ABSTRACT

The mineralogy and texture of the coarser clastic sediments exposed in a 940 feet long core at Smeekley in northern Derbyshire indicate that they are orthoquartzites with subordinate subgreywackes. The most abundant cement is quartz which was precipitated contemporaneously from the dominantly acidic waters at the site of deposition. Calcite, the second most common cement, was a primary precipitate in some cases but, together with kaolinite, has been partially redistributed later. Small, discrete pockets of primary chalcedonic silica and sericitic mica (?illite) also occur. At irregular intervals, the prevalent acid depositional conditions were locally modified probably by decomposing organic matter, to give conditions suitable for the precipitation of the calcite and siderite. Subsequ nt limonitisation of the siderite is the only mineralogical change which has been effected since the deposition of the sediments.