Authors: Whitney, B.B., Hengesh, J., and Clark, D.
Reference: 2022. Geological Society of America, Bulletin, Comment
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Location: Mojave Desert, 2021
Friends of the Pleistocene Pacific Cell Field Conference
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Three days of camping and geological intrigue in the Mojave Desert
Location: Praz-sur-Arly, 2021
SIGMA 2
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Location: Central Walker Lane, 2019
Friends of the Pleistocene Pacific Cell Field Conference
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Authors: Hengesh, J.V., Whitney, B.B.
Reference: 2016. Tectonics. 21pp. doi:10.1002/2015TC004103
Australia’s northwestern passive margin intersects the eastern termination of the Java trench segment of the Sunda arc subduction zone and the western termination of Timor trough along the Banda arc tectonic collision zone.
Differential relative motion between the Sunda arc subduction zone and the Banda arc collision zone has reactivated the former rifted margin of northwestern Australia evidenced by Pliocene to Quaternary age deformation along a 1400 km long offshore fault system. The fault system has higher rates of seismicity than the adjacent nonextended crustal terranes, has produced the largest historical earthquake in Australia (1941 ML 7.3 Meeberrie event), and is dominated by focal mechanism solutions consistent with dextral motion along northeast trending fault planes.
The faults crosscut late Miocene unconformities that are eroded across middle Miocene inversion structures suggesting multiple phases of Neogene and younger fault reactivation. Onset of deformation is consistent with the timing of the collision of the Scott Plateau part of the passive continental margin with the former Banda trench between 3.0 Ma and present. The range of estimated maximum horizontal slip rates across the zone is ~1.4 to 2.6mmyr_1, at the threshold of geodetically detectable motion, yet significant with respect to an intraplate tectonic setting.
The folding and faulting along this part of the continental margin provides an example of intraplate deformation resulting from kinematic transitions along a distant plate boundary and demonstrates the presence of a youthful evolving intraplate fault system within the Indo-Australian plate.
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Location: Crestone, Colorado, 2016
PATA Days
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Location: Mohawk Valley, 2015
Friends of the Pleistocene Pacific Cell Field Conference
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Authors: Whitney, B.B., Hengesh
Reference: 2015 Geomorphology 228, 579-596.
This study examines channel-scale morphodynamics of ephemeral streams in the onshore Carnarvon basin in arid west-central Western Australia.
The rivers in this region have low gradients, the landscape has low relief, and the rates of climatically and tectonically driven geomorphic processes also are low. As a result, the rivers in the Carnarvon alluvial plain are highly sensitive to minor perturbations in base level, channel slope, and fluvial energy. We use channel planform adjustments, stream gradient changes, and floodplain profiles across multiple ephemeral streams within a variety of catchments and flow regimes to determine if tectonically driven land level changes are affecting channel form and fluvial processes.
Growth of individual fold segments is shown to have altered stream and floodplain gradients and triggered repeated avulsions at structurally controlled nodes. Aligned perturbations in channel form across multiple channel-fold intersections provide systematic geomorphic evidence for the location and orientation of neotectonic structures in the region. These features occur as a belt of low relief anticlines in the Carnarvon alluvial plain.
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Authors: Whitney, B.B., Clark, D.J., Hengesh, J.V..
Reference: 2015, Geological Society of America Bulletin, 21 pp. doi:10.1130/B31313.1.
We have investigated the locations and patterns of neotectonic deformation in the Carnarvon basin along the Mesozoic rifted margin of Western Australia to evaluate the characteristics of post-Neogene tectonic reactivation.
Geological, geophysical, geotechnical, and bathymetric data demonstrate that preferentially oriented rift-era structures have been reactivated under the current neotectonic stress regime. The most recent pulse of neotectonic reactivation initiated during the Plio-Pleistocene (4.0 to 1.8 million years ago) and is ongoing. Reactivated structures in the region demonstrate a variety of styles of deformation consistent with dextral transpression.
Structural styles include both positive and negative flower structures, restraining and releasing bends, and hourglass structures. Barrow Island lies within a broad kinematic restraining bend that appears to warp the MIS 5e marine terrace on the island. Fold reconstructions of Neogene strata on the Cape Range and Barrow anticlines yield uplift rates consistent with uplift rates determined from folded late Pleistocene units in the Cape region.
Although tectonic rates are low compared to interplate settings, evidence for active tectonic deformation precludes this part of the Australian plate from being classified as a Stable Continental Region.
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Authors: Whitney, B.B., Hengesh, J.V., Gillam, D.
Reference: 2015. Tectonophysics, 686, 1-18. doi:10.1016/j.tecto.2016.06.008
Our paleoseismological study of faults and fault-related folds comprising the Mount Narryer fault zone reveals a mid- to late Quaternary history of repeated morphogenic earthquakes that have influenced the planform and course of the Murchison, Roderick, and Sanford Rivers, Western Australia.
The dominant style of deformation involves folding of near-surface sediments overlying discrete basement faults. Carbon-14, optically stimulated luminescence, and in situ–produced 10Be constrain the timing of the events and late Quaternary slip rates associated with fault propagation folds in tectonically uplifted and deformed alluvial channel deposits. A flight of five inset fluvial terraces is preserved where the Murchison River flows across the Roderick River fault.
These terraces, which we infer to be coseismic, are consistent with at least four late Quaternary seismic events on the order of moment magnitude (Mw) 7.1 within the last ~240 k.y. Secondary shears expressed on the folds indicate a component of dextral strike-slip displacement. Quaternary slip rates on the underlying faults range from 0.01 to 0.07 mm yr–1, with a total slip rate for the zone between 0.04 and 0.11 mm yr–1.
These rates are intermediate to those in the adjacent Mesozoic basin (>0.1 mm yr–1) and Precambrian craton (<0.005 mm yr–1) and so provide insight into how tectonic strain is partitioned and transferred across a craton margin.
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Authors: Whitney, B.B., Hengesh, J.V.
Reference: 2015. Geomorphology 241, 160-174 10.1016/j.geomorph.2015.04.010
A late Pleistocene (Marine Isotope Stage 5e) emergent marine sequence fringes the coastline of the Cape Region of coastal west central Australia and provides elevation and age control to characterize the locations and rates of crustal deformation.
There is a systematic measurable change in relative paleo sea-level elevations across the Cape Region. High-precision leveling of modern and Pleistocene shoreline features indicates the minimum elevation range of MIS 5e shoreline features along the coast is 10.4 m. This compares with the 2.5 m elevation range for observed modern shoreline analogs.
The lack of continuity of MIS 5e shoreline elevations along 300 km of coastline demonstrates continuing tectonic deformation along coastal anticlines in the Cape Region. Topographic expression of MIS 5e features indicates tectonic uplift consistent with late Neogene to Quaternary deformation on the Cape Cuvier and Cape Range anticlines. Post-MIS 5e tectonic uplift rates are up to 0.054 ± 0.035 mm/yr at fold axial locations. Estimated subsidence rates are −0.013 ± 0.034 mm/yr on fold limbs. While the estimated vertical tectonic deformation is small and the rates are low, the geomorphological data also demonstrate tectonic activity, not stability.
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Location: Busan, South Korea, 2014
PATA Days
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Authors: Melody, A. D., Whitney, B.B., Slack, C.G.
Reference: 2012. Bulletin of the Seismological Society of America 102, 2219-2224.
Evidence for active faulting in the Truckee Basin, north of Lake Tahoe, is observed in a meadow containing a scarp and small closed depression. Shallow, hand-dug trenches show offset marsh stratigraphy of Holocene age.
Lithostratigraphy descriptions and radiocarbon dates indicate the meadow was a marsh during the late Quaternary that was abruptly infilled with the deposition of the ∼7000 yr B.P. Tsoyawata tephra (Mt. Mazama). The tephra is offset up to 80 cm across a narrow, sub-vertical, north–south-striking fault zone. Additional offset of 30 cm occurred across the same structure during the late Pleistocene.
Our study provides direct stratigraphic evidence for at least one surface-faulting event during the Holocene, and another in the late Pleistocene, within the Truckee fault zone and provides new constraints on seismic sources capable of significant ground rupture and/or shaking in the greater Reno–Tahoe–Truckee area.
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Location: Barossa Valley, Australia, 2011
AEES
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Location: New Zealand, 2010
ANZGG
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Location: Denver, Colorado, 2010
GSA
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Location: Perth, Australia, 2010
AEES
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Location: Kelowna, British Colombia, 2009
GSA
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Location: Portland, Oregon, 2009
GSA
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Location: Basin and Range, 2009
Friends of the Pleistocene Pacific Cell Field Conference
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Authors: Carver, G., Sauber, J., Lettis, Wm., Witter, R., Whitney, B.
Reference: 2008. American Geophysical Union Monograph "Active Tectonics and Seismic Potential of Alaska." Jeffrey T. Freymueller, Peter J. Haeussler, Robert L. Wesson, Göran Ekström, (Editors). p 167-184.7
The Kodiak Archipelago is a 250-km-long group of islands in the western Gulf of Alaska within the forearc of the eastern Aleutian subduction zone above the southern part of the megathrust that ruptured during the great 1964 Alaska earthquake (Mw 9.2).
Widespread low-relief coastal surfaces on Kodiak Island and several adjacent islands, interpreted as late Quaternary raised marine terraces, were used to estimate uplift rates. We found that the uplift rate at Narrow Cape, situated within the Kodiak Shelf fault zone on the northeast coast of Kodiak Island, was 3-5 times higher than at other locations around the island. We attribute this higher rate of uplift, about 0.75 mm/yr, to upper crustal faulting in the Kodiak Shelf fault zone. GPS-measured strain at nine sites on two transects across Kodiak Island resolved onto the N45°E trend of the fault zone predicts left-lateral slip rates of 5-15 mm/yr.
Paleoseismic investigations of the Narrow Cape fault, one of several major faults in the fault zone, reveal up to 30-35 m of postglacial left-lateral offset on the fault. Faulted latest Pleistocene and Holocene sediments exposed in trenches on three subsidiary branches of the Narrow Cape fault record six or seven episodes of faulting. Ages for these faulting events were determined by using tephrachronology based on two 14C dated reference stratigraphic sections at the cape and suggest recurrence intervals of 1-2 ka.
The evidence of Holocene activity on the Narrow Cape fault and its subsidiary branches indicates that these faults are potential sources for large crustal earthquakes in the Kodiak Island region.
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Location: Kenai, 2007
Friends of the Pleistocene Alaska Cell Field Conference
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Location: Bellingham, Washington, 2007
GSA
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Location: Manix Basin, 2007
Friends of the Pleistocene Pacific Cell Field Conference
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Location: Anchorage, Alaska, 2006
GSA
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Location: Mendocino Triple Junction, 2006
Friends of the Pleistocene Pacific Cell Field Conference
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Authors: WHITNEY, Martha A.
Reference: Humboldt County, California, 2003.
Geological Society of America Abstracts with Programs. Vol. 37, No. 4, p.33
Transportational and depositional environments as evidenced by
phytoclast accumulations are compared with existing models of turbidite
deposition to define the dynamic offshore setting of late
Cretaceous-early Paleogene northwestern California.
This study examines
phytoclast concentrations within three depositionally related turbidite
units of northwestern California: the Yager terrane, Yolly Bolly
terrane and the Franciscan Central Belt Mélange. Although literature
on phytoclasts is abundant, studies of phytoclast deposition in the
deep-sea are limited. A better understanding of the transportational
and depositional history of turbidites is facilitated by an analysis of
phytoclast concentrations. SEM images of phytoclasts are compared with
images of in situ fossil wood fragments of the shallow marine Miocene
Saint George Formation.
This comparison illustrates degradation of
phytoclast structural tissue resulting from transportation and
subsequent processes. Details of flow events are captured in individual
phytoclast accumulations. Preferred orientations of relatively long
phytoclasts indicate possible flow direction. An examination of
phytoclast laminae relative to coarse and fine grained sediments
illustrates the usefulness of phytoclast laminae in the determination of
upward direction in turbidite stratigraphic sections. Random
orientations of phytoclasts adjacent to mudstone rip up clasts support
debris flow origins for portions of these deposits.
As sedimentology
attempts to narrow the definition of turbidite and incorporate flow
mechanics and rheology into more specific classifications such as
densites, debrites and gravites, the importance of the phytoclast
component should not be overlooked.
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Location: Central Alaska Range, 2005
Friends of the Pleistocene Alaska Cell Field Conference
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Location: Avawatz/Death Valley, 2005
Friends of the Pleistocene Pacific Cell Field Conference
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Location: Denver, Colorado, 2004
GSA
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Location: Santa Barbara, 2004
Friends of the Pleistocene Pacific Cell Field Conference
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Authors: MITCHELL, Martha A. and OSWALD, John A.
Reference: Humboldt County, California, 2003.
Geological Society of America Abstracts with Programs. Vol. 35, No. 6, September 2003, p.331
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A primary limitation of regional landslide mapping is the subjective nature of topographic and aerial photographic interpretation. For the past 5 years, extensive ground based mapping has been conducted at site specific levels for individual timber harvest plans within the ownership of the Scotia Pacific Company.
The associated engineering geologic evaluations provide an interpretation of the activity status and mode of failure of individual landslides. This information is reviewed, and at times modified, by regulatory agencies before the Timber Harvest Plan is approved. This process ultimately results in field verified, site specific landslide mapping of large portions of managed landbase.
The Scotia Pacific Company Geology Department recently began to compile, at a scale of 1:12,000, the extensive landslide mapping associated with approved Timber Harvest Plans. This work also involves the preparation of a database to accompany the map.
Each landslide is assigned a number that corresponds to specific attributes in the database. Attributes include the specific THP name and file number, the responsible firm, drainage subbasin, activity status, mode of failure, dimensions, and a field for miscellaneous notes. The many practical applications of the compilation maps and database include resource planning and allocation, prioritization of landslide prevention and mitigation measures, streamlining the required review of pertinent mapping and assisting foresters in the initial layout of timber harvest plans.
This poster presents the preliminary compilation map of Timber Harvest Planning-level landslide mapping to date for the ownership within the Van Duzen Watershed in Northern California.
Location: Seattle, Washington, 2003
GSA
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Location: Kings Canyon, 2003
Friends of the Pleistocene Pacific Cell Field Conference
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Location: Dixie Valley, 2002
Friends of the Pleistocene Pacific Cell Field Conference
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