Late Amazonian Glaciation at the Dichotomy Boundary on Mars:
Evidence for Glacial Thickness Maxima and Multiple Glacial Phases
           
James L. Dickson, James W. Head
Department of Geological Sciences, Brown University, Providence, RI 02912 USA,

David R. Marchant
Department of Earth Sciences, Boston University, Boston MA 02215 USA

Submitted to Geology, 27 August 2007

 View flyover (161.2 MB)

Multimedia File 1. This flyover is located in the Protonilus Mensae region at the dichotomy boundary of Mars, a scarp and set of massifs that define the boundary between the northern lowlands and the southern, heavily cratered uplands.  The flyover starts from above the north lowlands (41N, 305W) and provides a perspective view toward the isolated massifs and dichotomy boundary to the south.   In the foreground, at the valley incised into the mesa, is a lobate deposit interpreted as the remnant of a debris-covered glacier.  Notice how the distal margins of the glacier superpose the regional Lineated Valley Fill (LVF) deposits, themselves interpreted to be the remnants of a valley glacial landsystem. We then fly over the mesa and observe on the far valley wall across the valley a lobate glacier-like deposit that flows into, and terminates in, an elevated box canyon (~5 km across) to the south.  We interpret this feature to be a remnant of peak glacial activity (~2 km in total thickness) that filled the adjacent valley to the north and underwent significant sublimation and flow-reversal to yield the present-day deposits.  We then turn in place to the east to highlight the LVF deposits.  On the other side of the valley, another lobate deposit interpreted to be a remnant of a debris-covered glacier (with a terminal moraine) is seen superposed on the broader texture of the LVF.  As we move back from the valley, additional tributary-glacier systems are seen interacting with the broader LVF deposits, and the lobate glacier to the south that appears to have flowed uphill.  The present configuration suggests that the glacier level was once at the top of the lobe in the box canyon, about 920 meters above the current elevation of the LVF in the valley floor, and that the level was lowered by this amount in the terminal phases of this glaciation.  The debris-covered glacial-like lobe superposed on the LVF texture is evidence that a less extensive glaciation returned at a later time.  Image data from Mars Reconnaissance Orbiter CTX image P01_001570_2213_XI_41N305W, draped on Mars Express High Resolution Stereo Camera Stereo DTM from orbit h2908_0000.