INVESTIGATING THE RELATIONSHIP OF PALEOLIQUEFACTION DEPOSITS TO THE SEDIMENTARY ARCHITECTURE AT A SITE IN THE NEW MADRID SEISMIC ZONE

For this study, we examined paleoliquefaction features at a site in the New Madrid Seismic Zone (NMSZ) near Blytheville, AR. On satellite imagery, light-colored patches appear to delineate the margins of an abandoned channel of the Pemiscot Bayou. In a north-south drainage ditch that crosses the abandoned channel, two exposures corresponding to the light-colored patches were confirmed to be sand blows along the channel margins. Both northern and southern sand blows are composed of two depositional units and are connected to sand dikes that dip towards the channel. The sand dikes crosscut and the sand blows bury predominately silty soils. Weathering characteristics and the number of depositional units suggest that the sand blows formed during the same earthquake sequence. Soil lamellae observed in the southern sand blow indicates that is prehistoric in age. Radiocarbon dating of the soil buried by the northern sand blow provides a maximum constraining age of A.D. 428, suggesting that the liquefaction features formed during the A.D. 900 +/- 150 yr New Madrid event. However, other interpretations are possible and additional dating is needed to constrain the age of the features. Electric resistivity tomography data were collected along two N-S profiles oriented perpendicular to the abandoned channel to evaluate the relationship of the liquefaction features to the subsurface. Data from these surveys confirm that the sand dikes and sand blows, represented by tabular-shaped resistivity highs, formed along the margins of the abandoned channel. The fine-grained portion of the abandoned channel deposit, represented by resistivity lows, likely allowed for the increase in fluid pressure during ground shaking, and the contact between the abandoned coarser-grained channel deposit and the adjacent fine-grained overbank deposit may have guided fluid flow following liquefaction of the coarse-grained portion of the abandoned channel deposit. Cross-cutting relationships of the liquefaction features seen in both ditch exposures are correlated with similar relationships interpreted from the resistivity data. Results of the study contribute to understanding the factors in fluvial environments that control the location of liquefaction deposits and may help guide the search for paleoliquefaction deposits in future studies.