Transcript slides

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.
width
wavelength
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. 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
Uzboi-Ladon
Isidis rim
Gale crater
E. Meridiani
…
space-time
correlation?
large valleys
?
alluvial fans
how many episodes of climate-driven river formation?
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.
500 m
In elevation
e.g. Burr et al. 2009, Zimbelman & Scheidt 2012,
Kite et al. 2013, Kite et al. Nat. Geosci. in press
PSP_007474_1745 / ESP_024497_1745 (DTM)
(a 105 km2 sedimentary-rock basin, ~10°E of Gale)
~ 30m range
Advantages of Aeolis Dorsa
Basin-scale mapping distinguishes 102 m-thick river-deposit-hosting units
Kite et al., Nature
Geoscience, in press
= HiRISE DTMs
by Antoine Lucas
60 km
900 km E of Gale
smoothly
eroding,
fine-scale
channels,
retains
many
craters
F2 overlies
F1
400m
B20_017548_1739_XI_06S206W
Howard PNAS 2009
yardangs,
meander
belts,
retains
few
craters
Data reduction
102 wavelengths
(52 channels)
189 widths
(137 channels)
color:
modern
topographic
range (4m)
inspired by Howard & Hemberger, Geomorphology 1991
Similar approach for channel widths.
Dramatically different erosional expression, modest
change in river-deposit dimensions
38% change in median channel wavelength
Channel wavelength (m)
38% change in median channel width
Channel width (m)
no evidence for
changing with stratigraphic elevation (n=42)
modal is = 10-15
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
A tool to search for abrupt climate change on Mars
zstrat
F2
F1
repeat
103 x
CDF of breakpoints
from 103 trials:
zstrat
bootstrap
nominal
breakpoint
find breakpoints
abrupt
change
using nonparametric
method
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.
(4-20) Myr from embedded-crater frequency
(Kite et al., ‘Pacing Early Mars fluvial…,’ Icarus 2013)
1. Meander wavelengths
strat.
strat.
error
error
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)
2. River widths
strat.
error
1) Channel widths narrow upwards
2) Narrow channels rare/absent below contact, common above contact
Limitations and caveats
• Catchment area is
unknown
• Wider channel deposits
at higher stratigraphic
levels (F3)
• Taphonomy of
channels?
“rhythmite”
alluvial
fans
– 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
This talk
meander belts
river deposits
not observed
Variability in river discharge versus time isn’t enough to exclude orbital forcing
Kite et al., ‘Seasonal melting…,’ Icarus 2013
Mean
Nominal
bankfull
Q from
mean
Mean
Nominal
bankfull
Q from
mean
interpolated elevation, geologic break-point:
F2
(275±26)
m
42 m3 s-1
(21±2)
m
20 m3 s-1
F1
(402±18)
m
76 m3 s-1
(31±3)
m
43 m3 s-1
Change
1.5 x
Phase of orbital cycle
Total interval (4-20) Myr from embedded-crater
frequency (Kite et al., ‘Pacing fluvial…,’ Icarus 2013)
Eaton, Treatise on Geomophology, 2013
1.8 x
x JGR-E, 2010
2.1 x
Burr1.5
et al.,
snowpack temperature
interpolated elevation, break-point from hydrology:
Results using other interpolation methods & other break-points
above
m3 s- 18 m
TBD m3 sare
similar (274±16)m TBD
1
1
below
change
(410±19)m
TBD m3 s1
50%
30 m
F2
(320±26)m
- Consistent with orbital forcing
TBD m3 s1
67%
unit assigned from map (no interpolation)
TBD
1
m3 s-
(23±1)
m
TBD
1
m3 s-
Threshold
2009)
Evidence for 3 m amplitude
cut-and-fill cycles during F2
(wet-dry cycle in Burns Fm? Metz et al.
- Also consistent with multiple
transient events!
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.
End of
presentation
Relevance to Gale Crater
This Talk
latitude
Correlated in
models
of liquidwater
availabillity:
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