Subglacial water on Mars Options

[ngunn]

This topic has been discussed here over a spread of time and in various threads but not recently, I think. This article might be a good way to kick off some more discussion from a present day perspective if anyone's interested:
https://www.sciencedaily.com/releases/2020/...00803120154.htm

[serpens]

dburt, I've seen 'impact gardening' used to describe your hypotheses when reading over some of the past contributions on this and other forums, but I am not sure where. For some reason it struck a chord and no disrespect was intended. I don't think anyone would argue that impact effects, both base surge and ejecta did not contribute significantly to stratification, as did volcanism, aeolian, fluvial and lacustrine influences. As far as I am aware impact effects have been considered in analysis of rover investigations since the beginning. For example Frakik, Grotzinger and Edgar "Potential Recognition of Accretionary Lapilli in Distal Impact Deposits on Mars: A Facies Analog Provided by the 1.85 Ga Sudbury Impact Deposit". If I may quote from the abstract to the paper "While no impact-induced base surge deposits have been confirmed on Mars, it is likely that they will one day be discovered, and it is important to establish criteria for their recognition in the rock record". Personally I find the evidence for fluvial, deltaic and lacustrine deposition in Gale Crater compelling. The forthcoming contribution from Perseverance will no doubt provide another piece of the jigsaw puzzle.

[dburt]

Impact gardening is a well-understood and well-defined process of erosion by micrometeorites on airless worlds like the Moon. It is not a hypothesis, has no relevance to planets with an atmosphere, like early Mars, and certainly has no relevance to density currents. I was therefore astounded to see you use it so out of context, and would be equally astounded if your recollection of others using it was correct.

Regarding the article you cited, a glance at the author list told me basically all I need to know about it. It is an "apples to oranges" comparisons of impacts on Mars to the Sudbury impact which happened in shallow sea water (as did Chicxulub, that ended the age of dinosaurs). Land deposits by Sudbury have long since been eroded, as have virtually all marine deposits, save for a few widely scattered basal breccia deposits (possible tsunami deposits). A slightly less biased assessment is Calvin, W. M. et al., 2008, Hematite spherules at Meridiani: Results from MI, Mini-TES, and Pancam: Journal of Geophysical Research, v. 113, p. E12S37 which concludes (in its abstract): "no single terrestrial analog provides a model that can account for all attributes of the spherules on Mars". More recently, actual Mars concretions are described in detail by Sun, V.Z. et al., 2018, Late-stage diagenetic concretions in the Murray Formation, Gale crater, Mars: Icarus, 321:866-890 (you didn't recognize these on 06/09/17 because they weren't spherical enough). I noted that the article made no mention of or comparison with Meridiani spherules (or the very similar spherules at Gusev). Also it didn't mention the unusual detrital blueberries (actual spherules) in Gale discovered by members of this forum.

Personally I don't find the much abused Mars phrase "consistent with" very compelling, but that is my own preference as a practicing scientist. And I also am looking forward to observations by Perseverence, especially after I observed the large, young impact crater Hargraves not far away (I once co-authored a paper on paleomagnetism with Bob Hargraves). Apologies to the moderators for being so didactic; that is the professor in me, I guess.
dburt