sign in sign up
<<
Home , Eridania quadrangle, Orcus Patera, Terra Cimmeria

© Journal of Maps, 2013 S 171° E 172° E 173° E 174° E 175° E 176° E 177° E 178° E 179° E

° 1

3 ' cr A cr cr cr AHf He Geology of the Ariadnes Basin, AHr AHf AHr Ae NE , - 1:1Million

AHr 1,2 2 3 3,4 1 Npl A. Molina , M. A. de Pablo , E. Hauber , L. Le Deit and D. C. Fernández-Remolar

Ae Ae 1 Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Spain ([email protected]) S S 2 ° cr ° Geology Department (University of Alcalá), Alcalá de Henares, Spain 2 2

3 AHf 3 3 cr cr AHf Institute of Planetary Research (DLR), Berlin-Adlershof, Germany AHf 4 He cr Laboratoire de Planétologie et Géodynamique (Université de Nantes), Nantes, France cr Npl cr cr HNk cr AHr

AHr AHr 2 cr AHf AHf AHr MAP LEGEND DESCRIPTION OF THE MAP

The legend for this geological map is separated into geological units and Here we present our geological map of the Ariadnes basin on Mars, one of

S AHf S

° He ° geological/geomorphological elements. Under this lines, geologic characteristics several topographic depressions in the southern highlands, located between 3 3 and locations are briefly described for the eight units. Type locations are shown as in the east and in the west (Figure 1). These 3 AHf 3 symbols (white polygons in map), within a 1:500,000 scale CTX image. topographical features, which can be grouped into the Eridania system (or Below, a legend shows the symbolization of the geomorphic features, which are basin), have been hypothesized to host a lake (termed Eridania) on ancient B cr classified into tectonic, impact-related and erosional features, following USGS Mars (Figure 2). The area exhibits a well-preserved record of the boundary He 2 guidelines. Blue polygons show the crater counting areas used in Figure 3 and two between the and epochs (3.7 Gyr, Figure 3), providing an cr bright grey lines represent Figure 4 profiles location. excellent study area to investigate this important transitional period from a wetter to a drier surface environment. DESCRIPTION OF MAP UNITS AHf AHf This geologic mapping, based on texture and relief, was performed using high- Npl, NOACHIAN CRATERED PLAINS: resolution images (HRSC, CTX and THEMIS) and topographic data (MOLA and AHf Npl HRSC). Background image is a mosaic composed by HRSC images. The map cr AHf Highly cratered materials with relict relief, considered being the differentiates eight units, which type location (white polygons) and brief geologic HNk HNk Npl cr basement and oldest surface in our mapping area. It can be found description are provided in legend. Diverse tectonic and geomorphic elements

S AHf S were also mapped, which have been identified from the analysis of remote numerous channels carving its surface, especially dense gullies ° ° sensing data and contrasted with previous studies. Surface dating through 4 AHf 4 systems related with crater rims. 3 3 crater counting techniques yielded absolute model ages (Figure 3) and was AHf used to establish a regional stratigraphy (Figure 4) and a geological history. Ae HNk, HESPERIAN NOACHIAN KNOB FIELDS: GEOLOGICAL HISTORY cr Ae Npl Light-toned knobs, separated by dark material filling the space between them. They show remnants of a mesa-like surface and are To understand the geological evolution of the area, we performed crater counts Npl located at the bottom of the two main depressions and some isolated (Figure 3, left) of the most relevant surfaces, representing the different mapped AHf minor fields. Their flanks are carved by channels and gullies. geological units. The results together with the geologic interpretation of the He different units enable us constructing a hypothesized local stratigraphic sequence (Figure 3, right) and cross sections (Figure 4). From them we can cr He, HESPERIAN ELECTRIS DEPOSITS: infer the geological history of the area.

S S The Noachian Cratered Plains (Npl) unit is constitutes the basement and oldest

HNk Unconformable and mantle deposits that form mesas locally. Their ° cr ° surface in our mapping area, underlying all the other units. Middle and Late

5 5 morphology is consistent with eolian airfall deposits. Branched and 3 3 sinuous channels are a common feature on this unit and winkle ridges Noachian aqueous activity filled the Eridania Lake, contained in an appears at the eastern. interconnected system of depressions formed by an unknown process (probably AHf impact, or -tectonic processes). During the existence of the Eridania Ap AHf Lake, as one or several individual water bodies, clay (phyllosilicate) deposition AHr occurred on its/their floor(s) forming the Hesperian Noachian-aged Knob Fields AHr, HESPERIAN RIDGED PLAINS: (HNk) unit. These surfaces were modified by an undefined process (most likely some kind of fluvial erosion, combined with tectonic processes). Later, the Flat and smooth plains with superimposed sinuous ridges filling the AHf Hesperian Electris Deposits (He) were deposited. They are interpreted to be an cr deepest topographic depressions, interpreted as lava flows. Locally eolian airfall deposit, produced by volcanism, probably related to the same AHr He covered by eolian deposits. Fluvial activity is not relevant, though AHf pulse of magmatic activity that was responsible for the formation of the some clear examples of inverted channels can be observed. Amazonian Hesperian Ridged Plains (AHr). These lava flows cover the floors of cr most topographic depressions in the region, and are characterized by winkle AHf ridges. This volcanic activity could have been related to the increase of water S S

Ae, AMAZONIAN EVAPORITE DEPOSITS: activity in this period, which may have generated the Amazonian Evaporite ° Ap ° 6 6 Deposits (Ae). The location of this unit close to the Eridania Lake shoreline, 3 cr 3 This unit displays low IR reflectance and high albedo, and its texture from 800 to 1,000 meters above Mars datum, suggest a new period of activity at and location in some depressions at the outlet of channels is this paleolake during Hesperian to Amazonian transition. Finally, during the consistent with an evaporitic origin. They are located between 800 and Early Amazonian, a renewed period of aqueous activity occurs on Mars, cr 1,000 m of altitude, close to the proposed Eridania Lake shoreline. matching widespread resurfacing events in most of the area, and the formation of the Amazonian Ariadnes Plains (Ap) may correspond to lava flows or a AHr cr secondary alteration of the AHr unit material. He Ap, AMAZONIAN ARIADNES PLAINS: He 1 FIG. 3: CRATER COUNTING RESULTS AHr Thin material located at the SE of the Ariadnes basin, with high IR AND STRATIGRAPHIC SEQUENCE cr reflectance and low albedo. It displays flow marks, winkle ridges, and tracks. It may correspond to recent lava flows or a Crater counting was performed in the most relevant areas of the mapped secondary alteration of the AHr unit material. AHf AHf geological units. Craters larger than 5 kilometers were counted on HRSC S S

imagery for the full area, and up to 15 meters on CTX imagery for selected ° cr ° 7 7 areas. These areas were selected by their uniformity and the absence of 3 3 AHf, AMAZONIAN HESPERIAN FLAT-FLOOR CRATER INFILLING: deformation by ulterior structures, hence being representative of the units AHr HNk (named as AHr 1, AHr 2), He (named as He 1, He 2, He 3) and Ap. Their Heterogeneous deposits interpreted as a mixture of material (volcanic, location is shown in the main map as blue polygons. The full study area was cr eolian, lacustrine and colluvial deposits), filling medium-sized and used for the regional ages. AHr 2 B large impact craters. Their limited extension makes it difficult to A ' establish stratigraphic relations to other materials. We used statistical analyses of crater size-frequency distributions (left side of the plot) to provide an absolute model age range for each unit. We also take into account craters in underlying layers that are mostly, but not completely, He He cr, IMPACT CRATERS AND EJECTA: buried by the uppermost unit, so a formation age for the underlying unit is also Npl determined. Combining contact relationships between the units, their geologic He This unit includes impact crater-related materials. as ejecta and crater interpretation, and the crater counting ages, we have determined a stratigraphic He He 3 He cr rims. Several lobate and rampart ejecta blankets have been founded sequence for the area (right side of the plot), which is also illustrated as cross- cr He AHf cr in the area, as well as some possible pedestal craters. sections in Figure 4. Blue ellipses at the right show the timing of and outflow channel activity on Mars. 170° E 171° E 172° E 173° E 174° E 175° E 176° E 177° E 178° E 179° E

0 25 50 100 150 200 FIG. 1: LOCATION MAP: MARS GLOBE TOPOGRAPHY FIG. 2: LOCATION MAP: REGIONAL TOPOGRAPHY EXPLANATION OF MAP SYMBOLS km O Mars topographic globe, based on MOLA topography. Blue square shows MOLA colorized relief map of the Eridania system region. White line shows Scale 1:1,000,000 (at publication scale) extension of the location map (Figure 2) and red square extension of the the proposed Eridania Lake shoreline (900 meters above Mars' datum geologic map. The main topographic features on this hemisphere of the contour), the height that a hypothesized water table could have reached. Geographic Coordinate System: Mars 2000 spheroid (Semi-major axis: 3,396,190.0 m; Semi-minor axis: 3,376,200.0 m; Inverse flattening: 0.0058860) planet are labeled. Red square shows the extension of the main geological map.

180º Projection System: Equidistant Cylindrical (Central meridian: 180º) 150º E 150º W 170° E 180° 170° W

30º N 30º N FIG. 4: GEOLOGICAL CROSS SECTIONS

Two tentative geological cross-sections (A − A' and B − B') showing relations between different units obtained by contact relationships between the units and the ages 0º obtained by crater counting (Figure 3). The vertical exaggeration is 20. Profile locations are shown on main geological map as bright grey straight lines. 0º S

m 30º S

u 1.5 - °

t A

a cr Ae 0

d cr

' 3

s A'

r 1.0 - 30º S a

M Crater Arisia Mons Ap He AHr

e Npl v 0.5 - He o

b 150º W

a Ma'adim Vallis Crater

AHr AHr 150º E 180º m

k 0.0 - HNk

- 0.5 - - 0 - - - - 5- 0 Horizontal scale (km)

m Fig. 2 legend u 1.5 - S

t B

a AHf O ° d

' 0 s

r 1.0 - Scale 1:15,000,000 4 a Npl AHr

M cr km

e

v 0.5 - 0 200 400 800 o AHr b Ap a He

m B' Elevation, above Mars' datum k 0.0 - AHr HNk HNk km -

- 3 2 0 - 0.5 - - - - - 4 1 -1 0 50 Horizontal scale (km)