Lake Pavin paleolimnology and event stratigraphy

Abstract

In this chapter we present an up-to-date database of sedimentary sequences retrieved from Lake Pavin during the last 50 years in both oxic and anoxic waters. The detailed history of this mid Holocene crater lake can be reconstructed from the correlation of radiocarbon dated sedimentary sequences retrieved from the deep central basin, a subaquatic plateau and littoral environments. High-resolution measurements of sediment composition (diffuse spectral reflectance, XRF core scanning) combined with the analysis of organic matter composition and preliminary pollen and diatom assemblages investigations on selected sediment cores are used to reconstruct (i) the evolution since ca. 7000 cal BP of Lake Pavin limnology together with its radiocarbon reservoir effect and (ii) the impact of a wide range of subaquatic slope failure events. Such a multidisciplinary approach of Lake Pavin basin fill revealed contrasted sedimentation patterns just after the volcanic eruption and following the development of a dense vegetation cover along the slopes of the crater. Pavin sedimentation is rapidly and largely dominated by organic rich and finely laminated diatomite formation, but several short periods of enhanced mineral inputs might reflect the influence of wetter periods, such as the Little Ice Age. Over the last millennium two large subaquatic mass wasting events are also identified and may have significantly impacted its limnology. Four smaller scale sedimentary events related with more limited subaquatic slope failures are in addition identified, dated and correlated with regional historical earthquakes. One slope failure event may be eventually associated with a “moderate” limnic eruption in AD 1783. Since the end of the eighteenth century, enhanced subaquatic slope instabilities (and thus a higher sensitivity to regional seismicity) may have resulted from the perturbation of subaqueous sediment pore pressure after the artificial lake level drop by ca. 4 m.