Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p21d..06w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P21D-06
Physics
[0774] Cryosphere / Dynamics, [5416] Planetary Sciences: Solid Surface Planets / Glaciation, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Gemina Lingula (GL) on the North Polar Layered Deposits of Mars is an exceptionally interesting location, due in part to the recent discovery by radar of an earlier deposit underlying the present ice lobe, and due to evidence for past ice flow based on its surface topography. It has been claimed, however, that any past ice flow would have 'erased' the subsurface stratigraphic unconformity observed by radar, and thus that past ice flow is ruled out observationally. More precisely, the claim appears to be that discontinuities in layer slopes that define the unconformity would be diminished (below some detection threshold) by ice flow on a time-scale less than or equal to the time-scale of equilibration of surface topography by flow. Here we examine this claim quantitatively, using an extension of the ice flow model that accurately fits present-day topography between troughs on GL. We find that, because magnitudes of ice velocities decrease with increasing depth, time-scales for altering layer-slope discontinuities at depth exceed those for surface equilibration (which are governed primarily by near-surface velocities). We thus quantify, in a variety of scenarios, a time-interval during which surface topography characteristic of a flowing ice mass co-exists with only slightly modified pre-existing near-basal stratigraphy. This range of times can be especially large near topographic ice divides, which is precisely where the largest thickness of the older deposit is observed. We therefore conclude that observed radar stratigraphy is in fact consistent with more recent ice flow as indicated by inter-trough surface topography. Finally, we discuss how the presence and characteristics of the older deposit may help to constrain the duration of past ice flow.
Pathare Asmin
Waddington Edwin D.
Winebrenner Dale P.
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