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Potential Recognition of Accretionary Lapilli in Distal Impact Deposits on Mars: A Facies Analog Provided by the 1.85 Ga Sudbury Impact Deposit

Fralick, Philip and Grotzinger, John and Edgar, Lauren (2012) Potential Recognition of Accretionary Lapilli in Distal Impact Deposits on Mars: A Facies Analog Provided by the 1.85 Ga Sudbury Impact Deposit. In: Sedimentary Geology of Mars. SEPM Special Publication. No.102. Society for Sedimentary Geology , Tulsa, OK, pp. 211-227. ISBN 9781565763135.

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Our understanding of the significance and abundance of sedimentary strata on Mars has increased considerably during the last decade. The highly cratered surface of Mars leads to the prediction that impact ejecta deposits, possibly containing accretionary lapilli, should be part of the sediment record. While no impact-induced base surge deposits have been confirmed on Mars, it is likely that they will one day be discovered, and it is important to establish criteria for their recognition in the rock record. The recognition of ejecta deposits containing accretionary lapilli on Mars requires reliable facies models developed from known impact-generated strata on Earth. Sections through ejecta layers formed by the 1850 Ma Sudbury impact event provide data to begin development of such models. These deposits are laterally variable but generally show a vertical decrease in lithic clast size and, where present, an upward fining in accretionary lapilli. In thicker deposits, the accretionary lapilli–bearing portion of sections generally progresses upward from decimeter-scale beds of clast-supported lapilli interlayered with centimeter-scale sandstone beds, to parallel and undulatory laminated lapilli, and sandstones. These are overlain by lapilli stringers and isolated lapilli in parallel-laminated to cross-stratified sandstone. Both grain size and sedimentary structures indicate a succession deposited by an impact-generated base surge during decelerating flow. Thinner deposits of ejecta, possibly laid down on topographic highs, are commonly massive with reverse and normal grading. We compare the accretionary lapilli–bearing strata in the Sudbury ejecta deposits to proposed impact-generated base surge deposits in the Burns formation at Meridian Planum, Mars. Units comprising the Burns formation do not have the internal organization of spherule-bearing layers exhibited by the Sudbury ejecta deposits. Comparison with Sudbury ejecta layers and theoretical considerations indicate that the spherules developed in the Burns formation do not represent grains deposited by a base surge and are most likely diagenetic in origin. However, impact ejecta layers should be present in the sedimentary successions on Mars, and comparison with similar strata on Earth may lead to their eventual identification.

Item Type:Book Section
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URLURL TypeDescription
Grotzinger, John0000-0001-9324-1257
Edgar, Lauren0000-0001-7512-7813
Additional Information:© 2012 SEPM. Published: January 01, 2012. We would like to thank John Spray and Horton Newsom for critical reviews, in addition to comments by Editor Ralph Milliken, which led to improvements in the manuscript. Drafting of figures related to the Sudbury deposits was performed by Sam Spivik. Funding for this work was provided by Lakehead University and a Discovery Grant from the National Science and Engineering Research Council of Canada to P.W.F. The NASA Astrobiology Institute provided funding for J.P.G. and L.A.
Funding AgencyGrant Number
Lakehead UniversityUNSPECIFIED
National Science and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Series Name:SEPM Special Publication
Issue or Number:102
Record Number:CaltechAUTHORS:20180710-142559735
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87721
Deposited By: Tony Diaz
Deposited On:10 Jul 2018 21:37
Last Modified:03 Oct 2019 19:59

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