nai

Project Progress

We completed laboratory analyses of samples of iron deposits collected along the Rio Tinto basin, southwestern Spain (Fig. 1). Analyses included x-ray diffraction (XRD), Moessbauer, petrological, and paleontological investigations of collected samples. In consequence, we can now show how the primary iron deposits in the Rio Tinto system — hydronium jarrosite, shcwertmannite, and poorly ordered goethite — are transformed through diagenesis to produce iron deposits rich in coarse-grained hematite. Of relevance to Mars, the hematite forms as a stable product of diagenesis over a two million year span, not as an initial precipitate.

We also demonstrated that fossils, including fungal and bacterial microfossils, can be preserved in remarkable detail by goethites in the basin, although subsequent digenetic alteration to hematite commonly obliterates preserved fossils. Finally, we demonstrated that sedimentary features observable with Mars Explorer Rover’s (MER’s) pancam and navcam imagers include features identifiable as biological signatures. Foremost among these are streamers, created by the adherence of iron precipitates to filamentous microorganisms.

The Rio Tinto project provides a terrestrial analog to the Mars Meridiani Planumhematite landing site — indeed the only terrestrial analog in which both initial and diagenetically stabilized deposits have been studied.

Figure 1. Present day iron deposition along the Rio Tinto, Spain