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41 results on '"Hajek, Elizabeth A."'

13. Rivers in reverse: Upstream-migrating dechannelization and flooding cause avulsions on fluvial fans

Author

Edmonds, Douglas A., primary, Martin, Harrison K., additional, Valenza, Jeffery M., additional, Henson, Riley, additional, Weissmann, Gary S., additional, Miltenberger, Keely, additional, Mans, Wade, additional, Moore, Jason R., additional, Slingerland, Rudy L., additional, Gibling, Martin R., additional, Bryk, Alexander B., additional, and Hajek, Elizabeth A., additional

Published
2022
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16. StraboSpot Workshops and Community Engagement During Covid

Author

Tikoff, Basil, Newman, Julie, J. Douglas Walker, Williams, Randolph T., Roberts, Nicolas, Lusk, Alexander, Phillips, Noah, Chan, Marjorie, Duncan, Casey, Hajek, Elizabeth, Kamola, Diane, and Gordon, Stacia

Abstract

StraboSpot (StraboSpot.org) is a digital data system for collection, management and sharing of geologic data from the macro- to the microscale. Due to the pandemic, it was not possible to organize field-based workshops and fieldtrips in Summer 2020 for demonstrating and eliciting community feedback on the StraboSpot data system. Rather, we decided to run a series of week-long virtual workshops to familiarize practioners with the StraboSpot data system. Workshops were organized by discipline (sedimentology, structural geology, and petrology), each with approximately 100 participants, including U.S.-based and foreign scientists. The daily structure of the workshop was a 2-3 hour block with presentations from several StraboSpot team members, followed by an afternoon help desk. We reassigned participant support costs (originally intended for field-based meetings) to provide a small ($200-250) stipend to U.S.-based participants if they agreed to fully input a data set into StraboSpot and make it publicly available. This approach to increasing engagement – which was not part of original dissemination plan – was extremely successful. Workshop participants who signed up for the stipend were generally very engaged in the data system, provided important feedback on the design and vocabulary, and are highly likely to use StraboSpot in the future. Further, it helped to populate the database. People who received the stipend also presented their StraboSpot projects to the larger group on the last day of the workshop, often with an impressive data set. Because of Covid restrictions on fieldwork in summer 2021, we intend to continue providing stipends for young professionals (graduate students, post-doctoral fellows) to use the StraboSpot system for their thesis or project-based fieldwork. In addition to getting detailed feedback, we hope these testers will become a cohort of motivated users that will teach and encourage others to use the StraboSpot data system.

Published
2021
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17. Significance of channel-belt clustering in alluvial basins

Author

Hajek, Elizabeth A., Heller, Paul L., and Sheets, Benjamin A.

Subjects
Basins (Geology) -- Structure, Geomorphology -- Research, Tectonics (Geology) -- Research, River channels -- Structure, Alluvial fans -- Natural history, Earth sciences
Abstract

The distribution of channel deposits in alluvial basins is commonly used to interpret past changes in climate, tectonics, and sea level. Here we present preliminary evidence that longtime scale (~[10.sup.3]-[10.sup.5] yr) self-organization in fluvial systems may generate structured stratigraphic patterns spontaneously, in the absence of, or independent from, changing basin boundary conditions. A physical experiment and an ancient alluvial succession (Ferris Formation, latest Cretaceous--Paleogene, south-central Wyoming) both show stratigraphy where clusters of many closely spaced channel deposits are separated from each other by extensive intervals of overbank mudstones. Analysis using spatial point process methods shows that channel deposits in both basins are statistically clustered over intermediate basin length scales. In the experiment, external controls (base level, subsidence rate, and sediment/water supplies) were not varied, and therefore not factors in duster formation. Likewise, the ancient system lacks stratigraphic and sedimentologic evidence of external controls on channel clustering. We propose that channel dusters, as seen in this study, reflect a scale of fluvial self-organization that is not usually recognized in ancient deposits. This type of internally generated stratigraphy should be considered when reconstructing tectonic, climate, and sea-level changes from ancient basin fills and when correlating between outcrop belts or subsurface wells. doi: 10.1130/G30783.1

Published
2010

25. Is fine sediment in sandy riverbed deposits a proxy for paleo-sediment supply?

Author

Wysocki, Nathaniel and Hajek, Elizabeth

Subjects
bepress|Physical Sciences and Mathematics, bepress|Physical Sciences and Mathematics|Earth Sciences|Sedimentology, EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Geology, Stratigraphy, bepress|Physical Sciences and Mathematics|Earth Sciences|Geology, bepress|Physical Sciences and Mathematics|Earth Sciences|Geomorphology, bepress|Physical Sciences and Mathematics|Earth Sciences, Geology, Geomorphology, EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Stratigraphy, FOS: Earth and related environmental sciences, Sedimentology, EarthArXiv|Physical Sciences and Mathematics|Earth Sciences, bepress|Physical Sciences and Mathematics|Earth Sciences|Stratigraphy, EarthArXiv|Physical Sciences and Mathematics, EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Geomorphology, Earth Sciences, Physical Sciences and Mathematics, EarthArXiv|Physical Sciences and Mathematics|Earth Sciences|Sedimentology
Abstract

The amount of silt and clay supplied to rivers can be a primary control on the form and dynamics of channel networks, and it affects the distribution and interconnectedness of buried fluvial reservoirs. Despite its importance, it is difficult to reconstruct how much fine sediment was supplied to ancient rivers. The presence of silt and clay accumulations in sandy river deposits is often interpreted as an indication of variability in flow conditions due to seasonal stagnation or tidal influence, but it has not been tested whether these deposits can be used to evaluate how much fine sediment was transported in ancient rivers. Here we report results from a series of experiments designed to evaluate how much clay and silt are preserved in sandy riverbed deposits under constant and variable discharge conditions. Our results demonstrate that 1) clay-silt deposits, including drapes and lenses, form under constant high-discharge conditions, 2) the amount of fine sediment recovered from bed-material deposits is higher when more fine sediment is supplied, and 3) the fraction of fine sediment trapped during bed aggradation is higher than what is retained during bypass conditions. These results confirm that fine-sediment accumulations are not unique indicators of variable flow conditions and that the net retention of clay and silt in sandy riverbed deposits may be more indicative of the overall amount of fine sediment supplied to a river.

Published
2018

27. Palaeocene–Eocene Thermal Maximum prolonged by fossil carbon oxidation

Author

Lyons, Shelby L., primary, Baczynski, Allison A., additional, Babila, Tali L., additional, Bralower, Timothy J., additional, Hajek, Elizabeth A., additional, Kump, Lee R., additional, Polites, Ellen G., additional, Self-Trail, Jean M., additional, Trampush, Sheila M., additional, Vornlocher, Jamie R., additional, Zachos, James C., additional, and Freeman, Katherine H., additional

Published
2018
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34. Shallow marine response to global climate change during the Paleocene‐Eocene Thermal Maximum, Salisbury Embayment, USA

Author

Self‐Trail, Jean M., primary, Robinson, Marci M., additional, Bralower, Timothy J., additional, Sessa, Jocelyn A., additional, Hajek, Elizabeth A., additional, Kump, Lee R., additional, Trampush, Sheila M., additional, Willard, Debra A., additional, Edwards, Lucy E., additional, Powars, David S., additional, and Wandless, Gregory A., additional

Published
2017
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37. Taking the Pulse of the Earth's Surface Systems

Author

Larsen, Laurel, primary, Hajek, Elizabeth, additional, Maher, Kate, additional, Paola, Chris, additional, Merritts, Dorothy, additional, Bralower, Timothy, additional, Montañez, Isabel, additional, Wing, Scott, additional, Snyder, Noah, additional, Hochella Jr., Michael, additional, Kump, Lee, additional, and Person, Mark, additional

Published
2015
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40. Taking the Pulse of the Earth's Surface Systems.

Author

Larsen, Laurel, Hajek, Elizabeth, Maher, Kate, Paola, Chris, Merritts, Dorothy, Bralower, Timothy, Montañez, Isabel, Wing, Scott, Snyder, Noah, Hochella Jr., Michael, Kump, Lee, and Person, Mark

Published
2016

41. Evidence for enhanced fluvial channel mobility and fine sediment export due to precipitation seasonality during the Paleocene-Eocene thermal maximum.

Author

Barefoot, Eric A., Nittrouer, Jeffrey A., Foreman, Brady Z., Hajek, Elizabeth A., Dickens, Gerald R., Baisden, Tramond, and Toms, Leah

Subjects
*SEDIMENTS, *SEDIMENT transport, *ATMOSPHERIC models, *GLOBAL warming, *CONTINENTAL shelf, *FLUVIAL geomorphology
Abstract

The Paleocene-Eocene thermal maximum (PETM) was the most extreme example of an abrupt global warming event in the Cenozoic, and it is widely discussed as a past analog for contemporary climate change. Anomalous accumulation of terrigenous mud in marginal shelf environments and concentration of sand in terrestrial deposits during the PETM have both been inferred to represent an increase in fluvial sediment flux. A corresponding increase in water discharge or river slope would have been required to transport this additional sediment. However, in many locations, evidence for changes in fluvial slope is weak, and geochemical proxies and climate models indicate that while runoff variability may have increased, mean annual precipitation was unaffected or potentially decreased. Here, we explored whether changes in river morphodynamics under variable-discharge conditions could have contributed to increased fluvial sand concentration during the PETM. Using field observations, we reconstructed channel paleohydraulics, mobility, and avulsion behavior for the Wasatch Formation (Piceance Basin, Colorado, USA). Our data provide no evidence for changes in fluvial slope during the PETM, and thus no evidence for enhanced sediment discharge. However, our data do show evidence of increased fluvial bar reworking and advection of sediment to floodplains during channel avulsion, consistent with experimental studies of alluvial systems subjected to variable discharge. High discharge variability increases channel mobility and floodplain reworking, which retains coarse sediment while remobilizing and exporting fine sediment through the alluvial system. This mechanism can explain anomalous fine sediment accumulation on continental shelves without invoking sustained increases in fluvial sediment and water discharge. [ABSTRACT FROM AUTHOR]

Published
2022
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