Paper No. 8
Presentation Time: 3:45 PM
NEW FORMATION PROCESS FOR CALCIC PENDANTS, PAHRANAGAT VALLEY, NEVADA
Soil pendants are becoming increasingly important in understanding the evolution of Quaternary landforms in arid and semi arid regions of the world. This study focuses on soil pendants found in five geomorphic surfaces in the northern Pahranagat Valley, Nevada, that range in age from Early Pleistocene to Recent (Q1-Q5) and vary in lithology from dolomite to volcanic tephras. Soils developed upon these surfaces were described, and analyzed using classic field methods and laboratory methods including SEM, EDS, XRD, and petrography to examine the genesis of soil pendants. This study presents a new interpretation for soil pendant development. Key features observed in the Pahranagat Valley pendants provide evidence for precipitation at the clast-pendant contact suggesting that newer deposits may not always be found at the pendant terminus as other studies have suggested. These features include a void at the clast-pendant contact that remains open through pendant growth where precipitates such as calcium carbonate, silica and/or fibrous silicate clays may precipitate. This void area is present possibly due to thermal expansion or freeze-thaw differences between the parent clast and pendant. Other features present in these pendants include significant amounts of parent clast grains that are incorporated into the pendant, detrital grain and parent material displacement and/or dissolution and presence of the fibrous clay sepiolite. These features are found in Middle Pleistocene and older pendants of the study area. This newly proposed formation for soil pendants can explain some problems previously encountered with radiogenic dating of pendant laminae. This study is important to our understanding of Quaternary landforms and thier processes.