Ingleton: Pecca Quarry

Craven & Pendle Geological Society

Approaching Pecca Quarry

: Pecca Falls and Pecca Quarry :

Pecca Quarry

: Steeply dipping strata in Pecca Quarry :

Jointing in Pecca Quarry

: Jointing and cleavage Pecca Quarry :

Outline Geological History Of The Pecca Slates.

a) Late 19th Century Ingletonian Pecca Slates were assigned Lower Silurian, then shortly after, Ordovician.

b) Early 1900’s the Ingleton Series were assigned to the Precambrian.

c) Green (1917) in Pecca Quarry placed the Ingletonian rocks as Ordovician.

d) The 1920’s and onwards recognised that the angular unconformity between Carboniferous / Ingletonian was a significant feature.

e) In 1950 Leedal & Walker described the Ingleton rocks in terms of their sedimentary structures. The unfossiliferous nature and intense folding led to their reassignment to the Precambrian.

Current View

The Ingletonian strata all dip steeply to the SW and were originally thought to represent a continuous succession over 4km thick. A study by Leedal & Walker (1950, Geol. Mag. 87, 57-66) using way-up evidence from the fine beds reinterpreted the Ingletonian as isoclinally folded, and their inferred fold pattern has been adopted on the BGS 1:50 000 map and cross-section (Sheet 50, Hawes).

There are three lithofacies: sandgrade turbidite greywackes, green siltstones, mudstones and sandstones. A number of sedimentary features such as ripple cross lamination, flute casts, slump folds and intraformational breccias, have been used aid their interpretation as turbidite deposits. The very coarse quartz-feldspar-rich greywackes are commonly referred to as 'Ingleton granite', particularly by the quarrymen.

The Ingletonian is devoid of fossils and was traditionally thought to be of Precambrian age. However, the Beckermonds Scar borehole yielded one sample of Arenig acritarches, so an early Ordovician age for the 'Ingleton Group' has been adopted by BGS.

The enigmatic Ingletonian strata still attract much interest from geologists today. Recent research by looking at sedimentary structures and cleavage are once again challenging the stratigraphical position of these fascinating rocks.