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Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars

Rampe, E. B. and Grotzinger, J. P. and Siebach, K. (2017) Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars. Earth and Planetary Science Letters, 471 . pp. 172-185. ISSN 0012-821X.

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The Mars Science Laboratory Curiosity rover has been traversing strata at the base of Aeolis Mons (informally known as Mount Sharp) since September 2014. The Murray formation makes up the lowest exposed strata of the Mount Sharp group and is composed primarily of finely laminated lacustrine mudstone intercalated with rare crossbedded sandstone that is prodeltaic or fluvial in origin. We report on the first three drilled samples from the Murray formation, measured in the Pahrump Hills section. Rietveld refinements and FULLPAT full pattern fitting analyses of X-ray diffraction patterns measured by the MSL CheMin instrument provide mineral abundances, refined unit-cell parameters for major phases giving crystal chemistry, and abundances of X-ray amorphous materials. Our results from the samples measured at the Pahrump Hills and previously published results on the Buckskin sample measured from the Marias Pass section stratigraphically above Pahrump Hills show stratigraphic variations in the mineralogy; phyllosilicates, hematite, jarosite, and pyroxene are most abundant at the base of the Pahrump Hills, and crystalline and amorphous silica and magnetite become prevalent higher in the succession. Some trace element abundances measured by APXS also show stratigraphic trends; Zn and Ni are highly enriched with respect to average Mars crust at the base of the Pahrump Hills (by 7.7 and 3.7 times, respectively), and gradually decrease in abundance in stratigraphically higher regions near Marias Pass, where they are depleted with respect to average Mars crust (by more than an order of magnitude in some targets). The Mn stratigraphic trend is analogous to Zn and Ni, however, Mn abundances are close to those of average Mars crust at the base of Pahrump Hills, rather than being enriched, and Mn becomes increasingly depleted moving upsection. Minerals at the base of the Pahrump Hills, in particular jarosite and hematite, as well as enrichments in Zn, Ni, and Mn, are products of acid-sulfate alteration on Earth. We hypothesize that multiple influxes of mildly to moderately acidic pore fluids resulted in diagenesis of the Murray formation and the observed mineralogical and geochemical variations. The preservation of some minerals that are highly susceptible to dissolution at low pH (e.g., mafic minerals and fluorapatite) suggests that acidic events were not long-lived and that fluids may not have been extremely acidic (pH>2pH>2). Alternatively, the observed mineralogical variations within the succession may be explained by deposition in lake waters with variable Eh and/or pH, where the lowermost sediments were deposited in an oxidizing, perhaps acidic lake setting, and sediments deposited in the upper Pahrump Hills and Marias Pass were deposited lake waters with lower Eh and higher pH.

Item Type:Article
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Rampe, E. B.0000-0002-6999-0028
Grotzinger, J. P.0000-0001-9324-1257
Siebach, K.0000-0002-6628-6297
Additional Information:© 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Received 3 August 2016, Revised 3 April 2017, Accepted 12 April 2017, Available online 12 May 2017. The authors gratefully acknowledge support from the NASA Mars Science Laboratory Mission and the efforts of the MSL engineering and science operations teams. This manuscript was improved by thoughtful comments from Kathleen Benison and an anonymous reviewer.
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Subject Keywords:Mars; Gale crater; X-ray diffraction; diagenesis; acid-sulfate alteration
Record Number:CaltechAUTHORS:20170512-142701518
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Official Citation:E.B. Rampe, D.W. Ming, D.F. Blake, T.F. Bristow, S.J. Chipera, J.P. Grotzinger, R.V. Morris, S.M. Morrison, D.T. Vaniman, A.S. Yen, C.N. Achilles, P.I. Craig, D.J. Des Marais, R.T. Downs, J.D. Farmer, K.V. Fendrich, R. Gellert, R.M. Hazen, L.C. Kah, J.M. Morookian, T.S. Peretyazhko, P. Sarrazin, A.H. Treiman, J.A. Berger, J. Eigenbrode, A.G. Fairén, O. Forni, S. Gupta, J.A. Hurowitz, N.L. Lanza, M.E. Schmidt, K. Siebach, B. Sutter, L.M. Thompson, Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars, Earth and Planetary Science Letters, Volume 471, 1 August 2017, Pages 172-185, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77426
Deposited By: Tony Diaz
Deposited On:12 May 2017 22:21
Last Modified:20 Oct 2017 20:40

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