L12 How plate tectonics & climate shaped Ireland pt 2.

From deserts to coal swamps

Ireland at the equator 420 - 300 million years ago

Drift of Avalonia

Result of Avalonia

• amalgamation of Avalonia Laurentia and Baltica - with mountain belts formed during their collision

• creates a major continent: Laurussia or informally, Old Red Sandstone Continent

• transition from marine sediments to terrestrial (land-based) sedimentation at low palaeolatitudes south equator

Desert environments - shedding of mountains

• alluvial fans (scree slopes and debris flows)

• episodic river activity

• unconfined floods over floodplains

• aeolian (wind-blown) deposits

• lacustrine (i.e. lake) deposits

periodic rain storm in desert rivers can be very dangerous.

Early Devonian (400My)

• Brown bits are mountains

• Blue bits are ocean

N.B. don’t have to remember each detail just know the bits.

Eroded several years

Rounded clasts of cobble and boulder grade in matrix

alluvial fan deposits

→ game of throne = this is

The stormlands

Old Red Sanstone, Wexford

• It’s red because of the oxygenated airated environment and it’s above water → FE3+ so it’s not green coloured

Base of river channel

• carried lots of fragments previously

• high energy rivers

Early and Middle Devonian

• Sea is migrating northwards

• transgression → migrates over ireland

• lakes are formed though, massive lakes. periodically fill up and dry out.

Orcadian basin

• Lake in Scotland

• Colour coding types of rock

• Dark blue = deep, light blue = shallow, brown = river, pink = salts, boundaries of the river. going up and down generating salts at the side of the river.

• illustrates nature of sequence for only 70m out of ca 750m thickness

High lake stands (i.e. when lake level is low and system is dry)

• Cracks → dried up there

• Death valley environment I guess

High lake stands (i.e. when lake level is high and system is wet)

• Fossils of freshwater fish is discovered

• Deoxyenated are effectivley dead deep down, the fish slowly goes down to the bed and is fossilised.

End middle and Late Devonian

• coastal plain developed in the south

Lower carboniferous times (350-325Ma ago)

• Ireland is stretched north and south, reefs are developing and tropical oceans are developed.

Early Carboniferous (355 My)

Carboniferous limestone

• full of fossils

• crinoids = stalk with lots of arms.

Middle carboniferous 328My

• Dublin area was apart of the submarine rift, south of UCD has a fault (deer park)

• Deep parts are the dark blue

• Green bits are deltas and coal swamps, sediments are being formed as well = sandstones

Zn-Pb

• Light blue are limestone

• 4km dropped in navan

• 2km dropped in ucd, dublin

• black lines are faults

• these extend deep into the earth, zinc and lead being developed because of this

Irish Zn-b Orefield

• navan mines, 2km deep

Late Carboniferous (313My)

• clogging it up with all the deltas

• deltas have trees nearby, trees grow, die then more trees grow and have organic matter of coal/swamp.

• ireland is up now, not underwater anymore.

Central Clare Group, Western Ireland

• can be related to the melting ice of africa

• we’re in the tropics??

• africa is in the poles

Formation of coal forming environment

Spatial distribution of climatic belts during Permo-Carboniferous