Early Paleozoic Earth History Chapter 10 Early Paleozoic Earth History

The First Geologic Map William Smith, a canal builder, published the first geologic map on August 1, 1815

The First Geologic Map Measuring more than eight feet high and six feet wide, Smith's hand-painted geologic map of England represented more than 20 years of detailed study of the rocks and fossils of England England is a country rich in geologic history Five of the six geologic systems were described and named for rocks exposed in England Cambrian, Ordovician, Silurian, Devonian, and Carboniferous

Fuel for the Industrial Revolution Revolutionized Geology The Carboniferous coal beds of England helped fuel the Industrial Revolution, during the late 1700s and early 1800s William Smith, first began noticing how rocks and fossils repeated themselves in a predicable fashion while mapping various coal mines Smith surveyed the English countryside for the most efficient canal routes to bring the coal to market

Understanding Geology Gave Smith an Advantage Much of his success was based on the fact he was able to predict what rocks canal diggers would encounter His observations of the geologic history of England allowed William Smith to make the first geologic map of an entire county! We will use the same basic geologic principles William Smith used to interpret the geology of the Paleozoic Era

Paleozoic History The Paleozoic history of most continents involves major mountain-building activity along their margins and numerous shallow-water marine transgressions and regressions over their interiors These transgressions and regressions were caused by global changes in sea level that most probably were related to plate activity and glaciation

Geologic History of North America We will examine the geologic history of North America in terms of major transgressions and regressions rather than a period-by-period chronology and we will place those events in a global context

Pangaea-Like Supercontinent During the Precambrian continental accretion and orogenic activity led to the formation of sizable continents Movement of these continents resulted in the formation of a single Pangaea-like supercontinent, Pannotia

Cratons and Mobile Belts This supercontinent began breaking apart sometime during the latest Proterozoic By the beginning of the Paleozoic Era, six major continents were present Each continent can be divided into two major components a craton and one or more mobile belts

Continental Architecture Cratons are the relatively stable and immobile parts of continents and form the foundation upon which Phanerozoic sediments were deposited Cratons typically consist of two parts a shield and a platform

Shields Shields are the exposed portion of the crystalline basement rocks of a continent and are composed of Precambrian metamorphic and igneous rocks that reveal a history of extensive orogenic activity during the Precambrian During the Phanerozoic, however, shields were extremely stable and formed the foundation of the continents

Paleozoic North America The major cratonic structures and mobile belts of North America that formed during the Paleozoic Era Shield Mobile belts

Platforms Extending outward from the shields are buried Precambrian rocks that constitute a platform, another part of the craton, the platform is buried by flat-lying or gently dipping Phanerozoic detrital and chemical sedimentary rocks The sediments were deposited in widespread shallow seas that transgressed and regressed over the craton

Paleozoic North America Platform

Epeiric Seas The transgressing and regressing shallow seas called epeiric seas were a common feature of most Paleozoic cratonic histories Continental glaciation as well as plate movement caused changes in sea level and were responsible for the advance and retreat of the epeiric seas

Mostly Flat Lying Whereas most of the Paleozoic platform rocks are still essentially flat lying in some places they were gently folded into regional arches, domes, and basins In many cases some of the structures stood out as low islands during the Paleozoic Era and supplied sediments to the surrounding epeiric seas

Mobile Belts Mobile belts are elongated areas of mountain building activity They are located along the margins of continents where sediments are deposited in the relatively shallow waters of the continental shelf and the deeper waters at the base of the continental slope During plate convergence along these margins, the sediments are deformed and intruded by magma creating mountain ranges

Four Mobile Belts Four mobile belts formed around the margin of the North American craton during the Paleozoic Franklin mobile belt Cordilleran mobile belt Ouachita mobile belt Appalachian mobile belt Each was the site of mountain building in response to compressional forces along a convergent plate boundary and formed such mountain ranges as the Appalachians and Ouachitas

Paleozoic North America Mobile belts

Paleogeography Because of plate tectonics, the present-day configuration of the continents and ocean basins is merely a snapshot in time As the plates move about, the location of continents and ocean basins constantly changes Historical geology provides past paleogeographic reconstruction of the world Paleogeographic maps show the distribution of land and sea possible climate regimes and such geographic features as mountain ranges, swamps, and glaciers

Paleogeographic Maps Geologists use to construct paleogeographic maps paleoclimatic data paleomagnetic data paleontologic data sedimentologic data stratigraphic data tectonic data to construct paleogeographic maps which are interpretations of the geography of an area for a particular time in the geologic past

Paleozoic paleogeography The paleogeographic history of the Paleozoic Era is not as precisely known as for the Mesozoic and Cenozoic eras in part because the magnetic anomaly patterns preserved in the oceanic crust was subducted during the formation of Pangaea Paleozoic paleogeographic reconstructions are therefore based primarily on structural relationships climate-sensitive sediments such as red beds, evaporites, and coals as well as the distribution of plants and animals

Six Major Paleozoic Continents At the beginning of the Paleozoic, six major continents were present Baltica - Russia west of the Ural Mountains and the major part of northern Europe China - a complex area consisting of at least three Paleozoic continents that were not widely separated and are here considered to include China, Indochina, and the Malay Peninsula Gondwana - Africa, Antarctica, Australia, Florida, India, Madagascar, and parts of the Middle East and southern Europe

Six Major Paleozoic Continents Kazakhstan - a triangular continent centered on Kazakhstan, but considered by some to be an extension of the Paleozoic Siberian continent Laurentia - most of present North America, Greenland, northwestern Ireland, and Scotland and Siberia - Russia east of the Ural Mountains and Asia north of Kazakhstan and south Mongolia Besides these large landmasses, geologists have also identified numerous small microcontinents such as Avalonia (Belgium, northern France, England, Wales, Ireland, and the Maritime provinces and Newfoundland of Canada) 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 Global History In contrast to today's global geography, the Cambrian world consisted of six major continents dispersed around the globe at low tropical latitudes Water circulated freely among ocean basins, and the polar regions were mostly ice free By the Late Cambrian, epeiric seas had covered areas of Laurentia, Baltica, Siberia, Kazakhstania, China while highlands were present in northeastern Gondwana, eastern Siberia, and central Kazakhstania

Ordovician and Silurian Periods Plate movements played a major role in the changing global geography Gondwana moved southward during the Ordovician and began to cross the South Pole as indicated by Upper Ordovician tillites found today in the Sahara Desert Avalonia separated from Gondwana and collided with Baltica In contrast to Laurentia’s passive margin in the Cambrian, an active convergent plate boundary existed along its eastern margin during the Ordovician as indicated by the Late Ordovician Taconic orogeny that occurred in New England

Silurian Period Baltica, with attached Avalonia, moved northwestward relative to Laurentia and collided with it to form the larger continent of Laurasia This collision, which closed the northern Iapetus Ocean, is marked by the Caledonian orogeny The southern part of the Iapetus Ocean still remained open between Laurentia and Gondwana Siberia and Kazakhstania moved from a southern equatorial position during the Cambrian to north temperate latitudes by the end of the Silurian Period

Early Paleozoic Evolution of North America The geologic history of the North American craton may be divide into two parts the first dealing with the relatively stable continental interior over which epeiric seas transgressed and regressed, and the other dealing with the mobile belts where mountain building occurred In 1963 American geologist Laurence Sloss proposed that the sedimentary-rock record of North America could be subdivided into six cratonic sequences

Cratonic Sequences of N. America White areas represent sequences of rocks That are separated by large-scale uncon-formities shown in brown Appa-lachian oro-genies Cordilleran orogenies

Cratonic Sequence A cratonic sequence is The six unconformities a large-scale lithostratigraphic unit greater than supergroup representing a major transgressive-regressive cycle bounded by craton-wide unconformities The six unconformities extend across the various sedimentary basins of the North American craton and into the mobile belts along the cratonic margin

Global Transgressive and Regressive Cycles Geologists have also recognized major unconformity bounded sequences in cratonic areas outside North America Such global transgressive and regressive cycles are caused by sea-level changes and are thought to result from major tectonic and glacial events

High-Resolution Stratigraphic Analysis The subdivision and correlation of cratonic sequences provides the foundation for an important concept in geology sequence stratigraphy that allows high-resolution analysis within sedimentary rocks of time and facies relationships

Sequence Stratigraphy Sequence stratigraphy is the study of rock relationships within a time-stratigraphic framework of related facies bounded by erosional or nondepositional surfaces The basic unit of sequence stratigraphy is the sequence, which is a succession of rocks bounded by unconformities and their equivalent conformable strata

Sequence Stratigraphy Sequence boundaries form as a result of a relative drop in sea level Sequence stratigraphy is an important tool in geology because it allows geologists to subdivide sedimentary rocks into related units that are bounded by time-stratigraphically significant boundaries Geologists use sequence stratigraphy for high-resolution correlation and mapping, as well as interpreting and predicting depositional environments

The Sauk Sequence Rocks of the Sauk Sequence during the Neoproterozoic-Early Ordovician record the first major transgression onto the North American craton Deposition of marine sediments during the Late Proterozoic and Early Cambrian was limited to the passive shelf areas of the Appalachian and Cordilleran borders of the craton The craton itself was above sea level and experiencing extensive weathering and erosion

Cratonic Sequences of N. America White areas = sequences of rocks Brown areas = large-scale uncon-formities Sauk sequence

The Sauk Sequence Because North America was located in a tropical climate at this time and there is no evidence of any terrestrial vegetation, weathering and erosion of the exposed Precambrian basement rocks must have proceeded rapidly During the Middle Cambrian, the transgressive phase of the Sauk began with epeiric seas encroaching over the craton

Transcontinental Arch By the Late Cambrian, the epeiric seas had covered most of North America, leaving above sea level only a portion of the Canadian Shield and a few large islands These islands, collectively named the Transcontinental Arch, extended from New Mexico to Minnesota and the Lake Superior region

Cambrian Paleogeography of North America During this time North America straddled the equator Trans-continental Arch

The Sauk Sediments The sediments deposited The only difference on both the craton and along the shelf area of the craton margin show abundant evidence of shallow-water deposition The only difference between the shelf and craton deposits is that the shelf deposits are thicker In both areas, the sands are generally clean and well sorted and commonly contain ripple marks and small-scale cross-bedding

Sauk Carbonates Many of the carbonates are bioclastic composed of fragments of organic remains contain stromatolites, or have oolitic textures contain small, spherical calcium carbonate grains Such sedimentary structures and textures indicate shallow-water deposition

A Transgressive Facies Model Sediments become increasingly finer the farther away from land one goes Where sea level remains the same, in a stable environment coarse detrital sediments are typically deposited in the nearshore environment, and finer-grained sediments are deposited in the offshore environment Carbonates form farthest from land in the area beyond the reach of detrital sediments

A Transgressive Facies Model Recall that 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 This region provides an excellent example of sedimentation patterns of a transgressing sea The region of the Grand Canyon occupied the western margin of the craton during Sauk time, a passive shelf During Neoproterozoic and Early Cambrian time, most of the craton was above sea level deposition of marine sediments was mainly restricted to the margins of the craton on continental shelves and slopes

Transgression A transgression covered the Grand Canyon region. The Tapeats Sandstone represents the basal transgressive shoreline deposits that accumulated as marine waters transgressed across the shelf and just onto the western margin of the craton during the Early Cambrian

Cambrian Transgression Cambrian strata exposed in the Grand Canyon The three formations exposed along the Bright Angel Trail, Grand Canyon Arizona

Transgression The Tapeats sediments are clean, well-sorted sands of the type one would find on a beach today As the transgression continued into the Middle Cambrian, muds of the Bright Angle Shale were deposited over the Tapeats Sandstone

Continued Transgression The Sauk Sea had transgressed so far onto the craton by the Late Cambrian that in the Grand Canyon region carbonates of the Muav Limestone were being deposited over the Bright Angel Shale This vertical succession of sandstone (Tapeats) shale (Bright Angel) and limestone (Muav) forms a typical transgressive sequence and represents a progressive migration of offshore facies toward the craton through time

Time Transgressive Formations Cambrian rocks of the Grand Canyon region also illustrate how many formations are time transgressive that is, their age is not the same every place they are found Mapping and correlations based on faunal evidence indicate that deposition of the Mauv Limestone had already started on the shelf before deposition of the Tapeats Sandstone was completed on the craton

Time Transgressive Formations Faunal analysis of the Bright Angel Shale indicates that it is Early Cambrian in age in California and Middle Cambrian in age in the Grand Canyon region, thus illustrating the time- transgressive nature of formations and facies younger shale older shale

Cambrian Transgression Cambrian strata exposed in the Grand Canyon Observe the time transgressive nature of the three formations The three formations exposed along the Bright Angel Trail, Grand Canyon Arizona

Same Facies Relationship This same facies relationship also occurred elsewhere on the craton as the seas encroached from the Appalachian and Ouachita mobile belts onto the craton interior Carbonate deposition dominated on the craton as the Sauk transgression continued during the early Ordovician, and the islands of the Transcontinental Arch were soon covered by the advancing Sauk Sea By the end of Sauk time, much of the craton was submerged beneath a warm, equatorial epeiric sea

Cambrian Facies Block diagram from the craton interior to the Appalachian mobile belt margin showing 3 major Cambrian facies and the time transgressive nature of the units The carbonate facies developed progressively because of submergence of the detrital source areas by the advancing Sauk Sea

Upper Cambrian Sandstone Outcrop of cross-bedded Upper Cambrian sandstone in the Dells area of Wisconsin

Regression and Unconformity As the Sauk Sea regressed from the craton during the Early Ordovician, it revealed a landscape of low relief The rocks exposed were predominately limestones and dolostones that experienced deep and extensive erosion because North America was still located in a tropical environment The resulting craton-wide unconformity marks the boundary between the Sauk and Tippecanoe sequences

Ordovician Period Paleo-geography of North America The continent showing change in the position of the the equator The continent was rotating counter-clockwise

Cratonic Sequences of N. America White areas = sequences of rocks brown areas = large-scale uncon-formities Regression Tippecanoe sequence

The Tippecanoe Sequence A transgressing sea deposited the Tippecanoe sequence over most of the craton Middle Ordovician-Early Devonian Like the Sauk sequence, this major transgression deposited clean, well-sorted quartz sands The Tippecanoe basal rock is the St. Peter Sandstone, an almost pure quartz sandstone used in manufacturing glass that occurs throughout much of the midcontinent and resulted from numerous cycles of weathering and erosion of Proterozoic and Cambrian sandstones deposited during the Sauk transgression

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 carbonate- secreting organisms such as corals, brachiopods, stromatoporoids, and bryozoans

Dolostones and Shales Besides the limestones, there were also many dolostones Most of the dolostones formed as a result of magnesium replacing calcium in calcite, thus converting limestones into dolostones In the eastern portion of the craton, the carbonates grade laterally into shales These shales mark the farthest extent of detrital sediments derived from weathering and erosion of the Taconic Highlands a tectonic event in the Appalachian mobile belt

Tippecanoe Reefs and Evaporites Organic reefs are limestone structures constructed by living organisms, some of which contribute skeletal materials to the reef framework 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 that they do today regardless of the organisms involved

Modern Reef Requirements Because of the ecological requirements of reef-building organisms, present-day reefs are confined to a narrow latitudinal belt between 30 degrees north and south of the equator Corals, the major reef-building organisms today, 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

Size and Shape of Reefs The size and shape of a reef are mostly the result of the interaction between the reef-building organisms, the bottom topography, wind and wave action, and subsidence of the seafloor Reefs also alter the area around them by forming barriers to water circulation or wave action

Barrier Reefs Reefs typically are long, linear masses forming a barrier between a shallow platform on one side and a comparatively deep marine basin on the other side Such reefs are known as barrier reefs Reefs create and maintain a steep seaward front that absorbs incoming wave energy As skeletal material breaks off from the reef front, it accumulates as talus along a fore-reef slope

Barrier Reef Barrier Reef Fore-reef slope

The Lagoon The reef barrier itself is porous and composed of reef-building organisms The lagoon area is a low-energy, quiet water zone where fragile, sediment-trapping organisms thrive The lagoon area can also become the site of evaporitic deposits when circulation to the open sea is cut off Modern examples of barrier reefs are the Florida Keys, Bahama Islands, and Great Barrier Reef of Australia

Ancient Reefs Reefs have been common features since the Cambrian and have been built by a variety of organisms The first skeletal builders of reef-like structures were archaeocyathids These conical-shaped organisms lived during the Cambrian and had double, perforated, calcareous shell walls Archaeocyathids built small mounds that have been found on all continents except South America

Stromatoporoid-Coral Reefs Beginning in the Middle Ordovician, Stromatoporoid-coral reefs became common in the low latitudes, and similar reefs remained so throughout the rest of the Phanerozoic Eon The burst of reef building seen in the Late Ordovician through Devonian probably occurred in response to evolutionary changes triggered by the appearance of extensive carbonate seafloors and platforms beyond the influence of detrital sediments

Michigan Basin Evaporites The Middle Silurian rocks of the present-day Great Lakes region Tippecanoe sequence are famous for their reef and evaporite deposits The most significant structure in the region the Michigan Basin is a broad, circular basin surrounded by large barrier reefs These reefs contributed to increasingly restricted circulation and the precipitation of Upper Silurian evaporites within the basin

Silurian Period Paleogeography of North America during the Silurian Period Reefs developed in the Michigan, Ohio, and Indiana-Illinois-Kentucky areas

Other Types of Reefs Within the rapidly subsiding interior of the basin, other types of reefs are found Pinnacle reefs are tall, spindly structures up to 100 m high They reflect the rapid upward growth needed to maintain themselves near sea level during subsidence of the basin Besides the pinnacle reefs, bedded carbonates and thick sequences of salt and anhydrite are also found in the Michigan Basin

Northern Michigan Basin Northern Michigan Basin sediments during the Silurian Period

Stromatoporoid Reef Facies Stromato-poroid barrier-reef facies of the Michigan Basin

Evaporite Evaporite facies

Carbonate Facies Carbonate Facies

Tippecanoe Regression and Evaporites As the Tippecanoe Sea gradually regressed from the craton during the Late Silurian, precipitation of evaporite minerals occurred in the Appalachian Basin, Ohio Basin, and Michigan Basin In the Michigan Basin alone, approximately 1500 m of sediments were deposited, nearly half of which are halite and anhydrite

Origin of Thick Evaporites How did such thick sequences of evaporites accumulate? 1. When sea level dropped, the tops of the barrier reefs were as high as or above sea level, thus preventing the influx of new seawater into the basin Evaporation of the basinal 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 sedimentation by direct precipitation from seawater Vertical scale is greatly exaggerated

Basin Brines Because North America was still near the equator during the Silurian Period, temperatures were probably high

Basin Brines As circulation to the Michigan Basin was restricted, seawater within the basin evaporated, forming a brine Because the brine was heavy, it concentrated near the bottom, and minerals precipitated on the basin floor

Replenishment of Salt Some seawater flowed in over the sill and through channels cut in the barrier reefs, this replenishment added new seawater allowing the process of brine formation and precipitation of evaporites to repeat itself

Order of Precipitation The order and type of salts precipitating from seawater depends on their solubility, the original concentration of seawater, and local conditions of the basin Salts generally precipitate in order beginning with the least soluble and ending with the most soluble Therefore, the order of precipitation is calcium carbonate first, followed by gypsum and lastly halite

Interfingering Gypsum is the common sulfate precipitated from seawater, but when deeply buried, gypsum loses its water and is converted to anhydrite Many lateral shifts and interfingering of the limestone, anhydrite, and halite facies may occur, however, because of variations in the amount of seawater entering the basin and changing geologic conditions

Problems with the Model Thus, the periodic evaporation or seawater proposed by this model could account for the observed vertical and lateral distribution of evaporites in the Michigan Basin However, associated with those evaporites are pinnacle reefs, and the organisms constructing those reefs could not have lived in such a highly saline environment

Reefs in a Highly Saline Environ-ment? Organisms constructing reefs could not have lived in such a highly saline environ-ment

No Model Is Perfect How then, can such contradictory features be explained? Numerous models have been proposed, ranging from cessation of reef growth followed by evaporite deposition, to alternation of reef growth and evaporite deposition Although the Michigan Basin has been studied extensively for years, no model yet proposed completely explains the genesis and relationship of its various reef, carbonate, and evaporite facies

The End of the Tippecanoe Sequence By the Early Devonian, the regressing Tippecanoe Sea had retreated to the craton margin exposing an extensive lowland topography During this regression, marine deposition was initially restricted to a few interconnected cratonic basins and by the end of the Tippecanoe to only the mobile belts surrounding the craton

Domes and Basins As the Tippecanoe Sea regressed during the Early Devonian, the craton experienced mild deformation resulting in the formation of many domes, arches, and basins These structures were mostly eroded during the time the craton was exposed so that they were eventually covered by deposits from the encroaching Kaskaskia Sea

The Appalachian Mobile Belt Having examined the Sauk and Tippecanoe geologic history of the craton, we turn our attention to the Appalachian mobile belt, where the first Phanerozoic orogeny began during the Middle Ordovician The mountain building occurring during the Paleozoic Era had a profound influence on the climate and sedimentary history of the craton

Mountain Building Additionally, it was part of the global tectonic regime that sutured the continents together, forming Pangaea by the end of the Paleozoic The Appalachian region throughout Sauk time, was a broad, passive, continental margin Sedimentation was closely balanced by subsidence as thick, shallow marine sands were succeeded by extensive carbonate deposits

Iapetus Ocean During this time, the Iapetus Ocean was widening as a result of movement along a divergent plate boundary Beginning with the subduction of the Iapetus plate beneath Laurentia which was an oceanic-continental convergent plate boundary the Appalachian mobile belt was born

Appalachian Mobile Belt Evolution of the Appalachian mobile belt Neoproterozoic opening of Iapetus Ocean with passive continental margins and large carbonate platforms

The Taconic Orogeny The resulting Taconic orogeny, named after present-day Taconic Mountains of eastern New York, central Massachusetts, and Vermont was the first of several orogenies to affect the Appalachian region

Shallow-Water Deposition The Appalachian mobile belt can be divided into two depositional environments The first is the extensive, shallow-water carbonate platform that formed the broad eastern continental shelf and stretched from Newfoundland to Alabama It formed during the Sauk Sea transgression onto the craton when carbonates were deposited in a vast shallow sea The shallow water depth on the platform is indicated by stromatolites, mud cracks, and other sedimentary structures and fossils

Deep-Water Deposits Carbonate deposition ceased along the East Coast during the Middle Ordovician and was replaced by deepwater deposits characterized by thinly bedded black shales, graded beds, coarse sandstones, graywackes, and associated volcanics This suite of sediments marks the onset of mountain building, the Taconic orogeny

Eastern Sediment Source The subduction of the Iapetus plate beneath Laurentia resulted in volcanism and downwarping of the carbonate platform Throughout the Appalachian mobile belt, indications that these deposits were derived from the east, come from facies patterns, paleocurrents, and sedimentary structures The sediment originated where the Taconic Highlands and associated volcanoes were rising

Appalachian Mobile Belt Middle Ordovician transition to convergence resulted in orogenic activity

Evidence for Orogeny Evidence for the timing and origin of this orogeny comes from additional structural, stratigraphic, petrologic, and sedimentologic information For example, at many locations within the Taconic belt, pronounced angular unconformities occur where steeply dipping Lower Ordovician rocks are overlain by gently dipping or horizontal Silurian and younger rocks

Orogeny Timing Other evidence in the area from present-day Georgia to Newfoundland includes volcanic activity in the form of deep-sea lava flows, volcanic ash layers, and intrusive bodies These igneous rocks show a clustering of radiometric ages corresponding to Middle to Late Ordovician In addition, regional metamorphism coincides with the radiometric dates

Queenston Delta Clastic Wedge The final piece of evidence for the Taconic orogeny is the development of a large clastic wedge, an extensive accumulation of mostly detrital sediments deposited adjacent to an uplifted area and become 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 Taconic Highlands consists of thick, coarse-grained detrital sediments nearest the highlands and thins laterally into finer-grained sediments on the craton

A European Orogeny The Taconic orogeny marked the first pulse of mountain building in the Appalachian mobile belt and was a response to the subduction taking place beneath the east coast of Laurentia As the Iapetus Ocean narrowed and closed, another orogeny occurred in Europe during the Silurian

Caledonian Orogeny The Caledonian orogeny was essentially a mirror image of the Taconic orogeny and the Acadian orogeny and was part of the global mountain-building episode that occurred during the Paleozoic Era Even though the Caledonian orogeny occurred during Tippecanoe time, we will discuss it with the Acadian orogeny because the two are intimately related

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

Early Paleozoic Mineral Resources Early Paleozoic-age rocks contain a variety of important mineral resources, including sand and gravel for construction, building stone, and limestone used in the manufacture of cement Important sources of industrial or silica sand are the Upper Cambrian Jordan Sandstone of Minnesota and Wisconsin, the Lower Silurian Tuscarora Sandstone in Pennsylvania and Virginia, and the Middle Ordovician St. Peter Sandstone

Silica Sand The St. Peter Sandstone, the basal sandstone of the Tippecanoe sequence, occurs in several states, but the best-known area of production is in La Salle County, Illinois Silica sand has a variety of uses including the manufacture of glass, molds for casting iron, aluminum, and copper alloys and refractory bricks for blast furnaces It is also pumped into oil and gas wells to fracture the source rocks and provide permeable passageways for the oil or gas to migrate to the well

Salt and Oil Thick deposits of Silurian evaporites, mostly rock salt (NaCl) and rock gypsum (CaSO4•2H2O) altered to rock anhydrite (CaSO4) underlie parts of Michigan, Ohio, New York, and adjacent areas in Ontario, Canada and are important sources of various salts In addition, barrier and pinnacle reefs in carbonate rocks associated with these evaporites are the reservoirs for oil and gas in Michigan and Ohio

Lead and Zinc The host rocks for deposits of lead and zinc in southeast Missouri are Cambrian dolostones, although some Ordovician rocks contain these metals as well These deposits have been mined since 1720 but have been largely depleted Now most lead and zinc mined in Missouri come from Mississippian-age sedimentary rocks

Iron The Silurian Clinton Formation crops out from Alabama north to New York, and equivalent rocks are found in Newfoundland This formation has been mined for iron in many places In the United States, the richest ores and most extensive mining occurred near Birmingham, Alabama, but only a small amount of ore is currently produced in that area

Summary Most continents consisted of two major components a relatively stable craton over which epeiric seas transgressed and regressed, surrounded by mobile belts in which mountain building took place Six major continents and numerous microcontinents existed at the beginning of the Paleozoic Era and these were dispersed at low latitudes around the globe during the Cambrian

Summary During the Ordovician and Silurian plate movement resulted in a changing global geography Gondwana moved southward and began to cross the South Pole as indicated by Upper Ordovician tillite deposits The microcontinent Avalonia separated from Gondwana during the Early Ordovician and collided with Baltica during the Late Ordovician-Early Silurianwana During the Early Paleozoic (Cambrian-Silurian) Baltica and Avalonia moved northwestward relative to Laurentia and collided to form Laurasia during the Silurian

Summary Geologists divide the geologic history of North America into cratonic sequences that reflect craton-wide transgressions and regressions The first major marine transgression resulted in deposition of the Sauk Sequence At its maximum, the Sauk Sea covered the craton except for parts of the Canadian Shield and the Transcontinental Arch, a series of large northeast-southwest trending islands

Summary The Tippecanoe Sequence began with During Tippecanoe time, deposition of an extensive sandstone over the exposed and eroded Sauk landscape During Tippecanoe time, extensive carbonate deposition took place In addition, large barrier reefs enclosed basins, and resulted in evaporite deposition within these basins

Summary The eastern edge of North America During Tippecanoe time was a stable carbonate platform during Sauk time During Tippecanoe time an oceanic-continental convergent plate boundary formed, resulting in the Taconic orogeny, the first of three major orogenies to affect the Appalachian mobile belt

Summary The newly formed Taconic Highlands shed sediments into the western epeiric sea producing the Queenston Delta, a clastic wedge Early Paleozoic-age rocks contain a variety of mineral resources including building stone, limestone for cement, silica sand, hydrocarbons, evaporites, and iron ores