TOWARD UNDERSTANDING OF LATE DEVONIAN GLOBAL EVENTS: FEW ANSWERS, MANY QUESTIONS

The Late Devonian was an epoch of dramatic evolutionary and environmental changes linked primarily with the Frasnian-Famennian (F-F) mass extinction. Current contributions support a prolonged, multi-causal nature of the biodiversity crisis, which favors Earth-bound mechanisms rather than a worldwide cosmic catastrophe. The better understanding of the Late Devonian ocean-climate-biosphere system leads to several questions, being an agenda for future research:

1. Magnitude and rank of Late Devonian biotic changes. More detailed biodiversity studies are needed for the widened time framework, because the emerging severity of end-Givetian and end-Famennian extinctions contrasts with the currently overvalued significance of the stepwise F-F crisis.

2. Timing of the key boundaries. A lack of radioisotopic dates hampers any estimation of true biodiversity dynamics, and the integrated comparison with reported ages of impact craters and magmatic events.

3. Marine vs. terrestrial events. Insight into ecosystem changes and correlation should be strengthened by chemostratigraphy, exemplified by the carbon isotope link between marine and land-derived organic matters.

4. Cooling vs. anoxia. Further geochemical evidence is awaited to verify cooling pulses as the main stress factor in the F-F and end-Famennian marine settings, as well as their link to evolving weathering regimes on land.

5. High-resolution (bio)geochemical patterns. Isotope secular trends are poorly known at the intra-zonal and inter-basin scales. These data can also be used as a test of the ‘lag-time’ multiple impacts hypothesis, involving the mid-Frasnian Alamo Impact Event.

6. Near-equatorial vs. high-latitude domains. Refined data from extratropical successions, e.g., from the Kolyma block, are still awaited.

7. Tectonic and volcanic activities. An integrated analysis of tectonic and igneous events, possibly triggered by superplume activity, will serve to evaluate any probable link with the Late Devonian biospheric perturbations.

8. Cyclostratigraphic perspective. This progress includes growing research on magnetosusceptibility and various sea-level signatures to test whether their cause may lie in energy stimuli resulting from the Earth/Sun motions.