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