Alluvial Units Research Articles

Analisis Profil Bawah Permukaan Pantai Lumpue Kota Parepare

Lumpue Beach Subsurface Profile Analysis of Parepare City. This study aims to analyze the subsurface profile of Lumpue beach which is directly contaminated with activities around the coast. In this study, the Wenner Schlumberger method was used in the Lumpue beach area, Perepare City, South Sulawesi Province. The tool used is a multichannel geoelectric with a maximum length of 480 m in each trajectory, in this study there are 3 trajectories in which the first trajectory is 480 m with depth as deep as 91.2 m and the resistivity results obtained range from 0.207 -> 97.8 Ωm which identified as alluvium containing clay soil, silt soil, sandstone and pyroclastic rock bolder that has been contaminated by sea water. At lane 2 intersects the middle lane 1 with a length of 240 m and identified depths of 91.2 m, the recorded resistivity results range between 5.52 -> 623 Ωm where the resistivity value identifies the alluvium material, which contains clay, silt soil , sandstone that has been contaminated with water and the presence of some pyroclastic rock inserts that are contaminated by water. Whereas lane 3 intersects lane 1 at the end with a lenght of 240m and a depth of 91.2 m, while the recorded resistivity results range from 0.354 - 11776 Ωm where from the recorded resistivity results the material contained in lane 3 is the inserted alluvium material. by pyroclastic rocks. The area covered by the track is an area with alluvium material which is an alluvial unit and most of it is contaminated by water, either by sea water or fresh groundwater and is inserted by pyroclastic rocks.

ANALISIS STRATIGRAFI DAN RUMUSAN SEJARAH GEOLOGI DAERAH LIMBATO DAN SEKITARNYA, KABUPATEN GORONTALO UTARA, PROVINSI GORONTALO

Regionally, the research area is composed of volcanic and plutonic rocks. Stratigraphic data of the study area are still regional scale. This study aims to analyze detailed stratigraphic data and formulate the geological history of the Limbato area and its surroundings. The area located at coordinates 0º56’6” - 1º0’10.8” N dan 122º5’56.4” - 122º9’10.8” E, the area of the study is around 45 km². The method used in the research is scientific exploration by conducting a surface geological mapping survey. The geological surface in the form of field data collection and laboratory analysis. Field data in the form of lithology data and laboratory analysis in the form of petrology and petrographic analysis. The stratigraphy of the research area is divided into 4 (four) unofficial units, which are sorted from old to young, namely granodiorite units of Middle Miocene age, volcanic breccia units of Late Miocene to Early Pliocene, andesite units of Middle Pliocene and alluvial units of Holocene age.Stratigraphic analysis of the Limbato area is related to geological history. In the Middle Miocene period subduction formed plutonic rocks that produced granodiorite units, then during the Late Miocene volcanic eruptions resulted in volcanic breccia units. The activity was stopped at the time of the Early Pliocene. After the volcanic activity was stopped, then new magma activity occurred at the time of the Middle Pliocene resulting in an andesite unit. After all rock units have been deposited, an erosion process occurs in older units which results in an alluvial unit.

Analysis of Landslide Susceptibility Zone using Frequency Ratio and Logistic Regression Method in Hambalang, Citeureup District, Bogor Regency, West Java Province

Hambalang area is one of the regions susceptible to landslide events. This is due to unstable geological conditions and high rainfall. Administratively, research area included in Citeureup District, Bogor Regency, West Java Province. Astronomically, research area is located at the coordinates 106°51’30” - 106°53’30” East Longitude and 06°32’ - 06°34’ South Latitude. This study aims to determine the geological conditions of the study area and conduct susceptibility zoning in the Hambalang area using the method of Frequency Ratio and Logistic Regression. The geological conditions of the study area consist of geomorphology in the form of corrugated and flatland morphological units, stratigraphy consisting of claystone units, andesite units and alluvial units, and the structure of the Sumurbatu anticline. The parameters used to analyze the causes of landslide are slope, geology, rainfall, soil type, land use and distance from rivers. There were 19 landslide events identified in the study area. The relationship between occurrences of landslide and the parameters mentioned earlier can be quantified using the value of Frequency Ratio and Logistic Regression. Based on the results of the validation with the Frequency Ratio method, the AUC value of 0.6854 which shows the model of landslide susceptibility based on the selection of parameters and the adequacy of the landslide event data is good. The value of the frequency ratio of the model is divided into three zones of susceptibility, namely high (42.30%), moderate (20.34%) and low (37.36%). Based on the results of the validation with the Logistic Regression method, the AUC value of 0.762 also shows the landslide susceptibility model based on the selection of parameters and the adequacy of the landslide event data so that the Logistic Regression value of the model is divided into three susceptibility zones, namely high (56.89%), moderate (19.53%) and low (23.68%).

Geologi Daerah Geothermal Pangi Kabupaten Bone Bolango Provinsi Gorontalo

Geothermal is associated with volcanic that still has heat energy below the surface. Indonesia is a country with geothermal energy reserves of around 40%. There are 256 potential geothermal areas and only 7 locations have been utilized. Gorontalo has several geothermal manifestations, such as Lombongo, Pangi, Libungo, and Hungayono. The purpose of this study was to study the geology of the geothermal manifestations of Pangi, East Suwawa District, Bone Bolango Regency, Gorontalo Province. The research method is divided into field observations, laboratory analysis, and studio analysis. The results of this research show that the geomorphology in the study area is divided into 3 units, namely the Fluvial Plain, the Volcanic Hills, and the Structural Use Landscape. Alluvial Deposition Unit, Volcanic Breccia Unit, Tuff Lapili Unit, Andesite Unit, Granodiorite Unit, and Porphyry Diorite Unit.

Terrestrial 10Be and electron spin resonance dating of fluvial terraces quantifies quaternary tectonic uplift gradients in the eastern Pyrenees

The 120 km -longTêt River flows out of the Pyrenees to the Mediterranean. By displaying a mappable sequence of Quaternary alluvial units between the Pleistocene frontal moraines of the high range and the offshore sedimentary depocentres, its 1400 km2 watershed is well suited to quantifying gradients of topographic uplift. Five main generations of terrace treads had previously been inferred from constrasts in regolith weathering features, but here we present the first radiometric age constraints based on 15 ESR sediment burial ages covering the full sequence, and 3 vertical TCN age profiles restricted to three mid-sequence terraces. Analytically robust results were obtained for the oldest and uppermost terrace T5 (ESR age: 1099 ± 179 ka), for T3b (ESR age: 374 ± 47 ka, ∼MIS 10), and for T2 (ESR age: 174 ± 44 ka, ∼MIS 6). These results are consistent with the contrasts in weathering grade of the deposits. The TCN profiles only yielded minimum exposure ages but provided precise post-depositional denudation rates for the fluvial terrace treads. The land-to-sea geometry of the chronosequence also provided clues about valley incision rates in response to topographic uplift during the last ∼1 Ma. Based on a critical review of similar data obtained for other Mediterranean and Atlantic watersheds in the Pyrenees, the full regional correlation reveals that post-orogenic topographic uplift was substantial and relatively uniform throughout the entire mountain range. Patterns and magnitudes suggest a shared, probably subcrustal driving mechanism of Neogene and Quaternary mountain growth, with only subsidiary influence from isostasy, and climatic forcing.

Geology of the San Colombano hill, a Quaternary isolated tectonic relief in the Po Plain of Lombardy (Northern Italy)

ABSTRACTThe 1:10,000 geological map of the San Colombano hill covers 60 km2 in the Po Plain, south of Milan. The new and the historical surface geological data-sets are managed by a GeoDB aiming to contribute to re-interpret the Quaternary evolution at the Po Plain-Northern Apennine border. On the hill, the Calabrian shallow marine San Colombano Fm. unconformably overlies the truncated deeper-marine Miocene formations, up-thrusted by the external fronts of the Apennine Emilian Arc during Mio-Pliocene. Late Pleistocene alluvial units rest in unconformity above the marine succession both on the uplifted hilltop and on the surrounding plain. Fault-related offset of Late Pleistocene units, stratigraphic and morpho-structural evidences (facets, relic surfaces and drainage patterns), document the Quaternary tectonic history. Early to Middle Pleistocene ongoing thrust-folding at the northernmost buried reaches of the Emilian Arc was followed by Latest Pleistocene-Holocene transtension, possibly relating to the NNE striking Pavia-Casteggio lateral ramp.

Quaternary tectonic activity of Maradona Fault System, Central Precordillera, Argentina

Several parallel east verging thrusts with Quaternary tectonic activity have been identified in the eastern piedmont of Cordón de Las Osamentas, Central Precordillera of Argentina. We grouped these structures into the Maradona Fault System (MFS). The main morphostructural units, called mountainous and transitional, were analyzed. The form and evolution of these units are closely related to the geological structure of the area. With the morphotectonic analysis, we estimated the length of MFS and the affected alluvial levels. Besides, the morphology of the escarpments was determined through detailed transversal topographic profiles made in a sector where the alluvial levels are affected by the faults. This analysis allowed the recognition of several fault segments and the selection of the points that would present the best natural exposures of the fault- sedimentary deposits relationships. Topographic profiles performed with differential GPS let to identify centimetric fault scarps through slope changes observed in each transect orthogonal to the direction of the structures. Five natural exposures were identified allowing determination of the kinematics of the different fault sections and the deposits affected by these structures. In all the analyzed exposures, faults are reverse with low angle (thrust), dipping to the west and affecting Neogene deposits and alluvial units assigned to the late Pleistocene-Holocene. The Maradona fault system affects younger alluvial levels to the east, showing the gradual migration of the Andean deformation eastward. The progression of the deformation in this sector of Central Precordillera would have evolved according to a pattern of thrusts with angles in surface near 45°, with sequences of internal deformation and reactivation during the Pleistocene-Holocene. Finally, the SFM is regarded as a potential seismogenic source capable to produce earthquakes with magnitude >Mw 6 and hit the main populated centers of the province of San Juan (>700,000 inhabitants), and several dams built along the San Juan River.

Streambank Alluvial Unit Contributions to Suspended Sediment and Total Phosphorus Loads, Walnut Creek, Iowa, USA

Streambank erosion may represent a significant source of sediment and phosphorus (P) to overall watershed loads; however, watershed-scale quantification of contributions is rare. In addition, streambanks are often comprised of highly variable stratigraphic source materials (e.g., alluvial deposits), which may differentially impact in-channel P dynamics once eroded. The objective of this study was to quantify sediment and total phosphorus (TP) losses from four materials comprising streambanks within a 5218 ha watershed in Iowa, USA. Streambank-face surveys, erosion pins, and soil analyses were used to quantify surface area representation, recession, and losses of sediment and TP over a two-year period. Cumulative, whole-bank gross mean recession totaled 18.6 cm over two years, and material-specific gross mean recession ranged from 15.5 to 64.1 cm. Cumulative, whole-bank mean gross mass losses totaled 0.28 Mg sediment and 0.7 × 10−5 Mg TP per meter channel length. Annual sediment losses equated to 4–44% of historic suspended sediment loads. Stratigraphy was significant in gross material erosion and losses, with lower materials (i.e., bank toe region) exhibiting the greatest recession rates and cumulative recession. Weathered/colluvial material dominated total bank face surface area (88.3%), and contributed the greatest proportion of sediment and TP mass loss (66, 68%, respectively) versus other streambank materials.

Paleoseismological study of the southern Zongwulong Shan fault, Qilian Mountains, western China

The Tibetan plateau is prone to destructive earthquakes. A number of strong thrust events occurred in the recent past, seeming to migrate from south to north, to the Qilian Mountains area. Many active thrust faults are known in the Qilian Mountains, and most of them are capable of producing large earthquakes. Here we study the southern Zongwulong Shan (shan means mountain) fault that lacks any paleoseismology studies so far. This fault is the eastern boundary of the Qaidam and Qilian blocks, posing a threat to the populated area of Delingha in western China. In this paper, we document its Holocene rupture history based on paleoseismic trenches, and we assess the seismic risk in this area. We excavated two trenches across 4.5±0.5m high fault scarps in alluvial fans. We found ruptures that affect young alluvial units and almost penetrate the top thick loess unit. We show that four paleoearthquakes occurred in the Holocene with an average recurrence interval of 2300±500years. The most recent event happened between 272BCE and 572CE. Three older events probably occurred in the past 9.5±0.8ka.

Comparison of the Soil Dynamic Amplification Factor and Soil Amplification by Using Microtremor and MASW Methods Respectively

Single Station Microtremor method, which is widely used nowadays, is an effective and easy applicable method. In this study, dynamic amplification factor distributions of the study area were obtained using scenario earthquake parameters with single station microtremor data gathered at 112 points. In addition, a surface wave active method, which is known as MASW (Multichannel Analysis of Surface Waves), was applied at 43 profiles to calculate the soil amplification values. Dynamic amplification factor (DAF), soil amplification, the predominant soil period (PSP), geology and topography data of the study area were analysed together. Dynamic amplification factor and soil amplification values were obtained 2 or higher at about sea level parts of the study area which are generally composed of alluvial units. Additionally, in high altitude regions that are composed of volcanic rocks, relatively lower dynamic amplification factor and soil amplification values were obtained. The minimum amplification value in the study area was 1.15, while the maximum amplification value was 3.05 according to the dynamic amplification results and the soil amplification values were between 1.16 and 3.85 in harmony. It is seen that the obtained DAF values and the soil amplification values calculated from the seismic velocities are very similar to each other numerically and regionally. Because of this, it is concluded that the values of the soil amplification obtained by the MASW method and the calculated DAF values in this study are in harmony with each other. Although the depths of research in these two calculation methods are different from each other, the similarity of the results allows us to arrive at the result of how effective the ground layer is on the amplification. It has a great importance to calculate the amplification values and other dynamic parameters by in situ measurements for a planned plot because geological units can vary even at very short distances in heterogeneously distributed areas.

Local site effects evaluation for Aliağa/İzmir using HVSR (Nakamura technique) and MASW methods

The site effect plays very important role for planning design of structures and estimating seismic damage of existing structures, especially in seismicity active regions. Aliaga, located in the northern region of the Izmir City, is high seismically active region in western Turkey. We identified the dynamic properties of shallow soil for Aliaga district (western Turkey) in terms of the average shear-wave velocity for the top 30 m of soil (Vs30), predominant period (T 0) and vulnerability index (Kg). We created the microzonation map that classes the shallow soil according to National Earthquake Hazards Reduction Program (NEHRP). Shear-wave velocity (Vs) was evaluated using the 1-D multichannel analysis of surface waves at 34 sites. The microtremor measurements were taken at 58 stations with a grid spacing of 1000 m in Aliaga district. The acquired HVSR results show that the T 0 values change from 0.1 to 1.9 s, while the amplification factor (A 0) values change between 1.5 and 12. Soil classification results illustrate that northern part of the study area, located in alluvial unit, has lower Vs30 values. These values are observed within the range of 100–300 m/s. This part was classified as the D and E types according to NEHRP. In addition, the weak zones of the study area due to the local site effects were indicated by the Kg values which vary from 5 to 55. The northern part of the study area is high vulnerability index zone (Kg > 20). Last of all, we can mention that the northern part of our study area is the weakest zone according to the results of geophysical and geological data.

Late Quaternary drainage evolution in response to fold growth in the northern Chinese Tian Shan foreland

Alluvial units are important in understanding the interactions of antecedent drainage evolution with fold growth along the flanks of active orogenic belts. This is demonstrated by the Anjihai River in the northern Chinese Tian Shan foreland, which at present flows northward cutting sequentially through the Nananjihai anticline, the Huoerguos anticline, and the Anjihai anticline. Three episodes of alluviation designated as fans Fa, Fb, and Fc are identified for the Anjihai River. These three alluvial terrain features comprise a series of terraces, where the topographic characteristics, geomorphologic structure, and up-warped longitudinal profiles indicate continuous uplift and lateral propagation of the Halaande anticline and the Anjihai anticline over the past 50ky. Shortly after ~3.6ka when the oldest terrace during the period of the fan Fb sedimentation was formed, significant rock uplift at the overlapping zone of the Anjihai anticline and the Halaande anticline led to the eastward deflection of the antecedent Anjihai River. A series of local terraces with elevation decreasing eastward indicate the gradual eastward migration of the channel of the Anjihai River during the period of the fan Fc sedimentation. Finally the Anjihai River occupied the previous course of the Jingou River when the latter was deflected eastward in response to rock uplift of the Anjihai anticline, presently flowing across the eastern tip of the Anjihai anticline.

Asymmetrical niche determinism across geological units shapes phylogenetic tree communities in the Colombian Amazonia

We evaluate the role of differences in substrate age and environmental conditions, as represented by different geological units, in determining the phylogenetic structure and distribution of tree communities in the northwest Amazon. We used 412 0.1-ha plots distributed across the three main geological units (craton, tertiary and alluvial) in the Colombian Amazon, to answer the following research questions: i) To what extent do environmental filtering and dispersal limitation determine the phylogenetic composition of tree communities across geological units in the Colombian Amazon? and ii) Are there differences between geological units in the extent to which niche conservatism shapes the phylogenetic structure of indicator species (i.e., strong habitat-specialists) in tree communities? The results of our study give support for both environmental filtering and dispersal being important drivers of the phylogenetic structure and turnover of tree communities. Nonetheless, the extent to which geology explained the phylogenetic turnover of tree communities was surpassed by the geographic distance between plots, which was used to account for effects of dispersal limitation. This finding suggests that most of the lineages have had sufficient time to migrate and establish into adjacent geological units, contradicting claims that geological conditions are the dominant factors determining the distribution of tree communities across northwestern Amazonia. However, in the craton unit, indicator species were more closely related than expected by chance, while in the alluvial and tertiary units, observed relationships were not statistically different from null expectations. These results indicate that environmental filtering is asymmetrical among geological units, with the craton environment being the most restrictive. In contrast, the alluvial unit may be relatively easy to colonize and hence ecological strategies may be more labile through evolutionary history.

Dating of river terraces along Lefthand Creek, western High Plains, Colorado, reveals punctuated incision

The response of erosional landscapes to Quaternary climate oscillations is recorded in fluvial terraces whose quantitative interpretation requires numerical ages. We investigate gravel-capped strath terraces along the western edge of Colorado's High Plains to constrain the incision history of this shale-dominated landscape. We use 10Be and 26Al cosmogenic radionuclides (CRNs), optically stimulated luminescence (OSL), and thermally transferred OSL (TT-OSL) to date three strath terraces, all beveled in shale bedrock and then deposited upon by Lefthand Creek, which drains the crystalline core of the Front Range. Our study reveals: (i) a long history (hundreds of thousands of years) of fluvial occupation of the second highest terrace, T2 (Table Mountain), with fluvial abandonment at 92±3ka; (ii) a brief occupation of a narrow and spatially confined terrace, T3, at 98±7ka; and (iii) a 10–25 thousand year period of cutting and fluvial occupation of a lower terrace, T4, marked by the deposition of a lower alluvial unit between 59 and 68ka, followed by deposition of an upper alluvial package at 40±3ka. In conjunction with other recent CRN studies of strath terraces along the Colorado Front Range (Riihimaki et al., 2006; Dühnforth et al., 2012), our data reveal that long periods of lateral planation and fluvial occupation of strath terraces, sometimes lasting several glacial-interglacial cycles, are punctuated by brief episodes of rapid vertical bedrock incision. These data call into question what a singular terrace age represents, as the strath may be cut at one time (its cutting-age) and the terrace surface may be abandoned at a much later time (its abandonment age), and challenge models of strath terraces that appeal to simple pacing by the glacial-interglacial cycles.

A complex thrust sequence in western Himalaya: The active Medlicott Wadia Thrust

The recent activity of the Medlicott-Wadia Thrust (MWT) is investigated by geomorphic and tectonic studies in the Riasi zone, south of the Pir Panjal range (India, Jammu-Kasmir state of western Himalaya). In the Riasi area, the MWT forms a splay of five faults that dip northward. The recent activity of the splay is quantified using a set of deformed Quaternary alluvial units. The central branch of the thrust splay moved Precambrian limestones above Quaternary sediments and is sealed by 36 ± 3 ka (youngest OSL age) deposits. The other branches offset the top of a 15 ± 1 ka (youngest OSL age) alluvial fan by 180 to 120 m; the two southernmost branches form 17–34 m high non-cylindrical scarps and the two northernmost branches also offset the fan by ∼8 m and ∼54 m, respectively. A balanced cross-section parallel to the N210°E thrust motion suggests that the sequence of activity is complex: an in-sequence propagation is found for the three southern Tea, Scorpion and Rain faults and an out-of-sequence reactivation for the northern Pillar fault. Furthermore, several thrusts simultaneously activated for intervals of a few thousand years, whereas others are episodically inactive. Nearly 10 mm/yr of India-Eurasia convergence is regularly absorbed by the MWT, a value greater than the one estimated for the western segment of the MWT affected by the 2005 Kashmir earthquake, where the thrust tectonics interacts with the complex kinematics of the syntax. This work indicates that the MWT is very active and might be related to thick-skinned tectonics in the western Himalaya.

Reducing uncertainty with flood frequency analysis: The contribution of paleoflood and historical flood information

AbstractUsing a combination of stream gauge, historical, and paleoflood records to extend extreme flood records has proven to be useful in improving flood frequency analysis (FFA). The approach has typically been applied in localities with long historical records and/or suitable river settings for paleoflood reconstruction from slack‐water deposits (SWDs). However, many regions around the world have neither extensive historical information nor bedrock gorges suitable for SWDs preservation and paleoflood reconstruction. This study from subtropical Australia demonstrates that confined, semialluvial channels such as macrochannels provide relatively stable boundaries over the 1000–2000 year time period and the preserved SWDs enabled paleoflood reconstruction and their incorporation into FFA. FFA for three sites in subtropical Australia with the integration of historical and paleoflood data using Bayesian Inference methods showed a significant reduction in uncertainty associated with the estimated discharge of a flood quantile. Uncertainty associated with estimated discharge for the 1% Annual Exceedance Probability (AEP) flood is reduced by more than 50%. In addition, sensitivity analysis of possible within‐channel boundary changes shows that FFA is not significantly affected by any associated changes in channel capacity. Therefore, a greater range of channel types may be used for reliable paleoflood reconstruction by evaluating the stability of inset alluvial units, thereby increasing the quantity of temporal data available for FFA. The reduction in uncertainty, particularly in the prediction of the ≤1% AEP design flood, will improve flood risk planning and management in regions with limited temporal flood data.

Late Quaternary channel and floodplain formation in a partly confined subtropical river, eastern Australia

ABSTRACTAlong the eastern margin of Australia, hydrological variability reaches a peak in the subtropics of south‐east Queensland and many rivers have entrenched characteristics. To address the nature of entrenchment and the relationship with adjacent alluvium, this paper presents the results of detailed chrono‐stratigraphic analysis of alluvial units in the partly confined mid‐reaches of Lockyer Creek, Australia. Four sites were investigated using topographic, sedimentological and chronological data. Radiocarbon and single grain optically stimulated luminescence dating indicate a large proportion of the valley fill reflects a major phase of aggradation of fine‐grained alluvium from ca. 35 ka throughout the Last Glacial Cold Period. Synchronous incision of Pleistocene alluvial fills between 11.5 and 9.3 ka suggests the current entrenched Lockyer Creek formed in response to changes in late Quaternary climate. Holocene floodplains set within the entrenched Pleistocene valley floor have basal ages of ca. 7.5 ka, but whose proximal margins are still actively accreting. This Holocene fill has accreted over the mid‐ to late Holocene but overlaps with the contemporary hydrological regime. The sedimentary nature of the Holocene fill appears to be related to persistent antecedent controls in the form of bedrock and terrace constriction.

Modeling background radiation using geochemical data: A case study in and around Cameron, Arizona

This study compares high resolution forward models of natural gamma-ray background with that measured by high resolution aerial gamma-ray surveys. The ability to predict variations in natural background radiation levels should prove useful for those engaged in measuring anthropogenic contributions to background radiation for the purpose of emergency response and homeland security operations. The forward models are based on geologic maps and remote sensing multi-spectral imagery combined with two different sources of data: 1) bedrock geochemical data (uranium, potassium and thorium concentrations) collected from national databases, the scientific literature and private companies, and 2) the low spatial resolution NURE (National Uranium Resource Evaluation) aerial gamma-ray survey. The study area near Cameron, Arizona, is located in an arid region with minimal vegetation and, due to the presence of abandoned uranium mines, was the subject of a previous high resolution gamma-ray survey. We found that, in general, geologic map units form a good basis for predicting the geographic distribution of the gamma-ray background. Predictions of background gamma-radiation levels based on bedrock geochemical analyses were not as successful as those based on the NURE aerial survey data sorted by geologic unit. The less successful result of the bedrock geochemical model is most likely due to a number of factors including the need to take into account the evolution of soil geochemistry during chemical weathering and the influence of aeolian addition. Refinements to the forward models were made using ASTER visualizations to create subunits of similar exposure rate within the Chinle Formation, which contains multiple lithologies and by grouping alluvial units by drainage basin rather than age.

Sedimentation close to the active Medlicott Wadia Thrust (Western Himalaya): How to estimate climatic base level changes and tectonics

The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochronological methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces at its hangingwall are identified. The terraces have been dated by combining Optically Stimulated Luminescence (OSL) on fine-grained deposits and cosmogenic-nuclide dating (10Be) on sandstone pebbles sampled along depth profiles throughout the alluvial units. Three major allostratigraphic units were defined with upper surface ages estimated at ~4, ~15, and 36±3ka; the two older allostratigraphic units are encased terraces at the hangingwall but superposed sedimentary units at the footwall. They are related to phases of elevation of the river level (respectively 30 and 60m) at ~36–38 and 14–15ka and to a phase of extensive lateral incision before ~4ka. These units present vertical offsets induced by the MWT of 50, 190, and 375m, respectively. By taking the aggradation/incision rates at the footwall of the MWT into account, we found that the uplift of the hangingwall remains uniform since 36ka, with a value of ~10mm/yr. Therefore, the aggradation/incision events observed in the Riasi area cannot be ascribed to variations in the tectonic rates and are most likely driven by climatic fluctuations. The high uplift rate is possibly local and related to the Chenab recess, which affects the Himalayan frontal structure. Our results indicate that the MWT is an active growth fault, and one of the main emergences of the active Indian/Asian plate boundary in Western Himalaya.

Indirect geophysical characterization of geohazards in mantled karst environments in the Ebro Basin

Karst hazards in the central Ebro Basin are related to subsidence and collapses owing to evaporitic rocks located several tens of metres below the surface. In this type of karst (mantle karst) cavities propagate upwards through a non-soluble rock, in this case Quaternary alluvial deposits. The typical geological series comprises a heterogeneous alluvial unit underlain by a soluble, mainly gypsiferous, substratum and several water tables that usually present high conductivity variations. The highest concentration of karstic evidence is identified along the fluvial flood plain of the Ebro River where clayey deposits dominate at the surface. These boundary conditions produce complex environments for the evaluation of geophysical data related to i) karst activity, ii) the presence of cavities below the water table and within the substratum and iii) the variable sedimentary architecture of fluvial deposits. During the past ten years different geophysical techniques have been used in order to characterize karst hazards in the Central Ebro Basin. These experiences have enabled the evaluation resolution, discrimination characterization and finding of karstic evidence using different approaches. The main success in the application of these geophysical techniques has been the quantification of karst hazards from the record of subsidence processes through changes in density, magnetic susceptibility, apparent conductivity and structure of the alluvial deposits. However, the identification of cavities below the alluvial series still represents a serious handicap wing to nonunivocal interpretations and low resolution or penetration of geophysical techniques.