ABSTRACT

The Grindslow Shales and the Kinderscout Grit form the upper half of a basin filling sequence in the Namurian (Upper Carboniferous) of the Central Pennine Basin, England. The succession below the Grindslow Shales shows an upwards passage from deep basinal mudstones (Edale Shales) into proximal turbidites (Shale Grit).

Fourteen facies have been recognized in the Grindslow Shales and the Kinderscout Grit and grouped into five facies associations. (1) The Slope Association, which forms the lower part of the Grindslow Shales, is a coarsening upwards sequence, sonic 60 m thick, formed of fine-grained sediments deposited from suspension and interpreted as a slope deposit. (2) The Interdistributary Complex Association is also predominantly fine grained though with much more evidence of current activity and with a rapid and random variation in facies. The association forms the upper part of the Grindslow Shales and the finer units of the Kinderscout Grit.

The three other associations are composed of extremely coarse and pebbly sandstone. The first of these, (3) the Deep Fluviatile Channel Association involves three coarse sandstone facies lying in channels up to 40 m. deep, the facies sequence suggesting a waning current. The channels occur over a vertical range of some 60 m in the top of the Grindslow Shales. (4) The Deltaic Sedimentation Unit Association involves medium and large scale cross-bedding, the former always overlying the latter, which is in sets up to 40 m thick. The association represents the fore- and topset components of classical Gilbert-type deltas. This association directly overlies the Deep Fluviatile Channels and occurs at one discrete horizon over the whole area and in other parts of the basin. A sud en deepening is suggested, probably of a eustatic nature (5) The Migrating Fluviatile Channel Association forms the upper part of the Kinderscout Grit, where it is interbedded with units of the Interdistributary Complex Association. It consists of a fining upwards sequence of medium scale cross-bedded sandstone overlying an extensive, horizontal erosion surface, and sometimes passing up into rippled or parallel laminated finer sandstone. This association is interpreted as the deposit of a laterally migrating fluviatile channel.

Comparison of the sequence in the south of the basin with those of areas farther north suggests that the delta slope advanced rapidly during zone R₁c and that the eustatic rise suggested to explain the deltaic sedimentation trails manifests itself in some areas as a marine mudstone which is then overlain by a coarsening upward siltstone sequence.