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General Research Interests
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In essence, my research has two primary foci. I am interested
in tectonics and sedimentation primarily in compressional Cenozoic basins,
and I am working with various problems related to tectonic geomorphology
and late Cenozoic climates. The field of tectonic geomorphology has undergone
a massive revitalization in the past several years due to the advent of
new dating techniques, digital topography, high-resolution geodetic data,
and quantification of surface processes. At present this seems to me to
be one of the most exciting and diverse fields in geology, as it draws on
a multitude of disciplines and is beginning to reveal how climate, erosion,
and tectonics interact. In the realm of tectonic geomorphology, we are studying
the evolution of growing folds and faults, landscape responses to spatial
variations in deformation and climate, rates of surface processes (river
incision, landsliding), strain partitioning in oblique compression and extension,
and mass balances in rapidly eroding mountain belts.
Whereas structural geology, tectonics, and stratigraphy are more "mature" fields, there are many intriguing and unresolved problems. I like to try to bring together a combination of dating techniques, structural observations, mapped relationships, and stratigraphic data to understand how orogens have evolved, how faults interact, and how the competition between sedimentation, erosion, and deformation can be extracted from ancient landscapes. Present research projects in this area are examining intracontinental deformation in central Asia (the Tien Shan), thrust fault systems in China and New Zealand, sequencing and pacing of faulting events, interactions of growing structures with coeval geomorphic and depositional systems, river and glacier erosion in transient landscapes, growth of continental plateaus, and continental transtension. |
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Current, Recent, and Future Projects |
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New
Zealand: Following a recent project centered on the active Ostler
Fault zone, we have turned our attention to Fiordland and its contrasts
with the Southern Alps. We are studying our rock strength interacts with
surface processes to modulate rates of erosion. In addition, we are trying
to understand the erosional role of specific surface processes and the signature
of those processes in the landscape. Our work is combining cosmogenic nuclide
dating, rock-strength studies from lab scales to shallow seismic scales,
DEM analyses, and reconstructions of modern and paleo-climate gradients.
At longer time scale, we are integrating low-temperature thermochronologic
and tectonic studies to improve understanding of the evolution of Fiordland,
controls on its growth, and transitions along the Pacific-Australian plate
boundary from subduction to transform faulting.
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Tien
Shan of the Kyrgyz Republic and NW China: The Tien Shan continue
to be a source of provocative new data and a great place to test competing
hypotheses. This range is tectonically interesting because it is the most
rapidly deforming intracontinental mountain belt on earth: half of the Indo-Asian
conovergence is absorbed in the Tien Shan! Among its key attributes are:
a regional unconformity surface that provides a stunning structural and
geomorphic marker, excellent temporal control through magnetostratigraphic
studies, fabulous exposures, many nascent structures juxtaposed with more
“mature” ones, provocative along-strike changes in structures,
deformation rates and style. We are currently incipient indentation of the
orogen by the Pamir “indentor”, contrasting styles of basement
shortening and closure of intermonane basins, and the record of highly pulsed
shortening and its relationship to climate change across the broader Himalayan
orogen.
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Nepal:
We are continuing to study interactions among climate, erosion, and tectonics
in this spectacular mountain range. From our initial CD project focused
on the Marsyandi catchment in central Nepal, we have been expanding laterally
to examine more parts of the orogen. We have been combining remotely sensed
(TRMM satellite) rainfall data that can be processed to yield a much higher
resolution (5 x 5 km) than ever before attained in such mountainous regions.
These data are being used in investigate the controls on orographic rainfall
both across and along the entire Himalayan chain. The rainfall data are
also combined with DEMs to generate runoff and calculate discharge and stream
power. We are testing how robust specific stream power is as a proxy for
erosion and we are examining issues of steadiness versus unsteadiness in
the spatial and temporal evolution of the range. Some intriguing results
suggest trade-offs in the locus of erosion between the Greater and Lesser
Himalaya and significant shifts in the sites of greatest erosion over time.
We are currently designing tests for lateral advection of topography and
major drainage reorganization during Quaternary times.
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Collisional orogenic belts: We are studying ways to
document steady-state and pre-steady-state topography in several collisional
orogens, including the Tien Shan, Himalaya, Transverse Ranges, and Southern
Alps. In this analysis, we are using digital topography, cooling and denudation
histories, field surveys, and landscape properties. (with Mike Oskin and
Bodo Bookhagen).
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NE Tibet: As well as being the centerpiece of the Indo-Asian
orogen, surface uplift and outward growth of the largest topographic plateau
on Earth has profoundly impacted regional and global climate. In a team
supported by Continental Dynamics, we are studying the timing, style, and
rates of structural development of the plateau, the filling of sedimentary
basins, the history of river incision, and the change of climate since mid-Miocene
times. (With Peter Molnar, Marin Clark, Ken Farley, Carmie Garzione, Eric
Kirby, Gerard Roe, and many Chinese collaborators)
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California: Study of the structural expression resulting
from the change from extension to transtension in the northern Owens Valley
and White Mountains of eastern California-Nevada. This project utilizes
cosmogenic radionuclide exposure ages, tephrochronology, fission-track,
U-Th-He, and radiocarbon dating in conjunction with a lot of mapping and
surveying to develop an integrated picture of the Pliocene to modern deformation
in this region. This area is of particular interest because it is in a strongly
transtensional setting about which relatively little is known. We think
we will be able to improve dramatically on slip rate estimates for many
faults and to develop a new model for emergence of the White Mountains.
(work with Eric Kirby, Marith Rehies, Fred Phillips, and Nancye Dawars)
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