PROCEEDINGS OF THE SEVENTEENTH LUNAR AND PLANETARY SCIENCE CONFERENCE, PART 1
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. B13, PAGES E139-E158, NOVEMBER 30, 1986
The Stratigraphyof Mars
KENNETH
L. TANAKA
U. $. GeologicalSurvey,Flagstaff
A detailedplanetwide
stratigraphy
for Marshasbeendeveloped
fromglobalmapping
basedon Viking
imagesand cratercountingof geologicunits.The originalNoachian,Hesperian,
and AmazonianSystems
are divided into eight seriescorrespondingto stratigraphicreferents.Characteristiccrater densitiesand
materialreferentsof eachseriesare (1) Lower NoaehianIN(16)] (numberof eraten > 16 km in diameter
perl06km2)> 200]basement
material;
(2)MiddleNoachian
IN(16)= 100-200]
cratered
terrain
material;
(3) Upper Noaehian[N(16)= 25-100; N(5) = 200-400]intercraterplainsmaterial;(4) Lower Hesperian
IN(5) = 125-200]ridgedplainsmaterial;(5) UpperHesperian[N(5) = 67-125;N(2) = 400-750]complex
plainsmaterial;(6) LowerAmazonianIN(2) = 150-400]smoothplainsmaterial
in southern
AcidaliaPlanitia;
(7) Middle AmazonianIN(2) = 40-150]lava flowsin AmazonisPlanitia;and(8) UpperAmazonianIN(2)
< 40] flood-plainmaterialin southernElysiumPlanitia.Correlations
between
variouscratersize-frequency
distributionsof highlandmaterials on the moon and Mars suggestthat rocks of the Middle Noachian
Seriesare about 3.92-3.85b.y. old. Stratigraphicageseompi!edfor unitsand featuresof variousorigins
showthat volcanism,tectonism,and meteoritebombardmenthave generallydecreased
through Mars'
geologichistory.In recenttime, surficialprocesses
havedominatedthe formationand modificationof
rockunits.The overallstratigraphy
of Mars is complex,however,because
of temporalandspatialvariations
in geologicactivity.
appearance,to determinethe relativeagesof map units. These
units were classifiedand placedin three stratigraphicsystems:
Anewglobalgeologic
mapseries
at 1:15,000,000
scalederived the N oachianSystem,characterized
by rugged,heavilycratered
fromVikingimages
hasexpandedandimprovedourknowledge material;the HesperianSystem,whosebasewasdefinedas the
ofthegeologic
andstratigraphic
frameworkof Mars.Thisseries baseof the ridgedplainsmaterial;and the AmazonianSystem,
consists
ofthreemapscoveringthefollowingregions:thewestern which included relatively smooth, moderatelycrateredplains
equatorial
regionOat + 57ø,long0ø to 180ø [Scottand Tanaka, materialsand polar deposits.The namesfor thesesystemswere
1986]),theeasternequatorialregion(lat ñ 57ø, long !80ø to selectedfrom regionshaving representativeand widespread
360ø;R. Greeleyand J. E. Guest,unpublisheddata, !986), and exposuresof the materialsusedasreferents.
thenorthand southpolar regions(lat > + 55ø [Tanaka and
A new generationof local geologicmapsof Mars at different
Scott,1987].Thismapping,combinedwith previousstudiesand scaleswerebasedonimprovedimageryacquiredfromthe Viking
newcratercounts,forms the basisfor the most detailed formal orbiters[Scott et al., 1981;Dial, 1984;Scottand Tanaka,1984;
representation
of Martian geologichistoryto date.In this paper, Witbeckand Underwoo& 1984].All of theseworkersfollowed
I propose
newstratigraphic
series
andepochs
thatformdiscretethe time-stratigraphicsystemsdevelopedby Scott and Carr
stages
into which the evolutionof the planet'ssurfacecan be [1978]. The stratigraphic-system
boundarieswere defined by
divided.
usingdensitiesof cratershavingdiametersof 4-!0 km [Greeley
In an early study of the Martian surface,Soderblom et al. and Spudis, 1981]and 2, 5, and 16 km [Scott and Tanaka,
[1974]recognized
four stratigraphicdivisions:ancienteroded !984, 1986].In addition,Gurnis[1981]obtained
craterdensities
uplands,
cratered
(ridged)plainsinterpretedasvolcanic,Elysium for broad terrain units, and many workers focusedon local
volcanicrocks,and Tharsisvolcanicrocks. Formal geologic or regionalgeologichistoriesthat providecrater-density
data
mapping
of Marsbeganwith a 1:5,000,000-scale
mapseriesbased and stratigraphicrelations.
mainlyon Mariner9 images.Because
of the variedqu.ality and
The presentstudysetsfortha new,Viking-based
stratigraphy
resolution
of the imagesand the differencein mappingstyle of Mars in which I (!) establisha more detailedchronostraamong
theworkers,the stratigraphic
classification
systems
that tigraphicclassification
system,
(2) ascertain
the craterdensities
INTRODUCTION
theydeveloped
werecommonly
inconsistent.
Most authorsused andpossible
absolute
agesof the chronostratigraphic
units,(3)
a qualitative
approachto stratigraphic
ageby definingthree, deducerelativeagesof major geologicunits and features,(4)
four,orfiveimpact-crater
degradation
classes
[e.g.,Masursky presentstratigraphic
maps of the entire surface,and (5)
et al., 1978; Wise, 1979; Moore, 1980; respectively];
some summarize
the planet'sgeologic
historyin orderof epochs.
[Milton,1974;Masursky
et al., 1978;Wise,1979]usedcraterSUBDIVISION OF MARTIAN CHRONOSTRATIGRAPHICUNITS
density
datato determine
theoretical
absolute
agesfrom the
crateting
history
models
of Soderblom
etal.[1974]andNeukurn
The three-period,
time-stratigraphic
classification
established
andWise
[ 1976].
by
Scott
and
Carr
[1978]
is
useful,
widely
recognized,
and in
A formalizedstratigraphywas first presentedin the no need of fundamental revision. Subdivision of the chronol:25,000,000-scale
geologic
mapof Marsby Scottand Carr
systems
intoseriesisnowpossible
because
of recent
[1978].
Condit
[1978]counted
4- to 10-km-diameter
craters
and stratigraphic
and
ongoing
work,
particularly
on
the
western
region
of Mars
used
them,together
withoverlap
relations
anddegradational
[Scott and Tanaka, 1986], and is necessaryfor detailed
stratigraphic
work. For simplicityand utility, seriesnamesare
Thispaperisnotsubject
to U.S. copyright.
Published
in 1986by
adapted
from
systemnames and qualified with "Upper,"
theAmerican
Geophysical
Union.
"Middle," and "Lower." Referentswere pickedon the basisof
Paper
number6B7240.
prior usageand recognition,
established
stratigraphic
position,
E139
E140
TANAKA: THE STRATIGRAPHY
OF MARS
TABLE 1. Chronostratigraphic
Seriesand Referents
for Mars
Series
Referent
Upper Amazonian
Flood-plainmaterial,southernElysium
Middle Amazonian
Lower Amazonian
Lava flows, Amazonis Planitia
Planitia
Smoothplainsmaterial,Addalia
at differentlocalities.One areaof basementmaterialat lat•
S, long101o hasrelativelywellpreserved
craters[N(16)(number
Planitia
Upper Hesperian
Complexplainsmaterial,Vastitas
ofcraters
> 16kmin diameter
per106km2)--294:t:81].
Borealis
Lower Hesperian
The lowermost
part of thisbasement
materialis not exposed
and its top is embayedby Middle Noachiancrateredterrain
Ridgedplainsmaterial,Hesperia
Planurn
Upper Noachian
Middle
Noaehian
Intercraterplainsmaterial,eastof
ArgyrePlanitia
material.
Crateredterrain material,west of Hellas
Planitia
Lower Noachian
of about3 to 5 km.Generally,
rimsof superposed
impact
craters
aredegraded
andejectablanketsare not recognized.
Because
of thisdegradation,
craterdensities
arenot reliablefor relative.
agecomparison
between
materials
of theLowerNoachian
Se•
and unitsof otherseries;however,they appearto be useful
in determining
relativeagesof the rockunitswithintheseries
Basementmaterial, Charitum and
Otheroutcropsof materialembayedby thiscrateredterrain
material form basin rims that surroundHellas, Argyre,and
IsidisP!anitiae
andformPromethei
Rupes(southpolarbasin),
Nereidurn Montes
as well as isolatedmassifsand ridges,which are mostlyinthe
westernpart of Mars[ScottandKing, 1984].Materialofsimilar
at the baseof deepscarps,
such
areal extent, degreeof preservation,and, aboveall, represen- positionmayalsobe exposed
as those within Valles Marineris. Possiblythe material of the
tation of a distinctivegeologicepisode.In contrastto terrestrial
upperparts of the primitive
rockunits,theMartian unitsarelargelydefinedby theirsurficial Lower NoachianSeriesrepresents
crustof Mars formed by solidificationof a primordial,molten
characteristics,
and rock typesare inferred.Also, recognition
surfaceand bombardedby largeplanetesimal-size
objects.
of vertical changesin the units and descriptionof their bases
generallyare not possible.
The newlyproposed
seriesand their
referentsand crater densitiesare formally describedbelow (and Middle Noachian Series
summarizedin Tables1 and 2). Possibleabsoluteagesfor these
The Middle Noachian Series consists of cratered terrain
seriesare discussed
in a followingsection.
materialthat characterizes
most of the ruggedhighlandterrain
and scatteredcrateredterrain remnantsin the northernplain•
Lower Noachian Series
of Mars. Much of this material was mapped as "hilly and
Recent mapping [Scott and Tanaka, 1986] distinguished cratered" or "cratered plateau" materials by Scott and Cart
stratigraphically
lower"basement
material"fromthe widespread [1978] and was recentlyremappedas the "crateredunit ofthe
[Scott and Tanaka, 1986]. This rock unitis
crateredterrain material in many areason Mars. Both of these plateausequence"
materialsare part of the Noachian System[Scott and Cart, the most widespreadof the Noaehian System.The designation
1978]. The basementmaterialincludesunitspreviouslymapped of the Noaehian System was originally based on materialin
as "basin rim material" and "mountain material" belongingto the Noachisarea west of the Hellas impact structure.Thisarea
the Noachianand HesperianSystems[Scott and Carr, 1978]. (lat 40ø S, long320ø to 345ø) still appearsto be the mosttypical
The type area selectedfor the Lower N oachianSeriesconsists of crateredterrain, and it is selectedas the type area of the
of Nereidum and Charitum Montes, which form the uplifted Middle Noachian Series.Most other highlandregionsarepartly
rim material surroundingArgyre Planitia (Figure 1). The rim buffedor morehighlydegraded.The regionwestof SyrtisMajor
has an inside diameter of about 700 km and an outside diameter
Planurn,althoughhighly degraded,displaysone of the highest
of largeimpactcratersand double-tingbasinsonMain
of about 1400km, and at mostplacesit rises1 to 2 km above densities
the interior plain but lessthan 1 km abovethe surrounding In general,thecrateredterrainhasa ruggedsurfaceof moderately
plateau[ Wuet al., 1986].Thematerialisrugged,heavilycratered, high relief, marked by secondarycraters,channels,wrinkle
and faulted, and it forms hills, ridges, and massifsthat are ridges,and erosionalscarps.The rock unit embaysmaterial
generallyalignedconcentrically
with Argyre Planitia. Someof of the Lower NoachianSeriesin many areasand in turnis
the massifsand ridgesof northern Charitum Montes appear overlainby intercraterplainsmaterialof the UpperNoachian
similar in size to those within Valles Marineris that have relief
Series.
TABLE 2. Crater-density
Boundariesfor Martian Series
Series
Crater Density
(N = no.craters
> ( x ) kmdiam./10
6km2)
14(1)
N(2)
Upper Amazonian
<160
<40
Middle Amazonian
Lower Amazonian
160400
600-1600
40-150
150-400
Upper Hesperian
Lower Hesperian
Upper Noachian
1600-3000
3000-4800
400-750
750-1200
Middle Noachian
Lower Noachian
N(5)
N(16)
<25
25-67
67-125
125-200
200-400
>400
N(4-10)
<33
33-88
88-165
<25
25-100
100-200
>200
! 65-260
>260
Craterdensities
for N(1) andN(4-10)arederivedfromN(2) andN(5) valuesbasedon theassumption
of a-2 power-lawsize-frequency
distribution.
TANAKA:
THESTRATIGRAPHY
OFMARS
El41
180'
57'5
Fig. 1. Shaded-relief
mapof Marsshowinggeographic
nomenclature
usedin thisstudy;namesfollowedby an .asterisk
areprovisional
[ U.S. Geological
Survey,1985].
Densitiesof craters no more than a few kilometers in diameter
on the cratered terrain material are about the same as those
that are part of underlyingcrateredterrain material are partly
buried by intercrater plains material. Smaller craters are
ontheoverlying
intercrater
plainsmaterial[Tanaka,1985a]and commonlyrimlessandlargercratershavelow rims.Crater ejecta
thusaxenot helpfulin relative-age
determinations.
However, and floors are mostly buried. The intercraterplains surfaceis
largecraters
are morelikelyto be preserved
and recognizedsmootherthan crateredterrain, but it is dotted by many small
andto be usefulfor correlation.As a standard,cumulative cratersand locallycut by channelsor marked by wrinkle ridges.
densities
of craterslargerin diameterthan 16 km are usedfor Statisticsfor craters larger than about 5 km in diameter are
correlation
of materials
of thisseries
[Scottand Tanaka,1986]. fairly reliablefor relative-agedeterminations
(Table 3).
Although
therelative
stratigraphic
positions
amongtheUpper, Intercrater plains material overlies and embays Middle
Middle,
andLower
Noachian
aregenerally
evident,
thematerialsNoachian cratered terrain material throughout the Martian
overlap
incraterdensity
fromplaceto place.
highlands.In turn, it is locally overlainby other plainsmaterial
that is smoother, less cratered, and commonly ridged.
UpperNoachianSeries
Preliminarywork with Viking images[Scott and Tanaka, 1984]
did not show these relations;however, new, more complete
The"cratered
plateau
material"
wasdescribed
by Scottand mapping[Scott and Tanaka, 1986]doesshowthis stratigraphic
Cart[1978]
asdensely
cratered
butflatandsmooth
inintercraterdistinction.The intercraterplainsunit has few featuresthat can
areas.
Thisrockunitwasplaced
in theuppermost
partof the be usedto identifyits origin;it may have multipleorigins,such
Noachian
System.
Recent
mapping
byScott
andTanaka
[1986] aslava flows,flood-plaindeposits,and eolianfill.
shows
thesmooth
intercrater
areas
asa separate
unit(subdued
cratered
unitoftheplateau
sequence)
thatoverlies
thecratered Lower Hesperian Series
terrain
material.
Thisdistinction
permits
thedesignation
ofthe
Upper
Noachian
Series
asrepresented
bysuch
intercrater
plains
The Hesperian System was named for Hesperia Planum
material.
Thetypeareaselected
is eastof theArgyreimpact (Figure 1). The baseof the systemwas delineatedby the base
basin
inthevicinity
oflat45ø S,long15ø.Here,many
cratersof
the "ridged plains material" [Scott and Carr, 1978]. This
E 142
TANAKA:THE STRATIGRAPHY
OF MARS
TABLE 3. CraterDensitiesof SomeMartian GeologicUnits and Features
Unit or Feature
Crater
Density
(N= no.craters
> ( x ) kmdiam./106
km2)
N(1)
N(2)
N(5)
3OO-450
55
150-250
250-375
240-500
65-85
65-75
55-170
85
I00
N(16)
N(32)
Smoothplainsmaterial
southern Arcadia
southern Acidalia
Vastitas Borealis Formation
north of lat 55 ø N
south of lat 55 ø N
<50
Lava flows, Alba Patera
Noctis Labyrinthus
Lava flows, Ceraunius Fossae
Ridgedplainsmaterial
SW ElysiumPlanitia
Lava flows, Dorsa Argentea
Ridgedplainsmaterial
Synis Major Planurn
Acheron
150
150-170
Fossae
Intercraterplainsmaterial
Lower Hesperian
Upper Noachian
Cratered terrain material
700
950-1000
650-1200
165
240
60
160
300-400
300-550
30-100
120-240
Impact basins
Argyre
50
8O
130
Hellas
Isidis
map unit is extensiveand readily identifiable,and becauseit
still providesan excellentboundaryfor thebaseof the Hesperian
System,I considerit thereferentfor the LowerHesperianSeries.
The type areafor the unit remainsthe same,at lat 20ø S, long
245ø in HesperiaPlanurn.Here,the ridgedplainsmaterialforms
a smoothsurfacemarkedby a pattern of wrinkleridgessimilar
to thoseof the lunar maria. The ridgescommonlyexceed100
km in lengthand 10 km in width, and they overlapone another.
Some wrinkle ridgesare found on stratigraphically
higherand
lower rocks;however,thoseridgesare generallylesscommon
<30
30-100
After formationof the LowerHesperianridgedplainsmaterial
and beforedepositionof the lowermostAmazoniansmooth
plainsmaterial,extensivevolcanic,fluvial, and complexplains
unitswereemplaced[Scottand Tanaka,1986].ThereforeI have
selectedcomplexplainsmaterial(VastitasBorealisFormation)
to representthe Upper HesperianSeries.This unit is composed
of mottled,knobby, and patternedplains materialsin Vastitas
Borealis(Figure 1), which forms most of the lowland region
of Mars north of lat 40 ø N. The Vastitas Borealis
Formation
wasformerlymappedasa combinationof smooth(Amazonian),
and smaller.
cratered (Amazonian), mottled (Noachian), and rolling
Crater densitiesof the ridged plains materialgenerallyare (Hesperian)plainsmaterials[Scott and Carr, 1978].
Within the formation, densitiesof craters>2 km in diameter
in a restrictedrange [N(5)= 125-200] that can be used for
stratigraphiccorrelationswith other geologicunits.The ridged tend to be lower north of about lat 55ø N (Table 3), where
plainsmaterialoverliesor erabaysrocksof the UpperN oachian smallercratershaveprobablybeenerased.At >5 km diameter,
Seriesin areassouthof ChrysePlanitia, surroundingProtonilus however,crater densitiesare uniform and have valuesconsistent
'Mensac,and elsewhere.Wiseet al. [1979] postulatedthat the with their stratigraphicposition.
The members of the Vastitas Borealis Formation
are
material is composedof lava flows; Greeleyand Spudis[!981]
suggested
that the flowswereof low viscosityand wereerupted characterizedby complex surface features that includethe
at high effusionrates.
following:(1) a mottledalbedopatternof light cratermaterial
superposed
ondarkintercratermaterial,(2) smallknobsofvaried
density,(3) troughsthat form polygons5 to 20 km in diameter,
and(4) ridgesthat form both polygonaland concentricpatterns.
The Hesperian-Amazoniansystemboundarywas formerly The composition
of the materialsis unknownbut may include
definedby Scottand Carr [1978] asthe top of the ridgedplains lavaflows,sediments,
andpyroelastic
materials[Greeley
and
material and the base of the "crateredplains material."The Spudis,1981;McGill, 1985].Originsof the knobs,ridges,
and
Upper HesperianSeries
type area for the Amazonian Systemwas defined as lat 18ø
grooves
haveattributedto masswasting,periglacial
deformation,
N, long 165ø and mappedto includeboth crateredand smooth
volcanism,
andtectonism
[CarrandSchaber,1977;Scott,1979;
plains•.material
[ScottandCart, 1978
]. However,
thisareahas Pechmann,1980].
sincebeenfound to consistof smoothand ridgedplainsmaterial
[Scott and Tanaka, 1986]. Moreover, areasformerly mapped Lower Amazonian Series
as cra•tered
plainsmaterial
havenowbeenshown
by recent
geologicmappingto consistof manyunitsof thewesternvolcanic
As discussed
above,I redefinedthe baseof the Amazonian
assemblageand the Vastitas Borealis, Arcadia, and Elysium System
because
of complexities
newlydiscovered
by geologic
Formations[Scott and Tanaka, 1986; Tanakaand Scott, 1987; mappingof units at the baseof the system.The new referent
R. Greeleyand J. E. Guest,unpublisheddata, 1986].Scott and is the smoothplainsmaterialthat makesup the lowermost
Tanaka [1986] consideredthe base of the Amazonian System member
of theArcadiaFormation
[ScottandTanaka,
1986],
.to be the base of the Arcadia Formation, which includes the
whichisexposed
principallyin southernAmazonisandsouthern
smoothplainsmaterialwithinthe Amazonisquadrangle.
AcidaliaPlanitiae.
Thisrockunitis moderately
cratered
and
TA•/AKA: THr• STRATIGRAPHYOF MARS
E143
smooth,
andit surrounds
smallknobsandhighareasof older material,indicatingthat the depositsare perhapsonly tensof
materials.
Thetypeareaof thesmooth
plainsmaterialis at meters thick.
lat33ø N, long30ø. The unit overlies
ridgedplainsmaterial
CRATER-DENSITY BOUNDARIES FOR MARTIAN SERIES
insouthern
Amazonis
Planitia;
theVastitas
Borealis
Formation
inAcidalia
Planitia;
northern,
lowerflowsof AlbaPatera;and
Upper
Hesperian
flood-plain
deposits.
Lobate
flowscarps
and
Relative-agelimitsdefinedby craterdensitiesfor the Martian
series were derived from crater counts of referents and from
distributary
channels
in thislowermost
member
of theArcadia
Formation
in Amazonis
Planitiaindicatethat it is madeup other urdts of like statigraphicposition.Table 3 summarizes
craterdensitiesdeterminedin thisstudy.
Increasingdiameters
areusedfor crater-density
rangesof series
coljan
material.
Densities
of craters
largerthan2 kmin diameter
of increasingagefor severalreasons.First, imagesof most areas
fortheunit differfrom placeto place,indicating
differences
generallyallow identificationof cratersno smallerthan 1-2 km
inrelative
agesandperhaps
in craterdegradation.
in diameter. Second, a large proportion of craters several
partly
oflavaflows
andfluvialdeposits;
it mayalsoinclude
kilometers in diameter or less are obliterated on older surfaces.
Third, the densityof large cratersis generallytoo sparseon
MiddleAmazonianSeries
younger surfacesfor determining precise crater densities.
Smoothplains material in AmazonisPlanitia, which Another effectthat is not yet well studiedis differencein crater
characterizes
the AmazonianSystem[Scott and Carr, 1978], size causedby differenttarget-materialproperties[Boyce and
wasshownto be composedof five overlappingmembersof Witbeck, 1985].
the ArcadiaFormation [Scott and Tanaka, 1986]. Members
Generally,densitiesof craterslarger than 16 km in diameter
2and3,whicharelavaflows,aresimilarin stratigraphic
position
were determined for the Noachian referents. This diameter was
to someof the extensivevolcanicrocks of the TharsisMontes
Formationand to thick, degradedmaterialsthat composethe
lowerand middlemembersof the MedusaeFossaeFormation.
A Middle AmazonianSeriesis proposedto distinguishthe
usedin countsfor severalterraintypes[Gurnis,1981],and for
recentlymappedunitson Mars [Scottand Tanaka,1986].At
this diameterand greater,the effectof craterobliterationis
negligible[Woronow,1977].On Upper Noachianintercrater
position
ofthese
twomembers
oftheArcadia
Formation.
Their plainsmaterialandsomeolderresistant
terrains,
however,
craters
typeareaisatlat30øN, long160ø. Here,member
3 issmooth, as small as 5 km in diameter are sufficientlywell preserved
sparsely
cratered,
andmarkedby a fewscarps
that appearto to yield reliablerelativeagesfrom cratercounts.
betheedgesof lavaflows.It overliesthe lowermostmember
of the Arcadia Formation in Amazonis Planitia and erabays
For moderately
resurfaced
Hesperian
andLowerAmazonian
surfaces,5-kin-craterdensities
(N(5)) weremostlyusedin order
theOlympus
Monsaureoles,
andit isoverlain
byuppermembers to avoid obliterationeffectsand to maintain a sufficientsample
of the Arcadiain southernArcadia Planitia and apparentlyby size.On manyTharsisregionandnorthernplainsunits,crater
theupper
member
oftheMedusae
Fossae
Formation
insouthern densitieswere determinedat this 5-km size [e.g., Scott and
AmazonisPlanitia. Densities of craters >2 km in diameter are
useful
in correlating
rockunitsof MiddleAmazonianage.
Tanaka,1981b;PlesciaandSaunders,
1982;Dial, 1984;i44'tbeck
and Underwoo&1984;Table 3]. However, authorsof many
publishedcrater countscite densitiesfor Hesperianto
Amazonianunitsat othersizesas well [e.g.,N(4-!0), Condit,
1978;N(1), Neukumand Hiller, 1981].
Newmapping
of Marshasi-evealed
manyyoungunitsthat
For Middle and UpperAmazoniansurface,the 2-kin-crater
havefew superposed
kilometer-size
craters.These include densities
(N(2))areoptimalforgeneral
application.
Frequencies
uppermost
membersof the Arcadia,OlympusMons, Medusae of smallercratersof similarlyagedsurfacesrangewidelydue
Fossae,and Tharsis Montes Formations and polar, eolian, to secondarycraters,nonimpactcraters,and resurfacing
landslide,
debris-apron,and channelmaterials[Scott and [Soderblom
et al., 1974;Neukumand Wise,1976;Hartmann
Tanaka,!986; Tanaka and Scott, 1987]. Upper Amazonian et al., 1981].Fortheyoungest
surfaces,
however,
thestatistical
matehals
are noteworthybecauseof their relativeyouth and sample
of craters
2 kmin diameter
issmall,andcrater-density
theirconsequent
indicationof currentand potentialMartian data have little value.
geologic
activity.Recentmappingin southernElysiumPlanitia
Crater size-frequency
distributionsof Amazonianand
[Tanaka
andScott,1986;R. GreeleyandJ. E. Guest,unpublished Hesperian
Tharsis
plains
unitsfollowapproximately
a-2 power
data,1986]hasdelineatedvast,smoothflood-plainmaterialthat law for cumulative numbers of craters larger than 1 km
appears
to have been depositedby floods emanatingfrom [Hartmann,
1977;Tanaka,1985c].
On thebasis
of thispower
western
CerberusRupes.This unit is chosenas the referent law, densities
of N(1) and N(4-!0) craterswereconverted
to
fortheUpperAmazonianSeries;the type areais at lat 6ø N, N(2) andN(5) counts.
Thuscrater-density
rangesthat were
UPperAmazonianSeries
long208
ø. Theareaof thefloodplainexceeds
100,000
km2 determined
for Hesperian
andAmazonian
series
at 2- and5-
andit extends
fromlong168
b to 222ø (nearly3000km);it km diameterswereconverted
to N(!) andN(4-10)densities
for
ismorethan750km wideat long195ø. The unit consists
of easycross-reference
(Table2). TheN(1)values
should
beused
low-albedo
materialmarkedby light,wispystreaks.Channel cautiously
because
oftheirvariation,
asdescribed
above.
scarps
andteardrop-shaped
bars are observednear the source
In mostcases,
craterdensities
for the referents
spanthe range
and south and east of Oreus Patera. The east channel of the
given
inTable2.However,
small
areas
ofsome
unitshavecrater
floodplaincutsintomaterialsthat includethe MedusaeFossae frequencies
thatsuggest
overlap
intoadjacent
series.
and Arcadia Formations. Cited crater densities of the channel
floors
areN(1)<600[CarrandClow,1981]andN(1)<50[Scott
ABSOLUTE AGES OF MARTIAN EPOCHS
andTanaka,
1982].Sparse
cratering
of theentireregional
flood
Several models have been made to determine absolute ages
plainsupports
thesmaller
cratercount.Mostcraters
largerthan
The
about1 km in diameter
appearembayed
by theflood-plain of surfaceson Mars;theyremaina subjectof controversy.
E 144
Age
(b.y.)
TANAKA: THE STRATIGRAPHY
OF MARS
Lunar
Martian
Period•
Model
I
calibrationcurve. Similarly, heavily crateredterrain on Mars
Epochs
Model
2
0...
.,
.,
0.70
..
wasassigned
a !-km-crater
densityon thebasisof frequencies
oflargercraters
in Tempe
Terra(quadrangle
MC-3).Assuming
that the highlands
terrainsare all of aboutthe sameageand
accounting
for velocityeffects,
NeukumandWisededuced
that
thecrater-production
rateon Mars is 4.5 timeslowerthanon
the moon.They alsoindicatedthat Phobosis about4.5 to 4.6
1--
b.y. old, andthat a comparison
of craterdensities
between
.lO
.
Phobosand the Martian highlandssuggests
a 4.4 b.y. agefor
..
thehighlands.
Considering
crater-scaling
effects,
theysuggested
that the meteorold flux at Mars and the moon was the same
.,
within a factor of 2. On the other hand, reviewingthe crater-
2-
production
rateson Marsdetermined
by variousauthors
and
..
2.30
..
.
3--
3.10
•3.20
3.50
3.85
4-'
3.55
3.70
3.80
,3.92
4.40
4.6-
Fig 2. Chart showingmodelchronologies
for the moon and Mars.
Absoluteagesfor lunar periodsfrom g/ilhelms[1980, 1986].Inferred
agesfor Martian HesperianandAmazonianepochsarebasedon craterdensitiesof series(Table 2) and correlationto modelehronologies
of
Neulcumand Wise[1976](Model1) andHartmannet aL [1981](Model
2). Becauseof obliterationof smallerNoachiancraters,thesemodels
couldnot be useddirectlyfor the Noachianboundaries.
Neukurnand
Wise[1976]assigned
a 4.4 b.y.ageto crateredterrainmaterial(Middle
Noachianrocks)but gaveno age range;thusthe boundariesof this
epocharedashed.Noaehianagesderivedin thispaperare compatible
with the Hartmann model and are combinedwith the Hesperianand
Amazonianagesof that model.
modelsallow predictionof the relationbetweencrater density
and absoluteage of Martian surfacesbasedon (1) the same
relation derivedfor lunar rocksfrom sampledata, and (2) the
ratio of the crateringfluxes of Mars and the moon. Because
thesefactorsare not preciselydetermined,estimatesof craterproductionratesfor Mars differ considerably.
The resultsof
two dorrdnantcrater-chronology
methods,oneby Neukum and
Wise[1976]andanotherby Hartmannezal. [1981],demonstrate
the range in estimates.They are given in Figure 2, and the
methodsand assumptions
are briefly reviewedhere [seealso
the reviewby Cart, 1981,p. 61].
Neukumand Wise[1976]firstdevelopeda correlationbetween
N(I) and radiometricagesfor lunar sitesbasedon a review
of existingmodels.They then determineda "productionsizefrequencydistribution"(or calibrationcurve)for lunar craters
between0.3 and 20 km in diameterin the age range of 3 b.y.
to older than 4 b.y. [Neukum et al., 1975] and comparedit
to a similar distribution
considering
the astronomicaleffectsof known asteroidand
cometpopulations,
impactvelocities,
gravity,andenergyscaling,
Hartmannet al. [1981,p. 1080]suggested
a Martian craterflux
twicethat of the moonto be themostlikely, and a rangebetween
a factorof 1 and 4 to be possible.
The differenceof a factor of 2 in relative crater-production
rates betweenthe Neukum and Hartmann proposalscreates
quitedifferentchronologies
for the Martian epochs.A major
uncertaintyin the Neukum and Wise modelis the age of the
Martian highlands.Can this be ascertained
by usingonlythe
assumption
that the meteoroidpopulations
havethe samesizefrequencydistributionfor both planets?(This assumption
is
common to both chronologymodels.)An attempt is madein
the followingdiscussion.
The distributionof craterslarger than 10 km in diameter
on Noachiansurfacesdeviatesfrom a simplepower-lawfunction
and is more preciselyexpressedby a lognormaldistribution
[Woronow, 1977].Specifically,fewer smallercratersare found
than expectedfor a power-law distribution.The lognormal
distributionalsodescribesthe populationof ancientcraterson
the moon [Wilhelms et al., 1978]. On Mars, this distribution
may either (1) reflectthe actual ancientdistributionof impact
cratersthat, in turn, mayrepresenta populationof planetesimals
that bombardedthe planet[Strom and Whitaker,1976;Gumis,
!981] or (2) resultfrom intenseobliterationof smallercraters
that wereoriginallypart of a power-lawdistribution[Hartmann,
1973; Chapmanand Jones,1977]. Woronow[1977] indicated
from severallines of evidenceand theory that a simple powerlaw functiondoesnot explain the large-craterdistributionon
Mars, andthat craterobliterationwasmainlyconfinedto craters
<15 km in diameter.
Therefore
I assume that the Martian
populationof craterslarger than 15 km in diameter closely
reflectsthe initial distributionfor the Middle Noachian Epoch,
and that craters having smaller diametersare more fully
preservedon surfacesof higherstratigraphicpositions.
Highland surfaceson the moon and on Mars have similar
large-craterdistributions[Strom, 1979, Figure 20]. More
specifically,
thedistributionof lunarNectariancraters[ Wilhelms
et aL, 1978] is statisticallysimilar to that of Martian craters
(scaled
in sizeonthebasisof relativegravityandvelocityeffects)
on MiddleNoachianhighlandsurfaces
[ Tanaka,1984].In order
derived for Mars based on Mariner
to compare more accurately lunar and Martian crater
9 images.The Mars distributionwas found to be somewhat distributions, I modified the Martian distributions of craters
flatter. Neukumand Wise[1976] suggested
that this difference
was causedby the productionof cratershavingdiameters1.5
times larger on the moon than on Mars becauseof the greater
averageimpact velocityof meteoroldsbombardingthe lunar
surface.They assigneda frequencyof 1-km-diametercraters
to lunar highlandsthat havean age of 4.4 b.y. by projection
from the 100-kin-diameter crater population, using their
largerthan16km in diametersothatonlythecraterdistributions
of particularepochsare represented,
suchasin the lunar counts
by Wilhelmset al. [1978].Furthermore,I increased
thediameters
of Martian cratersby a factor of 1.3 to accountfor gravityand velocity-scaling effects [Tanaka, !984]. The lunar
distributions
arestatistically
distinctfromeachotheraccording
to a X2 testof binnedcrater-size
frequencies
with a 99%
TANAKA: THE STRATIGRAPHY
OF MARS
E145
acceptancecutoff (Table 4). I used countsby Gurnis[19.81]
to representthe craterdistributionsof time-stratigraphicunits
on Mars, and I subtracted
the frequencyof craterssuperposed
on intercraterplainsmaterial(Upper Noachian)from their
frequency on crateredterrain material (Middle N oachian),
leavinga remainderof Middle Noachiancraters.I did the same
for intercrater plains material and the Vastitas Borealis
Formation (Upper Hesperian)to derive a crater distributi6n
for the interval betweenthe Late Noachianand the Early
Hesperian.Binnedcountsfor cratersof Middle Noachianage
>16 km in diameter correlate with the lunar Nectarian crater
distribution(Table4). For craters>8 km in diameter,the Late
Noachianto Early Hesperiandistributioncorrelateswell with
that for the lunar Irabrian System[ Wilhelmset al., 1978] but
only fairly we!! with the lunar mare distribution[Hartmann,
1978], and the Late Hesperianto Amazonian distribution
matches
theaverage
lunarmareandCopernican-Eratostheni
.a:n
distributions[ Wilhelmset al., 1978].
The similarityin craterdistributionsof the Middle N oachian
Seriesand the NectarianSystemsuggests
that they may have
about the same averageage. This suggestioncan be accommodatedby the Hartmann model,which indicatesan agerange
of 3.8-4.2 b.y. (4.0 mostlikely) for the heavilycrateredterrain,
but not be the Neukum model, which requiresthat the age
of the Martian crateredterrain (Middle Noachian)be abo•.U;t
4.4 b.y. The crater-densityratio between Martian Middle
Noachian and lunar Nectarian surfacesis about 2.0, which•
suggests
that the periodsare similarin duration,basedon a
crater-production
ratioof2.0.Within
these
guidelines',
I .have':
set the limits of the Middle NoachianEpoch at 3.92 and 3.85
b.y.mthesameasthelunarNectarianPeriod(Figure2),
The Lower Noachian Series, then, is older than 3.92 b.y.
The baseof theLowerHesperian
Series,according
to thecrater;
densityboundary(Table2) and the Hartmannchronology,
is•
3.5 b.y. old. The Late NoachianEpochthus is assigned
the
periodfrom3.85to 3.5b.y.Thecraterdistribution
andinferred
age(3.85-3.10b.y.)of the intervalbetweenthe LateNoachian
and Early HesperianEpochson Mars nearly corresponds.
to.
that of the Imbrian Period on the moon [3.85-3.20 b.y.; Table
4; Wilhelms,1980,1986].Cumulativecraterdistributions
for
surfacesyoungerthan about3.5 b.y. on both the moon and
Mars generallyfollowa -2 powerlaw. Thesesurfaces
include.
thoseof lunar Eratosthenianand Copernicanrocks[<3.2 b.y.;
[Viihelmset aL, 1978, Figure 6; W'ilhelms,1980, 1986];!unar•
mare(3.8to 1.0b.y.;D. E. Wilhelms,personalcommurdcation;
1986);andMartianpost-Noachian
(<3.5b.y.)rocks.The Upper
Hesperianto UpperAmazoniancraterdistributionon Mars.
correlateswith the distributionsof theseyoungerlunar rock•s
(Table4).
STRATIGRAPHIC-AGEDETERMINATIONS OF GEOLOGICUNITS
AND FEATURES
Thereferents
(Table
1)andcrater-density
boundaries
(Tabl•,
2) for theseries
definedaboveformthebasisfor stratigraphic-.
agedeterminations
ofgeologic
unitsandfeatures
onMars.Many.•
cratercountsfor suchunitsand featuresare alreadypublished;,
additionalcountsperformedin order to completethis study
aregivenin Table3. (More complete
documentation
of many
of thesenewcountsisintended
for futurepublication.).
,:
Crater countsare generallypublishedin graph or tab,ula•r
form, and craterdensities
can be read directlyor adjustedto
one or more of the sizerangesshownin Table 2. Exceptions,
E 146
TANAKA:THE STRATIGRAPHY
OF MARS
are the data in Hartmannet al. [1981,Table8.6.1],whichare regions),surfaceproperties,and atmosphericeffects.Collecratiosof craterdensities
(mostlyat 4 km diameter)relativeto tively,theyhelpto unravelthe evolutionof theplanet.
a typicallunar-marecraterdistribution[in whichN(4) = 188].
Assumingthat the countsfollow a ~2 power4awdistribution Early NoachianEpoch
(which is approximate),I convertedthe ratios to N(5) by
The oldestexposedmaterialson Mars are: (1) basin-rim
multiplyingthem by a factor of 125 and to N(2) by usinga
materialsurrounding
Isidis,Hellas, Argyre,southpolar,and
factor of 750.
other
basins,
and
(2)
isolatedhilly or mountainousmatedfl.
Martian geologicunits and featuresin this study(Table 5)
These materialscharacteristically
have bold relief and are
are classified as follows:
embayed
by
cratered
plains
material.
The bold relief indicates
(1) Plains and highland units. Deposits that have
that
the
Martian
lithosphere
was
sufficiently
thick, cool,and
miscellaneous
(e.g..volcanic,eolian,mass-wasting,
impact)or
elasticduring this early period to preservelarge craterforms.
aregenerally
in therangeN(16)= 120to300;
(2) Volcanoes
andassociated
lavariows. Featuresthathave Craterdensities
however,becauseof substantialdegradationand fill withinlow
definitivevolcanicmorphologies.
(3) Channels. Includesoutflow,fretted,and runoff types. areas,the crater-densitydata commonly are not representative
(4) Fracture systems. Most are related to Tharsis of the age of the material. From superpositionrelationswith
uncertain origins.
crateredterrainmaterial,the LowerNoachianseriesisassigned
tectonism.
N(16) > 200. If the craterpopulationshave been degraded
in
a
consistent
fashion,
crater
counts
(Table
3)
indicate
that
the
than 200 km in diameter.
Generally, crater-densityages and stratigraphicrelations oldestof the three largestbasinsis Isidis, followedby Hellas
isalsosupported
bycomparisons
closely complement each other. Where crater densities andthenArgyre.Thissequence
of
determinedby variousauthorsare assigned
to series,the relative among the basinsof the relief and degreeof preservation
mountain-ring
structures.
Erosion
probably
was
not
the
main
agesof mostfeaturesarein fair agreement.Wherediscrepancies
exist, stratigraphicrelationsare used to determinethe relative causeof the lowerreliefof the olderbasinrims, as suggested
craters.
age as preciselyas possible.However, someof the featuresare by the moderateamount of obliterationof superposed
volcanicprovincesor volcanogroupsthat havehadlongperiods More likely,thegreaterdiameterof the olderbasinsandprobable
of activity; the inferred entire durationsare given in Table 5. higher crustal temperaturescausedgreater viscousrelaxation
The relativeagesof channels,fractures,and impactbasinswere of their rims. Most other Martian impact basinsidentifiedor
mostly determinedby overlaprelationsor cratercountsof the postulated[Schultzet al., 1982]appearolderthan or equivalent
surfacesthat they cut or overlie; only a few of the agesrefer in ageto the Middle Noachiancrateredplains,andtheirpositions
are designatedas Lower to Middle Noachian (Table 5). Other
to the features themselves.
isolated hilly material is exposedin relatively small patches
surroundingthe Tharsis region and in patchesin the eastern
STRATIGRAPHIC MAPS OF MARS
part of Mars; they may alsobe old basin-rimremnantsof old
To summarizethe vast amount of stratigraphicdata in a volcanicor tectonicmountains[Scott and King, !984].
simple, consistent,and legibleformat, the time-stratigraphic Knobby remnants of heavily cratered terrain occur in the
series describedabove are portrayed in map form. Formal northernplainsas far north as ScandiaColles(Figure 1) and
geologicmapping of Mars at 1:!5,000,000scalefrom Viking other localitiesnorth of the highland-lowlandboundaryscarp.
imagesis nearly complete[Scott and Tanaka, 1986; Tanaka Theiroccurrence
suggests
thatthenorthern,
topographically
low
and Scott, 1987;R. Greeleyand J. E. Guest,unpublisheddata, region (several kilometersbelow the highland surface)was
1986]and washeavilyreliedon to completea stratigraphic
map formedduringthe Early NoachianEpoch.This low regionis
of the entire surfaceof the planet. The spatial and temporal approximatelycircularand has a diameterof about 130
ø of
resolutionof thestratigraphic
mappingsurpasses
previouswork. latitude.Faultsradial and concentricto the Argyre,Hellas,and
The resultingmapsare shownon Plate la-c.
Isidisimpactbasinsformedduring the Early Noachianandon
A few exposures
consistof materialsthat wereeraplacedover into the Middle Noachian,accordingto cratercounts[ Wichman
longtimespans,suchascanyon-w• materialin VailesMarineils, and Schultz,1986]and transectionrelationswith plateaurocks.
etchedterrainnearthe southpole, and knobbyplateauremnants
in the northernplains. Thesematerialsare mostly Lower to Middle NoachianEpoch
Upper Noachian,but for simplicityall are shownas Middle
the final periodof
Noachianonthemaps.Likewise,theactivities
of manyvolcanoes The MiddleNoachianEpochrepresents
and fracture setscover wide age ranges,but only the latest or heavy bombardmenton Mars, when cratetingrateswerevery
averagesurfaceagesare presentedon the maps.Detailedage high and crater-production distribution may have been
[ Woronow,1977].Consequently,
manyof thesmaller
ranges,stratigraphic
relations,andcrater-count
sources
of these lognormal
units and featuresare compiledin Table 5. Overall, the maps impactbasinsare of this age (Table 5). Crater countsof the
providean easyreference
for the stratigraphic
positionsof all Middle NoachianSeriesreferent,the crateredterrainmaterial,
wereobtainedfrom the followingMars Charts:3, 10[Neukum
major units on Mars.
(5) Impact basins. Circular, multiringedstructureslarger
GEOLOGIC HISTORY OF MARS
and Wise,1976];20, 22, 23, 26 [Gurnis,1981];20, 23 (A. L.
Dial, Jr., personalcommunication,
1984);and 10, 11, 18,19,
24, 25, 26 [Tanaka,1985a].Crater densities
mostlyfall in the
In the following sections,the surfacehistory of Mars is range of N(16)-- 120 to 240, concentratedwithin the range
reviewed,addinga geologic
perspective
to thestratigraphic
maps of N(16) = ! 60 to 200. Resurfacingand erosionaleffectswere
on Plate 1. The individualepochsare characterizedby events minimizedfor the countsin this studyby avoidingintercrater
and activitiesthat are governedby planetesima!
bombardment, deposits
(mapped
asyounger
units)anddissected,
knobby,
and
the deepmantleandlithosphere
(manifested
byvolcanotectonicetchedexposures
[Scottand Tanaka,1984].Evenso, in some
TANAKA:THE STRATIGRAPHY
OF MARS
E147
t
....
J
E 148
TANAKA:THE STRATIGRAPHY
OF MARS
TANAKA:THESTRATIGRAPHY
OFMARS
E149
z
z
z
'T'
I--'
I::]
Z
El50
TANAKA:
THESTRATIGRAPHY
OFMARS
TABLE 5. Stratigraphyof Martian GeologicUnitsand Features
Unit or Feature
Stratigraphic
Cited CraterAges
Key GeologicRelations
Position
A.
Polar dunes,mantle, ice, and
layereddeposits
Plainsand Highland Units
UA (andlower?) MAm,UA{2)
Landslides
Olympus Mons
UA
none
Vailes Madneris
MA-UA
MA {3)
UA
none
MA-UA
MA(4),MA (5)
MA-UA
MA-UA (6)
=Olympus flows (UA)
<layered deposits(UH)
Debris aprons
Tharsis Montes
mensac terrain
Thick deposits,southern
Amazonis
Planitia
=Tharsis flows (UA)
<smoothplains(LA)
<smooth plains(LA-MA);
<--Olympus
M OhSaureoles
and Tharsisflows (MA)
Smooth plains
Malea
Planurn
Vastitas Borealis
UH
Layereddeposits,Vailes
UH
Marineris
Argyre and Hellas Planitiae
UN-UH
Ridged plainsmaterial
LH
Intercraterplainsmaterial
UN-LH
Crateredplainsmaterial
craters larger than 10 km in MN
LH(•),UH(4),UNLH(8),UH(9),
LH(•2),UN('6)
LN (17)
LN
B.
OlympusMons (including
aureoles)
MA(71,
LA-UA(8)
MN(8),MN(m
diameter
craters smaller than 10 km in UN-LH
diameter
Basement material
<ridged plains(LH)
<VastitasBorealis(UH),
Elysiumflows (UH-LA),
Chryseflood plains(UH)
UH(2),UH(8),LA(9), <ridged plains(LH); =
LH_LAI•0),
UH('•) Elysiumflows(UH);
>smooth plains(LA)
none
<Vailes Marineris (LH),
ouffiow channels(UH)
UNø),UHI•ø)
<--ridgedplains(LH), Dorsa
Argenteaplains(LH)
UN.LH('>,LH(8), ..<_intercrater
plains(UH-LH);
UH(9),LH('ø),LH- >Syria Planurnflows (UH),
UHin),UH(13),
VastitasBorealis(UH)
LH ('4)
UN-LH(8),UN(m, <crateredplains(MN);
UN_LH('51
>_ridgedplains(LH)
UH-LA (or higher) none
LA to UA
northern
Ceraunius
Fossae flows
Small Tharsis volcanoes
;>crateredplains(MN)
Volcanoes and Associated Lava Flows
LA(orlower)-UA MAm,UH-UA(?), <UlyssesFossae(LH),
UA(9),
=Tharsis flows (MA-UA);
UA ('31
Tharsis Montes (including
flows)
<basementmaterial (LN);
>intercraterplains(UN)
_<cratered
plainsdissection
(UN)
>_thickAmazonisdeposits
(MA-UA); >Tharsis flows
(MA)
<-Alba Pateraflows (LH-LA)
<ridged plains(LH)
UH(or lower)-UA
UH(a),LA('7)
UH-MA(1),LA-
U H-LA
MA(•),LA_UA
I•:),
LA-UA('3),UHUA(14),
LA(18)
UH_LA('5),
LH('s) >Tharsis flows(UH-MA)
UH-LA
Small volcanoes(?)
in northern UH-LA (or higher)
plains
none
Elysium volcanoes
UH-LA
UH('),LA{9),UH- <ridgedplains(LH);
LA{hI,UH_LA•31, <-VastitasBorealis(UH);
Syria Planumflows
UH
Alba Patera flows
LH-LA
Tempe Fossaeflows
LH-UH
none
DorsaArgentea
flows
SyrtisMajorflows
LH to UH
LH
LHis)
UN(11,
LH(8)
Highland
paterae
UN to LH
LH('),UN('ø),
MN to UN
UH('•)
none
UH_LA (18)
<-VastitasBorealis(UH)
>smooth plains(LA-MA)
UH(14),
UH(17)
<ridged plains (LH)
UN('),UH{4),UN- <CerauniusFossae(UN)
LH(71,
LA(9),LA(12),
UH('3),LH_LA('7),
LH ('8)
Highland volcanoes
<ridged plains(LH); =lower
Alba Pateraflows (LH-UH)
<ridgedplains(LH)
<intercraterplains(UN);
>VastitasBorealisplains
(UH)
>-ridgedplains(LH)
_<crateredplains(MN);
>ridgedplains(LH)
TANAKA:THE STRATIGRAPHY
OF MARS
TABLE 5.
Unit or Feature
Stratigraphic
El51
(continued)
Cited Crater Ages
Key GeologicRelations
Position
Channels
CerberusRupeschannel
Hrad, Tinjar, and Granicus
UA(6),MA=UA(•6) <smoothplains(MA)
UA
LA
<VastitasBorealis(UH);
=Elysium flows (LA)
UH(•)' UH.MA (4), <ridgedplains(LH);
LAt9),UH(•6},LH- ;>smoothplains(LA)
MA 1'8)
LA06},LH_UH('7), <ridgedplains(LH);
UH_LA 1•9)
=Thatsis flows (UH-LA);
none
Valles
Outflow channels,flood plains UH
and chaotic terrain
UH-LA
Mangala Vailes
>Medusae
Fretted channels
UN-UH
UN_MA ('s)
Small runoff channels
UN(or lower)
UN (•6)
Long,sinuouschannels(e.g.,
UN-LH
LH (•6)
Fossae material
(MA-UA)
<intercraterplains(UN);
=ridged plains(LH);
>_outflowchannels(UH)
<crateredplains(MN);
>ridgedplains(LH)
<intercraterplains(UN)
Ma'adim)
D.
Fracture Systems
CerberusRupes
Northeast of Ascraeus Mons
MA-UA
South of Ceraunius Tholus
LA-MA
none
=western Amazonis channel
MA-UA(•4),MA-
(UA)
=Tharsis flows(MA-UA)
UA ½•7)
LA-MA{•4),LA-
=Thatsis flows (LA-MA)
MA (•7)
ElysiumFossae
Eastern Memnonia
Daedalia
Fossae
Planurn
UH-LA
UH-LA
UH-LA
none
=Elysiumflows(UH-LA)
LA(m,UH_LA(•*) =Tharsis flows (UH-LA)
=Thatsis flows(UH-LA)
LH-LA(m,UHLA ('7)
East of Ceraunius Tholus
Labeatis Fossae
Fortuna Fossae
Alba and Tantalus Fossae
UH-LA
UH
UH
LH-LA
LH_LA(•4),
LA{•7) =Tharsis flows (UH-LA)
=Tharsis flows (UH)
UH04),UH(•7)
LH(2•,LH.LA18•
'
UHI20•
>Thatsis flows (MA)
<CerauniusFossae(UN);
=Alba Patera flows (LH-LA);
>smoothplains(LA)
_>SyriaPlanurnflows(UH)
NoctisLabyrinthus
LH-UH
Tempeand MareotisFossae LH-UH
UH (s)
Ulysses
Fossae
LH
UN-LH(7),LH-
>Olympusaureoles
(LA),
Uranius Fossae
Western Memnonia Fossae
Icaria Fossae
LH
LH
LH
Thaumasia Fossae
LH
UH (•4)
LH_UH ('4)
LH.UH ('4)
UN_LH (14)
UN_LH('•)
Tharsisflows (MA)
>Thatsis flows(UH)
>Tharsis flows(UH)
=intercraterplains(LH)
=intercraterplains(LH);
Nia Fossae
Vailes Marineris,
LH (or higher)
LH (•4)
>Syria Planurnflows(UH)
<ridgedplains(LH)
Main development
LH
none
Subsequent
faulting
UH-UA
none
Sirehum Fossae
Neetads Fossae
UH-LH
UN
UN_LH(•4),
UN(2ø) >Tharsis flows (UH)
Ceraunius Fossae
UN
ClaritasFossae(north)
UN
UN_LH04)
UN (m
Noctis Fossae
UN
UN(TM)
UN_LHo),MN(2ø) <ridgedplains(LH); =Tempe
Fossaeflows(LH-UH)
UN_LH (•)
Faultseastof ElysiumPlanitia UN
LN (2o)
Coracis Fossae
MN-LH
MN (•4)
Acheron Fossae
MN
UN (s)
ClaritasFossae(south)
MN
MNtm,MN(2ø)
Melas Fossae
Basin faults
MN
LN-MN
none
LN_MN12ø1
<ridgedflows(LH); >layered
depositsandoutflowchannels
(UH)
<layereddeposits(UH);
=landslides(MA-UA)
<crateredplains(MN-);
>ridgedplains(LH)
>Alba Patera flows (LH)
<south Claritas Fossae(MN-);
>Syria Planurnflows(UH),
NoctisLabyrinthus(LH-UH)
>Noctis Labydnthus(LHUH)
<knobbyterrain(MN?);
>ridgedplains(LH)
<basementmaterial (LN);
>Syria Planurnflows(UH)
>intercraterplains(UN)
<basement material (LN);
>north Claritas Fossae(UN)
>intercrater plains(UN)
>crateredterrain (MN);
>intercraterplains(UN)
E152
TANAKA:THE STRATIGRAPHY
OF MARS
TABLE 5.
Unit or Feature
Stratigraphic
(continued)
Cited Crater Ages
Key GeologicRelations
Position
E.
Impact Basins
none
Lyot
LA
Lowell
LH
none
Most impactbasins
LN-MN
none
South polar
LN
none
<Vastitas Borealis(UH);
>smooth plains(LA)
<intercraterplains(UN-LH);
>Thaumasia Fossae(LH)
>crateredplains(MN);
>intercrater plains (UN)
>crateredplains(MN)
Argyre
Hellas
Isidis
LN
LN
LN
MN181
MN181
LNIg)
>cratered
plains(MN)
>cratered
plains(MN)
>cratered
plains(MN)
"Stratigraphicposition"is determinedby crater countsand geologicrelations;N = Noachian, H
= Hesperian,A = Amazonian,L = Lower, M = Middle, U = Upper. "Cited crater age" is mostly
deducedfrom crater counts;includesgeologicrelationsfrom somestudies;countsmay be for only
part of the unit or feature;footnote is for referencebelow. "Key geologicrelations"are those most
helpfulin establishing
age;includesagesmore detailedthan in table(e.g., Tharsisflowsare subdivided);
< meansyoungerthan, = meanscontemporaneous
with, and > meansolderthan.
References:(1) Hartmannet aL [1981]; (2) Dial [1984];(3) Lucchitta[1979];(4) Masurskyet
aL [1977]; (5) Squyres[1978];(6) Scott and Tanaka[1982]; (7) Hiller et aL [1982]; (8) Table 3;
(9) Condit [1978]; (10) Greeley and Spudis [1981]; (11) Witbeck and Underwood [1984];
(12) Soderblomet aL [1974];(13) Plesciaand Saunders[1979];(14) Plesciaand Saunders[1982];
(15) Gurnis[1981]; (16) Carr and Clow [1981]; (17) Scott and Tanaka [1981b]; (18) Neukum and
Hiller [1981];(19) Masurskyeta!. [1986];(20) Wichmanand Schultz[1986].
placesmore than half the cratersare embayedby local deposits.
Densities of fresh, unembayedcratersgreaterthan about 4 km
in diameteronUpperNoachianintercraterplainsareconsistently
lower than densities of similarly sized craters on Middle
Noachian terrain [Tanaka, 1985a].
Also during the Middle Noachian (and possibly earlier),
Acheron, Claritas, Coracis, Nectaris, and Melas Fossaeand the
broad, arcuate ridge along the south edge of Softs and Sinai
Plana (Figure 1) were formed.
Late Noachian Epoch
During thisepochan earlyintercraterunit wasemplacedthat
overlies much of the older Martian highland material. Only
larger exposuresare mapped(Figure 3); many smallerpatches
are not shown. These materials are relatively smooth but have
channelsand wrinkle ridgesin places.Craterdensitiesfor this
unit range from N(16)= 30 to 100 and averageabout 90 in
the westernpart of Mars.
The intercraterdepositsarethickerin someareasthan others,
and crater densitiesare highly variable; many exposedcraters
are embayed.The distributionof cratersgreaterthan 8 km in
diameter is intermediate in form
between that of earlier
of distributions of fresh to degraded craters in the 5- to 15-
km-diametersizerange.The obliterationof smallcraters
may
be a resultof easilyerodedsurfacematerials,,
mantlingbye01ian
and volcanicdeposits,and wind and water erosionproduced
by a thickeratmosphereand warmer surfacetemperature.
High-resolutionimagesof the crateredand intercraterplains
showthat significanterosionor burial occurredin mostplaces
sufficientto obliteratepreexistingkilometer-sizecraters.Small
but densely arrayed channels dissect cratered terrain and
intercraterplainsmaterialandpredatethe ridgedplainsmaterial;
they appear to have formed by water runoff [th'eri, 1976;Cart
and Clow, 1981]. Larger runoff channelssuchas Ma'adim,A1Qahira, and Nirgal Vailes(Figuie 1) alsocut the crateredplains
and were formed at about the same time as the smaller channels.
Faultingwasextensivein the TharsisregionduringtheLate
NoachianEpoch,continuingat Claritas,Coracis,and Nectaris
Fossaeand commencingat Noctis and CerauniusFossae.Most
faults are orientedradially to Syria Planurn [Plesciaand
Saunders,1982]. More than 30 mountains(not shown)of
possible
volcanicoriginthat may haveformedduringthisepoch
occur from Claritas and Thau•asia Fossae west to Sirenurn
Fossae[Scottand Tanaka,1981a],at NectarisFossae[Roth
et aL, 1980],andat otherhighlandareas(including
Apollinaris
(lognormal)and later (power-law)distributions.The size- Patera).FissurevolcanismalongAcheronFossaeproduced
lava
frequencydistributions
of cratersabout2 to 4 km in diameter ffil within the arcuatestructure[Scott and Tanaka,1986].
are about the same for Middle Noachian to Lower Hesperian Although
theirageis notprecisely
established,
VailesMarineris
surfaces[Tanaka, 1985a].Furthermore,a densitymap of 0.6 mayhavebeeninitiatedbyfaultingat thistime.Eastof Elysium
to 1.2 km cratersfor most of Mars by Soderblomet al. [1974, Planitia, faults that bound wide grabenscut the knobby,
Figure5] indicates.
densities
thatcorrespond'to
Amazonian
and degraded
crateredterrainandthegrabensareembayed
byLower
Hesperianages.The lack of regionshavinghigh densities
of Hesperian
ridgedplainsmaterial;
thesefauksmayhaveformed
smallcratersindicatesthat nearlycompleteobliterationof these duringthe Late N oachian.
cratersoccurredduringthe Late Noachianandpossiblyearlier
as well. However, by Early Hesperiantime, surfaceswere Early HesperianEpoch
produced
thatshownoindication
ofobliteration
ofcraters
larger
than 1 km in diameter.Chapmanand Jones[1977,p. 525] have
The LowerHesperian
Seriesreferentis the ridgedplains
also indicatedthat an episodeof craterobliterationoccurred material,
whichischaracterized
bysmooth
surfaces
marked
by
duringan intermediate
stageof Martian history,on the basis long,sinuouswrinklesridges.This unit is extensiveandcovers
TANAKA: THE STRATIGRAPHY
OF MARS
E153
with a late stage
thefollowing
areas:
(1)partofthesouthern
edge
ofthenorthern large sheetflows and were contemporaneous
plains;
(2)plains
between
Elysium
andAmazonis
Planitiae;
(3)
of wrinkle-ridgeformation[Schaber,1982];probablecalderas,
in Tempe Fossae[Scott,
Hellas
Planitia;
and(4)manyhighplains
suchasLunae,Sinai, volcanoes,and tectonicdepressions
1982];and Alba Patera,whichproducedits northernand eastern
distalflows duringthis time [Dial, 1984]. Flows of this epoch
intercrater
highland
areas.In places,the VastitasBorealis alsomay have occurredaroundTharsisMontes, but they have
character
Formation
appears
to erabay
andencroach
ontheridged
plains beenobscuredbyyoungerflowsandtheirmorphologic
Syrtis
Major,
Hesperia,
andMalea
Plana
(Figure
1,Plate1).
Ridged
plains
alsooccur
in smallpatches
in craters
andin
material;
theformation
perhaps
results
from modification
of destroyedby fractures.
The NoctisLabyrinthus-Valles
Marinerisrift systemdeveloped
to
a
large
extent
during
the
Early
Hesperian Epoch. Also,
theridged
plainsmaterialis locallyhummocky
andknobby.
ridged
plains
material.
Forexample,
insouthern
Utopia
Planitia,
Hencemuchof the VastitasBorealisFormationmay have extensivefracturesformed on highlandsurfacessurrounding
mostof the Tharsisregionat Alba, Tantalus,Mareotis,Tempe,
originally
been
ridged
plains
material
emplaced
byvoluminous
eruptions
oflow-viscosity,
mafic
lava[Greeley
andSpudis,
1981]. Ulysses,Uranius, western Memnonia, Sirenurn, Icaria, and
Possible
localsourcesof the ridgedplainsmaterialinclude ThaumasiaFossae.Many of thesefracturesare radial to Syria
Hadriaca,
Tyrrhena,
Amphittites,
andPeneusPaterae(Figure Planum, and the youngestsurfacesthat they cut have counts
i).
of N(5) -- 219 to 115[Plesciaand Saunders,1982].This episode
ByEarlyHesperian
time,thecratering
ratewasmuchreducedof rifting and faultingwasperhapsthe mostintensein Martian
fromthat of the Noachianheavybombardment[Hartmann et
history.
al.,1981,
Figure8.6.3].Stratigraphic
relations
(Table5) suggest
thatthe double-tingimpact basinLowell is Early Hesperian Late HesperianEpoch
inage.Cumulative
size-frequency
distributions
of craters
more
than I km in diameter on most pristine Martian surfaces
The Upper Hesperian referent, the Vastitas Borealis
generally
follow
apower
law,similar
tothedistribution
ofcraters Formation[ScottandTanaka,1986],coversmostofthenorthern
onthelunarmafia[Hartmann,1978].Densitiesof craterslarger lowlandsin Acidalia,Isidis,Elysium,and Utopia Planitiaeand
all lowlandareasnorth of lat 55ø N (Figures1 and 2). Densities
of craterslargerthan 5 km in diameterfor the formationare
fortheridgedplainsreferent.On MaleaPlanum,ridgedplains remarkably uniform, ranging from N(5)--65 to 110 and
than 5 km in diameter for materials of this epoch are most
reliableat 5 km diameterand generallyrangefrom 125 to 200
averagingabout N(5) = 75 [Dial, 1984; Witbeck and
that mostof its surface
1981];
however,
someof the craterswithin the unit appear Underwoo&1984;Table3], suggesting
inarelatively
short
time.Counts
forcraters
larger
th•n
embayed
bytheridgedplainsmaterial.Countsof craterslarger formed
material
hasa slightlyhighercraterdensity[Hartmannet al.,
than4 km in diameteron LunaePlanumsuggest
that the ridges 2 km in diameter(N(2)),however,areerratic.Theyaregenerally
from a -2 power-lawprojection
from N(5)
areaboutthe sameageas the plainsmaterialsurroundingthe lowerthanexpected
counts
and
are
latitude
dependent.
North
of
lat
55ø N,
ridges
[Tanaka,1982],but the ridgeshavea higherdensityof
craters
2 to 4 km in diameterthantheplains.Burialof interridge N(2) -- 150-250andsouthof lat 55ø N, N(2) -- 250-375(Table
thatthecraters
farthernortharecomposed
areas
isevidenced
in easternSinaiPlanurn,wherehigh-resolution 3).Thistrendsuggests
to greatererosive
images
showlava flows originatingfrom the Syria Planurn of easilyerodiblematerialor weresubjected
region.
Intenseerosionof cratered terrain and intercrater plains in
processes,
or both.AlthoughtheVastitasBorealis
Formation
highland-lowland
scarp and around highlandremnantsin
1978].Volcanoes
andlavaflowswereemplaced
at thesouthwest
is confinedto the northernplains,knobbymaterialresembling
of theformation
wasproduced
in thecenter
thenorthern
lowlandsandalongthe highland-lowland
boundary theknobbymember
scarpprecededemplacementof ridged plains material. of HellasPlanitiaat nearlythesametime[N(5) = about60].
Althoughformationof the intercraterplainsmaterialhad
Deuteronilus
and Protonflus Mensae (large polygonal mesas
activityat manylargevolcanic
regions
on Mars
formedby development
of frettedchannelsin highlandsalong nearlyceased,
duringthis epoch,accordingto cratercountsof
thehighland4owland
scarp)were formed after depositionof commenced
UpperNoachianintercraterplainsmaterial(someof whichhas the vent areas and lava flows that emanate from these vents.
wrinkleridges),but they are embayedby ridgedplains.This Theseflowshavelobatescarpsand leveedchannelsand closely
stratigraphic
relation is also found in other areas along the resemblelava flows on Earth and the moon [Schaberet al.,
Utopia,Elysium,and westernAmazonisPlanitiae.The fretted and northeastendsof the Tharsisswell;in plainswestof Alba
channels
withinthemensacappearto be structurally
controlled Patera;and at SyriaP!anum,TempeTerra,ElysiumPlanitia,
[Sharp
andMalin,1975]andrelatedto ancientimpactbasins CerauniusFossae,and Dorsa Argentea.Possiblecindercones
inplaces
[Schultz
et al., 1982].Therim of Hellasimpactbasin in thenorthernplains[Freyetal., 1979]areprobablyalsoUpper
Thecomplex,
overlapping,
lobatelavaflowscommon
generally
hashigh reliefbut is absentwhere coveredby ridged Hesperian.
plains
material
alongthenortheast
andsouthedges.
Burialalone to manyof theseareasoverlieridgedplainsmaterial.Mostof
cannotexplainthis absence,becausethe ridged plainssurface these surfacesretain craterslarger than 1 km in diameter
isfound
wellbelowadjacent
basin-rim
material.
In manyother [Neukurnand Wise,1976;Scottand Tanaka,1981b]except
localities,
embayments
ofhighlydegraded
remnants
of highland for the Hesperianflowsnorth of Alba Patera,whosecrater
counts
(Table3)indicate
obliteration
of small(<5kmdiameter)
terrain
byridged
plaips
material
show
thatintense
degradation
preceded
theformationof ridgedplains.
Several
largevolcanicloci that eitherwerecoevalwith or
craters.
Fracturing
wasintense
atAlbaandTantalus
Fossae,
butweak
The faultsproducedaredominantlyradial
immediately
postdated
ridged
plains
material
produced
extensiveor absentelsewhere.
complexes
latein the Early Hesperian
Epoch.Thesecenters to Pavonis Mons and have crater densitiesof N(5)- 115 to
andSaunders,
1982].Theyoccurprimarily
onthe
include
apparent
calderas
onSyrtis
MajorPlanurn
thatproduced70 [Plescia
E154
TANAKA:THœSTRATIGRAPHY
OF MARS
lowerflanksof theTharsisswellat Labeatis,
Tempe,Mareoffs, reported
N(5)= 100andN(2)= 420.In northeastern
Arcadia
and eastern Memnonia Fossae and on southern Daedalia
Planitia,
N(2)isabout150to200.Variations
inthecrater
counts
Planurn.Riftingandcollapse
continued
at NocffsLabyrinthus mayin partbe attributable
to inclusion
of otherunitsinthe
andVallesMarineris,cuttingintoSyriaPlanurnflowsandridged areascounted
andto obliteration
of smallercraters.
Theunit
plainsmaterial[Scottand Tanaka,1986].Arcuatefaultspartly locallyconsists
of lavaflows[Scottand Tanaka,1986]butis
buriedby Tharsisflowsat FortunaFossae
mayformpartof mantied
in mostareas.Someof theunit,particularly
in Acidalia
a largevolcanotectonic
featureof aboutLateHesperian
age.
PlanitiaandnorthofTempeFossae,
maybecomposed
ofeolian
Deep erosionin the southpolar highlands
formedthe cavi or alluvialsediments
[ Witbeckand Underwood,
1984].
terrain(plateausmarkedby deep,irregularpits),cuttinginto
Stratigraphicrelationsand crater counts[Plesciaand
extensivelobateand sheetlikedepositsof probablelava-flow Saunders,
1979;Scottand Tanaka,1981b]indicatethatlava
offgin(DorsaArgenteaflows)of Late Hesperian
ageandolder flowswereemplaced
at thistime,mostlyfrom thelargeshield
[TanakaandScott,1987;Tables3, 5].
volcanoes
andfissures
around
Tharsis
Montes,
AlbaPatera,
Crater countsmadeby Masurskyet al. [1977]and Neukum and ElysiumMons. A few of the smallerTharsisvolcanoes
and Hiller [1981] of the outflow-channel
floorsindicatea wide werealsoactive.Someof thetharsisflowsenterednorthwestern
rangeof ages.However,Carrand Clow[1981]notedthat only KaseiValles[Scottand Tanaka,1986].Fault activity
was
crater countsof deeplyscouredchannelsurfacesmay be valid; localized around Tharsis volcanoesin southern Daedalia
smooth or lightly erodedsurfacesmay yield crater agesthat Planurn, eastern Memnonia Fossae,and south of Uranius
reflect resurfacingperiodsrather than channelingepisodes. Patera;aroundAlba Pateraat Alba andTantalusFossae;
and
Countsfor thedeeplyscoured
surfaces
andgradationalcontacts on the flanks of Elysium Mons, forming Elysium Fossae
of the flood-plainmaterialwith the VastitasBorealisFormation
in Chryse Planitia suggestthat outflow-channel
activity was
mostly restrictedto the Late HesperianEpoch.The channels
originatedfrom chasmataand chaotichighlandterrain. If the
chaotic terrain was formed by collapsedue to withdrawalof
subsurfacevolatiles,as is commonlybelieved,it is the same
age as the channels.Juventae and Ganges Chasmata contain
layereddepositsthat now appearas streamlined,moderate-size
(tensof kilometersacross),roundedhills risingabovethe valley
floors, showingthat, during Late Hesperiantime, deposition
[Mouginis-Mark et al., 1984].
The OlympusMons aureoleswereemplacedaboutthistime.
Oneof theaureoles
overlies
LowerHesperian
terraincutby
UlyssesFossae,and all of the aureolesunderlieUpper
Amazonian lava flows of Olympus Mons. The lowermost
aureoleswest of Olympus Mons are embayedby Middle
Amazonian
lavaflowsandplainsmaterial.Cratercounts
by
Hiller et al. [1982]indicatean Early Amazonianageforthe
aureoles;however,the cratercountsmay be unreliablebecame
of thedegraded
natureof theaureoles'
surfaces
[Morris,1982].
of layered material followed channel formation. In channels Widely varying explanationshave been postulatedfor the
east of Vailes Marineris and in Kasei Vailes,multipleterrace aureoles,but mostworkersascribeoriginsrelatedto volcanism
levelsin the channelsandchaoticterrainsuggest
multiplestages [McCauleyetal., 1972;Hodges
andMoore,1979;Morris,1982]
of channelformation. Flood-plainmaterialsfrom the channels or to gravityslideson the flanks of OlympusMons [Lopes
fan out into Chryse Planitia and grade into the lowermost et al., 1980;Francisand Wadge,1983;Tanaka,1985b].In either
member of the Arcadia Formation in western Acidalia Planitia
case, the aureole material must somehowbe a productof
[Scott and Tanaka, 1986]. The smoothplains here appear to volcanismin the OlympusMons area. The relativeageof
bury remnantsof sinuouschannels.The MangalaVailesoutflow- formationof the volcano'sbasalscarpis looselydefined
and
channel system,which largely originatesfrom a fracture in the maybeaboutthesameasthat of the aureoles.
Thusdevelopment
highlands west of Daedalia Planurn, debouchesinto southern of OlympusMons beganduringthis epochor earlier,andthe
Amazonis Planitia, cuts ridged plains material,and appears volcanohad probablyattainedmost of its presentsizebythe
contemporaneouswith Upper Hesperian-Lower Amazonian end of the epoch.
Tharsis flows [Masursky et al., 1986; Scott and Tanaka, 1986].
Some of the floor materialsin VailesMarineris are younger
Thus the Late Hesperian Epoch marks the major period of than middleHesperianlayereddepositsand olderthan Middle
outflow-channelactivity on Mars.
to Upper Amazonianslide deposits.The floor materials
are
Remnantsof smoothplainsdepositsare superposed
on the moderatelycut by the faultsof smallgrabensand arerelatively
ridged plainsmaterial of Malea Planurnand appear to occur uneroded.Duringthe HesperianPeriod,majorfaulting,filling,
in low areas(tingedby wrinkleridges)or belowejectablankets and erosion occurredwithin the Noctis Labyrinthus-Valles
of large impactcraters.The depositspostdatethe ridgedplains Marinerissystem,indicatingthat geologicactivitywasgreatly
and may in part be Late Hesperianin age, as indicatedby reduced
duringtheLowerAmazonianEpoch.Localsidecanyons
the apparentdensityof superposed
craters.
in westernVailesMarineriswereformedby headward
sapping
of plateaumaterialsthat includethe UpperHesperian
Syria
Early Amazonian Epoch
PlanurnFormation.Many of thesesidecanyonsappeartobe
controlledby buffed faults. At Mangala Vailes,cratercounts
The Lower Amazonianreferentis moderatelycrateredsmooth and stratigraphicrelationsindicate that narrow channels
the floorsof earlier,broad outflowchannels
during
plains material in southernAcidalia Planitia (Figures1 and dissected
2). This unit also occursin patchesin Amazonis,Arcadia, and the EarlyAmazonian
[Masurskyet al., 1986].Alsoduring
the
southernElysiumPlanitiaeand extendsasfar north aslat 68øN, EarlyAmazonian,
largefloods(producing
Hrad,Tinjar,and
north
of Alba and Tantalus Fossae. A similar unit occurs in
Granicus
Vailes),
debris
orpyroelastic
flows[Christiansen
and
the lowlands north of Protonflus Mensac (R. Greeley and J. Greeley,
1981;Tanaka
andScott,1986],
andlavaflows
emanated
E. Guest, unpublisheddata, !986). Crater countsin southern from northwestern
ElysiumFossaeinto UtopiaPlanitia.
Acidalia Planitia yield about N(5) = 55 and N(2) = 300 to 450.
Eventhough
theearlier
cratering
ratewasnowgreatly
reduced,
For easternAcidalia Planitia, Witbeckand Underwood[1984] the peak-ringbasin Lyot north of DeuteronilusMensacwas
TANAKA:T•/r. STRATIGRAPHY
OF MARS
E155
formed
in therocksof theVastitas
Borealis
Formation.
Lyot's in centralVailesMarineris[Blasius
et aL, 1977].Minorfaulting
extensive
secondary
craters
occuronsurrounding
highland
and also occurredin southernElysiumPlanitia, forminglong,
fractures (Cerberus Rupes)
lowland
surfaces
andareburiedby EarlyAmazonian
smooth arcuate, west-northwest-trending
plains
material
anddebris
aprons
[Ferguson
andLucchitta,
1985;that appearto cut UpperAmazonianplainsmaterialin places.
R.Greeley
andJ. E. Guest,
unpublished
data,1986].ThereforeThe channelmaterialthatis thereferentfor thisseriesappears
Lyotimpact
basinis aboutEarlyAmazonian
in age--theto haveissuedfromthesefractures[ TanakaandScott,1986].
The layered depositsin the north polar region, forming
youngest
impact
basin
onMars.
PlanumBoreum,areuncratered
at availableimageresolutions
[Dial, 1984].On the southpolarlayereddeposits
makingup
20-kin-diameter
crater
The referentfor the Middle Amazonian Epoch consistsof PlanurnAustrale,one fresh-appearing
because
theyeitherunderli•
lavaflowsin AmazonisandsouthernArcadiaPlanitiae(Figures isfound;othercratersaresubdued
on layereddepositsthat
1 and3), whichwere recentlymappedas members3 and 4 the layereddepositsor are superposed
buffed. Interpretationsof the origin of the
oftheArcadiaFormation[Scottand Tanaka,1986].The flows were subsequently
generally
formsmooth
plainsandhavesubdued
scarps
that layereddepositsand of the arcuatetroughsthat transectthem
the ageof the deposits.
Although
appear
lightly
mantled
[ScottandTanaka,
1986].Similar
plains areimportantin determining
occurin southernElysiumPlanitia. Crater countsfor eastern the paucityof cratersindicatesthat the deposits'surfacesare
reworked
Amazonis
Planitia by Hiller et al. [1982] yielded N(2)= 70; lessthana fewmillionyearsold,thematerialispossibly
over a muchlonger
Tharsis
flows of this epochhave N(2) = 90 to 120 [Scott and periodicallyand may have accumulated
Tan&a,1981b; Plesciaand Saunders,1982].Duringthe Middle time [Carr, 1982].
Middle
Amazonian
Epoch
At both poles,thelayereddeposits
aresuperposed
by residual
ice caps.Extents,compositions,
and depositionalratesof the
perhaps
to thehighland-lowland
boundary
between
theTharsis ice capsprobablychangegraduallybecauseof oscillationsof
the polar heatbudgetanddust-stormactivity.Theseoscillations
andElysium
regions.
A sequence
of thick, mostly light-coloredmaterial was are governedby Mars' rotationalobliquity(50,000-yearperiod)
(2,000,000-year
period).Due to seasonal
deposited
along the highland-lowlandboundary scarp in and orbitaleccentricity
AmazonianEpoch, volcanism was largely restrictedto the
TharsisMontes, Olympus Mons, the northern plains, and
southernAmazonis Planitia between Ulysses Fossae and
Apollinaris
Pateraandin southernElysiumPlanitia.Scottand
Tanaka
[1982]subdivided
thesedepositsinto sevenunitshaving
cratercountsrangingfrom N(1) -- 65 to 730, which indicate
a Middleto Late Amazonianage span.They wereinterpreted
tobeeitherpalcopolar
deposits
[SchultzandLutz-Garihan,1981]
or interbedded
ignimbrite and lava-flow deposits[Scott and
Tanaka,1982].Scott and Tanaka [1986] remappedthem into
three members of the Medusae Fossae Formation
lower and middle
members
were
considered
of which the
to
have
been
eraplaced
duringthe Middle AmazonianEpoch.
Craterdensitiesindicatethat some of the large landslides
within
VailesMarineris[Lucchitta,1979]werecrop!aced
during
thisepochand in the Late AmazOnian.A few normal faults
oriented
parallelto the valleywallscut the landslides
[Blasius
etal.,1977]andare obviouslyrecent.
Debris
apronsin ProtonilusMensacanddebrisflowsin fretted
channels
havecraterdensities
withinthe rangeof N(1) = 200
to 500[Masurskyet al., 1977; Squyres,1978], which are
consistent
with the ageof this series.However,the available
craterstatistics
are highly uncertainand somewhatolder or
younger
agesare possible.Some of the debrisapronsmay still
beactive
[Squyres,
1978].
Late
Amazonian
Epoch
dust-stormactivity,perennialwater ice is presentlyretainedat
the north pole [Kieffer et al., 1976]. Water ice may also be
present at the south pole, but it cannot be detectedbecause
the CO2 seasonalcap doesnot completelydissipate.Also, dust
depositionis greaterin the north polar region[Pollacket al.,
1979]. A dust mantle as much as 200 m thick [Squyres,1979]
apparentlyexistson the north circumpolarplainsbut is absent
or very thin in the southpolar region.
Extensivedunessurroundthe north pole [Tsoar et al., 1979;
Dial, 1984]but aresparsein equatorialancl.southpolar regions,
where they generallyoccurwithin impact cratersand valleys
and along the basesof scarps.Although roost of the dunes
may be active, a large, relativelystable set of dunesadjacent
to north polar layereddepositsin OlympiaPlanitia(Figure 1)
mayb• at leaseseveral
millionyearsold [Breedet al., 1979],
andthusmayhaveenduredthroughtheperiodicclimaticchanges
of Mars causedby orbital and rotational dynamics.The sand
(or sand-sizeaggregates
[Greeleyet al., 1982]) probably was
derived from sources such as the Vastitas Borealis Formation
[Tsoar et al., 1979], the polar layereddeposits[Breed et al.,
1979],or fluvial depositsformedby channelingin the northern
lowlands[McCauleyet al., 1980].
Landslidematerialsalongthe basalscarpof OlympusMons
are superposed
on UpperAmazonianlava flows.Many of the
landslidesin Vailes Marinefts lack craters and therefore may
alsobe UpperAmazonian.Concentrically
ridgeddebrisblankets
Thereferent
is a flood-plain
depositin southern
Elysium on the western flanks of the Tharsis Montes are about the same
Planitia
thatapparently
originated
fromCerberus
Rupes;
it ageasthevolcanoes'
youngest
flows[Scottand Tanaka,1981b].
extends
intoa large,smooth-floored
outflowchannelin western The modeof originof the blanketsisunknown.Lucchitta[ 1981]
Amazonis
Planitia
[Tanaka
andScott,1986].
Theunitismarked proposedthat theymay be recessional
morainesof formerice
bywidely
scattered
craters
generally
<1kmindiameter.
caps.Also,localdebrisapronsandflowsin thefrettedchannels
Smalllava-flowunits on the flanks of the TharsisMontes
and mensac,in Vailes Marineris, and along other high-latitude
andOlympus
Monsandsmooth
plainsmaterial
in southernscarpsare sparselycrateredand wereprobablyactiveduring
Arcadia
Planitia
havecraterdensities
of N(1)<160(Tables
3 the Late Amazonian.
and
5).Other
uncratered,
possibly
volcanic,
deposits
occur
along
faults
and
overlie
landslides
inValles
Marinefts
[Lucchitta,
1985].
Minor
structures
associated
withTharsis
volcanoes
thatformed
during
this
epoch
include
caldera
andcircumferential
flankfaults
SUMMARY AND CONCLUSIONS
A detailed analysisof the global stratigraphyof Mars,
ontheTharsis
Montes
andOlympus
Monsandrecent
faults supportedby new and revisedgeologicmapsbasedon the
E156
TANAKA: THE STRATIGRAPHYOF MARS
recentlycompletedViking l:2,000,000~scale
photomosaic
series constructs
occurred
mostlyin areaswherethelithosphere
was
of the planet,hasbeenpresented.Publishedcratercountsand thin[Comer
etal.,1985].
Gravimetry
ofMars[Sjogren,
1979]
stratigraphicanalyseswere usedin part, but new work was indicates
thatgravityanomalies
occuroveryounger
mass
features
centeredon geologicunitsandfeatureswhoserelativeageswere suchas TharsisMontes,OlympusMons, Alba Patera,
and
not well known. The geologic history of Mars has been
summarizedon geologicmapsshowingeighttime-stratigraphic
ElysiumMons.Suchfeatures
werepossibly
supported
byan
increased
flexuralrigidity(or thickness)
of the lithosphere
divisions that include all surface materials.
[Comeret al., 1985].
The three major time-stratigraphicperiods of Marsrathe
TheMartian
climatic
andvolatile
histories
areoiher
important
Noachian, Hesperian,and AmazonianSystems--developed
by factorsin the planet's
geologic
evolution.Fluvialactivity
was
Scott and Carr [1978] from Mariner 9 mapping have been widespread
during
Noachian
time,perhaps
aidedbya thicker,
subdividedinto eight epochs,basedon the eightcorresponding warmeratmosphere
anda warmersurfacethat allowedsurficial
time-stratigraphicseriesof deposits.Their inferredeventsare runningwaterand perhaps
evenrain. In Hesperian
time,
summarized
as follows:
however,
runoffchannels
ceased
to form.Instead,
voluminous,
(1) Early NoachianEpoch--Major impact-basinformation water-rich
aquifersin the highlandregolithweretapped,
(Isidis, Hellas, Argyre, and south polar); formation of the producingthe huge outflow channelsthat drainedintothe
northern lowlands.
northern lowlands. Also during the Hesperian, and in the
(2) Middle Noachian Epoch--Cratered terrain formation; Amazonian, ground ice was apparently responsiblefor
lognormalcrateringdistribution;faultingin southTharsis.
producing landslides, debris flows, channels, and other
(3) Late Noachian Epoch--Intercrater plains resurfacing; landforms.At present,subfreezing
temperatures
envelop
the
reduced cratering flux, transition to power-law cratering entiresurface
of the planet,andresurfacing
is dominated
by
distribution; intense erosion and runoff-channeldevelopment; eolian processes.
Theseprocesses
are observedprincipally
in
beginning of intense faulting centered at Syria Planum; the polar regions,where dust-stormand seasonalfrost activities
are strongest.
formation of highlandvolcanoesand ridges.
(4) Early HesperianEpoch--Ridged plains emplacement, The absoluteagesof the Martian epochboundariesaremodel
particularlyat Lunae,SyrtisMajor, Hesperia,andMalea Plana, dependentand are largelyuncertain.Accordingto two models
and in northern lowlands;burial and degradationof lowland discussedin this paper, most geologic activity (withinthe
cratered terrain; extensivefaulting centeredat Syria Planurn; Noachianand HesperianPeriods)occurredeither duringthe
major rifting at Noctis Labyrinthus-VallesMarineris; Alba first one billion years of surfacehistory [Neukum and IVac,
PateraandTempeTerravolcanism;frettedchanneldevelopment; 1976; Neukum and Hiller, 1981] or during the first two billion
formation of Lowell impactbasin.
years[Hartmann et al., 1981, Figure 8.6.3; this paper].Other
(5) Late HesperianEpoch--Resuffacing
of northernplains absolute-agemodels[e.g., Soderblomet al., 1974] generally
(by complex of lava flows, eolian deposits,and alluvial suggestcrater-flux historiesintermediatebetweenthe Neukum
sediments),then erosionof theseplains;major volcanismat and Wise and the Hartmann et al. models. A similar evolution
Tharsis Montes, Alba Patera, Terra Tempe, Syria Planurn, of crater size-frequency distributions demonstratesthe
from
Elysium Planitia, Ceraunius Fossae, and Dorsa Argentea; plausibilitythat impactson the moon and Mars originated
outflow-channel
development
by water flooding;depositionof the samepopulation of planetesimals.As in the caseof the
Vailes Marineris layereddeposits;waning Tharsistectonism; moon, however,we will firmly resolvethe absolutechronology
for the Martian surfaceonly after future missionsreturnrock
depositionof southpolarunconsolidated
material.
analysis.
(6) Early AmazonianEpochmLavaflows form northern samplesfrom selectedareasfor radioisotopic-age
smooth plains;local volcanicflows at TharsisMontes, Alba
Acknowledgments. I thankD. H. Scott,R. Greeley,andJ. E.Guest
Patera, and Elysium Mons; formation of Olympus Mons for permission
to useunpublished
stratigraphic
data andgeologic
maps
aureoles;formationof Lyot impactbasin.
on which parts of this paper, particularlythe stratigraphicmaps,
are
(7) MiddleAmazonian
Epoch--Continued
accumulation
of based.M. H. Can:, L. A. Rossbather,D. H. Scott, D. E. Wilhelms,
lavaflowsin northernplains,particularlyin AmazonisPlanitia; and J. R. Zimbelman reviewedthe manuscriptand providedmany
M. F. Tuesinkperformedsomeof the cratercounts
volcanismat TharsisMontesand OlympusMons;emplacement helpfulsuggestions.
presented,and N. K. Robertsonand A. Wassermandigitized
the
of thick, poorly consolidatedmaterial of MedusaeFossae stratigraphic
maps.Theresearch
in thispaperwassupported
byNASA
Formation;development
of debrisflowsandapronssurrounding
Deuteronilus and Protonilus Mensac; landslides in Valles
Marineris.
Work Order W-15,814.
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(ReceivedApril 30, 1986;
revisedAugust 22, 1986;
acceptedAugust22, 1986.)