Post by Tim Goudge, Department of Geological Sciences, Brown University, Providence, RI
There is much morphologic evidence that there was flowing water on the surface of Mars early in its history. Such evidence includes fluvial channels and valleys, often termed valley networks, (e.g., Pieri, 1980; Irwin, 2005a; Fassett and Head, 2008a) as well as paleolake basins that are fed by these valley networks (e.g., Goldspiel and Squyres, 1991; Cabrol and Grin, 1999, 2001; Irwin et al., 2005b; Fassett and Head, 2005, 2008b).
Image 1. Exposed layered deposit of probable lacustrine origin within an open-basin lake (-27.7°N, 76.1°E). Inset image (indicated by red box in main image) shows detailed layering within the exposed deposit. Main image is from the Context Camera (CTX) instrument (image number B02_010338_1518_XI_28S282W; ~5 m/pixel), and inset image is from the High Resolution Imaging Science Experiment (HiRISE) instrument (image number PSP_010338_1525; ~50 cm/pixel).
The best evidence for these basins actually having contained lakes is the presence of outlet channels (making the basins hydrologically open), as this requires ponding of water within the basin to at least the elevation of the outlet valley head before breaching to form an outlet channel (Fassett and Head, 2005, 2008b).
While there is clear morphologic evidence for paleo open-basin lakes based on observed inlet and outlet valley networks, the geologic evidence for deposition of sediment associated with these paleolakes is not as obvious. Of approximately 230 documented open-basin lakes, only about one-third show evidence for sedimentary deposits of probable lacustrine origin, such as deltaic deposits or exposed layered deposits (Image 1) (Goudge et al., 2012). Additionally, very few of these exposed sedimentary deposits show evidence for the presence of aqueous alteration minerals based on analysis of spectral reflectance data, which is likely to reflect the lack of such alteration phases within the watersheds of these paleolakes. Exposed lacustrine sedimentary deposits that do appear to contain aqueous alteration minerals are likely to have sourced these minerals from their watershed as opposed to having formed them in situ (e.g., Ehlmann et al., 2008; Dehouck et al., 2010; Ansan et al., 2011; Goudge et al., 2012).
Image 2. Open-basin lake (-11.5°N, 152.8°E) that has been resurfaced by volcanic flows. Inset image (indicated by red box in main image) shows embayment of the crater rim by the volcanic floor unit. Main image is a mosaic of High Resolution Stereo Camera (HRSC) nadir image h8425_0000 (~12.5 m/pixel) and CTX images B20_017403_1658_XN_14S206W and P07_003703_1682_XN_11S206W (~5 m/pixel) overlain on the Thermal Emission Imaging System (THEMIS) daytime infrared global mosaic (~100 m/pixel), and inset is HRSC nadir image h8425_0000
The reason so few of these paleo open-basin lakes contain exposed sedimentary deposits is due to their age. It is widely thought that the fluvial activity that fed these paleolakes ceased at approximately the boundary between the Noachian and Hesperian periods (~3.6-3.7 Ga) (Irwin et al., 2005b; Fassett and Head, 2008a). Therefore, these paleolakes have been subject to a variety of geologic processes over the past ~3.6-3.7 Gyr that have acted to resurface and modify their interiors. All of the identified open-basin lakes appear to be resurfaced or modified to some degree by such processes as volcanism (Image 2), glacial activity, or aeolian infilling. Of these resurfacing processes, volcanism appears to be the most widespread, having affected ~40% of identified open-basin lakes (Goudge et al., 2012).
Recommended Reading:
Ansan, V., et al. (2011), Stratigraphy, mineralogy, and origin of layered deposits inside Terby crater, Mars, Icarus, 211, 273–304.
Cabrol, N. A., and E. A. Grin (1999), Distribution, Classification, and Ages of Martian Impact Crater Lakes, Icarus, 142, 160–172.
Cabrol, N. A., and E. A. Grin (2001), The Evolution of Lacustrine Environments on Mars: Is Mars Only Hydrologically Dormant?, Icarus, 149, 291–328.
Dehouck, E., N. Mangold, S. Le Mouelic, V. Ansan, and F. Poulet (2010), Ismenius Cavus, Mars: A deep paleolake with phyllosilicate deposits, Planet. Space Sci., 58, 941–946.
Ehlmann, B. L., J. F. Mustard, C. I. Fassett, S. C. Schon, J. W. Head, D. J. Des Marais, J. A. Grant, and S. L. Murchie (2008a), Clay minerals in delta deposits and organic preservation potential on Mars, Nat. Geosci., 1, 355-358.
Fassett, C. I., and J. W. Head (2005), Fluvial sedimentary deposits on Mars: Ancient deltas in a crater lake in the Nili Fossae region, Geophys. Res. Lett, 32, L14201.
Fassett, C. I., and J. W. Head (2008a), The timing of martian valley network activity: Constraints from buffered crater counting, Icarus, 195, 61–89.
Fassett, C. I., and J. W. Head (2008b), Valley network-fed, open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology, Icarus, 198, 37–56.
Goldspiel, J. M., and S. W. Squyres (1991), Ancient Aqueous Sedimentation on Mars, Icarus, 89, 392-410.
Goudge, T.A., J. W. Head, J. F. Mustard, and C. I. Fassett (2012), An analysis of open-basin lake deposits on Mars: Evidence for the nature of associated lacustrine deposits and post-lacustrine modification processes, Icarus, 219, 211–229.
Irwin, R. P., R. A. Craddock, and A. D. Howard (2005a), Interior channels in martian valley networks: Discharge and runoff production, Geology, 33, 489–492.
Irwin, R. P., A. D. Howard, R. A. Craddock, and J. M. Moore (2005b), An intense terminal epoch of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake development, J. Geophys. Res., 110, E12S15.
Pieri, D. C. (1980), Martian Valleys: Morphology, Distribution, Age, and Origin, Science, 210, 895–897.
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