Radar-stratigraphic and modeling evidence for growth and episodic retreat of the north polar layered deposits, mars




Дата канвертавання17.04.2016
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RADAR-STRATIGRAPHIC AND MODELING EVIDENCE FOR GROWTH AND EPISODIC RETREAT OF THE NORTH POLAR LAYERED DEPOSITS, MARS.

Holt, J.W., Greve, R., Brothers, T.C., Smith, I.B. and Phillips, R.J. University of Texas Institute for Geophysics, 10100 Burnet Rd. Bldg. 196, 512-471-0487, jack@ig.utexas.edu


PRESENTATION PREFERENCE: Oral
PRESENTING AUTHOR: J.W. Holt
The North Polar Layered Deposits (NPLD) of Mars have long been considered to contain an important record of recent climate; however, age constraints and links to orbital forcing have not been established. A global ice accumulation model using orbital parameters since 10 Ma to drive surface temperature and ice mass balance predicts growth of the NPLD only after ~4 Ma, interrupted by 2-3 significant retreat events, and that the past ~0.5 Myr has been characterized by net deposition. Internal radar stratigraphy from SHARAD on Mars Reconnaissance Orbiter has revealed a history of accumulation and erosion that is quite consistent with this model. After the onset of broad NPLD deposition, two (or possibly three) major erosional episodes are evident from truncated radar reflectors mapped over large areas. An early erosional episode is associated with the initial formation of Chasma Boreale, which persisted through later deposition. A later episode caused significant retreat of NPLD margins, but little or no erosion in the interior. Subsequent reflectors that drape the upper erosional surface provide evidence for essentially continuous deposition since that time. This self-consistent scenario can be tested further by considering (1) observed longitudinal asymmetries in patterns of both deposition and erosion, (2) apparent periodicities of radar reflector properties within depositional sequences, and (3) the climatic processes required for the onset and migration of spiral troughs as constructional features.
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