We are approaching the end of the third year of mapping the Athabasca Valles region of Mars. The linework has been adjusted in response to new CTX images and we are on schedule to submit the 4 MTM quads (05202, 05207, 10202, 10207) and ac-companying paper by the end of this fiscal year

Hare, T.

Jaeger, W. L.

Keszthelyi, L. P.

Tanaka, K.

NASA Technical Reports Server

GEOLOGIC MAPPING OF ATHABASCA VALLES.  L. P. Keszthelyi1, W. L. Jaeger1, K. Tanaka1, and T. 
Hare1, 1U.S. Geological Survey, Astrogeology Team, 2255 N. Gemini Dr., Flagstaff, AZ  86001.   
 
 
Introduction:  We are approaching the end of the 
third year of mapping the Athabasca Valles region of 
Mars.  The linework has been adjusted in response to 
new CTX images and we are on schedule to submit the 
4 MTM quads (05202, 05207, 10202, 10207) and ac-
companying paper by the end of this fiscal year.   
Previous Work:  The study area is of special in-
terest for several reasons: (a) it is central to the contro-
versial and now disproven "Elysium Sea" [1,2]; (b) it  
contains one of the best preserved outflow channels on 
Mars [2-4]; (c) the lavas that drape the entire channel 
system are the best example of a turbulent flood lava 
anywhere in the Solar System [2,5]; (d) the extremely 
young lavas have interesting stratigraphic relationships 
with the long-puzzling Medusae Fossae Formation 
(MFF).  The map area also covers the confluence of 
lavas from the Elysium rise, multiple small vents, and 
vast flood lavas [6-9].  Moreover, the remnant knobs 
of ancient highlands in this region may help constrain 
the current nature of the Highlands-Lowlands Bound-
ary (HLB).   
Mapping Methodology:  Two factors drive us to 
map the Athabasca Valles area in unusual detail: (1) 
the extremely well-preserved and exposed surface 
morphologies and (2) the extensive high resolution 
imaging.  The mapping has been done exclusively in 
ArcGIS, using individual CTX, THEMIS VIS, and 
MOC frames overlying the controlled THEMIS IR 
daytime basemap.  MOLA shot points and gridded 
DTMs are also included.  It was found that CTX im-
ages processed through ISIS are almost always within 
300 m of the MOLA derived locations, and usually 
within tens of meters, with control.  The generally 
good SNR and minimal artifacts make the CTX images 
vastly more useful than the THEMIS VIS or MOC 
images.  Furthermore, even without control, the loca-
tion of the CTX images was better (compared to 
MOLA) than the controlled THEMIS IR mosaic.   
The bulk of the mapping was done at 1:50,000.  
The location of certain contacts is generally accurate to 
a few pixels (tens of meters).  Approximate contacts 
indicate that the actual contact (e.g., a flow margin) is 
not directly visible but the location can be inferred 
from a change in texture.  Where CTX data were not 
available, mapping was often done at 1:100,000 and 
most contacts are mapped as inferred/queried.  Some 
inferred contacts underneath thin lava and other man-
tling deposits are noted using the symbol for a buried 
contact.  Contacts within a flow field are labeled as 
"other" and show as white lines in Fig. 1.   
Athabasca Valles Flood Lava:  The central goal 
of this mapping project is to study the flood lava that 
Jaeger et al. [2] showed coating Athabasca Valles.  
Jaeger et al. [5] show that the flow was a turbulent 
flood of lava with eruption rates peaking around 107 
m3/s.  This flood lava is a proper lithochronologic unit 
that we have called the Athabasca Valles Lava (Aav).   
The Aav exhibits a series of lava facies, from 
drained channels near-vent to platy-ridged surfaces in 
the medial portion to inflated pahoehoe at the distal 
margins.  The most difficult contacts to identify are 
where the marginal inflated pahoehoe from different 
eruptions intermingle.  The most surprising aspect of 
the Aav is that some parts of it appear to be being ex-
humed from underneath ~100 m of the Medusae Fos-
sae Formation (MFF).   
Other Geologic Features:  Few events have taken 
place since the emplacement of the Aav.  There are 
patches of recent aeolian dunes and, as noted earlier, 
some mantling by the MFF and dust.  Some of the tec-
tonic features in the study area record young deforma-
tion, probably via reactivation of older faults.  For ex-
ample, a wrinkle ridge near the western edge of the 
mapped extent of Aav is coated by lava but also ap-
pears to have deformed it.   
We have also been able to decipher a large part of 
the sequence of lava flows erupted from small shields 
and fissures prior to the Aav.  These are found pre-
dominantly in the southeastern section of the map area.  
The widely distributed vents are divides into tholi, 
fissures, and point vents labeled with letters in Fig. 1.  
Most appear to have fissure segments generally paral-
lel to the Cerberus Fossae.  We are starting to see hints 
that some of the vents may have fed multiple erup-
tions, or at least long-lived multi-phase eruptions.  
These details can only be observed because of the ex-
tremely pristine nature of the flow surfaces.   
Remaining Work:  The mapping is largely com-
plete, though some more detail in the Elysium rise 
lavas is desired.  The supporting text and figures are 
not yet ready for submission but we still expect to 
submit the map by the end of FY09.   
References: [1] Murray J. B. et al. (2005) Nature, 
434, 352-356. [2] Jaeger W. L. et al. (2007) Science, 
317, 1709-1711. [3] Tanaka and Scott (1986) LPS 
XVII, 865. [4] Burr D. M. et al. (2002) Icarus, 159, 53-
73. [5] Jaeger W. L. et al. (in revision) Icarus. [6] 
Plescia J. B. (1990) Icarus, 88, 465-490. [7] Lanagan 
P. D. (2004) Ph.D Thesis, Univ. Arizona. [8] Keszthe-
lyi, L. et al. (2004) G3, 5, 2004GC000758.   
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https://ntrs.nasa.gov/search.jsp?R=20100017205 2019-08-29T19:04:45+00:00Z
 
Figure 1.  Export of ArcGIS project with THEMIS IR basemap overlain with colorized MOLA elevations and 
geologic linework (contacts and vent structures).  Vents for the smaller pre-Athabasca Valles Flood Lava flows are 
labeled.  Tholi are labeled ta, tb, and tc.  Fissures are marked with fa, fb, and fc while small vents are va, vb, and vc.  
Note that there are 4 separate locations that are all labeled va because they appear to have been simultaneously ac-
tive (feeding flows on both sides of a wrinkle ridge).  Fissure b is mapped having fed two separate flow fields, 
though it is possible that these are the products of different episodes of the same eruption.   
 
 
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Geologic Mapping of Athabasca Valles

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