## Breadcrumb

-  Publications 
-  Articles 

#           North polar region of Mars: Advances in stratigraphy, structure, and erosional modification      

      January 1, 2008    

We have remapped the geology of the north polar plateau on Mars, Planum Boreum, and the surrounding plains of Vastitas Borealis using altimetry and image data along with thematic maps resulting from observations made by the Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter spacecraft. New and revised geographic and geologic terminologies assist with effectively discussing the various features of this region. We identify 7 geologic units making up Planum Boreum and at least 3 for the circumpolar plains, which collectively span the entire Amazonian Period. The Planum Boreum units resolve at least 6 distinct depositional and 5 erosional episodes. The first major stage of activity includes the Early Amazonian (∼3 to 1 Ga) deposition (and subsequent erosion) of the thick (locally exceeding 1000 m) and evenly-layered Rupes Tenuis unit (Abrt), which ultimately formed approximately half of the base of Planum Boreum. As previously suggested, this unit may be sourced by materials derived from the nearby Scandia region, and we interpret that it may correlate with the deposits that regionally underlie pedestal craters in the surrounding lowland plains. The second major episode of activity during the Middle to Late Amazonian (∼<">∼<1 Ga) began with a section of dark, sand-rich and light-toned ice-rich irregularly-bedded sequences (Planum Boreum cavi unit, Abbc) along with deposition of evenly-bedded light-toned ice- and moderate-toned dust-rich layers (Planum Boreum 1 unit, Abb1). These units have transgressive and gradational stratigraphic relationships. Materials in Olympia Planum underlying the dunes of Olympia Undae are interpreted to consist mostly of the Planum Boreum cavi unit (Abbc). Planum Boreum materials were then deeply eroded to form spiral troughs, Chasma Boreale, and marginal scarps that define the major aspects of the polar plateau's current regional topography. Locally- to regionally-extensive (though vertically minor) episodes of deposition of evenly-bedded, light- and dark-toned layered materials and subsequent erosion of these materials persisted throughout the Late Amazonian. Sand saltation, including dune migration, is likely to account for much of the erosion of Planum Boreum, particularly at its margin, alluding to the lengthy sedimentological history of the circum-polar dune fields. Such erosion has been controlled largely by topographic effects on wind patterns and the variable resistance to erosion of materials (fresh and altered) and physiographic features. Some present-day dune fields may be hundreds of kilometers removed from possible sources along the margins of Planum Boreum, and dark materials, comprised of sand sheets, extend even farther downwind. These deposits also attest to the lengthy period of erosion following emplacement of the Planum Boreum 1 unit. We find no evidence for extensive glacial flow, topographic relaxation, or basal melting of Planum Boreum materials. However, minor development of normal faults and wrinkle ridges may suggest differential compaction of materials across buried scarps. Timing relations are poorly-defined mostly because resurfacing and other uncertainties prohibit precise determinations of surface impact crater densities. The majority of the stratigraphic record may predate the recent (<20 Ma) part of the orbitally-driven climate record that can be reliably calculated. Given the strong stratigraphic but loose temporal constraints of the north polar geologic record, a comparison of north and south polar stratigraphy permits a speculative scenario in which major Amazonian depositional and erosional episodes driven by global climate activity is plausible.

## Citation Information

## Related Content

                  -              Connect           

#### Jim Skinner

##### Supervisory Geologist 

Astrogeology Science Center

jskinner@usgs.gov

#### Corey Fortezzo

##### Research Geologist

Astrogeology Science Center

cfortezzo@usgs.gov

####             Kenneth Edward Herkenhoff, Ph.D. (Former Employee)          

##### Research Geologist

Astrogeology Science Center

#### Chris H Okubo, PhD

##### Deputy Center Director and Research Operations Lead

Astrogeology Science Center

cokubo@usgs.gov

928-556-7009

## Related Content

#### Jim Skinner

##### Supervisory Geologist 

Astrogeology Science Center

jskinner@usgs.gov

#### Corey Fortezzo

##### Research Geologist

Astrogeology Science Center

cfortezzo@usgs.gov

####             Kenneth Edward Herkenhoff, Ph.D. (Former Employee)          

##### Research Geologist

Astrogeology Science Center

#### Chris H Okubo, PhD

##### Deputy Center Director and Research Operations Lead

Astrogeology Science Center

cokubo@usgs.gov

928-556-7009

### Contact

####               Astrogeology Science Center          

2255 N. Gemini DriveFlagstaff, AZ86001United States

928-556-7000

928-556-7014

### Explore Search

                  - Mars; Planum Boreum; Vastitas Borealis
                  - Mars
                  -  Planum Boreum
                  -  Vastitas Borealis

View All **