Analogs of Earth Marbles to Mars Blueberries: Records of Groundwater History from Red Rock to Red Planet

Marjorie A. Chan¹, Brenda Beitler¹, William T. Parry¹, Jens Ormo², and Goro Komatsu^3
1 University of Utah, Salt Lake City, UT
² 2Centro de Astrobiología (INTA/CSIC), Instituto Nacional de Técnica Aeroespacial, Madrid, Spain
³ Università d’Annunzio, Pescara, Italy

Jurassic Navajo Sandstone coloration and concretions of southern Utah show a history of groundwater diagenesis and iron-oxide mobility. This example comprises an important Earth analog for newly discovered hematite concretions on Mars. Coloration from iron oxides (e.g., hematite, goethite) is an index to fluid pathways and compositions. These terrestrial sandstones are likely originally red early in the diagenetic history from small amounts of disseminated hematite. Bleaching by reducing solutions later mobilizes and removes iron on local to regional scales. Flow paths are controlled by host rock properties such as permeability, lithology, and sedimentology, in addition to stratigraphy and structure. When reduced waters carrying the iron meet and mix with oxygenated ground water, iron re-precipitates in concretionary forms. Concretions are typically spherical (like marbles) and develop through a self-organizing process.

This analog can help explain the remarkable hematite spherules (“blueberries”) on Mars. Although other terrestrial mechanisms can generate a spherule shape, only the concretion model is consistent with the Mars observations of hematite mineralogy, variable outcrop iron-oxide distribution, common spherules with in situ spaced organization, weathered aprons of the resistant nodules, unusual joined doublet and triplet morphologies, and apparent fracture/joint fills. The presence of hematite concretions implies groundwater flow. The potential role of biomediation in the precipitation of some terrestrial hematite concretions could also hold important clues in the search for life on Mars. Sedimentary analogs have tremendous value in planetary geology exploration and interpretation.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005