TY - JOUR
T1 - Surge deposit misidentification at Spor Mountain, Utah and elsewhere
T2 - A cautionary message for Mars
AU - Burt, Donald
AU - Knauth, L. P.
AU - Wohletz, K. H.
AU - Sheridan, M. F.
N1 - Funding Information:
In 1979, David Lindsey graciously shared his unpublished research with some of us and guided us in the field; we remain grateful for his generosity and open-mindedness. We also are grateful for the constructive comments by two reviewers, one of whom was Peter Kokelaar, and for organizing and editing by Tracy Gregg. Portions of our topaz rhyolite research were funded by grants (to DMB and MFS) from the U.S. Department of Energy and the U.S. National Science Foundation. More recently, we all are grateful to NASA and the Athena Science Team, and to P.I. Jim Bell in particular, for making raw images taken by the two Mars Exploration Rovers, Spirit and Opportunity, available daily on the web for all to see. This enabled us, and presumably millions like us, to explore the surface of Mars as vicarious field geologists, and to develop independent geological interpretations of rover observations. The first three authors are also grateful to the last (MFS) for so enthusiastically teaching us about pyroclastic surge deposits and their field interpretation. Finally, all of us acknowledge the memory of our former colleague Robert F. Dietz and his enthusiasm for Meteor Crater and other astroblemes.
PY - 2008/11/20
Y1 - 2008/11/20
N2 - Before base surges were described in association with nuclear blasts and explosive volcanic eruptions (especially, the 1980 eruption of Mount St. Helens, Washington), laminar and cross-bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin. One well-documented example involves the "water-laid tuffs" in and near the Spor Mountain beryllium mine, Utah; other examples abound. In light of how frequently volcanogenic surge deposits have been misinterpreted on Earth, extreme caution is urged for Mars studies. Contrary to what has been claimed, the markedly cross-bedded, salty deposits at Meridiani Planum on Mars need not have been formed by a combination of aeolian and aqueous processes, and their contained hematitic spherules need not have formed as aqueous concretions. Given the lack of indications of volcanism in the vicinity, and the planet-wide abundance of impact craters, deposition by surges associated with distant impact targets consisting of brine-soaked, locally sulfidic regolith is a reasonable explanation for all features observed, especially if diagenesis and weathering are considered. The uniformly sized and shaped, Ni-enriched blue-gray hematitic spherules would then be some type of vapor condensation spherules (including accretionary lapilli). A similar interpretation is possible for deposits in the Home Plate area, Gusev Crater. Unlike on the dry and atmosphereless Moon, salty impact surge deposits containing spherules should be common, and well-preserved, on Mars.
AB - Before base surges were described in association with nuclear blasts and explosive volcanic eruptions (especially, the 1980 eruption of Mount St. Helens, Washington), laminar and cross-bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin. One well-documented example involves the "water-laid tuffs" in and near the Spor Mountain beryllium mine, Utah; other examples abound. In light of how frequently volcanogenic surge deposits have been misinterpreted on Earth, extreme caution is urged for Mars studies. Contrary to what has been claimed, the markedly cross-bedded, salty deposits at Meridiani Planum on Mars need not have been formed by a combination of aeolian and aqueous processes, and their contained hematitic spherules need not have formed as aqueous concretions. Given the lack of indications of volcanism in the vicinity, and the planet-wide abundance of impact craters, deposition by surges associated with distant impact targets consisting of brine-soaked, locally sulfidic regolith is a reasonable explanation for all features observed, especially if diagenesis and weathering are considered. The uniformly sized and shaped, Ni-enriched blue-gray hematitic spherules would then be some type of vapor condensation spherules (including accretionary lapilli). A similar interpretation is possible for deposits in the Home Plate area, Gusev Crater. Unlike on the dry and atmosphereless Moon, salty impact surge deposits containing spherules should be common, and well-preserved, on Mars.
KW - Mars
KW - history
KW - impact
KW - surge deposit
KW - volcanic
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U2 - 10.1016/j.jvolgeores.2008.01.044
DO - 10.1016/j.jvolgeores.2008.01.044
M3 - Article
AN - SCOPUS:55649095529
SN - 0377-0273
VL - 177
SP - 755
EP - 759
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
IS - 4
ER -