# Presentation: 210358

## TRAVERSE ACROSS LOWER STRATA OF MERIDIANI PLANUM LAYERED DEPOSITS 

**TRAVERSE ACROSS LOWER STRATA OF MERIDIANI PLANUM LAYERED DEPOSITS**** **

**Alan D. Howard**
**Department of Environmental Sciences**
**University of Virginia**
**Jeffrey M. Moore**
**NASA Ames**

## General Concept

- We have explored only the top few meters of the >800 m thick stack of layered sediment in the Meridiani Planum region
- These layered deposits have the greatest areal extent and the most informative regional context of all layered deposit sequences
- We argue that these deposits accumulated as a sedimentary wedge at the edge of a large sea or ocean during the Noachian and are thus the most likely deposits to have incorporated organic compounds indicative of development of life

## The Regional Context

## A prominent topographic platform interrupts the northwestward slope of the gradual transition from highlands to lowlands

**A prominent topographic platform interrupts the northwestward slope of the gradual transition from highlands to lowlands**
**It occurs at elevations from about 0 to -1600 m with a sharp drop off to about -2000 m**
**We provisionally call this the *****Meridiani Bench***

## The purple line encloses the Meridiani Bench and separates the Cratered Highlands from the Arabia Lowlands

- Arabia Lowlands

- Cratered Highlands

- M.B.

**The purple line encloses the *****Meridiani Bench***** and separates the *****Cratered Highlands***** from the *****Arabia Lowlands***

## The blue area is underlain by layered sediments of the Meridiani Planum portion of the Meridiani Bench.

- MP

- These layered sediments include the hematite-rich deposits being visited by the Opportunity Rover as well as sulfate-rich deposits.
- We suggest that the entire Meridiani Bench, including the Meridiani Planum deposits, are underlain by a sedimentary sequence of sediments eroded from the Cratered highlands extending into a former sea or ocean extending up to at least -1500 m

## Prominent valley networks are shown in Cyan.  They do not extend below about -1500 m

- White arrows show the ULM outflow channel system that formed subsequent to the landforms discussed here
- The possibility of a high-level ocean or sea in this region has also been suggested by *Edgett and Parker *[1997], *Fairen et al. *[2003], *Fairen and Dohm *[2004], and *Clifford and Parker *[2001]

##   A topographic barrier may have created semi-enclosed conditions that encouraged evaporite deposition as part of the Meridiani Planum sequence.

-   A topographic barrier may have created semi-enclosed conditions that encouraged evaporite deposition as part of the Meridiani Planum sequence.
-   Mawrth Valles may have been excavated by overflows/density flows over this barrier.
-   Later outflow channel floods have breached this barrier.

## We do not have the space or time here to develop the supporting evidence for our scenario, but a paper is in preparation
Even if we are wrong, the presence of a thick sequence of layered deposits, hematite, hydrated minerals, and sufates warrants further exploration
Previous regional geologic investigations of the Meridiani  region have been published by Hynek et al. [2002], Arvidson et al. [2003] and Edgett [2005].
Edgett compares the region to the terrestrial Colorado Plateau

- Even if we are wrong, the presence of a thick sequence of layered deposits, hematite, hydrated minerals, and sufates warrants further exploration
- Previous regional geologic investigations of the Meridiani  region have been published by *Hynek et al. *[2002], *Arvidson et al. *[2003] and *Edgett *[2005].
- Edgett compares the region to the terrestrial Colorado Plateau

## The Proposed Site

- The steep, 300-400 m scarp defining the northwestern edge of the Meridiani Planum/Meridiani Bench deposits exposes probably the most complete section of the lower portions of the sequence, complementing the examination of the higher beds by Opportunity
- We have suggested a site near 354°E and 8°N permitting a traverse across this scarp

## “X” marks the spot, the line is the NW scarp

**“****X” marks the spot, the line is the NW scarp**

**X**

## IR Mosaic of Landing Site Region & 3 proposed sites

**IR Mosaic of Landing Site Region & 3 proposed sites**

## The Geologic Context

*Hynek et al.* [2001] and *Edgett* [2005] have provided geologic context
- Two prominent units define the sedimentary sequence occurring here:
- A lower set of beds which locally appears to incorporate fluvial channel deposits
- An upper sequence characterized by reticulate ridges of layered deposits

## (Edgett,2005)

**P=Plains-forming Unit**
**R=Ridge-forming Unit**
**S=Scarp Forming Unit**
**L=Lower Unit**

**X**

## (Hynek et al., 2002)

**(Hynek et al., 2002)**

**Cs=Cratered, Subdued**
**Cu=Cratered, Undivided**
**IL=Interior Layered**
**P1=Plains, Lower**
**P2=Plains, Upper**
**Ph=Plains, Middle**
**P3=Etched**

**X**

## Images of Region

## 1 - E2200443

**1 - E2200443**

**2 – E2200081**

## Slide 18

## VIS mosaic showing locations of detailed MOC images

**VIS mosaic showing locations of detailed MOC images**

## 1

**1**
**R1601540**

**Scarp in lower layered unit – possibly traversable**

## 2

**2**
**R1601540**

**In landing ellipse – somewhat scabby texture**

## 3

**3**
**R1601540**

**Upper ridged unit – probably can be sampled at various levels**

## Landing site thermal intertias ~200, about the same as the Opportunity site

**Landing site thermal intertias ~200, about the same as the Opportunity site**

## X

**X**

**Landing Site does not contain extensive exposures of hydrated minerals**

## A Possible Extended Mission Target

- The ~70 km crater about 20 km to the west of the landing site contains some of the best exposures of rhythmically-layered sediment on Mars
- The issue is feasibility of descending into the crater and traversing the rough floor

## E

**Landing Site Coordinates:**
**L1:  354.029°E  7.900°N**
**L2:  353.975°E  8.260°N**
**L3:  354.545°E  8.408°N**
**(listed in order of decreasing priority)**
**Regional Polygon Vertices:**
**352.91°E  8.64°N**
**354.72°E  8.49°N**
**354.61°E  7.95°N**
**353.09°E  7.25°N**

***E***

***‘******E***** ‘ is the potential extended mission target**

## Slide 27

**X**

**Landing site is within mantled portion of Arabia, but detailed images show lots of rock exposures**

## SummaryWhy Revisit Meridiani

- Meridiani (whether at our proposed site or elsewhere) contains probably the largest and best exposed layered deposits of probable fluvial or lacustrine origin on Mars.
- The Meridiani site occurs on a gradual transition from highlands to lowlands and thus provides abundant geologic context for interpretation of age and depositional environment.
- A strong case can be made that the Meridiani deposits were deposited into a large regional sea or ocean, either open or ice-covered.

## It is likely that a site can be found in the Meridiani Planum region that:
Provides an adequate landing environment
Provides close access to a thick sequence of the lower beds of the stratigraphic column
Contains accessible traverses
Contains low-energy fluvial or lacustrine depositional environments with abundant hydrated minerals and chemical precipitates
Affords dust-free exposures

- Provides an adequate landing environment
- Provides close access to a thick sequence of the lower beds of the stratigraphic column
- Contains accessible traverses
- Contains low-energy fluvial or lacustrine depositional environments with abundant hydrated minerals and chemical precipitates
- Affords dust-free exposures

## Issues with Site

- Local steep slopes within the 20-km ellipses
- Small-scale roughness on portions of the landing sites
- Located in a partially mantled portion of Arabia
- May not be able to access rhythmically-bedded deposits within crater
- No extensive exposures of hydrated minerals seen so far

## X

**X**

**Other potential landing site**
**locations with thick exposed**
**sequences of Meridiani layered**
**deposits (arrows)**

- The next slide shows other potential traverse locations, shown on V037200003 (left) and V04881003 (right)

## Slide 34