CONVERGENT ICE-FLOW INDICATORS IN THE PENOBSCOT RIVER VALLEY, BANGOR, MAINE -- EVIDENCE FOR A CALVING EMBAYMENT

The Penobscot River valley is in a moderate-relief portion of coastal Maine deglaciated ~14,000 to 14,500 cal yrs ago (Ridge, 2008). Glaciomarine deltaic sediments indicate sea-water depths ranging from 0 to 100 m in the valley during deglaciation (W.B. Thompson et al., 1989). Because one of the main controls on the rate of calving is water depth, some have suggested informally that a calving bay must have been present in the Penobscot River valley, but this has been disputed. According to Lowell (1994), a calving embayment did not develop in the Penobscot valley because the deep-water area was too narrow. The purpose of this study was to map ice-flow indicators and determine if major changes in ice-flow direction suggest the existence of a calving embayment in the Penobscot River valley near Bangor, Maine.

Flow indicators were mapped in the Bangor quadrangle region as part of a STATEMAP project. Syverson and Thompson (2008, MGS O-F Report 08-52) measured the orientations of 116 striations (non-unique flow indicators) and crag-and-tail features (unique flow indicators). The relative size criterion was used to evaluate ages of flow indicators. Data was analyzed using RockWorks99 to discern ice-flow patterns and calculate vector means. Only unique ice-flow direction data are reported here.

Ice flowed to the south (175° azi. vector mean, n=18) during the oldest event (flow maximum) throughout the map area. West of the Penobscot River, a continuous range of younger flow indicators becomes more easterly (100° azi. flow toward the river). East of the Penobscot River, a younger, robust westerly flow is indicated toward the river lowland (280° azi. vector mean, n=14). Flow indicators between 174° and 280° are lacking, suggesting a rapid change in flow direction. These flow direction changes are in an area with gentle surface slopes, so changes were not caused by ice sliding down the bedrock surface. Westerly flow away from the coast has not been observed previously in this part of Maine and is evidence for a calving embayment.

A narrow calving embayment (<2 km wide) must have existed in the Penobscot River valley near Bangor. Mapping planned for the 2009 field season in the higher-relief Hampden quadrangle to the south will continue to determine the extent of convergent ice-flow indicators and the calving embayment in the Penobscot valley.