Geology Report 2017

Members of the Field Society’s Geology Group made five field trips over the summer months of 2017, plus the visit to Hunstanton Cliffs. Additionally one was cancelled due to too few members being able to attend. One meet was a joint venture with the GeoLancs Group and worked well. Our final meet attracted more non-members than members which was encouraging.

Hunstanton Cliffs.

Members who visited Kings Lynn and went down to Hunstanton Beach were able to view the cliffs The geology features three distinctive formations – the Carstone Formation (orange) at the cliff base, followed by the Hunstanton Formation (red) formerly known as the Red Chalk, and the Ferriby Chalk (white) extending to the cliff top.

Brockholes Bird Reserve

Brockholes Bird Reserve next to the M6 Motorway at Preston owes its existence to the last glaciation. That ice and the meltwater produced from it led to the deposition of millions of tons of sediment in the lower Ribble Valley. Excavation of this sediment for sand and gravel has resulted in the lakes seen today. A granodiorite erratic weighing over 2 tons was transported by ice from the Lake District or south-west Scotland. The surface is smoothed by glaciation and fluvial processes. It was found just a few hundred metres away. Erratic boulders whose place of origin can be identified enable ice-sheet and glacier movement to be reconstructed. Although the valley occupied by the river has existed for many thousands of years, the present river channel was created only at the end of the last glaciation between 18 and 20 thousand years ago.

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. Soon after the period of rapid water flow a layer of sediment was deposited which raised the valley floor about four metres.Later, the river cut down into these, leaving remnants of the old flood-plain perched up above the river as a high terrace. This process of deposition followed by downcutting has been repeated four times since the ice melted, each time producing a new terrace at a lower level. All four terraces
existed at Brockholes before the site was excavated; now only fragments remain to be seen.

Little Mearley Clough

Little Mearley Clough, Pendle Hill (a SSSI) The type locality for Pendle Grit, and the oldest of the Millstone Grit group.This is probably the most complete of all the sections of the Bowland Shales in the vicinity of Pendle. At Little Mearley Clough just up from the farm the highest part of 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 – 35ft of micaceous sandy shale with many beds of sandstone up to about a foot thick. The whole section is highly fossiliferous (mainly  goniatites) and contains two Marine Bands. Just below the top of the Clough the prominent 17ft waterfall is made by the basal part of the Pendle Grit. The highest 20ft or so of the Bowland Shale Group consists of dark grey fissile shale with thin bands of rottenstone – directly overlayed by “course soft spheroidally weathered sandstone..Three feet of tough course gritstone makes the tip of
the fall.

Heysham

The group met by the power station and walked to the beach at Red Nab to see the Sherwood Sandstone (Group) rocks. These are Permo-triassic rocks found at a number of places along the coast of North-West England (approx. 229 to 271 Ma),red and white sandstone showing low-angle cross bedding.

Further along the coast we came to some Carboniferous, deltaic deposits, the local setting being swamps, estuaries and deltas, and shallow seas. These rocks were formed in marginal coastal plains with lakes and swamps, periodically inundated by the sea. Above a bed of limestone lay a red sandstone pockmarked with rootlets and Stigmaria (root) fossils; a sea level rise due to (global) melting of ice and local subsidence leaving a Paleosurface.

In the slack area between channels can be seen a deposit of mud and fine-grained sand,together with a fault breccia nearby, possibly a later infill. Trace fossils are any indirect evidence of ancient life. They refer to features not representing parts of the body of once living organism. Traces include footprints, tracks, trails, burrows, borings and bitemarks. Trace fossils provide information about the behaviour of ancient life forms.Sediments that have trace fossils are said to be bioturbated. Burrowed textures in sedimentary rocks are referred to as bioturbation. After lunch, on the beach below the church we examined Ward’s Stone sandstone, a sedimentary bedrock from approximately 318 – 322 Ma in the Carboniferous Period, the local environment previously dominated by rivers. One large boulder having a fine example of rip-up clasts.

Scar House

Scar House, Nidderdale which has fine examples of river mouth deposits. The dale is located at the northern end of the main Millstone Grit outcrop of the Central Pennines, which extends Southwards to Kinderscout. Stang quarry on the south side of the valley was opened from 1904 to 1915 to provide stone for Angram Dam further up the valley.

Scar House Reservoir was built by Bradford Corporation to supply drinking water to the Bradford area. Water is transferred down the Nidderdale viaduct without pumping! Work on the Dam/Reservoir began in Oct 1921 and took 15 yrs. Carle Side Quarry provided stone for Scar House Dam. The quarries exploited thick course sandstone beds, natural fracturing allowed it to be easily broken into large cube-like blocks. The dam trench was excavated in the Grassington Grit.

The quarry is on three levels -the rock is of Namurian age (Millstone Grit Gp) the sandstones and mudstones being river mouth deposits. The lowest sandstones of the Scar House Formation in the quarries at Carle Side were deposited by “voluminous density currents” beyond the mouth bar of a river. At the second level are prodelta sand lobes with flute marks on some bedding surfaces.
And the “… highest quarry level where medium-grained channel sandstones are displayed”. Higher strata are thinly bedded mouth bar sandstones overlain by mudstones. “The skyline feature is in Lower Follifoot Grit”.

The top level has the best fossils in both mudstone and sandstone – finer muddy layers “ full of trace fossils” (Cruziana) -sandstone “brilliantly preserved plant materials” -calamites suckowi – similar to modern horsetails. Also stigmaria (ficoides) – branching tree roots. We then walked across the moor to Stand Sykes to hunt for fossils.

Crummock Dale

Finally in September, Crummock Dale, one of the Craven inliers, to look at folding, an unconformity at Studrigg Scar, glacial striations, which have been observed at twelve locations in Crummock Dale, 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 cleaved calcareous siltstone of the Upper Ordovician (Ashgill) Norber Formation.”

“A glance at the limestone in the cliff just above footpath level reveals that it contains 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 indicating that they are not far-travelled and their size (some boulders reach almost 3m in diameter) revealing that they were eroded in a high energy environment. Consequently, it is likely that they are the products of the undercutting of a marine cliff that collapsed nearby about 340 Ma.”

“ ..a conglomerate that is associated with an unconformity is known as a basal conglomerate…”

And finally, after a bit of exciting scrambling we see the interface between the Ordovician muddy limestones and the Carboniferous rocks at the Carboniferous – Lower Palaeozoic unconformity.
Bibliography and sources.

Brockholes:

Ribble Valley Geotrails, Walk 2 Brockholes. Available at www.geolancashire.org.uk

Little Mearley Clough:
Geology of the country around Clitheroe. (Geological Survey of Great Britain), HMSO, 1961.

Carboniferous Geology, Bowland Fells to Pendle Hill, Ed. by Paul Kabrna.
Chapter 4. Pendle Hill – a turbulent past, by Ian Kane.

Nidderdale Sources:
Our Geological adventures
http://geologytrails.wordpress.com
Yorkshire Rocks and Landscape, A field guide. (1994) Y.G.S
Crummock Dale.
Yorkshire Rocks and Landscape, A Field Guide, Ed. Colin Scrutton.
Publ. by Yorkshire Geological Society,1994.
Field Excursion 1. Lower Palaeozoic rocks of the Craven Inliers, by Eric Johnson,BGS
jh,25/7/18, Ed. jd

2018-09-24T11:55:07+00:00

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