Edwin Kite , Antoine Lucas, John C. Armstrong, Oded Aharonson & Michael P. Lamb

1. River-deposit dimensions versus stratigraphic elevation in Aeolis Dorsa: resolving the great drying of Mars • Rationale: River-deposit dimensions constrain hydrology and climate on Early Mars, but stratigraphy is essential to build a time series of constraints on climate change • Today, use measurements of Early Mars river-deposit dimensions versus stratigraphic elevation to: • Characterize river-forming episodes • Constrain river discharge versus time. width wavelength Edwin Kite, Antoine Lucas, John C. Armstrong, Oded Aharonson & Michael P. Lamb

2. Environmental scenarios for precipitation-fed runoff on Early Mars vary widely: e.g. Haberle et al. 2012, Kite et al. Icarus 2013, Mischna et al. 2013, Segura et al. 2012, Urata & Toon 2013, Wordsworth et al. 2013 Andrews-Hanna & Lewis 2011 … • Early Mars rivers constrain magnitude, duration, intermittency, and number of wet events: e.g. Burr et al. 2010, Palucis et al. 2014, Irwin et al. 2005, Hoke et al. 2011, Williams et al. 2011, Morgan et al. 2014, Grant & Wilson 2012 Need error bars on geologic constraints to avert climate model overfitting River deposits record constraintssorely needed for Early Mars climate models Uzboi-Ladon Isidis rim space-time correlation? large valleys ? alluvial fans Gale crater how many episodes of climate-driven river formation? E. Meridiani … Omitted: later-stage and non-climate driven: e.g. Fassett et al. 2010, Hobley et al. 2014, Hauber et al. 2013, Kleinhans et al. 2010, Kraal et al.2008, Mangold et al. 2012, Harrison et al. 2011, Jones et al. 2011.

3. Advantages of Aeolis Dorsa (a 105 km2 sedimentary-rock basin, ~10°E of Gale) e.g. Burr et al. 2009, Zimbelman & Scheidt 2012, Kite et al. 2013, Kite et al. Nat. Geosci. in press ~ 30m range In elevation PSP_007474_1745 / ESP_024497_1745 (DTM) 500 m

4. Kite et al., Nature Geoscience, in press Basin-scale mapping distinguishes 102 m-thick river-deposit-hosting units = HiRISE DTMs by Antoine Lucas 60 km 900 km E of Gale yardangs, meander belts, retains few craters smoothly eroding, fine-scale channels, retains many craters overlies F2 F1 400m B20_017548_1739_XI_06S206W Howard PNAS 2009

5. 102 wavelengths (52 channels) 189 widths (137 channels) Data reduction inspired by Howard & Hemberger, Geomorphology 1991 Similar approach for channel widths. color: modern topographic range (4m)

6. Dramatically different erosional expression, modest change in river-deposit dimensions 38% change in median channel wavelength 38% change in median channel width Channel width (m) Channel wavelength (m) no evidence for changing with stratigraphic elevation (n=42) modal is = 10-15

7. Fluvial signatures of climate events on Earth Example: During planet-scale hyperthermal: rapid increase in sediment flux and discharge increased precipitation thick, wide, multistorey channel deposits Before planet-scale hyperthermal: thin, narrow single-story channel deposits Foreman et al., Nature 2012 See also: Ward et al., Science 2000 Amundson et al., GSA-B 2012

8. A tool to search for abrupt climate change on Mars zstrat F2 F1 repeat 103 x CDF of breakpoints from 103 trials: zstrat no evidence for abrupt change bootstrap find breakpoints using nonparametric method abrupt change nominal breakpoint also perturb bootstrapped points 0 # breakpoints breakpoint in bootstrapped data Results presented today are similar using planar, quadratic, IDW, and universal kriging methods for structure contour interpolation.

9. strat. error strat. error 1. Meander wavelengths (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing Early Mars fluvial…,’ Icarus 2013) • Meander wavelengths tighten upwards • Small meanders rare/absent below contact, common above contact

10. strat. error 2. River widths (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing Early Mars fluvial…,’ Icarus 2013) • Channel widths narrow upwards • Narrow channels rare/absent below contact, common above contact

11. Limitations and caveats • Catchment areais unknown • Wider channel deposits at higher stratigraphic levels (F3) • Taphonomy of channels? • e.g. Williams et al. Icarus 2013 • Role of aeolian deposition? • e.g. Milliken et al. GRL 2014, Kocurek & Ewing SEPM Sp. Pub. 2012, Kite et al. Geology 2013, Bridges & Muhs SEPM Sp. Pub. 2012 “rhythmite” alluvial fans This talk meander belts river deposits not observed

12. Variability in river discharge versus time isn’t enough to exclude orbital forcing Kite et al., ‘Seasonal melting…,’ Icarus 2013 Total interval (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing fluvial…,’ Icarus 2013) Phase of orbital cycle Eaton, Treatise on Geomophology, 2013 Burr et al., JGR-E, 2010 snowpack temperature Threshold Results using other interpolation methods & other break-points are similar - Consistent with orbital forcing Evidence for 3 m amplitude cut-and-fill cycles during F2 (wet-dry cycle in Burns Fm? Metz et al. 2009) - Also consistent with multiple transient events!

13. Conclusions • F2 records a distinct river-forming episode - after the big meander belts and before the alluvial fans. • ~40% reduction in river-deposit dimensions at or near the F1/F2 contact in Aeolis Dorsa • Consistent with ~2 x reduction in peak discharge across the contact. • 200m stratigraphy, (4-20) Myr total depositional interval • Goal: relate to quantitative models linking sed. & strat. to climate e.g. Kite et al., ‘Seasonal melting,’ Icarus 2013, Kite et al., ‘Growth and form …’, Geology 2013 More information: www.astro.princeton.edu/~kite With thanks to: Devon Burr, Alan Howard, Rebecca Williams, Robert Jacobsen, Lynn Carter, Bill Dietrich, Laura Kerber, Frederik Simons, Ross Irwin, Bill Dietrich, Alexandra Lefort, & Noah Finnegan for discussions, ideas, and inspiration.

14. End of presentation

15. Relevance to Gale Crater Correlated in models of liquid-water availabillity: This Talk Tharsis latitude MSL rover F2 Hellas longitude Early Mars water-availability model output (Kite et al., ‘Seasonal melting …’ Icarus 2013a) Correlated in lithology(?): Zimbelman & Scheidt, Science 2012