Geologic/Geomorphic Studies of : L.F. Bleamaster, III, Planetary Science Institute, 1700 E. Ft. Rd., Suite 106, Tucson, AZ 85719. [email protected]

Introduction: Over the course of the last two years I Planitia; c) to investigate the nature of the boundary have been working closely with David Crown on both between the east rim and in order to infer its scientific and educational projects, which have focused on mode of origin, age, and history of modification; and d) to various aspects of Dao and Harmakhis valles in the use small-scale surface morphology and small crater geographic region of northeast Hellas basin on Mars. In populations to examine finely-layered deposits, local addition, I have been writing proposals for my own erosion and redistribution of materials by the wind, and research, lo and behold, I actually got one. I will briefly and burial/mantling/exhumation of surfaces. broadly introduce a few of these projects, which are in Shifting Gears, New Studies in : The various stages of completion/development. objectives of this newly funded Mars Data Analysis Mantle Deposits and Gullies: Evaluation of high- Program project are to evaluate the role and extent of resolution images (Mars Orbiter Camera [MOC] and spatially variable modification processes (e.g., fluvial, Thermal Emission Imaging System [THEMIS]) allow us to volcanic, tectonic, glacial, mass wasting) on potentially systematic characterize the walls of Dao and Harmakhis deep and long-lived crustal structure along the Arabia Terra Valles. Variations in the wall morphology are classified dichotomy boundary. Revealing underlying macro-scale into three archetypes (exposed, mantled, and incised). structural patterns along the boundary may bring light to Gullies are exposed by removal of semi-competent the formation mechanisms responsible for the crustal mantling deposits, suggesting progressive development of dichotomy itself. Using Viking Orbiter, MOC and feature-types in an idealized sequence from i) mantled THEMIS images, and MOLA and Thermal Emission walls, to ii) incised mantle, and eventually iii) walls that Spectrometer data, this investigation will compare display exposed gullies. Analysis of latitude, elevation, and morphologic, morphometric, and geologic (including wall orientation of 420 representative sample sites reveals detailed stratigraphic analyses) differences along the Arabia spatial patterns that display preferential clustering of the Terra dichotomy boundary with special focus on three two end member morphologies: exposed gullies are favored specific transitional zones that span the topographic at lower latitude, higher elevation, and on east facing walls; demarcation of the boundary: 1) Arabia Terra to Acidalia mantled walls are more prevalent at higher latitude, lower Planitia (20°N, 20°W), 2) Arabia Terra to elevation, and on and southwest facing walls. These through (45°N, 325°W), and 3) morphologies and their patterns are consistent with the Arabia Terra to Vastitas Borealis north of Syrtis Major hypothesis that gullies emerge from beneath an ice-rich Planum (40°N, 290°W). Each of these sections display mantle that is degrading in response to local variations in different surface morphologies and provide areas of study total solar insolation. I will show some figures from our that encompass the broad spectrum of surficial processes recently submitted GRL manuscript [1] that support our that have acted along the dichotomy. This project will hypothesis. synthesize existing geologic and geomorphic maps as well Geologic Mapping in Hellas Planitia: We also are as provide new information (digital geologic map mapping three MTM quadrangles –40277, -45277, and – coverages, crater size frequency distributions, valley 45272, which cover the distal regions of Dao and morphology and morphometry (size, depth, width, Harmakhis Valles and the adjacent parts of Hellas Planitia. orientation, and fill material properties)), necessary to both Here, highly degraded highland terrains of the Hellas rim formulate new and evaluate existing hypotheses that contact the floor deposits of Hellas basin. The map area address the relative contributions of mass wasting, aeolian, includes valles and their floor deposits, remnants of rugged glacial, fluvial, volcanic, and/or tectonic modification basin rim materials, dissected channeled plains, and the processes, as well as the role crustal structure plays on basin floor deposits. Recent studies using MOC and modification along the Arabia Terra dichotomy boundary. THEMIS images coupled with Mars Orbiter Laser Drawing on team members’ (Co-Is David Crown and Dan Altimeter (MOLA) data suggest that the eastern basin rim Berman, and Collaborators Bill Hartmann and Mary is a large depositional shelf, with a series of elongate, Bourke) experience in geologic mapping, crater counting, sinuous channels extending toward Hellas Planitia and a fluvial and aeolian degradation, volcanism, and tectonics, concentration of finely-layered outcrops along a distinct this investigation will contribute significantly to our scarp that separates the basin floor from the surrounding understanding of the formation and subsequent rim. The later stages of Dao and Harmakhis Valles are modification of the crustal dichotomy boundary on Mars. interpreted to be dominated by collapse and sapping in a References: [1] Bleamaster III, L.F. and Crown D.A. volatile-rich substrate [2,3]. These observations and (2005, in review) GRL. [2] Crown, D.A., Bleamaster III, progressive highland terrain degradation from the highlands L.F., and Mest, S.C., 2004, Geologic Evolution of Dao inward toward the basin margin are consistent with ancient Vallis, Mars. Lunar and Planetary Science Conference lakes in the basin interior [4], as proposed earlier based on XXXV, abstract 1185. [3] Bleamaster III, L.F. and Crown, analyses of western Hellas [5]. D.A., 2004, Morphologic Development of Harmakhis Specific research objectives for geologic mapping of Vallis, Mars. Lunar and Planetary Science Conference eastern Hellas Planitia include: a) to reconstruct fluvial XXXV, abstract 1825. [4] Crown D. A., Bleamaster III, systems that dissect the Hellas rim; b) to characterize the L.F., and Mest, S.C. (2005, in review) JGR. [5] Moore J.M. extensions of Dao and Harmakhis Valles onto the basin and Wilhelms, D.E., (2001) Icarus, 154, 258-276. floor and to identify sediments contributed to Hellas