ANALYSIS OF TWO BURIED SOIL PROFILES ON THE MARGIN OF A SAND BLOW NEAR PORTLAND, ARKANSAS

Buried soils provide relative age constraints and paleoenvironmental information for paleoseismic investigations of liquefaction. A series of buried soils are identified in trench studies of liquefaction features in southeastern Arkansas. In this study, two buried soils and a modern surface soil were described in a 25-meter long trench near Portland, Arkansas. Analysis of grain-size distribution, carbonate content and clay mineralogy are being completed to determine origin of the soils. The data are interpreted in relation to multiple liquefaction events. The field data indicate presence of a surface soil overlying at least two buried soils. The surface soil is a silt loam and shows weak horizon development. The first buried soil is a clay-rich silt loam, shows weak Bt horizon development, and contains numerous silty sand-filled fractures. The second buried soil is a silty clay loam to clay, shows stronger horizon development, and is broken and brecciated. Color, carbonate content, fracturing and brecciation, and average grain size distribution vary between the north and south ends of the trench. Radiometric dating suggests the oldest buried profile is as much as ~5ka. The red clay content, extensive slickensides, and carbonate accumulation are consistent with vertic soil development, possibly under alternating wet and dry conditions. The middle profile is considerably younger and shows soil development more typical of an inceptisol or weak alfisol. This soil is formed from silt-rich parent material typical of late Holocene soils in the region. The middle profile in the southern part of the trench contains less carbonate and more gley colors than that of the profile in the northern part of the trench. The surface soil is a weakly developed inceptisol formed on silty blow sand. The results suggest that multiple liquefaction events affected soil development in the upper buried soil by causing poorly drained conditions in the area of the southern part of the trench and better-drained conditions in the area of the northern part.