Post on 23-Jul-2020
Large Scale Geologic Mapping in East
Candor Chasma: 2017 Status Report
Chris Okubo
3rd Planetary Data Workshop and Planetary Geologic Mappers
Annual Meeting, June 12-15, 2016
Flagstaff, AZ
Project overview
PGM Meeting 2017
• Large scale mapping in eastern Candor Chasma
• Strategically-located sites to learn more of the chasma’s geologic history
• Complements mapping done in western Candor
• Just published as USGS SIM 3359
Current status
PGM Meeting 2017
• Originally proposed to map three areas
• Each map area would comprise two H DEMs
• North Nia Mensa
• Mapping complete
• Results presented here
• Southeast Nia Mensa
• Mapping is underway
• Results next year
• South Juventae Mensa
• Dropped in favor of enhancing the N Nia Mensa map
N. Nia Mensa
PGM Meeting 2017 4 of 16
• Map area
• Defined by H stereo coverage
• Originally two adjacent H stereopairs; Now four DTMs
• X mosaic background
• Prominent features
• Trough network
• ”Nia Chaos”
• Large knobs
• Terraced fan deposit
• Massive sedimentary deposits
• “Nia Mensa”
• Geologic units
• Allostratigraphic
• Structural measurements
• Majority are bedding
• Few faults and other fractures
N. Nia Mensa
PGM Meeting 2017 5 of 16
• Map area
• Defined by H stereo coverage
• Originally two adjacent H stereopairs; Now four DTMs
• X mosaic background
• Prominent features
• Trough network
• ”Nia Chaos”
• Large knobs
• Terraced fan deposit
• Massive sedimentary deposits
• “Nia Mensa”
• Geologic units
• Allostratigraphic
• Structural measurements
• Majority are bedding
• Few faults and other fractures
Overview of Units
PGM Meeting 2017 6 of 16
• 12 units identified
• 3 surficial materials
• 6 sedimentary bedrock
• 2 subsurface-mobilized sediments
• 1 wall rock
Correlation of Units
PGM Meeting 2017 7 of 16
• 3 surficial materials
• Various eolian, colluvial, lacustrine sediments
• 6 sedimentary bedrock
• Conglomerates, sandstones, mudstones, evaporites
• 2 subsurface-mobilized sediments
• Injectites, mud flows
• 1 wall rock
• Breccia (landslide)
Digging deeper
PGM Meeting 2017 8 of 16
• Subsurface-mobilized sediments
• Terraced fan
Subsurface-mobilized sediments - Mudflows
PGM Meeting 2017 9 of 16
• Mudflows
• Associated with Nia Chaos
• Smooth, low-albedo areas
• Lobate/digitate margins
• Dotted with windows of underlying unit
• Up to 10 m thick in trough walls
Subsurface-mobilized sediments - Mudflows
PGM Meeting 2017 10 of 16
• Mudflows
• Associated with Nia Chaos
• Smooth, low-albedo areas
• Lobate/digitate margins
• Dotted with windows of underlying unit
• Up to 10 m thick in trough walls
Subsurface-mobilized sediments - Injectites
PGM Meeting 2017 11 of 16
• Injectites
• Found south of Nia Chaos
• Forms seams and irregularly-shaped mounds
• Cross-cuts other units
• Low albedoESP_031916_1730
Image is ~500 m
across
Terraced fan – Topography
PGM Meeting 2017 12 of 16
• Approximately 16 terraces identified
• Most have subtle topography
• Exception being terrace Q
NO VERTICAL EXAGGERATION
Terraced fan – Topography
PGM Meeting 2017 13 of 16
• Approximately 16 terraces identified
• Most have subtle topography
• Exception being terrace Q
Terraced fan – Origin of the terraces
PGM Meeting 2017 14 of 16
• Terraces traceable from fan deposit to adjacent bedrock
• Therefore erosional, most likely paleoshorelines
Putting it all together 1
PGM Meeting 2017 15 of 16
• Cross-section along ABCD
• General geologic history
Putting it all together 1
• Cross-section along ABCD
• General geologic history
• Formation of east Candor Chasma
• Deposition of sandstones, mudstones, evaporites in wet-playa setting (NMNvf)
• Deformation and block rotation of NMNvf
• Landsliding of wall rock (NCr)
• Widespread deposition of sandstones, mudstones in lacustrine setting (NMNh & NMNtl)
• Subaerial erosion, restoration of the moat
• Widespread deposition of sandstones in erg (NMds)
• Subaerial erosion
• Deposition of fan deposit (alluvial?)
• Development of deep water lacustrine system
Putting it all together 2
• General geologic history (continued)
• Shoreline erosion and terrace formation, subaqueous deposition of conglomerates, sandstones and mudstones (NMNws) during lacustrine transgression
• Rapid lacustrine regression to terrace Q
• Prolonged shoreline erosion and terrace formation, erosion of NMNws
• Rapid lacustrine regression below the level of Q and eventual loss of all surface water
• Gentle folding of all local units
• At some point injectites and mud flows emplaced
• Timing poorly constrained
• Must post-date deposition of NMNds
Future work
PGM Meeting 2017 18 of 16
• Finalize map, cross-section, DOMU, COMU, EOMS, figures, pamphlet text
• Submit for review by October 1st
• Contribute a paper to JGR Data Workshop/Mappers Meeting special issue
• Continue mapping to the east and west
• More mud flows/injectites and paleoshorelines
• Investigate outstanding questions from this work