Post by Dr. F. Salese, Marie Curie Postdoctoral Fellow, Faculty of Geoscience, Utrecht University.
Groundwater had a greater role in shaping the Martian surface and may have sheltered primitive life forms as the planet started drying up. Observations in the northern hemisphere show evidence of a planet‐wide groundwater system. The elevations of these water‐related morphologies in all studied basins lie within the same narrow range of depths below Mars datum (Image 1) and notably coincide with the elevation of some ocean shorelines proposed by previous authors. Most previous studies on Mars relevant groundwater have proposed models, but few have looked at the geological evidence of groundwater upwelling in deep closed basins in the northern hemisphere equatorial region. Geological evidence of groundwater upwelling in these deep basins is a key point that will help to validate present-day models and to better constraint them in the future.
Image 1: Morphologies inside several basins. a) Crater #15 shows the presence at the same time of delta, sapping valleys, debris and hummocky terrain. The basin floor is flat. b) Crater #12 shows stepped delta, terraces, shorelines and flow structures at about the same topographic elevations. c) Sapping valley and related stepped delta in crater #18. d) Sapping valley and related stepped delta along with fan and exhumed channels in crater #12. e) Crater #16 shows well-preserved outcrops of debris flow. f) Sapping valley with related delta at -4100m inside crater #22.
In order to understand if groundwater influences are expressed on a local, regional, or global scale, we focus our detailed geological analyses on the structure and stratigraphy of enclosed craters located in the northern equatorial regions, near the dichotomy boundary with floors below −4,000 m elevation. All the selected basins are located between 0°N and 37°N to limit the effects of current day ice on the observed morphological forms and deposits (Image 2). We focused on the northern hemisphere because this is where a large fraction of groundwater upwelling is predicted to have occurred (Andrews-Hanna et al., 2007, 2010; Michalski et al., 2013).
Image 2: Distribution of studied basins on Mars. Their distribution follows the dichotomy boundary and they are clustered in the Arabia and Amazonia quadrangles along two parallel lines aligned NNE-SSW in the first case and NNW-SSE respectively with high concentration in Arabia Terra and Amazonia.
Our work reveals evidence of some previously unrecognized water-formed features (delta, shorelines, sapping valleys, etc.) that have never been considered holistically, from the scale of the individual basin to the planet-scale context. These features are likely to have resulted from a process of groundwater upwelling followed by water table fluctuations and eventual groundwater recession (Image 3). The presence of a large number of water-formed features in all these deep basins (Image 1) is a compelling sign that Mars once had large amounts of water stored as groundwater that debouched into the intercepting craters to form lacustrine systems (Palucis et al., 2016).
The geological evidence presented in this work corroborates the Andrews-Hanna et al. (2010) theory of global-scale groundwater upwelling and supports the model presented by Michalski et al. (2013) but contests the assertion that McLaughlin crater is the only basin presenting geological evidence of groundwater upwelling. Although they focused on McLaughlin crater due to the strong spectroscopic evidence for upwelling, the authors also suggest there could be other craters presenting geomorphological evidence of groundwater upwelling that were not investigated in their work.
Image 3: Conceptual model, of Martian basins evolution and their relations with the groundwater storage, from the oldest (bottom) to the most recent stage (top). The model consists of three chronological stages. In the first stage, the crater was flooded and as a consequence sapping valleys with deltas, terraces, shorelines, and channels formed. During the second stage, there was a net drop in water levels (although there may have been a number of higher frequency water level fluctuations) and new landforms were created as a consequence of this process. In the final stage the crater became dry and exposed exhumed channels on the craters’ floors as well as all the landforms developed in the previous two stages. This model also introduces for the first time in the Martian geological literature the possible presence of “dike confined water” that can make the groundwater level shallower than the basal one, allowing the formation of sapping valleys and other water related morphologies even if, for instance, the groundwater basal level is deeper than the head of the sapping valleys.
If life once existed on Mars, it could have been preferentially confined to some protective water related niches (e.g., Carrozzo et al., 2017; Hamilton et al., 2018). Evidence of the past existence of long-standing bodies of water on Mars, such as lakes or deltas, has significant implications both for climate and life: groundwater-fed lakes could warm Mars’ climate (Tosca et al., 2018) and increase the chance that life forms might have existed and presently remain buried in the sediment. These deep basins (due to a lower gravity that implies less compaction of the pore space and lower heat flow that reduces the temperature constraints, see Michalski et al., 2013) arguably offer the best chance of finding evidence of past prebiotic chemistry or even past microbial life on the Red Planet.
Further Reading
Tosca, N. J., Ahmed, I. A. M., Tutolo, B. M., Ashpitel, A., & Hurowitz, J. A. (2018). Magnetite authigenesis and the warming of early Mars. Nature Geoscience, 11(9), 635–639. https://doi.org/10.1038/s41561‐018‐0203‐8
Carrozzo, F. G., Di Achille, G., Salese, F., Altieri, F., & Bellucci, G. (2017). Geology and mineralogy of the Auki Crater, Tyrrhena Terra, Mars: A possible post impact‐induced hydrothermal system. Icarus, 281, 228–239. https://doi.org/10.1016/j.icarus.2016.09.001
Hamilton, C. W., Mouginis‐Mark, P. J., Sori, M. M., Scheidt, S. P., & Bramson, A. M. (2018). Episodes of aqueous flooding and effusive volcanism associated with Hrad Vallis, Mars. Journal of Geophysical Research: Planets, 123(6), 1484–1510. https://doi.org/10.1029/ 2018je005543
Andrews‐Hanna, J. C., & Lewis, K. W. (2011). Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs. Journal of Geophysical Research, 116, E02007. https://doi.org/10.1029/2010je003709
Andrews‐Hanna, J. C., Phillips, R. J., & Zuber, M. T. (2007). Meridiani Planum and the global hydrology of Mars. Nature, 446(7132), 163–166. https://doi.org/10.1038/nature05594
Andrews‐Hanna, J. C., Zuber, M. T., Arvidson, R. E., & Wiseman, S. M. (2010). Early Mars hydrology: Meridiani playa deposits and the sedimentary record of Arabia Terra. Journal of Geophysical Research, 115, E06002. https://doi.org/10.1029/2009je003485
Palucis, M. C., Dietrich, W. E., Williams, R. M. E., Hayes, A. G., Parker, T., Sumner, D. Y., et al. (2016). Sequence and relative timing of large lakes in Gale crater (Mars) after the formation of Mount Sharp. Journal of Geophysical Research: Planets, 121, 472–496. https://doi.org/10.1002/2015je004905
Planetary Geomorphology Image of the Month 