Editing Permo-Triassic Sandstones, Bristol and Gloucester region

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==Permo-Triassic Sandstones==
 
==Permo-Triassic Sandstones==
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On the east side of the Worcester Basin an attenuated representative of the Bromsgrove Sandstone overlaps onto the London Platform and is itself overlapped by deposits of the overlying Mercia Mudstone Group farther east. On the west side of the basin, north of the River Severn at Sharpness, the Triassic is represented at outcrop by the Mercia Mudstone Group, which is strongly downfaulted against the Palaeozoic rocks. South of this the Mercia Mudstone Group margin is unfaulted and the limits of the main sandstone sequence beneath are unknown.
 
On the east side of the Worcester Basin an attenuated representative of the Bromsgrove Sandstone overlaps onto the London Platform and is itself overlapped by deposits of the overlying Mercia Mudstone Group farther east. On the west side of the basin, north of the River Severn at Sharpness, the Triassic is represented at outcrop by the Mercia Mudstone Group, which is strongly downfaulted against the Palaeozoic rocks. South of this the Mercia Mudstone Group margin is unfaulted and the limits of the main sandstone sequence beneath are unknown.
  
The basal sandstone sequence is absent in the Bristol–Mendip district, where the later Triassic rocks have overstepped directly onto the Coal Measures and older rocks. The sandstones reappear to the south within the Central Somerset Basin, which forms part of the south-west England ‘province’. Permo-Triassic sequences there, with the exception of the Budleigh Salterton Pebble Beds, which are considered by many to equate with the various ‘Bunter’ pebble bed horizons of the Midlands, cannot be clearly related to those of the Midlands. The thickest sequence so far proved in the southern area is in a borehole at Puriton, north of Bridgwater, where the lowest strata, not bottomed, comprised 177 m of uniform, brick-red, fine-grained sandstone with green spots and blotches and some inter-bedded siltstone. These are overlain by 65 m of red and grey sandstones with inter-bedded pebble and siltstone layers, and a well-marked basal conglomerate about 4 m in thickness. Some pebbles of Carboniferous limestone occur in this conglomerate, which has been equated with the Budleigh Salterton Pebble Beds; thus, by definition, the underlying beds are Permian in age. The nearest outcrops of corresponding rocks are outside the region on the west side of the Quantock Hills, where a somewhat similar succession, totalling 230 m in thickness and including a conspicuous representative of the pebble beds up to 30 m thick, is faulted against the Palaeozoic basement.
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The basal sandstone sequence is absent in the Bristol–Mendip district, where the later Triassic rocks have overstepped directly onto the Coal Measures and older rocks. The sandstones reappear to the south within the Central Somerset Basin, which forms part of the south-west England ‘province’. Permo-Triassic se- quences there, with the exception of the Budleigh Salterton Pebble Beds, which are considered by many to equate with the various ‘Bunter’ pebble bed horizons of the Midlands, cannot be clearly related to those of the Midlands. The thickest sequence so far proved in the southern area is in a borehole at Puriton, north of Bridgwater, where the lowest strata, not bottomed, comprised 177 m of uniform, brick-red, fine-grained sandstone with green spots and blotches and some inter-bedded siltstone. These are overlain by 65 m of red and grey sandstones with inter-bedded pebble and siltstone layers, and a well-marked basal conglomerate about 4 m in thickness. Some pebbles of Carboniferous limestone occur in this conglomerate, which has been equated with the Budleigh Salterton Pebble Beds; thus, by definition, the underlying beds are Permian in age. The nearest outcrops of corresponding rocks are outside the region on the west side of the Quantock Hills, where a somewhat similar succession, totalling 230 m in thickness and including a conspicuous representative of the pebble beds up to 30 m thick, is faulted against the Palaeozoic basement.
 
[[Category:Bristol and Gloucester region]]
 
[[Category:Bristol and Gloucester region]]

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