The Drewer quarry located in the Rhenish Massif is a well-studied outcrop that comprises Upper Devonian (Famennian) to Lower Carboniferous (Viséan) strata. Within the Drewer deposits two black shale intervals have been described that are linked to two global oceanic anoxic events, the Hangenberg Event and the Lower Alum Shale Event. The black shales associated with the Middle Tournaisian Lower Alum Shale Event contain abundant phosphatic concretions, which were investigated using thin section petrography, powder X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy. The concretions formed during several growth phases under anoxic and at least episodically sulphidic conditions within the sediment and served as a substrate for subsurface microbial mats that formed phosphatic microstromatolites. The microstromatolites occur either as partially branched columns of up to 600 µm in length attached to the phosphatic concretions or as smaller, bulbous aggregates surrounding the concretions. Element mapping identified the presence of pyrite and other metal sulphides within the phosphatic microstromatolites. The carbon and oxygen stable isotopic composition of phosphate-associated carbonate within the phosphatic microstromatolites suggests that the mat-forming microorganisms were probably anaerobic, chemotrophic microbial communities dwelling in the anoxic environment during the Lower Alum Shale Event. Such interpretation agrees with the deeper-water depositional setting of the Lower Alum Black Shale and its high content of organic matter, suggesting that chemotrophic microbial mats are potent agents of phosphogenesis in general, and of the formation of phosphatic stromatolites in particular.

In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the Devonian–Carboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper ‘ORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the Devonian–Carboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.

This paper is a contribution to the redefinition of the base of Carboniferous system. At present the criterion for the definition of the Devonian–Carboniferous boundary is the first occurrence of a conodont species. In order to evaluate the stratigraphic potential for new criteria for the definition of the Devonian–Carboniferous boundary, the distribution of conodont species of Bispathodus, Branmehla, Palmatolepis, Polygnathus, Protognathodus, Pseudopolygnathus and Siphonodella across the boundary is presented and discussed. An updated biozonation scheme across the boundary based on the First Appearance of Bispathodus ac. aculeatus, Bispathodus costatus, Bispathodus ultimus, Protognathodus kockeli, Siphonodella bransoni and Siphonodella duplicata is proposed, and it is suggested that the new criterion for the definition of the base of the Carboniferous system be the First Appearance Datum of Pr. kockeli or Si. bransoni.