Formation and Erosion of Layered Materials: Dust Cycle History of Eastern Arabia Terra, Mars

Eastern Arabia Terra is mantled in a layer of dust a few cm to a meter thick, yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine-grained material and a significant amount of erosion. Five craters in this region contain interior mound material that ranges in height from 1600 to 2100 meters above the crater floor. The fluted or yardang erosional pattern and the thermal inertia are suggestive of a weakly indurated material, and the extensive layering implies that these mounds were formed by a repeated process or processes. Although these materials primarily occur within craters, there are materials outside craters that have similar erosional features and fine laminations, suggesting that this deposit was once more extensive. The most likely process to form this material is the deposition and cementation of air-fall dust. This process is potentially related to martian obliquity changes, and may be analogous to processes that formed the polar layered deposits. The significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past tens of millions of years. Currently dust is accumulating in this region in years with planet-encircling dust events, but Global Circulation Model results indicate that dust devils may be removing slight amounts of dust from Arabia Terra. These observations suggest that the thickness of the dust mantle may not be currently increasing. Instead, deposition in years with dust events and dust removal in non-dust event years may result in an overall net balance of dust thickness in the low thermal inertia regions.