Team Yellowstone at “The Narrows” of the Yellowstone River.
Team Yellowstone had a successful and productive field season. We focused on the Gallatin River and Blacktail Deer Creek. The team managed frigid mornings, sweltering afternoons, hail, freezing rivers, driving rain, lightning, elk, grizzly bears, and temperamental survey equipment with aplomb. Using a GPS and a Total Station we surveyed more than 150 channel/valley cross sections and over 10 km of long profiles, accumulating over 13,000 points in the process. The team characterized the channel bed material by pebble counts, measuring over 25,000 pebble diameters! In addition to surveying, the team described stratigraphic sections and collected charcoal and wood samples for radiocarbon analyses. The team also collected over 50 soil probes for short-lived radionuclide analyses. The team met with the Park Archeologist to learn about cultural resources in Yellowstone. This included instructions on how to identify cultural materials in stratigraphic sections. The team also explored some of the thermal features of Yellowstone, did some wildlife viewing in the Lamar Valley, and learned about landslide hazards at Earthquake Lake. Back at Whitman, the team went to work on digitizing all of the field data and preparing samples for lab analyses. Currently, everyone is back at their home institutions and excited to dig into the data!
The Keck Wyoming team made up of Michael D’Emic (Adelphi University), Simone Hoffmann (New York Institute of Technology) and Brady Foreman (Western Washington University), as well as six students, Grant Bowers, Michael Ford, Richard Gonzalez, Danika Mayback, Emily Randall, and Isaac Sageman spent four weeks in the northern Bighorn Basin, Wyoming collecting 56 million-year-old fossils and placing them into geological context. We also had the pleasure to join Amy Chew and Ken Rose for a few days at their field site in the southern Bighorn Basin, visit the Illinois State University’s Geology Field Camp lead by David Malone, and get a behind the scenes tour at the Draper Natural History Museum in Cody by their Assistant Curator Corey Anco. Our field effort included collecting more than 100 crocodiles, turtles, and mammal fossils, including the early mammal Coryphodon, the first mega-herbivore after the Cretaceous-Paleogene extinction and the focus of our study. We already prepared 10 Coryphodon specimens in our field laboratory for histological thin sections. Grant Bowers and Danika Mayback will be using these and other histological samples to study changes in growth in Coryphodon through a major global warming event, the Paleocene-Eocene Thermal Maximum (PETM). Together with Richard Gonzalez’s project on finding relevant proxies for body mass estimates, these studies will help understand the growth mechanisms underlying body size evolution of Coryphodon in relation to environmental change. We also measured 15 stratigraphic sections and collected more than 90 sediment samples for isotope and pollen analysis from our new Coryphodon sites. Isotopes analyses conducted by Isaac Sageman will help place our localities in relation to the PETM and provide proxies for temperature and precipitation. Pollen analyzed by Michael Ford will help evaluate changes in plant distribution (and potential food resources of Coryphodon) throughout the PETM. Emily Randall will be investigating soil morphology in our stratigraphic sections. We plan to present this work at the spring GSA Rocky Mountain Section meeting in Utah in 2020.
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.
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.
