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 Five of the six geologic Paleozoic systems Cambrian, Ordovician, Silurian, Devonian, and Carboniferous We use the same basic geologic principles to interpret the geology of the Paleozoic Era

Cratons and Mobile Belts Pannotia supercontinent began broke apart 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 typically consist of two parts a shield and a platform

Platforms Extending outward from the shields are buried Precambrian rocks The sediments over the platforms were deposited in widespread shallow seas

Paleozoic North America Platform

Epeiric Seas The transgressing and regressing shallow seas called epeiric seas common feature of most Paleozoic cratons

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

Paleozoic North America Mobil belts

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, evaporates, and coals as well as the distribution of plants and animals

Six Major Paleozoic Continents 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

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, six major continents dispersed at low tropical latitudes polar regions were mostly ice free By the Late Cambrian, epeiric seas had covered most areas of Laurentia, Baltica, Siberia, Kazakhstania, China,

Ordovician and Silurian Periods 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 In contrast to Laurentia’s passive margin in the Cambrian, an active convergent plate boundary formed along its eastern margin during the Ordovician as indicated by the Late Ordovician Taconic orogeny that occurred in New England

Silurian Period Baltica moved northwestward relative to Laurentia and collided with it to form the larger continent of Laurasia This collision closed the northern Iapetus Ocean 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 comings and goings of epeiric seas the second dealing with the mobile belts 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 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

The Sauk Sequence Rocks of the Sauk Sequence during the Late Proterozoic-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 but 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 Sauk Sea 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

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 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

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 older Tapeats Sandstone

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-transgres- sive 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 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 due to 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 During the Early Ordovician, the Sauk Sea regressed. The rocks exposed were predominately limestones and dolostones that experienced deep and extensive erosion 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 The Tippecanoe basal rock is the St. Peter Sandstone, an almost pure quartz sandstone occurs throughout much of the mid-continent 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 the 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

Tippecanoe Reefs and Evaporites Organic reefs are limestone structures constructed by living organisms Reefs appear to have occupied the same ecological niche in the geological past

Modern Reef Requirements Present-day reefs grow between 30 degrees N and S of equator Reefs 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

Barrier Reefs Reefs create and maintain a steep seaward front typically long linear masses forming a barrier between a shallow platform a deep marine basin Reefs create and maintain a steep seaward front that absorbs incoming wave energy As skeletal material breaks off from the reef front, it accumulates along a fore-reef slope

Barrier Reef Barrier Reef Fore-reef slope

The Lagoon 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 reef systems are the Florida Keys, Bahama Islands, and Great Barrier Reef of Australia

Ancient Reefs Reefs have been common features since the Cambrian The first skeletal builders of reef-like structures were archaeocyathids

Stromatoporoid-Coral Reefs Beginning in the Middle Ordovician, stromatoporoid-coral reefs became common similar reefs throughout the rest of the Phanerozoic Eon

Michigan Basin Evaporites a broad, circular basin surrounded by large barrier reefs Reef growth caused restricted circulation and precipitation of Silurian evaporates within Upper Tippecanoe sequence of the basin

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

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

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

Order of Precipitation calcium carbonate first, followed by gypsum and lastly halite

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

The End of the Tippecanoe Sequence During this regression, marine deposition was initially restricted to a few interconnected cratonic basins By the Early Devonian, the regressing Tippecanoe Sea retreated to the craton margin exposed an extensive lowland topography

The Appalachian Mobile Belt the first Phanerozoic orogeny began during the Middle Ordovician

Mountain Building 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

Iapetus Ocean During this time, the Iapetus Ocean was widening along a divergent plate boundary the Appalachian mobile belt was born with the onset of subduction of the Iapetus plate beneath Laurentia

Appalachian Mobile Belt Evolution of the Appalachian mobile belt Late Proterozoic opening of Iapetus Ocean with passive continen-tal margins and large carbon-ate plat-forms

The Taconic Orogeny The resulting Taconic orogeny, named after present-day Taconic Mountains of eastern New York, central Massachusetts, and Vermont

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 Formed during the Sauk Sea transgression

Deep-Water Deposits Replaced by deep-water deposits (second depositional environment) during middle Ordovician 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

Sediment Source Sediment shed from the Taconic Highlands and associated volcanoes The subduction of the Iapetus plate beneath Laurentia resulted in volcanism and downwarping of the carbonate platform

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

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 between 440 to 480 million years ago In addition, regional metamorphism coincides with the radiometric dates

Queenston Delta Clastic Wedge The clastic wedge resulting from the erosion of the Taconic Highlands 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 As the Iapetus Ocean narrowed and closed, another orogeny also occurred in Europe during the Silurian (Caledonian Orogeny)

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 An Important sources of industrial or silica sand is the Middle Ordovician St. Peter Sandstone

Salt and Oil Thick deposits of Silurian evaporites, mostly rock salt (NaCl) and rock gypsum (CaSO4•H2O) altered to rock anhydrite (CaSO4) and are important sources of various salts In addition, barrier and pinnacle reefs are reservoirs for oil and gas in Michigan and Ohio

Summary Six major continents existed at the beginning of the Paleozoic Era four of them were located near the paleo-equator During the Early Paleozoic — Cambrian-Silurian Laurentia was moving northward and Gondwana moved to a south polar location, as indicated by tillite deposits

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 The geologic history of North America can be divided into cratonic sequences that reflect cratonwide transgressions and regressions

Summary The Sauk Sea was the first major transgression onto the craton At its maximum, it covered the craton except for parts of the Canadian Shield and the Transcontinental Arch, a series of large northeast-southwest trending islands The Tippecanoe sequence began with deposition of an extensive sandstone over the exposed and eroded Sauk landscape

Summary During Tippecanoe time, In addition, large barrier reefs extensive carbonate deposition took place In addition, large barrier reefs enclosed basins, and resulted in evaporite deposition within these basins The eastern edge of North America was a stable carbonate platform during Sauk time

Summary During Tippecanoe time The newly formed Taconic Highlands an oceanic-continental convergent plate boundary formed, resulting in the Taconic orogeny, the first of several orogenies to affect the Appalachian mobile belt The newly formed Taconic Highlands shed sediments into the western epeiric sea producing the Queenston Delta, a clastic wedge

Summary Early Paleozoic-age rocks contain a variety of mineral resources including building stone, limestone for cement, silica sand, hydrocarbons, evaporites and iron ores