Resolving the era of wet climates on Mars:Stratigraphy and paleohydrology of Aeolis Dorsa

Edwin Kite (Princeton), Antoine Lucas (U. Paris), John Armstrong (Weber State University), Oded Aharonson (Weizmann), Michael Lamb (Caltech),

Alan Howard (U. Virginia)

Rationale: River-deposit dimensions constrain Early Mars hydrology, but stratigraphy is essential to constrain Mars climate evolution models Today, use measurements of Early Mars river-deposit dimensions versus stratigraphic elevation to:1) Constrain intermittency of wet

conditions2) Constrain climate models.

wavelength

width

River deposits record constraintssorely needed for Mars climate evolution 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. 2013, Andrews-Hanna & Lewis 2011, Kite et al. Nature Geoscience 2014

102 mbar atmosphere needed to suppress evaporitic cooling Key geologic constraint – intermittency of wet conditions:

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, Fassett et al.2010, Hobley et al. 2014, Hauber et al. 2013.

Need error bars on geologic constraints to avert climate model overfitting

One-pass

Intermittent

Orbital forcingVolcanic forcingImpact-triggeredmetastable wetstatesImpact cataclysmThick early greenhouse

NAS

A/JP

L/M

SSS

Will

iam

s et

al.

Scie

nce

2013

Palu

cis

et a

l. JG

R 20

14

ESP_027807_1765PSP_008002_1750

F2

MSL rover

This Talk

)Elongitudela

titud

e

Thar

sis

Hellas

Early Mars water-availability model output (Kite et al., Icarus 2013a)

Zimbelman & Scheidt, Science 2012Kite et al., Nature Geosci. 2014

Aeolis Dorsa river deposits in global context:

Gale Aeolis Dorsaalluvial fans alluvial fans

Kite et al., in prep.geosci.uchicago.edu/~kite/stereo

1 cm

rhythmiterhythmite

Relatively young,post-Noachian (?)

0E 360E60S

60N

>108 yr time gap(embedded craters)

R-2

B20_

0175

48_1

739_

XI

R-1

How

ard

PNAS

200

9

400m

400m

e.g. Burr et al. 2009 & 2010 Kite et al. 2013 & in prep.

Stratigraphic context of river deposits suggests wet-dry alternations

Chan

nel d

epos

its

>3.2

km

stra

tigra

phic

thic

knes

s

rhythmitealluvial fans

rivers

>400 km E-W extent

Getting from stereopairs to stratigraphic logs

Errors: StratigraphicMeasurementOutcrop varianceMeasurement correlation

• Meander wavelengths tighten upwards• Small meanders rare/absent below 0m, common above 0m

(4-2

0) M

yr (

Kite

et a

l., Ic

arus

201

3b)

X transect 1(153.5ºE)transect 2(155ºE)transect 3(151ºE)

strat.error

1. Meander wavelengths (λ)

poor exposure

• Channel widths narrow upwards• Narrow channels rare/absent below 0m, common above 0m

strat.error

X transect 1(153.5ºE)transect 2(155ºE)transect 3(151ºE)

2. Channel widths (w)

(4

-20)

Myr

(Kite

et a

l., Ic

arus

201

3b)

poor exposure

# data points

Stra

tigra

phic

ele

vatio

n (m

)

0

Also: intermittency at 10m scale (correlatable basinwide using marker bed;Burr et al., 2010)

ESP_

0341

89_1

740

higher channel-depositproportion

lateral-accretion deposits

Logs show basin-wide discharge (Q) variability

Wavelength λ (m)

Width w (m)

Constraints on models of post-Noachian Mars climate evolution:

• Both short term intermittency and long-term intermittency.• A thicker atmosphere – and a way of removing it

Escape-to-space, or loss-to-ground (carbonate formation)?

Stochastic Mars climate evolution model:Uniform initial conditions: 3.5 Gya, 100 mbar

Liquid water availability model

(e.g. Kite et al. Icarus 2013)

Supply-limited carbonate

weathering in area of H2O(l)

update atmospheric pressure, solar luminosityescape to space scaled using ASPERA-3 data

scaled to UV flux of young Sunlike stars

Variable3.5 Gyr orbital

forcings(n = 100)

Armstrong et al. 2004

Ensemble approach

Obliquityeccentricity

Ls of perihelion

Obl

iqui

ty (°

) / P

atm

(mba

r)O

bliq

uity

(°) /

Pat

m

(mba

r)Late bursts of habitability on Mars-like planets: 1 example

atmosphericpressure

normalized areaof liquid-water

obliquity

Preliminary

long, globally-dryinterval

patchily,intermittently

wet

area of liquid w

ater

obliquity

atmospheric pressure

Metz et al. 2009, Edgar et al. 2014, Andrews-Hanna & Lewis 2011,

Head et al. 2009, Toon et al. 1980 …

Dry spells: Aeolian supply/ deflation?(e.g. Kocurek & Bridges, 2012)Wet spells: Cementation? (e.g. Milliken et al., 2014)

Obl

iqui

ty (°

) / P

atm

(mba

r)

Model Age (Gyr)

20 Myr

• Long dry intervals common– Laskar et al. Icarus 2004, Li &

Batygin ApJL 2014• Late-stage carbonate drawdown?

– 100x less carbonate than in Pollack et al. (1987), consistent with SAM δ13C

– Still need young, voluminous sedimentary reservoir for carbonate

longglobally-dry

interval

long, globally- dry interval

Preliminary

Late bursts of habitability on Mars-like planets: 3

different, equally likely scenarios

Obl

iqui

ty (°

) / P

atm

(mba

r)

wet

wet

Obl

iqui

ty (°

) / P

atm

(mba

r)

Obl

iqui

ty (°

) / P

atm

(mba

r)

Testing late-stage carbonate drawdown requires an extended Curiositytraverse

MAVEN

Test escape-to-space hypothesis

Upper Gale mound - above the sulfates: A representative sample

of the only geochemical reservoiradequate to explain the loss of habitability

via carbonate drawdown

Test loss-to-ground hypothesis:

Conclusions• Aeolis Dorsa records 1.5-2x reduction in river-deposit dimensions at or near

R-1/R-2 contact- Consistent with 3-4x reduction in peak discharge across the

contact.- 200m stratigraphy, (4-20) Myr total depositional interval

• Intermittency at multiple timescales (regional unconformities, river-deposit dimensions, marker beds).

• Constrains quantitative models linking sed. & strat. to climate evolution e.g. Kite et al., ‘Seasonal melting,’ Icarus 2013, Kite et al., ‘Growth and form …’, Geology

2013, Kite et al., ‘Low paleopressure …,’ Nature Geoscience 2014

With thanks to: Devon Burr, Kevin Lewis, Rebecca Williams, Robert Jacobsen, Lynn Carter, Bill Dietrich, Laura Kerber, Frederik Simons, Nicolas Mangold, Ross Irwin, Bill Dietrich, Alexandra Lefort, & Noah Finnegan for discussions, ideas, and inspiration.

More information: www.astro.princeton.edu/~ekite