Terrace Surfaces Research Articles

Climate-driven sediment aggradation and incision since the late Pleistocene in the NW Himalaya, India

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives.New surface-exposure dating of six terrace levels with in-situ cosmogenic 10Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4±3.2 ka and 43.0±2.7 ka (1σ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6±1.2 ka and 15.3±0.9 ka, while terraces sculpted into the upper Pleistocene–Holocene fan (AF2) provide ages of 9.3±0.4 ka (T3), 7.1±0.4 ka (T4), 5.2±0.4 ka (T5) and 3.6±0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision.

On-Surface Synthesis of Two-Dimensional Covalent Organic Structures versus Halogen-Bonded Self-Assembly: Competing Formation of Organic Nanoarchitectures.

The competition between the on-surface synthesis of covalent nanoarchitectures and the self-assembly of star-shaped 1,3,5-Tris(4-iodophenyl)benzene molecules on Au(111) in vacuum is investigated using scanning tunneling microscopy above room temperature. The molecules form covalent polygonal nanoachitectures at the gold surface step edges and at the elbows of the gold reconstruction at low coverage. With coverage increasing two-dimensional halogen-bonded structures appear and grow on the surface terraces. Two different halogen-bonded nanoarchitectures are coexisting on the surface and hybrid covalent-halogen bonded structures are locally observed. At high coverage covalent nanoarchitectures are squeezed at the domain boundary of the halogen-bonded structures. The competitive growth between the covalent and halogen-bonded nanoarchitectures leads to formation of a two-layer film above one monolayer deposition. For this coverage, the covalent nanoarchitectures are propelled on top of the halogen-bonded first layer. These observations open up new opportunities for decoupling covalent nanoarchitectures from catalytically active and metal surfaces in vacuum.

Pitted cobbles from mid-Holocene sites of NW sub-Himalayas of India

By exploring a region of the north-western sub-Himalayas, 74 fluvially rounded pitted cobbles mixed with other artefacts were collected from 16 sites. Each cobble had one to ten pits and, in most of the cases, the pits were placed irregularly on the surface and sides of the cobbles or overlapping each other. From the dating of the terrace surface, wherefrom the pitted cobbles were obtained in maximum number, and comparing it with the dates of the other sites from different parts of the world wherefrom such cobbles have been found, it can be affirmed that these artefacts (including the Soanian type tools associated with them) were fabricated during mid to late mid-Holocene. The pits appeared to be made intentionally for utilization and were not an outcome of any natural process. An experiment successfully replicated the pits found on these archaeological cobbles, indicating some possible functions. It can be concluded that the pits on these archaeological cobbles found in the part of the Indian sub-Himalayas appeared to be utility-oriented as they were made by percussions.

Silver/hydroxyapatite foam as a highly selective catalyst for acetaldehyde production via ethanol oxidation

In this study, highly dispersed sliver (Ag) nanoparticles supported on a hydroxyapatite showed a surprisingly high activity (1.38s−1 in turnover frequency (TOF)), selectivity (∼100%) and durability (∼100h) for the oxidative dehydrogenation of ethanol to acetaldehyde. The structure of Ag nanoparticles is characterized using transmission electron microscopy (TEM), X-Ray Diffraction (XRD), in-situ and ex-situ X-ray photoelectron spectroscopy (XPS) and temperature-programmed surface reaction (TPSR). Density Functional Theory (DFT) calculations on Ag(111) were performed to understand the mechanism of catalytic reactions at a molecular level. The calculation results revealed that the barrier for the formation of acetaldehyde is 38.6kJ/mol, and 126.4kJ/mol for CO2 formation, thus leading to high selectivity to acetaldehyde. By combination of DFT calculation and experimental work, it can be concluded that ethanol oxidation predominantly took place on the terrace surface although step surface are more active. This study provides a methodology to develop completely selective practical catalysts especially for the utilization of biomass.

An inlier of Jurassic rocks at the bottom of the Lena River valley

An inlier of Jurassic rocks is identified for the first time at the surface of the first terrace above a floodplain composed of Holocene sediments on the left side of the Lena River. It represents a block of Jurassic rocks similar compositionally to rocks in outcrops on the left slope of the river valley. It is shown that the block was displaced along faults in the Holocene. The rocks of the inlier are deformed, and the Paleogene–Neogene sequence covering the plateau (altitude approximately 200 m) is displaced in the stepwise mode to the level corresponding to the bottom of the Lena River valley (altitude approximately 100 m). The Holocene alluvium enveloping the inlier belongs to the constratal type being up to 40 m thick. Steep faceted morphostructures on the left slope of the Lena River valley coincide with the faults. The left slope of the valley is crossed exclusively by young incisions. It is assumed that Holocene movements may be reactivated in the future.

Rh nanoparticles with NiOx surface decoration for selective hydrogenolysis of C[sbnd]O bond over arene hydrogenation

Surface decoration strategy is applied to design NP catalyst for the selective hydrogenolysis of CO bond without hydrogenating benzene ring, which is critical in lignin conversion under hydrogen treatment. The synthesized NiOx/Rh NPs are featured with Rh core whose surface is partially blocked by NiOx, which segregated the surface terrace zones into smaller segments, preventing the coordination and hydrogenation of benzene rings. Moreover, the NiOx shows no electronic modification to the Rh core, thereby the blockage effect of NiOx only inhibits the hydrogenation of benzene ring but not affect the hydrogenolysis activity of Rh core.

Flexural deformation of marine terrace surfaces and geomorphic development around the Rokkasho fault, Aomori Pref., Northern Japan

Flexural deformation of marine terrace surfaces and geomorphic development around the Rokkasho fault, Aomori Pref., Northern Japan

TerraceM: A MATLAB® tool to analyze marine and lacustrine terraces using high-resolution topography

High-resolution topographic data greatly facilitate the remote identification of geomorphic features, furnishing valuable information concerning surface processes and characterization of reference markers for quantifying tectonic deformation. Marine terraces have been used as long baseline geodetic markers of relative past sea-level positions, reflecting the interplay between vertical crustal movements and sea-level oscillations. Uplift rates may be determined from the terrace age and the elevation of its shoreline angle, a geomorphic feature that can be correlated with past sea-levels positions. A precise definition of the shoreline angle in time and space is essential to obtain reliable uplift rates with coherent spatial correlation. To improve our ability to rapidly assess and map shoreline angles at regional and local scales, we have developed TerraceM, a MATLAB® graphical user interface that allows the shoreline angle and its associated error to be estimated using high-resolution topography. TerraceM uses topographic swath profiles oriented orthogonally to the terrace riser. Four functions are included to analyze the swath profiles and extract the shoreline angle, from both staircase sequences of multiple terraces and rough coasts characterized by eroded remnants of emerged terrace surfaces. The former are measured by outlining the paleocliffs and paleoplatforms and finding their intersection by extrapolating linear regressions, whereas the latter are assessed by automatically detecting peaks of sea-stack tops and back-projecting them to the modern sea cliff. In the absence of rigorous absolute age determinations of marine terraces, their geomorphic age may be estimated using previously published diffusion models. Postprocessing functions are included to obtain first-order statistics of shoreline-angle elevations and their spatial distribution. TerraceM has the ability to process series of profiles from several sites in an efficient and structured workflow. Results may be exported in Google Earth and ESRI shapefile formats. The precision and accuracy of the method have been estimated from a case study at Santa Cruz, California, by comparing TerraceM results with published field measurements. The repeatability was evaluated using multiple measurements made by inexperienced users. TerraceM will improve the efficiency and precision of estimating shoreline-angle elevations in wave-cut terraces in both marine and lacustrine environments.

Rapid fluvial incision and headward erosion by the Yellow River along the Jinshaan gorge during the past 1.2 Ma as a result of tectonic extension

In North China, the Ordos block located northeast of the Tibetan Plateau is regarded as a stable craton surrounded by the Yinchuan graben to the west, the Hetao graben to the north, and the Fenwei graben to the southeast. The major tectonic structure around this block in the Cenozoic reflects intensive extension as a response to the eastward extrusion of the Tibetan Plateau. Intermittent downcutting by the Yellow River, starting from the planation surface level on the Ordos block and penetrating the bedrock, resulted in the formation of the Jinshaan gorge. A series of well-preserved fluvial terraces was identified along this gorge, providing new insight into the far-field effect of the eastward extrusion of the Tibetan Plateau. Magnetostratigraphic records from the planation surface and uppermost terrace suggest that this gorge has been entrenched over its total length in the period from 3.7 to 1.2 Ma. A preliminary explanation is proposed here for the morphological evolution of the Yellow River in the Jinshaan gorge. On the basis of terrace correlation between seventeen geomorphic sections, multiwave headward erosion initiated by the Yellow River along this gorge has been reconstructed. This process may be attributed to the lowering of the base level (the Fenwei graben). This graben has been formed during the Cenozoic as the Tibetan Plateau extruded eastwards resulting in accelerated ground subsidence. A combined approach of magnetostratigraphy, pedostratigraphy, and optically stimulated luminescence (OSL) was adopted to establish a new geochronology for terraces in the gorge at 1.2 Ma, 1.1 Ma, 787 ka, 412 ka, 245 ka, 128 ka, 29 ka, and 11 ka. These ages provide an excellent framework for calculating the extension within the Fenwei graben. The average incision rate appears to be enhanced significantly since 412 ka, indicating a rapid extension within the Fenwei graben during this time.

Effect of Surface Site on the Spin State for the Interaction of NO with Pd<sub>2</sub>, Rh<sub>2</sub> and PdRh Nanoparticles Supported at Regular and Defective MgO(001) Surfaces

An attempt has been made to analyze the effect of surface site on the spin state for the interaction of NO with Pd2, Rh2 and PdRh nanoparticles that supported at regular and defective MgO(001) surfaces. The adsorption properties of NO on homonuclear, Pd2, Rh2, and heteronuclear transition metal dimers, PdRh, that deposited on MgO(001) surface have been studied by means of hybrid density functional theory calculations and embedded cluster model. The most stable NO chemisorption geometry is in a bridge position on Pd2 and a top configuration of Rh2 and PdRh with N-down oriented. NO prefers binding to Rh site when both Rh and Pd atoms co-exist in the PdRh. The natural bond orbital analysis (NBO) reveals that the electronic structure of the adsorbed metal represents a qualitative change with respect to that of the free metal. The adsorption properties of NO have been analyzed with reference to the NBO, charge transfer, band gaps, pairwise and non-pairwise additivity. The binding of NO precursor is dominated by the E(i)Mx-NO pairwise additive components and the role of the support was not restricted to supporting the metal. The adsorbed dimers on the MgO surface lose most of the metal-metal interaction due to the relatively strong bond with the substrate. Spin polarized calculations were performed and the results concern the systems in their more stable spin states. Spin quenching occurs for Rh atom, Pd2, Rh2 and PdRh complexes at the terrace and defective surfaces. The adsorption energies of the low spin states of spin quenched complexes are always greater than those of the high spin states. The metal-support and dimer-support interactions stabilize the low spin states of the adsorbed metals with respect to the isolated metals and dimers. Although the interaction of Pd, Rh, Pd2, Rh2 and PdRh particles with Fs sites is much stronger than the regular sites O2-, the adsorption of NO is stronger when the particular dimers are supported on an anionic site than on an Fs site of the MgO(001). The encountered variations in magnetic properties of the adsorbed species at MgO(001) surface are correlated with the energy gaps of the frontier orbitals. The results show that the spin state of adsorbed metal atoms on oxide supports and the role of precursor molecules on the magnetic and binding properties of complexes need to be explicitly taken into account.

Investigation of AlN thin film growth on MgO(111) substrates using low temperature helicon sputtering system

An aluminum nitride (AlN) thin film has been grown on annealed magnesium oxide (MgO) (111)-plane substrate using low temperature helicon sputtering system. Both AlN films on as-received and annealed MgO(111) substrate are single crystalline with AlN[0001] || MgO[111]. X-ray rocking curve shows that AlN film on annealed MgO exhibits superior crystalline quality, which means more suitable for AlN crystal growth. Two different growths were found for the deposition of AlN on annealed MgO. It is believed that the partially recovered substrate surface caused by annealing process provides atomic smooth surface terraces with small lattice mismatch for AlN crystal to grow in 2D mode, enhance grain size, and thus reduce the dislocation density. This is the first time demonstrated for the growth mechanism of single crystal AlN thin film prepared on MgO(111) by sputtering system.

Formation and reduction of pyramidal hillocks on InGaAs/InP(111)A

The formation and reduction of pyramidal hillocks on InGaAs/InP(111)A grown by metal organic chemical vapor deposition were investigated. The triangular pyramidal hillocks were observed on the InGaAs surface on on-axis InP (111)A grown at 650 °C. The hillocks disappeared when the vicinal InP (111)A substrates with an off-axis angle >0.4° were applied. The step and terrace surface of InGaAs on 4.0°-off InP (111)A were obtained. InGaAs on on-axis InP (111)A exhibited a hole concentration, mobility of Hall effect measurement, and full width at half-maximum of X-ray diffraction as 1.0 × 1017 cm−3, 56 cm2/V s, and 140 arcsec, respectively. In contrast, InGaAs on 2.0°-off InP (111)A exhibited 2.3–1017 cm−3, 142 cm2/V s, and 63 arcsec, respectively. We suggest that off-axis substrates enable a reduction of stacking faults, which leads to considerable improvement of crystallinity.

Using LiDAR data to characterize and distinguish among different types of raised terraces in a fjord-valley setting

Depositional terraces of diverse origin are common in Norwegian fjord valleys. They differ subtly morphologically and may be difficult to distinguish from one another without detailed field and stratigraphic investigation. We used LiDAR elevational data to describe previously identified glaciofluvial, glaciodeltaic, fluvial, and fluviodeltaic terraces in the Målselv valley, northern Norway, and show how they differ morphologically. Fluvial terraces are divided into two subtypes based on their difference in morphology. One type shows an undulating surface, often with a ridge-and-swale topography (scroll bars) associated with lateral accretion of moderate-to-high-sinuosity (meandering) channels, while the other shows remains of channels and braid bars associated with low-sinuosity channels. Fluviodeltaic terraces are generally flat and featureless, probably as a result of wave and tidal reworking of the terrace surface as it was raised above sea level. Glaciofluvial terraces show braided channel forms and occasional eolian dunes, while glaciodeltaic terraces are generally flat and featureless, in some cases having a moraine ridge on top and small beach ridges on the proximal, ice-contact slope. Terraces also show a distinct distribution pattern, with glaciofluvial and glaciodeltaic terraces graded to the marine limit occurring at higher elevations than fluviodeltaic and fluvial terraces. Based on the results presented here we show that a distinction can be made between different terraces based on morphological criteria revealed by LiDAR data. Such data should be acquired where possible to improve the quality of geomorphological mapping.

Late Pleistocene shortening rate on the northern margin of the Yanqi Basin, southeastern Tian Shan, NW China

How strain is distributed and partitioned on individual faults and folds on the margins of intermontane basins remains poorly understood. The Haermodun (Ha) anticline, located along the northern margin of the intermontane Yanqi Basin on the southeastern flank of the Tian Shan, preserves flights of passively deformed alluvial terraces. These terraces cross the active anticline and can be used to constrain local crustal shortening and uplift rates. Geologic and geomorphic mapping, in conjunction with high-resolution dGPS topographic surveys, reveal that the terrace surfaces are perpendicular to the fold’s strike, and display increased rotation with age, implying that the anticline has grown by progressive limb rotation. Combined with the open sinusoidal curve model and excess area method, we calculated uplift and shortening values for each terrace since abandonment. Using the published exposure ages of each terrace, we found the vertical uplift rate gradually decreased from ∼0.43 to ∼0.11mm/a, whereas the shortening rate remained constant at ∼0.3mm/a since the anticline began to grow. A fresh fault scarp, 0.4±0.1m high, is visible along the southern portion of the Ha anticline, and is interpreted to be the most recent evidence of seismic activity. Using an estimated rupture area and the length of the fresh offset created by this earthquake, we estimate that the main thrust underlying the Ha anticline has generated moderate (M<7) earthquakes in the past. The shortening rates of the Ha anticline from geomorphology agree with current GPS measurements cover-over the fold, and highlight the importance of determining slip rates for individual faults in order to resolve patterns of strain distribution across intermontane belts.

Digital landscapes of deglaciation: identifying Late Quaternary glacial lake outburst floods using LiDAR

AbstractHigh resolution DEMs obtained from LiDAR topographic data have led to improved landform inventories (e.g. landslides and fault scarps) and understanding of geomorphic event frequency. Here we use airborne LiDAR mapping to investigate meltwater pathways associated with the Tweed Valley palaeo ice‐stream (UK). In particular we focus on a gorge downstream of Palaeolake Milfield, previously mapped as a sub‐glacial meltwater channel, where the identification of abandoned headcut channels, run‐up bars, rock‐cut terrace surfaces and eddy flow features attest to formation by a sub‐aerial glacial lake outburst flood (GLOF) caused by breaching of a sediment dam, likely an esker ridge. Mapping of these landforms combined with analysis of the gorge rim elevations and cross‐section variability revealed a two phase event with another breach site downstream following flow blockage by higher elevation drumlin topography. We estimate the magnitude of peak flow to be 1–3 × 103 m3/s, duration of the event to range from 16–155 days, and a specific sediment yield of 107–109 m3/km2/yr. We identified other outburst pathways in the lower Tweed basin that help delineate an ice margin position of the retreating Tweed Valley ice stream. The results suggest that low magnitude outburst floods are under‐represented in Quaternary geomorphological maps. We therefore recommend regional LiDAR mapping of meltwater pathways to identify other GLOFs in order to better quantify the pattern of freshwater and sediment fluxes from melting ice sheets to oceans. Despite the relatively low magnitude of the Till outburst event, it had a significant impact on the landscape development of the lower Tweed Valley through the creation of a new tributary pathway and triggering of rapid knickpoint retreat encouraging new regional models of post‐glacial fluvial landscape response. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Tailoring Si(100) substrate surfaces for GaP growth by Ga deposition: A low-energy electron microscopy study

For GaP-on-Si(100) heteroepitaxy, currently considered as a model system for monolithic integration of III–V semiconductors on Si(100), the surface steps of Si(100) have a major impact on the quality of the GaP film. Monoatomic steps cause antiphase domains in GaP with detrimental electronic properties. A viable route is to grow the III–V epilayer on single-domain Si(100) with biatomic steps, but preferably not at the expense of reduced terrace widths introduced by miscut substrates. We have performed in situ investigations of the influence of Ga deposition on the kinetics of surface steps and terraces of Si(100) at substrate temperatures above 600 °C by low-energy electron microscopy. Starting from nearly equally distributed TA and TB terraces of a two-domain Si(100) surface, submonolayer deposition of Ga results in a transformation into a surface dominated by TA terraces and biatomic DA steps. This transformation is reversible, and Si(100) with monoatomic steps is recovered upon termination of the Ga flux. Under conditions of higher coverages (but still below 0.25 monolayer), we observe restructuring into a surface with TB dominance, similar to the findings of Hara et al. [J. Appl. Phys. 98, 083515 (2005)]. The occurrence and mutual transformations of surface structures with different terrace and step structures in a narrow range of temperatures and Ga deposition rates is discussed.

岩手県奥州市衣川区餅転付近における 低位段丘のC-14年代値と2008年岩手・宮城内陸地震の地震断層

岩手県奥州市衣川区餅転付近における 低位段丘のC-14年代値と2008年岩手・宮城内陸地震の地震断層

Tuning the Terrace and Step Stability of 6H-SiC (0001) for Graphene Film Deposition

Graphene is a 2D material with potential for almost any purpose, thanks to a combination of excellent characteristics, e.g. high electrical conductivity. Graphene grown on SiC wafers is one of the promising routes for graphene integration into planar technology electronic applications. Synthesis is based on the decomposition of a SiC single crystal surface at high temperature, where Si-terminated SiC substrates require the formation of the C buffer layer. In spite of numerous experimental and theoretical works the understanding and control upon crucial factors such as step and terrace stability or surface roughening is far from been fully comprehended and then technologically optimized. We present experimental results on the deposition of graphene onto Si-terminated 6H-SiC. We analyze the effect of ex situ and in situ conditionings of the SiC surface in the thermal decomposition and reconstruction of the SiC terraces, toward higher control upon the growth process of graphene films.

MODELLING OF MORPHODYNAMIC CRYOGENIC PROCESSES UNDER CHANGING NATURAL-TECHNOGENIC CONDITIONS (THE MOUTH PART OF THE KOLYMA RIVER AS AN EXAMPLE)

The data on cryogenic deformation rates of a surface of the Kolyma River terrace under various frost- climatic and technogenic conditions are given. The mathematical model of cryogenic morphogenesis under the impact of the technogenic factors and climatic changes is offered. A man-induced component of the cryogenic deformations of a terrace surface may exceed natural component by 7-20 times under the strong external influences on a frozen ground. Thus rate of local destruction of frozen deposits with macro-ice content 20-40% may reach 15-24 m/year.

Deformación co-sísmica de una terraza estuarial, Constitución, Chile Central

In the terrace Te, of Constitucion, many fractures and associated deformations of its platform appeared in the street pavements after the earthquake of 02.27.2010. On this basis, this work deals with the co-seismic deformation in this terrace, observed by means of survey of fractures and associated superficial deformations. The principal undulated and irregular surface of the terrace shows no difference between the profiles surveyed before and after the 2010 seism, with exception of those that represent a minor part in the northward sector. In exchange, the flagstones or slabs of pavement show brittle micro-deformations or pop up like array structures associated to micro fractures produced during the seism. There is great dissimilarity of size order between principal irregularities of the terrace surface (undulations) and micro-deformations. The principal irregularities of the terrace Te indicate that its undulated form is inherited and older than the seism of 02.27.2010. Only a minor part represents a 2010 co-seismic deformation with gentle warping of the inherited undulation during the seism. In exchange, the flagstone dislocations or brittle deformations shown as pop ups like array are co-seismic microforms. They appear only as small tectonic deformations in the epidermis of the inherited undulated surface. Their apparent random distribution is possibly the result of a complex interaction between the seismic waves and the inherited topography, producing strain structures.