7 research outputs found
Orbital Forcing of Martian Climate Revealed in a South Polar Outlier Ice Deposit
Deciphering paleoclimate on Mars has been a driving goal of Martian science for decades. Most research has addressed this issue by studying Mars' large polar layered deposits (PLDs) as a paleoclimate proxy, but the certainty to which we know the link between climate and orbit is debated. Here, we instead consider the record of other, smaller ice deposits located within craters separated from the PLDs using images from NASA's High Resolution Imaging Science Experiment camera and signal processing techniques. We show that the climate record in Burroughs Crater (72.3°S, 116.6°E) contains robust evidence of orbital forcing, with periodicities that have wavelengths of 15.6 and 6.5 m. The ratio of these dominant wavelengths is 2.4, the same as the ratio between the periods of Mars' obliquity changes and orbital precession. This result suggests orbital control of recent Mars climate, and would imply an average ice accumulation rate of 0.13 mm/yr over 4.5 Myr in this region. © 2022. The Authors.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Reexamining the Potential to Classify Lava Flows From the Fractality of Their Margins
Can fractal analysis of a lava flow's margin enable classification of the lava's morphologic type (e.g., pāhoehoe)? Such classifications would provide insights into the rheology and dynamics of the flow when it was emplaced. The potential to classify lava flows from remotely-sensed data would particularly benefit the analysis of flows that are inaccessible, including flows on other planetary bodies. The technique's current interpretive framework depends on three assumptions: (1) measured margin fractality is scale-invariant; (2) morphologic types can be uniquely distinguished based on measured margin fractality; and (3) modification of margin fractality by topography, including substrate slope and confinement, would be minimal or independently recognizable. We critically evaluate these assumptions at meter scales (1–10 m) using 15 field-collected flow margin intervals from a wide variety of morphologic types in Hawaiʻi, Iceland, and Idaho. Among the 12 margin intervals that satisfy the current framework's suitability criteria (e.g., geomorphic freshness, shallowly-sloped substrates), we show that five exhibit notably scale-dependent fractality and all five from lava types other than ‘a‘ā or pāhoehoe would be classified as one or both of those types at some scales. Additionally, an ‘a‘ā flow on a 15° slope (Mauna Ulu, Hawaiʻi) and a spiny pāhoehoe flow confined by a stream bank (Holuhraun, Iceland) exhibit significantly depressed fractalities but lack diagnostic signatures for these modifications. We therefore conclude that all three assumptions of the current framework are invalid at meter scales and propose a new framework to leverage the potential of the underlying fractal technique while acknowledging these complexities. © 2021. American Geophysical Union. All Rights Reserved.6 month embargo; first published: 25 March 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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Burial Depths of Extensive Shallow Cryptomaria in the Lunar Schiller–Schickard Region
Quantifying the volumes and geologic nature of lunar volcanic eruptions is important for constraining the thermal and geologic evolution of the Moon. Cryptomaria are effusive, basaltic lava flows on the Moon that were subsequently buried, and therefore hidden, by higher-albedo basin and crater ejecta. Radar offers the ability to probe the subsurface for geologic units not otherwise apparent at the surface. We use Arecibo/Green Bank Observatory and Lunar Reconnaissance Orbiter Mini-RF radar data sets to characterize maria and cryptomaria within the Schiller–Schickard region. We find significant variability in the radar backscatter across the region that does not correspond to previously mapped boundaries of maria and cryptomaria in the literature. We use the characteristic low backscatter (due to the attenuating nature in radio waves of some basaltic minerals) to analyze the distribution of cryptomaria. We use the reduction in radar backscatter to estimate burial depths of cryptomaria across the area. We present a new map of Schiller–Schickard cryptomaria and the local variability in the thicknesses of the light plains that bury the basalts. We find burial depths ranging from >100 m in the deepest areas to just a few to tens of meters in areas with shallow cryptomaria (particularly prominent in the southeast). These areas are generally contiguous with maria, allowing us to track mare lava flow units into the subsurface at mare/highland margins. We propose that ∼67% of the region contains surface or buried basaltic volcanism, which represents over twice (2.7× increase) the areal extent of cryptomaria reported in previous studies. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]