GEOARCHAEOLOGY AT LEETSDALE: RECONSTRUCTING PREHISTORIC LANDSCAPES OF THE UPPER OHIO VALLEY

The Leetsdale prehistoric site preserves a multi-component archaeological and alluvial stratigraphy on the third terrace (T-3) of the Upper Ohio River. This presentation reconstructs the terminal Pleistocene through Late Holocene history of the landform. We propose an allostratigraphic framework to incorporate key changes in the alluvial chronology of the site landscape, while simultaneously integrating the archaeological and paleoenvironmental signatures of the individual phases of occupation (Early Archaic to Euroamerican contact). The terminal phases of the Pleistocene are registered by coarse channel fills and sediment distributions indicative of a braided stream aspect. By Early Holocene times, channel geometry remained dynamic as the stream featured a meandering pattern with fining upward sediment sequences and weak and thin A-C soil profiles. The basal cultural features (Middle Archaic) are linked to the latter stages of migrating channel activity. The general geometry of a permanent channel trench, with attendant (overflow) back channel took form after 6000 B.P., as the terrace evolved into high and dry ridge overlooking the channel trench. Low frequency high discharge events and more sustained intervals of overbanking resulted in vertical accretion. The evolving Holocene T-3 sustained a series of short to medium term paleosols with underlying Bt and Bw horizons; parts of the landform demonstrate the presence of "welded" and/or multi-story soils, most of which house cultural deposits of the Middle Holocene and Late Archaic periods. The back channel appears to have been utilized as an aquatic resource for diverse groups of Late Archaic residents. Evidence for Middle Woodland through Euroamerican occupation are contained within the upper 0.5 to 1.0 m of the T-3 and also account for terrace segments inset within the T-3. The alluvial constructs are incorporated into a paleo-circulation paradigm that links circulation to Holocene fluvial dynamics and proposes that the prehistoric settlement and preservaion records are indicative of broader human ecological patterning for much of the Ohio Valley.