Presentation on theme: "River-deposit dimensions versus stratigraphic elevation in Aeolis Dorsa: resolving the great drying of Mars Edwin Kite, Antoine Lucas, John C. Armstrong,"— Presentation transcript:
River-deposit dimensions versus stratigraphic elevation in Aeolis Dorsa: resolving the great drying of Mars Edwin Kite, Antoine Lucas, John C. Armstrong, Oded Aharonson & Michael P. Lamb 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: 1)Characterize river-forming episodes 2)Constrain river discharge versus time. wavelength width
River deposits record constraints sorely needed for Early Mars climate models 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 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 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 Uzboi-Ladon Isidis rim Gale crater large valleysalluvial fans space-time correlation? E. Meridiani … how many episodes of climate-driven river formation? ?
500 m Advantages of Aeolis Dorsa (a 10 5 km 2 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)
Basin-scale mapping distinguishes 10 2 m-thick river-deposit-hosting units F1 Kite et al., Nature Geoscience, in press = HiRISE DTMs by Antoine Lucas smoothly eroding, fine-scale channels, retains many craters overlies 900 km E of Gale yardangs, meander belts, retains few craters Howard PNAS km F2 B20_017548_1739_XI_06S206W 400m
Data reduction inspired by Howard & Hemberger, Geomorphology 1991 Similar approach for channel widths. color: modern topographic range (4m) 102 wavelengths (52 channels) 189 widths (137 channels)
Dramatically different erosional expression, modest change in river-deposit dimensions 38% change in median channel wavelength 38% change in median channel width no evidence for changing with stratigraphic elevation (n=42) modal is= Channel wavelength (m) Channel width (m)
Foreman et al., Nature 2012 See also: Ward et al., Science 2000 Amundson et al., GSA-B 2012 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 Fluvial signatures of climate events on Earth
find breakpoints using nonparametric method A tool to search for abrupt climate change on Mars bootstrap F1 F2 repeat 10 3 x CDF of breakpoints from 10 3 trials: also perturb bootstrapped points z strat no evidence for abrupt change abrupt change z strat # breakpoints 0 nominal breakpoint breakpoint in bootstrapped data Results presented today are similar using planar, quadratic, IDW, and universal kriging methods for structure contour interpolation.
1)Meander wavelengths tighten upwards 2)Small meanders rare/absent below contact, common above contact (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing Early Mars fluvial…,’ Icarus 2013) strat. error strat. error 1. Meander wavelengths
2. River widths 1)Channel widths narrow upwards 2)Narrow channels rare/absent below contact, common above contact (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing Early Mars fluvial…,’ Icarus 2013) strat. error
Catchment area is 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 Limitations and caveats This talk alluvial fans meander belts “rhythmite” river deposits not observed
snowpack temperature - 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! Phase of orbital cycle Kite et al., ‘Seasonal melting…,’ Icarus 2013 Variability in river discharge versus time isn’t enough to exclude orbital forcing Threshold MeanNominal bankfull Q from mean Mean Nominal bankfull Q from mean interpolated elevation, geologic break-point: F2 (275±26) m42 m 3 s -1 (21±2) m20 m 3 s -1 F1 (402±18) m76 m 3 s -1 (31±3) m43 m 3 s -1 Change1.5 x1.8 x1.5 x2.1 x interpolated elevation, break-point from hydrology: above(274±16)mTBD m 3 s mTBD m 3 s - 1 below(410±19)mTBD m 3 s mTBD m 3 s - 1 change50%67% unit assigned from map (no interpolation) F2(320±26)mTBD m 3 s - 1 (23±1) mTBD m 3 s - 1 F1(420±18)mTBD m 3 s - 1 (35±2) mTBD m 3 s - 1 change1.31x1.7x1.67 Total interval (4-20) Myr from embedded-crater frequency (Kite et al., ‘Pacing fluvial…,’ Icarus 2013) Results using other interpolation methods & other break-points are similar Eaton, Treatise on Geomophology, 2013 Burr et al., JGR-E, 2010
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 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. More information:
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F2 MSL rover This Talk longitude latitude Tharsis Hellas Early Mars water-availability model output (Kite et al., ‘Seasonal melting …’ Icarus 2013a) Relevance to Gale Crater Zimbelman & Scheidt, Science 2012 Correlated in models of liquid- water availabillity: Correlated in lithology(?):