History and current processes of the Martian polar layered deposits

cap;flow;Mars;Martian;polar;stratigraphy;sublimation

Byrne, Shane ; Gurnis, Michael C.

University:California Institute of Technology

Department:Geological and Planetary Sciences

关键词: cap;    flow;    Mars;    Martian;    polar;    stratigraphy;    sublimation;   

Others  :  https://thesis.library.caltech.edu/2232/1/thesis.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

The Martian polar layered deposits constitute a detailed record of geologically recent environmental conditions. In this thesis I examine processes that have affected this history over timescales ranging from $approx10^2$ to $approx10^7$ Martian years. To complete the work in this thesis I developed a geographic database of the Martian polar regions to enable comparisons of different datasets spread over different missions.I report on the discovery of a large sand rich unit underlying the northern polar layered deposits. The presence of this unit suggests there once existed a radically different polar environment where there was no polar cap. A major new question now arises of where that water went during this time period and how the old polar cap (if there was one) was removed.I describe analysis and modeling of evolving landforms on the southern residual CO$_2$ cap. This modeling suggests that these landforms are underlain by a water ice layer. THEMIS observations were used to confirm this hypothesis. This limits the size of the residual CO$_2$ cap reservoir to no more than 5% of the current atmosphere, which puts an important constraint on models of atmospheric evolution. Analysis of the size distribution coupled with this modelingindicates a uniform age for a large group of these features, implying some environmental change on the order of Martian centuries ago.I examined geomorphologic evidence for flow processes at the margin of the south polar layered deposits. Indications of multiple episodes of previous flow are seen. However much evidence of brittle processes such as faulting, slumping and landsliding is also present. This leads to the conclusion that, during some periods, flow of the layered deposits is incapable of relieving the gravitationally generated stresses within the ice sheet. The evidence suggests that periods where flow was possible occurred intermittently and were separated by periods in which sublimation-based retreat of the ice dominated.