Energy resources: Coal
Energy resources: Coal

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Energy resources: Coal

1.3.2 Peat formation in raised mires

Mires can also form inland within low-lying depressions, provided the rate of precipitation exceeds the rate of evaporation (Figure 4a). Peat is impermeable and so its accumulation progressively impedes drainage. This attribute gives mires the ability to maintain a water table independent of the area surrounding them. Therefore, the water table rises as the peat layer increases in thickness, thus elevating the surface level of the mire (Figure 4b-d). Such raised mires are now thought to have been very significant environments for coal formation in the geological record.

Figure 4
Figure 4 The development of a raised mire: (a) a lake forms in a depression with floating dead vegetation encroaching from the margins; (b) a mire is formed by the lake filling with peat and establishing luxuriant vegetation: (c, d) the mire surface is progressively raised by accumulation of peat, accompanied by a decline in the vegetation.

Having identified the modern environments in which the coals of the future may currently be forming, the next section will look at the evidence from ancient coal-bearing rock sequences, to see whether they formed in environments similar to those in which peats accumulate today.

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