Submitted by Colin Robins (Claremont McKenna, Pitzer, and Scripps Colleges)
Team Dirt had an intense but wonderful summer getting started on their paleoenvironmental analysis of unique calcic and petrocalcic horizons in southern Nevada. Ethan Conley, Kurt Crandall, India Futterman, and Penelope Vorster worked with Colin Robins to measure sections, describe soil profiles, and collect soil and sediment samples from the 4 to 5 million-year-old soil geomorphic surface of Mormon Mesa and Flat Top Mesa, Nevada. Despite the 110-degree late-June desert heat and two rattlesnake encounters (one sidewinder and one Mojave green), the team collected over 150 samples and discovered two important new exposures. The new soil-stratigraphic sections will yield new resolution on Mormon Mesa’s geomorphic responses to climate shifts and tectonic events from the Pliocene to the Holocene. While most of Mormon Mesa shares one complex, composite soil profile, the two previously undiscovered sites at Flat Top Mesa exhibit younger, inset soil profiles developed within infilled arroyos that are now juxtaposed immediately adjacent to the older sequence. These younger profiles contain distinct micromorphological features and, critically for paleoclimate analyses, may have experienced fewer episodes of pedogenic carbonate dissolution and reprecipitation.
Having worked frenetically but carefully in Claremont to sort, crush, repackage, section, and ship samples back to their home institutions at Beloit, Mount Holyoke, Pitzer, and Vassar Colleges, the team is now beginning laboratory analyses including soil micromorphology and mineralogy, bulk geochemistry, and stable isotope geochemistry. The team will present preliminary data from these analyses as a joint poster at this year’s annual Geological Society of America Meetings in Indianapolis, Indiana.
Wyoming project students geared up for a day in the field.
Submitted by Brady Foreman (Western Washington University)
Ellen Currano (University of Wyoming), Marieke Dechesne (USGS), Regan Dunn (Field Museum), Brady Foreman (Western Washington University), and six undergraduates performed four weeks of field and laboratory research in southeastern Wyoming examining vegetation and fluvial responses to the Paleocene-Eocene Thermal Maximum (PETM), a major global warming event that occurred 56 million years ago. The research team measured numerous stratigraphic sections through fluvial, deltaic, and lacustrine sediments outside the tiny town of Hanna, Wyoming, and discovered and excavated fossil leaf sites. Students obtained over 500 geochemical samples at the field sites and processed them at the University of Wyoming. These data will help test hypotheses regarding the ancient global carbon cycle. Students also determined the ancient flow directions and conditions of the river and deltas from over 60 paleocurrent measurements, and obtained 30 sandstone samples for determining sediment source areas. The students also learned a new proxy methodology for estimating vegetation structure and density across ancient landscapes. They applied this technique to over 30 distinct stratigraphic levels spanning the PETM, and developed their own projects assessing the spatial variability of vegetation across the paleo-landscapes.
Glacier project students and Amy Myrbo analyzing cores in the LacCore lab.
Submitted by Kelly MacGregor (Macalester College)
Kelly MacGregor (Macalester College) and Amy Myrbo (LacCore, University of Minnesota) and eight Gateway students collected water and sediment transport measurements as well as lake core samples in the Many Glacier region of Glacier National Park, Montana in summer 2018. We spent two weeks in the field collecting data and sampling, and another two weeks at the LacCore laboratory conducting core descriptions and analysis. Students determined that Fishercap Lake was shallow (~1 m deep), and is unlikely to be a significant sediment trap in the valley system. They discovered a layer of gravel below ~50 cm of fine-grained sediment that may represent a period of lake dessication or possibly a major flooding event; radiocarbon dating (ongoing) will help constrain the timing of this event. In addition, Swiftcurrent Lake cores sampled three volcanic ash units from the western U.S., including the Mazama ash (Crater Lake, OR; 7.6 ka) and the Mt. St. Helens J ash (~13.7 ka). Coring along a transect across an inlet delta in Swiftcurrent shows increasing deposition rates with distance from the inlet stream.The students presented their work to Park Rangers, and talked daily with Park visitors during the project. They will be presenting the results of their research at two posters at the Geological Society of America meeting in November 2018.
Sediment Transport And Deposition In Fishercap Lake And The Swiftcurrent Valley, Glacier National Park, Montana, USA
Using Lake Cores To Analyze Sediment Transport And Environmental Change In Swiftcurrent Lake, Glacier National Park, Montana, USA
Keck Alaska 2018 research team standing on a thick sandstone bed of the Valdez turbidites near Meares Glacier at the end of Unakwik Inlet, Prince William Sound, Alaska.
Submitted by Cameron Davidson (Carleton College)
The Keck Alaska team made up of John Garver (Union College) and Cam Davidson (Carleton College), and six students, Will Fisher (Union), Victor Garcia (UT-Austin), Nick Gross-Almonte (Carleton), Alysala Malik (Carleton), Caitlin Noseworthy (St Norbert), and Mollie Pope (Union) spent four weeks in northern Prince William Sound, Alaska. We also had the pleasure of being joined by Caitlin’s research advisor, Professor Tim Flood (St Norbert College) for a few days while we were in Valdez. Our field effort included collecting over 70 samples from the Valdez and Orca Groups of the Chugach-Prince William terrane (CPW) along two roughly N-S transects across the Contact Fault. We already have mineral separates from 22 sandstones, with more in the pipeline, and have sent 36 volcanic and plutonic samples to the Hamilton Analytical Laboratory for whole-rock geochemistry. Will Fisher, Alysala Malik, and Nick Gross-Almonte will be using U-Pb zircon dating of detrital zircon from sandstone samples collected along the N-S transects to help constrain strike slip motion across various faults associated with the Contact Fault and to test if the rocks of the CPW were deposited in California and subsequently transported to Alaska, or if they more or less formed in place where we find then today. Mollie Pope is focusing on conglomerates found in the Orca turbidites and is using U-Pb zircon dating of detrital zircon from sandstone clasts to test models of sediment recycling in the CPW basin. Caitlin Noseworthy is using whole rock geochemistry from basaltic volcanic rocks associated with the so-called Glacier Island Ophiolite to test tectonic models for the emplacement of the ophiolite into the Orca turbidites, and Victor Garcia is using U-Pb dating and whole rock geochemistry to determine the age and origin of the Cedar Bay pluton that was emplaced into the CPW late(?) in its history. If all goes well we plan to present this work at the spring GSA Cordilleran Section meeting in Portland in 2019.
Catalina Gateway participants map tectonic blocks in mélange above clouds using digital mapping software.
Submitted by Zeb Page (Oberlin College)
Nine students along with Zeb Page, Nicollette Mitchell, and Clara Margaret Flood (Oberlin) and Jade Star Lackey (Pomona) used the variability of major and trace elements in garnets from metamorphic rocks on Catalina Island (California) to study fluid flow and melting process in subduction zones. Each group studied samples collected during the 2012 Catalina Keck Project using electron microscopy at Oberlin College, before traveling to California to conduct field work guided by their preliminary lab results. Finally, trace element analyses of garnet and lawsonite were conducted at Pomona College. The students broke up into three research teams each focusing on a particular sample of interest. The “Bee-Gees” looked at major and trace element records of slab melting in a subduction zone through the lens of a garnet amphibolite with large, 3cm diameter garnets. They found that major and trace element patterns were similar in a variety of samples with different garnet sizes and mineralogies, suggesting that similar processes had a hand in their formation. “Eastern Blok” studied metasomatic fluid flow in subduction zones using garnets in a tectonic block with a mineralogically distinct alteration rind, finding that garnet compositions can be used to distinguish garnets formed before, during, and after the influx of fluids. “Schis-toe-city” used trace-element mapping of garnets, a comparison of garnet and lawsonite rare earth element compositions, and back-scattered electron petrography to document the complicated polymetamorphic history of a blueschist block. Each of the three teams submitted an abstract to the fall national meeting of the American Geophysical union, and will present their results in Washington D.C. this December.