Development Of Alluvial Fans Research Articles

Timing and nature of alluvial fan development along the Chajnantor Plateau, northern Chile

Alluvial systems in the Atacama Desert provide a unique opportunity to elucidate the sedimentary response to climate variability, particularly changes in precipitation, in hyperarid environments. Alluvial fans along the eastern margin of the Salar de Atacama, adjacent to the Chajnantor Plateau in the Atacama Desert of northern Chile, provide an archive of climate-modulated sediment transfer and erosion at an extreme of Earth's climate. Three regional alluvial fan surfaces (Qf1 [oldest] to Qf3 [youngest]) were mapped along the western flank of the Chajnantor Plateau. The alluvial fans were examined with geomorphic and terrestrial cosmogenic 36Cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment. Alluvial fans in the study area are comprised of hyperconcentrated flow and boulder-rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes. Alluvial fan surfaces yield exposure ages that range from 49.6±4.4 to 194±12ka, while debris flow boulders yield exposure ages ranging from 12.4±2.1 to 229±53ka. Cosmogenic 36Cl exposure ages indicate that abandonment of alluvial fan surfaces Qf1, Qf2, and Qf3 date to 175±22.6ka (MIS 6), 134.5±9.18ka (MIS 6), and 20.07±6.26ka (MIS 2), respectively. A 36Cl concentration-depth profile through alluvial fan Qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation (6m in ca. 25kyr) followed by surface abandonment ca. 180–200ka. Our data support a strong climatic control on alluvial fan evolution in the region, and we propose that the alluvial fans along the margins of the Salar de Atacama form according to the humid model of fan formation.

Upstream controls on evolution of dryland alluvial megafans: Quaternary examples from the Kohrud Mountain Range, central Iran

Abstract The relative importance of tectonics, climate, base level and source lithology as the primary controls on the evolution of alluvial fans is highly debated. This study examines the role of upstream catchment characteristics on the evolution of alluvial megafans by examining three Quaternary fans (the Kalahrud, Zefreh and Mughar fans) along the flanks of the Kohrud Mountain Range in central Iran. These fans formed in a tectonically active basin under arid to semi-arid climatic conditions. The key differences between the evolutionary trends of these fans are that their catchments are underlain by different bedrock types and they have different catchment shapes and outlet characteristics. The catchment of the Kalahrud fan is in a sedimentary terrain with limited sediment supply, whereas the bedrock lithologies of the Zefreh and Mughar fans are fractured and weathered igneous rocks. However, the evolution of the Mughar fan is also controlled by the tilting of the catchment towards a wide apex and lateral shifting in the catchment outlet/fan feeder channel position. These variables resulted in relatively large-scale incision in the Kalahrud and Mughar fans that is absent in the aggradational trend of the Zefreh fan. Upstream lithological and structural controls are the dominant drivers behind the development and evolution of alluvial megafans.

Constraints on synrift intrabasinal horst development from alluvial fan and aeolian deposits (Triassic, Fundy Basin, Nova Scotia)

Abstract The Triassic Fundy rift basin in Nova Scotia is a large (>70 km wide) half-graben filled with alluvial, lacustrine and aeolian deposits. A major lithospheric lineament, the Cobequid–Chedabucto Fault Zone (CCFZ), which forms the tip of the Newfoundland–Gibraltar Fault Zone, occurs within the Fundy Basin. The timing of early movement on this important fault zone is poorly constrained. We present data from the alluvial and aeolian units that crop out adjacent to the CCFZ in the Minas sub-basin to determine the initiation of fault movement. We use the onset of alluvial fan deposition to infer when the fault became sufficiently active to create the intrabasinal topography and document the influence of fault activity on the intrabasinal drainage. The occurrence and preservation of aeolian deposits immediately adjacent to the CCFZ and concomitant with alluvial fan development suggests a wind shadow effect associated with the fault-generated topography. The onset of alluvial fan deposition associated directly with the fault occurred during Norian times, following an earlier phase of sedimentation in the Fundy Basin, and records a potentially important phase of plate reorganization during early Atlantic rifting.

Phases of alluvial fan development in a loess area, Lublin Upland, E Poland

Holocene alluvial fans are a record of the evolution of the environment and human impact over the last 10 000 years. The study presents the structure of fans at the mouth of gullies as well as their development in the loess areas of the Lublin Upland. Sediment-soil sequences of seven alluvial fans and the adjoining flood sediments and dry valley bottom sediments were studied in detail. The development of fans occurred in three phases: i) the Eneolithic; ii) the middle and late Bronze Age and the Hallstatt period and iii) the Middle Ages and the modern times. The middle phase consists of two sub-phases while last phase consists of three sub-phases: the early Middle Ages; the Little Ice Age; the 19th and first half of the 20th century. These phases were interspersed with longer or shorter periods of stabilization of the alluvial fan surface. The different course of land use changes in the catchments was the reason for this metachronous development of the alluvial fans. Our studies indicate that heavy and catastrophic rainfall and rapid thaw had a considerable role in the development of the alluvial fans. The establishment of roads along the axes of valleys and across the slopes had a key impact on alluvial fan development. The deforestation of the catchment was not an essential condition for the formation of gullies and alluvial fans.

Development and maintenance of a telescoping debris flow fan in response to human-induced fan surface channelization, Chalk Creek Valley Natural Debris Flow Laboratory, Colorado, USA

Channel change has been a constant theme throughout William L. Graf's research career. Graf's work has examined channel changes in the context of natural environmental fluctuations, but more often has focused on quantifying channel change in the context of anthropogenic modifications. Here, we consider how channelization of a debris flows along a bajada has perpetuated and sustained the development of ‘telescoping’ alluvial fan. Two-dimensional debris-flow modeling shows the importance of the deeply entrenched channelized flow in the development of a telescoping alluvial fan. GIS analyses of repeat (five different debris flows), high-resolution (5cm) digital elevation models (DEMs) generated from repeat terrestrial laser scanning (TLS) data elucidate sediment and topographic dynamics of the new telescoping portion of the alluvial fan (the embryonic fan). Flow constriction from channelization helps to perpetuate debris-flow runout and to maintain the embryonic fan and telescoping nature of the alluvial fan complex. Embryonic fan development, in response to five debris flows, proceeds with a major portion of the flows depositing on the southern portion of the embryonic fan. The third through the fifth debris flows also begin to shift some deposition to the northern portion of the embryonic. The transfer of sediment from a higher portion of the embryonic fan to a lower portion continues currently on the embryonic fan. While channelized flow has been shown to be critical to the maintenance of the telescoping fan, the flow constriction has led to higher than background levels of sediment deposition in Chalk Creek, a tributary of the Arkansas River. A majority of the sediment from each debris flow is incorporated into Chalk Creek as opposed to being stored on the embryonic fan.

Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey

The Erzincan pull-apart basin is located in the eastern section of the North Anatolian Fault System (NAFS). The tectonic evolution of this basin is mostly controlled by strike slip master faults of the NAFS. This study examines the topography–structure relationships in an effort to evaluate the tectonic signatures in the landscape, paying special attention to recent tectonic activity. In the study, the main focus is on the tectonic controls of the NAFS on the geomorphic evolution of alluvial fans and fan catchments in the Erzincan pull-apart basin. The observations of the amount of tilting of the alluvial fans (β) and its relation with morphometric (Asymmetry Factor (AF), Hypsometric Integral (HI), Fractal analysis of drainage networks (D)) properties of the fan catchments provide valuable information about the tectonic evolution of the basin area. The results of the analyses showed that the alluvial fan and fan catchment morphology in the pull-apart basin are mainly controlled by the ongoing tectonic activity of the NAFS. The fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin, and aggradation processes by causing channel migration, channel incision and tilting the alluvial fans.

Geomorphological analysis and evolution of an altered floodplain drainage system. The case of the Partido Stream (Spain)

The Partido Stream is a small torrential course that flows into the marsh of the Doñana National Park, an area that was declared a World Heritage Site in 1994. Before 1981, floods occurred, and the stream overflowed onto a floodplain. As an old alluvial fan, the floodplain has its singular orography and functionality. From the floodplain, several drainage channels, locally called caño, discharged into the marsh. The Partido Stream had the morphology of a caño and covered approximately 8km from the old fan to the marsh.The stream was straightened and channelised in 1981 to cultivate the old fan. This resulted in floods that were concentrated between the banks in the following years, which caused the depth of water and the shear stress to increase, thus, scouring the river bed and river banks. In this case, the eroded materials were carried towards the marsh where a new alluvial fan evolved.Control measures on the old fan were implemented in 2006 to stop the development of the new alluvial fan downstream over the marsh. Thus, the stream would partially recover its original behaviour that it had before channelisation, moving forwards in a new, balanced state. The present study describes the geomorphological evolution that channelisation has caused since 1981 and the later slow process of recovery of the original hydraulic-sedimentation regime since 2006. Additionally, it deepens the understanding of the original hydraulic behaviour of the stream, combining field data and 2D simulations.

Tectonic and climatic control on geomorphological and sedimentary evolution of the Mercure basin, southern Apennines, Italy

The morpho-tectonic and sedimentary evolution of the Mercure intramontane basin (Calabria–Lucania boundary, southern Apennines) has been assessed through facies analysis, morphostratigraphy and geomorphological correlation with adjacent areas.The Mercure basin, one of the most active seismogenic zones of the southern Apennines, is a favorable area for reconstructing the main stages of landscape evolution of the axial zone because of its capability to record changes in base level during the Quaternary. In addition, the presence of both erosional and depositional Palaeosurfaces is a useful marker for reconstructing tectonic and morphogenetic events, and hence to detect the role played by tectonics and climate in its genesis, evolution and extinction.The present study identifies the key role of tectonics and denudation, combined with high-frequency floods, as mechanisms controlling alluvial sedimentation in the study area. During endorheic conditions, denudational processes driven by pulses of extensional deformation of the basin margin caused strong alluvial inputs that resulted in the development of alluvial fans. Alluvial facies are mainly characterized by turbulent, subaerial, hyperconcentrated flood flows deposited during the glacial, semi-arid conditions of MIS 14. The retrogradational stacking pattern of the alluvial system indicates decreasing rates of tectonic activity along with declining river gradients.The Mercure coalescing alluvial fans were inundated by lake transgression during MIS 13 in response to (i) abrupt tectonic subsidence at the basin margins and (ii) large decrease of coarse sediment supply due to the interplay among climate, tectonics and catchment size changes. In this regard, it is suggested that tectonic control on the drainage network along with climate and long-term slope evolution may have caused marked pulses in sediment supply, thus influencing the arrangement of facies associations in the sedimentary succession. In addition, the study points out that the main tectonic landforms developed during each period of the landscape evolution well correspond with some active fault segments.

Late Quaternary alluvial fans at the eastern end of the San Bernardino Mountains, Southern California

Alluvial fans at the eastern end of the San Bernardino Mountains in Southern California provide a record of climate modulated sediment transfer and erosion, and are deformed and displaced in places by active faults. Alluvial fans within two study areas, the Mission Creek and the Whitewater River drainages, were examined using geomorphic, sedimentological, and 10Be terrestrial cosmogenic nuclide (TCN) surface exposure methods to define the timing of alluvial fan formation and erosion, and to examine the role of climatic, tectonic and autocyclic processes. These alluvial fan complexes were studied because they are amongst the best-preserved successions of alluvial fans in southern California and they are located at the mouths of two of the largest drainages, Whitewater River and Mission Creek, in the San Bernardino Mountains and traverse major faults, the Mission Creek and Banning. The alluvial fans comprise bouldery debris deposits that represent deposition dominated by flash flood and debris flow events. TCN surface exposure dating indicates that abandonment/incision of alluvial fan surfaces date to early in the Last Glacial or more likely the penultimate glacial cycle, to marine isotope stage (MIS) 4, and to the Holocene. The lack of alluvial fan ages during the latter part of the Last Glacial (MIS 2 and 3) suggests that there has been little alluvial fan lobe deposition/incision during that time. This is similar to findings for many other alluvial fans throughout the American Southwest, and supports the view that there is a strong climatic control on alluvial fan formation throughout this region. Furthermore, the oldest alluvial fan surfaces in the Mission Creek region are beheaded by the Whitewater River drainage, showing that the oldest alluvial fans in the Mission Creek region underwent significant capture by the Whitewater River drainage. This shows the autocyclic controls are also important on alluvial fan evolution in this region; but the importance of these processes to alluvial fan development in other regions of the American Southwest needs to be more fully assessed. The alluvial fans in the Mission Creek area traverse the Mission Creek fault, but are not deformed by it, which suggests that there may have been little if any movement along this fault since at least MIS 4. In contrast, alluvial fans in the Whitewater River study are displaced by active faults highlighting the influence of tectonism on alluvial fan development in this region. In addition to illustrating the importance of climatic controls on the development of alluvial fans in the American Southwest, a classic region for alluvial fan studies, this study illustrates the complex mixture of autocyclic and allocyclic factors that force alluvial fan development in tectonically active settings.

Meandering of Tributaries of the Tigris River Due to Mass Movements within Iraq

Tigris and Euphrates are the main rivers in Iraq. The former has 5 main tributaries while the latter has no tributaries within Iraq. All these rivers exhibit meandering and/or shifting of their courses due to many reasons; such as mass movements and alluvial fan's development. The meandering and shifting of river courses due to mass movements is dealt with in this study. Many examples are given from different parts of Iraq within different rivers and streams. In each case, the geology of the involved area is described; the reasons of the shifting and/or meandering of the river course are given. GIS technique was used to determine the coverage of the involved area. Landsat, Google Earth and DEM images were used to indicate the suffered areas from shifting and meandering of the rivers and streams. When possible, age of the shifting and/or meandering of the river and stream courses was estimated; using exposure age determination; mainly depending on the presence of river terraces, erosional forms, vegetation cover and the maturity of the involved area. Some of the given examples of shifting of river courses were found to be still active; others are inactive. In many cases, indications for very large mass movement phenomena were seen. Moreover, some of the large involved areas are highly populated, others includes few houses and/ or farms. The majority of the meanders are developed due to mass movement phenomena; others are caused by alluvial fans and/or tectonic features, lime plunging of anticlines.

Chronology of processes in high-gradient channels of medium-high mountains and their influence on the properties of alluvial fans

High-gradient channels are the locations of the greatest geomorphological activity in medium-high mountains. The channels' frequency and character influence the contemporary morphology and morphometry of alluvial fans. There is currently no detailed information regarding the frequency of these processes in high-gradient channels and the evolution of alluvial fans in medium-high mountains in Central Europe. This study in the Moravskoslezské Beskydy Mts. analysed 22 alluvial fans (10 debris flow fans and 12 fluvial fans). The processes occurring on the fans were dated using dendrogeomorphological methods. A total of 748 increment cores were taken from 374 trees to reconstruct 153 geomorphological process events (60 debris flow and 93 floods). The frequency of the processes has been considerably increasing in the last four decades, which can be related to extensive tree cutting since the 1970s. Processes in high-gradient channels in the region (affecting the alluvial fans across the mountain range) are predominantly controlled by cyclonal activity during the warm periods of the year. Probable triggers of local events are heavy downpours in the summer. In addition, spring snowmelt has been identified as occasionally important. This study of the relations affecting the type and frequency of the processes and their effect on the properties of alluvial fans led to the creation of a universal framework for the medium-high flysch mountains of Central Europe. The framework particularly reflects the influence of the character of hydrometeorological extremes on the frequency and type of processes and their reflection in the properties of alluvial fans.

Influence of water and sediment supply on the long‐term evolution of alluvial fans and deltas: Statistical characterization of basin‐filling sedimentation patterns

AbstractThe temporal and spatial variability of sedimentation, resulting from sediment storage and release and the lateral mobility of sediment transporting flows, imparts fundamental patterns into the stratigraphic record. Recent studies show that paleoenvironmental (allogenic) signals preserved in stratigraphy may be contaminated by internally generated (autogenic) sedimentation patterns; however, it is unclear how the magnitude of autogenic dynamics is related to allogenic forcings. Utilizing statistical methods, we quantify basin‐filling trends in three laboratory experiments where input water and sediment flux were varied. We use the compensation index and compensation time scale to estimate the strength of compensation, defined here as the tendency to fill topographic lows faster than would result from random deposit stacking, and to estimate the time scales over which autogenic processes operate. In the experiments, topography of channelized deltas formed by noncohesive sediment was monitored in a basin experiencing temporally and spatially uniform relative subsidence. Each experiment resulted in construction of a stratigraphic package in excess of 25 channel depths thick. We find that compensation strength in the experiments is not influenced by absolute magnitudes of water and sediment flux but does increase as a function of the ratio of water to sediment flux. A compensation time scale, defined as the maximum depth of a system's channels divided by the long‐term deposition rate, accurately defines the maximum time scale at which autogenic dynamics occur in all experiments. When applied to field‐scale systems, we predict that autogenic dynamics occur out to time scales between 5 and 150 kyr.

Late Quaternary paleodrainage reconstruction of the Maros River alluvial fan

The surface of the extensive Maros alluvial fan is densely (0.78km/km2) covered by paleochannels. The aim of the present study is to reconstruct the final (late Quaternary) stage of the alluvial fan development by identifying paleodrainage directions and determining morphology and pattern of the paleochannels and the age of their activity.On the surface of the alluvial fan, 18 meandering, braided, anastomosing, or misfit paleochannel zones were identified. The existence of these channels indicates that the main process of the fan development was avulsion rather than lateral channel shift, and the overbank floodplain accumulation played a minor role as the paleochannels were not buried. The oldest paleodrainages (A–C) shifted towards north from the east–west-axis of the alluvial fan, draining water to the Körös basin. The similar age (18.7±2.3ka–14.2±1.4ka) of the paleochannel zones indicates rapid avulsions or the coexistence of paleodrainages. In the northern half of the alluvial fan, the last large (D) paleodrainage change occurred 12.4±2.1ka, when the channel turned westward. A large meandering channel functioned for a period (12.4±2.1ka–9.6±1.3ka); and with the coexisting misfit channels, these channels drained a considerable amount of water (Qb=2500m3/s). In the next development phase (E paleodrainages), the Maros flowed north; but after a sharp bend, it turned toward the south, and it started to form the southern lobe of the alluvial fan. These channels existed between 8.5±0.9ka and 3.5±0.4ka and had a bankfull discharge of 1000–2000m3/s. The last (F) paleodrainage of the Maros River existed for a short time (1.9±0.3ka–1.6±0.3ka) and indicated decreasing discharge (Qb=1400m3/s). In the final phase of the alluvial fan evolution, the present-day course of the river was developed, and its discharge decreased further (680m3/s).

Late Miocene to Plio-Pleistocene fluvio-lacustrine system in the Karacasu Basin (SW Anatolia, Turkey): Depositional, paleogeographic and paleoclimatic implications

The sedimentary record of the late Cenozoic Karacasu Basin, a long-lived continental half-graben from southwestern Turkey, is characterized by siliciclastic and carbonate deposits. Sedimentation was controlled by an active NW–SE trending major normal fault along the basin's southern margin and by climatically-induced lake-level changes. Detailed facies analysis subdivides the entire Neogene–Quaternary basin-fill into three distinct litostratigraphic units representing paleogeographic changes and sedimentation patterns throughout the basin evolution.Sedimentation commenced in the late Miocene with the deposition of proximal–medial alluvial fan and fluvial facies (Damdere Formation; FA1). At this stage, alluvial fans developed in elevated areas to the south, prograding towards the basin center. At the beginning of the Pliocene, fresh to slightly alkaline, shallow lake deposits (FA2a) of the Karacaören Formation formed. The lake became open and meromictic conditions developed (FA2b). Pollen data from the FA2b facies show that climate was arid to humid. Climate probably changed cyclically through time producing alternation of Artemisia steppe (cold and dry periods) and more forested vegetation (warm and wet). The open lake facies passes upwards into lake margin facies (FA2c), but it was still dominated by alkaline to slightly saline lake conditions. Sedimentation was almost continuous from the late Miocene to Pleistocene.In the early Quaternary, the basin was dissected by the re-activation of basin bounding faults. The unconformable base of the overlying Quaternary deposits (Karacasu Formation; FA3) reflected the basin's transformation from a half-graben into a full-graben system. Oxygen isotope data from carbonates show an alternation of humid climatic periods, when freshwater settings predominated, and semiarid/arid periods in which the basin hosted alkaline and saline water lakes. Neotectonic activity has rejuvenated many of the basin-bounding faults, causing development of talus aprons and local alluvial fans. The basin was progressively incised by modern rivers that have largely smoothed out the topographic relief of the graben margins.

Human impact on alluvial fan development in a semi-arid region

Human impact on alluvial fan development in a semi-arid region

Post-tectonic limitations on Early Devonian (Emsian) reef development in the Gobi-Altai region, Mongolia

Pellegrini, A.F.A., Soja, C.M. & Minjin, C. 2011: Post-tectonic limitations on Early Devonian (Emsian) reef development in the Gobi-Altai region, Mongolia. Lethaia, Vol. 45, pp. 46–61. This study investigates a Lower Devonian (Emsian) carbonate sequence from the Chuluun Formation where it is exposed in the Gobi-Altai region of southern Mongolia. Quantification of abundance patterns across guild, morphotype and general taxonomic levels was based on stratigraphical and thin-section analyses. Comparison with other Emsian carbonate platforms allowed the factors that influenced community development in the wake of a tectonic perturbation to be determined. Our evidence reveals that potential reef-building biotas preserved in the Chuluun Formation experienced rapid colonization of a newly submerged carbonate platform following an episode of tectonic uplift and the development of a coastal alluvial fan. Although critical reef-building organisms were present, colonial corals and stromatoporoids exhibited limited vertical growth and showed no significant lateral expansion of individuals or biotic assemblages. Nor did those taxa experience significant increases in abundance, density, or size. We conclude that incomplete succession and the lack of reef development occurred most likely because of an unsuitable substrate, limited accommodation space and isolation that reduced colonization potential. □Community succession, Emsian, palaeoecology, reef suppression.

Timescales of alluvial fan development by precipitation on Mars

[1] Dozens of large, low-gradient alluvial fans are present within impact crater basins on the cratered highlands of Mars. The timescales and climate conditions that were required to generate such fans are unknown, but testable through our understanding of terrestrial hill slope erosion in the presence of precipitation. Previous estimates of fan formation time vary from years to millions of years. Here, we use an idealised physical model of 2-D catchment-fan evolution to present a framework within which the development of Martian alluvial fans should be considered. We simplify the erosional and depositional system so that there are only three variables: erodibility due to gravity, amount of water runoff due to precipitation, and catchment-fan boundary elevation. Within this framework, to generate large, low-gradient ( 108 yr if the substrate is extremely erodible relative to terrestrial examples.

Sedimentary records of rift to pull-apart tectonics in the Miocene Eoil Basin, SE Korea

The Miocene Eoil Basin, SE Korea, is a pull-apart basin formed by dextral crustal deformation during the backarc opening of the East Sea. The Gampo Conglomerate, the lowermost formation of the basin, provides significant information on how a pull-apart basin initiates and is filled by sedimentary strata. The formation consists of nonmarine conglomerates, sandstones, mudstones, and a variety of volcaniclastic deposits that were deposited in alluvial fans, delta slopes, braided streams, mouth bars, and lakes. These deposits are organized into several stratal packages (SP) with contrasting geometries. SP I at the base consists of mouth-bar to delta-front and volcaniclastic deposits, and shows rapid facies variations along the southeastern normal fault margins. SP I suggests that the early basin was bounded by multiple, incipiently developed normal faults with variable displacement and accommodation creation. SP II consists of thick alluvial-fan conglomerates and overlies SP I abruptly, suggesting sudden input of coarse-grained sediment from the uplifted footwalls. It is thickest near the central part of the southeastern normal fault margins, suggesting development of a large alluvial fan near a transfer zone. SP III consists mostly of mouth-bar sandstones, indicating abrupt subsidence of the basin and the transition from subaerial to subaqueous environments. SP IV consists of braided-stream conglomerates, suggesting gradual progradation of coarse-grained fluvial systems toward the basin when the extension and subsidence of the basin was slowed. SP V shows upward-deepening facies changes from braided-stream to mouth-bar deposits, suggesting resumption of basin subsidence. Notably, the cumulative thickness of SP III to SP V is thickest near the northeastern and southwestern strike-slip margins, suggesting migration of the loci of maximum subsidence from the normal fault margins towards the strike-slip margins after deposition of SP II. The change in stratal architecture suggests that the activity of the normal faults was dominant in the early stage of the basin evolution whereas the activity of the strike-slip faults became more pronounced afterwards. Overall, the stratal architecture of the Gampo Conglomerate appears to record the transition tectonics from rift to pull-apart during the incipient stage of a pull-apart basin development. The Eoil Basin is thus interpreted to have been hybrid in nature, influenced by the dynamic changes of the basin-margin faults, which were either normal or strike-slip.

Geoarchaeology and the value of multidisciplinary palaeoenvironmental approaches: a case study from the Tehran Plain, Iran

Abstract Tepe Pardis, a significant Neolithic–Chalcolithic site on the Tehran Plain in Iran, is, like many sites in the area, under threat from development. The site contains detailed evidence of (1) the Neolithic–Chalcolithic transition, (2) an Iron Age cemetery and (3) how the inhabitants adapted to an unstable fan environment through resource exploitation (of clay deposits for relatively large-scale ceramic production by c . 5000 BC, and importantly, possible cutting of artificial water channels). Given this significance, models have been produced to better understand settlement distribution and change in the region. However, these models must be tied into a greater understanding of the impact of the geosphere on human development over this period. Forming part of a larger project focusing on the transformation of simple, egalitarian Neolithic communities into more hierarchical Chalcolithic ones, the site has become the focus of a multidisciplinary project to address this issue. Through the combined use of sedimentary and limited pollen analysis, radiocarbon and optically stimulated luminescence dating (the application of the last still rare in Iran), a greater understanding of the impact of alluvial fan development on human settlement through alluviation and the development of river channel sequences is possible. Notably, the findings presented here suggest that artificial irrigation was occurring at the site as early as 6.7±0.4 ka (4300–5100 BC).

Late Holocene development of a Norwegian alpine alluvial fan affected by proximal glacier variations, episodic distal undercutting, and colluvial activity

The late-Holocene, especially post-Little Ice Age, evolution of Nystølen alluvial fan, Langedalen, Jostedalsbreen region, southern Norway, is investigated using a combination of evidence from surface morphology, recent aerial photography, lichenometric dating, hydrological reconstruction, stratigraphy, and sedimentology. The fan is of predominantly fluvial origin, but it was effectively influenced by variations in the extent of the Nystølsbreen glacier, which advanced onto the fan apex at its Little Ice Age maximum about A.D. 1750, by colluvial activity (primarily snow avalanche) and by the Langedøla River undercutting the fan toe. The fluvial signature is evident in the pattern of distributary channels, lobate boulder berms on the proximal fan surface, three characteristic sedimentary facies associations, and a general down-fan fining identified within stratigraphical sections. The glacier influenced fan development through inputs of sediment (till and glaciofluvial material) and by modification of the flood regime. Snow avalanches added volumetrically small quantities of characteristically coarse and angular colluvial sedimentary material, but debris flows were unimportant. Episodic undercutting of the fan toe initiated a sequence of events consequent on the fall in the local base level, which rendered the distal fan susceptible to headward erosion of box-sided gullies during flood events and their subsequent infilling by the coarse-grained sediment. The evidence is used to develop a new dynamic evolutionary model that reflects these spatial and temporal complexities of glacier-fed, alpine alluvial fan development and incorporates submodels of process interaction, sedimentary architecture, and gully erosion.