Chapter 10
Early Paleozoic Earth History
New York State Most surface rocks are from the Paleozoic
• 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
Paleozoic History of North America
• Cratons are stable and “immobile”a shield and a platform (granite-gneiss) form the foundation upon which
Phanerozoic sediments were deposited
Continental Architecture
• 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
Mobile Belts
• The transgressing and regressing shallow seas– common feature of Paleozoic
as evidenced by sediments depositednow forming the surface rock
in New York State
Epeiric Seas
MarcellusShale
Devonian Age
ConglomerateMt. Marion
Saugerties NY (exit 20 I-87
Oriskany Sandstone
Near Utica NY
How old are the Herkimer “diamond”
source rocks?
• 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
Paleogeographic Maps
• 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
Six Major Paleozoic Continents
• For the Late Cambrian Period
Paleogeography of the World
• For the Late Ordovician Period
Paleogeography of the World
• For the Middle Silurian Period
Paleogeography of the World
– epeiric seas transgressed and regressedOver the stable continental interior
– mobile belts where mountain building occurred
Early Paleozoic Evolution of North America
• White areas represent sequences of rocks That are separated by large-scale unconformities shown in brown
Cratonic Sequences of N. America
Cordilleraorogenies
Appalachiaorogenies
• A cratonic sequence is – a large-scale lithostratigraphic unit
representing a major transgressive-regressive cycle
bounded by cratonwide unconformities
Cratonic Sequence
Regressing Sea
• White areas = sequences of rocks
• 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
• 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
The Sauk Sequence:Middle Cambrian Period
• 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”
Highlands:Transcontinental Arch
• During this time North America straddled the equator
• Trans-continental Arch
Cambrian Paleogeography of North AmericaSauk Transgression
• 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
A Transgressive Facies Model
• 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
The Cambrian of the Grand Canyon Region
– The Tapeats Sandstone represents the shoreline depositsare 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
Evidence of Transgression
• Cambrian strata in the Grand Canyon
Cambrian Transgression
• The three formations exposed – along the Bright Angel Trail, Grand Canyon
Arizona
– Observe the time transgressive nature of the three formations
Cambrian Transgression
• 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
Regression and Unconformity
• White areas = sequences of rocks
Cratonic Sequences of N. America
Brownareas = large-scale”uncon-formities
• Regression
• Tippecanoe sequence
• Paleo-geography of North America– showing
change in the position of the the equator
• The continent – was rotating
counter-clockwise
Ordovician Period
Resulted in deposition of the St. Peter Sandstone – Middle
Ordovician
over a large area of the craton
Transgression of the Tippecanoe Sea
Outcrop of St. Peter Sandstone in Governor Dodge State Park, Wisconsin
St. Peter Sandstone
• 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
The Tippecanoe Sequence
• 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
Tippecanoe Reefs and Evaporites
Present-day reefs are 30 degrees north and south of the equator
• Corals require warm, clear, shallow water – of normal salinity for optimal growth
• with reef-building organisms
Present-Day Reef Community
• Block diagram of a reef showing the various environments within the reef complex
Reef Environments
• significant structure in the regiona 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 behindhalite, gypsum, sylvite
Michigan Basin Evaporites
• Paleogeography of North America Silurian Period
• Reefs developed in the Michigan, Ohio, and Indiana-Illinois-Kentucky areas
Silurian Period
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
Origin of Thick Evaporites – 1500 m(Gypsum, Halite)
• Silled Basin Model for evaporite sedimentation by direct precipitation from seawater
Silled Basin Model
• Because North America was still near the equator during the Silurian Period, – temperatures were probably high
Basin Brines
– 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 Appalachian Mobile Belt
• The resulting Taconic orogeny, – Today’s Taconic Mountains
• eastern New York, • central Massachusetts, • and Vermont
– First of 3 to form Appalachians
The Taconic Orogeny
• Transition to convergence resulted in orogenic activity
Appalachian Mobile Belt
• 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
• Queenston Delta clastic wedge • Taconic Highlands – coarse-
grained detrital sediments near the highlands
– thins laterally into finer-grained sediments on the craton
• 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
– Caledonian Orogeny
– was a mirror image of the Taconic Orogeny
Resources of Early PaleozoicSandstone, Salts, Gypsum, natural gas
Igneous minerals during orogeny