Fan Deposits Research Articles

The Zambezi deep-sea fan: mineralogical, REE, Zr/Hf, Nd-isotope, and zircon-age variability in feldspar-rich passive-margin turbidites

ABSTRACT We here present the first comprehensive provenance study of the Zambezi deep-sea fan, based on integrated petrographic, heavy-mineral, elemental-geochemistry, isotope-geochemistry, and detrital-zircon-geochronology analyses of middle Pleistocene to Holocene turbidites. The Zambezi Valley and Fan represent the submarine part of an ∼ 5000-km-long sediment-routing system, extending from the heart of the South African Plateau to the abyssal depths of the Indian Ocean. Sediment is derived not only from the African side, but also from Madagascar Island mostly via the Tsiribihina Valley. Being shed by two dissected rifted margins, detritus supplied from opposite sides of the Mozambique Channel shares similar feldspar-rich feldspatho-quartzose composition, although with significant differences in heavy-mineral and geochemical signatures. The εNd values of Madagascar sand are markedly more negative and TNd model ages notably older. Zircon grains yield mostly Irumide (late Stenian) U-Pb ages in African-derived sand and mostly Pan-African (Ediacaran–Cryogenian) U-Pb ages in Madagascar-derived sand, which also yields a few grains as old as Paleoarchean and many discordant ages reflecting Pan-African reworking of Archean cratonic rocks. Lower Valley and Lower Fan deposits have intermediate fingerprints, indicating that sediment supply from Madagascar is not much less than from Africa despite a much smaller catchment area, which can be explained by deposition of a conspicuous part of Africa-derived sediment in the Intermediate Basin confined between the Zambezi Shelf, the Beira High, and the Îles Éparses. By assuming that compositional differences between Quaternary submarine deposits and modern Zambezi River sands primarily resulted from sediment impoundment by large dams, we could evaluate the anthropogenic impact on natural sediment fluxes. Quaternary turbidites are somewhat higher in quartz and poorer in heavy minerals with higher relative amounts of durable ZTR species, and yield more Ediacaran, Neoarchean, and Carboniferous detrital-zircon ages than modern river sands. The Orosirian peak characterizing the Intermediate Basin sample points to prominent supply from the middle and upper parts of the Zambezi catchment in the middle Pleistocene. Rough calculations suggest that pre-dam Zambezi sediments were generated ≤ 10% in the upper catchment, ∼ 60% in the middle catchment, and only ≥ 30% in the lower catchment that provides the totality of sediment reaching the Indian Ocean today.

Sedimentology of the Ediacaran barite‐bearing cap dolostone from Gaolan, northern Three Gorges, South China

AbstractWhile Ediacaran cap dolostones research is a hot topic, detailed sedimentological analysis of barite‐bearing cap dolostones remains scarce. Here, new data are presented from Xiangerwan in northern Three Gorges, South China, to illustrate the sedimentary characteristics, depositional environment and formation mechanism of the barite‐bearing cap dolostone. In ascending order, the succession is divided into: (i) pebbly dolostone; (ii) dolostone with unusual sedimentary structures (for example, sheet cracks and tepee structures); and (iii) barite‐bearing facies. The gravels of the pebbly dolostone record the slow relative sea‐level rise during post‐glacial transgression, with a local terrestrial influence. Sheet cracks and tepee structures represent water escape structures in the supratidal and upper intertidal zone, and gently wavy stromatolites in barite‐bearing facies are deposits typical of the upper intertidal zone. In addition, primary radial length‐slow dolomite cements were originally precipitated at the seafloor. In general, the cap dolostone was formed in a shallow‐water ramp environment. The form and sedimentary characteristics of barites indicate a primary (syngenetic) origin and help to divide the barites into bladed (Type I) and needle‐like (Type II) variants. With the ongoing melting of the Marinoan glacier and water density stratification, the cap dolostone was gradually precipitated, accompanied by exotic gravels input. The stratification persisted, and special sedimentary structures were widely developed. Phosphorus and barium ions were brought up from the deep basin by upwelling, indicated by the flourishing stromatolites and barite fan deposition. Above the sediment–water interface, the Type I barite first grew upward from substrates, then the Type II barite could grow either in the reverse ‘V‐shape’ cavities between and within the Type I barite clusters, forming rhythm layers with bedded dolomite, or scattered in the laminae of stromatolites or surrounding dolomite. Finally, the formation of barite fans indicates the end of cap dolostone deposition and deeper water sedimentation.

Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains

Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., SrNd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The SrNd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions.

Heinrich events and tectonic uplift as possible drivers for late Quaternary fluvial dynamics in the western Peruvian Andes

Late Quaternary fluvial valley development in Peru is considered to be driven by summer insolation maxima in the precession cycle, which coincide with increased precipitation and rising lake levels in the central Andes. Our literature review, however, indicates that fluvial aggradation does not always coincide with summer insolation maxima but may also occur during transitions between insolation maxima and minima or even during summer insolation minima. Tectonic uplift as a driver of fluvial incision has not been considered in the current terrace formation models, despite the Peruvian margin being located above an active subduction zone. We present new chronologic, stratigraphic and geomorphic data of the Cañete River valley over the past 102 ± 6 ka. We mapped its fluvial terraces (11.5°-13° southern latitude) along a 75-km long reach perpendicular to the strike of the Andes. Five fluvial terraces and one floodplain level were identified with relative elevations of up to 181.1 m above the floodplain. Thirty-three (pIR) IRSL ages of eight fluvial terraces and one alluvial fan sediment sample showed that their ages in part correspond to summer insolation maxima of the precession cycle, but that a better match exists with pluvial periods that coincided with Heinrich events of the northern hemisphere and rising lake levels in the Andes. The chronology of terraces of the Cañete River agrees with those of previously studied fluvial systems between 7° and 16° southern latitude in Peru, suggesting a regional-scale fluvial response possibly to the Heinrich events. Reconstructed longitudinal profiles and terrace ages were utilised to calculate vertical incision rates. We calculated a mean rate of 1.8 ± 0.10 mm a −1 over the last 102 ± 6 ka, but incision rates varied considerably within this time period possibly in response to changes in the Qs: Qw ratio as a consequence of increased sediment input during the wet Heinrich events. A set of 1338 GNSS measurements of daily, vertical crustal deformation of the years 2009–2015 showed a continuous and positive trend in interseismic, accumulative vertical crustal movements with a time-averaged, crustal uplift rate of 1.9 ± 3.6 mm a −1 . The positive trend in vertical movements, together with data from literature suggest landscape rejuvenation along the forearc and western Cordillera in central Peru. It is proposed that maximally ∼0.5 mm a −1 of the total incision over the past 102 ka may possibly be related to nonrecoverable, interseismic deformation. Climate change-driven variations in the Qs : Qw ratio are superimposed on the long-term tectonic uplift trend, and both are considered the main drivers of fluvial incision. • Fluvial aggradation in response to wet Heinrich events. • Very rapid incision of 1.8 ± 0.1 mm a −1 since 102 ± 6 ka until the present. • GNSS measurements reveal crustal uplift rate of 1.9 ± 3.6 mm a −1 . • Crustal uplift main driver for fluvial incision and climate change as secondary driver. • The same pattern of aggradation and incision occurred along entire western Peru.

Testing the accuracy of OSL and pIR IRSL dating of young geoarchaeological sediments in coastal Peru

Luminescence dating of late Quaternary sediments in Peru is challenging, especially on the Peruvian coast. Earlier studies have shown that quartz grains often exhibit a thermally unstable, medium signal that caused the underestimation of Optically Stimulated Luminescence (OSL) ages. InfraRed Stimulated Luminescence (IRSL) dating has shown to produce more reliable ages, depending, amongst other factors, on the age model (Central or Minimum Age Model), and the IRSL signal. IRSL dating of geoarchaeological sediments has, however, hardly been carried out, let along validated, against an independent age dataset. This dating approach is, nonetheless, the only promising way to date the geological substrate in which many of Peru's archaeological sites are buried. Peru contains some of the oldest and most important archaeological heritage sites, yet not much is known of the environmental context in which many of its early civilizations prospered. A better understanding of which luminescence method works best could therefore help in a better understanding of the geological-stratigraphical context of many of Peru's sites. To investigate this matter more fully, we compared the luminescence dating results of seven sediment samples from the top layer of the Lima alluvial fan and from geoarchaeological layers of the Maranga Complex (San Miguel, Lima), with an independent dataset of sixteen 14 C ages. Our results showed that the quartz OSL ages always underestimated the expected ages due to a signal dominated by medium and slow components, and that the post-IR IRSL 225 (pIR IRSL 225 ) and IRSL 50 ages of K-feldspars, on basis of the Central Age Model (CAM), always overestimated the expected ages. The Minimum Age Model (MAM) on the other hand, correctly predicted the expected ages for the early Holocene, Lima alluvial fan sediments using the pIR IRSL 225 signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL 50 signal.

Morphological and hydrological analysis of volcanic flank valleys – Evidence for a volcanic origin

Valley networks incising the flanks of Martian volcanoes are potential evidence of geologically recent fluvial activity, either via geothermal heating of snowmelt and groundwater upwelling [Gulick and Baker, 1989, 1990; Gulick et al., 1997; Gulick, 2001; Hynek et al., 2010], or summit snowpack melt [Fassett and Head, 2006, 2007]; however, their origin remains uncertain [Carr, 2012]. In this study, detailed morphological, geometric and palaeohydraulic [Hack, 1957] analysis was performed on seven valley networks. Four are Martian valley networks incising the flanks of Alba Mons, Hecates Tholus and Ceraunius Tholus. Considering they may have a magmatic origin, the results of the analysis were compared to several Martian valleys incising volcanic plains and a lunar sinuous rille system, adjacent to Rimae Prinz, to determine whether they bear similarities and may have formed via a similar process. The morphologies of the three small valleys incising the flanks of Alba Mons, Hecates Tholus and Ceraunius Tholus are similar to those incising volcanic plains and the lunar sinuous rille (e.g., width:depth ratios of ∼3). In high-resolution imagery (Context Camera – 5 ​m per pixel; HiRISE - ∼0.5 ​m per pixel), pits can be observed throughout these valleys, which are potential evidence for collapsed lava tubes . The paleohydraulic analysis of these networks indicates that they did not likely form via precipitation-fed fluvial activity and, in some areas, the surface would cause drainage away from the valley trough. However, some of the volcanic flank valleys have small sedimentary deposits at their termination. A combination of these results indicate that they likely formed primarily as a result of tube-forming eruptions and subsequent lava tube collapse, followed by later periods of channel-forming eruptions. If subsequent fluvial activity did take place, resulting in the small sedimentary fans seen at the base of the some of the networks, it was likely the result of short-lived ice/snow melt, which flowed through the pre-defined lava channels. • Morphological and hydrological analysis of seven Martian valleys on volcanoes and volcanic plains, and one lunar rille. • The majority of the valleys bare resemblance with the lunar rille. • The valleys do not follow the scaling relationships expected for fluvial valley systems. • Most valleys likely formed from volcanic activity. • Some of these valleys were likely modified in post by fluvial activity.

Multi-scale, multi-style soft-sediment deformation structures preserved in Cenozoic fluvial deposits, southeastern Brazil: Evidence of impact shaking?

Soft-sediment deformation (SSD) structures preserved in sedimentary successions can record significant seismic events which occurred during or right after deposition. The integrated analysis of sedimentary facies, depositional architecture, and SSD data can determine the relative temporal relationship between deposition and deformational events, and reveal the origin and mechanisms involved in the deformation and the resulting structures. The São Paulo Formation in southeastern Brazil preserves Cenozoic alluvial deposits which characterize most of the geology of the homonymous metropolis area. This succession preserves fluvial channel and floodplain deposits, with associated debris-flow dominated alluvial fan deposits, and preserves abundant SSD structures in a wide range of dimensions and morphologies. These deformation structures include small- and large-scale folds, multi-scale vents of varied geometries, ball-and-pillow structures, and clastic dykes. Here we provide an integrated analysis of sedimentary facies, depositional architecture data, and SSD data from the São Paulo Formation, in order to discuss the deformation mechanisms and plausible triggering mechanisms responsible for the development of such structures. Our interpretation is that SSD structures in the São Paulo Formation were likely triggered by a Cenozoic meteor impact recorded by a crater near the study area.

Alluvial fans in the latest phase of the Messinian Salinity Crisis: An example from the Chaabet Et Tabbela Formation, northern Tunisia, Central Mediterranean

Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km.The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions.

Pliocene-Pleistocene lacustrine system in the Eastern Cordillera Basin, Colombia: Paleoenvironmental implications for diatomite deposition

The Plio-Pleistocene Tilatá Formation records a tectonic paleo-lake system in the Colombian Andes. This unit exhibits recurrent episodes of volcanism and diatomite deposits. Outcrop-based facies analysis of eight stratigraphic sections varying in thickness from 4 to 40 m indicates variations in the sediment supply, accommodation space, climatic conditions, water depth, and organic activity. Fourteen sedimentary facies are grouped into three facies associations (FAs) representative of alluvial, fluvial, and lacustrine settings. FA1 (alluvial fan deposits) corresponds to conglomerates, sandstones, and subordinated mudstones. FA2 (mixed fluvial system) represents sandy conglomerates, cross-bedded/massive sandstones, organic-rich mudstones, lignites, and diatomaceous mudstones. FA3 (lacustrine) comprises mainly organic-rich mudstones, diatomites, laminated sandstones, and tephra layers. The Upper Tilatá Formation reflects the evolution of an overfilled to a balanced-fill lake with a progradational-retrogrational-progradational stacking pattern. The organic facies revealed variations in the origin of the Amorphous Organic Matter (AOM) from aquatic to terrestrial, indicating episodes of shallowing when terrestrial conditions dominated. Seven families, eight genera, and eleven diatom species were identified in diatomites and diatomaceous mudstones, mainly in the lacustrine facies. The most abundant species was Aulacoseira ambigua, suggesting moderate energy in the water column (turbulence), solar light availability for photosynthesis, and mesotrophic to eutrophic conditions. The sedimentological record implies that bedrock, fluvial, pluvial, and volcanic input played a decisive role in nutrient supply for the proliferation of diatoms in the paleo-lake. This scenario is concordant with similar Quaternary depositional systems in northern South America.

The Carboniferous Langness Conglomerate Formation, Isle of Man; an alluvial fan rift-phase deposit

Re-examination of the Langness Conglomerate Formation (LCF) on the coast near Dreswick Harbour, Isle of Man, has established that it is over 65 m thick, twice previous estimates. It formed as a small stream-dominated fan deposit during syndepositional faulting which controlled thickness and facies variations. The sub-Carboniferous surface shows considerable relief, perhaps as much as 10 m and is intricately brecciated and channelled just beneath the base of the conglomerate indicating a pluvial climate even prior to deposition of the LCF. Palaeocurrent data shows that sediment was derived from the NNW. Low in the LCF the sediment is all local in origin, but more exotic material is present higher up. The succession matures texturally (sorting and rounding improve) and mineralogically (lithic sand decreases) upwards and the succession fines upwards. The finer, upper part onlaps northwards across the older Manx Group extending for over 4 km inland thinning to 8 metres. This is consistent with the view that the Isle of Man formed a regional high during the Lower Carboniferous. The LCF resulted from the initial fault movements that led to inundation of the Isle of Man High in the late Chadian to early Arundian.

Palynofloras, palaeoenvironmental change and the inception of the Paleocene Eocene Thermal Maximum; the record of the Forties Fan, Sele Formation, North Sea Basin

The Paleocene–Eocene Thermal Maximum (PETM) has previously been recorded in marine density flow sedimentary rocks of the Forties Member, Sele Formation, North Sea Basin. Two cored well sections with existing δ 13 C records were analysed for their total palynofloras. Using statistically defined microplankton groups and diversity data, the Sele Formation Unit S1 depositional sequence and its maximum flooding surface was identified in both wells. This highlighted that deposition of the Forties Fan complex began significantly earlier than the inception of the PETM in the proximal fan area. Palynofloras from the Central and West Axial fairways of the Forties Fan have previously been used to indicate increased rainfall, erosion and onset of Forties Fan deposition at the PETM inception. However, winterwet floodplain communities typify the coeval East Axial Fairway, whereas the dominance of swamp-derived communities in the West and Central Axial Fairway sediments reflects source palaeogeography overriding the regional winterwet climate signal. Palynofloras reflecting regional increased seasonality and lower moisture availability increase immediately before the PETM CIE onset, but reflect climate warming over the hyperthermal. However, there is no correlation between Forties Fan initiation and the PETM. NE Atlantic margin basin flank uplift in response to synrift volcanism is indicated as the driving mechanism behind Forties Fan inception. Supplementary material : Raw data, DCA graphs for microplankton, pollen and spore data and δ 13 C data for well 22/6-1 are available at https://doi.org/10.6084/m9.figshare.c.6080873

An updated global survey of alluvial fans on Mars: Distinguishing alluvial fans from other fan-shaped features through morphologic characterization

Alluvial fans formed on Mars during the late Hesperian to early Amazonian in a climatic transition from a time of regular surface water activity to the current dry and cold climate. The depositional environments recorded by alluvial fans represent the final era of potential habitability on the Martian surface. Alluvial fan deposits can often look similar to deltaic or fluvial systems in visible remote sensing images but are formed in depositional and climatic environments that are distinct from those that lead to other radial depositional features. In order to better constrain regional and global depositional environments and further inform the analysis of the sedimentary history of Mars, we expanded the global catalog of alluvial fans on Mars by adding newly identified features and characterizing all new and previously identified features based on morphologic parameters. Using planform shape, radius, average radial slope, and radial profile shape, we classified features as alluvial fans, possible alluvial fans, and non-alluvial radial features (NARFs), based on how closely they fit the morphologic definition of alluvial fans. Other radial-shaped depositional features form in more water-rich depositional environments whereas alluvial fans form by subaerial deposition in arid to hyper arid environments from sporadic high-energy flow events interspersed with long dry periods of inactivity. By identifying new features and distinguishing alluvial fans from other fan-shaped features in the global catalog, we have isolated distinct depositional environments on a local scale and updated the global perspective of the distribution and variety of aqueous depositional environments during the early history of Mars. Newly identified alluvial fans are found as far as 78°S latitude as well as in numerous locations within the Hesperian to Noachian transition unit along the dichotomy and occur both in craters and along non-crater topographic features, expanding the global range of alluvial fan environments into regions that previously have been overlooked.

Contrasting thermal histories for the Indian passive margins during syn‐ and post‐Gondwana break‐up: Insights from apatite fission‐track thermochronology

AbstractNew and published apatite fission‐track data provides evidence for differential exhumation between the eastern and western passive margins of southern India. The eastern margin records significant Late Jurassic to Early Cretaceous rifting‐triggered exhumation in response to Gondwana break‐up and minor Cenozoic cooling. In contrast, Meso–Cenozoic rifting and posterior tectonic events did not deeply exhume the basement of the western margin. The anomalous thick crust of the Western Dharwar Craton might explain why Mesozoic deformation in this area was subdued. In addition, the Cenozoic eastward tilting of the Indian plate and the onset of Bengal Fan sedimentation ca. 23 Ma allowed the accumulation of thick sedimentary sequences in the eastern coastal basins, probably inducing a flexural response of fault reactivation on the eastern margin. More generally, we demonstrate the influence of lithospheric strength and post‐rifting sedimentation to the exhumation history of passive margins.

Depositional architecture and aggradation rates of sand-rich, supercritical alluvial fans: Control by autogenic processes or high-frequency climatic oscillations?

Alluvial fans are important paleoclimatic archives, that may record high-frequency climatic oscillations. However, climate signals may be overprinted or even be destroyed by autogenic processes caused by channel avulsion and lobe switching. Here we present new data from two different Late Pleistocene (MIS 3–2) alluvial fan systems in northern Germany and compare these systems to experimental alluvial fans and other field examples. The selected fan systems formed under similar climatic and tectonic conditions, but differ in size, type, and drainage area allowing to estimate the role of climate and autogenic controls on flow processes, facies architecture, and fan-stacking patterns. Luminescence dating is used to determine the timing of fan onset and aggradation. Fan onset occurred in response to climate change at the end of MIS 3 when temperatures decreased and periglacial climate conditions were established in northern central Europe. A related increase in sediment supply and strongly variable precipitation patterns probably promoted fan formation. The major period of fan aggradation was approximately between 33 and 18 ka, followed by fan inactivity, abandonment, and incision during the Lateglacial. The highest aggradation rates occurred during the early stage of fan building, when up to 35 m thick sediment accumulated within a few thousand years. Sand-rich, sheetflood-dominated fans are related to larger, low-gradient fan catchments. Steep depositional fan slopes (5°–17°) and short-lived high-energy floods promoted supercritical flow conditions. Well sorted, sediment-laden, rapidly waning flows favored the deposition and preservation of supercritical bedforms and allowed for the aggradation of stable antidunes. Steep, dip-slope catchments enhanced stream gradients and promoted the transport of coarser sediments. These fans have lower gradient slopes (2–6°) and are dominated by channelized flows, alternating with periods of unconfined sheetfloods. Meter-scale coarsening upward successions, characterized by sandy sheetflood deposits at the base, overlain by multilateral or smaller single-story gravelly channel fills may be related to high-frequency climatic fluctuations or seasonal fluctuations in water and sediment supply. These coarsening-upward successions are commonly bounded by a paleo-active layer, from which ice-wedge casts penetrate downwards. The comparison to experimental fans and other field examples implies that the recurrent pattern of multistory, multilateral and single-story channel bodies with a lateral offset to vertical stacking pattern most probably was controlled by autogenic switch in an avulsion-dominated system. The change in deposition from alluvial-dominated processes to aeolian sedimentation with minor alluvial influences during the Lateglacial records alternation of dry and ephemeral wetter phases that are related to rapid climatic variations. The main phase of aeolian sand-sheet deposition probably correlates with Heinrich event H1 between approximately 18–16 ka and reflects sedimentation in response to aridification and high mean wind speeds.

Marginal fan thick lacustrine sedimentation: Implication for tectonics and/or climatic causes in Kathmandu basin

Very thick gravel deposits are widely distributed from southern marginal to central parts of the Kathmandu basin named as Itaiti Formation. This deposit is more than 120 m thick and deposited around 1 Ma, which is dominated by three types of facies and fans. The first stage fan is widely distributed near the mountain front where sediments aggradation is more active. The third stage fan is the youngest among three fans and is distributed on the present top surface and has covered lacustrine deltaic sequence of the Sunakothi Formation. Seven types of facies elements namely Gms, Gm, Gp, Sp, Sr, Sh, and Fl have been recognized among these three fans. Based on stratigraphic relationship among different geological formations, the first debris flow fans have been spreading over basement rocks and fluvial gravel facies before 1 Ma. This event has played a vital role in the initiation of an ancient lake in the Kathmandu basin. The second and third stage fans originated during the draining stages of the lake. The distal part of the second stage fan and third stage fan is interfingering with the lacustrine delta towards the center of the basin. The first stage debris flow fan was most probably generated by the recent uplift of the Mahabharat range. These gravelly fan deposits and the uppermost Siwalik conglomerate deposits may be synchronous to recent tectonic events throughout the Himalayas. The second and third stage fans have been initiated not only by the tectonics but also by climatic which is indicated by sedimentological and stratigraphic relations among formations.

Land-use evaluation and utilization advice research on debris flow disaster deposit area

The upstream Fujiang River are famous for their high mountains and narrow canyons, which results in a conflict of interest between local residents and land use. To make good use of precious land resources is a meaningful work for local people and government. Therefore, field surveys and theoretical analysis were carried out in the upstream Fujiang River to explore the land-use evaluation and utilization advice. Firstly, we analyzed the factors which affect the land use of debris flow depositional area. Secondly, we chose the factors of soil fertility quality, soil particle conservation, and the geological engineering condition to set up the land-use evaluation method. Thirdly, through index classification, we give the planting type, land-use type, construction type respectively, according to grading and assignment value for each factor, we built the debris flow disaster-prone land utilization mode R by using an analytical hierarchy process method. Lastly, taking Huangjiaba village as an example, based on the debris flow disaster land-use evaluation method and debris flow hazard evaluation, we identified four land-use scenarios. The results show that the value of the four scenarios is between 1.00 and 4.00, the four scenarios utilization advices are given based on each R-value and Huangjiaba natural condition. It also obtained that the developmental tendencies of the debris flow disaster areas appear to deposit recently, the frequency of debris-flow activity is evolving from high to stable, on making good use of debris flow deposit fan’s usage is necessary to explore the disaster prone land and avoid disaster loss. Further studies need to systematically consider more factors to evaluate debris flow and disaster-prone land utilization, which can provide a reference for the rural space planning and revitalization for the local government.

Characterization and evolution of a carbonate basin floor fan on a leeward side of an isolated carbonate platform, Sirte Basin, Libya

The recognition of carbonate basin floor fans and the interpretation of their formation and evolution are extremely crucial to the hydrocarbon exploration since they form important oil and gas reservoirs. There has been little research on the geometries and controlling factors of the carbonate basin floor fans from subsurface three-dimensional (3D) seismic and wireline log data. Most studies have been conducted on siliciclastic basin floor fans. Thus, this study characterizes the internal configuration and processes controlling the deposition of a lower Eocene carbonate basin floor fan system in the Sirte Basin in a sequence stratigraphic context through integrated 3D seismic and wireline log interpretations. The carbonate fan complex shows hummocky to undulated seismic geometries on vertical seismic sections and bounded by an unconformable sequence boundary at the base and a downlap surface at the top. It has an aerial extension of around 9 km from south to north along depositional dip and at least 8 km from east to west along strike. In well data, the fan system predominantly comprises limestone units intercalated with thin shale intervals. Log curves display an overall funnel-shaped trend, suggesting progradational stacking pattern. The vertical thickness of the fan complex varies from 120 to 165 m. The evolution of the carbonate fan was influenced by the interplay of accommodation space and sediment supply. A pre-existing topography, tectonic subsidence, and sea-level rise generated accommodation space for the deposition of the fan system, whereas sediment-gravity flows transported the fan sediments from the platform interior and margin to the basin floor. This study provides sedimentological and stratigraphic criteria to recognize and interpret the evolution of basin floor fans along isolated carbonate platforms from 3D seismic and wireline log data and may serve as an analog for ongoing and future studies on carbonate basin floor fans elsewhere.

Facies analysis and distribution of Late Palaeogene deep‐water massive sandstones in submarine‐fan lobes, NW Borneo

Deep‐water massive sandstones (DWMS) are characterized by large volumes of sand accumulations which are considered as potential reservoir intervals in deep‐marine environments. Lithological variations and bed thickness statistics are used to interpret the distribution of massive sandstones in a deep‐marine fan‐lobe system. These massive sandstones are interpreted based on lithological heterogeneities and detailed facies analysis in seventeen exposed sections of the Late Palaeogene deposits in Sabah, NW Borneo. Sedimentary logs containing details of lithology textures and structures were used to recognize nine sedimentary facies of DWMS. These lithofacies were then grouped into three sedimentary facies associations: (1) massive facies association with basal part of turbiditic Bouma sequence, (2) massive facies association having soft‐sediment deformation structures, and (3) massive facies association with erosional features. The facies analysis portrays inner to middle submarine fan deposition and was later applied to reconstruct the distribution of a channel‐lobe complex. Individual sandstone bed thicknesses vary from 1 m to more than 8 m and the number of massive sandstones in submarine lobes range from less than 10% to more than 50%. The thicknesses of massive sandstones in channels are more than 8 m, whereas distal lobes have thicknesses from 1–2 m only. These sandstones are concentrated in channels, proximal and medial lobe settings that can also be verified from calculating the average of all maximum thickness of massive sand intervals that is, 8.91 m. The lithological heterogeneities and the processes associated with the deposition of these massive sandstones are vital for potential hydrocarbon reservoirs in the deep‐marine environments around the globe.

Hunter-gatherer environments at the Late Pleistocene sites of Mwanganda's Village and Bruce, northern Malawi

Mwanganda's Village (MGD) and Bruce (BRU) are two open-air site complexes in northern Malawi with deposits dating to between 15 and 58 thousand years ago (ka) and containing Middle Stone Age (MSA) lithic assemblages. The sites have been known since 1966 and 1965, respectively, but lacked chronometric and site formation data necessary for their interpretation. The area hosts a rich stone artifact record, eroding from and found within alluvial fan deposits exhibiting poor preservation of organic materials. Although this generally limits opportunities for site-based environmental reconstructions, MGD and BRU are located at the distal margins of the alluvial fan, where lacustrine lagoonal deposits were overprinted by a calcrete paleosol. This has created locally improved organic preservation and allowed us to obtain ecological data from pollen, phytoliths, and pedogenic carbonates, producing a regional- to site-scale environmental context for periods of site use and abandonment. Here, we integrate the ecological data into a detailed site formation history, based on field observations and micromorphology, supplemented by cathodoluminescence microscopy and μ-XRF. By comparing local, on-site environmental proxies with more regional indicators, we can better evaluate how MSA hunter-gatherers made decisions about the use of resources across the landscape. Our data indicate that while tree cover similar to modern miombo woodland and evergreen gallery forest prevailed at most times, MSA hunter-gatherers chose more locally open environments for activities that resulted in a lithic artifact record at multiple locations between 51 and 15 ka.

Dose dependency of aliquot sizes and age models from modern alluvial fan deposits of Helan Mountain, China

Alluvial fan deposits are identified as evidence of regional climatic variations and tectonic events; therefore, it is crucial to establish absolute time series by dating alluvial fan deposits. Limited exposure to light poses a challenge to accurately estimating the buried ages for alluvial deposits with optically stimulated luminescence (OSL). This challenge has been positively developed by controlling the number of grains on each disk to measure and choosing suitable statistical models for the equivalence dose (De) distribution to analyze. In this research, three modern alluvial samples and one modern loess-like sample were collected from the Dashuigou alluvial fan of Helan Mountain, China. The De distributions of these four samples were studied by the application of small aliquots (1-, 3-, and 5-mm aliquots) of quartz OSL with the average dose model, central age model, unlogged minimum age model (MAM), lowest 5%, internal/external consistency criterion minimum age model (IEU), and finite mixture model. It is concluded that an overestimation of De lower than 1 Gy can be obtained using quartz OSL dating of 1-mm aliquots (∼50 grains) with MAM and IEU for the alluvial sediments. The lowest 5% method may underestimate the De values of the 1-mm aliquots for young samples. This research makes the dose dependency of aliquot sizes and age models more definite and opens up the possibility of dating paleoalluvial deposits to establish a chronological framework to decipher the implications of paleoclimates and tectonics.