Pendle Grit Formation
The Pendle Grit Formation (Late Mississippian (Serpuhovian) Pendleian E1 age) represents a lowstand sand-rich slope channel/fan complex deposited during the earliest major phase of siltciclastic input into the Bowland Sub-Basin. At the base of the Formation the basinal Bowland Shales are erosivley overlain by sand-rich submarine slope channels; smaller precursor events are generally rare, however the Pendle Grit (the sand-rich lower part of the Formation) is strongly diachronous across its base.
Initial sedimentation into the Bowland Sub Basin was largely dark, thinly intercalated, weakly calcareous, muddy silts and hemipelagic muds laid down mainly from suspension in the relatively deep, poorly oxygenated waters. Fully marine conditions are marked by 'marine bands' usually dominated by thick-shelled goniatites and signifying sea-level highstand of minor trangressive cycles superimposed on the general subsidence. These trangressive cycles are thought to be a product of eustatic sea-level changes caused by glacial fluctuations in the southern hemisphere.
The Pendleian sequence has three distinct minor cycles each marked at the base by a diagnostic goniatite (Cravenoceras leion, Tumulities (Eumorphoceras) pseudoblingue and Cravenoceras malhamense - all situated in the Upper Bowland Shale Formation). What followed was a huge influx of deep water turbidity sand flow systems that continued into the Arnsbergian and finally ceased when sea-level rose as marked by the Cravenoceras cowlingense marine band.
Of the four sand-bodies, the PENDLE, WARLEY WISE, GRASSINGTON and BRENNAND grits, only the Pendle Grit and Warley Wise Grit are exposed in the vicinity of Pendle Hill. In summary: the Pendle Grit was deposited in deep water, at the foot of a submarine slope, perhaps a few hundred metres deep. The sand was supplied from river deltas, with dense turbid flows flowing down the contours onto the floor of the basin. Repeated flows produced the distinct beds. The scale of this influx of sand into the basin is thought to be similar to the great river system, the Brahmaputra.
Warley Wise Grit: Faughs Quarry, Newchurch
Following the influx of the Pendle Grit, into the Craven Basin, the Warley Wise Grit was deposited on top as a basin-filling sequence. It is a typical example of progradational sand - dominated braid delta.
The Warley Wise Grit exposed in this quarry is a coarse to pebbly reasonably well-sorted sandstone. The quarry has good evidence of trough cross-bedding up to 1 to 2 metres high. In the base of the quarry larger trough cross-bedding can be seen and the sandstone is a little more pebbly.
Another good exposure of the Warley Wise Grit can be seen on Noyna Hill [Grid Reference SD902426] on the Colne-Foulridge boundary. The type section for the Warley Wise Grit is at Warley Wise Farm adjacent to the European Mid-Carboniferous Boundary stratotype at Stonehead Beck, Cowling.
Jenny Gill Quarry
Jenny Gill Quarry exposures show the basal channelised bedforms of the Pendle Grit. The grit is seen to cut down into the Upper Bowland Shales, though now difficult to make out in the disused quarry because of the gradual re-introduction of the natural vegetative cover. However the central sand-rich beds are easily accessible and show a variety of flute and groove marks.
The photograph shows the NE wall of the quarry. Here the channel appears very steep and may be formed by a synsedimentary fault.
From Jenny Gill Quarry it is instructive to follow the right of way onto Skipton Moor. Look for further outcrops of the Pendle Grit noticing the en echelon pulses of Pendle Grit sediment into the basin.
Type section for the Pendle Grit G.R. SD 7723860
The three roadside quarries at the Nick O' Pendle are easily accessible by car and accord splendid views of the Ribble Valley and the Burnley Basin.
The Pendle Grit is the oldest sandstone body in the Millstone Grit Group seen in the Central Pennines. These massive sandstones are fine to medium grade and yet curiously have always been referred to as "Pendle Grit. The Pendle Grit Formation is dominated by thin-bedded, fine micaceous sandstones. Some of the sedimentary features can be seen at outcrop. These include channels, erosion surfaces, linguoid ripples and mudflake lags and scours.
The photograph below is taken in the Nick O' Pendle North Quarry. Although it is a small quarry, the load casts and are well worth looking at.
The three roadside quarries illustrate the relationships between the late stage fill of one channel complex and tha basal units of a later complex. Sedimentary features to look out for include:
a) Amalgamation surfaces
b) Linguoid ripples
c) Shale clast breccias
Whilst at this particular locality ascend the slopes of Pendle Hill to note the sequence of meltwater channels left behind by the last glaciation. Although mind the 'Hang-Gliders' when you are there!! There is also a Dry Ski Slope nearby and plenty of opportunity of lunch at pubs in Sabden or perhaps the Spanish 'Hacienda' by the Ski Slope.
Wiswell Moor Quarry
G.R. SD 755 373
The route to Wiswell Moor Quarry by-passes Light Clough at G.R. SD751377. Moore (1936) has collected goniaites from the shales and calcareous mudstones. More importantly though this is the type locality for the goniatite Cravenoceras leion. Also found in the shales are characteristic bivalves such as Posidonia.
These quarries are probably the best exposed section through the Pendle Grit. Here there are about 80 metres of strata exposed including large bedding-plane exposures. Sedimentotogicaly the outcrops are comprised of thickly bedded sandstone channel bodies, individual beds may haveclast rich tops or intervals, commonly marking internal amalgamation surfaces. Scours and flutes are common at the bases of beds, and occasionally scoured surfaces are laterally persistent, a particularly good example is exposed in cross section. Bedding planes are udulose and commonly covered in shale clasts. Towards the top of the section beds tend to thin and siltstone beds become more frequent. At the very top of the sequence very well preserved starved ripples are found. There is a lot of fairly complex sedimentology here so we will spend some time examining the facies and architecture.