Pleistocene Fluvial Deposits Research Articles

A clino-unconformity between Late Pliocene to Early Pleistocene Hamada Formation and Middle Pleistocene fluvial deposits, Shimokita Peninsula, northeastern Japan.

A clino-unconformity between Late Pliocene to Early Pleistocene Hamada Formation and Middle Pleistocene fluvial deposits, Shimokita Peninsula, northeastern Japan.

Reconstructing the depositional history of Pleistocene fluvial deposits based on grain size, elemental geochemistry and in-situ 10Be data

Constraining depositional phases in braided river deposits can be challenging if only based on sedimentology or geochronology. In this paper, we explored how different data sources can provide complementary information on the depositional history of Pleistocene fluvial deposits. The study was realized on the Zutendaal gravels that outcrop in Northeastern Belgium. In an 8 m high exposure of gravel sheets, we collected bulk samples that were processed for grain size, elemental geochemistry and cosmogenic radionuclides. After dry sieving, we derived the D10, D50, D90, gravel and sand content. From the elemental geochemistry of the bulk samples, we calculated the Ti/Zr and Cr/Zr ratios as proxies for provenance, the Al2O3/SiO2 and Ba/Sr ratios for hydrolysis, and the MnO, Fe2O3 concentrations and the Fe2O3+MnOAl2O3 ratio for oxidation. The 10Be concentration-depth profiles are informative to identify phases of landscape stability characterized by depositional hiatuses. To verify the existence of any aberrant variation in 10Be concentration associated to provenance, the in-situ 10Be concentrations were contrasted with provenance and weathering indices. Differences in grain size, elemental geochemistry and in-situ 10Be between sedimentary units were evaluated based on Mann-Whitney tests, while Spearman correlation tests informed us on the co-variation between data sources. The outcrop in the Zutendaal gravels contains three depositional units with significant differences in grain size and chemical weathering extent, and representing distinct 10Be accumulation phases. The absence of correlation between provenance and oxidation proxies indicates that weathering is essentially intraformational or post-depositional. Sedimentary hiatuses were identified based on fining upward sequences and 10Be concentration-depth profiles, whereby local deviation in 10Be concentration at the top of the fining upward sequence provided information on the duration of the hiatus. The case study illustrates how co-variations in weathering, provenance, granulometry indices and 10Be concentration are informative for the depositional history of fluvial sediments, and landscape stability during the Pleistocene.

The revision of Quaternary stratigraphy of the Zrenjanin artesian well borehole profile (Banat, Vojvodina, Serbia)

The geological analysis of artesian borehole material from Sombor, Subotica, and Zrenjanin, was in the first campaign of detailed stratigraphic studies of Vojvodina in 1892-1895. The results of Quaternary stratigraphy from Zrenjanin were published by HalaVaTS more than a decade later (1914). The significance of the Zrenjanin, Sombor, and Subotica artesian well profiles for more than a century is considered the representative local profiles for the Quaternary stratigraphy of Vojvodina recognized by Serbian (Yugoslavian) and Hungarian geologists. Significant changes were after the taxonomical revision of molluscan material and its stratigraphic context, which was done through the excellent work of Krolopp in the 1970-ies. Unfortunately, the mentioned changes were not applied in the studies during the geological surveying of former Yugoslavia. The developments in Quaternary geology, changes in the Quaternary chronostratigraphic scale, and the results shown by this paper enable the lower Pleistocene fluvial deposits to be defined as the Pleistocene Corbicula beds, the Viviparus boeckhi Horizon. The lower Pleistocene at Zrenjanin was documented from 234.54 to 58.36 m depth. The interval between 234.54 and 208.50 m comprises the Upper Paludina ? Viviparus vucotinovici zone, while the Viviparus boeckhi Horizons were identified between 135.18 m and 58.36 m. The interval between 58.36 m and 37.75 m is defined as Pleistocene (lower- and Middle Pleistocene) based on sedimentological and the molluscan record. The interval from 37.75 m to 21.67 m depth was identified as Middle Pleistocene, according to its lithology and the paleontological material. The fluvial sediments? 21.69 m and 7.31 m depths cannot be determined according to the faunistic data; we can only consider them as Pleistocene age. The Holocene sediment and soil horizons ascend to a 2.90 m depth.

Provenance of Pleistocene Sediments in West Sarawak and Evidence for Pliocene Acid Magmatism in Central Borneo

Quaternary deposits in Borneo are commonly not assigned to any formation or group and are usually not studied in great detail but are important for understanding of the Pleistocene to Holocene climate and drainage evolution. This study presents a detrital zircon provenance analysis of two possible (Plio-) Pleistocene fluvial deposits in West Sarawak, indicating two very different source areas and paleo-river drainages. Those paleo-rivers resemble the present-day drainage but show much higher energy level deposits associated with higher sedimentation rates possibly as a function of (Plio-) Pleistocene climate and hinterland exposure. The deposits at Kampung Jangkar in western West Sarawak were entirely sourced by the uplifted Pueh batholith. In contrast, sediments in Petra Jaya district (northern Kuching city) were sourced by recycling of the Kayan Sandstone near the Bungo Range in the area of the town Bau. The Petra Jaya sediments have abundant Pliocene and some Late Miocene zircons. The Niut Volcanics south of West Sarawak are of this age, but are basic and could not yield significant zircons. It is therefore concluded that zircons came from acid igneous rocks of Pliocene age, as well as the Kayan Sandstone and Middle Miocene Bau Suite igneous rocks, where they formed a highland in the Bau-Bungo Range region which has been entirely removed by erosion.

High resolution architecture of neotectonic fault zones and post-8-Ma deformations in western Hungary: Observations and neotectonic characteristics of the fault zone at the Eastern Lake Balaton

Lake Balaton (Hungary), the largest lake in Central Europe, formed by the interplay of tectonic and external forces. Its shallow water and young soft sediments together allow to carry out ultra-high resolution reflection seismic surveys to investigate shallow tectonic structures and near surface stratigraphy at depth of ca. 0–30 m. To document neotectonics of the eastern lake basin and its onshore surroundings to the East, we have integrated new ultra-high-resolution seismic-reflection data with deeper penetrating multichannel lake and land seismic profiles, regional geological, geophysical and seismicity data, and geomorphological observations. Combined use of these different data sets provided an opportunity to understand better, how these different types and scales of structural features are linked. In our study area, late middle to late Miocene formations compose a deepening than shallowing sedimentary cycle from terrestrial clastic through offshore marl and deltaic sequence filling up the basin between ca. 8.6 to 7.5 Ma. The deltaic sequence is unconformably overlain by erosional remnants of late Pleistocene fluvial deposits and a mantle of latest Pleistocene to Holocene lake mud. Post-early Miocene deformation history involved two phases; a latest middle to early late Miocene transtension and a dominantly strike-slip regime with locally transpressional or transtensional character. The latter neotectonic phase reactivated the earlier faults and resulted in the propagation of 4 major fault zones across the complete late Miocene sequence. The resulting young faults show segmented geometry, stepovers, and connecting splays. The deformation also induced the modest but penetrative folding of the highest preserved Miocene deltaic sequence. The change in deformation style could happen during the late-stage of delta formation, at ca. 8 Ma although a slightly younger timing is not excluded. Faults imaged offshore apparently do not offset the Holocene lacustrine mud by discrete fractures, but the improved distribution map of recent seismicity and morphotectonic indices along their onshore continuations suggests that several segments of the fault pattern are still active, and might be capable of generating earthquakes. Integration of these different data provided an opportunity to understand better, how these different types and scales of structural features are linked and evolved one after another. • 4 fault zones and 4 types of folds were mapped below Lake Balaton. • Post-8-Ma neotectonic faults are the reactivation of earlier Miocene structures. • The mapped fault pattern serves as an example for the complexity of segmented fault zone. • Faults below the lake continue onland form a coherent structural pattern. • Recent fault activity is suggested by the new seismicity map.

The formation of Middle and Upper Pleistocene terraces (<i>Übergangsterrassen</i> and <i>Hochterrassen</i>) in the Bavarian Alpine Foreland – new numeric dating results (ESR, OSL, <sup>14</sup>C) and gastropod fauna analysis

Abstract. Until now, reliable chronological classifications based on numerical ages for many Pleistocene fluvial deposits in the Alpine Foreland were rare. In this study, new numeric data (ESR, OSL, 14C) from Middle and Upper (Late) Pleistocene Hochterrassen (high terraces) and Übergangsterrassen (transitional terraces) in the Bavarian Alpine Foreland are presented. The dating results imply that the Hochterrassen gravel sensu stricto were deposited during the penultimate glacial (MIS 6, Rissian), and that underlying older gravel accumulation are predominantly of penultimate interglacial (MIS 7, Riss–Riss interglacial) age. In some areas of the Hochterrassen in the Danube valley south of Regensburg (interglacial Hartinger Schichten, Harting layers), and in some areas of the Rainer Hochterrasse (basal gravel unit I), Hochterrassen gravels are underlain by much older interglacial gravel deposits. These interglacial basal gravel deposits illustrate that the downcutting of these valleys far away from areas of Pleistocene foreland glaciations happened predominantly during warm-temperate interglacial or late-glacial periods. One last interglacial (MIS 5e, Riss–Würm interglacial) Hochterrasse is morphologically preserved in the Isar valley. This Jüngere Moosburger Hochterrasse is composed of the Fagotienschotter (Fagotia gravel, named after the gastropod Fagotia acicularis). The next younger terraces are the Early to Middle Würmian (MIS 5d to MIS 3?) Übergangsterrassen (transitional terraces), whereas the younger one of the two Übergangsterrassen was formed most probably during the Middle Würmian (MIS 3).

Evidence of multiple thermokarst events in northeastern France and southern Belgium during the two last glaciations. A discussion on ‘Features caused by ground ice growth and decay in Late Pleistocene fluvial deposits, Paris basin, France’ ( )

The past thermokarst activities in valleys of northern France and Belgium covered the Upper Weichselian and the Upper Saalian periods. To develop in western Europe, thermokarst first requires an accumulation of ground ice close to the surface progressively stored along the glacial-time permafrost aggradation: it is regionally uncommon during the early glacials, especially on the plateau, but frequent during the Upper Pleniglacials in valleys. These features mostly relate to various frost mounds created by injection and segregated ices. The role of ice wedges is really very limited in this zone of southern extent of the European palaeo-permafrost on plateau and terraces. Thermokarst events are mostly susceptible to occur during the coldest part of the glacial. With a more progressive warming or a retrogressive thermokarst triggered by erosion, as in Arctic today, deformations are more gradual, in direct relation with the rheological properties of the sediments and usually local drainage. They are in concurrence with the vegetation dynamic that will limit its expression. Thermokarst events are in first order orbitally forced under control of a maximum insolation and a minimum in precession, as well as during the Weichselian and the Saalian. They are moreover, associated with abrupt warming transmitted by Dansgaerd Oeschger events. Snowiness and mild winter temperatures are probably the main triggers for thermokarst activity as of today. Other events can be triggered by solar activity as at 20 ka or perhaps enhanced by major ash splay as during the MIS 6b Zeiffen interstadial. Thermokarst events are usually followed on the continent by a reorganization of the rivers from braided to meandering systems.

Serpentinite‐Rich Gouge in a Creeping Segment of the Bartlett Springs Fault, Northern California: Comparison With SAFOD and Implications for Seismic Hazard

AbstractAn exposure of a creeping segment of the Bartlett Springs Fault (BSF), part of the San Andreas Fault system in northern California, is a ~1.5‐m‐wide zone of serpentinite‐bearing fault gouge cutting through Late Pleistocene fluvial deposits. The fault gouge consists of porphyroclasts of antigorite serpentinite, talc, chlorite, and tremolite‐actinolite, along with some Franciscan metamorphic rocks, in a matrix of the same materials. The Mg‐mineral assemblage is stable at temperatures above 250–300 °C. The BSF gouge is interpreted to have been tectonically incorporated into the fault from depths near the base of the seismogenic zone and to have risen buoyantly to the surface where it is now undergoing right‐lateral displacement. The ultramafic‐rich composition, frictional properties, and inferred mode of emplacement of the BSF serpentinitic gouge correspond to those of the creeping traces of the San Andreas Fault identified in the SAFOD (San Andreas Fault Observatory at Depth) drill hole. This suggests a common origin for creep at both locations. A tectonic model for the source of the ultramafic‐rich materials in the BSF is proposed that potentially could explain the distribution of creep throughout the northernmost San Andreas Fault system.

Response to the discussion by Van Vliet-Lanoë et al. of the paper ‘Features caused by ground ice growth and decay in Late Pleistocene fluvial deposits, Paris Basin, France’ (Bertran et al., 2018, Geomorphology 310, 84–101)

The response by Van Vliet-Lanoë et al. to our paper on potential thermokarst features in Pleistocene alluvial deposits from the Paris Basin (France) presents inconsistencies that we consider here successively. These are (1) the map of the maximum extent of Pleistocene permafrost in France, (2) the genesis of liquefaction and fluidization structures in periglacial environments, (3) the origin of thermokarst lakes and recumbent folds, (4) the depositional context of sandy units, and (5) the age of the studied deposits. All structures result from the interplay between (1) the growth and degradation of ice wedges, which are responsible for the development of a mound-like topography (badland thermokarst reliefs) on the edge of the alluvial terrace and from the initiation of ponding elsewhere on the terrace, (2) the degradation of lithalsa that developed later in the lacustrine deposits. The sequence was dated confidently to the Late Weichselian.

Dating of the stepped quaternary fluvial terrace system of the Yellow River by electron spin resonance (ESR)

Abstract Since the 1980's, the improvement of the electron spin resonance (ESR) geochronological method and its application to the dating of bleached quartz extracted from sediments currently permit to provide geochronological data on Pleistocene fluvial deposits. In the present study, we have applied this method on sediments carried out from the Yellow River terrace system in the sector of Zhongwei (Ningxia province, China). This alluvial system is composed of a set of stepped fluvial deposit remnants (T1 to T9) from the actual floodplain (T1) up to 160 m of relative height. The ESR ages obtained in this work, by placing the installation of the river terrace system in the Middle and Upper Pleistocene (between 712 and 60ka), give information in relation to the causes of the succession of terraces. The results show that the construction of the system seems not only linked to a continuous regional tectonic uplift in the Middle Pleistocene but that the succession of incisions also seems controlled by Quaternary climatic cycles.

Features caused by ground ice growth and decay in Late Pleistocene fluvial deposits, Paris Basin, France

Last Glacial fluvial sequences in the Paris Basin show laminated lacustrine deposits OSL and radiocarbon dated to between 24.6 and 16.6 ka in one site and overlying alluvial sandy gravel. A thermokarst origin of the lakes is supported by abundant traces of ground ice, particularly ice wedge pseudomorphs beneath the lacustrine layers and synsedimentary deformation caused by thaw settlement. The features include brittle deformation (normal and reverse faults) resulting from ground subsidence owing to ice melting and ductile deformations caused by slumping of the sediments heaved by the growth of ice-cored mounds. These correspond to lithalsas (or lithalsa plateaus) and/or to open system pingos. At least two generations of thermokarst are recorded and may reflect the millennial climate variability typical of the Last Glacial. The structures studied in quarries are associated with an undulating topography visible in 5-m DEMs and a spotted pattern in aerial photographs. The search for similar patterns in the Paris Basin indicates that many other potential thermokarst sites exist in the Last Glacial terrace (Fy) of rivers located north of 48°N when they cross the lower Cretaceous sands and marls. In some sites, the presence of organic-poor, fine-grained deposits presumably of lacustrine origin was confirmed by borehole data. The site distribution coincides broadly with that already known for ice wedge pseudomorphs. This study provides new evidence of permafrost-induced ground deformations in France and strongly suggests that thermokarst played a significant and probably largely underestimated role in the genesis of Late Pleistocene landscapes.

Successful combination of electron spin resonance, luminescence and palaeomagnetic dating methods allows reconstruction of the Pleistocene evolution of the lower Moulouya river (NE Morocco)

Based on a combination of Electron Spin Resonance (ESR) dating of quartz, luminescence dating of K-feldspar and palaeomagnetism, this study presents the first chronostratigraphic framework for the Pleistocene fluvial deposits of the lower Moulouya river in the Triffa basin (NE Morocco). K-feldspar pIRIR225 and pIRIR290 signals of all samples are saturated, suggesting fluvial deposition at least as early as the Middle Pleistocene (∼0.39–0.80 Ma). Consequently, further chronological information was obtained with ESR dating of quartz grains from the ancient Pleistocene fluvial deposits. As for ESR, the multiple centres approach provides equivalent dose values derived from the Al and Ti centres that mostly agree within 1σ-error, suggesting complete signal resetting from the former during fluvial transport. ESR dating results yield Calabrian deposition ages for all river profiles from ∼1.1 to ∼1.5 Ma. These ages are remarkably consistent with the palaeomagnetic results: the occurrence of mostly reversed polarity in the deposits indicates a Matuyama age (>0.78 Ma). While low incision rates in the Triffa basin (0.025 ± 0.003 mm/a) related to thrusting activity during the Calabrian could be inferred, the fluvial record points to an acyclic and discontinuous sedimentation pattern over the last ∼1.3 Ma. It thereby probably rules out climate as the main driver for fluvial aggradation in the lowermost sedimentary basin. At a regional scale, several indicators point to transient fluvial response resulting from major Quaternary tectonic activity along the Beni Snassen gorge, located directly upstream of the investigated basin. We suggest that a capture event at the margin of the uplifting Beni Snassen massif occurred between 1.04 and 1.36 Ma at the latest and subsequently led to the creation of the gorge.

Integrated study on the topographic and shallow subsurface expression of the Grote Brogel Fault at the boundary of the Roer Valley Graben, Belgium

The Grote Brogel Fault (GBF) is a major WNW-ESE striking normal fault in Belgium that diverges westward from the NW-SE striking western border fault system of the Roer Valley Graben. The GBF delimits the topographically higher Campine Block from the subsiding Roer Valley Graben, and is expressed in the Digital Terrain Model (DTM) by relief gradients or scarps. By integrating DTM, Electrical Resistivity Tomography (ERT), Cone Penetration Test (CPT) and borehole data, we studied the Quaternary activity of the GBF and its effects on local hydrogeology. In the shallow subsurface (<50m) underneath these scarps, fault splays of the GBF were interpreted on newly acquired ERT profiles at two investigation sites: one on the eastern section and the other on the western section, near the limit of the visible surface trace of the fault. Borehole and CPT data enabled stratigraphic interpretations of the ERT profiles and thereby allowed measuring vertical fault offsets at the base of Pleistocene fluvial deposits of up to 12m. Groundwater measurements in the boreholes and CPTs indicate that the GBF acts as a hydrologic boundary that prevents groundwater flow from the elevated footwall towards the hangingwall, resulting in hydraulic head differences of up to 12.7m. For the two investigation sites, the hydraulic head changes correlate with the relief gradient, which in turn correlates with the Quaternary vertical offset of the GBF. ERT profiles at the eastern site also revealed a local soft-linked stepover in the shallow subsurface, which affects groundwater levels in the different fault blocks, and illustrates the complex small-scale geometry of the GBF.

Late Quaternary tectonic switching of siliciclastic provenance in the strike-slip-dominated foreland of the Western Carpathians; Upper Morava Basin, Bohemian Massif

This study is focused on the lithology and provenance of late Quaternary fluvial deposits of the Upper Morava Basin a pull-apart basin situated at the contact of the Bohemian Massif and Western Carpathians. Late Cenozoic tectonic convergence between these two units caused differential subsidence along strike-slip faults of the Elbe-Odra zone, leading to a distinct horst-and-graben morphology of the Upper Morava Basin. The Pleistocene fluvial deposits are preserved in several terrace levels and partly buried under the present-day floodplain of the Morava River. This study is based on four cores (11–25m deep) drilled in the floodplain of two major depocentres of the basin, the Lutín Graben, and the Upper Morava Basin sensu stricto. The drill cores were analysed for grain size, pebble- and heavy-mineral composition, chemical composition of detrital garnets, bulk magnetic susceptibility, sediment colour (visible-light spectral reflectance) and bulk element geochemistry. Age interpretations are based on eight optically stimulated luminescence (OSL) analyses. The Upper Pleistocene sediments were deposited in a gravelly braided to transitional braided-meandering river in both the Upper Morava Basin s.s. and the Lutín Graben (the oldest OSL age is 161.5ka, corresponding to the late Saalian). Between the end of the Saalian and late Weichselian glaciations, the Morava River abandoned the Lutín Graben for the Upper Morava Basin s.s. where it flows up to the present day. The Pleistocene fluvial style contrasts with the present-day meandering to anastomosing fluvial style of the Morava River. The Pleistocene deposits were sourced from areas corresponding to the present-day Morava River catchment including crystalline units of the eastern Bohemian Massif and the Moravo-Silesian Carboniferous Basin. They also contain a considerable input from the Bohemian Cretaceous Basin. The composition of late Weichselian deposits from the Dub nad Moravou core (34.53±3.42ka and younger) differs from the older fluvial deposits representing the other cores. It indicates that a major provenance change occurred between the latest Saalian and the late Weichselian. In the late Weichselian, the Morava River started to recycle loess deposits, which cover large areas of its catchment. Based on OSL dating, it may be assumed that the Morava River turned from degrading (between 92.6±8.03 and 34.53±3.42ka) to aggrading in style (from 34.53±3.42ka to the present day) due to coeval tectonic movements in the UMB, which are indirectly indicated by present-day seismicity, geomorphic faults and palaeoseismic evidence. Both the tectonic context and fluvial deposition styles of the Upper Morava Basin show similar features to the Upper Rhine Graben of the Alpine foreland.

Geomorphology of Dra Abu el-Naga (Egypt): The basis of the funerary sacred landscape

A geological and geomorphological analysis has been performed in the necropolis of Dra Abu el-Naga in order to understand the role played by these two factors in the development of the sacred landscape. The investigation focuses upon two aspects of the development of the necropolis, the selection criteria for tomb location and the reconstruction of the ancient funerary landscape. Around 50 tombs were surveyed, analysing the characteristics of their host rock and classifying them according to a modified Rock Mass Rating Index, in order to understand how rock quality affected tomb construction. This analysis resulted in the definition of five rock-quality classes (I to V) from very good to very poor rock. The geological study also resulted in a proposed geological-geomorphological model for the evolution of this zone of the Theban necropolis that complements previous works by other authors. Due to the lack of precise dating evidence this chronology is a relative one and is based on the chronology given by other authors for similar deposits and events. Two catastrophic events, represented by mega-landslides, have been identified, the first one predates the deposition of early Pleistocene fluvial deposits, and the second one possibly occurred during the middle-late Pleistocene. Two weathering surfaces developed under wetter than present climatic conditions and have been tentatively correlated to the mid-late Pleistocene humid period and the African-Humid Period (early-mid Holocene).

Stratigraphic and lithologic characteristics of Pleistocene fluvial deposits in the Danube and Sava riparian area near Belgrade (Serbia)

The Quaternary sediments in the Danube and Sava riparian area near Belgrade have a considerable thickness. Several categories of deposits (fluvial-lacustrine, fluvial and aeolian) of Pliocene and Quaternary age have been identified. Their thickness, granulometric composition and paleontological features change depending on the distance from the recent Danube and Sava riverbeds. The Pleistocene fluvial deposits are underlain by sediments of the Late Miocene (Sarmatian and Pannonian) or the Plio-Pleistocene age, and are overlain by fluvial-palustrine deposits of the Pleistocene age and recent alluvial deposits. Pleistocene fluvial deposits that form a major part of the Quaternary sediments, have a great significance, since they are proved to be excellent collectors of ground water. Although these deposits are at lower altitudes in the area of Srem, they could be correlated with the high Danube and Morava terraces in Serbia and Drava in Croatia on the basis of their lithologic and paleontological features.

Stratigraphic and lithologic characteristics of Pleistocene fluvial deposits in the Danube and Sava riparian area near Belgrade (Serbia)

Stratigraphic and lithologic characteristics of Pleistocene fluvial deposits in the Danube and Sava riparian area near Belgrade (Serbia)

Geologic control on the evolution of the inner shelf morphology offshore of the Mississippi barrier islands, northern Gulf of Mexico, USA

Between 2008 and 2013, high-resolution geophysical surveys were conducted around the Mississippi barrier islands and offshore. The sonar surveys included swath and single-beam bathymetry, sidescan, and chirp subbottom data collection. The geophysical data were groundtruthed using vibracore sediment collection. The results provide insight into the evolution of the inner shelf and the relationship between the near surface geologic framework and the morphology of the coastal zone. This study focuses on the buried Pleistocene fluvial deposits and late Holocene shore-oblique sand ridges offshore of Petit Bois Island and Petit Bois Pass. Prior to this study, the physical characteristics, evolution, and interrelationship of the ridges between both the shelf geology and the adjacent barrier island platform had not been evaluated. Numerous studies elsewhere along the coastal margin attribute shoal origin and sand-ridge evolution to hydrodynamic processes in shallow water (<20m). Here we characterize the correlation between the geologic framework and surface morphology and demonstrate that the underlying stratigraphy must also be considered when developing an evolutionary conceptual model. It is important to understand this near surface, nearshore dynamic in order to understand how the stratigraphy influences the long-term response of the coastal zone to sea-level rise. The study also contributes to a growing body of work characterizing shore-oblique sand ridges which, along with the related geology, are recognized as increasingly important components to a nearshore framework whose origins and evolution must be understood and inventoried to effectively manage the coastal zone.

Stratigraphical position of pleistocene fluvial deposits of southeastern Srem and the Danube terraces in eastern Serbia

Pleistocene fluvial deposits have a significant distribution in Serbia, especially in the riparian area of the Danube and Sava in the southern part of the Pannonian basin. In this region these sediments are almost universally overlain by younger Pleistocene or Holocene deposits, and their thickness varies from 10 to 40 meters. Deposits of similar characteristics, that could be correlated to the synchronous ones in southern Srem, form high terraces of the Danube valley system. Morphologically, these terraces are of erosional-accumulation character. Some pre-Quaternary deposits of different composition and age are situated beneath the Pleistocene fluvial deposits. Significant height differences among these deposits in the part of southern Srem connected to the high terraces of the Danube are the consequence of differential tectonic movements which were expressed in subsidence of the Panonnian basin, and in stagnation or uplifting in the river valleys.

Inferring Fluvial Morphodynamics and Overbank Flow Control From 3D Outcrop Sections of A Pleistocene Point Bar, Dandiero Basin, Eritrea

Abstract Sedimentological and architectural data from three-dimensional larger vertical outcrops of Pleistocene fluvial deposits of the Dandiero Basin (Eritrean Danakil depression) are here used to reconstruct planform evolution of a meander bend and investigate the role of overbank flooding in sediment distribution on point bars. The point bar accumulated as part of a lowstand systems tract at the base of an incised valley cut into lacustrine mud. Selected outcrops transect a 1-km-long channel belt exposed parallel to the main fluvial transport direction. Sedimentological logs, outcrop line drawings, and paleocurrent and bedding measurements show that this outcrop belt represents a transverse section of an asymmetric fluvial point bar, which accumulated through migration of a channel 6 m deep and 70 m wide. This bar was characterized by early expansion followed by downstream accretion, which was abruptly interrupted by lacustrine deposition. The onset of downstream accretion started when the channel expanded to reach the more resistant valley wall. Sediment accreted on the downstream side of the point bar and accumulated both during bankfull discharge and overbank floods, with significant modification of the channel flow where the floodwater re-entered the main channel (i.e., riffle zone). In this zone, a secondary circulation cell triggered a shift of erosion toward the inner bank and scrolling on the downstream side of the point bar.