PRESERVATION POTENTIAL AND SOURCING BY GLACIAL AND PROGLACIAL SEDIMENTS ON THE MAINE COAST

Maine's glaciated coast has been affected by complex sea-level changes over the past 16 kyr. It is similar to New Brunswick, Newfoundland, Northern Ireland and other regions near the margins of former ice sheets. The modern coast and shelf display glaciated morphology and preserve glacial and proglacial sediments. These systems were reworked by coastal and fluvial processes during rapid initial relative sea-level fall from 60-80 m above present sea level 16 ka to 60 m below msl by 12.5 ka. Landforms and sediments were further reworked by littoral processes during the Holocene transgression. Preservation potential was influenced by the rate of sea-level change, as well as by coastal morphology and degree of sheltering. As rate of sea-level change slowed, more reworking occurred, allowing construction of spits, inlets and barriers as the original source was destroyed. The modern coast varies in morphology based on availability of point sources of coarse sediments, inputs of sand, or limitations of these materials that result in muddy embayments and rocky headlands. Much of central and eastern Maine is characterized by a dearth of sand and gravel near the shoreline or available from major rivers, resulting in the present “rock-bound coast” of Maine and its intervening muddy estuaries and embayments. Most Maine beaches are small pocket beaches. Most large sand beaches occur in southwestern Maine, where erosion of outwash plains and transport by rivers brought sand to the coast. The well-developed sandy barriers at the mouth of the Kennebec River arose from reworking of the offshore Kennebec Paleodelta, as well as continuing Holocene input of sand. Saco Bay has a small sandy lowstand terrace system offshore, but during the Holocene transgression its beaches were largely sourced by the Saco River. Wells embayment lies seaward of the sandy Sanford outwash plain, yet it lacks an offshore lowstand sand deposit. The Wells shelf contains preserved minor moraines, reworked to varying degrees into spits and inlet systems. The preservation of these features appears related to a rapid rate of sea-level rise prior to 11 ka at sea levels of -30 to -20 m. Nearshore relict lags of boulders indentify transgressed glacial features that sourced coastal systems for a limited time.