Test area notebookLibya Montes – Syrtis Major – Isidis Planitia – Hesperia Planum – Utopia Planitia HLB Jim Skinner
Utopia HLB Isidis Planitia Syrtis Major Amenthes Planum Terra Tyrrhena
Isidis Planitia 5,000,000 20,000,000
Previous regional units • I-1802: • Syrtis Major (Hs), Isidis Planitia (Aps, Hvr), Terra Tyrrhena (Npld, Hpl3, Hr, Nplh), Hesperia Planum (Hr “type locality”), AHt), Utopia HLB (Hr, AHpe, HNu), Libya Montes (Nplh, Hpl3, Nm) • SIM 2888: • Syrtis Major (HIs), Isidis Planitia (AIi), Terra Tyrrhena (Nl, Nn, HNn), Utopia HLB (HNn, HBu1, HIa) Libya Montes (Nl)
Critical issues in preliminary mapping of Skinner region • Differentiate marginal unit and/or group marginal unit with Isidis unit? • Continue splitting “boundary plains” Utopia Planitia 1 and 2 units? • How to define Libya Montes unit? And, should we separate all major basin rim materials? • How to separate highland rocks? • Amenthes Planum – true “ridged plains”?
Suggested units for test area • ABvi – basically same as Tanaka et al. (2005) and Scott et al. (1986-87) • ABvm – combines marginal unit and Isidis unit of Tanaka et al.(2005) • HBu1 – same as Tanaka et al. (2005) • HBu2 – same as Tanaka et al. (2005) • HNn – Nepenthes Mensae – requires better definition and criteria than defined in Tanaka et al. (2005) • Nml – partly equivalent to Tanaka et al. (2005) More expansive, including rugged areas, generally free of long channel branches; partly defined by structures (normal faults); slopes grade into Noachis unit • Nmu – NEW - Montane undivided, partly equivalent to Nm and m of VO-based maps; mapped where Libya grades southward to Hellas rim; difficult to discriminate, but there is hope • Nn1 - Roughly equivalent to Tanaka et al. (2005) • Nn2 - NEW – Old smooth plains and crater infill; may be equivalent in age to Nn3 • Nn3 - NEW – Noachis 3 – Old Nplr and Hr
Morphology • Channel mapping – effective with THEMIS at 50 to 60% transparency over MOLA hillshade • Still shows structure apparent in MOLA as well as thermal contrasts for channel mapping • Digitizing at 2,500,000 scale – appears optimal at global scale – better than 1:5M for placement accuracy • Channel id helps to define unit margins in broad swaths of highland terrain • Care needed to determine whether channel truncated through burial or change in subsurface rheology • Important to show, where possible, convergence of stream branches not consistently represented in VO maps • If no convergences, show flow direction? Abrupt truncation?
Structure • Major topographic scarps – dominate the circum-Isidis region • Amenthes Fossae form sets of linear depressions, no apparent offset, appear roughly circumferential to Isidis • Nili Fossae • Volcanic crater and scarps of Syrtis Major • Major wrinkle ridges on Syrtis Major • Syrtis is good unit to delineate superposition relationships with due to overlap and infill of crater highland terrains and protrusion of older Libya/Noachis-type units
Low-lying flat regions “palus”