Did Fluvial Landforms Form Under A Warmer Early Mars?

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1 Did Fluvial Landforms Form Under A Warmer Early Mars? N. Mangold, LPG Nantes/CNRS, France Acknowledgments: I warmly thank all colleagues and students having worked with me in the last 15 years.

2 Textbook representations of fluvial valleys on Earth Does this apply to Mars? Bedrock Climate Basin geometry Hydrology (transport) Alluvial/delta fan (deposition)

3 A 500 m thick Noachian plateau incised by fluvial erosion on Mars Downward Downward 5 km Geometry typical of precipitation (snow deposition and melting or rainfall) See talk by Ansan later for more on geometry CTX image

4 Valley networks: Inner channels 200 m HRSC Bedrock Climate 3 km Nanedi Vallis (Malin and Edgett, 2001) Gradual erosion ( outflow channels) Discharge rates of m 3.s -1 (Irwin et al., Geology, 2005) Earth-like discharge rates Basin geometry Hydrology (transport) Alluvial/delta fan (deposition) Channels often buried by sand Scarcity does not allow global hydrologic calculations

5 Valley networks: Bedrock control 200 m HRSC Bedrock Climate 3 km Nanedi Vallis (Malin and Edgett, 2001) Most valleys on Mars in volcanic bedrock No mountain range on Mars as on Earth (where erosion is controled by uplift) => Distinct style from usual terrestrial valleys Basin geometry Hydrology (transport) Alluvial/delta fan (deposition)

6 Valley networks: Bedrock control Nanedi Vallis Nirgal Vallis HRSC Sapping-like valleys may be formed by subsurface circulation (Laity & Malin, 1985) May not require surface water? (e.g. Goldspiel and Squyres, 1992) Control by groundwater possible (Harrison & Grimm, 2005; Glines & Fassett, 2011), but recharge by precipitation and a control by overland flows (e.g. Irwin et al., 2006) => Sapping and overland flows do not mutually exclude themselves

7 Valley networks: Bedrock control HRSC Echus Chasma plateau (Mangold et al., 2004, 2008) Google Earth Snake River Volcanic Plateau (Idaho)

8 Valley networks: Bedrock control ~50 m thick ash/sand Lava HRSC MOC Well-developed networks in erodible ash/sand layer over lava flows into which canyon forms

9 Valley networks: Bedrock control Period of time to develop dense valley networks depends on bedrock type (under various terrestrial climates): Ash deposits Lava flows 1,000-10,000 years 100,000-1 million years Late Hesperian phase (Mangold et al.,2004) Late Noachian phase (age from e.g. Fassett and Head, 2008, Bouley and Craddock, 2014) Incision into volcanic plateau and upper ash deposits 1,000 years-100,000years 10 km 30 km 500 m deep well developed valleys into thick massive Noachian bedrock >>100,000 years

10 Valley networks : Recent landforms Amazonian valleys (<3 Gy): Small poorly branched valleys, transient flows. (Gulick et al., 1992, Fassett et al., 2010, Mangold, PSS, 2012 ) Fluvial erosion on Mojave crater (Late Amazon., Williams et al., 2008) Poorly branched valleys on Lyot crater ejecta (3.1 Gy, Dickson,2009) Amazonian valleys in Newton crater (Parsons et al., 2014) Small fluvial landforms (< 50 km long) observed in Amazonian terrains Control by regional heat released from volcanoes or impact craters But snowmelt/supraglacial/subglacial channels suggest ice melting unrelated to impact or volcanoes (transient high obliquity periods?)

11 Depositional fans: Alluvial deposits Bedrock (poorly known) Climate (unknown) Basin geometry Hydrology (transport) Peace Vallis fan in Gale crater Palucis et al., JGR, 2014 Alluvial/delta fan (deposition)

12 Depositional fans: Alluvial deposits Peace Vallis fan in Gale crater Palucis et al., JGR, 2014 Concave topographic profile : no lake, subaerial deposits

13 Depositional fans: Alluvial deposits Dozens of alluvial fans in large craters (Moore and Howard, JGR, 2005) Ejecta poorly dissected bury Noachian valleys (Mangold et al., JGR, 2012) Alluvial fan Individual fans age: Late Hesperian to Early Amazonian (Grant and Wilson, 2011) Alluvial fans always present in Hesperian impact craters (with preserved ejecta and steep slopes) (Mangold et al., JGR, 2012). => Most alluvial fans belong to late stage phases (Late Hesperian or younger) 13

14 Delta as evidence for paleolakes MOC HRSC HRSC Eberswalde (Malin and Edgett, Science, 2003) Nepenthes Vallis (Irwin et al., 2005, Kleinhans et al., 2010) Subur Vallis (Irwin et al., 2005, Hauber et al., 2008) Delta fans are the key landforms signing the presence of paleolakes Tens of deltas identified, many in closed basins (crater lakes), but some on open basins (suggesting larger standing bodies of water) 14

15 Delta from morphology and topography MOC HRSC HRSC Eberswalde, Malin and Edgett, Science, 2003 Eberswalde-Holden Late Hesperian activity (Mangold et al., Icarus, 2012) Nepenthes Vallis (Irwin et al., 2005, Kleinhans et al., 2010) 15 Subur Vallis (Irwin et al., 2005, Hauber et al., 2008) Xanthe Terra fans Late Hesperian to Middle Amazonian (Hauber et al., 2013) Recent studies => many delta fans are actually Late Hesperian or younger Modeling => short-term episodes (<<10,000 years; e.g., Kleinhans et al., 2010) => Most delta fans do NOT sign the most intense fluvial period from the Noachian 15

16 Depositional systems in the Noachian For Noachian sediments, preservation is limited. Terby crater has 2 km thick deposits (500 times more volume than Eberswalde delta fan) much longer duration with standing body of water. Noachian sediments require the study of facies => Most of the morphology has been lost by erosion. Deposits in Terby (Wilson et al., 2007) Terby crater deposits in cross section (Ansan et al., 2011) 16

17 Depositional systems in the Noachian Early Hesperian lavas, no lake preserved 30 km Problem of preservation/burial of ancient deposits due to Early Hesperian volcanism that filled many craters in highlands (see e.g. Ody et al, this conf.) Most Late Noachian valley networks have no evidence of terminal deposits for this reason. The same limitation exists in a broader extent for northern plains for which a Noachian ocean won t ever be accessible due to burial by subsequent rocks.

18 Crater degradation: A stronger erosion in the Noachian Pioneer studies using Viking images (Craddock et al., 1990, 1997) => More intense erosion in the Noachian Fresh Fresh Hesperian Degraded Noachian craters Only Noachian craters display an heavy degradation Mangold et al., 2012 Noachian craters have been degraded: Slope is much lower than for fresh ones

19 Crater degradation: A gap of Noachian craters Modeling shows fluvial erosion is an adequate explanation (Matsubara et al., this conf.) The degradation of craters is visible in the crater counts plot There is a huge gap of Noachian craters < 20 km (Hartmann, 1999, Forsberg Taylor et al., 2004, Quantin et al., this conf.) Modeling of fluvial erosion with incoming impact craters (color circles show where drainage patterns form) Downturn in the frequency of craters < 50 km Matsubara and Howard, 2013 Diameter (km) Forsberg-Taylor et al., 2004

20 Conclusions Amazonian landforms (<2.5 Gy) Limited local flows => Transient flows in a cold climate Late Hesperian/Early Amazonian landforms ( Gy) Dendritic valleys exist, but on erodible bedrock Well-preserved delta and alluvial fans (Eberswalde delta, Gale crater alluvial fan) Low erosion rate based on impact craters Late stage episode(s) - May not require a too much warmer Mars (snowmelt in frozen Mars?) but significant differences (including Curiosity observ. at Gale crater). Noachian landforms (<3.5 Gy) Well-developed valley networks incising crustal bedrock (sustained activity) Poor preservation of deposits (buried, eroded) complicates the understanding Enhanced period of crater degradation at a global scale This is the «true» early Mars!

21 Key questions >150 locations with standing bodies of water Majority date from the Late Hesperian Which one are the true Noachian deposits? (see talk Goudge et al, today) What is the main control of post-noachian valleys / lakes: Craters, volcanoes, climate? (See talks by Irwin et al, Kite et al. later today) Late Noachian terrains display pedogenetic clay layers Are they related to the peak in fluvial erosion? (see talk by Carter et al., Loizeau et al., this afternoon) From Goudge et al., later today Clays at Mawrth Vallis plateau How to access the earliest buried sediments? How be sure we have early deposits? Find exhumed sediments in impact ejecta? In situ GPR for buried sediments? Ehlmann et al., 2013