New foraminifers in the Visean/Serpukhovian boundary interval of the Lower Limestone Formation, Midland Valley, Scotland

Abstract

The biostratigraphy of the upper part of the Mississippian Lower Limestone Formation in the Midland Valley, Scotland is revised using foraminiferal assemblages. This formation was previously assigned exclusively to the upper part of the Brigantian Substage (upper Cf6δ, P2or latest Visean), whereas the succeeding Limestone Coal Formation (barren of foraminifers and conodonts) was assigned to the Pendleian Substage (lower Cf7, E1or early Serpukhovian). The foraminifers, in particular those recorded from the Second Hosie and Top Hosie limestones and their lateral equivalents (Anvil and MacDonald limestones), are comparable to Serpukhovian assemblages from the Ukraine and Russia. Consequently, the Visean/Serpukhovian stage boundary is repositioned at the base of the Second Hosie Limestone. This assignment of the Second Hosie Limestone to the Pendleian is reinforced by the first occurrence of the ammonoidEmstites(Cravenoceras), although it occurs 1 m below the Top Hosie Limestone. Pendleian foraminiferal assemblages from northern England, its geographically closest equivalent, are similar but not well enough known for a detailed comparison. A few similarities are found between the foraminiferal assemblages from the Midland Valley and those from southwest Spain and North African basins. Faunas from the Second and Top Hosie limestones and their lateral equivalents allow us to propose an assemblage zone, valid for regional correlations within the British Isles, and the faunas can be potentially used as Serpukhovian markers for western Paleotethyan basins. Two new genera and species are described,Praeplectostaffella anvilensisn. gen. n. sp. andPraeostaffellina macdonaldensisn. gen. n. sp., and two new species,Tubispirodiscus hosiensisn. sp. andEuxinita pendleiensisn. sp.