The Carboniferous, 359 – 299 million years ago
At the end of the Devonian the sea spread across the Mendip area,
marking the beginning of a long phase of limestone deposition. Initially,
muddy sediments accumulated (Avon Group) in shallow, turbid waters,
but gradually the reef limestones that are characteristic of the
Carboniferous Limestone (Pembroke Limestone Group) became predominant.
The environment in which these rocks formed was analogous to the
Bahamas today, with tropical, warm, clear shallow water conditions
covering the Mendip region in the early Carboniferous.
Deposition of the Carboniferous Limestone was abruptly terminated
by the southward spread of sandy sediment that today forms the Quartzitic
Sandstone Formation. This sandstone formed part of a delta complex,
built out by rivers that drained a landmass (St George's Land) to
the north of the Mendip region.
Throughout the Upper Carboniferous the river deltas that now covered
the Mendip region were densely colonised by lush forests of giant
tree ferns, horsetails and club mosses. River channels meandered
through the forest and periodically the delta was flooded by the
sea. Thick peat deposits formed in this tropical swamp, eventually
becoming buried and transformed into coal.
A reconstruction of the paleogeography in the early Carboniferous.
in the early Carboniferous
Life in the late