Weathering of Quartzite on a Cryoplanation Terrace

• Main Authors: Bernard M. Lauriol, Andre ́ E. Lalonde
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Yukon; Old Crow
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.522.9132; http://www.geographie.uottawa.ca/PDF/blauriol/Lauriol_et_al_(1997)_b.pdf

Sub-horizontal cryoplanation terraces are ideal laboratories to study the weathering of rock in Arctic environments. The terraces are developed in mechanically isotropic rock, are generally not greatly perturbed by gravity processes, and show blocks that have been exposed to the weathering elements for varying time. The terrace studied, herein named the Ptarmigan terrace, is 180 m in length along the slope and occurs in Precambrian chlorite-bearing green quartzite on a mountain to the north of the village of Old Crow (Yukon). The blocks of quartzite on the terrace tread record two distinct weathering events. Near the talus, the blocks show a breakdown of the chlorite and the dissolution of accessory pyrite grains. The results of this first event are the production of a white quartzite with enhanced porosity and the nearly complete leaching of iron from the rock. The second event involves the reintroduction of iron to form rusty-brown rinds that are composed principally of goethite. These rinds increase in thickness with distance from the scarp towards the slope of the mountain. The second event is developed when iron is reintroduced into the porous rocks as water-soluble compounds are drawn into the blocks by capillary forces. Occasionally, a reddish-purple front, presumably composed of hematite, is