Lineated valley fill at the Martian dichotomy boundary: Nature and history of degradation

Kurzfassung

The fretted terrain of the Martian dichotomy boundary is a key region for investigating landforms related to creep of ice and debris as it exhibits landforms comparable to morphologies of periglacial environments. Although features known as lobate debris aprons, lineated valley fills and concentric crater fills have been studied in great detail, basic questions concerned with the composition and the style of emplacement and degradation still remain unanswered. This study focuses on morphologies which are located in a near�circular depression located at the dichotomy escarpment in Deuteronilus Mensae. Analysis of high�resolution image data suggests an early formation of these features as the result of backward thermokarstic degradation of highland terrain. Geologically younger processes caused deposition and degradation of an ice�rich mantling deposit, which ultimately led to formation of creep morphologies that might have even been active in the geologically recent past. Intermixing of both degradational landform units form complex patterns that cannot be explained by a late stage (glacial) process alone. Morphological comparisons of lineated valley fill units with concentric crater fill landforms in Utopia Planitia strongly suggest comparable emplacement and degradation styles of these features. The sequential development consisting of an initial probably widespread thermokarstic degradation followed by later cyclic deposition of volatile material and continual thermokarstic degradation suggests that the development of parts of the Martian fretted terrain is directly related to climatic variations in the planet�s history.