosion of the Taconic Highlands is referred to as the Queenston Delta • Queenston Delta clastic wedge – coarsegrained detrital sediments near the highlands – thins laterally into finergrained sediments on the craton • Taconic Highland s Caledonian Orogeny • The Caledonian orogeny was a mirror image of Taconic orogeny • Caledonians are similar age in Europe today. Caledonian Orogeny • The transition to convergence resulted in orogenic activity in North America and Europe – Caledonian Orogeny – was a mirror image of the Taconic Orogeny Resources of Early Paleozoic Sandstone, Salts, Gypsum, natural gas Igneous minerals during orogeny