HR: 1340h
AN: P13A-0981    [Abstracts]
TI: Is the Medusae Fossae Formation in southeastern Elysium, Mars, an ice rich deposit, superposing a frozen lake with a polygonal patterned ice crust and adjacent pingos?
AU: * Nussbaumer, J
EM: jurn@nhm.ac.uk
AF: Natural History Museum, Cromwell Road , London, SW7 5BD United Kingdom
AB: The Elysium region near the martian equator is thought to be an area associated with the youngest volcanic, fluvial and glacial activity seen so far on Mars. The relevant geological units are located in southeastern Elysium Planitia and include Aeolis (A), the Cerberus Plains (CP) and the Medusae Fossae Formation (MFF). Parts of the CP are situated at the end of the Athabasca Valles outflow channel and have been previously interpreted as either flood lava or outflow channel deposits. Bright platy material in the CP shows small scale, polygonal ground (MOC m0304228) and pingo-like cones, both are common in terrestrial permafrost. The surface of the platy material is broken up in plates, which sometimes show zoning features features (MOC e1201728), possibly from a sublimation process. The fill of any basin in Elysium would result in a magma or water lake. Clusters of cones are present on the CP, whereas many of these cones are near or eroding out from beneath the MFF or impact crater ejecta (MOC e1200416, m0800090, e1701551). Cones in Elysium planitia have been interpreted as Pseudovolcanoes or pingos. Pseudovolcanoes are formed by phreatomagmatic explosions owing to the flow of lava over wet ground. Terrestrial pingos (conical mounds in permafrost areas) are caused by the freezing and growing of water lenses in the ground. Ice lenses form either from former water bodies and lakes or as abandoned ice from sublimating glaciers. Scars of terrestrial pingos have been found next to former pleistocene ice sheets. The proximity of pingo-like cones to the MFF suggest that the cones accumulate subsequent to the erosion and/or sublimation of the MFF, a process likely related to the presence of permafrost soil. The MFF, previously interpreted as a volcanic airfall deposit, is superposed on the CP and shows drumlinoid, layered, sometimes triangular blade-like features (MOC m0305363, e0400568), interpreted as yardangs. Other explanations include penitents or ablation hollows. Terrestrial penitents are triangular blades, common on glaciers in the dry andes and can get up to 10 m high. They usually point in one single direction and are formed by strong solar rariation. Longitudinal, streamlined and parallel aligned accumulations are concentrated in fields (MOC m2000022) and seem to be the erosional remains of both impact crater ejecta and MFF. The similarity of surficial deposits on both MFF and impact crater ejecta suggests similar formation mechanism. The enhanced ice content proposed here for the MFF is in agreement with the former work of previous authors.
DE: 8404 Ash deposits
DE: 8450 Planetary volcanism (5480)
DE: 5416 Glaciation
DE: 6020 Ice
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting