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Upper Carboniferous

GEOLOGY: Rocks and Periods

Late Carboniferous Period (ca.300Ma)

William Conybeare

British geologist William Conybeare (1787-1857)

The Carboniferous System of rocks were named in 1822, by William Daniel Conybeare (1787 – 1857), after their high carbonaceous content in the form of the Coal Measures.

These beds were laid down between c.360 million and 299 million years ago in a variety of different environments when Britain was much farther south (equatorial).

Blakey 300moll

The geography of Earth ca. 300 million years ago

In the early Tournasian Stage thick fossiliferous marine limestones (Mountain Limestone) were laid down in a sea of varying depth, these are exposed in Upper Teesdale and on the Pennine Uplands.

A Middle episode, the Viséan, saw closer proximity of a landmass resulting in the deposition of massive sandstones with occasional mudstones and shell-beds dubbed the Millstone Grit. Further uplift saw the district transformed into a low-lying heavily vegetated delta-marsh, the fallen trunks of Palaeozoic trees forming the economically-important Coal Measures of the Westphalian stage.

The later Namurian stage saw the local crust subside and the sea re-invade the district when deltaic fans of sand were deposited along with inter-bedded thinner fossiliferous marine mudstone.

Carb Sandstone

An exposure of Namurian sandstone at Houghton-le-side

Within the Tees Valley and Darlington these rocks are only sparsely exposed, and then only in the far north-west of the Darlington district. Here can be found a few outcrops of massively-bedded coarse-grained Namurian sandstones of the Millstone Grit dating back to c.307 million years ago.

At-a-glance information:

Carboniferous strata underlie our area at depth but are only exposed northwest of Darlington and even there to a limited extent owing to the cover of glacial deposits.

They are, however, extremely well represented not far away, in the Yorkshire Dales, western County Durham and Northumberland. For example, there are good exposures along the Tees Valley in the neighbourhood of Barnard Castle.



By William Daniel Conybeare (1787 – 1857), in 1822, from the high carbonaceous content of the Coal Measures.

Equatorial (0° to 10°).

Hot & wet with drier intervals, high oxygen levels, drier towards close.

Cyclic, variable depression, resulting in basinal infill with thinner deposits on surrounding blocks. Uplift towards close.

Patchwork of rivers with deltas, well vegetated with coal-forming swamps. Short marine incursions.

Fault controlled blocks and troughs.

Major angular unconformity (Hercynian orogeny)
Pennine Coal Measures Group
Millstone Grit Group/Stainmore Formation
Alston Group
Continuous sequence from Lower Carboniferous

Cyclic sequences of limestones, mudstones, coals, seat earths (ganisters), sandstones and gritstones.
Extensive flora. Freshwater bivalves. Marine beds with bivalves, etc. and goniatites used as zone fossils.

Undulating eastern slopes of the Pennines.





Underlies whole area but Coal Measures absent.

Northwest Darlington (Stainmore Formation).

A few poor exposures mostly of sandstone in old quarries where the superficial deposits are thin or absent.



















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