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January 2, 2015

Quaternary Research paper on age of Willamette Valley Megafauna

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.

December 30, 2014

Geosphere paper on Pliocene rapid sediment aggradation in the Colorado River

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.

Howard, K.A., House, P.K., Dorsey, R.J., and Pearthree, P.A., 2015, River-evolution and tectonic implications of a major Pliocene aggradation on the lower Colorado River: The Bullhead Alluvium: Geosphere, p. GES01059.1, URL: http://geosphere.geoscienceworld.org/content/early/2014/12/22/GES01059.1.

Publications for 2015

Beeler, N. M., G. Hirth, A. Thomas, and R. Bürgmann (2015), Effective stress, friction and deep crustal faulting, Journal of Geophysical Research: Solid Earth, URL:http://onlinelibrary.wiley.com/doi/10.1002/2015JB012115/full.

Befus, K.S., Watkins, J., Gardner, J., Richard, D., Befus, K.M., Miller, N., and Dingwell, D., 2015, Spherulites as in-situ recorders of thermal history in lava flows, Geology, v. 42, no. 7, p. 647-650, url:http://geology.gsapubs.org/content/43/7/647.abstract

Bemis, S.P., Weldon, R.J., and Carver, G.A., 2015, Slip partitioning along a continuously curved fault: Quaternary geologic controls on Denali fault system slip partitioning, growth of the Alaska Range, and the tectonics of south-central Alaska: Lithosphere, p. L352.1, URL: http://lithosphere.geoscienceworld.org/content/early/2015/02/03/L352.1.

Bennett, S.E.K., Oskin, M.E., Dorsey, R.J., Iriondo, A., and Kunk, M.J., 2015, Stratigraphy and structural development of the southwest Isla Tiburón marine basin: Implications for latest Mio­cene tectonic opening and flooding of the northern Gulf of California: Geosphere, v. 11, no. 4, url:http://geosphere.gsapubs.org/content/early/2015/07/01/GES01153.1.abstract

Bodmer, M., D. R. Toomey, E. E. Hooft, J. Nábĕlek, and J. Braunmiller (2015), Seismic anisotropy beneath the Juan de Fuca plate system: Evidence for heterogeneous mantle flow, Geol, G37181.1, URL:http://geology.gsapubs.org/lookup/doi/10.1130/G37181.1

Bostock, M. G., A. M. Thomas, G. Savard, L. Chuang, A. M. Rubin (2015) Magnitudes and moment‐duration scaling of low‐frequency earthquakes beneath southern Vancouver Island, Journal of Geophysical Research: Solid Earth, 120.9, 6329-6350, url:http://onlinelibrary.wiley.com/doi/10.1002/2015JB012195/full

Brandsdóttir, B., Hooft, E.E.E., Mjelde, R., and Murai, Y., 2015, Origin and evolution of the Kolbeinsey Ridge and Iceland Plateau, N-Atlantic: Geochemistry, Geophysics, Geosystems, v. 16, no. 3, p. 612–634, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GC005540/abstract.

Byrnes, J.S., Hooft, E.E.E., Toomey, D.R., Villagómez, D.R., Geist, D.J., and Solomon, S.C., 2015, An upper mantle seismic discontinuity beneath the Galápagos Archipelago and its implications for studies of the lithosphere-asthenosphere boundary: Geochemistry, Geophysics, Geosystems, v. 16, no. 4, p. 1070–1088, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GC005694/abstract.

Carroll, D., Sutherland, D. A., Shroyer, E. L., Nash, J. D., Catania, G. A., and Stearns, L. A. (2015). Modeling turbulent subglacial meltwater plumes: Implications for fjord-scale buoyancy-driven circulation. Journal of Physical Oceanography45(8), 2169-2185.URL:http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-15-0033.1

Chen, J., and A. W. Rempel (2015), Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes, Journal of Geophysical Research: Solid Earth, 120(7), 5215–5237, URL:http://onlinelibrary.wiley.com/doi/10.1002/2014JB011641/full.

Colón, D.P., Bindeman, I.N., Ellis, B.S., Schmitt, A.K., and Fisher, C.M., 2015, Hydrothermal alteration and melting of the crust during the Columbia River Basalt–Snake River Plain transition and the origin of low-δ18O rhyolites of the central Snake River Plain: Lithos, v. 224–225, p. 310–323, URL: http://www.sciencedirect.com/science/article/pii/S002449371500081X.

Colón, D.P., Bindeman, I.N., Stern, R.A., and Fisher, C.M., 2015, Isotopically diverse rhyolites coeval with the Columbia River Flood Basalts: evidence for mantle plume interaction with the continental crust: Terra Nova, p. n/a–n/a, URL: http://onlinelibrary.wiley.com/doi/10.1111/ter.12156/abstract.

Crossey, L.C., Karlstrom, K.E., Dorsey, R., Pearce, J., Wan, E., Beard, L.S., Asmerom, Y., Polyak, V., Crow, R.S., Cohen, A., Bright, J., and Pecha, M.E., 2015, Importance of groundwater in propagating downward integration of the 6-5 Ma Colorado River system: Geochemistry of springs, travertines, and lacustrine carbonates of the Grand Canyon region over the past 12 Ma: Geosphere, p. GES01073.1, URL: http://geosphere.geoscienceworld.org/content/early/2015/05/13/GES01073.1.

Dorsey, R.J., and Langenheim, V.E., 2015, Crustal-scale tilting of the central Salton block, southern California. Geosphere, v. 11, no. 5, 19 pages, url:http://geosphere.gsapubs.org/content/early/2015/08/27/GES01167.1.abstract

Famoso, N.A., Davis, E.B., Feranec, R.S., Hopkins, S.S.B., and Price, S.A., 2015, Are Hypsodonty and Occlusal Enamel Complexity Evolutionarily Correlated in Ungulates? Journal of Mammalian Evolution, p. 1–5, URL: http://link.springer.com/article/10.1007/s10914-015-9296-7.

Field, E.H., Biasi, G.P., Bird, P., Dawson, T.E., Felzer, K.R., Jackson, D.D., Johnson, K.M., Jordan, T.H., Madden, C., Michael, A.J., Milner, K.R., Page, M.T., Parsons, T., Powers, P.M., Shaw, B. E., Thatcher, W. R., Weldon, R. J, 2015, Long‐Term Time‐Dependent Probabilities for the Third Uniform California Earthquake Rupture Forecast (UCERF3): Bulletin of the Seismological Society of America, URL: http://www.bssaonline.org/content/early/2015/03/05/0120140093.

Fusillo, R., F. Di Traglia, A. Gioncada, M. Pistolesi, P. J. Wallace, and M. Rosi (2015), Deciphering post-caldera volcanism: insight into the Vulcanello (Island of Vulcano, Southern Italy) eruptive activity based on geological and petrological constraints, Bull Volcanol, 77(9), 76–23, URL:http://link.springer.com/10.1007/s00445-015-0963-6.

Gérault, M., L. Husson, M. S. Miller, and E. D. Humphreys (2015), Flat‐slab subduction, topography, and mantle dynamics in southwestern Mexico, Tectonics,1892–1909, URL:http://onlinelibrary.wiley.com/doi/10.1002/2015TC003908/full.

Gurenko, A.A., Bindeman, I.N., and Sigurdsson, I.A., 2015, To the origin of Icelandic rhyolites: insights from partially melted leucocratic xenoliths: Contributions to Mineralogy and Petrology, v. 169, no. 5, p. 1–21, URL: http://link.springer.com/article/10.1007/s00410-015-1145-4.

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.

Handwerger, A. L., J. J. Roering, D. A. Schmidt, and A. W. Rempel (2015), Kinematics of earthflows in the Northern California Coast Ranges using satellite interferometry, Geomorphology, URL:http://www.sciencedirect.com/science/article/pii/S0169555X15300209.

Heath, B. A., E. E. E. Hooft, D. R. Toomey, and M. J. Bezada, 2015, Imaging the magmatic system of Newberry Volcano using joint active source and teleseismic tomography, Geochem. Geophys. Geosyst., 16, URL:http://onlinelibrary.wiley.com/doi/10.1002/2015GC006129/full

Howard, K.A., House, P.K., Dorsey, R.J., and Pearthree, P.A., 2015, River-evolution and tectonic implications of a major Pliocene aggradation on the lower Colorado River: The Bullhead Alluvium: Geosphere, p. GES01059.1, URL: http://geosphere.geoscienceworld.org/content/early/2014/12/22/GES01059.1.

Humphreys, E. D., B. Schmandt, M. J. Bezada, and J. Perry-Houts (2015), Recent craton growth by slab stacking beneath Wyoming, Earth and Planetary Science Letters, 429, 170–180, url:http://linkinghub.elsevier.com/retrieve/pii/S0012821X15005099.

Kimbrough, D. L., M. Grove, G. E. Gehrels, R. J. Dorsey, K. A. Howard, O. Lovera, A. Aslan, P. K. House, and P. A. Pearthree (2015), Detrital zircon U-Pb provenance of the Colorado River: A 5 m.y. record of incision into cover strata overlying the Colorado Plateau and adjacent regions, Geosphere, GES00982.1, URL:http://geosphere.gsapubs.org/content/suppl/2015/12/01/GES00982.1.DC1/982_SuppFile.pdf.

Knipping, J.L., Bilenker, L.D., Simon, A.C., Reich, M., Barra, F., Deditius, A.P., Lundstrom, C., Bindeman, I., and Munizaga, R., 2015, Giant Kiruna-type deposits form by efficient flotation of magmatic magnetite suspensions: Geology, p. G36650.1, URL: http://geology.gsapubs.org/content/early/2015/05/18/G36650.1.

Kuehl, S.A., C.R. Alexander, N.E. Blair, C.K. Harris, K.M. Marsaglia, A.S. Ogston, A.R. Orpin, J.J. Roering, A. Bever, E. L. Bilderback, L. Carter, C. Cerovski-Darriau, L.B. Childress, D.R. Corbett, R. Hale, E.L. Leithold, N. Litchfield, J. Moriarty, M.J. Page, L. E.R. Pierce, P. Upton, and J.P. Walsh, 2015, A Source to Sink Perspective of the Waipaoa River Margin, Earth Science Reviews, doi:10.1016/j.earscirev.2015. 10.001.

Kyriakopoulos, C., A. V. Newman, A. M. Thomas, M. Moore Driskell, and G. T. Farmer (2015), A new seismically constrained subduction interface model for Central America, Journal of Geophysical Research: Solid Earth, 120(8), 5535–5548, URL:http://onlinelibrary.wiley.com/doi/10.1002/2014JB011859/full.

LaMaskin, T.A., Dorsey, R.J., Vervoort, J.D., Schmitz, M.D., Tumpane, K.P., Moore, N.O., 2015, Westward growth of Laurentia by pre-Late Jurassic terrane accretion, eastern Oregon and western Idaho, United States: Journal of Geology, vol. 123, p. 233-267. url:http://scholarworks.boisestate.edu/geo_facpubs/264/

Loewen, M. W., and I. N. Bindeman, 2015, Oxygen isotope and trace element evidence for three-stage petrogenesis of the youngest episode (260–79 ka) of Yellowstone rhyolitic volcanism, Contrib Mineral Petrol, 170(4), 39–25, URL:http://link.springer.com/10.1007/s00410-015-1189-5.

Maguffin, S.C., Kirk, M.F., Daigle, A.R., Hinkle, S.R., and Jin, Q., 2015, Substantial contribution of biomethylation to aquifer arsenic cycling: Nature Geoscience, v. advance online publication, URL: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2383.html.

Marshall, J. A., J. J. Roering, P. J. Bartlein, D. G. Gavin, D. E. Granger, A. W. Rempel, S. J. Praskievicz, and T. C. Hales (2015), Frost for the trees: Did climate increase erosion in unglaciated landscapes during the late Pleistocene? Science Advances, 1(10), e1500715–e1500715, URL:http://advances.sciencemag.org/cgi/doi/10.1126/sciadv.1500715.

Moore, L.R., Gazel, E., Tuohy, R., Lloyd, A.S., Esposito, R., Steele-MacInnis, M., Hauri, E.H., Wallace, P.J., Plank, T., and Bodnar, R.J., 2015, Bubbles matter: An assessment of the contribution of vapor bubbles to melt inclusion volatile budgets: American Mineralogist, v. 100, no. 4, p. 806–823, URL: http://ammin.geoscienceworld.org/content/100/4/806.

Narkiewicz, M., Grabowski, J., Narkiewicz, K., Niedźwiedzki, G., Retallack, G.J., Szrek, P., and De Vleeschouwer, D., 2015, Palaeoenvironments of the Eifelian dolomites with earliest tetrapod trackways (Holy Cross Mountains, Poland): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 420, p. 173–192, URL: http://www.sciencedirect.com/science/article/pii/S0031018214006087.

Pelletier, J.D., Sweeney, K.E., Roering, J.J., and Finnegan, N.J., 2015, Controls on the geometry of potholes in bedrock channels: Geophysical Research Letters, v. 42, no. 3, p. 2014GL062900, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GL062900/abstract.

Plourde, A. P., M. G. Bostock, P. Audet, and A. M. Thomas (2015), Low‐frequency earthquakes at the southern Cascadia margin, Geophys. Res. Lett., 42(12), 4849–4855, URL:http://onlinelibrary.wiley.com/doi/10.1002/2015GL064363/full.

Portnyagin, M., S. Duggen, F. Hauff, N. Mironov, I. Bindeman, M. Thirlwall, and K. Hoernle (2015), Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems, Journal of Volcanology and Geothermal Research, 307, 133–155, url:http://linkinghub.elsevier.com/retrieve/pii/S0377027315002711.

Price, S.A., and Hopkins, S.S.B., 2015, The macroevolutionary relationship between diet and body mass across mammals: Biological Journal of the Linnean Society, v. 115, no. 1, p. 173–184, URL: http://onlinelibrary.wiley.com/doi/10.1111/bij.12495/abstract.

Retallack, G.J., Gose, B.N., and Osterhout, J.T., 2015, Periglacial paleosols and Cryogenian paleoclimate near Adelaide, South Australia: Precambrian Research, v. 263, p. 1–18, URL: http://www.sciencedirect.com/science/article/pii/S0301926815000959.

Roering, J.J., Mackey, B.H., Handwerger, A.L., Booth, A.M., Schmidt, D.A., Bennett, G.L., and Cerovski-Darriau, C., 2015, Beyond the angle of repose: A review and synthesis of landslide processes in response to rapid uplift, Eel River, Northern California: Geomorphology, v. 236, p. 109–131, URL: http://www.sciencedirect.com/science/article/pii/S0169555X15000963.

Royer, A.A., Thomas, A.M., and Bostock, M.G., 2015, Tidal modulation and triggering of low-frequency earthquakes in northern Cascadia: Journal of Geophysical Research: Solid Earth, v. 120, no. 1, p. 2014JB011430, URL: http://onlinelibrary.wiley.com/doi/10.1002/2014JB011430/abstract.

Schachtman, N. S., MacGregor, K. R., Myrbo, A., Hencir, N. R., Riihimaki, C. a., Thole, J. T., & Bradtmiller, L. I. (2015). Lake core record of Grinnell Glacier dynamics during the latest Pleistocene deglaciation and the Younger Dryas, Glacier National Park, Montana, USA. Quaternary Research, 84(1), 1–11. http://doi.org/10.1016/j.yqres.2015.05.004

Shulaker, D.Z., Schmitt, A.K., Zack, T., and Bindeman, I., 2015, In-situ oxygen isotope and trace element geothermometry of rutilated quartz from Alpine fissures: American Mineralogist, v. 100, no. 4, p. 915–925, URL: http://ammin.geoscienceworld.org/content/100/4/915.

Sizemore, H.G., A.P. Zent and A.W. Rempel (2015), Initiation and growth of Martian ice lenses,  Icarus doi:10.1016/j.icarus.2014.04.013, 251, 191-210, url:http://www.sciencedirect.com/science/article/pii/S001910351400205X

Sweeney, K.E., Roering, J.J., and Ellis, C., 2015, Experimental evidence for hillslope control of landscape scale: Science, v. 349, no. 6243, p. 51–53, URL: http://www.sciencemag.org/content/349/6243/51.

Thomas, A. M., and M. G. Bostock (2015), Identifying low-frequency earthquakes in central Cascadia using cross-station correlation, Tectonophysics, 658, 111–116, URL:http://linkinghub.elsevier.com/retrieve/pii/S0040195115003807.

Wallace, P.J., Kamenetsky, V.S., and Cervantes, P., 2015, Melt inclusion CO2 contents, pressures of olivine crystallization, and the problem of shrinkage bubbles: American Mineralogist, v. 100, no. 4, p. 787–794, URL: http://ammin.geoscienceworld.org/content/100/4/787.

Walowski, K.J., Wallace, P.J., Hauri, E.H., Wada, I., and Clynne, M.A., 2015, Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite: Nature Geoscience, v. 8, p. 404–408, URL: http://www.nature.com/ngeo/journal/v8/n5/abs/ngeo2417.html.

Watkins, J. M., and J. D. Hunt (2015), A process-based model for non-equilibrium clumped isotrop effects in carbonates, Earth and Planetary Science Letters, 432, 152–165, URL:10.1016/j.epsl.2015.09.042.

December 8, 2014

Two papers in latest issue of Geosphere

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.

November 14, 2014

Ecography paper on southern overprediction of paleo species distribution models.

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.

November 13, 2014

Nature paper on subduction-driven removal of continental lithosphere

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.

Levander, A., Bezada, M.J., Niu, F., Humphreys, E.D., Palomeras, I., Thurner, S.M., Masy, J., Schmitz, M., Gallart, J., Carbonell, R., and Miller, M.S., 2014, Subduction-driven recycling of continental margin lithosphere: Nature, v. 515, no. 7526, p. 253–256, URL: http://www.nature.com/nature/journal/v515/n7526/full/nature13878.html.
July 2, 2014

David Sutherland featured by NDTV for work on rate of Greenland Ice Sheet melting

Sutherland Greenland

UO Oceanographer David Sutherland has been recently featured by NDTV for his work on the rate of melting of Greenland’s Ice Sheet.

Read the story here.

November 9, 2013

Agate Beach Fieldwork

In February 2013, Dr. Edward Davis led a small crew of UO paleontology students to Agate Beach to measure section and collect fossils. Pictured are Amy Atwater (left) and Meaghan Emery.

November 8, 2013

Imaging a magma chamber beneath Newberry Volcano

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

Newberry Magma Chamber: The Movie

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.

Seismic wave propagation through a magma chamber - Newberry Volcano, OR

March 19, 2012

Sedimentary Archives of Active Tectonics

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.

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