Late pleistocene ice‐wedge casts and sand‐wedge relics in the wyoming basins, USA

• Published in: Permafrost and Periglacial Processes
• Main Authors: Nissen, Thomas C., Mears, Brainerd
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1990
• Subjects: Ice; permafrost; Permafrost and Periglacial Processes; wedge*
• Online Access: http://dx.doi.org/10.1002/ppp.3430010302; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fppp.3430010302; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppp.3430010302

Abstract Previous studies of late Pleistocene periglacial wedge relics in the present‐day steppe environment of the Wyoming plains are supplemented by laboratory analyses of the wedge‐filling materials. Field observations of the wedges now allow the differentiation of ice‐wedge casts, sand‐wedge relics and composite types, as well as epigenetic, syngenetic and polygenetic forms. The wedges penetrate both bedrock and unconsolidated Pleistocene deposits. The poorly sorted clastic wedge‐fills contain secondary pedogenic clays, clasts from abutting host materials and arkosic silty sands derived from late Pleistocene aeolian surficial deposits. Quartz grains in the coarser fractions of the wedge‐fills are well‐rounded and wind‐abraded, reflecting aeolian transport. Quartz particles displaying distinctive conchoidally fractured surfaces become increasingly abundant in the finer sand fractions—a phenomenon attributed to in situ , cryogenic weathering at the microscopic level. The wedges indicate a windswept permafrost environment characterized by thin or minimal snow covers. The abundance of sites where wedges penetrate weathered bedrock is attributed to the ongoing episode of late Cenozoic regional erosion in Wyoming.