Analysis of small-scale erosion data and a sequence of late Pleistocene flow reversal, northern New England

A sequence of latest Pleistocene ice-flow reversal, principally based on analysis of small-scale erosional features, has been reconstructed for northernmost New England. Single and crossing striations, together with small-scale stoss and lee or other erosional forms, provided more than 1,200 widely dispersed striation sets along with relative age data. The striations were grouped into grids from which vector-mean data were extracted and in turn five zones delineated, each characterized by similarities in ice flow. A sequence of six flow direction shifts between and within zones (for example, east-south-east flow gives way to north flow) was determined using a transition matrix of 159 striation sets. Nondirectional striation data, till-fabric measurements, and glacial-dispersal studies further complement the striation information.All these data were integrated to produce a sequence of ice flow that began with (interval A) east-southeast flow of the Laurentide ice sheet through Maine. Interval B involved a reversal of flow direction from eastward to northwestward in northern Maine, with development of an ice divide. During interval C, this divide strengthened and migrated southeastward, so that by interval D it occurred nearly 120 km southeast of the Quebec-Maine border. Interval E encompassed a final northward flow from the northern flank of the Boundary Mountains and the start of rapid, large-scale stagnation of the last glacier of northern New England.