ABSTRACT

The Shale Grit and Grindslow Shales (which together make up the Alport Group) lie between the Mam Tor Sandstones (turbidites) and the Kinderscout Grit (near-shore or coastal plain). All these formations are of Namurian (Upper Carboniferous) age and crop out in the North Derbyshire part of the Central Pennine Basin, England. The Shale Grit contains two main sandstone facies, 1, alternating parallel sided sandstones and mudstones interpreted as distal turbidites and 2, thick sandstones without mudstone partings interpreted as very near source, proximal turbidites. There are also three mudstone facies, silty mudstones, pebbly mudstones and thinly laminated black mudstones. The Grindslow Shales contain both of the Shale Grit sandstone facies, together with sandy mudstones, burrowed silty udstones, parallel bedded silty sandstones and carbonaceous sandstones.

The Shale Grit facies sequence indicates that distal turbidities are more abundant below, and proximal turbidities are more abundant in the upper part of the formation. In the Grindslow Shales the facies become sandier upward with thin turbidities restricted to the lower part and horizontal burrows restricted to the upper part. The Shale Grit and Grindslow Shales contain at least seventeen channels from 10 to 50 feet deep, which appear to have been both cut and filled by turbidity currents. The presence of deep channels in association with proximal turbidities suggests that the environment of deposition of the Shale Grit was a submarine fan, similar in most respects to the fans at the foot of the Monterey and La Jolla canyons. The Grindslow Shales were probably deposited on the slope bove the fan.

The sequence from the Mam Tor Sandstones (distal trubidites) via the lower Shale Grit (distal, with subordinate proximal turbidites) into the upper Shale Grit (proximal, with subordinate distal turbidites) suggests advance of a submarine fan southward into the North Derbyshire area. This southward advance of facies belts continued as the Grindslow Shales "slope" environment covered the fan, and was itself covered by the nearshore or coastal plain Kinderscout Grit.