Palaeokarst and its implication for the extinction event at the Frasnian-Famennian boundary (Guilin, South China)

A prominent palaeokarst within cyclic peritidal strata reported here at the Frasnian-Famennian boundary in Guilin, southern China, displays karren (scalloped surfaces), dissolution pits and pipes. The last contain residual soil (terra rossa), and are then filled with marine sediment of the overlying strata. The features of the palaeokarst, depth of pipes and amount of missing strata indicate a significant and long-lasting (> c. 50 ka) fall of sea level at the end of the Frasnian. The coincidence of the significant sea-level fall with the first stage of the Frasnian-Famennian mass extinction (which mostly affected shallow-marine and reef-dwelling fauna), and of the subsequent rapid sea-level rise with the second stage of the extinction (which mostly affected deeper-water organisms), reinforces the importance of sea-level change in this mass extinction.