Tackling species variation
In palynology, one of the ways to correlate distant sections in different palaeophytogeographic provinces is to use ‘bridge’ taxa – the few taxa which appear to be common to the provinces, despite their other differences. Bridge taxa become very important when there are no other ways to correlate, for example in non-marine sequences with no other fossils, or in sequences that have no dateable ash horizons. The problem is that bridge taxa may not be well described, or that conceptions of them in different palaeophytogeographic provinces may be different where different ‘schools’ of palynology have grown up. Traditional and formal (‘legal’) documentation in scientific journals - with a description, diagnosis and types can help us understand taxa, but not their full variability, their ‘taxonomic distance’ from their nearest neighbours or the way that they ‘grade’ into their taxonomic neighbours. Here we provide a gallery of images of palynological specimens from the Sakmarian GSSP at Usolka that will allow a full appreciation of specimens and taxa found in samples.
The Usolka section was ratified as the GSSP for the Sakmarian in 2020. Palynological samples were taken from the section, and reported on in Stephenson (2017) and then in Chernykh et al. (2020), though due to space constraints a palynological plate was not included. Although palynomorphs in the section are rather poorly preserved there were a considerable number of unidentified specimens, particularly of a suspected algal origin, that may have correlation potential; and there may be value in displaying specimens that could be recognised by palynologists working in other palaeophytogeographic provinces. The Sakmarian is problematic for correlation between Gondwana and Euramerica because its GSSP is based on conodonts which are extremely rare in Gondwana in the Cisuralian (Stephenson 2016).
Chernykh, V V, Chuvashov, B I, Shen, S-Z, Henderson, C M, Yuan, D-X, and Stephenson, M H. 2020. The Global Stratotype Section and Point (GSSP) for the base-Sakmarian Stage (Cisuralian, Lower Permian). Episodes. 2020; 43(4): 961-979.
Stephenson, M H. 2016. Permian palynostratigraphy: a global overview. In: Lucas, S G, and Shen, S Z. (eds) The Permian Timescale. Geological Society, London, Special Publications, 450; 321-347.
Stephenson, M. H. 2017. Preliminary results of palynological study of the Usolka section, location of the proposed basal Sakmarian GSSP. Permophiles, Issue #65, 7-1.