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