CALIBRATING AND UPDATING THE MAINE RELATIVE SEA-LEVEL CURVE IN A SEARCH FOR REGIONAL VARIATIONS IN CRUSTAL RESPONSES

As deglaciation of the Laurentide Ice Sheet occurred, the coastal lowlands of Maine were inundated by glaciomarine mud containing cold-water fauna between 15 and 11 ka (radiocarbon years). Radiocarbon dates from these well-preserved mollusks and barnacles provide constraints on the minimum level of paleo-sea level, but only when closely associated with shoreline and delta deposits can they constrain sea level well. Investigation of these datable fossiliferous localities has a long history, including Bloom (1963), Stuiver and Borns (1975), Belknap et al., (1987) and Retelle and Weddle (2001). Relative sea level fell rapidly from the postglacial highstand to a lowstand ca. 60 m below present 10.8 ka under the influence of isostatic rebound (Barnhardt et al., 1995). Post-lowstand transgression was equally rapid, to an interval of slower change –30 to –20 mbsl 10 ka to 7 ka (Kelley et al., 1992). This interpretation is the result of dated shells from inner shelf vibracores. New data further constrain the timing of the lowstand and onset of the plateau in the curve. The mid-late Holocene transgression is best constrained by data from salt marsh peats, which provide relatively precise indications of MHW. Recent advances in the use of foraminifera to determine paleoenvironments and the use of AMS dating further focus precision of the late Holocene curves (Gehrels, 1994; Gehrels et al. 1996, 2002). We sort the 348 sea-level data points by reliability, calibrate them uniformly, and interpret indicative meaning to a quantifiable error range. Comparison of older published and unpublished data to more complete modern studies is likely to never be totally resolved. However, preliminary results confirm the study by Gehrels and Belknap (1995) that there is no evidence of significant mid-to-late Holocene differential warping along the coast. We are comparing deglacial curves at various locations normal to the known isostatic uplift pattern to determine longer-term along-coast deformations. This detailed analysis ultimately can inform modeling of lithospheric responses on short time and spatial scales such as the margins of the Gulf of Maine for comparison to other regions.