QUATERNARY GEOLOGIC MAPPING IN RHODE ISLAND: UNDERSTANDING GLACIATED TERRAIN AT THE MARGIN OF LAURENTIDE ICE

Rhode island is uniquely situated at the southeastern margin of the Late Quaternary Laurentide Ice Sheet with a rich Late Wisconsinan record of glaciation and deglaciation. To better understand this record, Quaternary geologic mapping in Rhode Island, in cooperation with the StateMap program, is proceeding at two scales: high-resolution 1:24,000 and a more regional 1:100,000. Mapping is closely integrated with, and uses elements of, the RI Geographic Information System (RIGIS) and borings from the RI Department of Transportation (RIDOT). All map products will be digital using a combination of MapInfo®,ArcView®,and ArcInfo®. Metadata will be compliant with federal FGDC standards. High-resolution geologic mapping uses the morphosequence concept, associated groups of landforms and stratigraphic sequences deposited by glacial meltwater, to provide a basic map, correlate deglacial events and to construct a geologic history of specific areas. Regional mapping makes use of previously mapped (7.5 minute) USGS quadrangles, plus new detailed and reconnaissance mapping, to construct a deglacial history of the state. A cooperative program with RIDOT is constructing a digital database of boring logs for state, federal and some local projects for selected areas of the state. These boring logs will then be used to construct cross-sections and isopach maps of sand and gravel thickness. An important part of the regional mapping is the use of archived seismic reflection records, and new borings, to carry mapping into Block Island Sound, parts of Rhode Island Sound and Narragansett Bay. An important final product will be a Quaternary geologic map of the state at a scale of 1:100,000 that includes the geology of the Sounds and the Bay to provide a complete three dimensional picture of glacial deposits at this southeastern margin of Laurentide ice.