THE PETROGRAPHY OF THE MANSFIELD MARINE BAND CYCLOTHEM AT TINSLEY PARK, SHEFFIELD

Abstract

Summary The Mansfield (Aegir) Marine Band cyclothem in the Tinsley Park area exhibits the “classical” lithological sequence: marine band, non-marine shale and mudstone, siltstone and sandstone, rootlet bed, coal. Differences between two marine band sections, which occur within a kilometre and a half of one another, are attributed to sedimentological variations across a delta front. Authigenic free silica and clay minerals are quantitatively insignificant compared with the ubiquitous detrital complement. Apart from the well-known non-detrital minerals, pyrite and siderite (as well as a collophanous mineral, and in one section, ankerite), only zircon, rutile and apatite were significant heavy minerals in the marine strata. Other heavy mineral species are more common in the upper part of the cycle. Rutile in the cyclothem is believed to be dominantly (though indirectly) detrital whereas the morphology of apatite is more in keeping with a non-detrital origin. In general, many mineralogical features are consistent with a relatively mature suite of sediments. Brief reference is also made to the possibility that the neighbouring Don Monocline was a developing structure which may have influenced deposition.