1. Abridged Abstract:
Stepped
fans—conical
forms
with
stair-­‐step
topography—are
rela7vely
rare
on
both
Earth
and
Mars.
We
characterized
the
morphological
a?ributes
of
mar7an
stepped
fans
to
ascertain
variability
among
this
class
of
landform
and
assess
the
plausibility
of
forma7on
hypotheses.
Stepped
fans
and
their
associated
catchment
were
examined
in
CTX
and
HiRISE
image
data
to
document
their
size,
feeder
channel
system,
planimetric
form
and
step
spacing.
In
addi7on,
the
topographic
form
(step
heights
and
inter-­‐step
slope)
were
documented
for
select
stepped
fans
where
eleva7on
data
could
be
derived
from
HiRISE
stereo
image
pairs.
We
will
con7nue
to
refine
the
a?ributes
of
fans
within
each
category
through
further
interroga7on
of
fan
topography,
and
evaluate
whether
these
differences
reflect
dis7nct
processes.
This
study
could
yield
cri7cal
informa7on
regarding
Mars’
complex
history
of
standing
water
on
its
surface.
MORPHOLOGICAL ATTRIBUTES OF MARTIAN STEPPED
FANS
Evan
LEWIS1
Rebecca
M.E.
WILLIAMS2
Andrew
DE
WET1
1
Earth
&
Environment,
Franklin
&
Marshall
College,
415
Harrisburg
Ave,
Lancaster,
PA
17604-­‐3003
2
Planetary
Science
Ins7tute,
1700
East
Fort
Lowell,
Suite
106,
Tucson,
AZ
85719
Session
No.
307-­‐-­‐Booth#
333
Planetary
Geology
(Posters)
Wednesday,
4
November
2015:
9:00
AM-­‐6:30
PM
2015
GSA
Annual
Mee7ng
in
Bal7more,
Maryland,
USA
(1-­‐4
November
2015)
Paper
No.
307-­‐19
Presenta7on
Time:
9:00
AM-­‐6:30
PM
Fan 45: A Complex Stepped Fan Memnonia: A Simple Stepped Fan
Discussion
Conclusions
Sites Se.ng Type
Basin
Area
(km^2)
Fan
Area
(km^2)
Channel
Area
(km^2)
Strahler
Stream
Order
Surficial
Incision
Channel
Brink
Points
Avg.
Brink
Point
Spacing
(m)
Memnonia Crater Simple 3195 6.56 42.32 1st Remnant 13 427
Fan
15 Crater Complex 3778 18.03 16.64 2nd No 11 1868
Tyras Crater Simple 2029 77.41 182.75 2nd Remnant 10 1171
Fan
22 Crater Simple 892 23.38 17.53 1st No 6 523
Fan
27
Fre?ed
Canyon Complex 3337 45.94 33.77 2nd Remnant 9 4830
Fan
30
Ellipse
Crater Simple 553 10.38 430.57 3rd Remnant 6 900
Fan
34 Crater Simple 1164 14.05 8.87 1st No 5 467
Fan
37 Crater Simple 3291 66.61 29.76 2nd Remnant 10 2153
Fan
45 Crater Complex 852 55.27 27.52 1st Yes 15 406
Fan
46
Fre?ed
Canyon Simple 642 12.85 15.80 1st Yes 2 NA
Coprates
Fre?ed
Canyon Simple 620 38.31 113.59 1st Yes 21 623
Gale Crater Complex 18166 2.08 183.21 1st Yes 4 894
• Complex
fan
• Transect
bends
at
brink
point
8
and
begins
to
trend
more
southerly
sugges7ng
several
possible
phases
of
forma7on
• 15
Major
brink
points
• Mul7ple
channel
incisions
present
on
fan
surface
• Formed
in
a
crater
basin
• V-­‐shaped
feeder
channel
• Fan
height
approximately
400
m
• Fan
length
approximately
6,000
m
• Major
brink
points
mapped
by
following
steep
changes
in
slope
• Eleva7on
profiles
along
brink
points
plot
flat
over
large
distances
• Brink
points
follow
contours
of
equal
eleva7on
• Unusual
depression
formed
between
lobes
12
and
13
at
the
top
of
Memnonia
is
interpreted
as
late
stage
aeolian
erosion
• Lobes
13
and
12
seem
separate
according
to
slope
shade
but
appear
the
same
according
to
eleva7on
• Simple
fan
• Transect
is
linear
with
concentric
lobes
• 13
Major
brink
points
• No
channel
incisions
present
on
fan
surface
• Formed
in
a
crater
basin
• V-­‐shaped
feeder
channel
• Fan
height
is
approximately
175
m
• Fan
length
approximately
7,040
m
General Characteristics of Stepped Fans
• Simple
fans
were
triangular
in
map
view,
had
laterally
con7nuous,
concentric
lobes
and
had
roughly
equal
lobe
spacing
• Complex
fans
appear
to
have
superimposed
lobes
on
top
of
each
other,
were
irregularly
shaped
in
map
view
and
are
highly
variable
in
appearance
Mar;an
stepped-­‐delta
forma;on
by
rapid
water
release:
Kraal
et
al.
(2008)
Laboratory
experiments
conducted
by
Kraal
et
al
(2008)
suggest
that
morphological
features
observed
with
stepped
fans
on
Mars
could
be
explained
by
the
following
processes:
I. Feeder
channel
breaching
the
crater
wall
II. Alluvial
fan
deposi7on
on
crater
floor
III. Accumulated
sediment
on
valley
floor
decreases
infiltra7on
rate
and
increases
accumula7on
of
water
IV. Rising
water
levels
paired
with
con7nuous
deposi7on
form
stepped
delta
lobes
V. Con7nuing
sedimenta7on
would
yield
prograding
lobes
over
exis7ng
ones
VI. Con7nua7on
of
flow
without
sedimenta7on
would
yield
erosive
channels
on
fan
surface
A
A’
A
A’
A
A’
A
A’
Hypothesis
for
FormaJon
of
Stepped
Fans
Expected
morphological
features
and
observaJons
EvaluaJon
and
interpretaJon
1.
Volcanic
flows
• Lava
Vents
or
cones
• Volcanic
flow
textures
• No
evidence
of
ac7ve
or
relict
volcanism
observed
2.
Mass
was7ng
• Internal
layering
• Lobate
step
shape
• Unobserved
lobes
and
internal
layering
of
sediment
is
atypical
of
mass
was7ng
events
3.
Alluvial
fan
sheet
floods
• Integrated
drainage
network
• Discon7nuous,
nonconcentric
steps
• Nonconcentric
and
discon7nuous
steps
are
atypical
of
terrestrial
alluvial
fans
4.
Erosion
of
fan
• Wave
cut
benches
should
display
associated
shorelines
on
highlands
• Lack
of
shoreline
evidence
on
crater
rim
suggests
alterna7ve
forma7on
methods
5.
Fan-­‐delta:
Transgressive
case
• Integrated
drainage
network
• Dis7nc7ve
longitudinal
profile
• Some
fans
lack
incision
channels
on
surface
• Supported
by
Kraal
model
and
occurrence
of
incision
channels
on
fan
surface
suggests
subaerial
erosion
aler
stepped
fan
deposi7on
6.
Fan-­‐delta:
Regressive
case
• Integrated
drainage
network
• Dis7nc7ve
longitudinal
profile
• Incision
channels
observed
on
some
fan
surfaces
• Not
all
fans
exhibit
incision
channels
• Similar
to
the
transgressive
case,
only
not
all
fans
exhibit
incision
channels
on
their
surfaces
as
would
be
expected
with
a
regressive
model.
Background
37_2N51WÜ
1.5 0 1.50.75 Kilometers
34_10S306EÜ
0 0.45 0.9 1.35 1.80.225
Kilometers
22_8S214EÜ
0 1 2 3 40.5
Kilometers
21_16S205E
0 1 2 3 40.5
Kilometers
Ü 15_9N16E
0 1 2 3 40.5
Kilometers
Ü
Methods
• Lobes
on
stepped
fan
surfaces
were
mapped
along
the
top
of
the
lobe
• Lobes
were
mapped
by
observing
changes
in
slope
from
a
slopeshade
DEM
• To
be
considered
major
lobes
must
be
con7nuous
and
concentric
• Most
major
lobes
also
displayed
changes
in
albedo
as
a
result
of
the
change
in
slope
and
were
also
observable
via
satellite
imagery
• Not
all
shils
in
albedo,
observed
with
satellite
imagery,
represented
a
lobe
feature
Hypothesized
FormaJon
Methods
I. Volcanic
flow
deposits
II. Mass
was7ng
events
III. Erosion
of
alluvial
fan
by
means
of
erosive
wave
ac7on
IV. Alluvial
fan
deposi7on
V. Transgressive
deposi7on
of
fan-­‐delta
VI. Regressive
deposi7on
of
fan-­‐delta
Here
we
focus
on
evalua7ng
fan-­‐delta
scenarios,
consistent
with
prior
studies
laboratory
simula7ons,
and
terrestrial
analogs
(eg.
1-­‐8
references
from
proposal).
Memnonia
Fan
45
LocaJon
of
Stepped
Fans
on
Mars
Examples of Martian Stepped Fans
Incised
Chanel
1.
Classifica7on
of
‘simple’
and
‘complex’
fans
based
on
morphological
a?ributes
in
image
data
may
not
reflect
forma7on
process.
Ini7al
assessment
of
eleva7on
data
for
two
fans
illustrated
that
the
‘simple’
fan
had
a
dis7nct
character
in
the
upper
and
lower
reaches,
whereas
the
‘complex’
fan
had
a
simple
form.
This
result
highlights
the
importance
of
high-­‐resolu7on
eleva7on
data
as
landform
shape
is
not
always
discernible
in
image
data
alone.
4.
Fan
45
has
a
uniform
slope
of
~8
degrees
with
steps
every
~270
m
distance
and
~28
m
eleva7on
change.
The
change
in
fan
orienta7on
reflects
topographic
confinement,
rather
than
different
forma7on
processes.
Con7nuous
water
level
rise
may
result
in
equally
spaced
steps
(Muto
and
Steel,
2001a,
see
proposal).
2.
Longitudinal
profiles
for
the
two
Mar7an
stepped
fans
examined
only
slightly
differed
from
that
formed
in
the
laboratory
simula7on
(Kraal
et
al.,
2008),
and
suggest
that
stepped
fan
forma7on
may
involve
similar
processes
but
with
a
unique
development
scenarios
7ed
to
water
fluctua7ons
at
each
site.
-­‐
We
see
some
evidence
for
an
earlier
alluvial
fan
phase
in
the
fan
form
at
site
45
-­‐Although
Memnonia
fan
was
ini7ally
compared
to
the
laboratory
simula7on
by
Kraal
et
al.
(2008),
we
observe
the
steps
are
concentrated
on
the
mid
and
lower
fan,
not
the
upper
fan
as
in
the
simula7on.
Also,
the
lower
fan
has
two
pronounced
benches
that
may
reflect
stable
or
repeated
lake
levels
at
these
lower
eleva7ons.
Our
observa7ons
suggest
step
forma7on
is
associated
with
varia7ons
in
water
level.
Along-­‐step
profiles
are
horizontal,
consistent
with
shoreline
intersec7ons
with
the
fan
surface.
Future
work
will
examine
eleva7on
data
for
other
Mar7an
stepped
fans
and
inves7gate
what
details
of
discharge
and
lake
level
fluctua7ons
are
consistent
with
the
observed
mar7an
fan
shape.
Up
fan
Memnonia: A Simple Stepped Fan
Memnonia: Transects
Fan 45: Transects
Up
fan
Up
fan
Up
fan
Fan
45
Memnonia
Simple
Fan
Simple
Fan
Simple
Fan
Simple
Fan
Complex
Fan
Kraal Laboratory Model
Simple
Fan
3.
Memnonia
has
no
obvious
rela7onship
between
step
spacing
and
fan
slope.
The
fan
profile
has
three
components:
a
shallow
0.5
degrees
upper
fan
with
no
steps,
a
steeper
4
degree
mid-­‐fan
that
transi7ons
to
the
lower
fan
with
benches.
Where
steps
occur
(steps
4-­‐11,
below
-­‐2070
m),
they
have
~248
m
spacing,
but
the
ver7cal
drop
between
steps
varies
from
~
2
m
to
~
20
m.
Stable
lake
levels
may
have
formed
the
distal
benches.
The
complex
fan
45
exhibits
some
interes7ng
morphological
features:
• Surficial
incision
channels
easily
observed
along
the
delta
lobe
suggest
subaerial
fluvial
erosion
and
possibly
a
regressive
fan-­‐delta
deposi7onal
sepng
Incision
Channels
References:
-­‐Kraal,
Erin
R.,
et
al.
"mar7an
Stepped-­‐Delta
Forma7on
By
Rapid
Water
Release."
Nature
21
Feb.
2008:
973-­‐77
-­‐De
Villiers,
Germari,
Maarten
G.
Kleinhans,
and
George
Postma.
"Experimental
delta
forma7on
in
crater
lakes
and
implica7ons
for
interpreta7on
of
Mar7an
deltas."
Journal
of
Geophysical
Research:
Planets
118.10
(2013):
651-­‐70
-­‐Weitz,
Catherine
M.,
et
al.
"Forma7on
of
a
terraced
fan
deposit
in
Coprates
Catena,
Mars."
Icarus
184
(2006):
436-­‐51
The
topographic
profile
of
complex
fan
45
is
similar
in
many
ways
the
Kraal
laboratory
model
created
under
controlled
transgressive
water
level
condi7ons
• The
X-­‐X’
profile
to
the
right
shares
morphological
characteris7cs
with
the
Kraal
laboratory
controlled
profile
below.
Both
have
in
common
the
general
shape
and
placement
of
the
Crater
Floor
(CF),
Delta
Lobe
(DL)
and
Stream
Canyon
(SC)
in
profile.
X’
X
CF
DL
SC
A
A’
A
A’
To
the
lel
are
two
panels
illustra7ng
the
thermophysical
proper7es
of
fan
45.
There
is
a
subtle
change
that
occurs
as
a
func7on
of
fan
posi7on.
The
upper
fan
where
steps
occur
is
characterized
by
a
rela7vely
uniform
~230
7u
(thermal
iner7a
unit),
whereas
the
lower
fan
exhibits
an
increase
to
~290
7u.
These
values
are
consistent
with
weakly
to
moderately
indurated
sedimentary
deposits,
but
the
higher
thermal
iner7a
values
in
the
distal
part
of
the
fan
suggests
a
coarsening
outward
trend
that
is
consistent
with
the
inferred
change
in
deposi7onal
environment
from
subaerial
deposi7on
in
the
lower
reaches
to
subaqueous
deposi7on
upfan
in
a
lacustrine
environment.