ANALYSIS OF SITE STABILITY USING MAGNETIC SUSCEPTIBILITY AND GRANULOMETRY, CENTRAL DELAWARE RIVER BASIN

The Snyder Site Complex consists of multicomponent prehistoric Native American localities situated on landscapes adjacent to the Delaware River. Recent excavations at Site 28WA550 reveal a sequence of laminated deposits with several horizons showing incipient pedogenesis. Low-field magnetic susceptibility (MS) measurements of 30 subsamples (interval: 5 cm) show a peak at 510-551 μSI immediately below the plow zone, with a decreasing trend down-section to 160 cm (stratum XXII; 80-200 μSI range). This trend corroborates MS values measured in situ in an adjacent excavation. The standard deviation in MS values decreases substantially from 139 μSI to 30 μSI below 75 cm depth (stratum VIII). Camsizer granulometric data reveal a narrow mean grain size range of medium sand (1.5-2.2 ϕ), with higher variation below stratum VIII (0.20 vs. 0.09 ϕ). The samples are moderately sorted, with minor silt content. Only four samples show slightly negative skewness consistent with minor winnowing. In contrast, near-symmetrical positive skewness suggest fluvial or aeolian depositional mode. Evidence of landscape stability is corroborated by pedogenic lamelli and higher silt content. Lamelli require some time to develop and represent stable paleo-surfaces that are characterized by greater densities of cultural material. Our study demonstrates the utility of integrated textural and magnetic susceptibility datasets for: 1) resolving fine-scale stratigraphic trends and 2) establishing the basis for correlation with the electromagnetic signal response in georadar images, with an ultimate goal to reconstruct site formation processes marked by alternating phases of landscape stability and active deposition.