Don Quixote Pond Sediments: Surface and Subsurface Chemistry and Mineralogy

Abstract:

Don Quixote Pond, like Don Juan Pond in the South Fork of Wright Valley, Antarctica, is a model for calcium and chlorine weathering and distribution on Mars. It is located in the western part of the North Fork about 100 m above Mean Seawater Level; its brine is seasonally frozen [1]. Field observations show zones of discoloration which grow lighter with distance from the pond edges.

Four sediment cores, a set of radial surface samples, special surface samples, and samples of local rocks were obtained [2]. We report on chemical and mineral analyses of traverse samples and on two cores. Core DQ20 is a northeastern shoreline core. Its soluble salt concentration exceeds 200 micromoles/g in the top 5 cm, and then falls to less than 70 micromoles/g at the permafrost depth of 15 cm. These concentrations are low when compared to similarly positioned locations at Don Juan Pond and to cores from Prospect Mesa close to Lake Vanda, Wright Valley. Halite, soda niter, tachyhydrite and/bischovite are suggested from the ionic molar relationships

Measured halite concentrations of surface samples, collected along a traverse of 35 m from the pond outwards, range from over 5% to trace amounts, decreasing with distance. Gypsum is also present in almost all of these samples ranging from 0.2% to 2.6%, but does not exhibit a trend. However, in core DQ35, located at a distance of 15 m along the traverse, gypsum decreases from 2.5% to 0.6% from the surface to the permafrost depth of 12 cm.

While DQ35 and radial samples show high quartz and albite abundance, samples that contained visible encrustations and evaporites are low in these minerals and rich in highly diverse alteration products.

Don Juan Basin ponds may have formed by a complex surface water mobilization of weathering products [3] and local groundwater action [4,5]. In contrast, Don Quixote pond mineralogy and chemistry may be consistent with a less complex shallow and deep groundwater system origin [1].

[1] Harris H.J.H. & Cartwright K., 1981, in: Dry Valley Drilling Project, L.D. McGinnis, ed., Antarctic Research Series, 33, 193-214. [2] Gibson E. K. et al., 1983, Journal of Geophysical Research, 88, A912-A928. [3] Dickson J. L. et al., 2013, Sci. Rep. 3: 1166. [4] Englert P. et al., GSA Annual Meeting 2013, abs. T65, 11-4. [5] Harris H.J.H., 1981, Ph.D. Dissertation, Univ. of Illinois.