Team Wyoming in the Hanna Basin.
Team Wyoming measured 600+ meters of stratigraphic section comprising early Paleogene lakes, rivers, swamps, and deltas, including >70 measurements of paleodrainage conditions. The group constrained paleo-vegetation structure spanning global warming event (PETM) from about 100 measurements of fossil plant material. Their findings also included a new plant macrofossil site in Hanna Basin. In the laboratory, the group complete 400+ stable isotope measurements constraining carbon cycle variability from ~60 Ma through ~54 Ma, and identified the PETM global warming event using stable carbon isotopes.
Students collaborated with researchers at Chicago Field Museum and USGS. They also presented 5 abstracts as posters at the GSA Regional meeting in Manhattan Kansas and one lucky student presented at EGU in Vienna Austria.
Team Utah enjoying some shade during a break on the hill slopes.
Caroline, Charley, Curtis, and Madison have all been pushing hard to finish theses, classwork, and preparations for the upcoming GSA Cordilleran Section meeting in Portland, Oregon. They have tackled a range of questions involving the evolution of normal fault transfer zones, thinking about how fault segments propagate laterally and vertically through sedimentary strata, deforming the rock around them as fault segments interact.
Charley Hankla (College of Wooster) analyzed structural data from fractures within the transfer zone to put together a hypothesis of transfer zone evolution. Although most fractures across the transfer zone display orientations subparallel to the dominant fault segments, suggesting synchronous formation of faults and those fractures, Charley suggests that a major fault within the transfer zone grew northward over time, impacting the stress field around the fault, forming fractures that deviate from the dominant fracture orientation.
Caroline McKeighan (Trinity University) used a combination of fracture analysis based on 3D computer modeling of Unmanned Aerial Vehicle (UAV) video data and field-based structural data to develop a better picture of the distribution of fractures both horizontally and vertically across the transfer zone relative to a location where a single fault segment accommodates all extension. She found that where a single fault accommodates all extension, fracturing is intense but localized adjacent to the fault, but where several faults accommodate strain, in the transfer zone, fracturing is less intense but well-distributed within the rock between faults.
Curtis Segarra (Trinity University) used 2D geomechanical modeling to simulate the propagation of a normal fault through sedimentary strata. He found that the presence of layering allows for simultaneous, but discontinuous, plastic failure at multiple locations ahead of the propagating fault tip. Inter-layer stress accumulation is hindered by an increased number of layers, but regions of elevated stress occur further ahead of a propagating fault tip with more layers. His results indicate a predictable pattern of fracturing ahead of a propagating fault within layered strata.
Madison Woodley (Mt. Holyoke College) used a combination of field-based fracture orientation data and statistical cluster analysis to evaluate fracturing within the transfer zone relative to fracturing that occurred where only a single fault accommodates all extension. She found that fracturing at both localities have similar orientations, suggesting formation within the same stress field and at the same time. Madison also found that another fracture set in the transfer zone deviates from the dominant fracture set, which she hypothesizes has resulted in more strain accommodate where that set is present. Importantly, she documented significant clustering of fractures across the transfer zone, but at the single fault segment locality, fractures were more regularly spaced.
These results have implications for fracture network evolution and the nature of subsurface fluid flow in similar structural settings worldwide. We’re looking forward to presenting these data at Cordilleran Section GSA in Portland, Oregon, from May 14 – 17.
Watch the video of pre-field preparations.
Team Nevada (L to R: Kurt Crandall, Ethan Conley, Penelope Vorster, and India Futterman) prepare to measure section and describe profiles at Mormon Mesa.
Team Nevada discovered two new soil-stratigraphic exposures with younger, presumably late-Pleistocene soil profiles inset into the older Miocene-Pliocene Mormon Mesa soil profile. Micromorphological and stable isotopic analysis of samples from these profiles may provide new resolution into the geomorphic and climatic history of the region. Team Nevada dutifully headed into the field at 5 am every morning, yet still braved temperatures of up to 114° by 2 pm, and had close encounters with a sidewinder and a Mojave green on their final day. In all, Team Nevada collected over 130 samples from profiles and soil surface survey transects. Student thesis research, now in the manuscript stage for peer-reviewed journal submission, has yielded new or revised models for the genesis of pedogenic ooids and pedogenic carbonate laminae. Geochemical data from surface transects, in tandem with data from external collaborators, may also help reconstruct the history of Pleistocene-Holocene dust flux and micro-playa development across the Mormon Mesa surface.
Team members examining core in the LacCore facility
Eight Gateway students spent two weeks in the wilds of Glacier National Park in July 2018. They saw bears and moose almost every day, including waking up one morning to Park Rangers yelling “Bear in the camp”! The team collected lake sediment cores from two lakes (Fishercap and Swiftcurrent). In Swiftcurrent Lake the cores included volcanic ash units from the Mt. Mazama eruption (~7,600 years ago), and older eruptions from Glacier Peak and Mt. St. Helens. Students and project directors presented two posters at the Fall GSA meeting, and Kelly MacGregor and Amy Myrbo presented their model of Gateway projects at the Fall AGU meeting.
Team Catalina at their posters at the Fall AGU meeting in Washington DC.
Students started the project in Oberlin, learning about metamorphic geology, and collecting major element data using SEM/EDS. The then moved to the West Coast, visiting field sites on Catalina and collecting additional samples based on observations made in Oberlin. The final phase of the project took place at Pomona College where students collected trace element data on garnets, synthesized data, wrote abstracts, drafted figures, and made posters. Finally, most of the students came together to present on their posters at AGU. While at the meeting, the students had lunch with two prominent researchers of their field area and their graduate students and were able to discuss their results in a more relaxed environment.
Nine students collaborated on three posters. There were able to use rock textures observed by SEM, major and trace element analyses to show similar metamorphic histories preserved in garnet-hornblende of different textures and with and without plagioclase. A second team showed evidence of polymetamorphism in a garnet-blueschist block with late lawsonite. The their team was able to show different but overlapping metamorphic histories from garnets in a tectonic block and a texturally-late metasomatic rind.