Alluvial Fan Systems Research Articles

Stratigraphical, sedimentological and palaeofloristic characterization of the Sorocayense Group (Triassic) in Barreal depocenter, San Juan Province, Argentina

The northern area of Cuyo Basin (west‐central Argentina) corresponds to the Rincón Blanco half-graben, whose filling is arranged into the Rincón Blanco and Sorocayense groups. In the present study, we propose a new stratigraphic scheme for the Sorocayense Group in the Barreal depocenter (San Juan Province), revise the palaeoenvironmental interpretations, and organize and analyse the plant assemblages of previous and new fossiliferous levels. We defined three tectosedimentary sequences. The basal sequence represents the initial graben filling with pyroclastic flows, alluvial fan, and ephemeral fluvial systems, and is arranged in a new unit, the Cerro Colorado del Cementerio Formation. The middle sequence, including Barreal and Cortaderita formations, is characterized by sediment gravity flow deposits and different fluvial systems, with development of floodplains with vertisols and calcisols, and temporal ponds/lakes. In turn, the Cortaderita Formation was divided into the following lithostratigraphic members: Don Raúl and La Emilia. The upper sequence, represented by Cepeda Formation, was deposited by distributary fluvial and ephemeral fluvial systems. Twelve fossiliferous strata (EF) were recognized, which were all identified in the middle sequence: EF1 to EF3 in the Barreal Formation, EF4 to EF8 in the Don Raúl Member, and EF9 to EF12 in the La Emilia Member, both of Cortaderita Formation. The taphocoenosis found in the Barreal and Cortaderita formations were dominated by corystosperms, with conifers, cycadales, and peltasperms as subordinate forms. The available evidence from the taphofloras, palaeosols and palaeonvironments indicate the development of seasonal subtropical climates, which vary from arid or semi-arid in the basal sequence, sub-humid to semi-arid in the middle sequence, and arid or semi-arid in the upper sequence. On the basis of the new information, geological correlation and age of the lithostratigraphic units were accurately re-evaluated. Based on the palaeofloristic content and the correlation with the Rincón Blanco Group, it is possible to infer that the basal sequence was accumulated during late Early Triassic-early Middle Triassic, the middle sequence during the Middle Triassic, while the upper sequence was deposited in the early Late Triassic.

Geoarchaeology of the Water Canyon Paleoindian site, west‐central New Mexico

AbstractWater Canyon is a rare buried, multicomponent, stratified Paleoindian site in west‐central New Mexico. This paper presents a geoarchaeological assessment of the site as part of a broader interdisciplinary investigation of its paleoenvironmental history and archaeology. The archaeology is associated with ancient wetland deposits (Stratum 6) within an alluvial fan. The fan formed initially through the late Pleistocene. Formation of the fan stopped and wetland deposition began ~11,310 14C yr BP (~13,170 cal yr BP). Stratum 6 evolved via wetland deposition and cut‐and‐fill cycles. The bulk of Stratum 6 dates <10,300 14C yr BP (<12,200 cal yr BP). One, or possibly two, beds of bison bone, likely processing‐stations, were found on the margin of the paleowetland and date to ~9,200 14C yr BP (~10,400 cal yr BP) (lower bone bed) and ~8,200 14C yr BP (~9,150 cal yr BP) (upper bone bed). Farther out in the paleo‐wetland a probable kill site was discovered with an in situ Eden projectile point dated to at least ~8,955 14C yr BP (~10,070 cal yr BP). The wetland landscape returned to an alluvial fan system <8,000 14C yr BP (<8,900 cal yr BP) with two more cycles of fan deposition by ~6,500 cal yr.

Fluvial landscape evolution controlled by the sediment deposition coefficient: Estimation from experimental and natural landscapes

AbstractThe evolution of a fluvial landscape is a balance between tectonic uplift, fluvial erosion, and sediment deposition. The erosion term can be expressed according to the stream power model, stating that fluvial incision is proportional to powers of river slope and discharge. The deposition term can be expressed as proportional to the sediment flux divided by a transport length. This length can be defined as the water flux times a scaling factor ζ. This factor exerts a major control on the river dynamics, on the spacing between sedimentary bedforms, or on the overall landscape erosional behavior. Yet, this factor is difficult to measure either in the lab or in the field. Here, we propose a new formulation for the deposition term based on a dimensionless coefficient, G, which can be estimated at the scale of a landscape from the slopes of rivers at the transition between a catchment and its fan. We estimate this deposition coefficient from 29 experimental catchment–alluvial fan systems and 68 natural examples. Based on our data set, we support the idea of Davy and Lague (2009) that G is a relevant parameter to characterize the erosional and transport mode of a fluvial landscape, which can be field calibrated, with a continuum from detachment-limited (G = 0) to transport-limited behavior (G >0.4 from the studied examples).

The Ordovician-Silurian tectono-stratigraphic evolution and paleogeography of eastern Parnaiba Basin, NE Brazil

The Phanerozoic Parnaiba Basin (PB) occupies 600.000 km2 in northeastern Brazil and preserves one of the largest Ordovician-Silurian sedimentary record of western Gondwana, represented by the Serra Grande Group (SGG). This unit marks the initiation of the depositional history of Parnaiba Basin and comprises from the base to the top, the Ipu, Tianguá and Jaicós formations. Therefore the tectono-stratigraphy and paleogeography of SGG is key to unveil the genesis of PB and also the Ordovician-Silurian evolution of Gondwana. Here we present new sedimentological and tectono-stratigraphic surface and subsurface data from the eastern Parnaiba basin. Seven facies associations are described within the SGG: alluvial fan, braided river channel, outwash fan, lodgment till, shoreface, offshore and delta. They are assigned to each formation of SGG and, together with seismic and well data interpretation results, supporting a depositional model for this group. The lowermost portion of the Ipu Formation is represented by immature conglomerates in a scarp-related alluvial fan system, filling up NE-SW-elongated grabens aligned to the crustal scale Transbrasiliano Lineament. This implies that the early sedimentation of the Parnaiba Basin could relate to post-Brasiliano tectonic reactivations following the amalgamation of Gondwana. Upwards, the Ipu Formation grades to a braided river system. Its uppermost portion contains a glacial deposit, here named as the Ipueiras tillite and discontinuously preserved across the basin. This glacial record might be correlated to the Hirnantian Glaciation, a global episode of about 2 m.y. during the Ordovician-Silurian transition (c.a. 443.8 Ma), well documented in other Gondwanan basins from Africa (e.g. the Taoudeni and the Tindouf basins) and South America (e.g. the Amazonas and the Paraná basins). Above it, a 15 m thick layer of marine black shales represent the base of the Tianguá Formation and is interpreted as the maximum flooding event of Serra Grande Group. To the top and laterally, this unit grades to shoreface and deltaic facies associations and is coeval to the global deglaciation transgressive event of Early Silurian. Finally, the overlying Jaicós Formation is composed by braided river deposits in a regressive cycle, possibly related to isostatic rebound, closing the deposition of the Serra Grande Group. Regarding the paleocurrent pattern of this unit, the main northwestwards direction suggests a paleotopographic high in the central portion of western Gondwana.

Sequence palaeogeography, lacustrine basin evolution, and coal accumulation in the Lower Cretaceous Fuxin continental faulted basin, China

The Fuxin Basin is one of the major coal‐bearing basins in northeastern China with the coal seams mainly preserved in the Lower Cretaceous Fuxin Formation. The sequence stratigraphy, palaeogeography, basin evolution, and coal accumulation of the lacustrine coal‐bearing sequences in the Fuxin Formation were analysed based on borehole cores, well logs, and outcrop sections. Fifteen distinct lithofacies types were recognized with lithologies ranging from conglomerates, sandstones, siltstones, and mudstones to coals. Lithofacies are arranged into five facies associations representing alluvial fan, braided fluvial, meandering fluvial, fan delta, and lacustrine depositional systems. These facies associations collectively revealed a continental faulted basin setting. Based on the regional unconformities, basal scour surfaces of the incised valley fills sandstones, paleosols, or seat earths of coal seam on interfluves, and surfaces that mark abrupt depositional facies shifts, the Fuxin Formation was subdivided in two third‐order sequences. Palaeogeographic maps of each sequence have been reconstructed based on the contours of lithological parameters. The palaeogeographic units include alluvial fan, alluvial plain, channel (braided and meandering fluvial), fan delta, and lake. Preferred coal‐forming environments were mainly developed in the fan delta plain and fluvial back‐swamp. Compared with Sequence 1, the activity of basin‐margin faults and basement subsidence of the Sequence 2 gradually decreased, resulting in the lower rate of potential accommodation and less favourable conditions for peat accumulation. This background provided a basic understanding for the lacustrine basin evolution and coal accumulation. A six‐phase evolution model was proposed, which includes lowstand systems tract, early transgressive systems tract, late transgressive systems tract, early highstand systems tract, late highstand systems tract, and falling stage systems tract. The early and late TST of Sequence 1 and Sequence 2 were relatively beneficial stages for peat accumulation and coal development in the Fuxin Basin.

Paleoenvironment and age constraints of Paleoproterozoic alluvial fans in the Sao Francisco Craton, Brazil

The Ouricuri do Ouro Formation represents sedimentary deposits of the Statherian period in São Francisco Craton. Previous works have focused just on the Formation mapping, interpreting the depositional system only in general aspects. However, this study focuses on detailed facies analysis and geochronological investigations of the Ouricuri do Ouro Formation in the central area of São Francisco Craton, Brazil. Four facies associations are recognized: i) Proximal deposits dominated by non-cohesive debris flow; ii) Proximal sheetfloods; iii) Intermediate sheetfloods; and iv) Sandy plains of distal floods. Paleocurrent directions derived from cross-bedding indicate a radial pattern to NE-N. The vertical stacking of distal deposits overlying the proximal facies association suggests a retrogradation of the alluvial fan system, indicating a change in the dynamic of the depositional system. Retrogradation might have been caused by a decrease in the regional gradient declining of the tectonic activity or the retreat of the basin's margin faults system. Furthermore, the presence of higher frequency fining-upward cycles also suggests a climatic control in those deposits. These cycles could be results of the progressive decrease in flow capacity and competence, associated with a decrease of superficial runoff over time. Allied with the dominant paleocurrent, the geochronological data of four tuffaceous sandstones reveal the contribution of Rhyacian to Mesoarchean zircons, suggesting that they came with sediments transported from SW and S of the studied area during the Statherian. The transported sediments came from the southern portion of Gavião Paleoplate. The contribution of volcanic zircons recognized in the tuffaceous sandstones is related to syndepositional magmatism of Statherian Rift of Espinhaço Supergroup. The tuff layer at the base of drill hole (Sample FLV-61 A) contains a zircon age with dominant fraction represented by Statherian zircons defining the syn-sedimentary age of 1722 ± 13 Ma at the basal section of the Ouricuri do Ouro Formation. The present results and available geochronological data constraints the depositional interval of Lower Espinhaço Basin or Megasequence (in sense of Chemale et al., 2012; Guadagnin et al., 2015a, b) between <1.80 and >1.68 Ga in the Chapada Diamantina Region.

Development of a streamflow-dominated alluvial-fan system in the southwestern margin of Gyeongsang Basin (Lower Cretaceous): implications for initial basin-fill history

This paper focuses on the initial basin-fill processes in an extensional nonmarine back-arc basin. Sedimentary facies analysis in the southwestern part of the Gyeongsang Basin (Jinju Subbasin), Hapcheon area reveals that the succession consists of four facies assemblages. The assemblage I mainly consists of disorganized conglomerate deposited by flash floods in a streamflow-dominated alluvial fan. The assemblage II is dominated by stratified conglomerates and massive, stratified, and cross-stratified sandstones, showing architecture of stacked channels and bars. The assemblage III largely comprises massive, stratified to laminated, and trough cross-stratified sandstones, which are organized into channel-fill and bar-accretion structures. It most likely formed in sandy sinuous rivers. The assemblage IV comprises gray mudstone interlayered with fine sandstone, representing water-logged floodplains. Conglomerate and sandstone bodies formed in the fluvial systems appear to be randomly distributed within floodplain fines, displaying a great lateral and vertical lithologic variation. This study helps understand the complexity of basin-fill history, i.e., switching of fluvial networks in time and space, in contrast to the simple notion of margin-parallel stacking of lithostratigraphic units.

Determination of Tectonic Activity Based on the Morphology of Alluvial Fan Systems (Case Study: the Northern Slopes of Sabalan Volcanic Mount)

Determination of Tectonic Activity Based on the Morphology of Alluvial Fan Systems (Case Study: the Northern Slopes of Sabalan Volcanic Mount)

A revised stratigraphy of the Bida Basin, Nigeria

The Bida Basin is a NW-SE trending inland basin, stretching from Shegwa (NW) to Dekina (SE). It is approximately 350 km long and varies in width from 75 to 150 km. It is roughly elliptical in ground plan and runs perpendicularly to the western margin of the NE-SW trending Benue Trough Complex. Unlike other sedimentary basins in Nigeria, it is characterized by the absence of volcanics, carbonates and rocks of Tertiary age. Dedicated fieldwork carried out over the past four years revealed that the basin is underlain by mainly continental sediments with minor occurrence of marginal/shallow marine to freshwater flood-plain deposits. The initial basin fill is characterized largely by several cycles of simple, but amalgamated and/or stacked fanglomerates (alluvial fan) systems developed from several single stream breaches onto the proximal setting of the basin. These fanglomerates directly overly the Basement Complex and display a fining upward sequence. This unit is generally accepted as the Lokoja/Bida Sandstone. Our studies revealed that the Lokoja/Bida Sandstone is overlain directly by the oolitic/pisolitic ironstone of the Agbaja/Sakpe Ironstone which is in turn succeeded by a sequence of rocks generally referred to as the Patti/Enagi Formation, which is comprised of predominantly fine to medium-grained, grey and white sandstones, grey clays, carbonaceous silts and shales, and ubiquitous concretionary ironstone bands. This observation is opposed to the widely accepted view of previous workers that considered the Agbaja Ironstone as the youngest formation in the basin. This study further revealed that the sequence of rocks used to define the Patti Formation does not exist at the location of Mount Patti in Lokoja, rather, it is found in road cut sections, quarries and boreholes around the Ahoko Village. Following the rules for stratigraphic nomenclature, it is hereby proposed that the name ‘Patti Formation’ should be changed to ‘Ahoko Formation.’ A new geological map was made for the basin which clearly demonstrates the relationship of the formations.

Initial observations of water quality indicators in the unconfined shallow aquifer in Dili City, Timor-Leste: suggestions for its management

The management of groundwater quality is a critical issue in developing nations where sanitation and drinking water targets are commonly addressed by facilitating access to groundwater, which is then managed as a common-pool resource. We investigate the quality of the shallow unconfined groundwater in Dili’s alluvial fan system, which 50% of Dili’s rapidly growing population use for all their water requirements. Using the basic chemical and microbiological analyses that are locally available (sulfate, total hardness, fluoride, manganese, iron, ammonia, nitrite, nitrate, total coliform and E. coli) we show that the shallow wells commonly contain enhanced concentrations of dissolved solids and microbiological contaminants (total coliform and E. coli), relative to deeper wells. Cool, shallow wells are worse than warm equivalents. Elevated nitrate and nitrite pollution in the embassy district are tentatively attributed to affluence factors, such as lawn cultivation and water filtration equipment. Microbiological contamination, and associated manganese contamination of groundwater, mimic population patterns, but are concentrated in the finer grained sediments of the small fans and low-slope interdistributary areas. We suggest that rapid development and successful implementation of appropriate sanitation policy in Dili (and elsewhere) is required to address the problematic features of the shallow groundwater system. Success will be predicated on (1) the establishment of baseline data, and (2) development of a systems-thinking approach to holistic water resource management.

Study of sedimentary characteristic in Denglouku formation, southern Songliao basin, Northeast China

Based on geological and geophysical data (e.g., core observation, well-logging curves, logging, analysis assay, and seismic data), the sedimentary facies, characteristics and distributions of the Lower Cretaceous Denglouku formation in the southeast uplift region of southern Songliao Basin are analyzed. The study shows that four types of sandbodies developed in Denglouku formation: alluvial fan, fan delta, braided river and braided river delta. In the early stage of the transition period named D1 period, the deposition is significantly controlled by the fault depression, resulting in rapid unloading of the sediments. Five large-scale divided fault-depressions and two small fault depressions have been developed. The ancient uplift at the periphery of the fault depression refers to the main development area of alluvial fan depositional system, Fan delta deposits are distributed around the fault depression, and the fan delta front extends into the lake. During D2 (the end of the transition period), several geological processes exist: (1) the alluvial fan, fan delta, braided river, braided river delta and lake sediments developed; (2) the unified sediment unloading area is formed. Taking the community of the floodplain and shore-shallow lake contact zone as a boundary, the western part of the boundary mainly developed alluvial fan and braided river sedimentary system from the provenance highland in the western and northern, the east part mainly developed lacustrine facies massively. With the debris sediments of provenance highland injected into the lake basin successively, it constituted retrograde fan deltas in different scales. Among them, the fan delta front and braided delta front subfacies are the main enrichment reservoirs for oil and gas, which is the favorable facies of oil and gas exploration in the Denglouku formation in the future.

Pedosedimentary records of Holocene paleoenvironments in a dryland alluvial fan system in Sonora, NW-Mexico

In this work we present a detailed micromorphological analysis of a sequence of palaeosols and sedimentary units at La Playa archaeological site. This sequence is from the Late Pleistocene (Marine Isotopic Stage 2) to the Late Holocene. Complementing the micromorphological study, a geomorphological analysis is provided, in order to establish the origin of the landscape units. The results show that according to the geomorphology, La Playa constitutes an alluvial fan, formed by a complex, braided channel. The older unit, the San Rafael Palaeosol (SRP) is the most developed and has a set of features associated with the changing paleoenvironmental conditions such as weathering of the primary minerals, clay illuviation (evidencing humid conditions of the Terminal Pleistocene), pedogenic carbonate accumulation in the A horizon (related to dry environments of Altithermal). The SRP is buried by fluvial sediments, which include different facies interpreted as: floodplain, sandbars, and channels. These sedimentation events are associated with the end of the Altithermal period and evidence more active geomorphic processes, probably due to strong storms causing flooding and the migration of the main tributary. Above the sedimentary unit, the Boquillas Palaeosol (BOP), formed during the Late Holocene, is derived from fluvial-alluvial deposits causing a syn-sedimentary soil, with a more incipient development as indicated by micromorphological features.

Plio-Quaternary geology of the Paganica-San Demetrio-Castelnuovo Basin (Central Italy)

ABSTRACTWe present the geological map at 1:25,000 scale of the Plio-Quaternary Paganica-San Demetrio-Castelnuovo Basin corresponding to the epicentral area of the 6 April 2009 Mw: 6.29 L’Aquila earthquake. The map focuses on the relationships between the active tectonics and the Plio-Quaternary deposits and on the early evolution of this continental basin. Fine-scale geological field surveys, coupled with paleontological data, facies analyses, well logs and geophysical data interpretation, allowed to better understand the stratigraphy and to review the previously described stratigraphical units, resulting in the definition of eight synthems, spanning from late Piacenzian to Holocene. More precisely, the occurrence of a Caspiocypris species flock (ostracods) at the base of the sedimentary infill of the basin formed by a lacustrine system, suggests that the onset of deposition started in the late Piacenzian. The lacustrine system disappeared around the Gelasian/Calabrian transition, while the subsequent evolution of the sedimentary basin was characterized by the presence of fluvial and alluvial fan systems progressively entrenched into the lake deposits.The results of the above-mentioned activities are summarized in the attached geological map, where the Plio-Quaternary synthems and the active normal faults accountable for the significant seismicity were highlighted.

Geomorphic response to late Quaternary tectonics in the axial portion of the Southern Apennines (Italy): A case study from the Calore River valley

AbstractThe present study focuses on the morphotectonic evolution of the axial portion of the Southern Apennine chain between the lower Calore River valley and the northern Camposauro mountain front (Campania Region). A multidisciplinary approach was used, including geomorphological, field‐geology, stratigraphical, morphotectonic, structural, 40Ar/39Ar and tephrostratigraphical data. Results indicate that, from the Lower Pleistocene onwards, this sector of the chain was affected by extensional tectonics responsible for the onset of the sedimentation of Quaternary fluvial, alluvial fan and slope deposits. Fault systems are mainly composed of NW‐SE, NE–SW and W‐E trending strike‐slip and normal faults, associated to NW‐SE and NE–SW oriented extensions. Fault scarps, stratigraphical and structural data and morphotectonic indicators suggest that these faults affected the wide piedmont area of the northern Camposauro mountain front in the Lower Pleistocene–Upper Pleistocene time span. Faults affected both the oldest Quaternary slope deposits (Laiano Synthem, Lower Pleistocene) and the overlying alluvial fan system deposits constrained between the late Middle Pleistocene and the Holocene. The latter are geomorphologically and chrono‐stratigraphically grouped into four generations, I generation: late Middle Pleistocene–early Upper Pleistocene, with tephra layers 40Ar/39Ar dated to 158±6 and 113±7 ka; II generation: Upper Pleistocene, with tephra layers correlated with the Campanian Ignimbrite (39 ka) and with the slightly older Campi Flegrei activity (40Ar/39Ar age 48±7 ka); III generation: late Upper Pleistocene–Lower Holocene, with tephra layers correlated with the Neapolitan Yellow Tuff (~15 ka); IV generation: Holocene in age. The evolution of the first three generations was controlled by Middle Pleistocene extensional tectonics, while Holocene fans do not show evidence of tectonic activity. Nevertheless, considering the moderate to high magnitude historical seismicity of the study area, we cannot rule out that some of the recognized faults may still be active. Copyright © 2018 John Wiley &amp; Sons, Ltd.

The Impact of Reservoir Heterogeneities on High-Temperature Aquifer Thermal Energy Storage Systems. A Case Study from Northern Oman.

We conducted a geoscientific feasibility study for the development of a high-temperature thermal aquifer energy storage system (HT-ATES) outside the capital of Muscat, northern Oman. The aquifer storage is part of a solar-geothermal cooling project for the sustainable and continuous cooling of office buildings. The main concept is that excess solar energy will be stored in the subsurface through hot water injection and subsequently utilised as auxiliary energy source during peak demand times. The characterisation of aquifer heterogeneities is thus essential to predict subsurface thermal heat plume development and recovery efficiency of the storage system. We considered two aquifer systems as potential storage horizons, (i) a clastic-dominated alluvial fan system where individual channel systems in combination with diagenetic alterations constitute the main heterogeneities and (ii) a carbonate-dominated system represented by a homogenous layer-cake architecture. The feasibility study included a multidisciplinary approach from initial field work, geocellular reservoir modelling to finite element fluid flow and thermal modelling. Our results show that for the HT-ATES system, with a high frequency of injection and production cycles, heat loss mainly occurs due to heterogeneities in the permeability field of the aquifer in combination with buoyancy driven vertical fluid flow. An impermeable cap-rock is needed to keep the heat plume in place. Conductive heat loss is a minor issue. Highly complex heat plume geometries are apparent in the clastic channel system and ATES well planning is challenging due to the complex and interconnected high-permeable channels. The carbonate sequence shows uniform plume geometries due to the layer cake architecture of the system and is tentatively more suitable for ATES development. Based on our findings we propose the general concept of HT-ATES traps, incorporating and building on expertise and knowledge from petroleum and reservoir geology regarding reservoir rocks and suitable trap&seal geometries. The concept can be used as guideline for future high-temperature aquifer storage exploration and development.

Integrated Use of LANDSAT 8, ALOS-PALSAR, SRTM DEM and Ground GPR Data in Delineating Different Segments of Alluvial Fan System in Mahananda and Tista Rivers, West Bengal, India

In this study, visible near infrared, shortwave infrared spectral bands of Landsat 8 satellite sensor, two polarisation channel of L band ALOS-PALASAR sensor, SRTM-DEM derived digital elevation data were processed to delineate different geomorphic components of alluvial fans of Tista-Mahanada fan complex. We found image composite of independent components, principal components of Landsat 8 bands were effective in delineating proximal and distal fan segments. Fused images of Landsat 8 and ALOS data were used for enhancing incised distributaries and paleochannels. Field data on depositional sequence of fans, were used to substantiate the image based delineation. Topographic breaks along selected longitudinal profiles (identified with the changes in land use and drainage pattern) of digital elevation data were conjugately analysed using Landsat false colour composites. GPR survey along selected transect highlights the vertical dislocation in the recently deposited sequences of alluvial fan regime indicative of post depositional disturbances.

Bedrock structural control on catchment-scale connectivity and alluvial fan processes, High Atlas Mountains, Morocco

Abstract Lithology is acknowledged to be an important internal catchment control on flow processes to adjacent alluvial fans. However, the role of inherited structural configurations (e.g. bedrock attitude) in catchment connectivity and sediment transport is rarely considered. We examine four young (&lt;100-year-old) active tributary junction alluvial fan systems from the Dadès Valley in the High Atlas of Morocco in terms of their catchment-scale connectivity, sediment transfer and resulting alluvial fan processes. The catchments occur on the same lithologies (limestones and interbedded mudstones), but experience different passive structural configurations (tilted and structurally thickened beds). The fan systems react differently to historical peak discharges (20–172 m 3 s −1 ). Catchments containing tectonically thickened limestone units develop slot canyons, which compartmentalize the catchment by acting as barriers to sediment transfer, encouraging lower sediment to water flows on the fans. Syn-dip catchments boost connectivity and sediment delivery from translational bedrock landslides as a result of steep channel gradients, encouraging higher sediment to water flows. By contrast, translational landslides in strike-oriented drainages disrupt longitudinal connectivity by constricting the valley width, while the gradients of the main channels are supressed by the attitude of the limestone beds, encouraging localized backfilling. This diminishes the sediment to water content of the resulting flows.

Source‐to‐sink analysis in an active extensional setting: Holocene erosion and deposition in the Sperchios rift, central Greece

AbstractWe present a source‐to‐sink analysis to explain sediment supply variations and depositional patterns over the Holocene within an active rift setting. We integrate a range of modelling approaches and data types with field observations from the Sperchios rift basin, Central Greece that allow us to analyse and quantify (1) the size and characteristics of sediment source areas, (2) the dynamics of the sediment routing system from upstream fluvial processes to downstream deposition at the coastline, and (3) the depositional architecture and volumes of the Holocene basin fill. We demonstrate that the Sperchios rift comprises a ‘closed’ system over the Holocene and that erosional and depositional volumes are thus balanced. Furthermore, we evaluate key controls in the development of this source‐to‐sink system, including the role of pre‐existing topography, bedrock erodibility and lateral variations in the rate of tectonic uplift/subsidence. We show that tectonic subsidence alone can explain the observed grain size fining along the rift axis resulting in the downstream transition from a braided channel to an extensive meander belt (&gt;15 km long) that feeds the fine‐grained Sperchios delta. Additionally, we quantify the ratios of sediment storage to bypass for the two main footwall‐sourced alluvial fan systems and relate the fan characteristics to the pattern and rates of fault slip. Finally, we show that ≥40% of the sediment that builds the Sperchios delta is supplied by ≤22% of the entire source area and that this can be primarily attributed to a longer‐term (~106 years) transient landscape response to fault segment linkage. Our multidisciplinary approach allows us to quantify the relative importance of multiple factors that control a complex source‐to‐sink system and thus improve our understanding of landscape evolution and stratigraphic development in active extensional tectonic settings.

Distinct phases of eustatic and tectonic forcing for late Quaternary landscape evolution in southwest Crete, Greece

Abstract. The extent to which climate, eustasy and tectonics interact to shape the late Quaternary landscape is poorly known. Alluvial fans often provide useful indexes that allow the decoding of information recorded on complex coastal landscapes, such as those of the eastern Mediterranean. In this paper we analyse and date (using infrared stimulated luminescence (IRSL) dating) a double alluvial fan system on southwest Crete, an island straddling the forearc of the Hellenic subduction margin, in order to constrain the timing and magnitude of its vertical deformation and discuss the factors contributing to its landscape evolution. The studied alluvial system is exceptional because each of its two juxtaposed fans records individual phases of alluvial and marine incision, thus providing unprecedented resolution in the formation and evolution of its landscape. Specifically, our analysis shows that the fan sequence at Domata developed during Marine Isotope Stage (MIS) 3 due to five distinct stages of marine transgressions and regressions and associated river incision, in response to sea-level fluctuations and tectonic uplift at averaged rates of ∼ 2.2 mm yr−1. Interestingly, comparison of our results with published tectonic uplift rates from western Crete shows that uplift during 20–50 kyr BP was minimal (or even negative). Thus, most of the uplift recorded at Domata must have occurred in the last 20 kyr. This implies that eustasy and tectonism impacted the landscape at Domata over mainly distinct time intervals (e.g. sequentially and not synchronously), with eustasy forming and tectonism preserving the coastal landforms.

Risk factors of 12-month recurrence in patients with pancreatic ductal adenocarcinoma undergoing pancreatoduodenectomy

Studies of the palaeobiology of titanosaur eggs are significantly more common than studies of titanosaur-egg-bearing strata. Nevertheless, the latter provide significant insight into palaeoenvironmental conditions associated with the egg-laying behaviour. This study examines titanosaur-egg-bearing strata of the Upper Cretaceous Los Llanos Formation (La Rioja, Argentina) and relates them to the laying and preservation of titanosaur egg clutches. Los Llanos Formation is a predominantly sandstone succession throughout represented by palaeosol profiles. Five titanosaur egg clutches were recovered from the Bw horizon of an Inceptisol profile. This palaeosol type, named Tama pedotype, constitutes 69% of the entire succession, by thickness. Rare planar, and undulating lamination and cross stratification, quartz-grain surface microtextures and ventifacts are indicative of the interaction of fluvial-aeolian processes of sedimentation during accumulation of the parent material on the distal part of a coalescent alluvial fan system (bajada). Highly abundant root traces, reddish colour, clay coatings and calcium carbonate nodules testify that the Tama pedotype had abundant vegetation cover, and was developed in well-drained conditions under the influence of a semiarid climate regime. Palaeosol horizons with exaggerated thickness and diffuse boundaries indicate a cumulative pedotype, whereby the soil developed in response to continuous accretion via on-going sedimentary processes.Morphological features of eggshells suggest that titanosaurs dug holes in the topographic surface to lay eggs. Thus, palaeosols seem to have been putative areas for the laying of titanosaur eggs. Actually, it is uncommon for palaeosols to constitute sites for the preservation of eggs, since soils typically develop in response to long episodes of weathering. However, cumulative palaeosols can provide ideal conditions for egg burial and preservation. In cumulative soils, the residence time of an object within the weatherable thickness of a soil is reduced to < 103 years, thereby significantly increasing the long-term preservation potential of eggs.