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Prepared for the National Aeronautics and Space Administration

Geologic Map of MTM 35337, 40337, and 45337 Quadrangles, Deuteronilus 

Mensae Region of Mars

By Frank C. Chuang and David A. Crown

Pamphlet to accompany

Scientific Investigations Map 3079

2009

U.S. Department of the Interior

U.S. Geological Survey

1

INTRODUCTION

Deuteronilus Mensae, first defined as an albedo feature at 

lat 35.0° N., long 5.0° E., by U.S. Geological Survey (USGS) 

and International Astronomical Union (IAU) nomenclature, is 

a gradational zone along the dichotomy boundary (Watters and 

McGovern, 2006) in the northern mid-latitudes of Mars. The 

boundary in this location includes the transition from the rugged 

cratered highlands of Arabia Terra to the northern lowland 

plains of Acidalia Planitia (fig. 1). Within Deuteronilus Mensae, 

polygonal mesas are prominent along with features diagnostic of Martian fretted terrain, including lobate debris aprons, 

lineated valley fill, and concentric crater fill (Sharp, 1973a; 

Carr, 1996, 2001). Lobate debris aprons, as well as the valley 

and crater fill deposits, are geomorphic indicators of ground 

ice (Squyres, 1978, 1979, 1989; Lucchitta, 1984; Squyres and 

Carr, 1986), and their concentration in Deuteronilus Mensae 

is of great interest because of their potential association with 

Martian climate change (Head and others, 2003, 2005, 2006a,b). 

The paucity of impact craters on the surfaces of debris aprons 

and the presence of ice-cemented mantle material (Mustard and 

others, 2001) imply young (for example, Amazonian) surface 

ages that are consistent with recent climate change in this region 

of Mars.

North of Deuteronilus Mensae are the northern lowlands, 

a potential depositional sink that may have had large standing bodies of water or an ocean in the past (Parker and others, 

1989, 1993; Edgett and Parker, 1997; Head and others, 1999; 

Clifford and Parker, 2001; Kreslavsky and Head, 2002; Carr 

and Head, 2003; Fairen and others, 2003; Webb, 2004; Ghatan 

and Zimbelman, 2006). The northern lowlands have elevations 

that are several kilometers below the ancient cratered highlands 

with significantly younger surface ages. The morphologic and 

topographic characteristics of the Deuteronilus Mensae region 

record a diverse geologic history, including significant modification of the ancient highland plateau and resurfacing of lowlying regions. Previous studies of this region have interpreted a 

complex array of geologic processes, including eolian, fluvial 

and glacial activity, coastal erosion, marine deposition, mass 

wasting, tectonic faulting, effusive volcanism, and hydrovolcanism (see McGill, 2002).

The origin and age of the Martian crustal dichotomy 

boundary are fundamental questions that remain unresolved at 

the present time. Several scenarios for its formation, including 

single and multiple large impact events, have been proposed and 

debated in the literature (Wilhelms and Squyres, 1984; Frey and 

Schultz, 1988; McGill, 1989; Schultz and Frey, 1990; McGill 

and Squyres, 1991, Nimmo and Tanaka, 2005; Andrews-Hanna 

and others, 2008). Endogenic processes whereby crust is 

thinned by internal mantle convection (Wise and others 1979; 

McGill and Dimitriou, 1990; Zuber and others, 2000; Zhong 

and Zuber, 2001; Zuber, 2001) and tectonic processes have also 

been proposed (Sleep, 1994, 2000). Planetary accretion models 

and isotopic data from Martian meteorites suggest that the crust 

formed very early in Martian history (Solomon and others, 

2005). Using populations of quasi-circular depressions extracted 

from the topography of Mars, other studies suggest that the age 

difference between the highlands and lowlands could be ~100 

m.y. (Frey, 2006). Furthermore, understanding the origin and 

age of the dichotomy boundary has been made more complicated due to significant erosion and deposition that have modified the boundary and its adjacent regions (Skinner and others, 

2004; Irwin and others, 2004; Tanaka and others, 2005; Head 

and others, 2006a; Rodriguez and others, 2006). The resulting 

diversity of terrains and features is likely a combined result of 

ancient and recent events. Detailed geologic analyses of dichotomy boundary zones are important for understanding the spatial 

and temporal variations in highland evolution. This information, 

and comparisons to other highland regions, can help elucidate 

the scale of potential environmental changes.

Previous geomorphic and geologic mapping investigations of the Deuteronilus Mensae region have been completed 

at local to global scales. The regional geology was first mapped 

by Lucchitta (1978) at 1:5,000,000 scale using Mariner 9 data. 

This study concluded that high crater flux early in Martian history formed overlapping craters and basins that were later filled 

by voluminous lava flows that buried the impacted surface, 

creating the highlands. After this period of heavy bombardment, 

fluvial erosion of the highlands formed the canyons and valleys, 

followed by dissection that created the small mesas and buttes, 

and later, formation of the steep escarpment marking the present-day northern highland margin. After valley dissection, mass 

wasting and eolian processes caused lateral retreat of mesas and 

buttes, followed by eruption of flood lavas that covered parts of 

the current-day smooth plains and dissected highlands. Based 

on Viking Orbiter data, Greeley and Guest (1987) mapped 

the region at 1:15,000,000 scale and divided the map region 

into Noachian highland units, Hesperian ridged plains, older 

channel materials, and young slide materials (which include 

both discrete debris aprons and adjacent plains). Collapse and 

redistribution of highland materials occurred locally from the 

Late Hesperian into the Amazonian. Geologic mapping at 

1:1,000,000 scale of MTM quadrangles 30332, 35332, 40332, 

and 45332 in the Deuteronilus Mensae region by McGill (2002) 

defined several geologic units that are similar to those described 

herein. The geologic history of this region included Middle 

Noachian and Hesperian resurfacing, Hesperian and Amazonian crater lakes, and formation of Hesperian to Amazonian 

smooth and lineated materials. Recent geologic mapping by 

Tanaka and others (2005) at 1:15,000,000 scale of the Martian 

northern plains have identified four material units that cover the 

map region: a widespread Noachian unit of continuous cratered 

highland plateau and large mesas, a Hesperian-Noachian unit 

of collapsed materials from basal sapping and mass wasting 

that forms part of the lowlands, and two Deuteronilus Mensaespecific units related to Hesperian and Amazonian deposition of 

ice-rich, mass-wasted debris.

DATA AND GIS MAPPING TECHNIQUES

Digital base maps, images, and ancillary information from 

the U.S. Geological Survey (USGS) were used in the geological mapping of the Deuteronilus Mensae region in conjunc-
2

tion with Geographic Information Systems (GIS) software. 

Datasets include a full-resolution (~50 m/pixel) Viking Orbiter 

Mars Transverse Mercator (MTM) base map, full-resolution 

(~50 m/pixel) Thermal Emission Imaging System (THEMIS) 

daytime Infrared (IR) and Visible (VIS) wavelength mosaics 

(data through 3/05), individual THEMIS IR and VIS images, 

128 pixel/degree (~463 m/pixel) resolution Mars Orbital Laser 

Altimeter (MOLA) digital elevation model (DEM), gray and 

color synthetic hillshades of the MOLA DEM, and a 100-meter 

interval contour shapefile. The Viking base map is gap-free and 

covers the entire map region. Additional datasets used in our 

mapping and crater counts include a 256 pixel/degree (~231 m/

pixel) resolution publicly released THEMIS daytime IR mosaic 

from Arizona State University (ASU), a 20 meters/pixel Mars 

Express High-Resolution Stereo Camera (HRSC) image, and 

individually processed Mars Orbiter Camera (MOC) narrowangle images at resolutions higher than 12 meters/pixel. The 

THEMIS IR mosaic from ASU contains image data released 

subsequent to the USGS version, and covers the entire map 

region with ~17% data gaps. The HRSC image (h1483_0000_

nd2.img) provided continuous coverage of the eastern half of 

the map region (~51%) and was used for crater counts. MOC 

images were used in selected areas to examine the surface morphology in detail.

The Viking, THEMIS, and MOLA DEM from USGS 

were all processed using Integrated Software for Imagers and 

Spectrometers (ISIS) software produced by the USGS Astrogeology Team. Map-projected THEMIS mosaics and images 

were produced from individual raw, radiometrically calibrated 

data. The HRSC data were processed using a modified version 

of the Video Image Communication And Retrieval (VICAR) 

software from the German Aerospace Center. All of the digital 

data, with the exception of HRSC and THEMIS IR from ASU, 

are in Transverse Mercator map projection with a center longitude of 30.0° E. and a center latitude of 0.0° using the International Astronomical Union (IAU) 2000 shape model of Mars 

(Seidelmann and others, 2002). For consistency, the HRSC and 

THEMIS IR from ASU were spatially adjusted in GIS to closely 

match the Transverse Mercator data.

Geologic units were mapped primarily on the Viking 

MTM base mosaic using Environmental Systems Research 

Institute (ESRI) ArcGIS ArcView software. Other mosaics or 

images were used where changes in image quality or lighting geometry occurred in the Viking mosaic. Contacts and 

structures were manually digitized and saved in an ArcGIS 

geodatabase for archiving and distribution. ArcGIS shapefiles 

exported from the geodatabase were later imported into Adobe 

Illustrator CS using a MAPublisher software plug-in. Relative 

age constraints for the geologic units were derived by counting 

the number and size distribution of superposed impact craters 

within the areas of each unit (for example, see Tanaka and 

others, 1992). The unit boundaries were digitized on Viking 

MTM and THEMIS daytime IR mosaics, and the surface 

area of each unit (polygon) was auto-calculated in ArcGIS. 

Impact craters were first counted using HRSC data covering 

the eastern half of the map region, followed by counts on the 

western half using Viking and THEMIS data. Although impact 

craters were more easily identified in the HRSC data due to its 

higher inherent resolution, craters down to 0.5 km in diameter 

could still be confidently identified in Viking and THEMIS 

data. Impact craters ,< 0.5 km in diameter were not counted. 

For all craters with a diameter > 0.5 km, the location, diameter 

(rim crest-to-crest), and image base used (Viking + THEMIS 

or HRSC) were recorded and saved in the geodatabase. Table 1 

summarizes the size-frequency data for the cumulative number 

of craters > 2, 5, and 16 km in diameter normalized to 106

km2. Figure 2 is a plot of the N(2) and N(5) crater data for all 

geologic units.

STRATIGRAPHY

Definitions of the geologic units are based on a combination of surface characteristics, contacts, and superposition relations in the image datasets that indicate differences in relative 

age. A total of eleven geologic units are defined and are divided 

into four groups: plateau material, plains material, impact crater 

material, and surficial material. Plateau material consists of the 

continuous ancient highland plateau and outcrops of the plateau 

in the form of polygonal mesas and small knobs scattered within 

the plains. Plains material consists of relatively flat expanses of 

smooth to hummocky deposits in low-lying areas north of the 

continuous highland margin. Impact crater material consists of 

rim, floor, and ejecta deposits of impact craters in a variety of 

preservation states, and Cerulli impact crater. Surficial material 

consists of lobate debris aprons and smooth fill deposits. 

Relative age determinations for the geologic units are primarily based on observed superposition relations in the Viking 

and THEMIS mosaics, MOLA DEM, and crater densities for 2, 

5, and 16 kilometer diameter craters (Tanaka, 1986; Tanaka and 

others, 1992). Several units have low numbers of superposed 

craters and their crater size-frequency data were not used in age 

designations. Figure 2 and table 1 show that N(2), N(5), and 

N(16) values for a given geologic unit do not always support 

designation of a single period or epoch because of differences 

in the number of craters in some size ranges relative to others. 

The complex geologic history of the region, including extensive 

erosion of ancient highland surfaces, has preferentially removed 

smaller craters on some surfaces. However, crater density data 

were generally useful in supplementing or refining observed 

relations to help constrain age ranges. In some cases, age designations were based strictly on observed superposition, crosscutting, and contact relations of the geologic units (table 2). The 

locations of some of these relations, which are described in the 

following sections on material types, are shown in figure 3.

For consistency with an earlier geologic map by McGill 

(2002), which is adjacent to the eastern margin of this map, we 

used the primary and secondary attributes of surface materials in the identification and nomenclature of mapped units 

(for example, see Rotto and Tanaka, 1995). This resulted in 

defining units based on both stratigraphy and geomorphology/

inferred erosional history. While this approach is different from 

planetary and terrestrial maps that follow a purely stratigraphic 

framework, it allows a visual representation of the overall geologic evolution similar to that shown by McGill (2002).
3

Plateau Material

Cratered highlands form most of the continuous plateau 

extending from the southern margin of the map region to the 

northern margin of Arabia Terra. Within the plateau and its 

remnants, three material units are identified. Lower smooth plateau material (unit Nplsl) consists of large flat mesa-like blocks 

north of the continuous plateau margin with top surface elevations ranging between –3,700 and –3,800 m. The blocks have 

low relief, generally no more than 100 m along their edges, with 

relatively featureless surfaces and sparse numbers of superposed 

craters. This material often underlies upper smooth plateau 

material to form layered polygonal mesas (lat 46.6° N., long 

21.4° E.) that are topographically higher than adjacent smooth 

and mottled plains. This relation is clearly evident in Viking 

data and at local scales in THEMIS VIS images (fig. 4). The 

lower smooth plateau material unit forms parts of the Hesperian 

older channel and ridged plains units in the Mars eastern equatorial region geologic map by Greeley and Guest (1987), and 

unmapped, small outcrops of the widespread Noachian Noachis 

Terra unit within the local Amazonian Deuteronilus Mensae 2 

unit in the northern plains geologic map by Tanaka and others 

(2005). The lower smooth plateau material unit is similar to the 

dark plateau unit mapped by McGill (2002).

North of the continuous plateau margin, upper smooth 

plateau material (unit Nplsu) occurs as high-standing polygonal mesas and smaller individual knobs or clusters of knobs 

within the northern lowlands. The top surfaces of mesas have a 

muted appearance compared to the plateau with low numbers of 

impact craters, most of which are less than a kilometer across in 

diameter. The steep mesa walls are smooth at Viking resolution, 

but in THEMIS VIS images, small alcoves are visible along 

the walls (fig. 5). Mesas have surface elevations ranging from 

–1,250 to –3,600 m that gradually decrease northward from the 

plateau margin. The mesas are topographically higher than the 

surrounding plains and surficial materials. A large high-standing 

circular mound at Deuteronilus Colles (lat 42.0° N., long 21.7° 

E.) includes irregular rounded knobs of smooth plateau materials. The knobs range in size from hundreds of meters to a 

few kilometers across. The mound lies at the center of a larger 

semi-circular area rimmed by polygonal mesas north of the continuous plateau margin (see fig. 1). The upper smooth plateau 

material unit is included as part of the highland terrain units in 

the Mars eastern equatorial region geologic map by Greeley and 

Guest (1987) and as part of the widespread Noachis Terra unit 

by Tanaka and others (2005). The upper smooth plateau material unit is similar to the smooth plateau unit mapped by McGill 

(2002).

South of the continuous plateau margin, upper smooth plateau material is characterized by a cratered surface with minor 

channels and large closed depressions. These surfaces have 

abundant primary impact craters up to a few tens of kilometers 

in diameter. Small sinuous channels, up to several kilometers 

long and a kilometer wide, cut parts of the plateau surface. The 

channels are not well developed and do not have prominent 

deposits at their termini. Several large closed depressions with 

irregular blocks or knobs of the plateau surface (fig. 6) are contained within a sub-circular basin in the plateau (lat 36.8° N., 

long 22.3° E.). The knobs and blocks range in size from a few 

hundred meters to several kilometers across. A few blocks have 

greater relief along one side of the block, suggesting that the top 

surface is tilted down into the surrounding smooth fill materials 

(fig. 7). Other blocks appear to expose at least two prominent 

layers along their margins (lat 36.6° N., long 23.2° E.). Much 

of the smooth plateau near the margin has been modified by the 

formation of fretted valleys (for example, Mamers Valles) and 

lobate debris aprons.

Dissected plateau material (unit Npld), found in association with upper smooth plateau material in the continuous 

highland plateau, exhibits surfaces that have been modified 

primarily by impact craters up to a few tens of kilometers in 

diameter and sinuous channels that are hundreds of meters to 

several tens of kilometers long and several hundred meters 

wide, similar to those in the upper smooth plateau materials. 

The number and apparent density of channels are much greater 

in this unit than in upper smooth plateau materials. The channels are concentric to the sub-circular basin (see fig. 6), and 

dissected plateau surfaces near the basin have gentle slopes 

(0.5–2.0° from MOLA data). The transition to adjacent upper 

smooth plateau material is often gradational and at the same 

relative elevation. Parts of the dissected plateau surface have 

been modified by secondary crater fields extending from Cerulli 

impact crater. The dissected plateau material unit forms part of 

the highland terrain units in the Mars eastern equatorial region 

geologic map by Greeley and Guest (1987) and part of the 

widespread Noachis Terra unit by Tanaka and others (2005). 

The dissected plateau material unit is similar to the hummocky 

plateau unit mapped by McGill (2002).

The three plateau material units represent the section of 

ancient highlands whose upper surfaces have been modified 

to various degrees by erosion and redistribution of material. 

The upper and lower smooth plateau materials together, form a 

layered sequence of the highlands. The dissected plateau material represents zones that have been influenced more by fluvial 

surface modification. The units themselves presumably consist 

of a combination of interbedded volcanic, sedimentary, and 

impact crater deposits.

Plains Material

North of the continuous plateau margin, most of the lowlands not covered by surficial materials consist of two plains 

units.

Smooth plains material (unit HNps) has relatively featureless surfaces that cover low-lying areas adjacent to plateau and 

impact crater materials. The smooth plains in turn, are covered 

in many locations by debris apron material. In some cases, small 

pockets of smooth plains are exposed where debris apron margins have either not fully converged or have receded (lat 44.8° 

N., long 24.0° E.). Where adjacent to mottled plains material, 

the elevations of the units are generally similar, with no embayment of mottled plains. A few isolated topographic lows within 

the smooth plains (lat 46.0° N., long 21.2° E.) have dark albedo 

surfaces in Viking MTM, MOC, and THEMIS VIS images 

compared to the rest of the plains (fig. 8). In MOC images, the 
4

dark areas appear patchy, with wind streaks radiating out along 

their margins. Scattered clusters of small circular to irregular 

knobs (denoted by stipple pattern), with larger knobs mapped as 

upper smooth plateau material, are present in some portions of 

smooth plains material (lat 43.5° N., long 21.7° E.). Most of the 

smooth plains material is mapped as either Amazonian slide or 

Hesperian older channel materials in the Mars eastern equatorial region map by Greeley and Guest (1987) and as the early 

Hesperian Deuteronilus Mensae 1 unit by Tanaka and others 

(2005). The smooth plains material unit is similar to the smooth 

lowland plains unit mapped by McGill (2002). 

Mottled plains material (unit Hpm) is topographically 

variable, consisting of bright flat-topped surfaces and lower 

dark hummocky surfaces in the Viking MTM base map (fig. 9). 

The margins of flat-topped surfaces are mostly bounded by low 

scarps, with an elevation difference of less than 100 m to the 

lower hummocky surface. The scarps are more apparent in low 

sun illuminated Viking images than in MOLA topography. Several resistant round knobs of upper smooth plateau material are 

scattered within the lower hummocky surface (lat 45.8° N., long 

20.5° E.). The mottled plains have similar elevations to adjacent 

smooth plains materials, but are lower than upper and lower 

smooth plateau materials. This unit is not differentiated from the 

Hesperian older channel unit by Greeley and Guest (1987) or 

from the early Hesperian Deuteronilus Mensae 1 unit by Tanaka 

and others (2005) because of the differences in map scale. There 

is no single equivalent unit mapped by McGill (2002).

Plains materials include sedimentary deposits derived from 

erosion and local redistribution of the surrounding highlands 

and (or) from sources located in the northern lowland plains. 

Plains materials have accumulated in low-lying areas north of 

the continuous plateau margin. They consist of both smooth and 

mottled plains materials with the latter having a higher degree 

of topographic variability. Smooth plains materials may have 

been redistributed by flow, possibly facilitated by the incorporation of ice.

Impact Crater Material

Impact craters are a defining characteristic of the highland 

plateau (Tanaka and others, 2005), and where ejecta blankets 

and (or) crater rim materials are well defined, they are mapped 

as distinct units. Much of the southern portion of the map is 

covered by ejecta related to Cerulli impact crater. Other impact 

crater materials are located primarily in the continuous plateau, 

with lesser numbers in the lowland plains. There are numerous 

rimless craters throughout the older plateau materials (units 

Npld, Nplsu, Nplsl) that are part of the overall degradational 

signature of these units, but not mapped as individual crater 

material units. Three types of crater materials are identified 

based on their preservation state. Only impact craters with 

diameters greater than 3 km have been mapped.

Cerulli crater material (unit Ncc) is characterized by a 

continuous ejecta blanket and a pronounced, continuous rim 

(diameter = 125 km) that is elevated relative to the surrounding 

surfaces. Numerous channels cut the interior walls of the crater 

(lat 32.8° N., long 22.1° E.) and the outer portions of the ejecta 

blanket. The ejecta deposits are moderately preserved, and the 

floors of numerous low-lying flats in and around the crater rim 

are covered with smooth fill material. Secondary craters and 

crater fields are scattered throughout the ejecta blanket and 

extend onto other geologic units. Several linear grooves are 

radial to the crater center.

Highly degraded crater material (unit c1) is characterized 

by a partial to discontinuous rim with little or no relief relative to the surrounding surfaces or ejecta blanket (if present). 

These are significantly modified deposits that form the ejecta, 

rims, and floors of impact craters. The ejecta of a few craters 

could only be identified from brightness differences in THEMIS 

daytime IR data (lat 42.7° N., long 21.0° E.). The crater floors 

are often partially or entirely covered by smooth fill or debris 

apron materials. Moderately degraded crater material (unit c2) 

is characterized by a continuous rim with minor relief relative to 

the surrounding surfaces and a continuous to semi-continuous 

ejecta blanket. These deposits form the ejecta, rims, and floors 

of impact craters. The deposits generally have smooth to pitted 

surfaces. Well-preserved crater material (unit c3) is characterized by a pronounced, continuous rim with significant relief 

relative to the surrounding surfaces and a continuous ejecta 

blanket. These crater materials exhibit little degradation and 

form the ejecta, rims, and floors of fresh impact craters. Some 

ejecta lobes have rampart margins (lat 42.4° N., long 22.4° E.) 

that range from thin, tongue-like flow lobes that extend from the 

hummocky outer rim area to larger circular lobate flow lobes 

with escarpment terminations and lineated grooves that extend 

radially from below the rim crest.

Surficial Material

Surficial material generally covers all plateau and plains 

materials in the map area. Two material units are identified.

Debris apron material (unit Ada) occurs as smooth lobate 

deposits with gentle surface slopes (0.4°–8.0° from MOLA 

data) that surround and extend beyond the bases of mesas, 

knobs, crater rims, and fretted valley walls. Debris apron 

surfaces have lineations parallel or transverse to apparent flow 

direction. Deposits near the base of the slope are sometimes 

partially covered by one or more apron deposits from above, 

forming successive lobate fronts. Near the plateau margin (lat 

39.8° N., long 23.0° E.), bulbous lobes extend through breaks 

in the plateau materials (fig. 10). Several of the lobes have 

margins that are deflected around obstacles such as blocks of 

upper smooth plateau material (fig. 11). Along the margins of 

the mound at Deuteronilus Colles, THEMIS IR and VIS images 

show at least one lobe that has flowed onto the adjacent smooth 

plains (fig. 12). Apron materials often embay other units such as 

impact crater, plains, and plateau materials. In a few cases, portions of the apron margin have ridges of apron material, forming 

a ribbed appearance (fig. 13, denoted by stipple pattern). At the 

bases of some knobs and fretted valleys, a 1- to 2-km-wide gap 

is apparent between the slope base and the head of the debris 

apron. This unit forms part of the Amazonian slide materials in 

the Mars eastern equatorial region map by Greeley and Guest 

(1987) and part of the Deuteronilus Mensae 2 unit by Tanaka 
5

and others (2005). Debris apron material is most similar to 

and consistent with debris apron materials mapped by McGill 

(2002).

Smooth fill material (unit Afs) occurs as deposits with 

relatively featureless surfaces that cover low-lying areas below 

scarps, between plateau blocks in collapse depressions, at the 

margins of some fretted valleys adjacent to plateau materials, 

and on the floors of many impact craters. The floor of Cerulli 

impact crater, as well as small local flats along its rim, exhibit 

smooth fill material. The margins of smooth fill materials do not 

have relief or lobate forms. The largest craters with fill material, 

excluding Cerulli, have concentric grooves that follow the shape 

of the crater walls (lat 36.8° N., long 22.3° E.). Some collapse 

depression floors have patches of small knobs (not individually 

mapped, but denoted by stipple pattern) scattered within the 

smooth fill, producing a hummocky appearance (see fig. 6). The 

smooth fill materials are local deposits that are not mappable 

at the scale of the Mars eastern equatorial region geologic map 

by Greeley and Guest (1987) and the northern plains geologic 

map by Tanaka and others (2005). The smooth fill material unit 

is most similar to the older and younger smooth plains units 

mapped by McGill (2002).

Overall, surficial materials represent the most recent 

phase of erosion and deposition in the map region. These are 

sediments that accumulated in local low-lying regions and are 

derived from remnants of the ancient highland plateau, impact 

crater materials, and younger plains units. Smooth fill and 

debris apron materials are likely composed of talus and debris 

shed from adjacent hillslopes mixed with eolian deposits that 

cover the surfaces of older exposed units. Debris aprons have 

clear indications of flow in the form of bulbous lobes, flow lineations, and deflection around obstacles. Flow of debris apron 

materials is likely facilitated by the incorporation of ice. In high 

resolution MOC images, debris aprons and some smooth fill 

surfaces appear to be covered by mantle deposits that exhibit a 

variety of textures.

STRUCTURAL FEATURES

Several morphologic features provide both direct and 

indirect evidence for tectonic activity in the map region. These 

features include wrinkle ridges, grabens, and closed depressions. Wrinkle ridges and grabens are not abundant, and are 

located primarily in the ancient highland plateau (Lucchitta, 

1976, 1977; Chicarro and others, 1985; Plescia and Golombek, 

1986; Watters, 1988, 1991, 1993; Zuber, 1995). Most ridge axes 

are linear, but some are curved along their lengths. Grabens in 

the map area are generally short, narrow linear depressions, 

not the wide prominent forms typically found in regions such 

as Coloe Fossae and Nili Fossae. The closed depressions are 

large features that may have initially formed by collapse of an 

unstable surface but have widened over time through erosion 

and mass wasting along their margins. Disruption and modification of the continuous plateau from tectonic activity early in the 

history of Mars may have led to the development of fracture 

lanes (McGill, 2002), which isolated portions of the plateau, 

leading to the formation of polygonal mesas. The presence of 

these structural features indicates that plateau materials in the 

Deuteronilus Mensae region have been modified by surface 

instability and deformation, along with subsidence and collapse 

(see discussion section).

DISCUSSION

Plateau Modification and Closed Depressions

Within upper smooth plateau material, three prominent 

large, elongate, closed depressions 300–500 m deep contain 

numerous polygonal blocks and rounded knobs (lat 35.7°–37.7° 

N., long 21.0°–23.6° E., see fig. 6). The blocks do not appear 

to be rotated but some have sloped upper surfaces dipping in 

toward the depression floor suggesting that they have been 

tilted. The top surfaces of some blocks are at an elevation 

that is similar to, or higher than, the surfaces surrounding the 

depressions, which indicates that parts of the original surface 

surrounding the blocks have subsided or collapsed. We interpret 

the blocks and knobs to be in-situ remnants of plateau materials that have further subsided and been eroded over time. The 

blocks or knobs have different sizes and abundances, indicating 

different states of highland modification.

A fundamental issue regarding the origin of the depressions is removal of subsurface support that allowed subsidence 

and collapse to occur. Their lack of apparent outlets, either 

along the depression margins or surface channels outside of 

the depressions, suggests that material was not likely removed 

by fluvial processes. Winds have the ability to remove and (or) 

redistribute some surface materials; however, a growing surface 

depression may also trap eolian deposits. It is unclear that wind 

alone could remove hundreds of cubic kilometers of material 

to form these depressions. If volatiles were present in plateau 

materials, then sublimation of ice could remove some of the 

total volume from near the surface, but it is unclear how much 

of this ice was interstitial or what fraction could become trapped 

at depths far below the surface.

The loss of material could be related to volatile-rich zones 

at depth that were once, or still are, present in the plateau. The 

development of fractures and (or) release of volatiles could have 

been initiated by a variety of processes. Solution collapse where 

soluble rock below an insoluble layer undergoes dissolution by 

the passage of groundwater is a possibility. This process is difficult to assess due to the lack of discharge areas near the depressions that would indicate subsurface water migration, lack of 

evidence for exposed diagnostic minerals such as carbonates 

from THEMIS IR data, and mantling of the surface by eolian 

deposits and other mass-wasted fill materials. Buried subsurface 

heterogeneities (for example, sedimentary layers with different 

permeabilities, faults, and impact craters, see [Malin and Edgett, 

2001] or [Edgett and Malin, 2002]) may have created volatilerich lenses or zones. If these volatiles were mobilized, then 

they could have destabilized the overlying materials, resulting 

in fracturing and subsidence or collapse of the surface. The rise 

and intrusion of magma bodies such as volcanic sills or dikes 
6

could have mobilized volatiles in the subsurface. Although there 

is no clear surface expression of exposed intrusive bodies in the 

plateau, their existence at depth cannot be ruled out. Another 

possible contributor to the disruption, fracturing, and movement of subsurface materials are large impacts (Newsom, 1980; 

Melosh, 1989; Clifford, 1993; Williams and Greeley, 1994). 

Ground shaking from the seismic energy released by an impact 

is likely to have disrupted the subsurface plateau materials, producing fractures that could grow, leading to subsidence and (or) 

collapse. Overall, subsidence and (or) collapse has played an 

important early role in the modification of this region and other 

regions of Mars (McCauley and others, 1972; Sharp, 1973b;

Schonfeld, 1979; Nummedal and Prior, 1981; Tanaka and 

Golombek, 1989; Davis and Golombek, 1990; Crown, 2005; 

Rodriguez and others, 2005, 2006).

Assessment of Potential Lowland Water Bodies

The existence of a large ocean, or oceans, covering the 

northern lowlands of Mars was first proposed by Parker and 

others (1989, 1993) on the basis of geomorphic features in 

Viking Orbiter images attributed to coastal processes. The putative ocean was thought to be present during the Noachian Period 

and as late as the Early Amazonian Epoch. This hypothesis has 

recently been reevaluated using hydrological models, climate 

models, and from a variety of new datasets beginning with the 

Mars Global Surveyor (MGS) mission (Head and others, 1999; 

Malin and Edgett, 1999; Thomson and Head, 1999; Clifford and 

Parker, 2001; McGill, 2001; Carr, 2001; Withers and Neumann, 

2001; Kreslavsky and Head, 2002; Fairen and others, 2003; 

Carr and Head, 2003; Webb, 2004; Ghatan and Zimbelman, 

2006; Perron and others, 2007). Results from these studies have 

been mixed, some of which support a large body of water, but 

most requiring further investigation due to insufficient evidence 

or alternative process(es) that could produce similar geomorphic 

features.

Malin and Edgett (1999) describe in detail the geomorphic 

features and textural changes that should be present if an ocean 

or other persistent body of water once existed and retreated 

on the surface. Geomorphic features include beach ridges, 

bars, spits, wave-cut terraces or platforms, and fluviolacustrine 

deltas. Textural changes could include the presence of clays or 

other fines or the formation of evaporite minerals. Horizontally 

bedded sediments or layers such as hyaloclastic tuffs, maars, or 

other constructs from underwater volcanic eruptions would also 

be an indicator that a former ocean or lake was present.

Our analysis of Viking, THEMIS, MOC, and MOLA data 

in the map region did not yield diagnostic geomorphic features 

such as flat benches, ridges, or other topographic signatures 

along plateau escarpments or mesa walls where a shoreline 

would be expected. Older Noachian to Hesperian surfaces along 

the dichotomy boundary and in the lowlands are mostly covered 

by large expanses of debris apron material, making it difficult 

to find such changes along a potential shoreline (Tanaka and 

others, 2003, 2005). Resistant rock outcrops with consistent 

elevation levels are present along some escarpments and mesa 

walls, but many are discontinuous in places, and these outcrops 

may be related to different material layers rather than indications of past sea-level stands. Consistent changes in albedo or 

surface roughness were also not observed. The entire Deuteronilus Mensae map region is located within the Contact 1 (Parker 

and others, 1989, 1993) or Arabia shoreline area (fig. 1) as 

defined by Clifford and Parker (2001).

The lack of distinct geomorphic features related to coastal 

activity does not preclude the hypothesis that an ocean or other 

former standing bodies of water were once present along the 

continuous plateau margin (Scott and others, 1995). One of the 

challenging issues with identifying such features is their preservation over billions of years. If these features were formed as 

early as the Noachian Period, it is unlikely they would remain 

identifiable due to erosion and redistribution of materials. If 

the Arabia shoreline or any others were previously present in 

this region, they would pre-date the young resurfacing that has 

occurred (debris aprons and surficial fill). Erosion of the escarpment and the formation of lobate debris aprons would have 

caused plateau retreat and altered possible topographic evidence 

of relict features related to coastal processes.

GEOLOGIC HISTORY

The following description of the geologic history is based 

on photogeologic interpretation of the landforms and surfaces 

observed in combination with age constraints from crater sizefrequency data.

Noachian Period

During the Noachian Period, the highland plateau, likely 

volcanic and sedimentary materials reworked by impacts 

(Tanaka and others, 2005), may have once covered much of 

the plains north of the current continuous plateau margin, but 

has been modified since by tectonics, impacts, and surface fluid 

flow. The current-day polygonal mesas and linear segments of 

fretted valleys suggest that tectonic activity (Banerdt and others, 

1992), perhaps related to formation of the dichotomy boundary (see Watters and McGovern, 2006 and references therein), 

may have produced fracture lanes (McGill, 2002) and facilitated 

development of a structural fabric with roughly orthogonal 

cracks or joints in upper and lower smooth plateau, and dissected plateau materials (Kochel and Peake, 1984). To what 

depth this fabric extends is unknown, but where tectonic activity (or impact cratering) caused breakup of the crust, these sites 

would have been candidates for widening along cracks, faults, 

or other subsurface discontinuities by erosion. The modification 

and isolation of plateau materials by tectonic and (or) impact 

cratering during the Noachian Period likely influenced the later 

development of polygonal mesas in the Deuteronilus Mensae 

region.

Tectonic activity may have also played a role in tilting the 

plateau materials such that they gently slope down into the present-day lowland plains north of the continuous plateau margin 

(McGill, 2000, 2001). A north-dipping slope is consistent with 

the decreasing surface elevations of individual mesa tops in 
7

MOLA data. Further analyses of the topography from the continuous plateau to the northern extent of polygonal mesas show 

similar elevations for near-boundary mesas and the continuous 

highlands, but differences in the elevations of far-boundary 

mesas (fig. 14). These differences, along with the general 

decrease in impact craters northward of the continuous plateau, could be attributed to an erosional event that removed the 

upper portion of upper smooth plateau materials, similar to the 

Noachian resurfacing identified by McGill (2002). This major 

resurfacing event is difficult to assess in the map region due 

to the Hesperian and Amazonian resurfacing that has modified 

and covered much of the older Noachian units. Alternatively, 

the difference may be related to the general decrease in plateau 

elevation towards the north (slopes down into the lowlands). 

A clear stratigraphic relation exists between upper and lower 

smooth plateau materials; upper smooth plateau material consistently overlies lower smooth plateau material. This sequence 

and their shared contacts suggest that lower smooth plateau surfaces may be exposed lower layers of plateau materials. Surface 

erosion of the ancient highland plateau likely occurred during 

the Late Noachian to possibly Early Hesperian Epoch, prior to 

the formation of fretted valleys, polygonal mesas, and collapse 

depressions.

Coeval with regional tectonic activity are impact events 

that formed craters and basins now preserved as semi-circular 

structures rimmed by plateau material. The mound of small 

rounded knobs at Deuteronilus Colles may be the central peak 

of one of these impact structures. These features may have been 

buried at various depths within the ancient plateau (Edgett and 

Malin, 2002), and their presence could have influenced the 

subsequent erosional patterns of highland materials. Sediments 

(and perhaps volatiles) trapped within these structures may 

have been more easily subjected to collapse and erosion relative to rim materials, thus forming the semi-circular structures 

exposed on the surface today. These ancient structures and 

smaller impacts, in combination with tectonic activity, likely 

caused further disruption and fracturing of subsurface materials 

to form megaregolith (Clifford, 1981), creating an environment 

that facilitated the migration of fluids within the subsurface 

and to the surface. These fluids may have been sufficient to 

cause minor fluvial dissection, producing the dissected plateau 

materials. Alternatively, the fluids may be related to periods 

of sustained flow from surface runoff by precipitation or other 

sources (McCauley and others, 1972; Sharp and Malin, 1975; 

Baker, 1982; Baker and others, 1992; Carr 1996). Observations 

that surface dissection is not widespread and mostly confined to 

dissected plateau surfaces suggest a subsurface source and (or) 

efficient infiltration through unconsolidated surface materials 

with reemergence and dissection in select localities.

Cerulli impact crater has numerous channels along its 

interior walls and within its ejecta blanket. These channels 

indicate post-impact surface fluid flow (Mouginis-Mark, 1987). 

The presence of flow lobes within the ejecta blanket (Melosh, 

1989) provides additional evidence that plateau materials may 

have been volatile-charged during the Noachian and on into the 

Hesperian Period. Although impact melt could also produce 

similar channels (Howard and Wilshire, 1975) and atmospheric 

effects on the impact ejecta curtain could produce multi-lobed 

patterns (Schultz and Gault, 1979), the preferred explanation 

is the presence of subsurface volatiles (Mouginis-Mark, 1987; 

Melosh, 1989). There is uncertainty about the specific timing 

of the Cerulli impact event but based on the N(5) crater density 

value, it was likely Middle to Late Noachian.

Hesperian Period

The formation of laterally and vertically heterogeneous 

highland terrain and the disruption and fracturing of the plateau 

from tectonic and impact processes in the Noachian Period 

likely created conditions for subsidence and (or) surface collapse, as evidenced by the closed depressions with in-situ blocks 

of upper smooth plateau material. Although there are no morphological features that indicate fluid flow exiting the depressions, subsurface fluid migration and possible dissolution (see 

discussion section) could have been a contributing factor to loss 

of support and subsequent collapse or subsidence of the overlying plateau (Chuang and Crown, 2007). Continued erosion of 

the collapse depressions caused widening of their margins, 

infilling of mass-wasted wall materials, and an overall transition from polygonal blocks to smaller remnant rounded knobs, 

producing hummocky floors. McGill (2002) noted the presence 

of former lakes within old impact craters during the Hesperian 

Period. However, similar to the lack of observed inlets or outlets 

for the collapse depressions, the lack of crater-intersecting 

inlet valleys or channels indicates that fluvial activity related to 

lacustrine environments may have been more well developed or 

persistent east of this map area.

Breakup and erosion of the plateau, particularly north of 

the present-day continuous margin, further isolated portions 

of smooth plateau materials, causing gradual retreat of block 

margins that reduced their size, producing the isolated blocks 

and clusters of polygonal mesas now present in the lowlands. 

This activity may have also modified individual crater forms 

and basins. Erosion likely involved both physical and chemical weathering of plateau materials including ice sublimation 

and melting, cracking from thermal expansion and contraction, 

wind abrasion, and other processes such as mass wasting. Talus 

deposits along block margins may have incorporated ice from 

water vapor that diffused into the soil and froze when Mars had 

a thicker atmosphere (Clifford and Hillel, 1983; Clifford, 1993; 

Mellon and Jakosky, 1993; Carr, 1996) and (or) been covered 

by ancient ice-rich mantling deposits in a manner similar to that 

postulated for recent Martian climate regimes (Mustard and 

others, 2001; Milliken and others, 2003; Christensen, 2003). 

Redistribution of these deposits may have occurred by ice creep 

processes (Squyres, 1978, 1979; Lucchitta, 1984; Squyres and 

Carr, 1986) or by mass flows facilitated by ice-rich interior 

zones (Baker, 2001). In addition, ice lenses buried at depth 

in the highland plateau may have facilitated failure and mass 

wasting of plateau materials. The coalescence and flow of these 

deposits, along with mantling and reworking of eolian materials 

likely formed the smooth plains. This activity is likely an older 

stage of ice-rich flow that may be similar to the younger debris 

aprons observed in the region. Some isolated areas have smaller 

rounded knobs within the smooth plains. The knobs may be 
8

remnant blocks of upper smooth plateau materials that have 

not been completely eroded. In the area east of this map region, 

McGill (2002) suggested that an erosional event that formed 

the fretted valleys and terrain may have been a result of sapping 

and surface-water flow. Although these processes are plausible 

for this map region, the evidence of collapse structures suggests 

that development of fretted valleys may have been facilitated 

by the widening of pits and (or) cracks along the margin of the 

continuous plateau due to erosion and mass wasting. The preserved elongate collapse depressions within a remnant highland 

basin in the map region may represent an initial stage of plateau 

breakup, with continued collapse-dominated phases leading to 

formation of fretted terrain valleys and mesas. The eventual formation of polygonal mesas and knobs at the expense of masswasted plateau materials is consistent with a previous study of 

the Deuteronilus Mensae region by Kochel and Peake (1984).

In the northernmost portion of the map region, areas where 

upper and lower smooth plateau materials are not present, topographically variable materials form the uneven mottled plains. 

The origin of the mottled plains is unknown but their formation 

could be related to further erosion and redistribution of highland plateau units, a transition from the cratered highlands to 

the northern lowlands (for example, the mottled plains includes 

sedimentary deposits with sources in the lowlands), or bright 

patches of Lyot crater ejecta deposits on top of smooth dark fill 

materials that have not been covered by smooth plains or other 

younger surficial materials. These bright patches are within 120 

km of the observed margin of the continuous ejecta blanket of 

Lyot crater (diameter = 215 km). The formation and redistribution of plains materials likely ended late in this period with most 

of the lowlands covered by smooth or mottled plains materials.

Amazonian Period

Ice-driven resurfacing along the margins of polygonal 

mesas, knobs, and fretted valleys, along with infilling of debris 

in low-lying areas, played a dominant role during this time 

period. Smooth fill materials cover the floors of closed depressions, the margins of some fretted valleys adjacent to plateau 

materials, impact craters including Cerulli crater, and the small 

low-lying flats along the rim of Cerulli crater. Within closed 

depressions, smooth fill materials are likely talus and blocks of 

eroded wall materials mixed with some eolian deposits; within 

impact craters, the smooth fill materials are likely a combination of eolian, mass-wasted, and (or) fluvial deposits mixed 

with possible impact melt or impact brecciated rocks that cover 

the crater floor. In a few of the well-preserved impact craters, 

concentric ridges form a pattern of grooved fill. The formation 

of these ridges is likely from the interaction of convergent flows 

of ice-rich materials toward the crater center (Squyres, 1978; 

1979). Alternatively, the ridges could be remnants of eroded 

air-fall deposits that exhibit similar morphologies (Zimbelman 

and others, 1989). Deposition of smooth fill materials likely 

occurred to different extents at different times and in different 

locations throughout the map region; deposition of smooth fill is 

assumed to be Amazonian and may have continued into the Late 

Amazonian Epoch.

Lobate debris aprons surround and extend beyond the 

bases of mesas, knobs, crater rims, and fretted valley walls. 

In most cases, multiple apron lobes have converged to form a 

single apron mass (see Pierce and Crown, 2003) that spreads 

over plains and impact crater materials. The surface lineations, convex-up margins (see cross section A–A’ in fig. 14), 

and deflection of apron margins around obstacles indicate 

downslope flow of material. Lobate debris aprons have been 

interpreted and modeled as a variety of possible features including rock glaciers, ice-rich mass movements, or debris-covered 

glacial flows (Lucchitta, 1984; Baker, 1991; Colaprete and 

Jakosky, 1998; Baker, 2001; Mangold and Allemand, 2001; 

Crown and others, 2002, 2003, 2006; Mangold, 2003; Pierce 

and Crown, 2003; Turtle and others, 2003; Head and others, 

2005; Li and others, 2005; Chuang and Crown, 2005a,b,c, 

2006). However, it is unclear what abundance and distribution 

of ice exists within the aprons, and whether the source of the 

ice was from the ground (related to the ancient Martian cryosphere [Carr, 1996]) or from recent periods of cold climate due 

to obliquity-driven changes (Laskar and Robutel, 1993; Touma 

and Wisdom, 1993; Head and others, 2003). Recent studies of 

localized mantle deposits within the source areas of gullies suggest that snowpacks could also be a possible source of ice even 

under current-day conditions (Christensen, 2003). The abundance of debris aprons throughout this map region is consistent 

and in agreement with debris aprons mapped by McGill (2002), 

which indicates that ice-rich movement of debris has occurred 

over a significant period of Martian history and that debris 

aprons are older than the mantle deposits.

In many locales near the bases of knobs and fretted valleys 

(lat 40.1° N., long 23.6° E. and lat 45.8° N., long 23.1° E.), a 

gap up to 2 km wide is apparent between the base of the hillslope and the head of the debris apron (see fig. 5). This gap may 

represent an area where the upper apron margin has retreated 

or a period in which the apron mass has advanced downslope, 

but with a cutoff in supply. Similar gaps, described as moats, 

are observed in MOLA profiles of lobate debris aprons in 

eastern Hellas (Pierce and Crown, 2003). The successive lobate 

fronts of debris aprons near the continuous plateau margin 

suggests that major apron forming events may be episodic. 

Although there is a lack of evidence for current downslope flow 

of individual aprons, the positions of terminal margins where 

multiple fronts are observed along a slope are similar, indicating movement as a single coherent mass even though individual 

lobes may form due to obstacles at the front. Thus, at least two 

apron-forming events are apparent, and they suggest periods of 

sustained debris supply from mass wasting and incorporation 

of ice to facilitate flow of materials. The occurrence of a ribbed 

pattern of ridges along some apron fronts suggests that either 

partial retreat of the apron margin or apron deposition over an 

uneven pre-existing surface (see fig. 13) may have produced the 

ribbed appearance. In terms of partial retreat, the ridges may 

be accumulations of basally scoured and (or) talus materials 

that now mark the former extent(s) of the aprons (Hauber and 

others, 2008).

Debris-apron surfaces within a network of theater-headed 

alcoves and cirque-like accumulation zones in a T-shaped fretted valley (lat 37.7° N., long 24.0° E.) near the eastern edge of 
9

the mapping region suggest that some debris aprons are analogous to terrestrial valley glaciers (Head and others, 2006b). The 

aprons were observed to have parallel, converging, chevron-like 

flow lineations, convergent fold structures, and flow constriction through narrow valley passages. Head and others (2006b) 

suggested that these are well-preserved features of past glacial 

ice flow and that significant climate change must have occurred 

during the Late Amazonian Epoch to cause sustained snow and 

ice accumulation to feed the valley glaciers. They also suggest that, if debris aprons are analogous to terrestrial glaciers, 

then sublimation till may have protected the surface and kept 

ice cores intact up to the present time. Although the similarity 

in surface morphology is striking, most debris aprons in the 

map region do not share these same characteristics. This suggests that either the conditions for glacial flow were somehow 

confined to this fretted valley or that preservation of glacial flow 

features is relatively poor for debris aprons in this region.

Contemporaneous with or subsequent to the growing 

extent of debris aprons was the deposition and partial removal 

of mantle deposits on debris apron, polygonal mesa, plains, and 

plateau surfaces. A variety of surface textures, particularly on 

debris aprons, indicate the presence of these mantle deposits, 

including smooth surfaces with minor pitting, knobby, lineated, 

and an undulating ridge-and-valley surface (Mangold, 2003; 

Pierce and Crown, 2003). These textures at THEMIS VIS scale 

are common on most debris aprons in the map region and are 

likely formed within a layer of ice-cemented dust or other fines 

(fig. 15). Sublimation of ice in the mantle deposit may have 

liberated the dusty material, which is subsequently redistributed by eolian processes. Overall, the mantle deposits appear 

to be similar to the mantling deposits prominent throughout the 

mid-latitudes of Mars (Carr, 2001; Mustard and others, 2001; 

Mangold, 2003; Pierce and Crown, 2003; Milliken and others, 

2003; Chuang and Crown, 2005a).

ACKNOWLEDGMENTS

We appreciate the thorough and constructive comments by 

James Skinner and George McGill, which improved the quality 

of this map. We thank Bob Sucharski at the U.S. Geological 

Survey for generating the digital base maps and other GIS data 

for our map work. This report is based upon work supported by 

the National Aeronautics and Space Administration under Grant 

No. NNG04GI85G issued through the Planetary Geology and 

Geophysics Program. This map is PSI Contribution 447.

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Table 1. Crater Size-Frequency Data and Relative Age Determinations

[Craters counted using Viking MDIM, THEMIS daytime IR, and HRSC data (see fig. 2, Data and GIS Mapping Techniques section for more details). N(2), N(5), and N(16) r≥ 2, 5, and 16 km in diameter normalized to 106 km2; only cumulative totals > 4 are used to determine ages. Error = ±((N0.5)/A) x 106 km2, where A = area. Age ranges are 

density boundaries by Tanaka (1986); EA, Early Amazonian; MA, Middle Amazonian; LA, Late Amazonian; EH, Early Hesperian; LH, Late Hesperian; EN, Early Noachian; M

Unit Name

Unit

label

Area

(km2)1

No. ≥ 0.5

km

No. ≥ 2

km

No. ≥ 5

km

No. ≥ 16

km N(2) N(5) N(16)

N(2) age

range

Smooth fillmaterial

Afs 5285 6 0 0 0 --- --- --- --- 

Debris apronmaterial

Ada 43089 31 7 0 0 162±61 --- --- EA-MA 

Well-preserved crater material

c3 11664 66 4 0 0 --- --- --- --- 

Moderately degraded crater material

c2 10036 21 3 1 0 --- --- --- --- 

Highly degraded crater material

c1 2524 11 0 0 0 --- --- --- --- 

Mottled plainsmaterial

Hpm 8015 20 5 2 0 624±279 --- --- EH-EA 

Smooth plainsmaterial

HNps 33917 115 28 9 1 825±156 265±88 --- EH-LH 

Cerulli cratermaterial

Ncc 26510 255 22 10 3 830±177 377±119 --- EH-LH 

Dissected plateaumaterial

Npld 19667 247 24 12 0 1220±249 610±176 --- LN-EH 

Upper smooth plateaumaterial

Nplsu 45935 394 68 31 10 1480±179 675±121 218±69 ≥ LN 

Lower smooth plateau material

Nplsl 4766 10 1 0 0 --- --- --- --- 

1Estimated using sinusoidal equal-area projection with a spherical shape definition for Mars (axes=3396190 m). 2Relative age range is primarily based on measured crater densities (where available), with adjustments from observed stratigraphic relationships (see table 2 for contact relat

highland plateau units as N(2) ranges may reflect younger surface modification. Note that these ranges may differ slightly from those in the Correlation of Map Units, which 

regional geologic history.
15

Table 2. Contact Relations of Geologic Units

Unit Name

Unit

label Younger than

Contact relations1

Overlaps with2 Older than

Smooth fill

material

Afs Nplsu, Npld, Ncc,

c1, c2, c3

Ada ---

Debris apron

material

Ada Nplsu, Nplsl, Npld, Hpm, 

HNps, c1, c2, c3

Afs ---

Well-preserved crater 

material

c3 HNps, Npld, Nplsu c2 Ada, Afs

Moderately degraded 

crater material

c2 c1, Hpm, HNps, Ncc, 

Npld, Nplsu, Nplsl

c3 Ada, Afs

Highly degraded crater 

material

c1 Nplsu, Nplsl, Npld, Ncc --- Ada, Afs, c2, Hpm, 

HNps

Mottled plains

material

Hpm c1, Nplsu, Nplsl, HNps --- Ada, c2

Smooth plains

material

HNps c1, Nplsu, Nplsl --- Ada, Hpm, c2, c3

Cerulli crater

material

Ncc Nplsu, Npld --- c1, c2, Afs

Dissected plateau

material

Npld --- Nplsu, Nplsl Ada, Afs, Ncc, c1, c2, c3

Upper smooth plateau

material

Nplsu Nplsl Npld Ada, Hpm, HNps, c1, c2

Lower smooth plateau 

material

Nplsl --- Npld Ada, Afs, Hpm, HNps, 

Ncc, Nplsu, c1, c2, c3

1

Contact relations are for units that share in common, one or more geologic contacts. 2

Exhibits one or more locations where contacts between units are topographically or stratigraphically equivalent.