1.7.1 Carboniferous mires
During the late Carboniferous, mires developed over vast areas of the UK. Much of today's land area was an extensive, low-lying plain bordering a sea to the south (a sea that was soon to be the site of a mountain-building episode). Any mountains that existed lay hundreds of kilometres to the north. Large river systems meandered southwards across these plains.
At that time, the UK lay in tropical latitudes, almost on the Equator (see Figure 33). The low plains were covered by extensive forests: the Carboniferous equivalent of the present-day tropical rainforests (see Figure 2c). However, most of the 'trees' were hollow, not solid, and more closely resembled modern horsetails than modern trees. No flowers or birds existed, but insect and reptile life was abundant in the forests.
Tropical storms were probably as common then as they are today. Such storms would devastate vast areas of forest, reducing trees and plants to jumbled leaves, branches and crushed hollow logs. The same storms would also have caused extensive flooding. After this devastation, the forest would quickly reestablish itself, only to be devastated again by subsequent storms. The forest floor was probably often metres deep in rotting vegetation destined to become peat and, much later, coal.
In the late Carboniferous, cycles of global sea-level rise and fall resulted from the melting and re-growth of continental ice sheets in the Southern Hemisphere. Consequently, numerous mire-flooding-sediment infill-mire episodes occurred on low-lying coastal plains, which led to thick sedimentary successions with numerous coal seams.
A.Mudstone with freshwater shells
a.Peat accumulations on the swampy areas of a delta plain
b.Distributary stream channels cutting through the delta plain
c.Fossil soil beneath the mire
d.Deposits laid on delta plain in times of flooding
e.Shallow lakes and lagoons on the delta plain
A (e); B (d); C (b); D (c); E (a).