干旱区生态环境知识资源中心

We describe the morphology and spatial relationships between composite-wedge polygons and Mars-like gullies (consisting of alcoves, channels, and fans) in the hyper-arid Antarctic Dry Valleys (ADV), as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground. Gullies in the ADV arise in part from the melting of atmospherically derived, wind-blown snow trapped in polygon troughs. Snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions. Ice-cemented permafrost provinces an impermeable substrate over which meltwater flows, but does not significantly contribute to meltwater generation. Relationships between contraction crack polygons and sedimentary fans at distal ends of gullies show deposition of fan material in polygon troughs, and dissection of fans by expanding polygon troughs. These observations suggest the continuous presence of meters-thick ice-cemented permafrost beneath ADV gullies. We document strong morphological similarities between gullies and polygons of Mars and those observed in the ADV Inland Mixed microclimate zone. On the basis of this morphological comparison, we propose an analogous, top-down melting model for the initiation and evolution of martian gullies that occur on polygonally-patterned, mantled surfaces. (c) 2009 Elsevier Inc. All rights reserved.