McLennan, S. M. and Bell Iii, J. F. and Calvin, W. M. and Christensen, P. R. and Clark, B. C. and de Souza, P. A. and Farmer, J. and Farrand, W. H. and Fike, D. A. and Gellert, R. and Ghosh, A. and Glotch, T. D. and Grotzinger, J. P. and Hahn, B. and Herkenhoff, K. E. and Hurowitz, J. A. and Johnson, J. R. and Johnson, S. S. and Jolliff, B. and KlingelhC6fer, G. and Knoll, A. H. and Learner, Z. and Malin, M. C. and McSween Jr, H. Y. and Pocock, J. and Ruff, S. W. and Soderblom, L. A. and Squyres, S. W. and Tosca, N. J. and Watters, W. A. and Wyatt, M. B. and Yen, A. (2005) Provenance and diagenesis of the evaporite-bearing Burns formation, Meridiani Planum, Mars. Earth and Planetary Science Letters, 240 (1). pp. 95-121.
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Impure reworked evaporitic sandstones, preserved on Meridiani Planum, Mars, are mixtures of roughly equal amounts of altered siliciclastic debris, of basaltic provenance (40 B1 10% by mass), and chemical constituents, dominated by evaporitic minerals (jarosite, Mg-, Ca-sulfates B1 chlorides B1 Fe-, Na-sulfates), hematite and possibly secondary silica (60 B1 10%). These chemical constituents and their relative abundances are not an equilibrium evaporite assemblage and to a substantial degree have been reworked by aeolian and subaqueous transport. Ultimately they formed by evaporation of acidic waters derived from interaction with olivine-bearing basalts and subsequent diagenetic alteration. The rocks experienced an extended diagenetic history, with at least two and up to four distinct episodes of cementation, including stratigraphically restricted zones of recrystallization and secondary porosity, non-randomly distributed, highly spherical millimeter-scale hematitic concretions, millimeter-scale crystal molds, interpreted to have resulted from dissolution of a highly soluble evaporite mineral, elongate to sheet-like vugs and evidence for minor synsedimentary deformation (convolute and contorted bedding, possible teepee structures or salt ridge features). Other features that may be diagenetic, but more likely are associated with relatively recent meteorite impact, are meter-scale fracture patterns, veins and polygonal fractures on rock surfaces that cut across bedding. Crystallization of minerals that originally filled the molds, early cement and sediment deformation occurred syndepositionally or during early diagenesis. All other diagenetic features are consistent with formation during later diagenesis in the phreatic (fluid saturated) zone or capillary fringe of a groundwater table under near isotropic hydrological conditions such as those expected during periodic groundwater recharge. Textural evidence suggests that rapidly formed hematitic concretions post-date the primary mineral now represented by crystal molds and early pore-filling cements but pre-date secondary moldic and vug porosity. The second generation of cements followed formation of secondary porosity. This paragenetic sequence is consistent with an extended history of syndepositional through post-depositional diagenesis in the presence of a slowly fluctuating, chemically evolving, but persistently high ionic strength groundwater system.
|Uncontrolled Keywords:||NIL AREP;|
|Subjects:||03 - Mineral Sciences|
|Divisions:||03 - Mineral Sciences|
|Journal or Publication Title:||Earth and Planetary Science Letters|
|Page Range:||pp. 95-121|
|Depositing User:||Sarah Humbert|
|Date Deposited:||02 Feb 2011 17:10|
|Last Modified:||23 Jul 2013 09:59|
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