Ninth International Conference on 2019 (LPI Contrib. No. 2089) 6367.pdf

THE FIRST FIELD GEOLOGIC MAPS ON MARS: ANOTHER LEGACY FROM AND . Crumpler, L.S.1 and the Athena Science Team, 1 New Mexico Museum of Natural History & Science, 1801 Mountain Rd NW, Albuquerque, NM, 87104, USA, [email protected]

Introduction: Field geologic maps have been pre- the rock types and relative stratigraphic positions of pared from in situ (on the ground or "field") observa- separated outcrops were compared, correlated, and tions during the traverse of Mars Exploration Rovers mapped along the traverse and plotted on a merged Spirit and Opportunity [1, 2]. These maps are the first orthographic panorama and MRO/HiRISE tests of field geologic mapping methods at the human image base out to a radius of 20 m (Fig. 1). The 20-m scale on another and were developed for docu- limit of the field geologic maps from Spirit and Oppor- menting the complex field relations observed by Spirit tunity is based on experience in the ability to detect and Opportunity. Future missions of landed science on differing lithologies with increasing distance using the Moon and Mars, including both robotic and human MER Navcam images. The attitude of planar contacts exploration, will benefit from the systematic and con- were determined from field methods such as along- tinuous recording of information and the correspond- strike and down-dip viewing and estimates from con- ing field hypotheses afforded by using methods similar tacts on geologic sections. to those discussed here. Methods: Over a decade and a half ago the MER Science Team established the methods for efficient rover operation by codifying field geologic methods [3]. The rovers were designed to replicate the capabili- ties of a field geologist [3]: 20-20 color vision (Pan- cam), a rock hammer (), a hand lens (Microscopic Imager), the ability to test for basic minerals (mini-TES, Mossbauer), and "lab analysis of elemental abundances" (APXS). These tools sufficed for detailed mapping at sub-meter length scales. Sev- eral kilometers of geomorphically diverse but litho- logically monotonic terrain were traversed initially by both rovers. Figure 1. Principles of reconnaissance in situ strip geologic mapping. In situ mapping on Mars is comparable to field The textures, structures, mineralogy, chemistry, and geologic mapping on Earth in an area of extensive cover: macro- and microscopic petrography of outcrops were lithology, structure, and contacts are compared between systematically examined in during Spirit and Oppor- stations and continuity derived from correlation of petrogra- tunity’s traverses in the and on the rim phy in outcrops and multiple stratigraphic determinations of crater. Unlike previous planetary maps, true petrographically defined lithologies and the con- Results: The results are records in map format of the tacts between them were identified from observations lithology, stratigraphy, and structure determined by on the ground at individual outcrops. High-resolution field (in situ or ground-based) observations along two MRO/HiRISE images provided bases for mapping geologic traverse mapping swaths, each 40 meters contacts and other observations. Map production from wide and several kilometers long. Ultimately Spirit this data used the same methods that are applied in mapped 0.17 km2 along its 4.3 km traverse within Co- geologic mapping on Earth: (1) The observed locations lumbia Hills and Opportunity mapped 0.47 km2 along of identified lithologic units and contacts were plotted its 12 km trek on the rim of the complex on a base map. (2) exposures with the same or similar , Endeavour. A local example of the final petrography were correlated and compared from site to map, in this case showing multiple impact breccia li- site. Field petrography provided a reliable method of thologies and large-scale through-going faults is shown correlation between outcrops. While geochemical in Figure 2, the upper half of Perseverance Valley. analyses were illuminating on many fronts, the exten- With the location of contacts between lithologic sive and localized alteration of many protoliths are in units and their attitudes determined and placed in the some cases problematical for outcrop-to-outcrop cor- context of local DEM derived from Navcam ranging relation. (3) The contacts, respective overlapping char- and from HiRISE DTMs, we were able to construct acteristics and time series of emplacement of different true geologic cross sections. These both document the lithologic exposures were plotted on the local base. (4) structure and provide predictions about stratigraphy The attitudes of structures and foliations were com- and structure testable during traverses beyond the local piled on the map base. Similarities and differences section. They also provide insight into the context of between examined rocks and outcrops were noted and complex exposures. When placed in the stratigraphic Ninth International Conference on Mars 2019 (LPI Contrib. No. 2089) 6367.pdf

Figure 2. In situ geologic map from Opportunity's traverse down the upper Perseverance Valley, west rim of Endeavour crater. Identification of the contact between the impact ejecta and pre-impact substrate enabled clarification of some per- plexing geochemical trends and lithologic complexities.

and structural context several pieces of the complex geochemical puzzle have begun to fall into place and Figure 3. Structure section based on field mapping of con- hypotheses for disparities and correlations between tacts between lithologic units, stratigraphic correlation, and sites are somewhat better conceptualized [4, 9]. attitude of outcrops (A) during traverse across the flanks and summit of the Columbia Hills by Spirit [1], and (B) section Spirit in the Columbia Hills: The Common case of through rim of Endeavour crater during Opportunity’s tran- Up-hill is Down-stratigraphy on Mars. Variable alter- sect of Marathon Valley [7]. ation, deep erosion, and complex stratigraphy made quantitative geochemical correlations between out- Summary. In situ or field geologic mapping on Mars crops perilous as Spirit summited the Columbia Hills. was developed in the course of executing Spirit and However, the petrologic and lithologic protolith of Opportunity’s missions on Mars. While the methods many outcrops remains and served as a basis for rec- were not anticipated for use on Mars, the design of the ognizing similar units at widely separated locations. mission with “the basic tools of a field geologist” [1] Ultimately the Columbia Hills were determined from provided an obvious basis for its creation. The con- basic stratigraphic correlation and from the pattern of struction of a geologic map from field geologic obser- bedding attitudes to be a succession of layered materi- vations is an important development in Mars science, als draping a precusor massif [1, 5] (Fig. 3A). We be- expanding the geologic characterization of Mars from lieve this "up-hill is down-stratigraphy" arrangement photogeologic to actual in situ ("ground truth") meas- of the Columbia Hills is common on Mars because of urements of petrologic, structural, stratigraphic, and the preservation in the landscape of the results of early geomorphic information of surface materials in a local partial landscape erosion of a stratigraphically rich lithologic context over several kilometers of traverse. global geology. Future missions, both robotic and human, will benefit Opportunity on Endeavour crater: Field Geology from documenting geology using methods similar to on the Topographic Rim of a Complex Impact crater. that used by Spirit and Opportunity. The structure and stratigraphy of complex impact cra- References: [1] Crumpler, L.S. et al. (2011) J. Ge- ters is beginning to emerge from Opportinity's traverse ophys. Res., 116; [2] Crumpler, L.S. et al. (2015) J. Geophys. along the west rim of the 22 km-diameter Endeavour Res., 120; [3] Squyres S. W. et al. (2003) JGR-, doi: crater [2; 4; 6; 7; 8; 9]. Mapping of the attitudes of the 10.1029/ 2003JE002121; [4] Mittlefehldt, D. W., et al.(2018) planar contact between the upper and lower Shoemaker JGR-Planets, doi: 10.1002/2017JE005474 [5] McCoy T. J. et formation and the attitudes pervasive foliations in out- al. (2008) JGR, doi: 10. 1029/ 2007JE003041; [6] Grant et al crops at several locations, including Marathon and Perseverance Valleys, shows that inboard of the crater (2016) Icarus, doi:10.1016/ j.icarus. 2015.08.019; [7] Crum- rim units dip inward toward the crater interior (Fig pler, L.S. et al. (2019) LPSC 50 abstract 1179; [8] Hughes 3B). The prevalence of vertical joints, dipping folia- M. N. et al. (2019) JGR-Planets, doi: 10.1029/ 2019 th tions, and fault zones together with variable perme- JE005949; [9] Arvidson et al (2019) 9 Mars Conf, abstract ability of breccias may exert a fundamental control on 6084. groundwater and sites of more intense alteration.