Archaeological Geology and Postglacial Development of the Central Penobscot River Valley, Maine, USA

The purpose of this interdisciplinary study is to provide a geological and environmental context for the Late Pleistocene and Holocene Native American occupation of the central Penobscot River Valley, Maine. In addition, this work provides a model for the regional synthesis of geological, archaeological, and paleoenvironmental data in order to examine large-scale patterns of archaeological site formation and preservation. The postglacial central Penobscot Valley experienced varied and rapid landscape changes. Withdrawal of the Laurentide Ice Sheet was followed by marine transgression and regression. Subaerial exposure initiated landscape development. The postglacial Penobscot River rapidly excavated a channel through glacial sediments, creating a series of fluvial terraces. Fluvial erosion formed local, bedrock base levels that separated the river from the influence of sea level, trapping coarse-grained sediment within the channel, and initiating fine-grained sedimentation on floodplains, along islands, and at tributary mouths. Localized isostatic adjustment, in the form of a northwestward migrating postglacial forebulge affected local drainage patterns. This included decreasing the discharge of the Penobscot River by shifting the outlet of the state\u27s largest lake, Moosehead, from the Penobscot watershed into that of the Kennebec River. In the areas to either side of the Penobscot River, a combination of low relief and impermeable sediments led to the formation of extensive lakes. Initially unproductive, by the Early Holocene, these lakes hosted a rich marsh ecosystem before vegetational succession produced the peatland-dominated landscape seen today. Native American occupants of the region lived within this dynamic environment, and adapted their subsistence strategies to the shifting mosaic of habitats and resources. This study illustrates that site formation and preservation are strongly influenced by local geology and environment, and that these factors play an important part in the understanding of past lifeways. Additionally, this effort demonstrates the usefulness of regional geological and environmental context in the identification of areas of high archaeological potential, and develops a model applicable to fluvial settings in glaciated terrains, worldwide