Geology Report 2018

Brockholes Bird Reserve owes its existence to the last glaciation. The ice and the meltwater produced led to the deposition of millions of tons of sediment whose excavation for sand and gravel has resulted in the lakes seen today. Erratic boulders whose place of origin can be identified enable ice-sheet and glacier movement to be reconstructed.
Although the valley has existed for many thousands of years, the present river channel was created only at the end of the last glaciation. Melting ice produced large volumes of water which cut the valley floor to about its present width. At the time meltwater probably occupied the whole of the valley floor.

Little Mearley Clough

Little Mearley Clough.
Photo: Jim Hutchinson.

Little Mearley Clough on the side of Pendle Hill is the type locality for Pendle Grit, and the oldest of the Millstone Grit group. Below this is probably the most complete of all the sections of the Bowland Shales in the vicinity of Pendle. Just above the farm the Worston Shale Group is exposed. Thereafter it is all Bowland Shales, calcareous shales and shaly mudstones.

The prominent 8ft waterfall is made by the lowest leaf of the Pendleside Sandstone. The upper leaf is just below the moorland boundary wall and comprises 35ft of micaceous sandy shale with many beds of sandstone up to about a foot thick. The whole section is highly fossiliferous, containing mainly goniatites.

Our group joined with GeoLancs members to visit Heysham on Morecambe Bay. We met by the power station and walked to the beach at Red Nab to see the Sherwood Sandstone rocks. These are Permo-triassic rocks, red and white sandstone showing low-angle cross bedding. A short distance along the coast we examined some Carboniferous, deltaic deposits. After lunch we saw Ward’s Stone Sandstone containing rip-up clasts.

Sherwood Sandstone rocks at Red Nab

Sherwood Sandstone rocks at Red Nab.
Photo: Jim Hutchinson

Upper Nidderdale is located at the northern end of the main Millstone Grit outcrop of the Central Pennines, which extends southwards to Kinder Scout. Carle Side Quarry provided stone for the construction of Scar House Dam.The quarry is on three levels. The rock is of Namurian age, sandstones and mudstones being river mouth deposits. The lowest sandstones of the Scar House Formation in the quarries at Carle Side were deposited by currents beyond the mouth bar of a river. At the second level are prodelta sand lobes with flute marks on some bedding surfaces. At the highest quarry level medium-grained channel sandstones are to be seen. At the undulating base of the higher channel a conglomerate with abundant siltstone rip-up clasts can be viewed. Higher strata are thinly bedded mouth bar sandstones overlain by mudstones. The top level has the best fossils in both mudstone and sandstone.

Carle Side quarry and Scar House dam

Carle Side quarry and Scar House dam.
Photo: Jim Hutchinson.

Finally, in September, we visited Crummockdale, one of the Craven inliers, to look at folding, an unconformity at Studrigg Scar, glacial striations, the source of the Norber Erratic boulders and Nappa Scars. There the Sub-Carboniferous unconformity is exposed. Pebbly limestone and conglomerate onlap a palaeocliff in calcareous siltstone of the Upper Ordovician (Ashgill) Norber Formation. The limestone in the cliff just above footpath level reveals many angular to sub-rounded clasts of both types of rock. These were eroded from the basement beds by the invading Carboniferous Sea. Their shape indicates that they did not travel far.

Report: Jim Hutchinson.
The Geology Group Co-ordinator is Jim Hutchinson.

2018-11-01T12:50:33+00:00

Upcoming Events

  1. South Georgia and the South Sandwich Islands

    Antarctica

    December 10 @ 19:30 - 21:30
  2. Grass Wood Grassington

    Grass Wood

    December 20 @ 10:00 - 16:30
  3. The Big Dig, Long Preston

    Long Preston’s Archaeological Results

    January 14, 2019 @ 19:30 - 21:30