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Home , Echus Chasma, Newton (Martian crater), Nirgal Vallis

Did Fluvial Landforms Form Under A Warmer Early ?

N. Mangold, LPG Nantes/CNRS, France

Acknowledgments: I warmly thank all colleagues and students having worked with me in the last 15 years. Textbook representations of fluvial valleys on Earth

Does this apply to Mars? Climate Bedrock

Basin geometry

Hydrology (transport)

Alluvial/delta fan (deposition)

Mangold, 8th Mars Conference A 500 m thick plateau incised by fluvial erosion on Mars

Downward

Downward

5 km CTX image Geometry typical of precipitation (snow deposition and melting or rainfall)

See talk by Ansan later for more on geometry Mangold, 8th Mars Conference Valley networks: Inner channels

HRSC Climate Bedrock 200 m

Basin geometry

3 km

Nanedi Vallis (Malin and Edgett, 2001) Hydrology • Gradual erosion (≠ ) (transport)

• Discharge rates of 300-5000 m3.s-1 Alluvial/delta fan (Irwin et al., Geology, 2005) (deposition)  Earth-like discharge rates

• Channels often buried by sand  Scarcity does not allow global hydrologic calculations Mangold, 8th Mars Conference Valley networks: Bedrock control

HRSC Climate Bedrock 200 m

Basin geometry 3 km

Nanedi Vallis (Malin and Edgett, 2001) Hydrology • Most valleys on Mars in volcanic bedrock (transport)

• No mountain range on Mars as on Earth (where erosion is controled by uplift) Alluvial/delta fan (deposition) => Distinct style from usual terrestrial valleys

Mangold, 8th Mars Conference Valley networks: Bedrock control

Nanedi 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 Mangold, 8th Mars Conference Valley networks: Bedrock control

HRSC Google Earth Echus plateau (Mangold et al., 2004, 2008) Snake River Volcanic Plateau (Idaho) Mangold, 8th Mars Conference 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 Mangold, 8th Mars Conference Valley networks: Bedrock control

Period of time to develop dense valley networks depends on bedrock type (under various terrestrial climates):

Ash deposits 1,000-10,000 years Lava flows 100,000-1 million years

Late Noachian phase (age from e.g. Fassett Late phase and Head, 2008, Bouley and Craddock, 2014) (Mangold et al.,2004)

10 km 30 km Incision into volcanic plateau and upper ash deposits 500 m deep well developed valleys into thick massive Noachian bedrock 1,000 years-100,000years >>100,000 years Mangold, 8th Mars Conference 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 crater Poorly branched valleys on valleys in (Late Amazon., Williams et al., 2008) crater ejecta (3.1 Gy, Dickson,2009) 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?)

Mangold, 8th Mars Conference Depositional fans: Alluvial deposits

Climate Bedrock (unknown) (poorly known)

Basin geometry

Hydrology (transport)

Alluvial/delta fan (deposition) fan in crater Palucis et al., JGR, 2014 Mangold, 8th Mars Conference Depositional fans: Alluvial deposits

Peace Vallis fan in Gale crater Concave topographic profile : Palucis et al., JGR, 2014 no lake, subaerial deposits Mangold, 8th Mars Conference Depositional fans: Alluvial deposits

Dozens of alluvial fans in large craters Ejecta poorly dissected bury Noachian valleys (Moore and Howard, JGR, 2005) (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 Mangold, 8th Mars Conference Delta as evidence for paleolakes

MOC HRSC HRSC

Eberswalde (Malin and Nepenthes Vallis (Irwin et al., 2005, Subur Vallis Edgett, Science, 2003) Kleinhans et al., 2010) (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 Mangold, 8th Mars Conference Delta from morphology and topography

MOC HRSC HRSC

15 , Malin and Nepenthes Vallis (Irwin et al., 2005, Subur Vallis Edgett, Science, 2003 Kleinhans et al., 2010) (Irwin et al., 2005, Hauber et al., 2008) Eberswalde- Xanthe Terra fans Late Hesperian to Middle Amazonian Late Hesperian activity (Hauber et al., 2013) (Mangold et al., Icarus, 2012) • 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 Mangold, 8th Mars Conference Depositional systems in the Noachian

• For Noachian sediments, preservation is limited.

• 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) Mangold, 8th Mars Conference 16 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. Mangold, 8th Mars Conference 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

Noachian Degraded craters

Only Noachian craters display Mangold et al., 2012 an heavy degradation

Noachian craters have been degraded: Slope is much lower than for fresh ones

Mangold, 8th Mars Conference 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 Downturn in the frequency of craters < 50 km (color circles show where drainage patterns form)

Diameter (km) Matsubara and Howard, 2013 Forsberg-Taylor et al., 2004 Mangold, 8th Mars Conference Conclusions

Amazonian landforms (<2.5 Gy) • Limited local flows => Transient flows in a cold climate

Late Hesperian/Early Amazonian landforms (3.5-2.5 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!

Mangold, 8th Mars Conference 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 control of post-Noachian valleys / lakes: Craters, volcanoes, climate? (See talks by Irwin et al, Kite et al. later today) From Goudge et al., later today

• Late Noachian terrains display pedogenetic clay layers Are they related to the peak in fluvial erosion? Clays at plateau (see talk by Carter et al., Loizeau et al., this afternoon)

• 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

Mangold, 8th Mars Conference