Quantifying the community turnover of the uppermost Wenlock and Ludlow (Silurian) conodonts in the Baltic Basin

The Homerian to Ludfordian interval of the mid to late Silurian Period was a time of significant changes in conodont communities, global climate, oceanographic patterns and biogeochemical cycles. The Mulde and the Lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in Earth's history. The Silurian Baltic Basin is the most suitable locality, globally, for studying these perturbations to the ocean-atmosphere system, since there is an extensive record of conodont taxa occurrences, their communities, and their environments spanning across shore-face to open-ocean settings. In this study, we present new conodont and δ13C data from the upper Homerian to Ludlow interval from two core sections – Gėluva-99 and Gėluva-118, representing shelfal environments, and the numerical conodont data from the Viduklė-61 section, from deep-water settings, and compare them with patterns of conodont diversity change, as revealed in the data-rich Milaičiai-103 core section. For this purpose, we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross-recurrence plots – the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns. The cross-recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms. The results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records. Moreover, the sudden state transitions detected in the cross-recurrence plots suggest that the Lau Event was of great importance for conodont community evolution in the studied time slice.