Bearnstow’s Geological History, from 20,000 Years Ago

By Julie Brigham-Grette and Daniel Miller, Department of Geosciences, University of Massachusetts–Amherst

Around 20,000 years ago, the Laurentide Ice Sheet covered a vast area of northern North America, including almost all of New England. In Maine, the timing of glacial retreat can be can be estimated from various land­scape features and through the use of radiocarbon dating of certain rem­nants of marine shells. Through this work, scientists have estimated that glaciers retreated from southern and central Maine roughly 14,500–12,000 years before present.1

The glaciers had scoured the land and pro­duced basins that would eventually become the many ponds and lakes we enjoy in our region today. Furthermore, since the land was de­pressed from the weight of the ice, the ocean moved inland with glacial retreat. There is evidence that the ocean reached far­ther inland than Parker Pond, meaning that this area was likely sub­merged underwater for a brief time period.2 (See the red dot on the map to locate Parker Pond.) The Presumpscot Formation is the name given to the marine muds that were deposited during this time (the clay in the bed of our own Uncle Daniel’s Brook was laid down at this time).3

After this brief period of time, most likely less than 2,000 years, the land started to rebound and rise above sea level. Following this, vegeta­tion slowly migrated northward, shifting from tun­dra to a heavily forested landscape from roughly 10,000 to 7,000 years before present.4 Since then, the landscape has undergone compar­atively little change until modern times and European settlement of the region.5

References:

1. Borns Jr., H.W., Doner, L.A., Dorion, C.C., Jacobson Jr., G.L., Kaplan, M.R., Kreutz, K.J., Lowell, T.V., Thompson, W.B., Weddle, T.K., 2004. The deglaciation of Maine, U.S.A., in: Gibbard, J.E. and P.L. (Ed.), Developments in Quaternary Sciences, Quaternary Glaciations-Extent and Chronology Part II: North America. Elsevier, pp. 89–109.
2. MGS, 2010. Evidence for a Calving Embayment in the Penobscot River Valley, Bangor Mane. Maine Geological Survey. Evidence for a calving embayment in the Penobscot River Valley, Bangor, Maine.
3. Maine Geological Survey. 2000. A General Introduction to the Presumpscot Formation: Maine’s “Blue Clay.”
4. Davis, R.B., Jacobson Jr., G.L., 1985. Late glacial and early Holocene Landscapes in northern New England and adjacent areas of Canada. Quaternary Research 23, 341–368. doi:10.1016/0033-5894(85)90040–7.
5. Anderson, R.S., Jacobson, G.L., Davis, R.B., Stuckenrath, R., 1992. Gould Pond, Maine: late-glacial transitions from marine to upland environments. Boreas 21, 359–371. doi:10.1111/j.1502–3885.1992.tb00040.x.