MAPPING THE LIMIT OF THE PENOBSCOT RIVER VALLEY CALVING EMBAYMENT, HAMPDEN 7.5' QUADRANGLE, MAINE

The Penobscot River valley of south-central Maine is an area of moderate relief that underwent deglaciation ~14.5 ka. During deglaciation, sea water was ~100 m deep in the Penobscot valley in the Hampden area (W.B. Thompson et al., 1989), and highlands in the southern part of the Hampden area were more than 100 m above the marine limit. Hughes et al. (1985) proposed that calving bays were important in the Gulf of Maine during deglaciation, but this idea has been controversial. According to Lowell (1994), a calving embayment did not develop in the Penobscot valley because the deep-water area was too narrow. Work in the Bangor area has revealed ice-flow convergence toward the Penobscot valley -- strong evidence for a calving embayment (Syverson and A.H. Thompson, 2008). The purpose of this study was to seek ice-flow evidence for the former calving embayment immediately south of Bangor.

As part of a STATEMAP project, we mapped ice-flow indicators on bedrock surfaces in the Hampden 7.5’ quadrangle. Striation sets (showing non-unique flow direction) and crag-and-tail features (showing unique flow direction, rarely seen) were described and measured. Relative ages of these flow indicators were determined using the relative-size criterion. RockWorks99 software was used to plot rose diagrams and determine modal values.

The deepest (hence oldest) flow indicators reveal ice flow toward the S/SE throughout the entire Hampden quad. In the northern part of the map area, ice-flow indicators demonstrate a change from a southerly flow maximum (175^o azi. mode, n=10) to a younger ice-flow event trending WNW/ESE (315^o/135^o azi. mode, n=28). The N/S striae set (165^o azi. mode, n=29) is still present in the southern highlands (>100 m a.s.l. and above the marine limit), but deviations from the flow maximum are rare (n=4) and seem consistent with local topographic control.

In the Bangor area directly to the north, Syverson and Thompson (2008) attributed evidence of westerly ice flow toward the Penobscot River to a calving embayment. The non-unique WNW/ESE flow indicators in the northern part of the Hampden quad likely represent ice flow WNW toward a calving embayment in the Penobscot River valley. The southern highlands of the Hampden quad lack secondary flow indicators and likely mark the southern limit of the Penobscot valley calving embayment.