RECONSTRUCTION OF LATE-GLACIAL MARINE PALEOECOLOGY IN NORRIDGEWOCK, MAINE

As the Laurentide glacier retreated north at the end of the last glacial period, central and coastal Maine were flooded by the ocean. Clay deposits in Norridgewock Maine hold a record of abundant mussel, clam, barnacle and other marine fossils that likely lived in a shallow, tidal post-glacial Kennebec “Bay”. But what did this “bay” look like? What can the sediments and faunal assemblages tell us about the deposition in this area? Located in central Maine ~70 km inland from the present shoreline, the fossiliferous muds are located at an elevation of 75m on the western bank of the Kennebec River. Exposed gravel pit faces and ground-penetrating radar data collected show nearshore marine beds prograding towards the Kennebec River. Although much of this site is thinly bedded silts to very fine sands, the fossils are restricted to clay-rich beds at the eastern end of the deposit. The fossil assemblage here is low in diversity, dominated by 6 to 7 species, but they are in high abundance. Some of these fossils include: Mytilas Edulis, Hiatella artica, Trichotropis borealis (Boreal Hairy Shell), and Macoma balthica. The fossils are laterally limited and appear to be concentrated in pockets, finding large quantities in one section but then no fossils just 5 cm away. Microfossils are present in the formation as well but not in large quantities. Microscopic analysis of the sand fraction showed large amounts of angular quartz grains, which may have inhibited microfossil preservation. Taken together, these data indicate preservation of shallow-water fauna in a tidal-flat environment on the margins of a more active fan-delta near the shore of this embayment.