Variations in Layered Deposits at the North Pole of Mars: Stratigraphy Along a Trough and Evidence for CO2 Loss

Details Variations in Layered Deposits at the North Pole of Mars: Stratigraphy Along a Trough and Evidence for CO2 Loss Variations in Layered Deposits at the North Pole of Mars: Stratigraphy Along a Trough and Evidence for CO2 Loss

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p42a..02m&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #P42A-02

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5462 Polar Regions

Scientific paper

The martian polar layered deposits, first observed in Mariner 9 images, are exposed in troughs in the polar caps and are widely considered to be sedimentary deposits of water ice, solid CO2, CO2 clathrate hydrates, and dust in unknown proportions. Studies based on Viking images concluded that the layers record a history of climate changes possibly related to the orbital variations of Mars; the details of the formation processes are still unknown. Observations made by the Mars Orbiter Camera (MOC) onboard the Mars Global Surveyor (MGS) reveal that the layers are thinner and more numerous than Viking images suggested; moreover, the individual layers show considerable variation in thickness, resistance to erosion, and conformity. Comparison of images along a single trough reveals that individual layers may be traced for distances over 500 km. However, stratigraphic comparisons between two regions of layered terrain are often difficult due to surface frost. Examination of high resolution images of individual layers reveal distinctive surface textures including pitted surfaces. The pits may be caused by the exposure of CO2-rich layers at the surface. While water ice is probably a major component of the northern polar cap, we could expect the presence of CO2-rich layers in the form of clathrate layers or layers of solid CO2 with possible admixture of water ice. Such layers could form as deposits of CO2 frost buried by water ice and may be related to climate variations either due to obliquity excursions or to release of volatiles through volcanic activity or groundwater breakout. Under some conditions buried CO2 and H2O ice deposits are likely to be "metamorphosed" to form clathrate. Both clathrate and solid CO2 are unstable at current atmospheric conditions. If CO2-rich layers were exposed in the trough walls, sublimation of CO2 and decomposition of clathrate into gaseous CO2 and water ice would occur. Sublimation and/or decomposition would gradually propagate into the exposed layer until the layer is sealed with water ice. The water ice could be cold trapped due to endothermic sublimation or produced as part of the decomposition of clathrate. Thus, we anticipate bands of local depressions in the trough surface in association with the layers of material unstable at current atmospheric conditions. The pitted layers may be depressions formed by this process.

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