Preserved within sedimentary rocks is a record of planetary history. At any time sediments are providing a sampling of the exposed crust. Using sedimentary compositions, it is possible to evaluate the tectonic, climatic and geographic conditions under which a sedimentary rock was deposited. Since sediments are present throughout much of history of Earth and Mars, it is possible to trace the evolution of the surfaces of these planets.

The interests of Professor McLennan lie in evaluating the evolution of planetary crusts and surfacial processes using the chemical composition of sedimentary rocks. It is now clear that there have been active sedimentary environments operating on Mars, especially early in its history. Recently, Professor McLennan has been involved with evaluating the chemical and mineralogical composition of Martian surface materials in terms of sedimentary provenance, sedimentary processes, and crustal composition.

Recent research projects include the following:

1. Mars Exploration Rovers and Mars Odyssey Mission Support and Research
   Professor McLennan is a member of the science teams for the 2003 Mars Exploration Rover mission (Spirit and Opportunity). Graduate students Brian Hahn and Nick Tosca and undergraduate Scott Perl are student collaborators on this mission. Their role is to support mission planning and operations and to carry out research using the most recently returned data from Mars. In addition, Professor McLennan is also a participating scientist on the 2001 Mars Odyssey Gamma Ray Spectrometer instrument and along with graduate student collaborator Brian Hahn, is carrying out research into global-scale surficial processes and crustal evolution on Mars.
   
   
2. Sedimentary Geochemistry on Mars
   Chemical analyses of surface rocks and soils returned during the Viking, Pathfinder, Spirit and Opportunity missions coupled with mineralogical and chemical data from a variety of orbital missions, provide important constraints on the geological history of Mars. With graduate student Brian Hahn and former graduate student Joel Hurowitz (currently JPL/Caltech postdoc), Professor McLennan is currently funded through the NASA Mars Data Analysis Program to evaluate these results in terms of crustal evolution the various sedimentary processes that may have operated at the Martian surface during its history.
   
   
3. Surficial Processes on Mars: Experimental Approaches
   Recent data from the Mars rovers and orbital missions indicate that variety of unusual evaporite minerals may have been important surface deposits over much of the geological history of Mars. Evaporative processes can be experimentally simulated in the laboratory. With graduate student Nick Tosca, Professor McLennan is funded through the NASA Mars Fundamental Research Program to perform a series of experiments that simulate potential Martian evaporative processes and thus provide useful tests to the various models that have been proposed.
   
   
4. Geochemical evolution of the terrestrial continental crust using sedimentary rock compositions, with long-time collaborator S. Ross Taylor (Australian National University) and former Stony Brook graduate student Sidney Hemming (Associate Professor, Columbia University).

Taylor, S. R. and McLennan, S. M. (1985). The Continental Crust: Its Composition and Evolution. Blackwell (Oxford), 312pp.

McLennan, S.M. (1989) Rare earth elements in sedimentary rocks: Influence of provenance and sedimentary processes. Rev. Mineral. 21, 169-200.

McLennan, S.M., Taylor, S.R., McCulloch, M.T. and Maynard, J.B. (1990) Geochemical and Nd-Sr isotopic composition of deep sea turbidites: Crustal evolution and plate tectonic associations. Geochim. Cosmochim. Acta 54, 2015-2050.

McLennan, S. M., Hemming, S., McDaniel, D. K. and Hanson, G. N. (1993) Geochemical approaches to sedimentation, provenance and tectonics. In: M. J. Johnsson and A. Basu (Eds.) Processes controlling the composition of clastic sediments. Geol. Soc. Amer. Spec. Paper 284, 21-40.

Hemming, S. R., McLennan, S. M. and Hanson, G. N. (1994) Lead isotopes as a provenance tool for quartz: Examples from plutons and quartzite, northeastern Minnesota. Geochim. Cosmochim. Acta, 58,4455-4464.

Taylor, S. R. and McLennan, S. M. (1995) The geochemical evolution of the continental crust. Rev. Geophys. , 33, 241-265.

McLennan, S. M. and Taylor, S. R. (1996) Heat flow and the chemical composition of continental crust. J. Geol., 104, 369-377.

Lev, S. M., McLennan, S. M. and Hanson, G. N. (1999) Mineralogic controls on REE mobility during black-shale diagenesis. J. Sed. Res., 69, 1071-1082.

McLennan, S. M. (2000) Chemical composition of Martian soil and rock: Complex mixing and sedimentary transport. Geophys. Res. Lett., 27, 1335-1338.

Hemming, S. R. and McLennan, S. M. (2001) Pb isotope compositions of modern deep sea turbidites. Earth Planet. Sci. Lett., 184, 489-503.

McLennan, S. M. (2001) Crustal heat production and the thermal evolution of Mars. Geophys. Res. Lett., 28, 4019-4022.

McLennan, S. M., Bock, B., Compston, W., Hemming, S. R. and McDaniel, D. K. (2001) Detrital zircon geochronology of Taconian and Acadian foreland sedimentary rocks in New England. J. Sed. Res., 71, 305-317.

McLennan, S. M. (2003) Sedimentary silica on Mars. Geology, 31, 315-318.

Tosca, N. J., McLennan, S. M., Lindsley, D. H. and Schoonen, M. A. A. (2004) Acid-sulfate weathering of synthetic Martian basalt: The acid fog model revisited. J. Geophys. Res., 109, E05003, doi:10.1029/2003JE002218.

Squyres, S. W., Grotzinger, J. P., Arvidson, R. E., Bell III, J. F., Christensen, P. R., Clark, B. C., Crisp, J. A., Farrand, W. H., Herkenhoff, K. E., Johnson, J. R., Klingelhöfer, G., Knoll, A. H., McLennan, S. M. and 5 others (2004) In-situ evidence for an ancient aqueous environment on Mars. Science, 306, 1709-1714.

McLennan, S. M., Bell III, J. F., Calvin, W. and 29 others (2005) Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani Planum, Mars. Earth Planet. Sci. Lett. 240, 95-121.

Tosca, N. J., McLennan, S. M. et al. (2005) Geochemical modeling of evaporation processes on Mars: Insight from the sedimentary record at Meridiani Planum. Earth Planet. Sci. Lett. 240, 122-148.

Tosca, N. J. and McLennan, S. M. (2006) Chemical divides and evaporite assemblages on Mars. Earth Planet. Sci. Lett. 241, 21-31.

Hurowitz, J. A., McLennan, S. M., Tosca, N. J., Arvidson, R. E., Michalski, J. R., Ming, D. W., Schöder, C. and Squyres, S. W. (2005) In-situ and experimental evidence for acidic weathering on Mars. J. Geophys. Res. 111, E02S19, doi:10.1029/2005JE002515.

McLennan, S. M., Taylor, S. R. and Hemming, S. R. (2006) Composition, differentiation, and evolution of continental crust: Constraints from sedimentary rocks and heat flow. In: M. Brown and T. Rushmer, eds. Evolution and Differentiation of the Continental Crust. Cambridge Univ. Press, pp. 92-134.

Hahn, B. C., McLennan, S. M., Taylor, G. J., Boynton, W. V. and 8 others and The Odyssey GRS Science Team (2006) Mars Odyssey gamma-ray spectrometer elemental abundances and apparent relative surface age: Implications for martian crustal evolution. J. Geophys. Res. (in press).

“Sedimentary Petrology at the MER Sites”: NASA/JPL Mars Exploration Rover Participating Scientist Program

“Global Perspective of Surficial Processes on Mars Using Mars Odyssey Gamma Ray Spectrometer”: NASA/JPL 2001 Mars Odyssey Participating Scientist Program

“Evaporative Processes on Mars: Constraints from Experiments and Modeling”: NASA Mars Fundamental Research Program