Geological processes affecting paleolandscape preservation in submerged areas The chronology, rate, and magnitude of relative sea level rise following glacial retreat is a function of the relationship between eustatic flooding, sedimentation and isostatic rebound as a result of glacial melting (McMaster 1984). Initially, the rate of sea level rise in the study area was relatively fast. At about 11,500 B.P., sea level was estimated to have reached a point about 165 ft (50 m) lower than today. Just 1,500 years later, sea level had risen more than 65 ft (20 m) to a level about 98 ft (30 m) lower than present. Therefore at about 10,000 years ago, the coastline off of southern Rhode Island was located near the foot of the large deltaic deposits that we have identified as potential sand and gravel borrow areas. The general trend of rapid sea level rise during this period did not follow a smooth curve, but instead fluctuated and was punctuated by episodes of still-stand and negative sea level oscillations during times of climatic cooling and glacial advance (Xxxxxxx and Xxxxxxx 1980). As glacial ice volumes decreased, the rate of sea level rise gradually slowed. In general, episodes of marine transgression are frequently periods of erosion, a destructive process that creates less than ideal depositional sequences from an archaeological perspective. Marine transgression can be thought of as proceeding in one of two basic ways: 1) by “shoreface” retreat, when the coastline slowly regresses inland; or 2) by “stepwise” retreat, when in- place drowning of coastal features occurs (Waters 1992). Shoreface retreat describes the erosion of previously deposited sediments by wave and current processes as the shoreline transgresses, and is the dominant inundation regime during the marine transgression process (Waters 1992). As the glaciers melted and sea level rose, shoreface erosional zones sequentially passed across the subaerially exposed portions of the harbor floor. Older sediments that had been deposited in coastal and terrestrial environments inland of the shoreline would have been reworked, first by the swash and backwash processes of the beachface, then by waves and currents. The erosion of the shoreface associated with transgression would have reworked these deposits into a thin unconformable geological unit of transgressive lag (i.e., gravel and coarse sand deposits) forming the top of a time-transgressive geological unit known as a marine unconformity (i.e., the surface defined by the top of the buried paleo...
