I AM LOOKING FOR A NEW POST DOC STARTING JANUARY 2023
July 2020-June 2023
P2C2: COLLABORATIVE RESEARCH: RAPID CLIMATE CHANGE DURING THE MIOCENE CLIMATE OPTIMUM: A PROXY-MODEL COMPARISON
The Miocene is characterized by a cooling trend punctuated by abrupt episodes of warming during the early to middle Miocene known as the Miocene Climate Optimum (MCO) (~17-14 Ma; Kürschner et al., 2008; Holbourn et al., 2015). The MCO is one of Earth's most recent prolonged warming events, recorded both in the ocean and on the continents (e.g., Zachos et al., 2008; Song et al., 2018), with a peak global surface temperature ~8oC warmer than today (Goldner et al., 2014 and references therein). The MCO serves as a benchmark to understand future climate change. Although the marine record of the MCO is well documented through geochemical data (e.g. δ18O) from oceanic detritus, the continental record remains sparse. This is primarily because most of the continental record is inherently discontinuous. Thus, despite its significance, we know very little about the MCO continental climate record; this data gap hinders our ability to distinguish the temperature responses between land and sea, and thus, limits our ability to use the MCO as an analog for future climate change. With this project, we plan to utilize key geological and geochemical records of climate variability across the MCO in combination with Earth system model simulations to provide insights into the mechanisms driving the MCO. From these results, we can better understand mechanisms of global warming, its relationship with CO2, and inform future climate predictions.
I am looking for a new graduate student to work on this project starting in Fall 2022!
NSF funding started on August 2019
TIMING OF COOLING AND EXHUMATION OF LARAMIDE UPLIFTS INFORMS MODELS OF FLAT-SLAB SUBDUCTION
This project intends to determine the ages of uplift of the major mountain ranges that together constitute the Rocky Mountains of the western interior United States. These ranges are referred to in the geological literature as "Laramide uplifts", after the city and county of Laramie, Wyoming, which is situated in the region where these uplifts are notably developed. The timing of uplift of the Laramide ranges is poorly understood, but critical for assessing the shape and movement direction of tectonic plates in the eastern Pacific basin and western regions of the North American plate. This work is important to the public for several reasons: (a) The Rocky Mountains are the definitive landscape of the mountain west, a landscape that has inspired writers, artists, entrepreneurs, emigrants, and scientists for more than 200 years; yet, no consensus exists among geologists to explain the origins of these mountains. (b) By virtue of its high elevation and north-south orientation, this spectacular landscape impacts the ecology and climate of the entire U.S. (c) The Laramide region is of enormous economic importance to the U.S., containing strategically important groundwater, mineral, and hydrocarbon resources. (d) Although the Laramide uplifts are no longer "active", results of this project will useful for understanding seismic hazards in regions on Earth today where similar tectonic processes are still active (for example, western South America and southern Alaska). Finally, a group of undergraduate and graduate students will be trained in the context of this project.
The primary objective of this project is to determine the timing of exhumation of Laramide uplifts in Montana, Wyoming and Utah. This is essential to inform tectonic and geodynamic models of the Laramide orogeny, which is generally attributed to flat-slab subduction. Such models rely heavily on spatio-temporal patterns of Laramide uplift. Flat-slab subduction of oceanic plateaus and aseismic ridges are important geodynamic phenomena in convergent margins, with respect to regional plateau uplift, termination of arc magmatism, and active seismicity in the overriding plate. This project will apply a multi-component dating approach, including apatite fission track and (U-Th-Sm)/He thermochronology, which, when combined with thermo-kinematic modeling and the record of sedimentation, will constrain the cooling and erosion histories of the Laramide region. Regional patterns in timing and distribution of uplift events will provide constraints for plate tectonic models of the western U.S. Knowledge gained by this research will be exportable to other active and ancient flat-slab tectonic systems such as southern Alaska, Central America and western Argentina.
We are looking for a PhD starting in Fall 2020 to work on this project.
NSF EAR-Tectonics, funding ongoing
ARE REMNANTS OF THE TIBETAN PLATEAU PRESERVED IN THE SOUTHERN HIMALAYAN THRUST BELT?
The Himalaya of Nepal is one of Earth's most rugged and rapidly eroding landscape, with local relief greater than 5,000 meters and a morphology dominated by deep fluvial incision. This regional pattern of relief is broken in western Nepal, where the Bhumichula plateau represents a approximately 250 square kilomter area of low-relief (200-400 meters), but high-elevation (4200-4800 meters) ground isolated amidst surrounding deeply incised topography resembling that of Tibet. This projects investigates how and when the Bhumichula plateau formed. Determining whether the Bhumichula plateau formed as a low-elevation surface that was later uplifted and incised, or whether it was high standing from its earlier stages and part of a larger Tibetan plateau and was later modified by surface processes, is significant for the understanding of the mechanisms forming high topography on Earth. High elevation features such as the Himalaya and Tibet are a product of tectonic processes over geological time, which are responsible today for the location and magnitude of earthquakes. The Himalayas and Tibet also play a significant role on climate by driving the Asian monsoon and thus control the distribution of fresh water on our planet. Important societal outcomes deriving from this project include training of graduate students This project also supports the training of graduate and undergraduate students in an important science, technology, engineering and mathematics discipline (STEM), thereby contributing to the increased economic competitiveness of the United States. The project also contributes to the broadening of underrepresented groups in STEM, thereby promoting diversity in science. and minorities, female research scientists, and promotes diversity in science. It also is supporting the development of an online virtual field trip experiences for general education and upper division classes.
This is a muldisciplinary invesgation that uses geological mapping, low-temperature thermochronology, cosmogenic nuclide dating, geomorphological analysis, stable isotope paleoaltimetry, and 40Ar/39Ar geochronology to determine the age of basement rocks, the timing of deformation, erosion/incision and uplift of the Bhumichula plateau in western Nepal. Although other low-relief, high-elevation surfaces have been identified in the Himalaya, none has been investigated with the complete array of methods to be employed in this work. A principal goal of the project is to establish a workflow for how to analyze and interpret these low-relief surfaces in general, which are common features in the Himalaya to the east of Nepal. This study is the first attempt to apply such a wide array of techniques to unravel the history of landscape development in the India-Asia collisional environment, including the first attempt to determine paleoelevation on the southern slope of the Himalaya. Three main hypotheses will be tested: (1) BP formed as a low-elevation surface that was uplifted to high elevation and incised by antecedent and headward eroding rivers; (2) the BP is a remnant of a once much larger paleo-Tibetan landscape that reached nearly to the front of the Himalaya during the Miocene, and has been etched northward by headward erosion since that time; and (3) the BP formed in response to drainage reorganization and feedbacks between drainage area, erosion, and elevation.
COLLABORATIVE RESEARCH: TECTONIC SIGNIFICANCE OF LONG RUN-OUT COARSE-GRAINED FACIES IN THE CORDILLERAN FORELAND BASIN
Sediments deposited in basins in front of fold-and-thrust belts, also known as foreland basins, record the tectonic growth and development of the belts. One prevalent model for sedimentation in these basins is that fine-grained sediments in record tectonic growth of the thrust belt whereas coarse-grained sediments accumulate during periods of thrust belt inactivity. This project aims to test this model using innovative methods to determine the timing of sedimentation in the Idaho-Wyoming fold-and-thrust belt. A successful challenge of the prevalent model has the potential to change geological understanding of how fold-and-thrust belts belts develop. This is of particular importance because the Idaho-Wyoming thrust belt and associated foreland basins host important hydrocarbon resources. A better understanding of basin development will provide important insights into hydrocarbon exploration. The project would advance other desired societal outcomes through: (1) full participation of women in STEM; (2) improved STEM education and educator development through engagement of a K-12 science teacher or undergrad student in the UTeach program, and participation in the Geoscience Teacher Symposium for K-12 science teachers; (3) increased public scientific literacy and public engagement with STEM through development of displays and videos for the University of Arizona Flandau Center; and (4) development of a globally competitive STEM workforce through training of graduate and undergraduate students.
For over two decades foreland basin stratigraphers and sedimentologists have used the two-phase model of foreland basin subsidence to interpret stratigraphic sequences in foreland settings. This model hypothesizes that episodes of fine-grained distal sedimentation are the syntectonic response to orogenic growth and rapid flexural subsidence, whereas coarse-grained distal facies accumulate during periods of thrust belt inactivity, erosion, and isostatic rebound. This research project will test this model using geo/thermochronologic and magnetic polarity stratigraphic study of mid- to Upper Cretaceous foreland basin deposits in northeast Utah and southwest Wyoming, a classic foreland. Detrital geochronology (U-Pb on detrital zircon and apatite) and thermochronology (apatite fission track) will determine detrital lag-times (the time difference between the exhumation age of a sediment grain from the source terrane and its depositional age in the basin). Second, better age control in the poorly dated proximal part of the basin fill will be established by using magnetic polarity stratigraphy on fine-grained interbeds within thick alluvial fan deposits located adjacent to major thrust faults. This combined approach allows accurate correlation of the proximal and distal facies, and establishment of the time difference between exhumation and depositional ages of the distal, coarse-grained intervals. Long lag-times in the distal coarse-grained facies and irregular long-term trends in lag-time, this would support the two-phase model whereas relatively brief (<5 Myr) lag-times and a steady to decreasing lag time trend would indicate that coarse-grained sediments prograded directly into the distal basin during tectonic events in the thrust belt and therefore would nullify the two-phase model.
Jan 2021-Jan 2026
TANGO: TRANSANDEAN GREAT OROGENY
Orogenic belts play a major role in global atmospheric and oceanic processes, chemistry, and evolution; biosystems are directly controlled by orogenic belts. Nevertheless, one of the outstanding scientific question remains: how does plate tectonics produce mountains? Earth’s orogenic belts are commonly classified as either of collisional or cordilleran type based on the nature of the lithospheric plates involved. Whereas conceptual models have been developed based on accretion-driven orogenic systems, no model adequately explains cordilleran-type orogenic systems such as the Andes. The Andes are especially important because they span ~70° of latitude across several global climate zones and exert first-order controls on ocean circulation and climate. Yet, a comprehensive time-space framework linking processes and mechanisms controlling the architecture and morphology of the Andes is still lacking. Persistent questions include: Are differences in crustal thickness, shortening, and width of the Andes merely a function of differences in erosion, climate, or inherent continental plate structure or are deeper mantle processes operating to control these attributes? Is the lithosphere alone responsible for orogenic evolution, or does the deeper mantle exert a first-order control? How are mantle-generated stresses transferred into the continental lithosphere, where orogens are located? Why was Andean crustal thickening delayed until the Cenozoic, even though much longer-term subduction was ongoing along the western margin of South America? We plan to test existing mantle- and lithosphere-scale models by resolving the position of the subducting slab through time, the slab geometry, the spatio-temporal history of deformation, uplift and subsidence and by comparing surface geology data with the geometry of the lower and upper plates along two transects characterized by different physical configurations. This research will integrate geophysics, geodynamic modeling, structural geology, basin analysis, petrology and geochemistry to investigate the effects of slab geometry, slab penetration (into the lower mantle), forearc underplating, and the presence or absence of a craton on crustal thickening and surface evolution (subsidence and uplift).