Description and Genesis of Buried Sand-Filled Soil Wedges Near Flagstaff, Arizona

Abstract

Sand-filled soil wedges developed in buried soils at two sites near Flagstaff, Arizona, are 13-to 30-cm wide at the top, 50-to 80-cm deep, and form nonsorted polygons about 1 to 1.5 m in diameter. These features are smaller than most periglacial (sand and ice) wedges formed in continuous permafrost and larger than most dessication cracks. Size and characteristics of the wedges most resemble those of seasonal frost cracks (primordial soil wedges) formed by intense frost action and/or a combination of frost action and dessication. Such wedges may develop either in the active layer above discontinuous or sporadic permafrost or beyond the permafrost limit in areas where mean annual temperature (MAT) is near 0°C. Thus, occurrence of these features suggest MAT was some 7° to 8°C below that of today during their formation. Distribution of pollen and glacial and periglacial features in the area suggest paleotemperatures were cold enough to produce such wedges during full glacial conditions. Stratigraphic relations and relative degree of development of associated soils suggest the wedges in Flagstaff are of late Wisconsin age whereas those located 34 km north of Flagstaff are pre-Wisconsin in age. [

Environmental change recorded in sediments from the Marmes rockshelter archaeological site, southeastern Washington state, USA

“…If the polygonal cracking in the Harrison horizon noted by Fryxell is a relict periglacial feature, it would imply MAT's of ∼ -5°C. Alternatively, the patterned ground may represent seasonal frost cracks that can form in non-permafrost zones (Karlstrom, 2001). We believe that the isotopic record is correct in that changes in moisture and temperature were relatively small compared to more exposed, upland locations, and that the canyons mediated climatic extremes.…”