Pleistocene and Holocene glacier thicknesses, transport histories and dynamics inferred from SEM microtextures on quartz particles

Abstract

Recent analyses of microtextures on quartz particles (63–2000 μm) from Quaternary tills in Antarctica, Germany, southern Ontario, western Wyoming, Tibet, the Austrian Alps, and Mount Kenya show that glacial fracture and abrasion microfeatures may be used to infer the thickness, transport history and ice dynamics of Pleistocene and Holocene glaciers. Quartz sands emplaced by continental and mountain ice were studied by SEM after transport over variable distances in glaciers estimated to range from 150 m to 1500 m in thickness. Relative differences in ice thicknesses, distances of transport, and/or ice dynamics appear to have determined the frequency of occurrence and type of microtextures occurring on sand‐size particles. Subparallel fracture microfeatures tend to increase in frequency over a greater proportion of particle surfaces with increasing ice thickness and distance of transport. Conchoidal fractures, the most typical in quartz, and to some degree crescentic gouges abound on fragments emplaced by continental ice. Other possible fracture and fragmentation mechanisms, producing features of generally glacial origin, involve low velocity impacts induced by stick‐slip mechanisms, under variable cryostatic stresses, producing fracturing and abrasion across particle surfaces. Their generation implies high local contact stresses associated with high strain rates.