Quaternary Alluvial Fans Research Articles

Spatial and Temporal Analysis of Geologic Slip Rates, Cucamonga Fault, California, USA: Implications for Along‐Strike Applications and Multi‐Fault Rupture

AbstractTo constrain fault processes and hazard, fault slip rates may be extrapolated over different fault lengths or time intervals. Here, we investigate slip rates for the Cucamonga Fault (CF). The CF is located at the junction of the Transverse Range fault system with the San Andreas and San Jacinto Faults, and it is hypothesized to connect with these faults, promoting the propagation of large, multi‐fault earthquakes. Previous work has shown that CF displacements on late Quaternary alluvial fan surfaces are highly variable along strike. We present two new 10Be surface exposure ages from depth profiles on the alluvial fans. Slip rates are consistent with a rate of 1.4 ± 0.3 m/kyr over time intervals of ∼20, ∼30, and ∼40 kyr. If the CF participates in multi‐fault ruptures, then these earthquakes occur either rarely or with sufficient regularity to maintain apparently steady rates over multiple intervals. We also explore along‐strike fault displacement variability using a calibrated morphological model. The model successfully reproduces scarp profiles and indicates that fault displacement variability can be explained in part by scarp age but not uplift rate. We infer that both erosion by ephemeral gullying and distributed deformation contribute to fault displacement variability, although both are difficult to detect confidently without excavations across the scarp. These investigations show that better characterization of cumulative‐slip variability along strike may improve accuracy and precision of slip rates. Slip rates that do not consider epistemic uncertainties may not be suitable for extrapolation over longer fault sections.

Tectonic geomorphology and Quaternary fault slip rates in the Tsambagarav Massif, Mongolian Altai

AbstractThe NNW‐striking Mongolian Altai is a Late Cenozoic dextral strike–slip deformation belt affected by the far‐field stress caused by the collision between India and Eurasia. The Tsambagarav Massif is bounded by faults, has a triangular plan shape, and attains the highest elevation of the belt. This massif is adjacent to the central segment of the Hovd fault, which is the largest fault in the Mongolian Altai. Here, we use 10Be surface exposure dating, radiocarbon dating, and paleoseismic trenching to reveal deformation patterns and Quaternary slip rates for two range‐bounding faults: the Tsambagarav dextral reverse fault and the Lower thrust fault. The Lower thrust exhibits thrusting motion along the low‐angle structural fabric of the basement rock and cuts Quaternary alluvial fan deposits, vertically offsetting their surfaces by 3.9–5.1 m, with fault scarps extending several kilometres along‐strike. The Tsambagarav dextral reverse fault is characterized by strike–slip motion along the high‐angle structural fabric of basement rock. Various surface deformation features indicate recent dextral strike–slip, including displacements of Late Quaternary moraine by ~50 m. Dividing the measured displacements by 10Be surface exposure ages of alluvial fan surfaces (for the Lower thrust) and moraine (for the Tsambagarav dextral reverse fault) gives a reverse slip rate of 0.3–1.7 mm/yr for the Lower thrust and a horizontal slip rate of 1.7–2.6 mm/yr for the dextral reverse fault. Radiocarbon ages of animal bones in a pond deposit accumulated along an associated tensional crack indicate that the last earthquake that caused a surface rupture occurred between 1924 and 1708 cal yr BP. Our study suggests that strain partitioning has occurred on the faults of the Tsambagarav Massif.

Analysis of a travertine system controlled by the transpressional activity of the Alhama de Murcia fault: The Carraclaca site, eastern Betic Cordillera, Spain

Continental carbonates, such as travertines and tufas, formed from CO2-rich groundwater degassing as it emerges at the Earth’s surface, are often associated with major crustal-scale faults. The Carraclaca site, in the Lorca-Totana section of the Alhama de Murcia Fault, Spain, presents a complex geomorphological landscape controlled by active tectonics. The geology here records the interaction between Quaternary alluvial fans, travertines, and a pop-up structure developed in a transpressional section of the fault. The Alhama de Murcia Fault is an 80 km long left-lateral strike-slip fault that is one of the main seismogenic structures in the Iberian Peninsula. In this work, we examined the relation between travertine precipitation in the Carraclaca site and the tectonic activity of this fault zone through morphological and geochemical studies. The δ13C and δ18O isotopic signals indicate that the carbonate deposits are hydrothermal. In addition, the 87Sr/86Sr ratios in the samples suggest subsurface fluid interaction with the Miocene sediments and the Alpujárride basement, located below the alluvial deposits. Tectonic activity in the Alhama de Murcia Fault might generate the opening of deep water circulation in the crust every time a seismic event occurs, giving rise to hydrothermally derived carbonates precipitation. Deep waters rise and reach the surface interacting with meteoric waters, resulting in travertine formation. Therefore, the Carraclaca carbonate deposits study can inform us about the seismogenic cycle of the fault in the Lorca-Totana section.

Climatically- and tectonically-controlled development of the late quaternary alluvial fan in the north piedmont of Zhongtiao Shan (ZTS), north China

The evolution of alluvial fans is controlled by the tectonic setting and climatic fluctuations. This study focused on the Lidian alluvial fan in the northern piedmont of Zhongtiao Shan, north China, to study the fluvial responses to paleoenvironmental changes since the late Last Glacial Maximum. In combination with series of accelerator mass spectrometry (AMS) 14C dating data on fan sediments, sedimentary analyses indicated that the primary fan accumulation was controlled by episodic millennium-scale debris and sheet flood flow related aggradation during 13.3–13.0, 12.7–11.3, 6.2–4.5, and 4.5–2.8 cal ka BP. Between the accumulation periods, the fan process was dominated by aeolian paleosol-and-loess sequence development and the reworking of fan clasts. Considering regional hydraulic conditions and sediment flux, we proposed that the millennium-scale episodic debris flow related fan aggradation during 13.3–13.0, 12.7–11.3, and 4.5–2.8 cal ka BP was controlled by high-volume sediment influx of the permafrost and physical weathering during cold events. The millennium-scale sheet flood-dominated fan aggradation event during 6.2–4.5 cal ka BP was related to the abrupt coarsening and high sediment yield forced by tectonic uplift. We also suggest that the scattered distributed channelized floods and debris backfilling sediments within the fine-grain layers indicate that the deposition of irregular fan lobe accumulation coincided with hydraulic shifts over shorter temporal scales.

Seismic Reflection Imaging of the Low‐Angle Panamint Normal Fault System, Eastern California

AbstractShallowly dipping (<30°) low‐angle normal faults (LANFs) have been documented globally; however, examples of active LANFs in continental settings are limited. The western margin of the Panamint Range in eastern California is defined by a LANF that dips west beneath Panamint Valley and has evidence of Quaternary motion. In addition, high‐angle dextral‐oblique normal faults displace middle to late Quaternary alluvial fans near the range front. To image shallow (<1 km depth), crosscutting relationships between the low‐ and high‐angle faults along the range front, we acquired two high‐resolution P wave seismic reflection profiles. The northern, 4.6‐km‐long profile crosses the 2‐km‐wide Wildrose graben and the southern, 0.8‐km‐long profile extends onto the Panamint Valley playa, ~7.5 km S of Ballarat, CA. The profile across the Wildrose graben reveals a robust, low‐angle reflector interpreted to represent the LANF separating Plio‐Pleistocene alluvial fanglomerate and Proterozoic metasedimentary deposits. High‐angle faults interpreted in the seismic profile correspond to fault scarps on Quaternary alluvial fan surfaces. Interpretation of the reflection data suggests that the high‐angle faults vertically displace the LANF up to 80 m within the Wildrose graben. Similarly, the profile south of Ballarat reveals a low‐angle reflector, which appears both rotated and displaced up to 260 m by high‐angle faults. These results suggest that near the Panamint range front, the high‐angle faults are the dominant active structures. We conclude that at least at shallow (<1 km) depths, the LANF we imaged is not active today.

Morphology and characteristics of eight Oxisols in contrasting landscapes of Costa Rica

Oxisols have been previously reported in Costa Rica. However, few studies provided specific data to corroborate their presence and explain their genesis under different soil-forming factors. This study was performed with the aim to confirm Oxisols occurrence in different landscapes and parent materials in Costa Rica. Eight pedons were sampled, described, characterized, and classified according to Soil Taxonomy in five landscapes. All pedons studied presented clay contents above 40% in surface horizons. Subsurface horizons presented red colors, high contents of low-activity clay minerals with cation exchange capacity values at pH 7 (CEC7) less than 16 cmolc kg−1 clay and less than 9.6% weatherable minerals in the sand fraction. The suborders Ustox, Udox and Perox were identified. Among the Ustox, three contrasting subgroups were identified: Kandiustalfic Eustrustox, Plinthic Kandiustox, and Anionic Acrustox. Conversely, soils classified into the suborder Udox presented the same great group: Kandiudox; with three subgroups identified: Typic Kandiudox, Plinthic Kandiudox, and Rhodic Kandiudox. In addition, one pedon was classified into the suborder Perox, with the subgroup Andic Haploperox.The diversity in geologic materials (basaltic, pyroclastic, and sedimentary rocks), geomorphology (mountains, plains, dissected volcanic cones, and Quaternary alluvial fans), and the climatic conditions (total annual rainfall ranged from 1853 to 5780 mm year−1) observed in the studied areas made possible the diverse taxonomic classification for the eight Oxisols. Results obtained confirmed occurrence of Oxisols in Costa Rica and verify soil classification from previous literature reports. Our findings in soil genesis and forming factors enhance the knowledge in pedogenesis and properties of advanced weathering stage soils in Central America.

Morphotectonics of the northern Bogd fault and implications for Middle Pleistocene to modern uplift rates in southern Mongolia

Assessing the activity of strike-slip faults is often facilitated by cumulative offsets of morphological features. The December 4th 1957 Mongolia earthquake, generally referred to as the “Gobi Altai” or “Bogd” earthquake, had MW 8.1 and created long and complex surface ruptures of c. 350 km length along the Bogd fault that cuts across the foothills of the Gurvan Bogd mountains. Several left-laterally and vertically displaced Quaternary alluvial fans and morphogenic markers show cumulative offsets, allowing for an assessment of the effect of repeated earthquakes and active tectonics on landscape evolution. We propose to expand the active tectonic record along this fault up to a Middle Pleistocene time scale that spans regional climatic fluctuations, i.e. repeated glacial-interglacial cycles, and hence varying erosional and depositional rates.Five main drainage areas crosscutting the North Ikh Bogd segment of the Bogd fault were analysed and compared in terms of hypsometry, drainage steepness and alluvial fan slope inclination. Along the mountain front, deposits from all drainages form multiple alluvial fan levels that reflect recurring deposition-incision cycles. Previously published ages, as well as the spatial distribution of these fan levels, suggest that their incision and abandonment is induced by regionally dominant climate fluctuations. However, the increase of fan slope angles over time and the increased intensity of sub-surface folding observed in ground-penetrating radar profiles, suggests that cumulative tectonic uplift also has a strong impact on alluvial fan morphology. Estimates of the increase of fan slope angles as a result of cumulative tectonic uplift imply that Middle Pleistocene to modern vertical slip rates along the North Ikh Bogd segment of the Bogd fault are in the order of 0.9–1 mm/yr. However, much slower vertical slip rates along individual fault segments, ranging between 0.06 ± 0.01 mm/yr and 0.28 ± 0.07 mm/yr, indicate that uplift of the Ikh Bogd plateau occurs as a result of distributed deformation across multiple parallel fault strands within bedrock as well as alluvial fans. Our results emphasise the importance of regional studies along active faults that take into account the complexity of surface ruptures as well as the occurrence of related structures that can accommodate deformation.

Subsurface characterization of quaternary scarps and their possible connection to main structures of the western margin of Precordillera, San Juan, Argentina

The El Tigre fault provides a significant example of Pliocene-Quaternary tectonic activity at the West of Precordillera, receiving considerable attention in the last years. However, longitudinal thrusts of the nearest Sierra del Tigre and a minor piedmont deformation belt identified in its western piedmont are still poorly understood. The present work comprised a detailed map of the geomorphological features of tectonic origin and Quaternary alluvial fan terraces located between the Sierra del Tigre and the El Tigre fault. Several topographic and geoelectrical profiles across minor fault and fold scarps were surveyed to define the displacement scarps, the geological structure geometries at subsurface and their relationship with main structures. Geoelectrical models allowed us to recognize three geoelectrical levels: A (> 200–300 Ω.m) correlated to Pleistocene alluvial fan terraces Q4 and Q3; B (ranging from 50 to 300/450 Ω.m), under level A and correlated to the Neogene substratum (Rodeo Formation); C (< 30–40 Ω.m) intercalated in level B, conforming aquifers (20 and 40 m deep) within the Neogene substratum. Subvertical conductive zones (10–40 Ω.m) were correlated to high angle (~60°-80°) reverse faults, which are associated with open anticlines and synclines that affect the Quaternary levels and the Neogene substratum. The structural style interpreted here allows us to conclude that the main piedmont thrust is a frontal splay of the backthrust of the Sierra del Tigre with western vergence. A better connection to the compressive deformation component, which uplifts the range, instead of to the strike-slip deformation component of the El Tigre Fault is demonstrated. This tectonic propagation probably happens during Middle-Upper Pleistocene to Holocene. The observations show that minor deformation belt is subjected to piedmont compressive movements while the El Tigre Fault absorbs the strike-slip movements, so a local partition of the deformation in the western margin of Precordillera probably happens during Quaternary.

Quaternary Thrusting in the Central Oman Mountains—Novel Observations and Causes: Insights from Optical Stimulate Luminescence Dating and Kinematic Fault Analyses

For the first time, Quaternary thrusts are documented within the Central Oman Mountains to the northwest of the Jabal Akhdar Dome. Thrusts with a throw of up to 1.1 m displace Quaternary alluvial fan conglomerates. These conglomerates have an Optical Stimulate Luminescence (OSL) age of 159 ± 7.9 ka BP and were deposited during MIS 6 (Marine Isotope Stage). The thrusts occur in two sets. Sets 1 and 2 formed during NE/SW and NW/SE shortening, respectively. Set-1-thusts correlate with the present-day stress field of NE/SW shortening which is related to subduction in the Makran Subduction Zone, and they strike parallel to the main continuous fold axis of the Jabal Akhdar and Hawasina windows. Set-2-thrusts correspond to NW/SE shortening and Plio-Pleistocene contractional structures in the southwestern Jabal Akhdar Dome. Set-2-thrusts are probably related to local variations of the present-day stress field originating from the Musandam area which is a part of the Zagros Collision Zone. Both thrust sets mimic the main thrust directions (NW/SE and NE/SW) within the Permo-Mesozoic allochthonous units (Semail Ophiolite, Hawasina napps) of the larger study area. The investigated thrusts imply some reactivation of the Hawasina and Semail thrusts due to far-field stress either from the Makran Subduction Zone and/or the Zagros Collision Zone. The ongoing tectonic activity of this part of the Oman Mountains, which has been considered of moderate activity, is for first time identified by structural data as contractional.

Late Quaternary landscape evolution and bioclimatic change in the central Great Plains, USA

AbstractA systematic study of floodplains, terraces, and alluvial fans in the Republican River valley of south-central Nebraska provided a well-dated, detailed reconstruction of late Quaternary landscape evolution and resolved outstanding issues related to previously proposed Holocene terrace sequences. Stable carbon isotope (δ13C) values determined on soil organic matter from buried soils in alluvial landforms were used to reconstruct the structure of vegetation communities and provided a means to investigate the relationships between bioclimatic change and fluvial activity for the period of record. Our study serves as a model for geomorphological and geoarcheological investigations in stream valleys throughout the central Great Plains and wherever loess-derived late Quaternary alluvial fans occur, in particular.Holocene alluvial landforms in the river valley include a broad floodplain complex (T-0a, T-0b, and T-0c), a single alluvial terrace (T-1), and alluvial fans that mostly grade to the T-1 (AF-1) and T-0c (AF-0c) surfaces. Remnants of a late Pleistocene terrace (T-2), mantled by Holocene (Bignell) loess, are also preserved, and some Holocene alluvial fans (AF-2) grade to T-2 surfaces.Radiocarbon ages suggest that the T-1 fill and AF-1 fans aggraded between ca. 9000–1000 yr B.P. Hence, nearly all of the Holocene alluvium in the river valley is stored in these landforms. Sedimentation, however, was interrupted by several periods of landscape stability and soil formation. Radiocarbon ages from the upper A horizons of buried soils in the T-1 and AF-1 fills, indicating approximate burial ages, cluster at ca. 6500, 4500, 3500, and 1000 yr B.P. Also, based on the radiocarbon ages, the T-0c fill and AF-0c fans were aggrading between ca. 2000–900 yr B.P. Given that the T-0c fill and upper parts of the T-1 fill were both aggrading after ca. 2000 yr B.P., we suggest that the T-1 surface was abandoned between ca. 4500–3500 yr B.P., but subsequent aggradation of both the T-1 and T-0c fills occurred due to large-magnitude flood events during the late Holocene.The δ13C data indicate a shift from ∼40% C4 biomass at ca. 6000 to ∼85% at ca. 4500 yr B.P. We propose a scenario where (1) a reduction in C3 vegetation after 6000 yr B.P. destabilized the uplands, resulting in an increase in sediment supply and aggradation of the T-1 fill and AF-1 fans, and (2) the establishment of C4 vegetation by ca. 4500 yr B.P. stabilized the uplands, resulting in a reduction in sediment supply and subsequent incision and abandonment of the T-1 and most AF-1 surfaces. The proposed timing and nature of landscape and bioclimatic change are consistent with regional records from the central Great Plains.

Gradients in climate, geology, and topography affecting coastal alluvial fan morphodynamics in hyperarid regions – The Atacama perspective

Abstract Along the coast of the hyperarid Atacama Desert, late Quaternary alluvial fans emerge from the Coastal Cordillera to the Pacific Ocean between 20.5°S and 25.5°S. Coastal alluvial fans (CAF) show, in comparison to the interior fans of the Atacama Desert, pronounced recent activity. However, the complex interplay between climate, lithology, and tectonics affecting the CAF morphodynamics in such hyperarid coastal settings needs to be better understood. We therefore aim at assessing the major factors driving CAF activity and evaluate their effects along gradients. We conducted an extensive study relating climatic, lithologic, and tectonic characteristics to fan and catchment geomorphology of 123 CAF. Geomorphometric analyses are based on the 12.5 m TanDEM-X WorldDEM™, catchment lithology and faults are extracted from 13 regional geological maps, and the frequency of heavy rainfall events capable of activating CAF is derived from a Weather Research and Forecasting (WRF) regional climate model. Our results point to a primary climatic control on CAF morphodynamics shown in functional relationships with catchment hydromorphometric characteristics reflecting a high susceptibility to debris flows – the main CAF-constructing process. Catchment properties along the latitudinal gradient reflect the source of significant precipitation events: frontal systems and cut-off lows which mainly originate in the extratropics and become increasingly rare towards the north. The frequency of precipitation extremes can only be correlated to the hydromorphometry and geomorphic maturity of catchments that feature a high degree of sediment transport potential and generally do not cut back far into the Coastal Cordillera. Related to the strongly reduced influence of the Pacific precipitation source towards the east, this additional climatic transition is governed by the orographic effect of the steep W-E gradient in topography. In contrast, source-area lithology is of negligible relevance for CAF catchment morphometry and fan activity. An important indirect influence of tectonics, however, can be seen in the long-term (neo)tectonic activity within the Coastal Cordillera, which in turn shapes catchments and controls the topography.

Late Quaternary alluvial fan evolution along the coast of the hyper-arid Atacama Desert - the interplay between climatic and tectonic control

Ponencia presentada en: 21th European Geosciences Union EGU General Assembly: Vienna, Austria, 7-12 april, 2019

Gone with the wind: dune provenance and sediment recycling in the northern Rub’ al-Khali, United Arab Emirates

The Rub’ al-Khali dune field in southern Arabia is the largest sand sea in the world. Deciphering the palaeoenvironmental history of the Rub’ al-Khali is critical to understanding its role as a barrier to human migration, dispersal and settlement. To determine sediment provenance and transport pathways, we combined data from a geological mapping project with traditional heavy mineral optical point-counting methods, heavy mineral geochemical fingerprinting and detrital zircon U–Pb geochronology of Miocene and Quaternary sediments in the United Arab Emirates (UAE). Detrital zircon U–Pb age spectra demonstrate that most Neogene and Quaternary sediments in the UAE are ultimately sourced from the Precambrian Arabian Shield. Heavy mineral and geochemical signatures indicate that the dune sands are locally recycled from the deflation of Miocene sandstones and Quaternary siliciclastic palaeodunes exposed along the Arabian Gulf coast, whereas carbonate palaeodunes along the Gulf coast are derived from the deflation of sediments deposited by the Tigris–Euphrates River system in the Gulf during Pleistocene lowstands. In the eastern Emirates, Miocene and Quaternary alluvial fan deposits emanating from the Hajar Mountains have an ophiolitic heavy mineral signature. The data reveal new insights into the origin and development of the Rub’ al-Khali dune field. Supplementary material: A map, details of the geochronology methods and a full dataset are available at https://doi.org/10.6084/m9.figshare.c.4290350

Geomorphology of Talacasto alluvial fan, Precordillera of San Juan, Argentina

ABSTRACTWe present a 1:50,000 geomorphological map of the Talacasto river alluvial fan (93 km2), located in the Central Andean Precordillera of Argentina. The aim of this map is to identify and classify dynamic and potentially destructive geomorphological processes such as gully erosion, headward erosion, concentrated erosion, laminar erosion and similar features that are present in an alluvial fan, so as to identify unstable sectors for public infrastructure. This map is the result of combining remote sensing data, aerial photographs analysis and fieldwork. Landforms and active geomorphological processes are identified, classified and illustrated for this Quaternary alluvial fan. Four Quaternary landscape subunits were classified, taking into account morphogenetic characteristics and erosional processes such as: (1) Exhumed and erosional landforms inducted by neotectonic activity; (2) Alluvial landforms; (3) Polygenetic landforms covered in glacis; and (4) Playa lake landforms. The presence of desert pavements and salt-hardened subsoil formations contributes to the generation and transmission of surface runoff during summer heavy rains, causing alluvial hazards and damages in routes and roads.

Late Pleistocene-Holocene strain release by normal faulting along the Main Boundary Thrust at Logar in the northwestern Kumaon Sub Himalaya, India

A prominent NW-SE trending linear fault, the Logar Fault, which vertically displaced the Quaternary alluvial fan (Logar fan) was delineated previously at Logar village in northwestern Kumaon Sub Himalaya. Based on the surface expression of the discontinuous scarp, and its expression on the satellite data, the fault has been further extended on either sides to a total length of ∼9.5 km, which in part lies in the older Himalayan mega thrust zone of weakness, the Main Boundary Thrust (MBT). The distinctive south side up scarp maintains linearity throughout its length, cut across the Logar mega fan and thus form as a normal fault within the compressive regime. Logar normal fault has truncated and uplifted a remnant of the Logar fan by >15 m since its deposition ∼20ka, based on the OSL dates of the fan sediments. A trench excavation survey across the Logar Fault scarp for paleoseismic investigation was carried out at Bairasari village. Variable height of the fault scarp along its strike suggests multiple faulting events that occurred along the same fault yielded a cumulative vertical height from 15–38 m. The OSL ages from the footwall show multilevel surfaces deposited between 20 and 8.7ka. However, in the hanging wall, the base of the vertically stacked deposits show an age ∼20ka. The OSL age in the bottom unit of the trench in the hanging wall suggest commencement of post faulting deposition of the units after 20ka. In the footwall, younger ages of 11 and 8.7ka probably represent the youngest dated activity of the fault. The ages obtained across the fault shows that the 20ka deposits are displaced. The nature of faulting of Logar fan suggest its genetic link with seismic activity in this region. The geomorphic expression of the Logar Fault along the Himalayan mega thrust suggest subsequent tectonic activity along the MBT. The active Logar normal fault identified north of the Himalayan Frontal Thrust (HFT) indicates that elastic strain released within the hanging wall is not limited to the front, but it is dispersed above the decollement over a broad area.

Quaternary deformation in the Gorubathan recess: Insights on the structural and landscape evolution in the frontal Darjiling Himalaya

The Gorubathan recess in the Darjiling frontal Himalaya is an unusual and unique region in the Himalaya as the Ramgarh thrust (RT) rather than the MFT defines the mountain front and the width of the Himalayan arc or the N-S aerial distance between the foreland (27.0947°N, 88.8744°E) and the Tibet Plateau (27.6781°N, 89.1175°E) is merely ∼70 km here. South of the mountain front, blind faults have deformed several Quaternary alluvial fans and formed scarps over a ∼35 km N-S zone. We first used field observations and fold-thrust belt concepts to re-interpret thrust nomenclature and geometry in the recess by correlating structures and lithology with the adjacent Dharan salient across the salient-recess separating Gish Transverse fault (GTF) and renamed the locally recognized faults to their regional equivalents. We then used Real Time Kinematic Global Navigation Satellite Systems (RTKGNSS) corrected SRTM 30 m C-Band data to compute geomorphic indices along with their uncertainties. Our results indicated that neotectonic deformation has generated an active but mature landscape in the Gorubathan recess. Quantitative topographic profiles based on RTKGNSS measurements reveal neotectonic warping and formation of geomorphic scarps on the fan surfaces. Geomorphic scarps form due to motion along thrusts but are not actual fault scarps. These profiles were used to model topographic growth and perturbation of fan slopes by active thrusting and fault-propagation folding by Boundary Element Method based dislocation modelling. Results indicate activity through much of the Quaternary on the Ramgarh thrust, a hanging wall imbricate and a rejoining splay in its footwall as well as the Main Boundary thrust. Comparison of modelled and measured topographic profiles in the recess points to erosion of the fault-related scarp-tops in the deformed alluvial fans on the windward side of the SW monsoon in both the Gorubathan and the Samsing-Matiali fans. Our integrated methodology improves the understanding of coupled fault-generated deformation and topographic growth and may be applied across the entire Himalayan front.

Miocene to Quaternary tectonostratigraphic evolution of the middle section of the Burdur-Fethiye Shear Zone, south-western Turkey: Implications for the wide inter-plate shear zones

The Burdur-Fethiye Shear Zone (BFSZ) is a 75- to 90- km wide and 300-km-long transtensional left-lateral shear zone which is located in one of the most tectonically active regions in south-western Turkey. A considerable number of studies suggested contradictory models of the evolution and Neogene stratigraphy of the BFSZ and in most cases, the local river and alluvial fan deposits were mapped together with the lacustrine sediments and assigned a Pliocene age. We present new field data, fault kinematic analyses, and DEM and earthquake data to characterize the tectonic controls and extent of the middle section of the BFSZ including Acıpayam, Çameli and Gölhisar basins. Our field observations revealed two distinct sedimentary sequences that unconformably overlie the pre-Neogene basement. The first sequence begins with middle-upper Miocene meandering- and braided-river sediments of the Gölhisar Formation, which transition upward into lacustrine sediments of the upper Miocene-lower Pliocene İbecik Formation. This sequence is overlain by upper Pliocene-lower Quaternary alluvial fan conglomerates, mudstones and claystones of the Dirmil Formation. The basin deposits located in the middle section of the BFSZ consist of lacustrine sediments of a late Miocene lake that likely evaporated due to the Messinian salinity crisis. Fault kinematic analysis and DEM and earthquake data indicate that the middle BFSZ can be characterized as a heterogeneous left-lateral transtensional shear zone rather than a major fault system. Our findings suggest that the middle section of the BFSZ developed under the influence of progressive counter clockwise rotation of south-western Turkey, the Aegean graben system and the Cyprus and Hellenic arcs since the middle Miocene.

Transition from collision to subduction in Western Greece: the Katouna–Stamna active fault system and regional kinematics

Transition from subduction to collision occurs in Western Greece and is accommodated along the downgoing plate by the Kefalonia right-lateral fault that transfers the Hellenic subduction front to the Apulian collision front. Here we present an active tectonic study of Aitolo-Akarnania (Western Greece) that highlights how such a transition is accommodated in the overriding plate. Based on new multi-scale geomorphic and tectonic observations, we performed an accurate active fault trace mapping in the region, and provide evidence for active normal and left-lateral faulting along the Katouna–Stamna Fault (KSF), a 65-km-long NNW-striking fault system connecting the Amvrakikos Gulf to the Patras Gulf. We further show that the Cenozoic Hellenide thrusts located west of the KSF are no longer active, either in field observation or in GPS data, leading us to propose that the KSF forms the northeastern boundary of a rigid Ionian Islands-Akarnania Block (IAB). Cosmic ray exposure measurements of 10Be and 36Cl were performed on a Quaternary alluvial fan offset along the KSF (~50 m left-lateral offset). A maximum abandonment age of ~12–14 ka for the alluvial fan surface can be determined, giving an estimated KSF minimum geological left-lateral slip rate of ~4 mm year−1, in agreement with high GPS slip rates (~10 mm year−1). Despite this high slip rate, the KSF is characterized by subdued morphological evidence of tectonic activity, a gypsum-breccia bedrock and a low level of seismicity, suggesting a dominantly creeping behavior for this fault. Finally, we discuss how the IAB appears to have been progressively individualized during the Pleistocene (younger than ~1.5 Ma).

Denudation intensity and control in the Chinese Tian Shan: new constraints from mass balance on catchment‐alluvial fan systems

AbstractTectonics and climate are usually seen as the main controlling factors of denudation rates, which seem to rise with the tectonic activity and to decrease when the climate becomes drier. However, the low denudation rates observed in semi‐arid to arid contexts are generally measured on orogenic plateaus where the respective influence of the flat relief and the dry climate cannot really be unravelled. The Chinese Tian Shan was chosen as a case study. In the northern piedmont of this mountain range, a series of well‐preserved Quaternary alluvial fans offer the opportunity to perform a mass balance study at the scale of several catchment areas and several hundreds of thousands of years. Based on a geometrical reconstruction of these fans, the volumes of sediments exported out of 10 drainage basins during the Middle–Late Pleistocene (from ∼300 to ∼12 kyr) and the Holocene (from ∼12 kyr to present) have been estimated. From these volumes, an average denudation rate of ∼135 m/Myr was determined in the Tian Shan Range for the last 300 kyr. In agreement with other mass balances performed in the same area, the typical denudation intensity of the northern Tian Shan is thus of a few hundred meters per million years at most, regardless of the space and time scales considered. From a comparison with denudation rates in other mountain ranges throughout the world, we suggest that a dry climate can dramatically limit the denudation intensity even in active orogenic systems with a high topographic gradient like the Tian Shan. As a result, the time required to reach equilibrium between denudation and rock uplift in these systems could be extremely long (i.e. of more than several million years). Copyright © 2016 John Wiley &amp; Sons, Ltd.

Quaternary alluvial fans of Ciudad Juárez, Chihuahua, northern México: OSL ages and implications for climatic history of the region

Alluvial fans formed from sediments derived from erosion of the Juarez Mountains in northernmost Mexico have a significant flood impact on the Ciudad Juarez, which is built on the fan system. The northern part of Ciudad Juarez is the most active; further south, older parts of the fan, upon which the rest of the city is built, were largely eroded by natural processes prior to human habitation and subsequently modified only recently by human construction. Three aeolian sand samples, collected from the uppermost (youngest) parts of the fan system in the city area, in places where human intervention has not disturbed the sediment, and constrain the latest dates of fan building. Depositional ages of the Quaternary alluvial fans were measured using Optically Stimulated Luminescence (OSL) on aeolian sands that have inter-fingered with alluvial fan material. These dates are: a) sample P1, 31 ka; b) sample P2, 41 ka; c) sample P3, 74 ka, between Oxygen Isotope Stages (OIS) 3 to 5. They demonstrate that fan development, in the area now occupied by the city, terminated in the Late Pleistocene, immediately after what we interpret to have been an extended period of erosion without further deposition, lasting from the Late Pleistocene to Holocene. The three dates broadly correspond to global glacial periods, implying that the cool, dry periods may reflect periods of aeolian transport in northern Mexico in between phases that were wetter to form the alluvial fans. Alluvial fan margins inter-finger with fluvial terrace sediments derived from the Rio Bravo, indicating an additional component of fan dissection by Rio Bravo lateral erosion, presumed to be active during earlier times than our OSL ages, but these are not yet dated. Further dating is required to ascertain the controls on the fan and fluvial system.