Geologic mapping and stratigraphic analyses of MTM -30247, -35247, and -40247 quadrangles are being used to characterize the Reull Vallis (RV) system and to determine the history of the eastern Hellas region of Mars. Studies of RV examine the roles and timing of volatile-driven erosional and depositional processes and provide constraints on potential associated climatic changes. This study complements earlier investigations of the eastern Hellas region, including regional analyses [1-6], mapping studies of circum-Hellas canyons [7-10], and volcanic studies of Hadriaca and Tyrrhena Paterae [11-13]. Key scientific objectives for these quadrangles include 1) characterization of RV in its "fluvial zone," 2) analysis of channels in the surrounding plains and potential connections to and interactions with RV, 3) examination of young (?), presumably sedimentary plains along RV that embay the surrounding highlands, and 4) determination of the nature of the connection between segments 1 and 2 of RV

Crown, D. A.

Mest, S. C.

NASA Technical Reports Server

GEOLOGIC MAPPING OF MTM -30247, -35247 AND -40247 QUADRANGLES, REULL VALLIS  
REGION OF MARS. S.C. Mest1,2 and D.A. Crown1, 1Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 
106, Tucson, AZ  85719-2395, mest@psi.edu; 2Planetary Geodynamics Lab, NASA GSFC, Greenbelt, MD  20771. 
 
Introduction: Geologic mapping and stratigraphic 
analyses of MTM -30247, -35247, and -40247 
quadrangles are being used to characterize the Reull 
Vallis (RV) system and to determine the history of the 
eastern Hellas region of Mars. Studies of RV examine 
the roles and timing of volatile-driven erosional and 
depositional processes and provide constraints on 
potential associated climatic changes. This study 
complements earlier investigations of the eastern Hellas 
region, including regional analyses [1-6], mapping 
studies of circum-Hellas canyons [7-10], and volcanic 
studies of Hadriaca and Tyrrhena Paterae [11-13]. Key 
scientific objectives for these quadrangles include 1) 
characterization of RV in its “fluvial zone,” 2) analysis 
of channels in the surrounding plains and potential 
connections to and interactions with RV, 3) examination 
of young (?), presumably sedimentary plains along RV 
that embay the surrounding highlands, and 4) 
determination of the nature of the connection between 
segments 1 and 2 of RV. 
 
Project Status: This analysis of RV includes 
preparation of the geologic map of MTM quadrangles -
30247, -35247, and -40247 (compiled on a single 1:1M-
scale base). The current map area is included in 
previous Viking-based mapping efforts at regional [5,6] 
and local (1:500K; MTM -30247) scales. Crater size 
frequency distributions compiled for the regional 
analysis of RV [5,6] will be used in conjunction with 
newly generated crater statistics for units mapped in the 
current study using the new datasets (e.g., MOC, 
THEMIS, CTX and HiRISE). This mapping effort will 
synthesize past results and new analyses, completing 
MTM-scale mapping of the entire RV system. 
 
Mapping Results: This section describes results 
derived from mapping of MTMs -30247, -35247, and  
-40247 combined with results from previous regional 
[5,6] and local mapping efforts of this area. 
 
Highland degradation: Small valley networks and 
channels dissect highland terrains in this area. Most 
fluvial features are found in low-lying areas and appear 
to erode a sedimentary unit that fills intermontane areas 
[5-8]. These networks consist of narrow (<1 km) valleys 
up to several tens of kilometers in length and exhibit 
rectilinear patterns. Valley and network morphologies 
suggest they could have formed by combinations of 
runoff and sapping processes. 
Several large craters in the map area exhibit 
degraded rims, parallel interior gullies, and eroded 
ejecta blankets. Several craters also contain debris 
aprons that extend from the craters’ interior walls onto 
their floors. Most craters in the map area are partially 
filled by smooth or hummocky deposits. The range of 
crater preservation and the presence of gullies and 
debris aprons suggest that a combination of fluvial 
processes and mass wasting is responsible for erosion 
and degradation of highland craters [2,5-8,14-18]. 
 
Tectonism: Wrinkle ridges and ridge rings are the most 
prominent tectonic features, found predominantly in the 
northern part of the map area within ridged plains. Two 
dominant trends are observed—NE–SW (Hellas radial) 
and NW–SE (Hellas concentric)—indicating either 
multiple stress regimes were active concurrently or the 
stress regime shifted over time [19-21]. Crosscutting 
relationships suggest that ridge formation occurred after 
plains emplacement (Early Hesperian) and prior to 
collapse events and fluvial dissection associated with 
the formation of upper RV (mid-Hesperian?) [5,6]. 
 
Reull Vallis System: Segment 1 (S1) and part of 
Segment 2 (S2) of RV are found within the map area. 
S1 (~240 km long, 8–47 km wide, 110–600 m deep) is 
found in the eastern part of the map area within MTMs  
-30247 and -35247 and displays erosional scarps, scarp-
bounded troughs, small theater-headed channels that 
converge at a large (~50 km across) depression, 
streamlined inliers of ridged plains material, and scour 
marks on the canyon floor. To the south, RV narrows 
then opens into a series of irregular scarp-bounded 
basins that also contain blocks of ridged plains material 
on their floors. Floor materials are generally smooth 
within S1 and likely include fluvial deposits, as well as 
debris contributed by collapse of the vallis walls. The 
overall morphology of S1 suggests formation by a 
combination of subsurface and surface flow and 
collapse of ridged plains material; this segment is 
believed to be the source area for at least some of the 
fluids that carved RV downstream [5,6,22]. 
An obvious surface connection between S1 and S2 
is not apparent. Recent work using HRSC data suggests 
that the intersection of S1 and S2 marks the site of the 
Morpheos basin that formed in an early stage of RV's 
evolution [23,24]. It is believed that water flowing south 
from S1 accumulated in the Morpheos basin and was 
released to carve S2. 
Segment 2 consists of morphologically distinct 
upper (S2-U) and lower (S2-L) parts. Contained within 
MTM -40247, S2-U displays sinuous morphology and 
extends for ~240 km through degraded highlands. S2-U 
(6 to 13 km wide, 110 to 650 m deep) exhibits features 
indicative of surface flow including layering or 
terracing along canyon walls, and braided gullies 
incised in floor material [5,6]. 
A portion of S2-L occurs in the southwest part of 
the map area, and begins where a narrow (1–2 km 
wide), shallow (~100 m deep) gully downcuts into the 
canyon floor [5,6]. This part of S2-L extends for ~70 
https://ntrs.nasa.gov/search.jsp?R=20080041004 2019-08-29T19:11:00+00:00Z
km before opening into a large basin west of the map 
area [7,8]. Here, S2-L displays steep walls and a 
relatively flat floor, and is narrower (6 km) and 
shallower (140–350 m) than the remainder of S2-L to 
the west [7,8]. Unlike S2-U, S2-L does not display 
features on its floor indicative of fluvial erosion, though 
the canyon contains small-scale layering or terracing 
(tens to hundreds of meters thick) along its walls near 
the transition. Floor material consists of debris infilling 
the canyon from fluvial deposition and wall collapse, 
and exhibits pits and lineations that parallel the vallis 
walls similar to lineated valley fill in fretted terrain. 
The morphology of S2 suggests initial formation by 
fluvial processes and subsequent modification by 
collapse and mass wasting. Several narrow, steep walled 
and flat-floored channels enter S2-U suggesting fluvial 
contributions to RV. These tributaries begin within and 
cut through various units including the basin–rim unit 
and smooth plains [5,6]. 
 
Regional Stratigraphy: The northern part of the map 
area is composed primarily of ridged plains material, 
initially believed to have been emplaced as flood lavas 
[25-27], although no obvious flow fronts are visible. 
Subsequent fluvial activity and deposition of sediments 
have significantly modified portions of the ridged plains 
in this area. Inter-ridge areas display relatively smooth 
and featureless surfaces except for the presence of low-
relief scarps and small sinuous channels, interpreted to 
be fluvial in origin. MOC images show that inter-ridge 
areas contain dune features indicating eolian 
redistribution of sediments [5,6]. 
Analyses of the map area to date indicate that 
highland materials are surrounded and embayed by at 
least two plains units identified in previous mapping 
studies: dissected and smooth plains [5,6]. Dissected 
plains material, previously mapped as ridged plains 
[27], is found in MTM -35247 along the western edge 
of the map and between S1 and S2, and in the southeast 
part of the map area. This unit is characterized by a 
smooth surface dissected by narrow sinuous channels 
and low-relief scarps, and displays a few eroded wrinkle 
ridges. The contact between the ridged plains and 
dissected plains is gradational in most places, but the 
lack of high concentrations of pristine wrinkle ridges in 
dissected plains material allows it to be distinguished 
from ridged plains material [5-8]. Dissected plains 
material is interpreted to consist of volcanic and/or 
sedimentary materials eroded by fluvial processes. 
Smooth plains material, originally mapped as part 
of the smooth plateau unit [27], is found adjacent to S2 
of RV, embays highland units where they are in contact, 
and exhibits lobate terminations in some locations [5-8]. 
In high-resolution images, smooth plains display low-
relief scarps, small channels, pits and small-scale 
undulations suggesting sublimation and collapse of 
volatile-rich material, as well as modification by fluvial 
and eolian processes. Along S2-U of RV, smooth plains 
material shows a fluted scarp boundary, whereas along 
most of S2-L, smooth plains material extends to the 
canyon wall [7,8]. Smooth plains are interpreted to be a 
mixture of sediments deposited from overflow of RV 
and at the termini of valley networks, and may also 
include materials deposited via mass wasting [5-8]. 
Mass wasting formed some of the youngest 
deposits in the map area. Debris aprons [1,5-8,16-18] 
and other viscous flow features [28,29] are found along 
highland massifs and crater walls, and are interpreted to 
consist of debris mass-wasted from steep slopes. 
Massif-associated features typically have uniform or 
mottled albedo, lobate frontal morphologies, and appear 
to be composed of multiple coalescing flows. Crater-
associated features are relatively small and display 
mottled albedo, relatively featureless surfaces, and 
arcuate to lobate fronts. Some crater floor deposits 
contain rings concentric to the crater walls, similar to 
concentric crater fill [30,31]. 
 
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Geologic Mapping of MTM -30247, -35247 and -40247 Quadrangles, Reull Vallis Region of Mars

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