THE ERODED SURFACE OF THE MEDUSAE FOSSAE FORMATION EAST OF AND SURROUNDING APOLLINARIS PATERA

The Medusae Fossae Formation (MFF) is an enormous, easily erodible deposit of likely ignimbritic materials divided into three (Upper, Middle, and Lower) members, located near the Martian equator between 170° and 240° E, and is considered Amazonian in age. This study centers on the MFF west of the Tharsis volcanic center, nearby and surrounding Apollinaris Patera (166° E to 184° E, 4.0° N to -12.6° N). Here we focus on: 1) the orientation and topography of yardang fields within the study area, 2) comparing daylight and night Thermal Emission Imaging System (THEMIS) images of the different MFF members and 3) the topography of the MFF across its three members. We examine these main points to determine the nature of the induration and compositional differences among the MFF members, and their implications as to the overall composition of the MFF.

We utilized THEMIS, Context Camera (CTX), and High Resolution Imaging Science Experiment (HiRise) images to study bidirectional and streamlined yardangs. Both types of yardangs show an array of different topographies, which indicate differences in induration and prevailing wind directions during their formation. We constructed a bidirectional rose diagram for the bidirectional yardangs that yielded frequent trends of 170º and 180º. Then, we plotted the orientations of the less common streamlined yardangs, which had common trends of 0° and 350°. Both types of yardangs appear on all three members of the formation. Using the program JMARS, we compared THEMIS Day IR 100m Global Mosaic and THEMIS Night IR 100m Global Mosaic of the MFF members of the study area. After identifying the members’ borders using the daylight mosaic, we studied the night mosaic for differences in the members’ induration. The Lower member is the most indurated, due to an overall brighter appearance in the night mosaic. Topographically, we found that MFF changes from southeast to northwest in that the Upper member is lowest and the Lower member is highest.