Carboniferous

Question 1

When was the Carboniferous period?

Answer 1

360 - 290 mya

Question 2

Describe the Palaeogeography of the Carboniferous period.

Answer 2

The Rheic sea closed as part of the Variscan orogeny leading to the formation of major fold structures , thrusts and granite emplacements over south western England. Although the effects were felt mainly over Cornwall ( hydrothermal deposits), the orogeny caused a variety of folds and faults over Southern Britain.
The Rheic sea separated North America, Greenland , Britain and Scandanavia from the rest of Gondwanaland. Carboniferous rocks occur widely over Britain. An area of land separated the South of England and Wales from the Midlands and Northern England. This slowly subsiding block is called St Georges land. There was a large amount of vegetation on this upland area which eventually formed the Coal Measures

Question 3

How did the sea level change in this period?

Answer 3

At the start of the Carboniferous period the Caledonian Mountains had been eroded down to low levels and the Rheic Sea (shallow shelf
sea) had invaded the southern low lying parts of the British area. The worldwide rise in sea levels (Eustatic change) can be put down to two reasons:
A melting of ice sheets around the Antarctic and an increase in plate tectonic activity around Mid-Atlantic ocean ridges.
This tectonic activity may have caused sea levels to rise due to displacing water onto surrounding continental shelves.

Question 4

Describe the marine life during the Carboniferous period.

Answer 4

During the Carboniferous , marine life evolved. Goniatites as zonal fossils, corals and Brachiopods were common in the early limestones of the period.
Large trees and land plants – Lycopods and tree ferns provide much of the vegetation in the swamps of the coal measures.

Question 5

What are deltas and how do they grow?

Answer 5

The British area was astride the equator and the shallow early Carboniferous seas were very warm and laid down shallow water tropical carbonates (limestone and Dolomite)
Later these shallow seas were invaded by deltas flowing in from the adjacent high ground. Progradation refers to the growth of a river delta farther out into the sea over time.

Question 6

Describe the formation of coal measures and cyclothems.

Answer 6

The climate then became humid and these deltas started to support swamps and Tropical Rainforests. The rapidly changing deltas ,
combine with many transgressing and regressing seas inundated the swamp areas. The burial and decay of the vegetation led to the formation of the coal measures.
Many carboniferous rocks display sequences showing that there are repeated cycles of rock successions. These repeated cycles are called
cyclothems depositing beds between 5 – 20m thick.