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Home , Arica (crater), Thaumasia Plateau

GEOLOGIC INVESTIGATION SERIES I–2650 U.S. DEPARTMENT OF THE INTERIOR Prepared for the ATLAS OF : THAUMASIA REGION U.S. GEOLOGICAL SURVEY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION SHEET 3 OF 3 85° 90° 80° 9 0.6 8.15 0.54 95° 75° 8 0.5

) 7 2

tb ) 70 2 100° ° KM 6 0.4 2 KM 2 5 ch 0.3 4 ° 65° 105 3 2.98 0.2

r DENSITY FAULT

(NUMBER/10 0.14 Nfd (KILOMETER/10 2 1.77 FAULT-LENGTH DENSITY FAULT-LENGTH 0.1 0.08 Hpld 1 0.61 0.02 0.16 7 x 10–3 ° 60 0 0 110 Sinai Planum Thaumasia ° ch 1234 5 1234 5 ABSTAGE STAGE Planum Figure 15. Histograms representing areal density of fault length (A) and number of faults (B) per stage in Thaumasia region of Mars.

° 55 115 ° ° –15 –15 °

NO. CRATERS LARGER STAGES FOSSAE OTHER STRUCTURES SYSTEM THAN 2, 5, AND 16 KM N 0 25 KILOMETERS HISTORY DIAMETER N 0 100 KILOMETERS PER 1,000,000 KM2 2516

Figure 19. Furrow (arrow heads) which occurs along a preexisting Figure 10. Stage 3 tributary channels of southeast flank of Coprates 40 or less rise dissect wrinkle ridges (r) of younger ridged plains material and join graben downslope of large (broad arrow) that into first-order channels (ch) at a break in slope. Triangular faceted may have formed as a result of the impact event. (Viking image Solis 50 bedforms (tb; interpreted as cuestas) indicate differential erosion of 606A50); resolution 249 m/pixel) tilted rock layers. Symbols Nfd and Hpld denote fractured and dissected 60 Planum material and younger dissected material, respectively. (Viking image ° –20 70 –20 ° 465A13; resolution 63 m/pixel.) Daedalia 80 90 100

Table 2. Principal geologic features and their relative ages for major physiographic provinces 5 Planum of the Thaumasia region of Mars. 150 Province Geologic features and their relative ages A. Rifting and collapse structures. Late –Hesperian 200 B. Coprates East Wrinkle ridges. Early Hesperian Nb Nf C. Coprates Broad ridges, tilted rock layers (cuestas and hogbacks caused by tectonic tiliting and

g2 differential erosion), and wrinkle ridges; small (≤10 km wide) and large grabens and faults and fault and rift systems; depressions; individual valleys and troughs 300 50 and valley and trough networks; mountains and volcanoes. Noachian–Early HNpld Marineris/ Valles ° –25 Hesperian –25 ° HNf Syria Planum Hpld Claritas Fossae D. Thaumasia Planum Wrinkle ridges; small grabens. Late Noachian–Early Hesperian 400 E. Sinai Wrinkle ridges; small grabens only cut older material outcrops. Mostly Early Nf 75 g2 4 Hesperian

Hpld Valles Warrego 500 ch Thaumasia Fossae F. Syria-Solis Lava flows; small grabens. Mostly Late Hesperian ch 600 100 G. Thaumasia highland Small and large grabens, large faults, and intersecting dense concentrations of Wrinkle ridges Wrinkle Coracis, Melas, and Nectaris Fossae Nf Thaumasia highland rifts grabens; fault and rift systems; broad ridges and tilted rock layers (cuestas and 700 hogbacks) along edge of Thaumasia plateau; mountains, volcanoes, and Hpld

Broad ridges and large scarps featureless plains; individual valleys and troughs and valley networks.

3 HESPERIAN 800 HNf Noachian–Early Hesperian Coprates rise 900 150 Nf H. Daedalia Lava flows; plateaus and mountains (volcanoes or massifs); small grabens. Mostly g3 1000 d Early Hesperian–Amazonian Argyre structures I. Daedalia southeast Featureless plains; small grabens; subdued wrinkle ridges. Mostly Early Hesperian n 1200 200 25 J. Sirenum Small grabens; large scarps; individual valleys and valley networks; volcanoes. a HNf 2 Noachian–Early Hesperian l HNr ° –30 K. Argyre Featureless plains within topographic lows; mountains and plateaus; large scarps and –30 ° tb T faults and small grabens; drainage basins comprising valley networks; large h Hpl 300 75 3 valley forms, irregular depressions, furrows, and highly subdued ridges of all h g HNr ?? shapes and sizes. Noachian–Hesperian a i 400 100 u N 0 50 KILOMETERS H 1 m 500

a NOACHIAN a Figure 11. Stage 3 tributary channels (ch) of along 600 150 s i i edge of Thaumasia plateau, which dissect stage 2 graben (g2), ? a s join into first-order channels at a break in slope where they dissect 200 Hesperian plains materials. Narrow stage 3 graben (g3) cuts Noachian H a and Hesperian materials; tilted beds (tb) similar to those of figure 10 Table 3. Map unit information for Thaumasia region. Table 4. Total area of geologic units i are visible. Symbols Nb, Nf, HNpld, HNf, HNr, Hpl , and Hpld denote 250 per period for Thaumasia region. g m 3 Unit Number Area h u basement complex, older fractured material, intermediate dissected ? ? ? ?? ? name of outcrops (km2) Stage Period Total area (km2) ° –35 material, intermediate fractured material, older ridged plains material, –35 l ° a a smooth unit of the plateau sequence, and younger dissected material. Figure 16. Chart comparing stages of geologic activity in Thaumasia region with significant sets of fea- Nb 50 163,520.66 1 Noachian* 3,397,630.40 n d h (Viking image 606A54; resolution 247 m/pixel.) tures (tectonic and erosional). Size of solid areas roughly proportional to degree of exposed deformation; Nplh 26 53,490.47 1 Hesperian 2,681,394.67 T question marks indicate where large uncertainty exists in commencement of structural activity. Crater Nah 3 44,673.36 1 Amazonian 36,872.94 chronology from Tanaka (1986). Nak 6 5,428.28 1 *Includes Noachian-Hesperian units. Includes Hesperian-Amazonian units. c1 106 144,935.14 1 Nfc 11 41,666.11 1 dome 9 2,277.65 1

Npl1 20 356,138.03 1 Nf 23 608,851.60 1 a Nple 2 21,553.51 1 Nfd HNfc Npld 32 119,135.38 1 b lf Nfd 17 208,912.34 1

c Npl2 25 206,419.71 1 – Nfd 40° 40 – ° HNf HNade 6 254,601.78 2 Nfd f HNr HNu 7 11,913.14 2 Nf Nfd c2 13 202,011.21 2 g1 HNpld 4 41,925.51 2 Hr HNf 41 281,392.23 2 HNf c HNt 13 95,991.25 2 HNf 1 Nfd g2 hb HNr 4 437,188.19 2 HNfc 3 18,890.31 2 Hpl3 Ht HNafs 4 9,826.13 2 Ht 1 g3 1 HNcht 5 2,691.62 2 HNplt 2 64,196.69 2

Hpl3 73 492,460.03 3 Hpld 4 75,091.87 3 Nfd ° –45 –45 ° Hch 3 626.49 3 Contact—Dashed where approximately located or gradational Hr 3 623,334.36 3 Hpld Depression or caldera Ht1 1 183,840.68 3 hb 85° 0 50 KILOMETERS Ht2 2 92,782.97 3 90° 80° N c Channel—colored according to stage Hf 5 122,488.61 3 95° 75° ch Hr Hsl1 5 279,312.62 4 100° 70° Al Furrow—colored according to stage Figure 12. Fresh-appearing, V-shaped channel (a–c) in fractured and Hsl2 3 435,357.16 4 Channel in lava flow dissected material (Nfd), which heads near a fault (outside of image Hsu 1 210,500.46 4 ° 65° 105 area, northeast of a), breeches a small impact crater (b and c) and AHt3 1 165,599.36 5 SCALE 1 : 4 440 910 (1 mm = 4.44091 km) AT –35° LATITUDE continues onto intermediate fractured material (HNf). Volcano (HNfc) cs 26 27,644.22 5 CONFORMAL CONIC PROJECTION and its lava flows (lf) are mapped as younger flow and construct ABN 0 50 KILOMETERS N 0 50 KILOMETERS ° 60 Avfr 1 1,613.78 5 110 –15° ° material (unit HNfc). Small furrows (f) downslope from volcano may At 1 4,132.81 5 –20° represent a correlation between channeling and volcanic activity. Stage 5 –25° Avfs 6 3,030.68 5 –30° INTERIOR—GEOLOGICAL SURVEY, RESTON, VA—2001 1 grabens (g1) are buried by intermediate fractured material (HNf); ° –50 Figure 17. A, Cuestas (c) and hogbacks (hb), which are caused by tectonic tilting and differential erosion, Al 1 451.43 5 –50 ° –35° 55 ° Stage 2 grabens (g ) are buried by member 1 of the Montes 115 ° 2 and channels (ch) of the southeast part of Coprates Rise. Symbols c , Nf, Nfd, Hpl , Hr, and Hpld denote –40° 1 3 Formation (Ht1); Stage 3 grabens (g3) cut member 1 of the Tharsis material of degraded craters, older fractured material, fractured and dissected material, smooth unit, –45° Montes Formation. Mottled appearance of image may be due to clouds. –50° younger ridged plains material, and younger dissected material. (Viking image 610A44; resolution 224 100 0KILOMETERS 100 200 300 400 500 600 700 800 900 1000 (Viking image 57A05; resolution 232 m/pixel) m/pixel) B, Wind River Mountains of Wyoming that display similar morphologic features to Coprates rise. (Landsat TM image; plate 97 of Short and others, 1976).

85° 130° 120° 110° 100° 90° 80° 70° 60° 50° 40° 10° SINAI PLANUM HNf Hpl c g Nb 3 ES Table 5. Area, fault, and channel and furrow data per stage Ht HNfc c1 HNf NT 2 Nf ° 55 Nfd for Thaumasia region. O 115 THAUMASIA A ° M ° [Minimum lengths of faults (sheet 2) and channels and furrows (sheet 3) –15 F HNf 0° mapped are 1.98 km and 0.96 km, respectively] 3 c HNf Claritas SOLIS E g m 1 PLANUM 0.16 H HNpld Hr HNr 1.6 0.16 Total Number Total length Number of Total length of ARSIS B ch sae Nb Nf D f e 1.45 Stage area of of faults channels channels and TH PLANUM 0.14 Fos 1.4 1.34 0.14 (km2) faults (km) and furrows furrows (km) VAL DAEDALIA Nfd t ris –10° LES Fossae alas Fossae ) Nb 2

PLANUM M 1.2 ) 0.12 Nb s

2 1 1,977,002.29 10,620 161,045.24 3,105 26,509.48 SYRIA Necta KM 2 PLANUM IS C 1 KM 0.1 2 1,420,628.11 2,043 42,320.50 1,928 20,584.65 Figure 7 (right). Large mountain (in- HNpld y 2 u 2 3 1,590,625.04 1,196 28,153.65 469 4,697.72 THAUMASIA LAND terpreted as volcano; broad arrow) with Nb Nb HIGH 0.8 0.08 SINAI PLANUM PLANUM S 4 925,170.26 174 5,670.13 0 0.00 platea summit depression (interpreted as cal- HNf THAUMASIA Coracis –20° G Fossae Thaumasia c 0.6 0.06 5 202,472.30 14 316.80 1 9.43 Claritas dera; ) and dissected flanks (channels; HNpld f HIGHLAND A Hr Fossae 8 f

ch) occurs along southwest edge of (NUMBER/10 SOLIS THAUMASIA HNpld r e

Edge u (KILOMETER/10 0.4 0.04 Fossae g 0.03 PLANUM Thaumasia plateau near highly faulted Nb f i 0.29 J t f Nfd o Nectaris terrain (narrow grabens; g). Volcano a 0.2 CHANNEL/FURROW DENSITY 0.02 –30° r e Claritas Melas of f A Fos formed during the period of younger r –3 –4 K Hpld CHANNEL/FURROW LENGTH DENSITY 4 x 10 5 x 10 nd Hpl3 0 0 sae Nfd I construct-forming activity. Symbols i HNr 1235 1235 Fos Coracis sia Highla Ht1 HNf Nb HNf Thaumasia Nfd, HNf, HNfc, Ht1, and Ht2 denote ch Lowell R ABSTAGE STAGE Fossae Thauma fractured and dissected material, inter- Fossae HNpld Thaumasia Nb Highland J c Figure 18. Histograms showing total channel and furrow length density per stage (A) and number of –40° mediate fractured material, younger Nb HNf channels and furrows per stage (B) of Thaumasia region. 0 200 KILOMETERS flow and construct material, and mem- HNf

asia ° bers 1 and 2 of the For- HNr HNf sae –50 mation, respectively. (Viking image HNf 1 sae Nf Thaum Figure 3. Photomosaic of Thaumasia region showing major physiographic provinces and edge of –50° Fos ARGYRE 567A76; resolution 198 m/pixel.) PLANITIA Thaumasia plateau. Letters correspond to usage in table 2. Warrego Lowell N 0 50 KILOMETERS N 0 50 KILOMETERS Valles Hpld

Nb –60° Figure 8A. Warrego Valles, a well-defined, stage 2 and 3 channel sys- Figure 1. Index map showing Thaumasia region of Mars. Region is dominated by Thaumasia plateau tem of intermediate dissected material (unit HNpld), occurs along south N 0 50 KILOMETERS Table 1. Cumulative crater densities and ages of geologic units in Thaumasia region of Mars. (edge of plateau shown by dashed line), which includes high plains of Syria, Sinai, Solis, and Thaumasia edge of Thaumasia plateau; lower part (1) of channel (ch) trans- [Crater statistics were completed for 96.6% of the total map region] ects stage 2, older ridged plains material (unit HNr). Tributary (2) of Plana and surrounding Thaumasia highland that is fractured by Thaumasia, Claritas, Coracis, and Nectaris HNr 1 2 HNade main drainage system follows and cuts across a stage 2 graben; tribu- Average crater density [Crater age ] Fossae. 103 HNpld Nb Figure 13. Part of western Thaumasia Planum province showing 2 3 2 Nfd tary head (3) and stage 2 graben (g) of a rift system also cut stage 2 c2 Geologic unit name Symbol *Area (km ) Type N(2) N(5) N(16) Unit age Nfd younger ridged plains material (unit Hr) burying older ridged plains intermediate fractured material (HNf). Symbols Nb, Nfd, and Hpl3 Nb HNf ch Hpl3 Member 3 of Tharsis Montes Formation AHt 166,759 t 408±50 [LH-EA] 84±22 [LH-EA] LH-EA denote basement complex, fractured and dissected material, and smooth material (unit HNr; contact between the two ridged plains materials is 3 Hpl s 366±47 [LH-EA] 42±16 [EA] g 3 shown by broad arrows), faults (f), and western part of a crater's ejecta unit of the plateau sequence, respectively. Fluvial processes highly 0 100 200 KILOMETERS blanket (c). These relations indicate that extensional tectonism of the Upper member of Syria Planum Formation Hsu 210,309 t 585±53 [LH] 95±21 [LH] 5±5 [EH] LH 115° 110° 105° 100° 95° HNfc Hpl3 modified stage 1 materials, including northeast-trending faults (f). (Vik- –15° Thaumasia province largely ceased during the Early Hesperian, but s 580±53 [LH] 90±21 [LH] 5±5 [EH] Nf ing image 532A16; resolution 170 m/pixel.) Hpl3 Key compressional tectonism may have continued. (Viking image 608A49; Younger flows of lower member of Syria Planum Formation Hsl2 436,307 s 504±34 [LH] 53±11 [EA] 7±4 [EH] LH Hpl3 Contact, dashed where approximate Stage 2 channel Older flows of lower member of Syria Planum Formation Hsl 281,560 t 583 46 [LH] 114 20 [EH-LH] 11 6 [EH] LH v HNfc resolution 219 m/pixel) 1 ± ± ± 102 Scarp —Line marks top of slope; barb Depression or caldera Stage 3 channel s 579±45 [LH] 110±20 [EH-LH] 11±6 [EH] points downslope Hpl3 Stage 1 furrow Younger fractured material of PHPA4 Hf 115,972 t 543±68 [LH] 95±29 [LH-EA] 9±9 [EH] LH Mare-type (wrinkle) ridge Stage 1 fault, dotted where buried Nf Stage 2 furrow s 543±68 [LH] 95±29 [LH-EA] 9±9 [EH] HNt HNade Broad ridge (>3 km wide) Stage 2 fault, dotted where buried g Narrow, linear ridge (<2 km wide) Stage 3 fault, dotted where buried Member 2 of Tharsis Montes Formation Ht2 92,680 t 701±87 [EH-LH] 194±46 [LN-EH] 43±22 [LN-EH] EH lv s 669±85 [EH-LH] 162±42 [LN-LH] 43±22 [LN-EH] Nf Figure 8B. Geologic map of Warrego Valles region showing erosional and tectonic structures. Stages 2 Member 1 of Tharsis Montes Formation Ht1 194,508 t 694±60 [EH-LH] 113±24 [EH-LH] 15±9 [EH] EH –20° and 3 channel system, Warrego Valles, dissects Noachian/Early Hesperian rock materials and modifies and s 663±58 [LH] 82±21 [LH-EA] 10±7 [EH] Nf Nb destroys older fault systems mainly of stage 1. See sheet 1 for descriptions of map units. Younger dissected material of PHPA4 Hpld 74,247 s 1037±118 [EH] 148±45 [EH-LH] EH AHt3 101 4 HNf Younger ridged plains material of PHPA Hr 632,513 t 694±33 [LH] 161±16 [EH] 25±16 [LN-EH] EH HNpld s 672±33 [LH] 139±15 [EH-LH] 19±6 [LN-EH] Hpld HNf Smooth unit of plateau sequence of PHPA4 Hpl 500,602 t 1125±47 [EH] 210±21 [LN-EH] 22±7 [LN-EH] EH ch 3 Ht s 1075±46 [EH] 160±18 [EH] 12±5 [EH] HNr 2 AHt3 Troughed material of PHPA4 HNplt 64,627 s 851±115 [EH-LH] 139±46 [EH-LH] 16±16 [LN-EH] LN-EH N 0 50 KILOMETERS G HNf HNr Nplh Smooth floor unit of circum-Argyre materials HNafs 9,805 t 1122±338 [N-EH] 306±177 [MN-EH] LN-EH

F IN NUMBER PER MILLION SQUARE KILOMETERS DENSITY, CRATER HNr s 1020±323 [N-LH] 204±144 [LN-EA] HNade G –25° 4 D D Nplh Intermediate dissected material of PHPA HNpld 45,912 t 1481±180 [N] 305±82 [LN] 22±22 [LN-EH] LN-EH V Figure 4. Stage 2 faults and grabens (g) of a rift system cut a possible 100 s 1285±167 [N-EH] 109±49 [EH-EA] M 0 1 2 N 0 50 KILOMETERS 10 10 10 4 volcano (v) that formed during the period of younger (Late A B c Nfc Older ridged plains material of PHPA HNr 496,792 t 968±44 [EH] 213±21 [LN-EH] 28±8 [LN-EH] LN-EH S CRATER DIAMETER, IN KILOMETERS c1 1 Noachian/Early Hesperian) construct-forming activity. Crosscutting c1 Terraced material of PHPA4 HNt 87,864 t 1081±111 [EH] 285±57 [LN] 34±20 [LN-EH] LN-EH D relations of stage 2 channels (ch) with the rift system, volcano, and HNplt G T s 1059±110 [EH] 262±55 [LN] 34±20 [LN-EH] V Npld surrounding geologic units suggest that channels formed concurrently Figure 5. A, Hesperian–Noachian surface modified by a well-defined channel system of stage 2 (or younger), Intermediate fractured material of PHPA4 HNf 270,407 t 1010±61 [EH] 266±31 [LN] 48±13 [LN] LN-EH R with volcanotectonic activity. Symbols Nb, Nf, Nfd, HNf, HNt, HNfc, s 958±60 [EH] 215±28 [LN-EH] 33±11 [LN-EH] dissected and etched unit of the circum-Argyre materials (unit HNade). Superposed craters (solid arrows) and T HNpld, Hpl denote basement complex, older fractured material, T S 3 highly eroded craters (open arrows) mark dissected and etched surface. (Viking image 535A25; resolution 154 Dissected and etched unit of circum-Argyre materials HNade 254,890 t 1146±67 [N-EH] 369±38 [MN-LN] 63±16 [LN] LN-EH T fractured and dissected material, intermediate fractured material, B Nb HNplt s 891±59 [EH] 118±22 [EH-LH] 12±7 [EH] –30° m/pixel) , Graph showing crater densities of total (partly buried, degraded, and superposed craters; black boxes) S Nf terraced material, younger flow and construct material, intermediate and superposed only (red circles) crater populations for all outcrops of dissected and etched unit. Note distinct Younger flow and construct material of WVA5 HNfc 18,919 t 1480±280 [N-EH] 317±130 [MN-EH] 53±53 [MN-EH] LN-EH Figure 2. Mars Digital Image Mosaic (MDIM) merged with color of part of MC–17SE (northwest part dissected material, and smooth unit of the plateau sequence, separation between material (Late Noachian) and resurfacing (Early Hesperian) age at larger diameters. Nplh s 1269±259 [N-EH] 106±75 [EH-EA] 4 of Thaumasia region). Arrows indicate large scarps (S), ridges (R), volcanoes (V), lava flows (lv) that respectively. (Viking image 384S16; resolution 248 m/pixel.) Subdued cratered unit of plateau sequence of PHPA Npl2 218,561 t 1606±86 [N] 545±50 [MN] 124±24 [MN-LN] MN-LN Nfd bury stage 3 faults of Claritas Fossae, mountains (M), and eastern bounding fault (F) of Thaumasia rift HNf s 1299±77 [N] 238±33 [LN] 46±15 [LN] system (Plescia and Saunders, 1982). Scarps and ridges are interpreted to be cuestas and hogbacks Fractured and dissected material of PHPA4 Nfd 212,311 t 1437±82 [N] 325±39 [LN] 99±22 [MN-LN] MN-LN D Nf formed by tectonic warping and differential erosion of crustal material. HNplt Older dissected material of PHPA4 Npld 112,824 t 1675±122 [N] 541±69 [MN] 124±33 [MN-LN] MN-LN 3.5 x 106 Nfd s 1365±110 [N] 239±46 [LN-EH] 18±13 [LN-EH] 3.39 x 106 ch D Etched material of PHPA4 Nple 22,416 t 1606±268 [N] 491±148 [EN-LN] 178±89 [EN-LN] MN-LN 3.0 x 106 s 1338±244 [N-EH] 223±100 [LN-LH] 2.68 x 106 Hpld 4 HNplt N Older fractured material of PHPA Nf 630,233 t 1453±48 [N] 424±26 [MN-LN] 108±13 [MN-LN] EN-LN 2.5 x 106 0 100 KILOMETERS Older flow and construct material of WVA5 Nfc 40,406 t 2203±234 [N] 569±119 [EN-MN] 99±50 [MN-LN] EN-LN

6 4 2.0 x 106 1.98 x 10 Cratered unit of plateau sequence of PHPA Npl1 430,909 t 1673±62 [N] 610±38 [EN-MN] 202±22 [EN-MN] EN-MN N 0 50 KILOMETERS N 0 50 KILOMETERS 0 50 KILOMETERS Basement complex of PHPA4 Nb 168,733 t 2157±113 [N] 581±59 [EN-MN] 190±34 [EN-MN] EN-MN 1.59 x 106 A B C Figure 14. Viking image exemplifying detailed mapping of complex 6 1.42 x 106 1.5 x 10 structure of a small part of western Thaumasia region; mapped Basin-rim unit of circum-Argyre materials Nah 54,551 t 1027±137 [EH] 568±102 [EN-MN] 202±61 [EN-MN] EN-MN Hilly unit of plateau sequence of PHPA4 Nplh 59,638 t 2733±214 [N] 989±129 [EN] 335±75 [EN] EN-MN 1.0 x 106 9.25 x 105 structures were collated on 1:5,000,000-scale map base. Arrow Figure 9. A, Stage 2 troughs (T) of southern part of Coprates Rise head near large depressions (D; interpreted to have formed by collapse) and stage 2 grabens (G); large scarp (S) indicates deformed highland plains (also see fig. 2), which are marked 1Average crater density N(D) equals number of craters larger than diameter D per million square kilometers. 2Relative ages based on time-stratigraphic scale from Tanaka (1986) reflect material ages (see text); N = Noachian, H = Hesperian, A = Amazonian, E = Early, M = Middle, and L = Late. In 5.0 x 105 probably formed by tectonic activity associated with development of Coprates rise. Symbols Nb, Nf, Nfd, Npld, c1, HNr, HNplt, and Hpld denote basement complex, older fractured by large scarps, ridges, and a volcano (Nfc) with summit depression. Any use of trade, product, or firm names in this publication is for

PALEOEROSIONAL MAP OF THE THAUMASIA REGION, MARS AREA, IN SQUARE KILOMETERS few instances, crater age varies from unit age because of crater counts of individual unit areas, large crater density error margins, and distinct map relations. 2.02 x 105 material, fractured and dissected material, older dissected material, material of degraded craters, older ridged plains material, troughed material, and younger dissected material, Symbols Nplh, Nfc, Nf, Nfd, HNf, Ht , and AHt denote hilly unit, older descriptive purposes only and does not imply endorsement by the 3.69 x 104 2 3 3Type of crater count; superposed (s) and total (t), which includes superposed and highly eroded, partly buried impact craters. In most cases, type t reflects material age and in some cases U.S. Government. 0 By respectively. (Viking image 610A42; resolution 222 m/pixel.) B, Large troughs (T) dissect flanks of Hadriaca Patera. Large channels (ch) head near large depressions (D; flow and construct material, older fractured material, fractured and underlying material age, whereas, type s reflects emplacement mainly of relatively thin lava flows, mantling, or resurfacing age. For sale by U.S. Geological Survey, Information Services, Box 25286, Noachian Hesperian Amazonian 1234 5 4 interpreted to have formed by collapse). (Viking image 625A18; resolution 235 m/pixel.) C, Layers of ignimbrite (large arrow) near Arica, Peru, of the central Andes that were dissected material, intermediate fractured material, and members 2 and Plateau and high-plains assemblage of Scott and Tanaka (1986). Federal Center, Denver, CO 80225, 1–800–ASK–USGS ABPERIOD STAGE 5Western volcanic assemblage of Scott and Tanaka (1986). James M. Dohm, Kenneth L. Tanaka, and Trent M. Hare emplaced during the Early Miocene have been tilted by the Andes orogeny, resulting in distinct pattern of parallel troughs (narrow arrows indicate drainages; Alfred McEwen, 3 of the Tharsis Montes Formation. (Viking image 641A72; resolution *Values vary slightly with those of table 3 because (1) minor revisions of contacts of preliminary map and (2) some units of this table include areas of crater materials that were separated out 2001 Figure 6. Histograms representing amounts of geologic units per period (A) and per stage (B). University of Arizona, oral and written commun., 1996; Landsat TM image). 261 m/pixel.) in the geologic map (that is, units c1, c2, cs). Printed on recycled paper