5:15 PM - 7:15 PM
[MIS18-P02] Grain size distribution analyses of rootless tephra far-sighting future Mars landing mission
Keywords:Mars, rootless cone, rootless tephra, grain size distribution
Hydrothermal systems considered widely existed/existing on Mars are expected to be habitable environments. Researchers believe Mars was once wet due to the existence of an ocean three billion ago and subsurface ice today. If volcanic activity occurs in that environment, hydrothermal systems may be formed. Such possible hydrothermal systems are among the survey candidates for future Mars landing explorations.
Rootless cones, formed in hydrothermal systems, are potential targets for habitable environment exploration on Mars. They are small volcanic landforms formed by repeated explosions caused by lava covering water-logged sediments. On Mars, for example, they are found in Central Elysium Planitia and Amazonis Planitia (Greeley and Fagents, 2001). Cone edifices are composed of fragments of lava and water-logged sediments (rootless tephra). Therefore, it is possible to investigate the former water-logged sediments (substrates) on the surface, which are difficult to reach because they are beneath the covering lava. In other words, we can easily access past subsurface information that may contain information about past habitable worlds.
It has been reported that the substrates are found heterogeneously in the cone edifice and more abundant in particular stratigraphic layers (Hamilton et al., 2017). Rootless cone edifices comprise alternating layers of lapilli-size pyroclast layers and are partially constituted by possible pyroclastic density current deposits (PDC layers). Hamilton et al., 2017 described that the PDC layer is rich in substrates. However, this description is not derived from a direct measurement and extrapolates based on the grain size distribution of rootless tephra. Furthermore, this report is for the specific rootless cones, Cone 53 in Raudholar, Iceland. Therefore, we reveal where the stratigraphy of the cone edifice has more basement deposits in rootless tephra to contribute to future Mars exploration.
In this study, we measured the grain size distribution of rootless tephra collected in Iceland. 40 rootless tephra samples were collected from 10 cones at five sites (Kopasker, Lake Myvatn, Laxardalur, Landbrot, and Raudholar). The grain size distribution of the collected rootless tephra was measured by dry-sieving from -4Φ to 3Φ at 1Φ intervals. We used GRADISTAT v8.0 (Blott and Pye, 2001) for grain size analysis.
The grain size analysis showed differences in mean grain size, sorting, kurtosis, and skewness due to cone formation environments and stratigraphy differences. The majority of rootless tephra samples have poor sorting. On the other hand, several samples were well-sorted. In addition to a preliminary report of the results of the grain size analysis, we will discuss the appropriate outcrops for rootless tephra investigations on Mars.
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Greeley and Fagents, 2001, JGR, 106(E9), 20527-20546.; Hamilton et al., 2017, Bull. Volcanol., 79:11.; Blott and Pye, 2001, Earth Surf. Process. Landforms 26, 1237–1248.
Rootless cones, formed in hydrothermal systems, are potential targets for habitable environment exploration on Mars. They are small volcanic landforms formed by repeated explosions caused by lava covering water-logged sediments. On Mars, for example, they are found in Central Elysium Planitia and Amazonis Planitia (Greeley and Fagents, 2001). Cone edifices are composed of fragments of lava and water-logged sediments (rootless tephra). Therefore, it is possible to investigate the former water-logged sediments (substrates) on the surface, which are difficult to reach because they are beneath the covering lava. In other words, we can easily access past subsurface information that may contain information about past habitable worlds.
It has been reported that the substrates are found heterogeneously in the cone edifice and more abundant in particular stratigraphic layers (Hamilton et al., 2017). Rootless cone edifices comprise alternating layers of lapilli-size pyroclast layers and are partially constituted by possible pyroclastic density current deposits (PDC layers). Hamilton et al., 2017 described that the PDC layer is rich in substrates. However, this description is not derived from a direct measurement and extrapolates based on the grain size distribution of rootless tephra. Furthermore, this report is for the specific rootless cones, Cone 53 in Raudholar, Iceland. Therefore, we reveal where the stratigraphy of the cone edifice has more basement deposits in rootless tephra to contribute to future Mars exploration.
In this study, we measured the grain size distribution of rootless tephra collected in Iceland. 40 rootless tephra samples were collected from 10 cones at five sites (Kopasker, Lake Myvatn, Laxardalur, Landbrot, and Raudholar). The grain size distribution of the collected rootless tephra was measured by dry-sieving from -4Φ to 3Φ at 1Φ intervals. We used GRADISTAT v8.0 (Blott and Pye, 2001) for grain size analysis.
The grain size analysis showed differences in mean grain size, sorting, kurtosis, and skewness due to cone formation environments and stratigraphy differences. The majority of rootless tephra samples have poor sorting. On the other hand, several samples were well-sorted. In addition to a preliminary report of the results of the grain size analysis, we will discuss the appropriate outcrops for rootless tephra investigations on Mars.
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Greeley and Fagents, 2001, JGR, 106(E9), 20527-20546.; Hamilton et al., 2017, Bull. Volcanol., 79:11.; Blott and Pye, 2001, Earth Surf. Process. Landforms 26, 1237–1248.