Bayesian analysis of ultra-high-resolution ostracod record reveals the tempo and structure of the late Wenlock Mulde Event

The late Wenlock Mulde/lundgreni Event or the ‘Big Crisis’ was one of the most significant extinction events, sea level regressions and global carbon cycle perturbations of the early Palaeozoic. It was first detected in graptolite and conodont fossil records which represent the pelagic realm. The impact of the event on benthic communities is less understood, and the overall understanding of the community collapse and recovery suffers from lack of resolution. Here we present an ultra-high-resolution (<10 Ka) record of benthic ostracod assemblages from the shelfal zone of the Silurian Baltic Basin (Lithuania). This record is segmented using newly developed time-contiguous community clustering algorithm which revealed the stages of collapse and recovery. The Bayesian geochronology approach constrained the most probable duration of event to 260 Ka, which suggest half an order of magnitude shorter duration than previous estimates. The collapse leading to and recovery from the Mulde/lundgreni Event happened on time scales of tens of thousands of years. This sharp event did not result in apparent ostracod extinctions; it caused the state shift in their biodiversity metrics and their relation to abundance. This pattern implies the transition of ecosystems through a critical tipping point to an alternative community assemblage pattern in the mid-Silurian.