Jarðsaga 1

- Saga Lands og Lífs –

Ólafur Ingólfsson

The Middle Paleozoic World- Great changes in the Earth Systems –

Orogenic Events

Development of the continents during the Middle Paleozoic

• Avalonia and Baltica collide withLaurentia, causing the build-up of the Appalachian Mt´s and the Scandinavian mountain chain.

• Subsequent erosion led to thicksedimentary accumulations and thedeposition of the “Old Red Sandstone” in areas that were close to the Equator.

• Chemical weathering rates on land increase dramatically due to spread of terrestrial vegetation.

Major developments of life duringthe Silurian and Devonian time

• Life diversified rapidly after theOrdovician mass extinction and surpassed the Ordovician adaptive radiation

• The broad, shallow epicontinental seasof the Silurian and Devonian were optimal environments for development of life

• In the tropical zone, a diversecommunity of organisms builtreefs larger than any that had formed during early Paleozoic times

Major developments of life during Silurian and Devonian...

• More advanced predators, includingjawed fishes, arrived on the scene

• Land habitats were progressivelycolonized. Plants were restricted tomarshes in the Silurian, but were forming large forests by Late Devonian

• The first known insects and thefirst vertebrate animals on land are also of Devonian age

Falling CO2 in the atmosphere

Development of soils accelerates in the Middle Paleozoic

Baltica on a collision corse with Laurentia

since Ordovicium...

Silurian configuration of continents

http://jan.ucc.nau.edu/~rcb7/global_history.html

The Avalonian-Acadian-Caledonian Orogeny

Europe (the BalticPlate) collideswith NorthernLaurentia, andAvalonia collides with southern Laurentia during the Silurian and Devonian.

http://www.science.ubc.ca/~eoswr/lithoprobe/slide.html

• By the late Silurian, the small continent of Avalon wasapproaching N. America A shallow sea covered the interior of the N. American continent. • The continent-continentcollision lasted approximately 30 My. • As the Acadian mountainsrose, large rivers courseddown their western slopes, spreading sand and gravel across the region.

The AcadianOrogeny in N

America

• The rivers deposited the hugeCatskill Delta. The delta was made upof conglomerates closest to themountains, and gradually graded intosands, then shales further away and eventually turbidites. These deposits now make up the Catskill Mountains in southeastern New York.

The Acadian orogenyThe Acadian Orogeny was the result of collision of Europe with northern portions of Laurentia and added another permanent terrane to the eastern cratonic margin This collision:

- overprinted Taconian metamorphic ages - intruded abundant granite - built another high eastern mountain range that shedanother clastic wedge that coarsens to the east called the Catskill clastic wedge; - the Catskill redbeds are the North American mirrorimage of the Old Red Sandstone in Great Britain formed in northwestern Europe's Caledonian Orogeny- the tectonic unit composed of Laurentia and Europewas called Laurussia – The Supercontinent of Pangea was in the making...

The AppalachianMts

Appalchian geologyThe Appalachians are a orogenic belt developed along the eastern margin of the North American craton

The Appalachinas areconstructed by a seriesof events, includingrifting apart of RondinaSupercontinent; sedimentation in an ocean; closure of the ocean by subduction; and later collision between two continental plates...

Satellite picture of the Appalachians

Geological terrains shaped by the Acadian-Caledonian orogeny

TheAppalachians

Hills and ridges

History of the mountainsAbout 750 million years ago, the Rodinasupercontinent began to pull apartbecause of expansion of the continentalcrust. 540 million years ago, thecontinental crust split into pieces that drifted apart. Seawater spread into low areas between crustal plates and, in time, formed new oceans.

The extent of Oceansabout 480 million yearsago. The present-dayUnited States is outlined in white, and the equator shown as a dashed yellow line.

History of themountains...

About 470 million yearsago, the motion of thecrustal plates changed, andthe continents beganmoving toward each other. As the plates moved closer together, fragments of oceanic crust, islands, and other continental masses collided with the eastern margin of ancestral North America.

TheTaconicOrogeny

TheAcadianOrogeny

And the story continued...The ocean continued to shrinkuntil, about 300 million yearsago (The Carboniferous), thecontinents that were ancestralto North America and Africacollided. Huge masses of rocks were pushed west-ward along the margin of North America and piled up to finish forming the mountains that we now know as the Appalachians.

The Birth of a Mountain: http://pubs.usgs.gov/gip/birth/birth.pdf

Diagrammatic history of major continents

The Plutons of Appalachia

As blocks of continental crust rodeacross one another, some rocksbecame so hot that they melted. When molten rock remains deepbelow ground, it cools andcrystallizes to form bodies of rockthat arecalled igneous plutons. Some plutons are now exposed at the land surface due to erosion of overlying rock. The plutons are composed of granite and similar rocks. Plutons are scattered throughout the Southern Appalachians like plums in a pudding.

GranitesBanded granite from New Hampshire

A xenolith of olderbasalt in youngergranite. Acadia National Park, Maine

Dykes and sills

Basaltic dykes that cutthrough older metamor-phised rocks. Acadia National Park, Maine

An example of the tectonicsof the Appalachians

The collision of continental plates is alsoexpressed in the rocks by tectonicdisplacements, folds and faults. Oneplace where the effects of the faultingcan be seen is in Cades Cove in the GreatSmoky Mountains National Park. In a normal sequence, younger rocks are deposited on top of older ones. However, in Cades Cove, the limestone that makes up the floor of the cove is younger than the rocks in the surrounding mountains. The older rocks of the surrounding mountains moved over the lime-stone on a low-angle fault

Roadside geology

Landscape shaped by faultingMany faults have beenidentified throughoutthe SouthernAppalachian Mountainsand the Valley and Ridge province. Huge masses of rock moved along these faults for distances of 60 miles or more.

Geology and history...Faults act as channels for migrationof fluids and were a key factor in localizing gold in certain zones.

In 1829, newspaper articlesdescribed vast riches of gold inCherokee land in North Georgia. Thousands of miners quicklyflocked to the area with dreams of quick riches. They washed gravel from banks of the streams to search for gold.

The Trail of Tears

The frenzy caused by the discovery of gold hastenedthe removal of the Cherokees by a forced march toOklahoma during the winter of 1837–38. More than one-third of the Cherokee people who started the march died along the way, on what is now known as the Trail of Tears

Another story of geology and history... The Black Hills

The Black Hillsare the surfaceexpression of andome, that roseup in connection with the creation of the Rocky Mountains early in the Cenozoic EraSee: Stanley, pg. 252

Paleozoic and Mesozoic strata flank crystalline Archean rocks thaterosion has exposed in the centre of the dome. The Black Hills containone of the worlds richest gold occurrances. The gold comes from Archean rocks that were metamorphised in early Proterozoic times. The gold probably precipitated from warm fluids or gases percolatingthrough cracks and faults...

The Black Hills Dome

The gold of the Black HilllsThe region was the homeland of SiouxIndians who had been given the land by theFort Laramie Treaty in 1851. The uncoveringof gold in the Black Hills in 1874 caused an onrush of settkers, which were forbidden to entry under treaty terms with the Sioux .

General Custer and his crave for gold

In 1876, general Custer, seeking fame as anIndian killer and fortune as a prospector for gold, led his men into the most devastatingdefeat ever suffered by the US army at the hands of the Indians. 269 soldiers were killed by the Sioux in the battle at Little Big Horn.

The Homestake Gold MineMore than 1 billion USD worth of gold has been mined in the Homestakemine, opened in 1876, in the Black Hills. It is still one of the richest gold mines in the world...

See: Stanley, pg. 333

Geology sets the pattern...

Continental drift through hundreds of millions of years sets the stage for thepatterns of human settlement, travel,

transportation routes, history etc

Most of Earth’s gold, silver andcoppermines are located on Precambrian

shields

A worthwhile visit tothe Appalchians...

A visit to the Tertiary in Iceland

The Acadian-Caledonian Orogeny

The Baltic plate collides with the Laurentia plateduring the Devonian, causing the Caledonian orogeny.

The Caledonian OrogenyCaledonian Orogeny: Continental collision involving North Americaand Europe led to mountain building and associated sedimentationacross most of Ireland, Wales, northern England, Scotland andNorway. This orogeny is parallel in timing and cause to the Acadian Orogeny of the northern Appalachians during the Devonian. A large landmass--the so-called Old Red Continent--resulted with sediment accumulation around the uplifted mountains.

Caledonian Orogeny: The mountain-building event that occurredwhen England and Scotland collided around 430 million years ago. Prior to the orogeny, Scotland formed part of the continent of Laurentia and England formed part of the continents of Avalonia and Baltica. Between these continents lay an ocean called the Iapetus. Plate tectonics caused the continents to move towards each other, closing the ocean.

Geology of Scotland

http://www.scottishgeology.com/regional_geology/map_regions.html

The Caledonian in ScotlandThe Caledonian Orogenydeformed and folded variousolder sedimentary rocks, which were also metamor-phosed, with the recrystali-sation of sandstones toquartzites and mudstones toslates. There was also the intrusion of granite magama, derived from the actual partial melting of rocks lower within the crust, where the heat and deformation caused by the continental collision, was most intense.

Scandinavian mountains: Caledonian orogeny

Fennoscandiaroughly corre-sponds to thecrystalline BalticShield, comprised mainly by either reworked Archean rocks or Lower Proterozoic basement.

Main Scandinavian stage of Caledonian orogeny is known to be Middle to Late Silurian age.

Formation of the ScandinavianMountains during the Caledonian orogeny

Skoðið þessa vefsíðu frá háskólanum í Tromsö –

mjög fróðleg um myndun fjalla almennt og í Noregi

sérstaklega:

http://www.ig.uit.no/~kaarek/geology_intro/mountains.swf

The Red Continent

The Old Red SandstoneThe Old Red Sandstone, in contrast to the typical formations of the Devonian, is largely a continental formation, laid down infreshwater and on land as a result of the erosion of the highlands of the Silurian period. It is very thick in Scotland (> 10 km) and contains a large assemblage of well-preserved fossils, particularly of the Devonian fishes.

Formation of the Old Red Sandstone

Silurian graywacke

Old Red Sandstone

The ORS was deposited between Late Silurian and Early Carbonifer-ous, between ca. 420-320 MY, as a product of weathering of the Acadian-Caledonian mountains. The environment was hot, desert-like, probably with torrential rains.

The red color is caused by oxidizediron that stain the colorless quartzsand grains. It takes only a couple of percent of the red iron materials to give the sandstone its red color.

References, web resources etcStanley, Earth System History, chapter 13

The Birth of a Mountain: http://pubs.usgs.gov/gip/birth/birth.pdf

Um myndun fjalla í Skandinavíu við Kaledonisku fjallamyndunina: http://www.ig.uit.no/~kaarek/geology_intro/mountains.swf

http://www.science.ubc.ca/~eoswr/lithoprobe/slide.html

http://www.scottishgeology.com/regional_geology/map_regions.html

http://www.toyen.uio.no/palmus/galleri/blader/blad_x03.htm

http://www.ucmp.berkeley.edu/silurian/silurian.html

http://www.palaeos.com/Paleozoic/Silurian/Silurian.htm

http://jan.ucc.nau.edu/~rcb7/global_history.html

http://gpc.edu/~pgore/geology/geo102/silurian.htm

http://www.earth.ox.ac.uk/~conallm/Caled.pdf

http://www.nrm.se/lig/fennmap.html.en

http://www.ucmp.berkeley.edu/ordovician/ordovician.html