BASAL PEATS AND THE CRITICAL LEADING EDGE OF HOLOCENE TRANSGRESSION

Salt marsh peats provide potentially crucial information for the establishment of detailed Holocene relative sea-level curves. Advances in dating in the 1990’s to present, and establishment of salt marsh foraminifer paleoecological transfer functions have allowed ever-more precise measurement of paleo-sea levels. However, stratigraphic characterization of these marshes remains crucial. Basal peats have been preferred as reliable sea-level indicators since the 1970’s to avoid complications due to compaction. However, basal peats represent the former leading edge of transgression, and may be formed from various brackish and upland fringe environments. Our recent work on salt marshes invading freshwater bogs and brackish marshes in Maine confirm the complexity of this transition. Some other researchers have attempted sea-level curves with within-marsh peats, in detailed reconstructions of vertical relationships within a single core, or closely grouped cores, that often are interpreted as rapidly wiggling sea levels. Our recent work on the surface of Maine marshes lead us to urge caution with this approach, as salt marsh pools and pans have proven to be very active sources of change at the surface of New England-type salt marshes. The growth, expansion, drainage and recolonization of pools on a cycle of only a few decades could be misinterpreted as sea-level changes, unless carefully duplicated at multiple sites on a marsh and within a region. Active pool formation and drainage could also be misinterpreted as tidal creek migration, storm erosion, or other stratigraphic influences. A holistic approach to stratigraphy as well as detailed analysis of samples for floral and foraminiferal paleoecology is necessary to see the full picture of change in these systems