HR: 0800h
AN: P31C-0547    [Abstracts]
TI: Possible Glacial Erosion of Interior Layered Deposit Mounds in Central Candor Chasma
AU: * Chapman, M G
EM: mchapman@usgs.gov
AF: US Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001, United States
AU: Dumke, A
AF: Freie Universitaet Berlin, Maltesertr. 74-100, Berlin, D-12249, Germany
AU: Michaels, G
AF: Freie Universitaet Berlin, Maltesertr. 74-100, Berlin, D-12249, Germany
AU: Neukum, G
AF: Freie Universitaet Berlin, Maltesertr. 74-100, Berlin, D-12249, Germany
AB: Within Candor Chasma, there are 5 mesas or mounds (Candor and Baetis Mensae and 3 unnamed mensae to the east) of interior layered deposits (ILDs) that encircle the central Chasma low and have v- and wedge-shaped terminations that point toward this basin. Several datasets (Viking, MOLA, MOC, THEMIS, and HRSC) show features, analogous to glacial landforms, deposited on and carved into these ILD flanks and into the dark materials that embay them and also cover the chasma floor (Chapman et al., 2004, 2005). Five canyons (1 west of Candor Mensa and 4 between the five ILD mounds) are observed to terminate at the floor of central Candor Chasma. West of Candor Mensa, canyon 1 shows a pair of side-bounding ridges that may be possible lateral moraines, one on the west side of the southern mensa horn. This canyon is headed by a 3- forked (or pronged) headwall (centered at about lat 6.5° S., long 74°) that is very similar to analog glacial cirques. More erosional features can be observed up slope from this possible cirque. Canyon 2, between Candor and Baetis Mensae, is bound on the sides by possible lateral moraines and can be traced to a possible cirque on the wall between Ophir and Candor Chasmata. Just below this possible cirque (west of Baetis) the canyon contains a narrow central ridge that may be a medial moraine. Canyon 3, east of Baetis Mensa, shows numerous grooves cut into its floor and eroded, stair-stepped ridges of dark material on the canyon terminus at the central Candor Chasma floor. Analogous terrestrial terminal ridges can form as glaciers shrink and recess back from a point of maximum extent, each ridge may be a depositional end moraine that marks a hiatus in the recession process. Canyon 4, centered at about lat 6.5° S., long 71.4° and between the two unnamed ILD mounds east of Baetis Mensa, is a short hanging wall canyon again bound by sets of ridges (lateral moraines?). Canyon 5, between the easternmost ILDs of central Candor Chasma, shows 2 terraces or valley headwalls (centered at about lat 7° S., long 71.1°) that may be cirques within dark floor material. The ILD mounds bounding this canyon have been sheared off at level heights close to that of the possible cirque headwalls. This shearing is well shown on THEMIS image V10551002 and MOC images: E1700142 and E1900200. Between the sheared mounds, both ILD and dark material in the northernmost canyon floor is cut by grooves that are parallel to the canyon. An area of pits, possible kettle holes formed in dark material, is shown best on THEMIS image V11175002. HRSC topographic measurements indicate that many cross-sections along these 5 canyons have u-shaped profiles. Collectively, cirques, level shearing of ILD rock materials, lateral and terminal ridges (moraines), erosional grooves, and u-shaped canyons can not be formed by any other process than ice erosion and glacial processes. That these possible ice-formed features occur in dark and young (Geissler et al., 1990; Lucchitta, 1990) floor materials indicates that the putative ancient glaciers were relatively very young: an unusual find in equatorial Mars that signals a very different climate from that of the present. We are currently using HRSC DEMs to measure the topographic heights of cirques, shear levels, and medial ridges, to estimate a volume of the possible glacial ice cover in the area.
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 5415 Erosion and weathering
DE: 5416 Glaciation
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting