Lewis A Owen

This data set contains complete trench logs PDF format and plain image mosaics of the trench walls with no interpretation in JPG format. Image resolution is 2,950 pixels per meter of trench wall. We provide versions of the trench logs with and without interpretations so others can work with the raw data and evaluate our observations. This data set also includes a detailed description of the ground-penetrating radar surveys performed around and between trenches at the study area along the western flank of Sierra El Mayor. These data show evidence for at least six major surface ruptures during the past 17 ka on the Cañada David detachment, which is a low-angle normal fault in northern Baja California, Mexico. Recurrence intervals show little variability and range from 2.5 to 3 ka. These findings suggest that the seismogenesis and mechanical behavior of this severely misoriented fault are very similar to, if not indistinguishable from, other more optimally oriented faults with similar slip rates. This contrasts with the observation that large earthquakes demonstrably associated with such faults are exceedingly rare in catalogs of global seismicity and adds to the controversy surrounding our understanding of how fault geometry and orientation affects the conditions for failure.

... et al., 2001). Lewis A. Owen 204 equilibrium line altitude (ELA) depression to be c.800 m. Figure 3 shows the positions of the landforms that Holmes & Street-Perrott (1989) believe are unequivocally moraines. They were able ...

The western margin of the Sierra El Mayor (SEM), in northeastern Baja California, is controlled by an active, top-to-the-west, low-angle normal fault named the Canada David detachment (CDD) that accommodates part of the extensional component of shearing between the Pacific and North American plates. The CDD has a length of 60 km and shows a curvilinear trace with two major antiformal and synformal megamullion pairs. Late Quaternary slip has produced a broad array of Quaternary scarps cutting alluvial fans along nearly the entire length of the CDD. Detailed mapping reveals eight regional strath terraces distinguished by surface weathering characteristics, soil profile development and relative elevation. Relative height between terraces increases in domains where the CDD and basin deposits are being uplifted due to either the basinward migration of faulting (e.g., rolling hinge) or flexural uplift in antiformal megamullion domains. Linear diffusion analysis of 46 synthetic fault scarps, with a calculated angle of repose Θo = 28.75°, reveal fault scarp domains exhibiting both multi-modal and unimodal distribution of diffusion ages (kt). Uni-modal domains are typically younger, but there is no systematic variation in scarp age with distance along the CDD. Scarps yielding negative kt ages (i.e. scarps steeper than Θo) are common in the north, near inferred locations of important historic seismic events. Microseismicity drops off significantly adjacent to these very young scarp arrays, which likely reflects a recent post-seismic stress drop. Domains of high seismic risk are identified by high microseismicity and lack of young scarps. Minimum estimates of the diffusivity constant (k) are calculated by coupling scarp diffusion ages and 10Be surface exposure ages of the faulted deposits. In the southernmost SEM a Q6 terrace with a minimum surface exposure age t = 233±6.6 ky (weighted mean of six rock samples) is cut by scarps with an average kt = 11.25±9.31 m2, which yields a minimum k = 0.05±0.04 m2/ky. Scarps cutting Q4 terraces yield diffusion ages (kt = 0.16±0.04 m2) consistent with the inferred post-glacial age of the four youngest terraces.

Tectonic landforms associated with transform plate margins and strike–slip faults vary from the plate boundary scale to the regional and local scale, and they help provide an understanding of the dynamics and the nature of structural and landscape development. Classic examples of these plate margins and fault systems include: the Pacific-North American plate boundary incorporating the San Andreas fault and the eastern California shear zone-walker Lane; and the Pacific-Australian plate boundary; the Caribbean-North American plate boundary; and intracontinental strike–slip systems of the Himalayan-Tibetan orogen. New advances in remote sensing, geochronology, and tectonic geodesy are helping to better resolve patterns of deformation and landscape development along these fault systems.

The influence of the 08 October 2005 Kashmir earthquake and subsequent snow melt and monsoon rainfall on slope stability was evaluated using repeat photography in the Kashmir Himalaya of northern Pakistan. Sixty-eight landslide-affected locations were selected and photographed in November 2005, May/June 2006, June 2007, and August 2007 to evaluate all potential geomorphic changes. Eighty percent of the locations showed no or very little change, 11% of the locations showed a partial vegetation recovery on the slopes, while 9% showed an increase in the landslide area. All those locations that showed an increase in landsliding were located along rivers and/or roads. The small change in landslide extent is remarkable given that the region experienced one of the heaviest monsoon seasons in the last decade and is counter to earlier predictions of accelerated slope erosion by landsliding in the immediate years following the earthquake. Extensive fissures and ground cracks at many localities, however, still present a potential of future landsliding under wetter conditions.

The Lahul Himalaya of northern India provides an excellent natural laboratory to define rates of denudation and exhumation in an active mountain belt because its Quaternary history -- derived from well-preserved and dated successions of landforms and sediments -- is well established. Building on previous tectonic and geomorphic studies, terrestrial cosmogenic nuclide (TCN) 10Be surface exposure dating and apatite (U-Th)/He (AHe) thermochronology was applied along the Chandra Valley to quantify rates of fluvial incision and exhumation. TNC ages on successive strath treads at four locations along the Chandra River and one of its tributary rivers, between Batal and Khoksar, range from 0.56 to 5.36 ka, yielding post-glacial (after 10 ka) rates of fluvial incision of 1.5 to 13.5 mm/a. The highest rates are associated with straths along a narrow canyon-like stretch of the main drainage (Chandra River) and an associated tributary valley. These are an order of magnitude greater than those of gentler, broader alluviated reaches of the Chandra. The highest rates may suggest a change in uplift or landscape incision modulated by glacial fluctuation. AHe ages from leucogranite exposed near the Chandra River and at higher elevations in steep, deeply gorged, glaciated side valleys range between 1.46 and 2.51 Ma, marking a pulse of rapid cooling and denudation during the Late Pliocene-Quaternary. These TNC and AHe data suggest enhanced denudation of the region during the Quaternary and provide some of the first quantitative data for rates of landscape evolution in the Lahul Himalaya of northern India.

Temporal,and spatial changes,in glacier cover throughout,the Late Quaternary in Tibet and,the bordering,mountains,are poorly defined because of the inaccessibility and vastness of the region, and the lack of numerical dating. To help reconstruct the timing and extent of glaciation throughout Tibet and the bordering mountains, we use geomorphic mapping and ,Be CRN surface exposure datingshows that the formation of moraines

ABSTRACT 15.1 INTRODUCTION The concept of the glaciated valley landsystem was introduced by Boulton and Eyles (1979) and Eyles (1983b), to describe the characteristic sediments and landforms associated with valley glaciers in upland and mountain environments. By focusing on the scale of the whole depositional basin, the glaciated valley landsystem has a broader compass than most of the other landsystems explored in this book, which are specific to particular depositional environments. Indeed, glaciated valley landsystems may incorporate ice-marginal, supraglacial, subglacial, proglacial, periglacial and paraglacial landsystems, recording the juxtaposition and migration of very different depositional environments. Additionally, because glaciated valleys occur in every latitudinal environment from equatorial to polar regions, the dimensions of climate and glacial thermal regime add even more variability. Thus the 'glaciated valley landsystem' should be regarded as a family of landsystems, which exhibits considerably more variety than suggested by the original Boulton and Eyles model (Fig. 15.1). Despite this variability, landsystems in glaciated valleys tend to have certain recurrent features, as a result of two main factors: 1. the strong influence of topography on glacier morphology, sediment transport paths and depositional basins 2. the importance of debris from supraglacial sources in the glacial sediment budget. In this chapter, we emphasise the contrasts between glaciers with limited supraglacial debris ('clean glaciers') and glaciers with substantial debris covers in their ablation zones ('debris-covered glaciers'), although it should be recognized that intermediate forms occur between these end members. Before examining the landsystems of glaciated valleys, we begin by considering debris sources and transport pathways through valley glaciers, and the ways in which debris cover influences glacier dynamics. 15-Evans-Glacial-15-ppp 5/27/03 2:38 PM Page 372

Geomorphic models such as the glacial buzz saw and denudational unloading and understanding the significance of active tectonics on geomorphic systems can be elucidated by quantitatively defining rates of erosion and sediment transfer in active mountain systems. To this end, we examine the topographically and morphometrically asymmetrical Ladakh Range to quantify the significance of tectonic influence on geomorphic systems. Morphometric analysis and10Be cosmogenic radionuclide dating of 13 fluvial sediment samples from active channels was undertaken in 6 catchments to define erosion rates. North facing catchments of the central Ladakh Range have erosion rates of 0.056±0.012 mm/yr and 0.074±0.011 mm/yr, while south facing catchments have rates of 0.020±0.003 mm/yr, 0.020±0.003 mm/yr, and 0.039±0.008 mm/yr. Rates of erosion in north facing catchments are approximately two times higher than rates of erosion in south facing catchments. This data confirms that the tectonic tilting of the Ladakh Range and active rock uplift (~ 1 mm/yr) on the northern side of the range has had a significant impact on the rate of erosive geomorphic processes. However, the increased erosion on the northern side of the range is not keeping pace with rock uplift on the northern side of the range. Morphometric analysis shows that the maximum and average elevations increase at nearly the same rate across the Ladakh Range with higher elevation on the northern side. This precludes the possibility of long-term denudational unloading from having a significant feedback into the tectonic tilting of the range.

Mountain geodynamics represent highly scale-dependent interactions involving climate, tectonic, and surface processes. The central Karakoram in Pakistan exhibit strong climate–tectonic feedbacks, although the detailed tectonic and topographic responses to climate ...

Low-temperature apatite (U-Th)/He (AHe) thermochronology on vertical transects of leucogranite stocks and 10Be terrestrial cosmogenic nuclide (TCN) surface exposure dating on strath terraces in the Lahul Himalaya provide a first approximation of long-term (10 4-10 6 years) exhumation rates for the High Himalayan Crystalline Series (HHCS) for northern India. The AHe ages show that exhumation of the HHCS in Lahul from shallow crustal levels to the surface was ~ 1-2 mm/a and occurred during the past ~ 2.5 Ma. Bedrock exhumation in Lahul fits into a regional pattern in the HHCS of low-temperature thermochronometers yielding Plio-Pleistocene ages. Surface exposure ages of strath terraces along the Chandra River range from ~ 3.5 to 0.2 ka. Two sites along the Chandra River show a correlation between TCN age and height above the river level yielding maximum incision rates of 12 and 5.5 mm/a. Comparison of our AHe and surface exposure ages from Lahul with thermochronometry data from the fastest uplifting region at the western end of the Himalaya, the Nanga Parbat syntaxis, illustrates that there are contrasting regions in the High Himalaya where longer term (10 5-10 7 years) erosion and exhumation of bedrock substantially differ even though Holocene rates of fluvial incision are comparable. These data imply that the orogen's indenting corners are regions where focused denudation has been stable since the mid-Pliocene. However, away from these localized areas where there is a potent coupling of tectonic and surface processes that produce rapid uplift and denudation, Plio-Pleistocene erosion and exhumation can be characterized by disequilibrium, where longer term rates are relatively slower and shorter term fluvial erosion is highly variable over time and distance. The surface exposure age data reflect differential incision along the length of the Chandra River over millennial time frames, illustrate the variances that are possible in Himalayan river incision, and highlight the complexity of Himalayan environments.

Tibet and the bordering mountains are the most extensively glaciated tract outside the polar regions, exerting an important influence on regional and global environmental change. The glacial system provides water for many hundreds of millions of people in central Asia, and variations in the glacial and associated hydrological systems have profound socio-economic and political consequences. Yet despite the regional and global importance of glaciation in High Asia, the dynamics, extent and timing of Quaternary glaciation in this region are poorly understood and defined. This is partially because of the inaccessibility and vastness of the region, and hence lack of field studies. During recent years, however, numerous ice core and glacial geologic studies have begun to examine some of the more accessible mountain ranges in High Asia to help quantify the nature of Late Quaternary paleoclimatic change in the region. While the new ice core records provide high resolution data defining the magnitude and frequency of climatic oscillations, mainly for the Late Pleistocene and Holocene, the glacial geologic data is enabling reconstructions of the extents of former glaciers to be determined for the last several glacial cycles. Taken together, these data suggest that regional patterns and timing of glaciation throughout the region reflect temporal and spatial variability in the south Asian monsoon and, in particular, regional precipitation gradients, as well as cooling cycles that are broadly associated with Heinrich event. Understanding these patterns of glaciation and the forcing factors are essential for helping to develop and test climatic models that are critical for predicting the likely consequences of global warming on the glaciological and hydrological systems of Central Asia.

The Tibetan Plateau is a global scale feature that has a profound influence on regional and global climate and is, in turn, itself influenced by the Asian monsoon and mid-latitude westerlies. Changes in the extent of glaciers and snow cover on the Tibetan Plateau help ...

Late Quaternary slip across the Cañada David detachment has produced an extensive array of Quaternary scarps cutting alluvial-fans along nearly the entire length (~ 60 km) of the range-bounding detachment. Eight regional alluvial-fan surfaces (Q 1 [youngest] to Q 8 [oldest]) are defined and mapped along the entire Sierra el Mayor range-front. Terrestrial cosmogenic nuclide 10Be concentrations from individual boulders on alluvial-fan surfaces Q 4 and Q 7 yield surface exposure ages of 15.5 ± 2.2 ka and 204 ± 11 ka, respectively. Formation of the fans is probably tectonic, but their evolution is strongly moderated by climate, with surfaces developing as the hydrological conditions have changed in response to climate change on Milankovitch timescales. Systematic mapping reveals that the fault scarp array along active range-bounding faults in Sierras Cucapa and El Mayor can be divided into individual rupture zones, based on cross-cutting relationships with alluvial-fans. Quantitative morphological ages of the Laguna Salada fault-scarps, derived from linear diffusive degradation modeling, are consistent with the age of the scarps based on cross-cutting relationships. The weighted means of the maximum mass diffusivity constant for all scarps with offsets < 4 m is 0.051 and 0.066 m 2/ka for the infinite and finite-slope solutions of the diffusion equation, respectively. This estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of Laguna Salada.

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Glacial geological evidence from throughout the Himalaya-Tibet shows the existence of expanded ice caps and extensive valley glacier systems during the late Quaternary. Whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied is a topic of much contention. This is mainly because the lack of organic material needed for radiocarbon dating that has hindered past progress in glacial reconstruction. However, the application of optically stimulated luminescence and terrestrial cosmogenic nuclide (TCN) methods has recently expanded the number of chronologies throughout the region helping to test glacier synchoneity. Yet, limits to the precision and accuracy available with these methods and, more importantly, geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to Milankovitch timescales (several ka). All the published TCN ages for moraine boulders and glacially eroded surfaces in the Himalayan-Tibetan orogen have been recalculated to assess synchroneity of glaciations, and well-dated sites have been re-evaluated. Locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation. Glaciers throughout monsoon-influenced Tibet, the Himalaya and the Transhimalaya are likely synchronous both with climate change resulting from oscillations in the South Asian monsoon and with Northern Hemisphere cooling cycles. In contrast, glaciers in Pamir in the far western regions of the Himalayan-Tibet orogen advanced asynchronously relative to the other regions that are monsoon-influenced regions and appear to be mainly in phase with the Northern Hemisphere cooling cycles. Broad patterns of local and regional variability based on equilibrium-line altitudes have yet to be fully assessed, but have the potential to help define changes in climatic gradients over time.

Quaternary vertical slip rate estimates along the southern Sierra Nevada frontal fault zone in California are not well constrained due to the absence of absolute ages on offset Quaternary geologic markers. This study presents new geologic and geochronologic evidence for late Pleistocene to Holocene extension across the southern Sierra Nevada frontal fault zone from Oak Creek to just south of Lubken Creek by incorporating geologic field mapping, tectonic geomorphology and beryllium-10 cosmogenic radionuclide geochronology. The southern escarpment of the Sierra Nevada exposes numerous NNW-striking, east-facing, en echelon normal fault scarps that offset three distinct Quaternary surfaces. The oldest alluvial fan surface, Qf1, is generally smooth and overlain with scarce, typically strongly weathered granitic boulders that are well-embedded into the alluvial surface. Qf2 surfaces are incised into Qf1 surfaces and characterized by ridge and ravine topographic patterns, and moderately weathered granite boulders. Qf2 surfaces are, in turn, incised by Qf3 surfaces, which are distinguished by a bar and swale surface morphology and large abundant unweathered granite boulders. The youngest fan surfaces are Qf4, which are defined by active or recently abandoned channels. Beryllium-10 cosmogenic radionuclide surface exposure dating of twenty-nine granitic boulders from these surfaces provide the age of deposition and abandonment: 140 ± 34 ka for Qf1, 64 ± 16 ka for Qf2, 23 ± 7 ka for Qf3a, 5 ± 1, and 4 ± 1 ka for Qf4. These ages are consistent, within error, of published ages for surfaces elsewhere in the region. Topographic profiles measured across normal fault scarps that cut and offset these surfaces yielded minimum vertical surface offsets of 40.8 ± 8.2 m for Qf1 surfaces, 21.9 ± 4.4 m for Qf2 surfaces, 10.2 ± 2.0 m for Qf3a, and 6.4 ± 1.3 m for Qf3c surfaces. Qf4 surfaces did not show evidence of offset. These data suggest late Pleistocene vertical slip rates of 0.3 to 0.4 ± 0.1 mm/yr since ~140 ka to ~23 ka and 1.4 mm/yr since ~5 ka. If we assume a fault dip of 60°, then the late Pleistocene and Holocene horizontal extension rate across this part of the Sierra Nevada frontal fault zone is 0.2 ± 0.1 and 0.8 ± 0.2 mm/yr. Our slip rate estimates are the same as or somewhat slower than slip rate estimates elsewhere along the Sierra Nevada frontal fault zone and are comparable to late Pleistocene slip rate estimates across the Basin and Range Province.

Z. Geomorpli. NF Suppl.-Vol, 130 263-276 Berlin ■ Stuttgart March 2003 The timing and style of Late Quaternary glaciation in the La Ji Mountains, NE Tibet: evidence for restricted glaciation during the latter part of the Last Glacial Lewis A. Owen, Ma Haizhou, Edward Derbyshire, ...

The Sierras Pampeanas (Pampean Ranges) of Argentina are characterized by mountain blocks bounded by reverse faults, whose last stage of uplift has been attributed to the shallowing of the Nazca plate (&lt; 11Ma). These faulted blocks constitute a prominent surface feature of the Pampean flat-slab in the Central Andes (27°-33°S), as well as a modern analog of the Rocky Mountains Laramide uplifts in North America. Evidence of Quaternary activity has been reported along main bounding structures. However, the lack of exposures suitable for paleoseismological analysis has hampered most attempts to address key questions on the Quaternary deformation history and the seismogenic potential of these intraplate faults. New data obtained at the El Molino section of the Comechingones fault in the southeastern Sierras Pampeanas, shows a Quaternary-active short-cut of the main bounding structure of the Comechingones uplifted block. In addition, new excavations across the fault trace near Merlo vil...

ġThe timing and extent of glaciations during the Late Quaternary in the South Shetland Islands, West Antarctica were defined using field mapping, geomorphic analysis and radiocarbon dating. Landforms of glacial erosion and deposition, in particular subglacial meltwater channel erosion, suggest that at least three glaciations occurred during the late Quaternary within the study region. During the global LGM, glacial troughs

ABSTRACT Big Bone Lick (BBL) in northern Kentucky, USA has been a critical geologic site in the historical development of North American Quaternary vertebrate paleontology since the 1700s. Sedimentology, geoarcheology, paleontology, accelerator mass spectrometry radiocarbon and optically stimulated luminescence dating, and stable carbon and nitrogen isotope analyses were undertaken to develop a chronostratigraphy and history of erosion and deposition for the site to provide a foundation for understanding taphonomy, and species extinction and adaptation to periods of climatic and environmental change. Three geomorphic surfaces are recognized at BBL representing significant periods of floodplain aggradation since the last glacial maximum (26.5–19 ka) dating to the Oldest Dryas (Tazewell, 25–19 ka), the Older Dryas (Cary, 14–12 ka), and late Holocene (5 ka to the present). Unconformities suggest significant periods of degradation during the transitions from cold and dry to warm and moist climates from the Oldest Dryas (Tazewell) to Bølling Oscillation, from the Older Dryas (Cary) to the Allerød, and from the Younger Dryas (Valders) to the Holocene Climatic Optimum. Increased anthropogenic activities since ~ 5 ka may have increased soil upland erosion and floodplain aggradation. Stable isotopes demonstrate that the landscape has been dominated by C3 vegetation since the last glacial maximum.

The Atlas Mountains of Morocco constitute a natural laboratory for studying interactions between tectonics and surface processes in convergent zones. The tectonic forcing of the system is well understood, where a combination of crustal and mantle processes contributed to surface uplift. A growing database on magnetostratigraphic dating of synorogenic sediments, low-temperature thermochronology and surface exposure dating constrain the relationships between