MICROFOSSILS IN TIDAL SETTINGS AS INDICATORS OF SEA-LEVEL CHANGE, PALEOEARTHQUAKES, TSUNAMIS AND TROPICAL CYCLONES

Fine-grained sediments deposited in low-energy, inter-tidal, settings are an archive of sea-level change, and the occurrence of paleo-earthquakes, tsunamis and tropical cyclones. Some of the best reconstructions of these coastal processes have been derived from microfossils such as pollen, diatoms and foraminifera that accumulate in salt-marsh and estuarine environments. Early microfossil work in the coastal zone employed pollen as an indicator of vegetation and as a chronostratigraphic marker. Use of diatoms and foraminifera has become increasingly widespread because their distribution is closely linked to tidal elevation. Here, we discuss the use of microfossils in estuarine and salt-marsh sediments to reconstruct sea level along subsiding coastlines in temperate regions. We also describe how microfossils from isolation basins are used to reconstruct sea level along coastlines experiencing uplifting coastlines. Microfossils can also estimate land-level changes along tectonically active coasts associated with paleoearthquakes. We explain the use of transfer functions for calculating quantitative estimates of past environmental conditions from microfossil data. Accurate and precise RSL reconstructions permit tide gauge and satellite altimetry-based measurements to be evaluated in the context of longer term changes. Finally, we reveal how microfossils are used to reconstruct the recurrence of tsunamis and tropical cyclones from the sedimentary deposits these high energy events leave behind. Coastal risk assessment and hazard mitigation requires datasets on centennial and millenial temporal scales to capture natural variability and multiple occurrences of the largest, but least frequent events.