Faculty Research Highlight
The UO Geobiology research group, headed by Qusheng Jin, recently published a letter in Nature Geoscience, which documents evidence that microbial activity in groundwater is an important source of mobile arsenic. This publication, led by Scott Maguffin, has implications for the safety of well water in the Willamette Valley and other regions with rocks that could feed microbial metabolisms with arsenic.
Edward Davis is a contributing author on a paper in the latest issue of Quaternary research, headed by Danny Gilmour of Portland State University. This study used high-precision AMS radiocarbon dating to determine the ages of the latest megafauna found in the Willamette Valley, here in western Oregon. The dates span the range 15,000 to 13,000 years ago, ending at the onset of the Younger Dryas cold snap but extending well beyond the end of the Missoula Floods, 15,000 years ago.
Gilmour, D.M., Butler, V.L., O’Connor, J.E., Davis, E.B., Culleton, B.J., Kennett, D.J., and Hodgins, G., 2015, Chronology and ecology of late Pleistocene megafauna in the northern Willamette Valley, Oregon: Quaternary Research, v. 83, no. 1, p. 127–136, URL: http://www.sciencedirect.com/science/article/pii/S0033589414001161.
Becky Dorsey is third author on a paper in the February 2015 issue of Geosphere. Howard et al. investigate the early Pliocene river-laid Bullhead Alluvium, exposed along the lower Colorado River downstream of Grand Canyon. They find that it records a massive pulse of sediment aggradation shortly after integration of the Colorado River system. This rapid aggradation likely was caused by: (1) release of sediment stored along upper parts of the lower river corridor; (2) a wave of incision up western Grand Canyon; and (3) accelerated erosion of regolith, surface deposits, and nonresistant Tertiary bedrock on a relict Miocene landscape of the Colorado Plateau.
We’ve had two papers published in the latest issue of Geosphere:
First, the study by Fattaruso, Cooke, and our Becky Dorsey uses 3D boundary-element models to simulate crustal deformation for different interpretations of the geometry of the southern San Andreas fault and smaller secondary faults in southern California. When compared to observed vertical motions in the Coachella Valley, Santa Rosa Mountains, and Mecca Hills, the model results suggest that this section of the fault dips steeply northeast, in contrast to existing models that assume the fault is vertical.
Fattaruso, L.A., Cooke, M.L., and Dorsey, R.J., 2014, Sensitivity of uplift patterns to dip of the San Andreas fault in the Coachella Valley, California: Geosphere, v. 10, no. 6, p. 1235–1246, URL: http://geosphere.geoscienceworld.org/content/10/6/1235.abstract.
Additionally, this study by Mackey (PhD UO 2009), and our own Sammy Castonguay, Paul Wallace, and Ray Weldon, dates the timing of normal faulting and emplacement of a lava field on the margins of ancient Fort Rock Lake. They find evidence for a period of synchronous normal faulting and dike-fed cinder cone activity about 14,000 years ago, with minimal movement since.
Mackey, B.H., Castonguay, S.R., Wallace, P.J., and Weldon, R.J., 2014, Synchronous late Pleistocene extensional faulting and basaltic volcanism at Four Craters Lava Field, central Oregon, USA: Geosphere, v. 10, no. 6, p. 1247–1254, URL: http://geosphere.geoscienceworld.org/content/10/6/1247.abstract.
In this month’s issue of Ecography, Edward Davis published a study that found a consistent mis-match between Ecological Niche Models of mammal species distributions during the Last Glacial Maximum (~20,000 years ago). This work suggests that niche models that are used to predict range shifts under future warming would be better calibrated if they also included data from Pleistocene and Holocene fossil distributions.
Davis, E.B., McGuire, J.L., and Orcutt, J.D., 2014, Ecological niche models of mammalian glacial refugia show consistent bias: Ecography, v. 37, no. 11, p. 1133–1138, URL:http://onlinelibrary.wiley.com/doi/10.1111/ecog.01294/abstract.
In that same issue, Davis has an editorial with Jenny McGuire discussing the future of conservation paleobiogography.
McGuire, J.L., and Davis, E.B., 2014, Conservation paleobiogeography: the past, present and future of species distributions: Ecography, v. 37, no. 11, p. 1092–1094, URL:http://onlinelibrary.wiley.com/doi/10.1111/ecog.01337/abstract.
Our own Gene Humphreys just published a paper in today’s issue of Nature (11/13/2014). The study is about how subduction can remove the mantle lithosphere along a continental margin, leaving it vulnerable to later tectonics and volcanism. The authors describe a type of interaction where subduction propagates along a continental margin that has a subduction zone perpendicular to the margin. Two cases are explored in this paper: the Caribbean-South America margin and the Mediterranean-Moroccan margin.
Prof. Emilie Hooft and M. Sc. Matthew Beachly investigated the magma chamber beneath Newberry volcano in central Oregon.
A 10-minute documentary for the general public explains their research
In 2008, a team of community members, undergraduate and graduate students, technicians, and scientists installed seismometers at short intervals (300 m) along a 30-km line across the volcano to record an explosion. The experiment recorded seismic waves passing around a magma chamber and later waves from energy that passed through the magma body. They combined seismic first-arrival travel-time tomography with waveform modeling of the secondary arrival to constrain the size and melt volume of the magma chamber beneath Newberry. Emilie and Garron Hale (CASIT) worked with two Digital Arts seniors, Adam Paikowsky and Hayden Steinbock, to generate the documentary.
Wherever the Earth’s surface sinks down in response to applied tectonic forces, sediments are deposited to fill the space created by subsidence. Examples of actively subsiding basins include the Ganges River plain in India, the Mississippi Delta, and the San Francisco Bay. As sediments accumulate they store a record of the local environment, depositional processes, and changing climate. Sedimentary deposits also contain a wealth of information about ancient faults, structures, and regional tectonic forces that drive basin subsidence. When sediments are later revealed by uplift and erosion, stratigraphers can extract information from the deposits to reconstruct histories of landscape evolution, climate change, and crustal deformation in tectonically active regions.
Becky Dorsey and her students use sediments to study the San Andreas fault system in southern California and NW Mexico, where it makes up the active plate boundary between the Pacific and North American plates. Because the shape of the plate boundary is highly irregular, the crust is subjected to complex deformation as the two plates grind past each other. We want to know when faults have turned on and off and how their behavior has changed through time, to help us understand controls on crustal deformation and landscape evolution. Sedimentary rocks in this region preserve a record of alternating basin subsidence and uplift over the past ~8 million years, reflecting a complex history of fault initiation, growth, and destruction.The Fish Creek – Vallecito Basin contains a remarkably well exposed record of these processes.
Basin analysis also has yielded new insights into the birth and evolution of the Colorado River. As the Pacific plate in southern and Baja California moves obliquely away from North America, this motion has opened up a deep gash, or “rupture” in the old continent that represents the early stage of a new ocean basin (see image on right). The Colorado River first entered the Salton Trough lowland about 5.3 million years ago, concluding a major integration event that completely reorganized river drainages in the Colorado Plateau region. Vigorous erosion by the Colorado River has transferred a large volume of crust from the stable continental interior to deep basins embedded in the active plate boundary over the past 5-6 million years (see related Paper). Thus we see that processes of fluvial erosion and sedimentation in this setting play a major role in regional-scale recycling of the Earth’s crust.