Alluvial fans

Fluvial sediments are valuable paleoenvironmental archives of the Quaternary. Since besides environmental factors they are also affected by local tectonics or intrinsic processes, large instead of small catchments should be studied. In drylands covering ca. 45% of the global terrestrial surface large river systems are generally missing, and most river systems are small rivers originating from mountain ranges. Their sediments are potentially interesting paleoenvironmental archives, but are often affected by intensive tectonics. During this study, to obtain a robust regional paleoenvironmental signal a small river system in the southwestern Binaloud Mountains in semi-arid NE Iran was exemplarily studied with a combined approach that encompassed both alluvial fan and catchment. By using geomorphological mapping and numerical dating, fluvial aggradation followed by incision was independently identified in larger areas or in different parts of the river system ca. 95-88 ka, 40 ka, 20 ka, around/after the Pleistocene/Holocene transition and possibly ca. 2.6 ka. These could be linked with regional and over-regional paleoenvironmental data. Furthermore, large boulders on the alluvial fan suggest anthropogenic destabilisation of the catchment during the last decades. Despite strong local tectonics the fluvial dynamics was mostly controlled by paleoenvironmental changes and human activity. This indicates that despite their small size, such river systems form valuable paleoenvironmental archives in drylands where other archive types are largely missing.

Reflectance spectrophotometry potentially provides a rapid method of investigating the changing characteristics and composition of marine sediments. Recognizing this, the Ocean Drilling Program has permanently deployed a commercially available, handheld spectrophotometer, the Minolta CM-2002, aboard the JOIDES Resolution. The present study evaluated shipboard spectral data obtained from Amazon Fan cores during Leg 155 using the Minolta instrument. These data were compared to spectra measured from comparable Leg 155 core samples using a shore-based, research-grade, Perkin-Elmer Lambda 6 spectrophotometer. The spectral signal is muted in the percent-reflectance curves from the wet sediments analyzed aboard ship when compared to percent-reflectance curves generated from dry core samples on shore. However, when both sets of reflectance curves are processed using a first-derivative transformation, shipboard and shore-based analyses are quite similar and suggest that useful, accurate spectral data can be obtained from wet core sediments at sea. This observation is further supported by factor analysis of parallel (shipboard vs. shore-based) data sets (400-700 nm) produced by the two instruments. The same four factors are present in both data sets, but do not necessarily explain a similar amount of variance. These factors are related to hematite plus goethite, clay minerals, organic matter, and carbonate content. The shore-based spectral data set was subjected to further factor analysis to determine if additional compositional information could be extracted using the increased accuracy and extended wavelength range (250-850 nm) of the laboratory instrument. This analysis produced one additional factor, probably chlorite; separated hematite and goethite into two factors; and clarified the nature of the clay mineral factor as probably a combination of illite and montmorillonite. By calculating factor scores, semiquantitative estimates of concentrations of variations of these sediment components were calculated downhole for several Leg 155 sites. The Amazon Fan sediments represent a rigorous test of the spectral technique because most of the sediments are dark and show little variation in the visible region of the electromagnetic spectrum. Nevertheless, it was possible to extract compositional information from the spectra. Our investigations also lead us to make the following important recommendations for using the Minolta CM-2002 spectrophotometer at sea. First, if wet core surfaces must be covered with plastic film during spectral measurements to protect the instrument, only Glad Cling Wrap (a brand of clear plastic food wrap) should be used because this brand does not significantly distort the spectra of the sediments. Second, when calibrating the Minolta instrument, the white calibration cap should not be covered by the clear plastic wrap used to cover the cores. Third, the Minolta instrument should be set to exclude the specular component (SCE setting) for all measurements, and the optional granular-materials cover for the instrument (CM-A40) should not be used. These recommendations will ensure that the spectral data can be compared directly to data generated by laboratory-grade spectrophotometers.

The present study deals with the fault-sourced, alluvial-fan deposits of the Plio-Pleistocene Upper Valdarno Basin (Northern Apennines, Italy). Different phases of alluvial fan aggradation, progradation and backstep are discussed as possible effects of the interaction among fault-generated accommodation space, sediment supply and discharge variations affecting the axial fluvial drainage. The Upper Valdarno Basin, located about 35 km SE of Florence, is filled with 550 m palustrine, lacustrine and alluvial deposits forming four main unconformity-bounded units (i.e. synthems). The study alluvial-fan deposits belong to the two uppermost synthems (Montevarchi and Torrente Ciuffenna synthems) and are Early to Middle Pleistocene in age. These deposits are sourced from the faultbounded, NE margin of the basin and interfinger with axial fluvial deposits. Alluvial fan deposits of the Montevarchi Synthem consist of three main intervals: i) a lower interval, which lacks any evidence of a depositional trend and testify balance between the subsidence rate (i.e. fault activity) and the amount of sediment provided from the margin; ii) a coarsening-upward middle interval, pointing to a decrease in subsidence rate associated with an augment in sediment supply; iii) a fining-upward, upper interval (locally preserved), documenting a phase of tectonic quiescence associated with a progressive re-equilibration of the tectonically-induced morphological profile. The basin-scale unconformity, which separates the Montevarchi and Torrente Ciuffenna synthems was due to the entrance of the Arno River into the basin as consequence of a piracy. This event caused a dramatic increase in water discharge of the axial fluvial system, and its consequent embanking. Such an erosional surface started to develop in the axial areas, and propagated along the main tributaries, triggering erosion of the alluvial fan deposits. Alluvial-fan deposits of the Torrente Ciuffenna Synthem accumulated above the unconformity during a phase of tectonic quiescence, and show a fining-upward depositional trend. This trend was generated by a progressive decrease in sediment supply stemming out from upstream migration of the knickpoints developed during the embanking of the axial system.

Blair, T.C., 2000, Sedimentology and progressive tectonic unconformities of the sheetflood-dominated Hell's Gate alluvial fan, Death Valley, California: Sedimentary Geology, v. 132, p. 233-262.

The Hell's Gate alluvial fan of northern Death Valley has an area of 49.5 km 2 , a radius of 11.8 km, and a smooth 5–3 sloping surface interrupted by shallow (0.5 m), radially aligned gullies 1–4 m wide. Facies analysis of 1–14 m high exposures at 45 sites reveals that the fan is built almost entirely by water-flow processes. Two facies deposited by sheetflooding dominate the exposures from apex to toe. The main one (Facies A), comprising 80–95% of the cuts, consists of sandy, granular, fine to medium pebble gravel that alternates with cobbly, coarse to very coarse pebble gravel in planar-stratified couplets 5–20 cm thick that are aligned parallel to the fan surface. Facies B, comprising 0–10% of the exposures, consists of 10–40 cm thick wedge-planar beds of sandy pebble gravel in backsets dipping 5 to 24. Both Facies A and B are produced by infrequent sediment-charged flash floods from the catchment, and accumulate on the fan from supercritical standing waves of an expanding sheetflood. Antidune backsets are deposited during the buildup stage of the standing-wave cycle, and the couplets during the washout stage. The autocyclic growth and destruction of standing waves during a single sheetflood produces 50–250 cm thick sequences of multiple couplets with backsets. Couplets prevail over antidunes due to the selective preservation of deposits of the standing wave washout phase. Three minor facies comprise 5–20% of the fan exposures. The most common one (Facies D) is pebbly cobble gravel in lenticular beds typically 5–25 cm thick that overlie erosional scours into sheetflood deposits. It comprises gravel concentrated in gullies by fine-fraction winnowing of sheetflood units during recessional flood or by secondary overland flows. Though common on the fan surface, this facies is stratigraphically limited. Facies C consists of medium-to very fine-grained eolian sandsheet deposits 5–30 cm thick present on the distal fan in association with gully-fill gravel. It forms by wind reworking of the fan surface, and by sand transport from the adjoining erg. Facies C and D gully-fill and eolian deposits together comprise bounding beds that divide successive sheetflood sequences. They record secondary processes active on the surface between infrequent sheetfloods that mainly aggrade the fan. The fifth fan facies (Facies E) consists of lakeshore gravel deposited along the distal fan when it was transgressed by Lake Manly during latest Pleistocene time. The medial 3.8 km part of the Hell's Gate fan is uplifted and backtilted 1 to 16 into a tectonic ridge formed during strike-slip motion along the North Death Valley fault. Progressive intrafan unconformities, each likely initiated during one large earthquake, are common in these deposits. Two to eight sheetflood units capped by gully-fill or eolian facies are exposed within unconformity-bounded intervals, indicating that fan-aggrading catastrophic sheetfloods on a given part of fan are 2 to 8 times more frequent than earthquakes that cause backtilting.

Determinations of soil moisture and sediment availability in arid regions are important indicators of local climate variability and the potential for future dust storm events. Data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer were used to derive the relationships among potential soil erosion, soil moisture, and thermal inertia (TI) at the spatial scale of aeolian landforms for the White Sands Dune Field between May 2000 and March 2008. Land surface apparent thermal inertia (ATI) data were used to derive an approximation of actual TI in order to estimate the wind threshold velocity ratio (WTR). The WTR is a ratio of the wind velocity thresholds at which soil erosion occurs for wet soil versus dry soil. The ASTER-derived soil moisture retrievals and the changes through time at White Sands were interpreted to be driven primarily by precipitation, but the presence of a perched groundwater table may also influence certain areas. The sediment availability of dunes, active playa surfaces and the margin of the alluvial fans to the west were determined to be consistently higher than the surrounding area. The sediment availability can be primarily explained by precipitation events and the number of dry days prior to the data acquisition. Other factors such as vegetation and the amount of surface crusting may also influence soil mobility, but these were not measured in the field. This approach showed the highest modeled sediment availability values just days prior to the largest dust emission event at White Sands in decades. Such an approach could be extended to a global monitoring technique for arid land systems that are prone to dust storms and for other regional land surface studies in the Sahara.

Fine grained shaly sands of the Mahwis Formation (Haima Group) form one of the reservoir intervals of the Marmul field. Six lithofacies can be distinguished from cores: shale clast conglomerates, trough cross-stratified sands, horizontally stratified sands, massive sands, rippled sands and interbedded shales and sands. Horizontally stratified sands make up 45% of the cored reservoir. Two scales of fining upward sequence occur. Small sequences are 0.3-1.5 m thick and are interpreted as sheetflood deposits on the distal portions of semi-arid alluvial fans. Sedimentary Geology, 28, 79-95. -1984. Facies model for a sandy ephemeral stream and clay playa complex; the Middle Devonian Trentishoe Formation of North Devon, U.K. Sedimentology, 31, 697-715. WALKER, R. G. 1984. General introduction; Facies, facies sequences and facies models.

La partie centrale de la plaine du Souss s'étend entre le Haut Atlas au nord et l'Anti-Atlas au sud sur 40 km de large. Sa morphologie montre une prédominance des formes héritées, tant dans les régions proximales des piémonts que dans leurs parties distales. Dans les régions proximales subsistent les restes d'au moins trois générations principales de cônes de déjections, plus étendus et plus aplatis sur le piémont anti-atlasique que sur le piémont atlasique, les deux premières étant conservées grâce aux cimentations et encroûtements calcaires. La troisième génération de cônes, cônes adventices, essentiellement limono-sableuse en surface, occupe les parties moyennes et distales. Le système morphogénique majeur est hérité de la transition plio-pléistocène « pliovillafranchien ». De cette époque la plaine conserve les parties apicales encroûtées des cônes et le soubassement carbonaté de sa région centrale, entre El Freija et Ouled Teïma, témoins de l'existence de paléolacs. Ce système déjà consolidé est aussi tectonisé. Dans les régions distales, la vallée actuelle du Souss entaille à peine d'épaisses accumulations carbonatées, restes d'au moins deux générations de paléolacs contemporaines des cônes anciens. Depuis la transition Pléistocène-Holocène, les cônes adventices et le lit majeur de l'oued Souss donnent naissance, en surface, à un modelé fluvio-éolien particulièrement actif.

La ciudad de Cartago se caracteriza por ser un área vulnerable a eventos sísmicos y volcánicos, desbordes los ríos y presencia de grandes frentes de deslizamiento registrados en el área, Este trabajo pretende evaluar éstos fenómenos. palabras clave: lahares, conos de deyección, coladas de lava, deslizamientos, riesgo Industrial, sismos.

Alluvial fan development in Alpine areas is often affected by catastrophic sedimentary processes associated with extreme floods events, causing serious risks for people living on the fans. Hazard assessment in these areas depends on proper identification of the dominant sedimentary processes on the fans. Data from a set of 209 alluvial fans from the central Alps of Italy are presented in this paper and analysed with the help of various statistical techniques (linear regression, principal components analysis, cluster analysis, discriminant analysis and logistic regression). First, we used modern sedimentary facies and historical records (flood events since 15th century), to distinguish between the two dominant sedimentary processes on alluvial fans: debris flows and streamflows. Then, in order to analyse the main controls on past and present fan processes, 36 morphological, geological and land-use variables were analysed. As with observations for arid-environment fans, catchment morphology is the most influential factor in the study area, whereas geology and land use are minor controls. The role of climatic change and landsliding within the catchments also seems to be very important and is discussed. Statistical techniques also help in differentiating groups of alluvial fans by sets of controlling factors, including stage and type of evolution. Finally, by using discriminant analysis and logistic regression, we classified alluvial fans according to the dominant sedimentary process, with a success rate ranging between 75 and 92 per cent.

O principal propósito deste estudo é descrever a geometria e a mineralogia associada ao meio poroso bem como identificar possíveis mecanismos de dano a formação no Membro Carmópolis (Cretáceo Inferior) no campo de petróleo de Siririzinho, Bacia de Sergipe-Alagoas, nordeste do Brasil. Os reservat6rios situam-se entre as profundidades de 400 e 600m. Descrição de testemunhos, microscopia óptica convencional, MEV e analises petrofísicas e químicas das águas intersticiais foram utilizadas para interpretação do modelo deposicional e dos eventos diagenéticos, e para a reinterpretação de testes de laboratório de suscetibilidade a água doce previamente realizados em plugs de testemunhos e que conduziram a conclusões opostas: Monteiro (1980) identificou que as permeabilidades das amostras eram altamente sensíveis ao fluxo de água doce enquanto Branco (1986) concluiu que o fluxo de água doce não causava muitos danos à permeabilidade. Os reservatórios são conglomerados Iíticos e arenitos com estratificações cruzadas, com intercalações de folhelhos, siltitos e calcários laminados, capeados por gipsita e halita. Os Iitoclastos são fragmentos de rochas metamórficas. Um modelo deposicional de leques aluviais progradantes sobre um sistema lacustre parece explicar a deposição do Membro Carmópolis. A porosidade média é 18% com as melhores permeabilidades nas fácies mais grossas. A porosidade primária intergranular é dominante, mas contagens de pontos em lâminas delgadas indicam que pelo menos 29% da porosidade é secundaria, principalmente relacionada a dissolução de feldspatos. Outros tipos incluem intragranular ern fragmentos de rochas metamórficas, em graãs de quartzo corroídos, encolhimento de argilas, vugular e intergranular por dissolução de cimento carbonático. 0 revestimento de grãos detríticos por corrensita (um argilomineral interestratificado expansivo) e extensiva dolomitização são importantes eventos diagenéticos. A corrensita ocorre próximo ao topo do membro Carmópolis, refletindo sua associação bastante comum com evaporitos. A dolomitização parece ter ocorrido antes e depois da geração da porosidade secundaria, e cálculos termodinâmicos indicam que as águas intersticiais se encontram saturadas ou próximo ao equilíbrio com respeito a dolomita nas condições de reservat6rio (50°C). As diferenças nas conclusões dos testes de suscetibilidade a água doce previamente conduzidos são atribuídas a diferenças mineralógicas nas amostras coletadas para os testes: Monteiro (1980) realizou os testes em amostras de arenitos ricos em corrensita, ao passo que Branco (1986) utilizou amostras de arenitos livres de corrensita, Por este estudo, pode-se também estimar razoavelmente bem a magnitude do dano à permeabilidade causado por um fluxo de ágna doce em função do teor de corrensita na amostra, sugerindo adicionalmente que o alto teor de Fe+3 da corrensita pode constituir fonte de dano a formação durante tratamentos ácidos.

Alluvial and fluvial fans are the most widespread depositional landforms bordering the margins of long-lived highland regions and actively subsiding continental basins, across a broad spectrum of tectonic and climatic settings. Their significance is relevant not only to the local morphodynamics of mountain regions and proximal basinal sectors, but also to the long-term evolution of sediment-routing systems, affecting the propagation of stratigraphic signals of environmental change and the preservation potential of stratal successions over much larger spatial scales than those they occupy. Subaerial fan systems archive information on the palaeoclimate, local tectonic history and landscape response to various allogenic factors, although our ability to decipher such information is still limited. Early recognition of alluvial fans dates from the late nineteenth century, but a coordinated research community on these systems has been active only over the last few decades and the full relevance of fluvial fan systems to the geomorphology of present day continental basins and to the interpretation of ancient stratigraphic successions has been convincingly demonstrated only over the last decade. This introductory chapter summarizes advances in our knowledge of alluvial and fluvial fans, identifies potential new lines of future inquiry, and presents the contributions to this volume in the context of the current state of research.

This paper reports a study of the Tista megafan in the foothills of Darjeeling Himalaya. Spread over parts of India and Bangladesh, the megafan is bounded by the Mahananda River to its west and the Tista River to the east. The Atrai and Karatoya Rivers flow through its axial part. The megafan covers an area of ~ 18,000 km2. Near its apex the surface slope is ~ 0.19°, that declines to 0.01° near the toe. The east–west transverse profile of the megafan is broadly upward convex, with gently sloping (~ 0.01°) flanks. Maximum width and the length of the megafan are about 145 km and 166 km respectively. The highest point near the megafan apex is ~ 150 m above the Brahmaputra alluvial plain. The Tista River flanking the megafan has an average annual discharge of 609 m3/s with highest average monthly discharge exceeding 2000 m3/s during monsoon. Most of the other channels currently traversing the megafan are plains-fed, and compared to Tista and Mahananda Rivers these channels have lesser discharge, higher sinuosity, and decreased widths. A radiating network of abandoned channel belts can be identified in satellite images of the megafan. Each of these major paleochannels is associated with numerous crevasse channels in the distal part of the megafan, forming an intricate network of radial drainage on the megafan surface.Three distinct depositional lobes can be recognised on the Tista megafan. Each of the lobes is identified by a set of ancient and modern radial drainage systems. The lobe boundaries are marked by discordance in drainage network of adjacent lobes. The relative ages of the lobes, as tentatively determined from the drainage discordances, indicate that the megafan first built up the eastern lobe (lobe 1), then shifted to the west to form lobe 2, and finally switched again eastward giving rise to the smallest lobe located close to the mountain front (lobe 3). Although broadly upward convex in cross profiles, subtle reflections of multiple lobes are apparent in some of the cross profiles. Study of the old maps published between 1794 and 1945 reveals that some of the present-day plains-fed rivers, like the Tangon, the Atrai and the Karatoya, were directly connected to the Himalayan catchment basins prior to the late eighteenth century. Archaeological excavations along the banks of these rivers appear to support this paleodrainage configuration. Eight facies and five facies associations were recognised in the uppermost megafan sediments. Facies associations suggest deposition from high-energy sandy streams in the proximal area and deposition from mixed load, sinuous streams and flanking marsh or lake in the distal part of the lobes. Paleocurrent data are consistent with a southwestward spreading paleochannel pattern recognised within the studied part of the megafan.Multiple lobes typify megafans ocurring in different parts of the globe. The existence of the mutiple accretionary lobes in Tista megafan, its radial drainage pattern, its concave-upward longitudinal and convex-upward transverse profile shape make it morphologically comparable with other high-gradient alluvial fans observed in nature and those produced in the laboratory. These morphological features denote the similarities between the small, high-gradient alluvial fans and large, low-gradient megafans, and that in turn may be indicative of the commoness in certain controlling factors between these two depositional systems.

This study indicates the possible long-lasting impacts of deep-seated gravitational slope deformation (DGSD) on erosional and mass movement processes. DGSD-features are common large-scale landforms in the crystalline basement rocks of the Central Alps of Austria. Inactive forms are related to paraglacial (nonglacial processes directly conditioned by former glaciation and deglaciation) rock slope adjustment processes acting after glacier retreat towards the end of the Late Glacial period. The near-surface metamorphic bedrock of DGSD-features is generally disintegrated. Such rock type favours erosion and the formation of small landslides. Field data, laboratory analyses, aerial photographs, and GIS-based terrain analyses are used to describe the different geomorphic effects of an extremely disintegrated rock slope. The studied DGSD Hauser Kaibling (13.6 km 2 ) is located in central Austria. During the Last Glacial Maximum the adjacent valley glacier reached an altitude of approximately 1900 m a.s.l. Glacier retreat in combination with the unfavourable tectono-metamorphic setting caused gravity-induced stresses to act. Subsequent sediment build-up in the main valley restabilised the slope. Linear erosion cut a number of gullies into the lower part of the DGSD. Calculated mean erosional denudation rates at incised valley sections range from 0.5 to 2.6 mm a − 1 since deglaciation. Smaller active landslides on the sides of the steep gullies draining the DGSD contribute to high denudation rates. Active landsliding is favoured by: (i) fragmented rock, (ii) steep slopes, (iii) supply of surface and subsurface water by rain and snowmelt, and (iv) human impact. Debris flows and debris-charged flood events occurred frequently in the past. During such events, material was transported from the unstable slopes to the populated alluvial fans. Thus, knowledge about the spatial distribution and the stage of development of DGSDs (active and currently inactive) provides an important basis for risk management measures. Geomorphology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h Fig. 11. High hazard zone at the alluvial fan of the Ennsling Creek: (A) village in close vicinity to the torrent; (B) hazard zoning map of the Austrian Avalanche and Torrent Control for the Village of Ennsling; (C) debris retention dam (constructed in 2002) at the head of the alluvial fan (aerial photograph (1995) source: © GIS-Steiermark).

A Remote Sensing (RS) and Geographical Information System (GIS) based study has been carried out in part of upper Assam valley, NE India to delineate two important fluviomorphological changes that took placed in the confluences of Dihang, Dibang and Lohit rivers; and in increasing valley width of the River Brahmaputra. The study is conducted with TM+ and MSS 25 years time gapped satellite imageries of year 1986 and 2011. This study reveals that within this period by the phenomena of river capturing the main stream of Lohit river is diverted along Dangori river and presently flows along the south of Dibrusaikhowa. As a consequence of this divergence, the confluence point of Dibang and Lohit rivers which was formerly located at Saikhowaghat, near Sadiya at northeast of Dibrusaikhowa, is shifted towards southwestern side of Dibrusaikhowa by about 59.76 km in valley length (areal about 54 km). However, the confluence between Dibang and Dihang rivers shifted westward about 3.34 km from the Kobo Chapori. The changes were also attributed by broadening of the valley width of the rivers. There is a total loss of 846 km 2 area due to migration of river bank lines or river enlargement up to 86% of the original size measured in 1986. The average rate of bank line migration is about 115m per year in some sections.

High-resolution seismic data have been used to study the ice-stream-fed North Sea Fan, deposited from approximately Marine Isotope Stage (MIS) 12 and onwards. Located at the outlet of the Norwegian Channel on the SE Nordic Seas continental slope, the 110,000 km 2 fan is dominated by glacigenic debris flows and slide debrites. The fan is divided in two provinces by the volcanic Møre Marginal High. The proximal province has been characterised by alternation between deposition and erosion, while the distal province has been dominated by deposition. From wMIS 12 until the present the fan has received R32,000 km 3 of sediments. Age constraints on fan stratigraphy provided by core investigations indicate that the Fennoscandian ice sheet advanced to the shelf edge during MIS 2, 6, 8, 10 and probably 12. The fan experienced megaslides in late wMIS 6, 9 and during wMIS 11-12. q

Los abanicos aluviales morfodinámicamente activos que han sido construidos por depósitos torrenciales, representan áreas altamente inestables, cuyas condiciones definen escenarios de amenaza para las poblaciones asentadas sobre ellos. Se consideró analizar los parámetros físicos y morfométricos de las cuencas de la vertiente norte de “El Ávila”, como controles sobre el desarrollo y la morfología de sus abanicos. La metodología comprendió: (a) caracterización de la morfología de los abanicos; (b) mediciones de la morfometría de las cuencas y de los abanicos; (c) construcción de perfiles de cauces principales sobre los abanicos, y perfiles topográficos de éstos; (e) estimación de las superficies de afloramientos litológicos en las cuencas; y (f) correlación entre parámetros morfométricos de los abanicos y de las cuencas. Los abanicos exhiben morfologías del tipo retrollenado desde el frente montañoso, con coalescencia en algunos sectores, y solapamiento en el caso del abanico Quebrada Seca sobre el abanico Punta El Caribe. Sus perfiles longitudinales y transversales muestran las típicas formas cóncava y convexa respectivamente, con ligeras variaciones en sus trazos. Se comportan de igual forma como abanicos-deltas, dado que parte de sus extensiones (depósitos) se encuentran bajo las aguas marinas. Son abanicos de pequeñas dimensiones (áreas entre 0,79 Km2 y 5,71 Km2) y pendientes longitudinales entre 1,67 % y 9,10 %. La litología predominante en cada cuenca, ejerce gran influencia en la morfología, desarrollo y extensión de su abanico. Los parámetros morfométricos de los abanicos de mejores correlaciones con los de las cuencas, son el área y la pendiente de atrincheramiento.

Active deformation structures have an incidence in topography that can be quantified by using geomorphic indices. Most of these indices have been checked in faulted regions with high-deformation rates. The application of several geomorphic indices (hypsometric curve analysis, normalized stream-length gradient, and valley width-to-valley height ratio) to the drainage network of the southern limb of the Sierra de Las Estancias antiform (Internal Zones, eastern Betic Cordillera), where low-rate active folding has been recognized, allows us to investigate the suitability of these indices to identify active structures in such a scenario. Hypsometric curves clearly identify regions with recent uplift and young topography, but they do not provide any constraint on the location of active folds. Local valley width-to-valley height index variations have been detected just coinciding whit the position of ENE-WSW active folds. Normalized stream-length gradient index serves to locate active folds in areas of hard rock substratum, but not in those areas with soft sediments (Neogene-Quaternary sedimentary basins). This is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors. In view of these results, we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low-rate uplift related to active folding, with the best results obtained in hard rock areas.

An aeolian dune field migrating to the east encroached on the toes of alluvial fans in the Teruel Basin (eastern Spain) during a short interval in the Late Pliocene (ca 2·9 to 2·6 Ma), when Northern Hemisphere glaciation and strong glacial–interglacial cycles began. Preservation of the dune field was controlled by syn-sedimentary activity of a normal fault. Ephemeral water discharge eroded aeolian sands and formed V-shaped channels in which aeolian sandstone blocks accumulated. The incorporation of loose aeolian sand in wadi waters modified the sediment/water ratio, changing the physical properties of the flows as they penetrated the aeolian dune field. The erosion and cover of aeolian dune foresets by sheetflood deposits suggest that dune-damming caused the intermittent ponding of water behind the dunes and its flashy release. The arid climate in the Late Pliocene western Mediterranean realm favoured the transport of windblown sediments from northern Africa and western Mediterranean land masses into the Mediterranean. The formation of the studied aeolian dune field (2·9 to 2·6 Ma) and possibly others (for example, the Atacama, Namib and Sahara deserts) correlates with a strong increase of the influence of obliquity, which can be attributed to the combination of a regional expression related to the reduced effect of precession due to a minimum in the long-period (2·3 Ma) eccentricity cycle and a remote expression of the onset of the Northern Hemisphere glaciation.

This work analyses the morphotectonic setting of the Adriatic piedmont of Central Italy, in order to outline the role of tectonics in the development of the fluvial landscape in this area. Particularly, it focuses on the Sangro River, which flows in the southern Abruzzi, from the Apennines, through the piedmont, to the Adriatic coast. The piedmont area developed in a marine environment from the Pliocene to the Early Pleistocene resulting in the deposition of a clayey-sandy sequence. Afterwards, regional uplift processes with NE tilting led to the deposition of a regressive conglomeratic sequence, as the area evolved into a continental environment. This work is based on the qualitative and quantitative study of drainage patterns and on the analysis and correlation of selected morphological evidence of tectonics on fluvial terraces, in order to define the role of tectonics in the geomorphological evolution of the lower Sangro River valley. The drainage network and its statistical azimuthal distributions are analysed; the distribution and the transverse and longitudinal profiles of fluvial terraces are investigated and the morphological evidence for tectonics is then assessed: river bends, linear valleys, beheaded and hanging valleys, counterflow confluences of streams. Space and time correlation of these features allows us to highlight the effects of regional uplift, tilting, and local tectonics on drainage development. Following the emergence of the piedmont area (Middle Pleistocene), uplift and tilting determined a SW-NE consequent and parallel drainage. Progressive incision shaped the Sangro valley as a consequent valley. Local tectonics along NNW-SSE and WNW-ESE faults and fractures resulted in the incision of linear valleys, beheading the previous SW-NE drainage, and controlled the development of a rectangular drainage network (late Middle Pleistocene). The drainage network was then rearranged by selective erosion processes, maintaining a strong inheritance from of its Middle Pleistocene configuration. Geomorphology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h 157 L. D'Alessandro et al. / Geomorphology 102 (2008) 145-158

Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development. For this purpose, high frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor AlHaditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area. The most surprising result of the survey is the absence of evidence of a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth.
Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate mineral as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and
physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.

Ž Dated shorelines of late Pleistocene pluvial Lakes Lahontan Great Basin Desert, northwest . Ž . Nevada and Mojave Mojave Desert, eastern California provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late Pleistocene to early Holocene. Two sets of alluvial fan systems have been mapped: the Stillwater fans, feeding Lake Lahontan; and the Zzyzx fans, feeding Lake Mojave. Their contrasting morphologies suggest different responses of the two fan systems to late Pleistocene to early Holocene climatic change. At the time the Stillwater fan systems underwent minimal sedimentation, with the catchment hillslopes apparently stable. The Zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes. There was a major phase of hillslope debris-flow activity, followed by fanhead trenching and distal fan progradation. Both areas were wetter and colder in the late Pleistocene than they are today, but during the transition to the Holocene the Zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the Southwest. Vegetation reconstructions for the late Pleistocene to the early Holocene suggest that catchment hillslopes in the Mojave supported a desert shrub vegetation, but those in the Stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations. Contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the Pleistocene to ) Corresponding author. 0341-8162r99r$20.00 q 1999 Published by Elsevier Science B.V. All rights reserved.

Los abanicos aluviales morfodinámicamente activos que han sido construidos por depósitos torrenciales, representan áreas altamente inestables y de amenaza para las poblaciones asentadas sobre ellos. Se
analizan las características geomorfológicas de los abanicos del piedemonte norte del macizo El Ávila. La metodología consideró: caracterización de a morfología de los abanicos; mediciones morfométricas de las cuencas y abanicos; estimación de superficies de afloramientos litológicos; y correlación entre parámetros morfométricos de abanicos y cuencas de drenaje. Exhiben morfologías del tipo retrollenado con coalescencia en algunos. Sus perfiles longitudinales y transversales muestran las típicas formas cóncava y convexa. Se comportan de igual forma como abanicosdeltas, parte de sus extensiones se encuentran bajo las aguas marinas. Son abanicos de pequeñas dimensiones y pendientes bajas. La litología ejerce gran influencia sobre la morfología, desarrollo y extensión de éstos, aspectos vinculados de igual manera con la morfometría de las cuencas de drenaje.

This study constructed a database for 690 alluvial fans in humid regions of Japan, Taiwan and the Philippines, and analyzed their slopes and other morphometric parameters such as the area and relief ratio of the source area. This type of comprehensive geomorphological research on alluvial fans in humid regions has been limited, although numerous studies have dealt with fans in arid and semi-arid regions. Semi-conical depositional landforms larger than 2 km 2 and steeper than 0.118 (0.002 m/m) were selected as alluvial fans. About 60% of the fans formed during the Holocene and the rest (40%) formed during the Pleistocene. Mean fan slopes for both all the Quaternary fans and Holocene fans follow a lognormal frequency distribution. The distribution also fits slopes of fans belonging to a certain areal range. The area and relief ratio of the source area, which correlate well with the fan slope, also follow a lognormal distribution, indicating the dimensions of fan/basin systems vary gradually rather than abruptly. These findings contrast with a previous notion that depositional landforms rarely have slopes of 0.58 (0.009) to 1.58 (0.026) and hence only semi-conical landforms steeper than 1.58 should be called alluvial fans. D

Near Innsbruck city (Austria, Eastern Alps), following the Last Glacial Maximum (LGM), an alluvial fan-totalus slope succession was supplied from a carbonate-rock cliff more than 1000 m in height. 234 U/ 230 Th ages of 9.5 to 9.37 isotope kyrs of diagenetic cements in the alluvial-fan succession suggest that the fan/talus deposit accumulated mainly during late-glacial to, perhaps, early Holocene times. The deepest-exposed interval of the fan succession contains cracked lithoclasts probably fractured by overburden from late-glacial ice; this interval is topped by an intra-sequence unconformity. Following final glacial retreat, and rapid aggradation of the alluvial fan and talus slope, the geomorphic regime changed to erosion, as recorded by fanhead trenching and cutting of fluvial terraces, abandonment and vegetating of scree slopes, and excavation of 'talus flatirons'. The changeover from the accumulation of fan and talus to abandonment and dissection probably took place during the terminal late-glacial interval to perhaps the early Holocene. This erosional regime persists until present. A record of rapid late-glacial to early Holocene accumulation of an alluvial fan/talus deposit followed by: (i) abandonment and vegetation growth, combined with (ii) cutting of intra-sequence unconformities of limited lateral extent, is typical of Alpine mountain-flank deposystems situated at comparatively low altitudes. This record consists of (a) an autocyclic component, that is, progressive lowering of sediment input due to onlap and burial of freshly-deglaciated mountain flanks supplying alluvial fans and talus slopes, and (b) an allocyclic component, that is, deglacial climatic warming and upward rise of an altitudinal range with a maximum number of freeze-thaw cycles ('talus window'), also leading to progressive vegetation-induced hillslope stabilization and lowering of scree production.

The Arabo-Persian Gulf, generally considered as a classical carbonate basin, in fact also includes important terrigenous systems whose nature and geometry are related closely to the tectonic framework. The Gulf is bordered along its northeastern periphery by an active alpine system which constitutes a major source of both siliceous and calcareous detritus. There are four types of terrigenous discharge which are classified according to their structural relationships. Numerous alluvial fans terminate ephemeral consequent streams draining the flanks of anticlines forming the external parts of the Zagros Mountain belt. Alluvial-fan deltas studied in detail in southeastern Iran terminate semi-permanent streams which flow along major synclinal axis. They are composed mainly of fine carbonate detritus, part of which accumulates as spectacular marine mud banks. Two major types of delta occur. Relatively small marine deltas, associated with permanent antecedent streams which cross the Zagros fold system, are scattered along the Persian shoreline. The other is the a major deltaic complex which is associated with the Tigris-Euphrates Rivers. This system has prograded along the main axis of the Gulf, the resulting Mesopotamian Plain filling at least half of the original basin which, in early Quaternary times, extended from Hormuz to Syria.

The Morichito piggyback basin (MPB) is a SW-NE-oriented depocenter in the Eastern Venezuelan Foreland Basin (EVFB). This piggyback basin formed by overlying the Pirital thrust during the middle to late Miocene as a result of oblique collision between the Caribbean and South-American Plates. The MPB covers an area encompassing approximately 1000 km 2 between the Serrania del Interior range and the Pirital high, which is a hanging wall uplift along the Pirital thrust that acts as a confining barrier on the southern boundary of the MPB. Previous studies have tried to address the tectonostratigraphic significance of the MPB, but new biostratigraphic information and recently acquired 3D seismic data have allowed us to expand the understanding of this basin. The MPB occupies a relatively small area of the EVFB; however, the MPB contains a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in the EVFB.

The purpose of this study was to evaluate the effects of three agricultural processing wastes (APWs) on aggregate formation and aggregate stability in a sandy loam textured soil (Typic Xerofluvent) in Antalya, Turkey. The effects of APW applications on aggregate formation and aggregate stability were observed for different aggregate size groups (>4; 4e2; 2e1; 1e0.5; 0.5e0.25; 0.25e0.050 and <0.050 mm). Sugar Beet Pulp (SBP), Apple Pomace (AP) and Cotton Gin Waste (CGW) were applied to soil as fresh material (dry weight basis 0, 10, 20 and 40 t ha À1 ), and a greenhouse pot experiment was conducted using a completely randomized design with five replicates of each treatment. The study consisted of two periods. The first period (P1) consisted of a six-month incubation period (1st sample period). The second period (P2) is a six-month period and includes an eight-week green bean (Phaseolus vulgaris L.) growing process (2nd sample period). At the end of the first six months and fourteen months in total, aggregate formation and aggregate stability were determined and their correlation to different C sources was explained. At the end of the experiment, formation of aggregates was increased with increase in the application level of organic wastes in particular intermediate aggregates. Increase in the incubation time significantly enhanced the formation of particular macroaggregates. Soil aggregate stability of all aggregate sizes generally increased with the increasing in the level of implementation. In addition, incubation time effects on aggregate stability for macroaggregates were not significant, but significant for macro and microaggregates.

This work characterized the sink and source/mobility of As in the As-affected sedimentary aquifers of the southern Choushui River alluvial fan, central Taiwan. Major mineral phases and chemical components were determined by XRD and X-ray photoelectron spectroscopy (XPS). The partitioning of As and Fe among cores were determined by sequential extraction. Based on XPS results, the primary forms of Fe were hematite, goethite and magnetite. Sequential extraction data and the XRF analysis indicated that Fe oxyhydroxides and sulfides were likely to be the major sinks of As, particularly in the distal-fan. Furthermore, Fe oxyhydroxides retained higher As contents than As-bearing sulfides. The reductive dissolution of Fe oxyhydroxides, which accompanied high levels of HCO À 3 and NH þ 4 concentrations, was likely the principal release mechanism of As into groundwater in this area. The dual roles of Fe oxyhydroxides which are governed by the local redox condition act as a sink and source in the aquifer. Ionic replacement by PO 3À 4 and HCO À 3 along with seasonal water table fluctuation, caused by monsoons and excessive pumping, contributed specific parts of As in the groundwater. The findings can be used to account for the inconsistency between Fe and As concentrations observed in groundwater.

Decades of research have demonstrated that gravel-bed rivers exhibit multiple spatial scales of landform nonuniformity. Landform features such as valley wall oscillations, alluvial fans, terraces, river meanders, point bars, boulder clusters, and logjams contribute to river corridor heterogeneity. Further, studies have shown that the locations of riffles and pools in gravel-bed rivers are closely associated with the spatial pattern of river corridor morphological variability. These studies imply (but do not directly test) that persistence of riffles and pools through time is also conditioned by landform variability. Mechanistically, it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing. In such circumstances, can variation in valley width influence channel morphology, forcing riffle-pool location and persistence? To address this question, research was performed on a valley-confined, wandering, gravel-bed reach of the regulated lower Yuba River, California, USA that is incising from reduced sediment supply and flow regulation after a historic period of mining-related valley sedimentation. This study quantified stream planform change 1984-2006 and elevation change 1999-2006 using eight aerial photo sets and two digital elevation models, and it qualitatively assessed channel change in older aerial photos going back to 1937. Analysis revealed that the river has undergone rapid incision (0.11 m/year) and planform change in response to frequent floods, yet eight riffles persisted in the same locations, which coincided with the locally wide areas of the valley. Longitudinal profiles revealed that deep pools were associated with long valley constrictions. Geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes.

Abstract: The primary factors that control alluvial fan evolution still remain in question particularly for the
Holocene. Holocene centennial- and millennial-scale climate fluctuations are relatively subtle and more frequent
than those of glacial/interglacial transitions, therefore intrinsic factors such as rock type or basin size are
hypothesized to moderate significantly the influence of Holocene climate and climate change on alluvial fan
processes. Here, we examine variability in styles and rates of alluvial fan aggradation along a single mountain
front that is characterized by basins of varying size and rock type (carbonate versus granite). Basin rock type is
more closely correlated to variability in the episodic nature and magnitude of alluvial fan aggradation than is
basin area. Bedrock physical and chemical weathering properties control sediment delivery to the piedmont and
thus influence alluvial fan aggradation. We suggest that the particle size of grus produced by weathering of
granitic rocks fosters sediment mobilization and alluvial fan aggradation during episodes of increased precipitation
in the Holocene. Sediment mobilization during wetter climates is also possibly enhanced by droughtrelated
fires and vegetation loss that occurred during preceding drier periods. In contrast, carbonate outcrops
weather to both dissolved materials and clastic sediment and relatively rapid cementation of talus precludes its
transportation out onto the piedmont under almost all Holocene climatic conditions. If the scale of past
Holocene climate change is the closest analogy to current global change, this study documents some mechanisms
by which different rock types can exert dramatically different effects on landscape response to those
changes.

Alluvial fans and fan deltas can, in principle, have exactly the same upstream conditions, but fan deltas by definition have ponding water at their downstream boundary. This ponding creates effects on the autogenic behaviour of fan deltas, such as backwater adaptation, mouth bars and backward sedimentation, whereas alluvial fans may lack these effects. Hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions, whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein. To isolate the effects of the upstream and downstream boundaries, five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions. Similar to the fan deltas, the alluvial fans build up by sheet flow, whilst quasi-regular periods of incision cause temporary channelized flow. Incision is followed by channel backfilling, after which the fan returns to sheet flow. The channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas. The difference is caused by morphodynamics at the downstream boundary. In a fan delta, the flow expansion of the channel causes deposition of all the sediment, which forms a mouth bar and causes strong backfilling. In an alluvial fan, on the other hand, the slope break at the fan perimeter causes some deposition, but transport is not reduced to zero. Consequently, the backfilling in alluvial fans is less pronounced than in fan deltas. Other published experiments support this trend: removal of the mouth bar by a river leads to permanent channelization, whilst pronounced mouth-bar formation in highly channelized deltas promotes backward sedimentation. The experimental results for this study predict that, when alluvial fans prograde into lakes or deep rivers, they transition to fan deltas with increasingly deeper channels and thicker backfill deposits.

The Wadi Araba Valley is a morphotectonic depression along part of the Dead Sea Transform (DST) plate boundary that separates the Arabian plate on the east from the Sinai subplate on the west. The Wadi Araba fault (WAF) is one of the main strike-slip faults between the Gulf of Aqaba and the E-W trending Khunayzira (Amatzayahu) fault that bounds the southern end of the Dead Sea. Just south of the Dead Sea, the WAF cuts across several generations of alluvial fans that formed on tributaries to the Wadi Dahal after the regression of Late Pleistocene Lake Lisan ca. 15 ka. Geomorphic and stratigraphic evidence of active faulting, including left-laterally offset stream channels and alluvial-fan surfaces, yielded fault slip-rate data for the northern segment of WAF. Typical cumulative displacements of 54 m, 39 m, and 22.5 m of stream channels and alluvial-fan surfaces across the fault were measured from detailed geologic and topographic mapping. The 54 m offset of the oldest alluvial-fan surface (Q f 1) occurred after the final lowering of Lake Lisan (16-15 ka) and before 11 ka yielding a slip-rate range of 3.4 mm/yr to 4.9 mm/yr. Based on radiocarbon ages of charcoal and landsnail shell samples from the buried Q f 2 alluvial-fan deposits exposed in trenches excavated across the fault, the 39 m and 22.5 m offsets occurred after 9 ka and 5.8 ka, respectively. These data yield a slip-rate range between 3.9 mm/yr and 6.0 mm/yr. The small variability in these slip-rate estimates for different time periods suggests that the northern Wadi Araba fault has maintained a relatively constant slip rate in the past 15 ka. We calculate an average slip rate of 4.7 ± 1.3 mm/yr since 15 ka based on the three separate displacements and age estimates. Five separate offsets of 3 m were measured from gully bends and the offset of small fault-scarp alluvial fans. These displacement data suggest a coseismic slip of 3 m in the last earthquake, or a cumulative slip of 3 m in the past few earthquakes. A maximum slip of 3 m correspond to a Mw 7 earthquake that ruptures about 49 km of fault length. Using an average slip rate of 4.7 ± 1.3 mm/yr together with a 3-m slipper event suggests a maximum earthquake recurrence interval of this fault segment of 500 to 885 years. Table 1. Geologic estimates of lateral slip rates on the Dead Sea transform fault system Fault segment Evidence Amount of Age of Slip rate Authors offset datum DST offset Miocene 40-45 km 7-12 Ma 3.5-6 mm/yr Freund et al., 1968 fault system rocks 7-10 Ma 4-6 mm/yr Freund et al., 1970 3.1-3.7 Ma 9-15 mm/yr Steinitz et al., 1978 Pliocene-7-10 mm/yr Garfunkel Pleistocene et al., 1981 (4-5 Ma) Last 1,000-1.5-3.5 mm/yr Garfunkel 1,500 years (seismic slip rate) et al., 1981 Yammuneh offset Homs basalts 8 km Miocene-5-10 mm/yr Garfunkel fault Pliocene et al., 1981 offset Litani river 5 km 1-2 Ma 5-10 mm/yr South-Central Methodo offset channels 100-150 m post-Lisan 10 mm/yr Garfunkel Jordan fault et al., 1981 Central Wadi offset alluvial fans 3 km 0.3-0.6 Ma 5-10 mm/yr Garfunkel Araba fault et al., 1981 DST fault offset of E-W 2.1 mm 817 years ∼ 2.5 mm/yr Marco et al., (Hula area) trending walls in the 1997 Crusader Ateret Fortress Southern Wadi offset alluvial fans 150 m 20-23 ka 7.5 mm/yr Zak and Freund, Araba fault 1966 Arava fault offsets in 15 km Late Pliocene 3-7.5 mm/yr Ginat et al., drainage basins and or early 1998 alluvial fans Pleistocene Northern Wadi slumps 6.4 mm/yr El-Isa and Mustafa, Araba fault in Lisan deposits (seismic slip rate) 1986 Northern Wadi offset of the late 500 m 77-140 ka 2-6 mm/yr Klinger et al., Araba fault Pleistocene Dahal preferred rate 2000a alluvial fan of 4 mm/yr Northern Wadi offset gullies and 54 m 16-11 ka 3.4-4.9 mm/yr Niemi et al., Araba fault fan surfaces on 39 m 9-6.5 ka 4.3-6.0 mm/yr this paper tributaries to Wadi 22.5 m 5.8 ka 3.9 mm/yr Dahal avg. 4.7±1.3 mm/yr

The geomorphic evolution of Makhtesh Ramon, a feather-shaped erosional valley, and the Nahal Neqarot drainage system to the south occurred largely in response to tectonic activity along the Dead Sea Rift and its western shoulder. Remnants of Miocene clastic sediments (Hazeva Formation) deposited on an erosional peneplain that formed over this area during the Oligocene epoch provide a datum plane for reconstructing subsequent fluvial evolution. These clastic remnants are presently located on the shoulders of Makhtesh Ramon at various elevations. The peneplain truncating the Makhtesh Ramon block has been tilted 0.7% northeastward since the Pliocene epoch (post-Hazeva Formation), whereas that of the Neqarot syncline, south of the Ramon, has been tilted 1.2%. The elliptical exposure of friable Lower Cretaceous sandstone, exposed in the core of the truncated Ramon structure, governed the development of a new ENE directed (riftward) drainage system through capture of streams that previously drained toward the Mediterranean Sea to the northwest. Incised fluvial gaps in the southern rim of Makhtesh Ramon and alluvial fan relicts within Makhtesh Ramon attest to original drainage into the Makhtesh from the south. Remnants of the Plio -Pleistocene Arava Conglomerate on the eastern end of the Neqarot syncline contain clasts from rocks exposed within Makhtesh Ramon, also indicating that streams flowed into the Makhtesh from the southern Neqarot block through the western gaps, then turning eastward and exiting the Makhtesh via the next (Sha'ar-Ramon) gap to the east. Further down-faulting of the Neqarot block during Mid -Late Pleistocene time led to westward retreat of the Neqarot valley and capture of the last stream flowing northward into the Ramon, leaving the modern Makhtesh Ramon isolated from the southern drainage system. D

As principais discordâncias regionais do Uruguai separam o (i) embasamento metamórfico Pré-Ediacarano, (ii) as coberturas tafrogênicas do Ediacarano e (iii) as coberturas devonianas e posteriores. Embora haja consenso sobre o significado desta última discordância, é polêmica a discussão a respeito do limite entre o embasamento e as coberturas tafrogênicas. No presente trabalho é revisado este limite, discutindo-se a Formação Barriga Negra e suas relações com o embasamento metamórfico (Grupo Lavalleja) e plutônico (Granito de Polanco). A Formação Barriga Negra constitui uma espessa sucessão de conglomerados, arenitos conglomeráticos, arenitos e pelitos. Em sua base, sobre discordância litológica com o embasamento, esta formação é representada por conglomerados diversos, desde brechas com calhaus e matacões angulosos até arenitos conglomeráticos com lentes de conglomerados com seixos, interpretados como depósitos de leques aluviais e de rios entrelaçados de clima árido. Estas litofácies basais trazem uma característica fundamental e diagnóstica da posição estratigráfica e estilo tectônico deposicional: os clastos dos conglomerados registram sempre a área-fonte vizinha. A associação de litofácies psamíticas e pelíticas sobreposta evidencia um evento de transgressão, registrado em depósitos de face litorânea e de costa-afora afetados por tempestades. Estes depósitos são recobertos por sucessões estratocrescentes de leques deltaicos e aluviais. No Rio Grande do Sul, a unidade que apresenta sucessão estratigráfica análoga -e também posterior a granitos correlacionáveis ao de Polanco -é designada como Grupo Santa Bárbara do Supergrupo Camaquã.

This paper combines stratigraphic and sedimentological data with XRD, petrographic and SEM techniques in order to investigate the fluvial and alluvial fans that were developed during the Oligocene and the Lower Miocene in the central area of the northern Ebro Basin (Spain), and their respective source areas. The proximal sectors of the coeval depositional systems can be separated on the basis of lithofacies criteria. Conglomerate features reveal that the source areas for the alluvial fans were limited to the South Pyrenean Sierras, whereas those of the fluvial fans included more northern Pyrenean areas, such as the Axial Zone or the clastic Tremp-Graus Basin. Far from the basin margin, the distal alluvial facies interdigitate with the middledistal fluvial deposits. In these areas, only detailed mineralogical and petrographic analysis of the rocks can determine their origin. Thus, the methods used have allowed us to differentiate between authigenic and detrital phases. On the basis of these observations, three different types of coarse sandstone petrofacies have been distinguished: (1) carbonate-rich sandstone, (2) high-quartz sandstone and (3) high lithic-fragment sandstone (rich in shale and feldspars grains). The first corresponds to the alluvial samples and corroborates the South Pyrenean Sierras as alluvial fans source area. The high-quartz and the high lithicfragment sandstone correspond to the fluvial samples and evidence that the drainage basin of the fluvial fans included the clastic Tremp-Graus Basin and the Axial Zone. The high lithic-fragment petrofacies is representative of the most ancient fluvial rocks whereas the high-quartz sandstone corresponds to the recent and nonconforming fluvial rocks. This change in the fluvial petrofacies allows us to recognise the changing importance of each region as a source area of the fluvial fans over time, which can be correlated with Pyrenean tectonic activity during the Oligocene. D

Many engineering geology and structural geology aspects have been used in this study, to point out the suitability of the site for artificial recharge to alluvial aquifer, such as; rocks and soil types, seepage rate, structures and lineaments. The area is under lied by basement rocks with considerable thickness (10 to 15 m) of alluvial deposit. Overall soil type is sandy soil and its seepage rate is 34.56 Liter per hour. The most existing lineaments are trending toward NW direction while rocks foliation dipping toward WWN direction. The site is satisfied to be artificial recharge.