Northeastern Section - 53rd Annual Meeting - 2018

Paper No. 44-6
Presentation Time: 1:30 PM-5:30 PM


BEATON, Andrew and HUBENY, J. Bradford, Geological Sciences, Salem State University, 352 Lafayette Street, Salem, MA 01970

The deglaciation of New England is well constrained through studies that have utilized chronologic strategies such as radiocarbon dating of lake sediment, glacial lake varve counting and cosmogenic nuclide exposure age dating. Despite our current state of knowledge, spatial gaps remain in locations in which chronologic data are lacking. Northeastern Massachusetts (NE MA) is one such region with little direct geochronologic control. Work from Southern New England and Maine have constrained ice retreat in NE MA to between 18,600+/-400 and 14,582+/-1077 cal years BP, respectively, however detailed ice marginal temporal constraints are lacking in NE MA. To better constrain the deglaciation of NE MA, Dogtown Moraine was studied. The moraine is a prominent end moraine located on Cape Ann, MA, with pronounced exposures within Dogtown Commons, Gloucester, MA. This region was previously mapped (Stone et al., 2006) and the surficial geology interpreted. We revisited exposures of the Dogtown Moraine and conducted additional fieldwork to identify suitable boulders for cosmogenic nuclide dating. Three specific boulders were identified as excellent candidates based on geomorphic context and position, suggesting that they have not moved since their deposition. They each displayed minimal erosion and post-depositional glacial features. All boulders were identified as granites and dimensions ranged between approximately 2 to 4 meters in length and 1 to 3 meters in height. The top surfaces of the boulders were free of significant accumulation of sediment and debris and represented the most elevated surfaces in their immediate vicinities. We decided to analyze three boulders to assess chronological precision. The upper 2 cm of the top exposed surfaces of these boulders were sampled using a diamond encrusted drill bit and a hammer and chisel. Sample masses were chosen to ensure adequate 10Be concentrations based on quartz content, elevation, and hypothetical exposure age. Samples were prepared to isolate quartz from the other rock components and will be oxidized to BeO for analysis. Pending Accelerator Mass Spectrometer analysis 10Be concentrations will provide constraints on the age of the Dogtown Moraine, and subsequently the deglaciation of this region of New England.