Deltas and Turbidites in Martian Lake Settings: Implications for the Occurrence of Organic Matter, Water Body Distribution and Sediment Dispersal
Thousands of impact features exist on the surface of Mars. Of those, 179 were identified historically as containing evidence of standing bodies of water, including showing evidence of fluviolacustrine features such as deltas, sedimentary terracing, layered deposits, and shorelines (Cabrol and Grin, 1999). In addition, some of these features have been interpreted to show evidence for Noachian salars and sabkhas formations (Forsythe and Blackwelder, 1998). Of those craters interpreted to have contained standing water, 52% are believed to show evidence of deltaic deposition. These deltas are reported to be as large as 600 m thick fed by a continuous fluvial channel over 100 km long. Although much has been learned of the nature of lacustrine setting on Mars, many of these observations were derived from lower resolution Viking images (ranging in resolution from 46 to 230 m per pixel). Newer Mars Global Surveyor (MGS), Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) have instigated a reexamination at much higher resolution of many previously identified features, as well as the identification of newer fluviolacustrine regions. The MOC system, with a resolution 1.4 x 6.0 m/pixel has greatly enhanced the detail with which we can examine surface morphology. A range of deltas appear to exist, as well as high reflectivity distal deposits interpreted as delta front turbidites. The existence of deltas and associated turbidites implies a density contrast in incoming versus lake water. The steepness of the drainage terrain surrounding many of the lakes, as well as the interpreted episodicity of discharge suggest the probably occurrence of hyperpycnal flows as a major mechanism of sediment dispersal in the Martian lake environments. Newer analysis of supposed deltas show exhume meanders, chute cutoffs, enable calculation of potential flow parameters in paleo-Martian channels, allow for calculation of distributary density and bifurcation angles. Turbidite parameters can be modeled on the basis of subjective but viable data.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009