Quaternary sedimentology east of Thunder Bay, Ontario; implications for five Paleoindian sites

Abstract

A geoarchaeological investigation was north of Highway 11/17, 34km east of Thunder Bay, Ontario. Five archaeological sites (Mackenzie 1, Mackenzie 2, RLF, Woodpecker 1, and Woodpecker 2) and seven additional sediment exposures were examined for stratigraphic analysis to accompany the archaeological excavations. River-mouth sediments at 268m asl and a series of deltas indicate that the study area was subaqueous while placement of the Superior lobe prevented drainage to the Superior basin. This elevation is consistent with Lake Beaver Bay, an ice-contact lake that received glacial meltwater from the north (the Hudson Bay lobe) as well as the south (the Superior lobe). This is demonstrated by southward and northward prograding deltaic sequences within the study area. As the Superior lobe made its final retreat, Lake Beaver Bay dissipated into the Superior basin marking the beginning of the Minong phase, likely around 9,900 14C yrs BP. Additional sequences representing river-mouth, beach shoreface, and deltaic depositional environments indicate that a series of shorelines within the study area represent subsequent Minong lake levels. The highest, and likely oldest of these strandlines is an erosional feature at 256m asl, consistent with wave-cut terraces previously identified in the Thunder Bay region. Relative lake level drops occurred, likely due to a combination of gradual erosion of the Nadoway Point sill and isostatic rebound of the recently deglaciated land. Beach and river-mouth sequences representing subsequent shorelines are located at 249m, 243m, and 240m asl. Artifacts on each of these beach terraces suggest they were occupied by Paleoindian groups.