Modeling of Iron Oxide Concretion Formation: Complexities and Sensitivities of Fluid Interactions on Earth and Mars

Chan, Marjorie A.¹, Jens Ormö², Anthony Park³, Michael Stich², Virginia Souza-Egipsy², Goro Komatsu⁴ (1) University of Utah, Salt Lake City, UT (2) 2Centro de Astrobiología (INTA/CSIC), Instituto Nacional de Técnica Aeroespacial, Madrid, Spain (3) Sienna Geodynamics & Consulting, Inc, Bloomington, IN (4) Università d’Annunzio, Pescara, Italy

Abundant iron oxide concretions of the Jurassic Navajo Sandstone of southern Utah and those in the Burns formation at Meridiani Planum, Mars share common physical attributes of occurrence, spheriodal shapes, sizes, and distribution patterns in porous eolian deposits. Both the field occurrences and modeling of terrestrial analogs are extremely important in interpreting the rich new Mars Exploration Rover (MER) data. Terrestrial concretions indicate different iron mobility and precipitation patterns that provide the basis for input parameters in numerical computer simulations and chemical bench tests to understanding the processes of fluid interactions responsible for iron-oxide concretion growth.

Three numerical simulations show the development of self-organized nucleation centers upon supersaturation. Simulations cover 1-D models of simple diffusion that produce few nucleation bands, to models with both diffusive and advective mass-transfer mechanisms. Model sensitivities show that acidic conditions can cause iron to stay in solution longer to produce nucleation centers that are farther from the input source.

Laboratory bench tests with reactions of FeSO₄ or Fe(NO₃)₃ with KOH show how the precipitation of iron sulfates or iron-hydroxides may form. Rinds may show inward growth depending on the concentration of the iron source in relation to the surrounding fluid. Complex factors such as concentration and flux, time, and multiple events can create banded patterns during rind growth. The comparisons of the terrestrial examples with numerical and laboratory models have strong implications for understanding similar hematite concretions and the history of liquid water and, thus, the potential of similar processes at Mars environments.