Microfossils in Tidal Settings as Indicators of Sea-Level Change, Paleoearthquakes, Tsunamis, and Tropical Cyclones

Abstract: Fine-grained sediments deposited in low-energy, inter-tidal settings are an archive of sea-level change and the occurrence of paleoearthquakes, 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. In this chapter, 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 undergoing uplift. 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. 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.