Chemo-stratigraphy in the Murray Formation Using ChemCam

Friday, 18 December 2015: 14:10
2007 (Moscone West)
Diana L Blaney1, Ryan B Anderson2, Nathan Bridges3, John Bridges4, Fred J Calef III1, Samuel M Clegg5, Laetitia Le Deit6, Martin R Fisk7, Olivier Forni8, Olivier Gasnault9, Linda C Kah10, Rachel Emily Kronyak10, Nina Lanza5, Jeremie Lasue8, Nicolas Mangold6, Sylvestre Maurice8, Ralph Milliken11, Douglas W Ming12, Marion Nachon13, Horton E Newsom14, William Rapin9, Kathryn Stack1, Dawn Y Sumner15, Roger C Wiens16 and MSL Science Team, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)USGS Astrogeology Science Center, Flagstaff, AZ, United States, (3)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (4)University of Leicester, Leicester, United Kingdom, (5)Los Alamos National Laboratory, Los Alamos, NM, United States, (6)LPGN Laboratoire de Planétologie et Géodynamique de Nantes, Nantes Cedex 03, France, (7)Oregon State Univ, Corvallis, OR, United States, (8)IRAP, Toulouse, France, (9)Universite de Toulouse, Toulouse Cedex 4, France, (10)University of Tennessee, Knoxville, TN, United States, (11)Brown University, Providence, RI, United States, (12)NASA Johnson Space Center, Houston, TX, United States, (13)University of Nantes, Nantes, France, (14)University of New Mexico Main Campus, Albuquerque, NM, United States, (15)University of California, Davis, Earth and Planetary Sciences, Davis, CA, United States, (16)Space Science and Applications, Los Alamos, NM, United States
Curiosity has completed a detailed chemo-stratigraphy analysis at the Pahrump exposure of the Murray formation. In total >570 chemical measurements and supporting remote micro images to classify texturally were collected. Chemical trends with both stratigraphic position and with texture were evaluated. From these data emerges a complex aqueous history where sediments have interacted with fluids with variable chemistry in distinct episodes.

The ChemCam data collected at the nearby “Garden City” (GC) vein complex provides constraints on the chemical evolution of the Pahrump. GC is thought be stratigraphically above the Pahrump outcrop. Fluids producing the veins likely also migrated through the Pahrump sediments. Multiple episodes of fluids are evident at GC, forming distinct Ca sulfate, F-rich, enhanced MgO, and FeO-rich veins. These different fluid chemistries could be the result of distinct fluids migrating through the section from a distance with a pre-established chemical signature, fluids locally evolved from water rock interactions, or both.

Texturally rocks have been classified into two distinct categories: fine grained or as cross-bedded sandstones. The sandstones have significantly lower SiO2, Al2O3, and K2O and higher FeO, and CaO. Fine grained rocks have further been sub-classified as resistant and recessive with other textural features such as laminations and pits noted.The strongest chemical trend in the fine-grained sandstones shows enhancements in MgO and FeO in erosion-resistant materials compared to fine grained recessive units, suggesting that increased abundance of Mg- and/or iron-rich cements may provide additional strength. The MgO and FeO variations with texture are independent of stratigraphic locations (e.g resistant material at both the bottom and top of the outcrop both are enhanced in MgO and FeO). The presence of the GC MgO and FeO rich veins provides additional evidence for fluids rich in these elements were present in the outcrop. Other elemental trends results including SiO2, Al2O3, K2O and Na2O will be explored in addition to key trace element signatures such as Li, Cr and F to understand the chemical evolution of the outcrop.