Mississippian

© Craven & Pendle Geological Society

Geological History

The Craven Inliers is a good place to view the early Carboniferous marine transgression onto the truncated remnants of folded Lower Palaeozoic rocks.  The photograph to the right demonstrates this very well.  The classic angular unconformity separates grey-green turbidite sandstones and conglomerate of the Ingleton Group (Arenig in age) with the sub-horizontally bedded Carboniferous limestone.  The unconformity represents a time gap of about 150 MA.  This first transgression was the first of many cycles on several scales.  The six stages of the Dinantian are in fact based on the six mesothem cycles.  The transgressions and regressions in the Dinantian were comprehensively accounted for by Dr. W. H. C. Ramsbottom in 1973. (Transgressions and Regressions in the Dinantian: a new synthesis of British Dinantian stratigraphyPYGS. Vol.39, part 4, No. 28 pp. 567 - 607).

In the Craven Basin bioclastic limestones and calcareous shales are characteristic of this deep subsiding basin.  Evidence of such cyclicity is clearly shown below in the photograph.  Notice the shallow water limestone horizons punctuated by a return to deeper water black shales.  This outcrop by Scar House Reservoir is located in Upper Nidderdale.

In the transition zone between the Craven Basin and Askrigg Block, and the area around Clitheroe, marginal reef limestones were deposited in mid to late Dinantian times.  The earlier Clitheroe build-ups of deeper water Chadian age are in fact Waulsortian mud mounds as opposed to the transition zone (Cracoe / Malham / Settle) apron-reefs which formed in a shallower environment.

The shelf margin, especially around the Sykes area in the Forest of Bowland marks a transitional area between the deep water Craven Basin sediments and the quiet water carbonate muds and sands of the Lancaster Fells carbonate platform.  There are good examples of slumping at Sykes Quarry showing this changeover.

As we reach the late Mississippian (Dinantian), minor cyclicity becomes more evident and is perhaps best known as the Yoredale Cycles ( a term derived from the old name for Wensleydale).  Basically, the Yoredales mark a period in Mississippian history where there was a steady influence of southward prograding deltas.  The Yoredale facies extends up into the Pennsylvanian and hence a new chapter begins.