Browsing by Author "Siebach, Kirsten"
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Item Differences between modern and ancient Martian grain size distributions may reveal different paleoatmospheric conditions and provenance(Rice University, 2023) Preston, Sarah Lucille; Siebach, KirstenGrain size distributions in eolian (wind-blown) deposits encode information about the atmospheric conditions that enabled their transport and deposition, and grain shape encodes information about provenance and postdepositional processes. Gale crater is a ~3.7 Ga impact crater with a vast diversity of exposed sedimentary strata indicative of a varied depositional history during the ear ly Hesperian epochs (Banham et al., 2018). The Stimson sandstone is a ~3 Ga unit of eolian sandstone in Gale crater that appears to have a coarser grain size distribution than the nearby Bagnold Dunes, an active dune field (Banham et al., 2018; Weitz et al., 2018). In this work, I hypothesize that the Martian paleoatmosphere had a different density than Mars’ current atmosphere, and that the source of the Stimson sandstone may have been more coarse than the source of the Bagnold dunes, leading to ancient sandstones with different grain size distributions than modern active sand dunes. To approach this question, I analyze images from the Mars Science Laboratory (MSL) Curiosity’s Mars Hand Lens Imager (MAHLI) and Remote Micro Imager cameras to determine the grain size distribution of targets. Additionally, I qualitatively describe grain shape and appearance, including roundedness, sphericity, pitting, and color, along with chemical composition where possible, to determine whether differences in grain size distributions can be attributed to provenance. From these results, I explore the role of paleoclimate and provenance in generating the grain size distribution seen in the Stimson. These results will help determine the provenance of the Stimson, as well as ancient Martian atmospheric conditions, in turn providing insights into the wet-to-dry transition and, potentially, the habitability of ancient Mars.Item Final Report on Degradation of "Scholar's Way" for the Museum of Fine Arts, Houston(2023-05-02) Rajan, Bavan; Siebach, KirstenThe purpose of this project is to understand the chemical processes that contribute to the degradation of “Scholar’s Way,” a trio of heavily altered basalt sculptures at the Museum of Fine Arts, Houston (MFAH). They were installed at the MFAH in 2020 after their creation in 2018 by South Korean artist Byung Hoon Choi. The work sits in a shallow pond in the museum’s sculpture garden, exposed to Houston’s warm humid climate and regular HCl from treatments to prevent algae growth. After less than 3 years, fragments of the sculptures have been lost, the surfaces have altered in coloration, and salt-like minerals regularly precipitate on the sides of the sculptures. The mineralogy of the sculptures and associated precipitates can inform the MFAH of how and why “Scholar’s Way”, as well as other outdoor sculptures, might be degrading, as well as what steps they can take to preserve their artwork. Visual and Near Infrared Spectroscopy, speciation modeling from the pond’s water chemistry, Electron Dispersive X-ray spectroscopy, and Electron Probe Microanalysis were used to determine 1) the chemical composition of the water features and sculptures, which reveal plausible degradation mechanisms, 2) potential ongoing mineral dissolution, and 3) the drivers of salt precipitation from the pond. These results, along with recommendations to preserve the work, have since been presented to the MFAH in the attached executive summary and technical report.Item The Fate of Nitrogen in Highly Reducing Magmatic Systems: Implications for the Parent Body Partial Melting and Magma Ocean Crystallization in the Inner Solar System(2021-01-22) Falksen, Emily; Dasgupta, Rajdeep; Siebach, KirstenEvolution of nitrogen (N), a life-essential volatile element, in highly reduced magmatic systems is key for the origin of N on terrestrial planets formed via accretion of reduced chondritic parent body materials, planetesimals, and embryos, which themselves underwent partial or complete differentiation. To investigate the stability of N-bearing minerals in partially molten silicate-rich systems as well as solubility of nitrogen in silicate melts and silicate minerals, we performed laboratory experiments at pressures (P) of 1.5-3.0 GPa and temperatures (T) of 1300-1600 °C in a graphite capsule with oxygen fugacity conditions ranging from IW – 5.87 to IW – 8.35. All experiments yielded silicate melt + nierite (Si3N4) + Fe-rich alloy melt + N-rich vapor ± sinoite ± cpx. Sinoite was restricted to above 1400-1500 °C, while cpx was restricted to below these temperatures. Solubility of nitrogen and Nitrogen Concentration at Silicon-Nitride Saturation (NCNS) increases with increasing pressure and temperature and ranges between 3.57 and 9.46 wt %. Using high pressure N solubility data from this study and similar solubility data for silicate melts at ambient and low pressures, we derive the following N solubility model N(ppm)=〖P_(N_2)^0.5*exp〗(8.12(±1.56)+(1000*(-12.23(±2.81)-0.61(±0.29) P_total^0.5 ))/T-1.45(±0.06)(∆IW)) +P_(N_2 )*exp(7.96(±0.48)-18.59(±7.17) X_MgO+2.57(±0.94)(NBO/T)) where T is temperature in K, P_(N_2 ) is partial pressure of N2 in GPa, P_(total ) is the equilibrium pressure in GPa, IW is the log oxygen fugacity relative to the IW (oxygen fugacity imposed by coexistence of Iron, Fe, and iron oxide, wüstite) buffer, XMgO is the mole fraction of MgO in the silicate melt, and NBO/T is total non-bridging oxygen relative to tetrahedral cations (NBO/T = (2 × Total O)/T – 4, where T = Si + Ti + Al + Cr + P (e.g. (Mysen et al., 1982)). Solubility of nitrogen in cpx was measured to between 1.51 and 2.05 wt% and resulted in cpx/silicate melt partition coefficients for nitrogen of ~0.4 to ~0.2. These cpx/silicate melt nitrogen partition coefficients (DNcpx-melt) are much larger than that previously estimated at more oxidizing conditions, suggesting N maybe less incompatible during thermal processing of rocky reservoirs at extremely reducing conditions. Similar to previous studies, N also shows lithophile behavior at extremely reduced, graphite saturated conditions, with partition coefficient of N between Fe-rich alloy melt and silicate melt to be between 0.2 and 0.7 at our experimental conditions. While partition coefficient of N between cpx and Fe-rich alloy melt was found to be between 1.6 and 2.1, but there lacks enough data to determine a dependence with P-T-fO2. The application of our N solubility data and model suggests that mobilization of N from the deeper, partially molten reservoir to shallower reservoirs is possible in reduced planetesimals and internally differentiated meteorite parent bodies. Similarly, enrichment of N in the planetary atmosphere may be a result of gradually more oxidizing accreting materials, which would lead to N being more and more incompatible during internal and external magma ocean processing of rocky bodies.Item When is Drone Photogrammetry Useful for Flood Risk Assessment?(Rice University, 2021-05) Sheldon, Jessica; Siebach, KirstenDrone technology and the high resolution datasets it enables stand to revolutionize our understanding of the Earth’s surface. This research is Houston specific, and studies how drones can be used to systematically collect photogrammic data to detect environmental changes, and how that data is valuable for flood planning purposes. This data is the culmination of three years of research. Prior to this year, the focus has been learning to fly the drone, learning the image processing Pix4D and ArcMap 10.5, and creating a workflow for accurate image collection processing. This study has collected three separate datasets of the study area at Buffalo Bayou using a DJI Phantom 4 Pro drone. This data was then processed and modeled in Pix4D to create digital elevation models (DEMs). The DEMs were calibrated and analyzed in GIS, and compared to the publicly available 2018 LIDAR data. Our research catalogs high resolution change over time of our study area, and documents the process of how drones can be used to systematically observe change over time. Additionally, our data highlights the difference in resolution between a low elevation drone flight versus a higher elevation LIDAR scan.