THE PALYNOLOGICAL RECORD OF LAKE SEDIMENTS AND APPLICATION TO PALEOSEISMOLOGY (Invited Presentation)

Eastern North America is an intraplate region characterized by potentially damaging earthquakes with long recurrence intervals. Seismic risk, however, is difficult to assess because of short historic records, and there are few confirmed post-glacial faults. The abundant lakes in the region are natural archives of post-glacial sedimentation. The deep basins of lakes are typically comprised primarily of organic matter fixed by aquatic algae and their consumers, with small quantities of biogenic carbonates or silica and aeolian mineral particles disseminated in gyttja. Analysis of historic seismic events has shown that sudden increases in allochthonous sediments (together with fossils of terrestrial and shoreline origin in deep-water sediments) characterize sudden-onset events such as mass transport and seiches. The acid-resistant component of sediments (both the identifiable remains of organisms, i.e., palynomorphs, and the particulate and amorphous organic matter that constitute the palynofacies) can reflect the sudden influx of allochthonous materials to deep lake basins. Regional pollen stratigraphies allow the ages of these sudden influxes to be estimated, and if coeval events can be identified in multiple lakes, a common regional-scale trigger – such as paleoseismicity – can be inferred, extending the record beyond the relatively short historic period in eastern North America.