NASA Technical Reports Server (NTRS) 19940011820: Geomorphic processes in the Argyre-Dorsa Argentea region of Mars

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by  NASA Technical Reports Server (NTRS)

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GEOMORPHIC PROCESSES IN THE ARGYRE-DORSA ARGENTEA REGION OF MARS;
J.S. Kargel, U.S. Geological Survey, 2255 N (iemmi I)r., Flagstaff, AZ 86001
Introduction. Among many indications of possible ancient Martian glaciation are sinuous eskerlike ridges
in southern Argyre Planitia and tile Dorsa Argentea region [1, 2]. But, in photogeology, other interpretations are
"always possible, and what appears eskerlike to one set of eyes may appear quite different to another.
Interpretations of these ridges are about as numerous as observers, who collectively have suggested nine distinct
hypotheses! Martian sinuous ridges have been interpreted as wrinkle ridges, lava flows, igneous dikes, elastic
dikes, linear sand dunes, spits or bars, examples of reverted stream topography, or glacial crevasse fill [3-g]. Wifll
Mars Observer en route to Mars the prospects for a narrowing of the debate are bright. The esker hypothesis will
gain support if Mars Observer images show flintthe ridges contain boulders, that tim ridges are layered and contain
channel structures, that the ridges are modified by thenno "karst, or that the ridges occur in close, logical
associations with other glacial landfom_s such as flutes, oriented gr(_wes, and moraines. In the meantinm, tile
evidence presented below I_lsters the esker hypothesis, challenges certain alternative ideas, and draws a tentative
geomorphic connection between the sinuous ridges of Argyre and those of Dorsa Argentea.
Data. Sinuosity is a key aspect of Martian sinuous ridges. This characteristic of the Manizm ridges is
compared with sinuosities of suggested terrestrial analogs ill Figs. 1-4. These comparisons conf'lrnl timt, in scale
and sinuosity, Martian sinuous ridges resemble many terrestrial river channels and eskers and may be dislmguished
from terrestrial linear dunes, qhe data for wrinkle ridges and sinuous ridges overlap considerably, but wrinkle
ridges tend to be less sinuous than sinuous ridges; other morphologic aspects of wrinkle ridges clearly distinguish
them from sinuous ridges, including lhe tendency of wrinkle ridges to form en echelon patterns and to have
asynunetric cross profiles• One cannot easily role out the existence of conditions unique to Mars or to these
regions of Mars that might have contributed to fommtion of unusual wrinkle ridges or sand dunes or some oflmr
feature. However, a simpler explanation is that the patterns of Martizm sinuous ridges resemble terrestrial channels
and eskers because all these features were deposited by channelized water flows. This explanation is also
consistent with the hypothesis of inverted stre:un topography, but the occurrence of oflmr l'X)ssible glacial landh)nns
in the Argyre and Dorsa Argentea regions favors the esker analog.
Figure 5 shows a longitudinal topographic profile from a mountainous region (,lear 79° Slat, 350° long) to
what is believed to be tile proximal end of l)orsa Argentea ridges, to the distal end, ',along a deep channel incised
through the Charitum Montes, and into the area of sinuous ridges in Argyre Pianitia. Although topographic
uncertainties are large, the dau_ are consistent witi_ a continuous down-gradient from tim mountainous region
(where peaks probably exceed 7000 m in elevation) to tim floor of Argyre. If the Mars Observer laser altmmter
confirms this gradient, it will be a powerful argument favoring a gravitationally driven fluid-flow origin of tile
sinuous ridges. Such a gradient also is consistent with an integrated interpretation of sinuous ridges and other
landfonns of possible glacial origin in the Dorsa Argentea and Argyre regions.
Conclusions. The sinuosities of Martizm sinuous ridges are comparable with ti_osc of terrestrial rivers and
eskers. The esker hypothesis is favored because other plausible glacial landfonns occur in Ihe Argyre and Dorsa
Argentea regions. Glacial features in these two regions may well have been related to the movement of all ice
sheet from the south polar area across Dorsa Argentea and into Argyre Planitia.
References. [1] Kargel, J.S. and R.G. Strom (1992) Geology, 20, 3-8. [2] Kargel, J.S. and R.G. Strom
(1991) Lun. Planet. Sci.. XXll, 683-684. [3] Carr, M.H. and 12 otimrs (1980) Viking Orbiter Views of Mars,
Washington, I).C., U.S. Government Printing Office, p. 136. [4] lit)ward, A.D. (1981) Repts. Planet. Geol. Prog.,
NASA TM-84211, 286-288. [5] Parker, T.J., D.C. Pieri, and R.S. Saunders (1986) Repts. Planet. GeM. Prog.,
NASA TM-88383, 468-470. [6] Tanaka, K.L. and D.H. Scott (1987) Geologic map of the pohtr regions of Mars,
U.S. Geol. Surv. Misc. Inv. Ser. Map 1-1802-C. [7] Ruff, S.W. and R. Greeley (1990) Lun. Planet. Sci., XXI,
1047-1048. [8] Metzger, S.M. (1991) Lun. Planet. Sci., XXII, 891-892.
Figure captions. Figure 1.Sinuosities of Martian sinuous ridges in Argyre region (solid circles) and Dorsa
Argentea region (solid squares) and of Canadian eskcrs (open squares).
Figure 2. Sinuosities of Argyre's ridges (solid squares) and terrestrial eskcrs (large circles) and rivers
(Yangtze, small circles; Niger, triangles; middle Porcupine, diamonds; and lower Porcupine, open squares).
Figure 3. Sinuosities of sinuous ridges in Argyre region (solid ditunonds) and I)orsa Argentea region (solid
squares), and of terrestrial linear saald dunes (Simpson Desert, Australia, open circles; N_unib Desert, southern
Africa, open squares; and Erg (_hech, North Africa, open diantonds).
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ridgesinI.unaePlanun(lopencircles)
Figure5 I.ongitudimtdopographgicradienint DorsaArgenlema_dArgyreregions(seetext).
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