Seasonal melting and the formation of sedimentary rocks on Mars, with predictions for the Gale Crater mound

A model for the formation and distribution of sedimentary rocks on Mars is proposed. The rate-limiting step is supply of liquid water from seasonal melting of snow or ice. The model is run for a O(10^2) mbar pure CO2 atmosphere, dusty snow, and solar luminosity reduced by 23%. For these conditions snow only melts near the equator, and only when obliquity >40 degrees, eccentricity >0.12, and perihelion occurs near equinox. These requirements for melting are satisfied by 0.01-20% of the probability distribution of Mars' past spin-orbit parameters. Total melt production is sufficient to account for aqueous alteration of the sedimentary rocks. The pattern of seasonal snowmelt is integrated over all spin-orbit parameters and compared to the observed distribution of sedimentary rocks. The global distribution of snowmelt has maxima in Valles Marineris, Meridiani Planum and Gale Crater. These correspond to maxima in the sedimentary-rock distribution. Higher pressures and especially higher temperatures lead to melting over a broader range of spin-orbit parameters. The pattern of sedimentary rocks on Mars is most consistent with a Mars paleoclimate that only rarely produced enough meltwater to precipitate aqueous cements and indurate sediment. The results suggest intermittency of snowmelt and long globally-dry intervals, unfavorable for past life on Mars. This model makes testable predictions for the Mars Science Laboratory rover at Gale Crater. Gale Crater is predicted to be a hemispheric maximum for snowmelt on Mars.Comment: Submitted to Icarus. Minor changes from submitted versio

Geophysical Investigations of Near-Surface Structure on the Earth and Mars

I use remote sensing and active seismic methods to investigate near-surface structure on the Earth and Mars. These studies provide insight into styles of crustal deformation acting on continental margins in regions of extension, as well as paleoclimates that shaped the polar ice caps on Mars. I map the overall structure of the ice-rich Planum Boreum deposit at the north pole of Mars using 178 orbits of Mars Advanced Radar for Subsurface and Ionosphere Sounding data, and find no deflection of the lithosphere beneath the ice load. Bright, laterally extensive subsurface reflectors in the radargrams define the surface underlying Planum Boreum, as well as the interface between the two main units, the stratigraphically older Basal Unit and the stratigraphically younger North Polar Layered Deposits. The volumes of these units, and the overall edifice, are determined to the greatest accuracy possible to date. On Earth, I use a GPS campaign network in the state of Jalisco to investigate tectonic motion and interseismic deformation in the area. The consistent magnitude and direction of station velocities on the Jalisco Block suggest that it is moving rigidly with respect to North America. We constrain extension across the bounding fault zones of the block to values that are slow compared to relative rates of motion at nearby plate boundaries. I study another continental rift zone, in the Ross Sea, Antarctica, with refraction seismic data collected during research cruise NBP0701. I construct velocity models from 71 sonobuoys that detect deep structure in the oceanic crust of the Adare Basin and the crust of the Northern Basin, which lies to the south on the continental shelf. We demonstrate the importance of using multi-channel seismic data to correct for ocean currents and changes in ship navigation, the finite-difference modeling techniques necessary for accurately determining 1D velocity profiles for each sonobuoy, and for tying true velocities to the multi-channel seismic images of subsurface structure. We construct 2D velocity profiles using widely spaced sonobuoys in the Adare Basin, and using overlapping sonobuoys along some lines in both basins, and across the shelf break, to investigate crustal structure in the region. Detection of the Moho at 5.5 km below the seafloor by one sonobuoy suggests relatively thin oceanic crust in the Adare Basin, and flat velocity contours across the margin suggest continuity in crustal structure between the two basins

Time, tides and tectonics on icy satellites

In the outer solar system, we cannot use the radiometric dating techniques applied in terrestrial geology. We also lack the detailed understanding of the correspondence between crater size-frequency distributions and absolute ages that lunar samples has given us in the inner solar system. Additionally, many geologically interesting icy satellites are insufficiently cratered to yield precise relative ages. Thus we must find other ways to construct geological chronologies In this work I develop two techniques. The first compares the linear tectonic features covering Jupiter's moon Europa to modeled tensile fractures resulting from tidal stresses due to the nonsynchronous rotation (NSR) of the satellite's decoupled, icy, lithospheric shell. The amount of shell rotation required to align a feature with the stress field resulting from NSR is used as a proxy for time. This translation is potentially convolved with a phase lag between the tidal potential and the stresses it induces, resulting from the shell's partially viscous response to the NSR forcing. The geography of individual lineaments is found to be no more consistent with NSR stresses than chance would predict, however, the ensemble of global lineaments displays a non-uniform apparent rate of lineament formation throughout the time period recorded by the surface. This non-uniformity may be explained either by steady state fracture formation, activity, quiescence and erasure, or by a transient episode of tectonics. The second technique encodes the myriad superposition relationships evident between Europa's tectonic features as a directed graph enabling algorithmic analysis. The observed superposition relationships are generally insufficient to construct complete stratigraphic stacks, but we can calculate the degree to which they corroborate or contradict another hypothesized order of formation. We find that they tend to corroborate the hypothesis that the lineaments are tensile fractures due to prograde NSR stresses. Together these results offer cautious support for the idea that Europa's shell rotates independently of its silicate interior, and demonstrate techniques useful in comparing tectonic features on other icy satellites to hypothesized mechanisms of formation

PUDL Raw EIA Form 861

<p>Raw US Energy Information Administration (EIA) Form 861 Data, archived from <a href="https://www.eia.gov/electricity/data/eia861/">https://www.eia.gov/electricity/data/eia861/</a></p> <p>This archive contains raw input data for the Public Utility Data Liberation (PUDL) software developed by <a href="https://catalyst.coop">Catalyst Cooperative</a>. It is organized into <a href="https://specs.frictionlessdata.io/data-package/">Frictionless Data Packages</a>. For additional information about this data and PUDL, see the following resources:</p> <ul> <li><a href="https://github.com/catalyst-cooperative/pudl">The PUDL Repository on GitHub</a></li> <li><a href="https://readthedocs.org/projects/catalystcoop-pudl/">PUDL Documentation</a></li> <li><a href="https://zenodo.org/communities/catalyst-cooperative/">Other Catalyst Cooperative data archives</a></li> </ul> <p> </p&gt

PUDL Raw EIA Form 860M

<p>Raw US Energy Information Administration (EIA) Form 860M data, archived from <a href="https://www.eia.gov/electricity/data/eia860m/">https://www.eia.gov/electricity/data/eia860m/</a></p> <p>This archive contains raw input data for the Public Utility Data Liberation (PUDL) software developed by <a href="https://catalyst.coop">Catalyst Cooperative</a>. It is organized into <a href="https://specs.frictionlessdata.io/data-package/">Frictionless Data Packages</a>. For additional information about this data and PUDL, see the following resources:</p> <ul> <li><a href="https://github.com/catalyst-cooperative/pudl">The PUDL Repository on GitHub</a></li> <li><a href="https://readthedocs.org/projects/catalystcoop-pudl/">PUDL Documentation</a></li> <li><a href="https://zenodo.org/communities/catalyst-cooperative/">Other Catalyst Cooperative data archives</a></li> </ul> <p> </p&gt