Paper No. 5
Presentation Time: 2:45 PM
THE MIRACKINA PALEOCHANNEL IN SOUTH AUSTRALIA AS AN ANALOG FOR PAIRED SINUOUS RIDGES ON MARS
WILLIAMS, Rebecca M.E.1, IRWIN III, Rossman P.
1, MCCLELLAND, Phillip
2 and BURR, Devon M.
3, (1)Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, (2)Ultramag Geophysics Pty Ltd, 21 Cowmeadow Road, Mount Hutton, 2280, Australia, (3)Earth and Planetary Sciences, University of Tennessee, 306 Earth and Planetary Science Building, 1412 Circle Dr, Knoxville, TN 37996-1410, williams@psi.edu
The Mirackina paleochannel, located north of Coober Pedy in South Australia, is a dendritic network with meandering course that preserves the flow path (>200 km) of an Early Miocene river in inverted relief. The landform is extensively dissected and segmented by erosion and is now defined by a line of ridges and mesas with 30-40 m relief above the surrounding plains. The upper portion of the ridges is massive sandstone that is variably cemented by silica and iron oxides. Cross-bedded, medium to coarse-grained quartz sandstone, with occasional centimeter-scale silcrete nodules, is observed on vertical exposures 5-10 m from the ridge crest. Prior investigations concluded that the channel margins were locally cemented by silcrete from groundwater discharge at springs, whereas the central channel fill was largely uncemented and has been removed by erosion. The resulting morphology is intermittent, paired ridges that outline much of the former flow path, with the channel remnants dipping towards the channel center.
Study of terrestrial inverted channels is important for identifying distinguishing attributes to evaluate and interpret sinuous ridge networks on Mars, many of which are interpreted as fluvial deposits preserved in inverted relief. In particular, the twin ridges of the Mirackina paleochannel provide a terrestrial analog for sinuous ridges on Mars with paired ridges, two of which are located in the Aeolis/Zephryia Plana (AZP) region. One of these examples was previously interpreted as an esker based in part on rounded morphology and elevation variations in the longitudinal profile. However, this explanation was always problematic given the absence of additional evidence for glacial activity in the region. A HiRISE stereo anaglyph (~1 m/px) reveals twin ridges that define portions of the sinuous ridge, rather than the rounded shape inferred in lower resolution images. The example of the Mirackina paleochannel suggests a plausible alternative hypothesis: groundwater flow cementation of channel margins producing lateral ridges. This hypothesis is consistent with the inferred fluvial origin of other AZP sinuous ridge networks, obviates the need for special circumstances for this one example, and explains the lack of other glaciogenic features in the region.
