Recurrence and Cross Recurrence Plots Reveal the Onset of the Mulde Event (Silurian) in the Abundance Data for Baltic Conodonts

One of the severest perturbations of the Silurian marine environment is the mid-Homerian Mulde bioevent. This event proceeded in several temporal steps, which, according to some authors, implies possible globally synchronous perturbation. The dynamic pace and consequences of these perturbations, as well as their effects on conodont community dynamics, are largely unknown. Here I used so-called recurrence and cross recurrence plots to test the hypothesis of common forcing of the Mulde event on conodont abundance dynamics at the regional scale. The results of the analysis of two Lithuanian sections from the Baltic basin revealed that in the uppermost part of the lundgreni graptolite biozone there was sharp transition in the recurrence patterns. Pre-Mulde Homerian time was characterized by high-amplitude fluctuations and a low recurrence rate. On the other hand, the Mulde interval state was characterized by low abundance and a high recurrence rate with longer horizontal, vertical, and diagonal lines of the recurrence plot, which implies transition to a more ordered (irregularly periodic), stable (laminar) dynamical state. The cross recurrence plot analyses of Lithuanian and Polish core data show a close coherence of this pattern at the regional scale, which is expected for widespread critical transition in ecosystem structure. Additionally, with appropriate regression techniques, cross recurrence plots of conodont abundance allow correlation of sections without prior input from other kinds of stratigraphical information. This shows the potential of conodont abundance as a potent tool in revealing the effects of the Mulde event at the regional scale and coherent dynamical patterns of recurrence that can inform stratigraphic correlation.