Geomorphic Observations Research Articles

Active Fault-Related Folding beneath an Alluvial Terrace in the Southern Longmen Shan Range Front, Sichuan Basin, China: Implications for Seismic Hazard

Abstract The devastating 2008 M w 7.9 Wenchuan earthquake, China, demonstrates that the central and northern parts of the Longmen Shan are currently active. Evidence for active faulting and folding in the southern Longmen Shan, however, remains poorly documented. In this paper, we define the structural geometry, fault kinematics, and seismic hazard of the Qiongxi thrust fault system (QTF) along the southern Longmen Shan range front by integrating deep and shallow seismic‐reflection data and geomorphic observations. The QTF is a 50 km long, north–south‐trending set of faults and associated folds that exhibit geomorphic evidence of Quaternary surface deformation. Geomorphic observations and seismic‐reflection data reveal that these faults dip steeply to the east and merge at depth with a blind, west‐dipping thrust ramp. The trend and reverse sense of slip along the QTF indicates that the structure accommodates east–west crustal shortening. Based on uplift of stratigraphic horizons across the fault zone, we define a Late Pliocene–to–Early Pleistocene fault slip rate of 0.2–0.3 mm/yr and a Middle Pleistocene–to–present rate of 0.4–1.2 mm/yr on the west‐dipping thrust ramp. This ramp soles to a basal detachment in the Triassic section at a depth of 4.5–5.5 km. To the west, this detachment steps down onto a blind, northwest‐dipping thrust termed the Range Front thrust. A rupture of the QTF in combination with the Range Front thrust could generate an M w 7.8 earthquake with average displacement of 5.7 m. This type of earthquake source poses significant hazards to the adjacent, highly populated Sichuan basin. Online Material: Figures detailing cross sections and 3D surfaces, additional reflection profiles, and dating information.

Tectonic and Hydrothermal Activities in Debagh, Guelma Basin (Algeria)

Quaternary and Pliocene travertines, deposited from hot springs, can reveal much about neotectonic and hydrothermal activity. The aim of this work is the understanding of the actual tectonic activity in the Guelma Basin and in one of its spa structures. Gravity data were collected during a field study in the Hammam Debagh (HD) area and then analyzed to better highlight the architecture of its subsurface underlying structures. This analysis was performed by means of a Bouguer anomaly, upward continuations, and residual and derivative maps. Comparison of gravity maps, field geology, geomorphic observations, and structural maps allowed us to identify the major structural features in the Hammam Debagh. As a result, we confirm the position of the Hammam Debagh active fault which is superimposed to the hydrothermal active source in the NW-SE direction characterized by a negative gravity anomaly.

Plio-Quaternary extensional tectonics of the Central Anatolian Plateau: a case study from the Tuz Gölü Basin, Turkey

The Tuz Gölü Basin is the largest sedimentary depression located at the center of the Central Anatolian Plateau, an extensive, low-relief region with elevations of ca. 1 km located between the Pontide and Tauride mountains. Presently, the basin morphology and sedimentation processes are mainly controlled by the extensional Tuz Gölü Fault Zone in the east and the transtensional İnönü-Eskişehir Fault System in the west. The purpose of this study is to contribute to the understanding of the Plio-Quaternary deformation history and to refine the timing of the latest extensional phase of the Tuz Gölü Basin. Field observations, kinematic analyses, interpretations of seismic reflection lines, and ^{40}Ar/^{39}Ar dating of a key ignimbrite layer suggest that a regional phase of NNW-SSE to NE-SW contraction ended by 6.81 ± 0.24 Ma and was followed by N-S to NE-SW extension during the Pliocene-Quaternary periods. Based on sedimentological and chronostratigraphic markers, the average vertical displacement rates over the past 5 or 3 Ma with respect to the central part of Tuz Gölü Lake are 0.03 to 0.05 mm/year for the fault system at the western flank of the basin and 0.08 to 0.13 mm/year at the eastern flank. Paleo-shorelines of the Tuz Gölü Lake, vestiges of higher lake levels related to Quaternary climate change, are important strain markers and were formed during Last Glacial Maximum conditions as indicated by a radiocarbon age of 21.8 ± 0.4 ka BP obtained from a stromatolitic crust. Geomorphic observations and deformed lacustrine shorelines suggest that the main strand of the Tuz Gölü Fault Zone straddling the foothills of the Şereflikoçhisar–Aksaray range has not been active during the Holocene. Instead, deformation appears to have migrated towards the interior of the basin along an offshore fault that runs immediately west of Şereflikoçhisar Peninsula. This basinward migration of deformation is probably associated with various processes acting at the lithospheric scale, such as plateau uplift and/or microplate extrusion.

Geomorphic coupling between hillslopes and channels in the Swiss Alps

ABSTRACTThe coupling relationships between hillslope and channel network are fundamental for the understanding of mountainous landscapes' evolution. Here, we applied dendrogeomorphic methods to identify the hillslope–channel relationship and the sediment transfer dynamics within an alpine catchment, at the highest possible resolution. The Schimbrig catchment is located in the central Swiss Alps and can be divided into two distinct geomorphic sectors. To the east, the Schimbrig earth flow is the largest sediment source of the basin, while to the west, the Rossloch channel network is affected by numerous shallow landslides responsible for the supply of sediment from hillslopes to channels. To understand the connectivity between hillslopes and channels and between sources and sink, trees were sampled along the main Rossloch stream, on the Schimbrig earth flow and on the Rossloch depositional area. Geomorphic observations and dendrogeomophic results indicate different mechanisms of sediment production, transfer and deposition between upper and lower segments of the channel network. In the source areas (upper part of the Rossloch channel system), sediment is delivered to the channel network through slow movements of the ground, typical of earth flow, shallow landslides and soil creep. Contrariwise, in the depositional area (lower part of the channel network), the mechanisms of sediment transfer are mainly due to torrential activity, floods and debris flows. Tree analysis allowed the reconstruction of periods of high activity during the last century for the entire catchment. The collected dataset presents a very high temporal resolution but we encountered some limitations in establishing the source‐to‐sink connectivity at the catchment‐wide scale. Despite these uncertainties, for decennial timescales the results suggest a direct coupling between hillslopes and neighbouring channels in the Rossloch channel network, and a de‐coupling between sediment sources and sink farther downstream, with connections possible only during extraordinary events. Copyright © 2012 John Wiley & Sons, Ltd.

Geomorphic constraints on Middle Yangtze River reversal in eastern Sichuan Basin, China

The Yangtze, the longest river in Asia, was hypothesized to be assembled through a series of Cenozoic capture events, such as the reversal of Middle Yangtze River and the capture of Upper Yangtze River, but the history remains largely unknown. Here, we present new geomorphic observations in the structural context of the eastern Sichuan Basin, namely the Eastern Sichuan fold belt, and identify an important drainage divide along the “midline” of this arc-shape fold belt. Based on longitudinal profile analysis, we find that the river capture events more likely occurred in the syncline valleys of low-relief landscape. Our results yield a new perspective on Middle Yangtze River reversal, and we propose that the “midline” drainage divide, rather than the Three Gorges, was the starting site of Middle Yangtze River reversal. In this manner, the reversal could have been accomplished by a sequence of river reversal over range-parallel segments in syncline valleys with less impact on the pre-existing drainage system in eastern Sichuan Basin.

Short- and long-term studies of sediment dynamics in a small humid mountain Mediterranean basin with badlands

Badland landscapes are the main sediment sources in the Vallcebre area (Eastern Pyrenees, Catalonia, Spain). Short-term studies (up to 3-years long) carried out between 1980 and 1994 were used to estimate the rates of both denudation on bare surfaces and sediment production at the plot scale, to analyse the seasonal dynamics of bedrock weathering and regolith behaviour, and to study the relationships between geomorphic activity and herbaceous plant colonisation. Since 1990, stream flow and suspended sediment loads have been monitored using three gauging stations equipped with infrared backscattering turbidimeters, ultra-sonic beam attenuation solids sensors and automatic water samplers. The combination of the two different approaches has been useful for a better perception of the dynamics of the badland systems and to assess the long-term contribution of these areas to the basin sediment loads. Badland erosion at the event scale for a period of 15years was simulated with the KINEROS2 model and allowed the long-term comparison between badland erosion and sediment yield at the small basin scale. Badlands are the main source of sediment in the basin for most of the events, but infrequent runoff events cause the removal of sediment stores and the activation of other sediment sources. The analysis of the uncertainty of sediment yield measurements for a range of record durations demonstrated that long records are needed for obtaining acceptable results due to the high interannual variability. Relatively low-cost short-term geomorphic observations may provide information useful for assessing the long-term sediment production in these basins with badland areas only if the observations are used to implement a model able to simulate long-term observations.

Ice‐avalanche impact landforms: the event in 2003 at the glacier nördliches bockkarkees, hohe tauern range, austria

Kellerer‐Pirklbauer, A., Slupetzky, H. and Avian, M., 2012. Ice‐avalanche impact landforms: the event in 2003 at the glacier Nördliches Bockkarkees, Hohe Tauern Range, Austria. Geografiska Annaler: Series A, Physical Geography, 94, 97–115. doi:10.1111/j.1468‐0459.2011.00446.xABSTRACTThe hanging glacier Nördliches Bockkarkees (47°07′21″N; 12°44′00″E) represents the only Austrian glacier that formed large and hazardous ice avalanches over the last decades. Only one major ice avalanche was released between August 1993 and July 2011 underlying the rareness of such large ice avalanches in the Austrian Alps. The ice avalanche happened on 26 June 2003 and was very unusual for two reasons: First, the ice avalanche occurred suddenly without major signs of glacier instabilities even a few days before the event. Second, the ice avalanche was released very early in the season. Ice and debris with a volume of 300-000m3 avalanched over a vertical distance of 1200 m. The main deposits with a volume of 250-000m3 and a debris content of 10% formed a flat avalanche cone in the Käfer Valley covering 82-000m2. This paper focuses on geomorphic and glaciological field measurements and observations at and below the ice avalanche deposit and its vicinity after the event. Studies were made (a) at the deposited material itself, (b) at the reshaped land surface below the deposit after ice melt, (c) at the front and margin of the deposit, and (d) outside the deposit. Our study reveals different types of ice‐avalanche impact landforms comparable to landforms caused by snow avalanches. It is shown that ice avalanches charged with debris at the Nördliches Bockkarkees are important in forming and reshaping erosional and depositional landforms along the track. However, the conservation potential of these landforms is low.

Automatic geomorphic feature extraction from lidar in flat and engineered landscapes

High‐resolution topographic data derived from light detection and ranging (lidar) technology enables detailed geomorphic observations to be made on spatially extensive areas in a way that was previously not possible. Availability of this data provides new opportunities to study the spatial organization of landscapes and channel network features, increase the accuracy of environmental transport models, and inform decisions for targeting conservation practices. However, with the opportunity of increased resolution topographic data come formidable challenges in terms of automatic geomorphic feature extraction, analysis, and interpretation. Low‐relief landscapes are particularly challenging because topographic gradients are low, and in many places both the landscape and the channel network have been heavily modified by humans. This is especially true for agricultural landscapes, which dominate the midwestern United States. The goal of this work is to address several issues related to feature extraction in flat lands by using GeoNet, a recently developed method based on nonlinear multiscale filtering and geodesic optimization for automatic extraction of geomorphic features (channel heads and channel networks) from high‐resolution topographic data. Here we test the ability of GeoNet to extract channel networks in flat and human‐impacted landscapes using 3 m lidar data for the Le Sueur River Basin, a 2880 km2 subbasin of the Minnesota River Basin. We propose a curvature analysis to differentiate between channels and manmade structures that are not part of the river network, such as roads and bridges. We document that Laplacian curvature more effectively distinguishes channels in flat, human‐impacted landscapes compared with geometric curvature. In addition, we develop a method for performing automated channel morphometric analysis including extraction of cross sections, detection of bank locations, and identification of geomorphic bankfull water surface elevation. Using the slope plotted along each channel‐floodplain cross section, we demonstrate the ability to identify and measure the height of river banks and bluffs. Finally, we present an example that demonstrates how extracting such features automatically is important for modeling channel evolution, water and sediment transport, and channel‐floodplain sediment exchange.

Topographic evolution of the Sierra Nevada measured directly by inversion of low-temperature thermochronology

At present, there are at least two competing ideas for the topographic evolution of the Sierra Nevada. One idea is that the Sierra Nevada was formed as a monocline in the Cretaceous, marking the transition from the Great Valley forearc basin to the west, and a high Nevadaplano plateau to the east, similar to the west flank of the modern Altiplano of the Andes. Both the thermochronologic imprint of local relief and the stable isotopic evidence of a topographic rain shadow support this hypothesis. A second idea, supported by geomorphic observations, suggests that the Sierra gained a large fraction of its present elevation as recently as the Pliocene. This recent surface uplift could have been driven by convective removal of the lower part of the lithosphere, the isostatic response to Basin and Range faulting, and/or by changes in dynamic topography associated with deep subduction of the Farallon plate. Here we present the first comprehensive analysis of low-temperature thermochronology in the Sierra Nevada, which indicates that both ideas are likely correct. We show that thermochronology can resolve surface uplift as well as exhumation by measuring long-wavelength topographic evolution relative to sea level. Uplift measurements are possible whenever there is sufficient constraint on vertical rock velocity. The tilting of isochrones, defined as surfaces of equal cooling age, provide this constraint in the Sierra Nevada. Three new factors further distinguish our analysis. The first is that we allow for the local relief and the long-wavelength topography to evolve independently. Second, we use Al-in-Hb barometry to constrain the initial depth of emplacement for the Sierra Nevada plutons. Third, our analysis is tied to a sea-level datum by using the paleo-bathymetric record of the Great Valley basin, where it transitions to the Sierra Nevada batholith. Results indicate that westward tilting of the Sierra Nevada accounts for 2 km of uplift since 20 Ma. Topographic relief increased by a factor of 2. These findings suggest that the Sierra Nevada lost elevation through most of the Tertiary but regained much of its initial elevation following the onset of surface uplift in the Miocene.

Toward quantifying geomorphic rates of crustal displacement, landscape development, and the age of glaciation in the Venezuelan Andes

We present the results of dating glacial landforms in Venezuela using 10Be terrestrial cosmogenic nuclide (TCN) analysis and optical stimulated luminescence (OSL). Boulders on the La Victoria and Los Zerpa moraines of the Sierra Nevada that mark the extent of the local last glacial maximum (LLGM) yield 10Be TCN surface exposure ages of 16.7±1.4ka (8 samples). About 25km to the west in the drainage basin of the Río Mucujún, 10Be TCN dates for boulders on moraines at La Culata in the Sierra Nevada Norte yield a younger average age of 15.2±0.9ka (8 samples). The data suggest that glaciation across the Venezuelan Andes during the LLGM was asynchronous. The LLGM in Venezuela may be broadly concurrent with Heinrich Event 1 at ~16.8ka, implying that glaciation here is dominantly temperature driven. A moraine inset into the older laterofrontal moraines of La Culata has an age of 14.1±1.0ka (5 samples); it may have been deposited by a small Late Glacial readvance. Right-lateral offsets of the La Victoria and Los Zerpa moraines by the Boconó fault are each ~100m. The 10Be TCN based Boconó fault slip rate is about <~5.5 to 6.5mma−1, notably less than the total right-lateral slip of 12±2mma−1 of shear documented across the Andes from geodesy. The 10Be TCN dating of boulders on a faulted alluvial fan along the northwestern range front at Tucanízón yields a late Pleistocene uplift rate of the Andes at between ~1.7±0.7mma−1. Glacial outwash has produced valley-fill sequences within the central Andean valley along the trace of the Boconó fault and Río Chama. The valley-fill has been incised to produce the ‘meseta’, a terrace surface that sits >100m above the Río Chama and on which the major city of Mérida is built. Geomorphic observations indicate that the meseta deposits were largely derived from the glaciers of La Culata. The OSL dating suggests that the final aggradation of the valley-fill deposits occurred rapidly over a period of about 5 to 6ka and that the surface was abandoned and initially incised at ~30ka. The result implies Venezuelan valley fills record phases of aggradation that are likely modulated by climate change on glacial/Milankovitch timescales.

Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault: Implications for the northern margin of the Central Anatolian Plateau, Turkey

Surface uplift at the northern margin of the Central Anatolian Plateau (CAP) is integrally tied to the evolution of the Central Pontides (CP), between the North Anatolian Fault (NAF) and the Black Sea. Our regional morphometric and plate kinematic analyses reveal topographic anomalies, steep channel gradients, and local high relief areas as indicators of ongoing differential surface uplift, which is higher in the western CP compared to the eastern CP and fault‐normal components of geodetic slip vectors and the character of tectonic activity of the NAF suggest that stress is accumulated in its broad restraining bend. Seismic reflection and structural field data show evidence for a deep structural detachment horizon responsible for the formation of an actively northward growing orogenic wedge with a positive flower‐structure geometry across the CP and the NAF. Taken together, the tectonic, plate kinematic, and geomorphic observations imply that the NAF is the main driving mechanism for wedge tectonics and uplift in the CP. In addition, the NAF Zone defines the boundary between the extensional CAP and the contractional CP. The syntectonic deposits within inverted intermontane basins and deeply incised gorges suggest that the formation of relief, changes in sedimentary dynamics, and &gt;1 km fluvial incision resulted from accelerated uplift starting in the early Pliocene. The Central Pontides thus provide an example of an accretionary wedge with surface‐breaking faults that play a critical role in mountain building processes, sedimentary basin development, and ensuing lateral growth of a continental plateau since the end of the Miocene.

Young, active conjugate strike–slip deformation in West Sichuan: evidence for the stress–strain pattern of the southeastern Tibetan Plateau

The active kinematics of the eastern Tibetan Plateau are characterized by the southeastward movement of a major tectonic unit, the Chuan-Dian crustal fragment, bounded by the left-lateral Xianshuihe–Xiaojiang fault in the northeast and the right-lateral Red River–Ailao Shan shear zone in the southwest. Our field structural and geomorphic observations define two sets of young, active strike–slip faults within the northern part of the fragment that lie within the SE Tibetan Plateau. One set trends NE–SW with right-lateral displacement and includes the Jiulong, Batang, and Derong faults. The second set trends NW–SE with left-lateral displacement and includes the Xianshuihe, Litang, Xiangcheng, Zhongdian, and Xuebo faults. Strike–slip displacements along these faults were established by the deflection and offset of streams and various lithologic units; these offsets yield an average magnitude of right- and left-lateral displacements of ∼15–35 km. Using 5.7–3.5 Ma as the time of onset of the late-stage evolution of the Xianshuihe fault and the regional stream incision within this part of the plateau as a proxy for the initiation age of conjugate strike–slip faulting, we have determined an average slip rate of ∼2.6–9.4 mm/year. These two sets of strike–slip faults intersect at an obtuse angle that ranges from 100° to 140° facing east and west; the fault sets define a conjugate strike–slip pattern that expresses internal E–W shortening in the northern part of the Chuan-Dian crustal fragment. These conjugate faults are interpreted to have experienced clockwise and counterclockwise rotations of up to 20°. The presence of this conjugate fault system demonstrates that this part of the Tibetan Plateau is undergoing not only southward movement, but also E–W shortening and N–S lengthening due to convergence between the Sichuan Basin and the eastern Himalayan syntaxis.

The Caribbean–North America–Cocos Triple Junction and the dynamics of the Polochic–Motagua fault systems: Pull‐up and zipper models

The Polochic‐Motagua fault systems (PMFS) are part of the sinistral transform boundary between the North American and Caribbean plates. To the west, these systems interact with the subduction zone of the Cocos plate, forming a subduction‐subduction‐transform triple junction. The North American plate moves westward relative to the Caribbean plate. This movement does not affect the geometry of the subducted Cocos plate, which implies that deformation is accommodated entirely in the two overriding plates. Structural data, fault kinematic analysis, and geomorphic observations provide new elements that help to understand the late Cenozoic evolution of this triple junction. In the Miocene, extension and shortening occurred south and north of the Motagua fault, respectively. This strain regime migrated northward to the Polochic fault after the late Miocene. This shift is interpreted as a “pull‐up” of North American blocks into the Caribbean realm. To the west, the PMFS interact with a trench‐parallel fault zone that links the Tonala fault to the Jalpatagua fault. These faults bound a fore‐arc sliver that is shared by the two overriding plates. We propose that the dextral Jalpatagua fault merges with the sinistral PMFS, leaving behind a suturing structure, the Tonala fault. This tectonic “zipper” allows the migration of the triple junction. As a result, the fore‐arc sliver comes into contact with the North American plate and helps to maintain a linear subduction zone along the trailing edge of the Caribbean plate. All these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates.

Late Miocene–Pliocene deceleration of dextral slip between Pamir and Tarim: Implications for Pamir orogenesis

The timing of the late Cenozoic collision between the Pamir salient and the Tien Shan as well as changes in the relative motion between the Pamir and Tarim are poorly constrained. The northern margin of the Pamir salient indented northward by ~ 300 km during the late Cenozoic, accommodated by south-dipping intracontinental subduction along the Main Pamir Thrust (MPT) coupled to strike-slip faults on the eastern flank of the orogen and both strike-slip and thrust faults on the western margin. The Kashgar–Yecheng transfer system (KYTS) is the main dextral slip shear zone separating Tarim from the Eastern Pamir, with an estimated cumulative offset of ~ 280 km at an average late Cenozoic dextral slip rate of 11–15 mm/a (Cowgill, 2010). In order to better constrain the slip history of the KYTS, we collected thermochronologic samples along the eastward-flowing, deeply incised, antecedent Tashkorgan–Yarkand River, which crosses the fault system on the eastern flank of the orogen. We present 29 new biotite 40Ar/ 39Ar ages, apatite and zircon (U–Th–Sm)/He ages, and apatite fission track (AFT) analysis, combined with published muscovite and biotite 40Ar/ 39Ar and AFT data, to create a unique thermochronologic dataset in this poorly studied and remote region. We constrain the timing of four major N-trending faults; the latter three are strands of the KYTS. The westernmost, the Kuke fault, experienced significant dip-slip, west-side-up displacement between > 12 and 6 Ma. To the east, within the KYTS, our new thermochronologic data and geomorphic observations suggest that the Kumtag and Kusilaf dextral slip faults have been inactive since at least 3–5 Ma. Long-term incision rates across the Aertashi dextral slip fault, the easternmost strand of the KYTS, are compatible with slow horizontal slip rates of 1.7–5.3 mm/a over the past 3 to 5 Ma. In summary, these data show that the slip rate of the KYTS decreased substantially during the late Miocene or Pliocene. Furthermore, Miocene–present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of Tarim rather than a significant decrease of the northward velocity of the Pamir.

Paraglacial gravitational deformations in the SW Alps: a review of field investigations, 10 Be cosmogenic dating and physical modelling

Abstract Catastrophic deep-seated landslides (DSL) are generally considered to be the result of large slope deformations also known as deep-seated gravitational slope deformation (DSGSD). This paper aims to build a synthesis of multiple studies made in the Tinée Valley (southern French Alps) to assess the geometrical, kinematical, mechanical and chronological relationships between these two gravitational processes. At the scale of the valley, data issued from geological, geomorphological and 10 Be dating indicate a clear geometrical link between DSGSD and DSL occurring at the base of the slope and suggest that gravitational slope evolution began after the glacial retreat (13 ka BP). This is supported by the example of the well-documented La Clapière slope. A continuous evolution process is characterized geometrically and temporally from geomorphic observations and analogue modelling. Coupling structural, geomorphological, physical and chronological studies allowed us to propose a four-dimensional (4D) deformation model mechanically correlated with progressive failure concept. The validity and variability of this reference site are discussed at the valley scale (taking Isola and Le Pra slope deformation as examples). It allows a rough estimation of the state of slope deformation at the valley scale to be constructed and the slope evolution with time to be considered. This 4D model could then be considered as a reference for other deep-seated gravitational slope deformations in comparable Alpine valleys.

ARROYOS AND AGRICULTURE

Archaeologists debate the scale, degree of integration, and level of socio-political complexity of the polity centered on Chaco Canyon. The economic organization of the Chacoan system is fundamental to these debates, yet relatively little research has been directed at investigating agricultural potential, a basic variable. To add to a small but growing body of relevant information, we evaluated the agricultural potential of the Pueblo Pintado Great House community using earth science techniques. Geomorphic observations, pedological (soil) studies, and archaeological data suggest that the inhabitants practiced multiple agricultural techniques and farmed several settings as a strategy for reducing risk. Farming on the floodplain of Chaco Wash probably was particularly productive. Continued research of this type, both in the canyon and at outlying communities, could further illuminate which models of the Chacoan system are most plausible.

Deuterium and oxygen isotopes, paleoelevations of the Sierra Nevada, and Cenozoic climate

Although geomorphic observations suggest that the Sierra Nevada has tilted so that the crest has risen 1–2 km since late Miocene time, deuterium and oxygen-18 isotope concentrations in Cenozoic geologic materials decrease eastward across California and Nevada similarly to those in modern, orographically induced precipitation, as if little change in Sierra Nevadan elevations has occurred since Eocene time. Orographic precipitation, however, depends on the amount of moisture in the atmosphere, which in turn can be much larger in warm air, as in Eocene or Oligocene time and in summer, than in the cooler air characteristic of present-day, dominantly winter, precipitation. Moreover, the integrated rainout of vapor, and hence presumably in stable isotope concentrations in the remaining vapor, depends largely on the difference in heights traversed by air masses, not slopes of mountain ranges. Thus, if due simply to orographically induced rainout, both Eocene and Oligocene variations in deuterium isotopes across the Sierra Nevada and Miocene–Quaternary differences in deuterium and oxygen isotopes between the Great Valley of California and the Basin and Range place only weak constraints on the slope or past elevations of the Sierra Nevada. They do not necessarily contradict the inference that the crest of the Sierra Nevada has risen 1000 m or more since late Miocene time.

Slip partitioning in the northeast Pamir–Tian Shan convergence zone

Based on a detailed analysis of satellite imagery combined with field geologic and geomorphic observations, we have mapped late Cenozoic folds and faults in the northeastern Pamir–Tian Shan convergence zone. It is a unique example to understand intracontinental ongoing mountain building within India–Eurasia collision system. In the front of northeastern Pamir, our investigations reveal that the NW-WNW-trending folds display a right-stepping en echelon pattern and NW-WNW-striking faults are mainly characterized by south-dipping thrusts with an extensive dextral strike-slip component. Drainage systems across the active faults show a systematic right-lateral offset. In contrast, structural style of the ENE trending fold-and-thrust belts are predominated by south–north directed shortening southwest of the Tian Shan. Our results also infer that oblique thrusting accommodates as long-term dextral slip rate of ca. 4.0 mm/yr during the late Cenozoic time north of the Pamir topographic front. Tectono-stratigraphic evidence suggests that the tectonic deformation was initiated at ca. 3–5 Ma in the study area. We suggest that intracontinental mountain building in the Pamir–Tian Shan convergence zone should be attributed to the crustal shortening caused by folding and thrusting as well as block rotation related to strike-slip faulting within the India–Eurasia collision system.

Cold and dry processes in the Martian Arctic: Geomorphic observations at the Phoenix landing site and comparisons with terrestrial cold desert landforms

We analyze Surface Stereo Imager observations of rocks, sediments, and permafrost‐related landforms in the vicinity of the Phoenix lander, comparing the imaged features to analogous examples of physical weathering and periglacial processes observed in the Antarctic Dry Valleys. Observations at the Phoenix landing site of pitted rocks, “puzzle rocks” undergoing in‐situ breakdown, perched clasts, and thermal contraction crack polygon morphologies strikingly similar to terrestrial sublimation polygons, all strongly suggest that stable (non‐churning) permafrost processes dominate the Phoenix landing site. Morphological evidence suggests that cold‐desert processes, in the absence of wet active‐layer cryoturbation, and largely driven by sublimation of buried ice (either pore ice, excess ice, or both) are shaping the landscape.

Late Quaternary normal faulting and its kinematic mechanism of eastern piedmont fault of the Haba-Yulong Snow Mountains in northwestern Yunnan, China

The regional geologic and geomorphic observations show that an active arcuate normal fault constitutes the main boundary fault of the Haba-Yulong Snow Mountains (HYSM). This fault is called eastern piedmont fault of Haba-Yulong Snow Mountains (HYPF). The fault consists of two segments with differential trend; the northern segment is NW-trending and NE-dipping and the southern section is S-N trending and E-dipping. Three sets of fault scarps cutting late Quaternary landforms and their dating results indicate that the fault is a prominent Holocene active fault and its throw rates are 0.3–1.4 mm/a during late Quaternary. The geometry and kinematics of the fault suggest that the arcuate normal faulting or rifting are typical surface deformation pattern at the two tips of the Z-shaped rift zone of northwestern Yunnan, which is related to regional east-west extension accompanying clockwise rotation of micro-block.