DEVELOPING A CONCEPTUAL MODEL FOR DE GEER MORAINE ORIGINS IN THE SEACOAST REGION OF NEW HAMPSHIRE

During the last glacial period, the Laurentide ice sheet (LIS) dramatically modified the landscape in New England and produced a variety of erosional and depositional glacial landforms. Previously unrecognized clusters of regularly spaced low-relief ridges have recently been discovered in the Seacoast region of New Hampshire from newly acquired light and detection ranging (LiDAR) data flown in 2010-2011. Based on their morphometry and distribution, these features are interpreted as De Geer moraines that formed during the deglaciation of the LIS. De Geer moraines are widely recognized as products of ice margin retreat in glaciomarine settings, but specific modes of moraine genesis are debated. The goal of this work is to develop a conceptual model for the formation of De Geer moraines in the Seacoast region of New Hampshire. Detailed stratigraphic and sedimentological investigations were conducted on two morphometrically distinct moraines in the towns of Durham and Lee, New Hampshire, in order to reconstruct past depositional environments and emplacement mechanisms. An excavator was employed to dig a trench perpendicular to each ridge crest to examine a cross-section of the deposits. Individual sediment facies were classified and described, and samples were taken for pebble fabric analyses, anisotropic magnetic susceptibility (AMS), and grain size analyses. The ridge in Lee is composed predominantly of massive clay and silt-rich till and sheared Kittery Formation (metasedimentary rock), whereas the ridge in Durham contains friable, graded, sandy/gravely till and angular clasts of the Exeter Formation (diorite). Results from pebble fabric analyses suggest lodgment and meltout till signatures in the Lee and Durham ridges, respectively. AMS results are in progress and will be used to determine if similar preferred orientations also exist within the fine-grained matrix mode of the sediment. Grain size analyses are being conducted to link sediment facies within each ridge to depositional settings and potential formational mechanisms. Outcomes of this project are anticipated to further our understanding of the processes that drive De Geer moraine genesis and provide new insight into glacier dynamics and ice sheet retreat patterns in New Hampshire during the last deglaciation.