Fluvial Floodplain Research Articles

Optically stimulated luminescence dating of young fluvial deposits of the Middle Elbe River Flood Plains using different age models

In the last few decades optically stimulated luminescence (OSL) dating has become an important tool in geochronological studies. The great advantage of the method, i.e. dating the depositional age of sediments directly, can be impaired by incomplete bleaching of grains. This can result in a scattered distribution of equivalent doses (DE), leading to incorrect estimation of the depositional age. Thoroughly tested protocols as well as good data analysis with adequate statistical methods are important to overcome this problem. In this study, samples from young fluvial sand and flood plain deposits from the Elbe River in northern Germany were investigated to compare its depositional ages from different age models with well-known historical dates. Coarse grain quartz (100–200 μm and 150–250 μm) and polymineral fine grains (4–11 μm) were dated using the single aliquot regenerative (SAR) dose protocol. The paleodose (DP) was calculated from the DE data set using different approaches. Results were compared with the development of the Elbe River, which is well-documented by historical records and maps covering the last 1,000 years. Depending on the statistical approach it can be demonstrated that depositional ages significantly differ from the most likely depositional age. For the investigated coarse grain quartz samples all ages calculated from the MAM-3UL, including their uncertainties, are within the historical documented age. Results of the polymineral fine grain samples are overestimating the historically documented depositional age, indicating undetectable incomplete bleaching. This study shows the importance of using an adequate statistical approach to calculate reliable OSL ages from fluvial sediments.

Pre-vegetation fluvial floodplains and channel-belts in the Late Neoproterozoic–Cambrian Santa Bárbara group (Southern Brazil)

One key element to the understanding of the dynamics of pre-vegetation fluvial systems is the reconstruction of processes operating on their floodplains given that, in modern systems, channel banks and floodplains are the environments most affected by plant colonization. Notwithstanding, few pre-vegetation floodplains have been described, and major questions regarding their most basic characteristics are still unresolved. In order to address these questions, detailed analysis of coeval channel-belt, fluvial floodplain and alluvial-fan deposits from the Santa Bárbara Group (Late Neoproterozoic to Early Cambrian, southern Brazil) was performed. While floodplain facies resemble ephemeral stream deposits, being coarser-grained than modern floodplains and marked by the stacking of flood event cycles, channel-belt deposits show composite bars, which do not present conclusive evidence for high water discharge variation. The floodplain deposits show particular features common to other pre-vegetation fluvial systems, such as better preserved small-scale structures, lack of bioturbation, and abundance of cross-laminated sandstones, while other features differ from previous depositional models, namely abundant mudcracks and evidence of soil formation. The lateral variation of depositional systems recorded in the Santa Bárbara Group shows contrasting signatures of water discharge variation in sand-dominated coeval environments, and offers an example of the relation between different alluvial environments before the evolution of land plants.

Sedimentary environment changes of the Ningshao Plain since the later stage of the Late Pleistocene: Evidence from palynology and stable organic carbon isotopes

A 45.3-m long core was collected from near the Hemudu civilization site (Luojiang county, Zhejiang Province; 29°59.064′N, 121°21.754′E), which is located in the Ningshao plain on the southern margin of Hangzhou Bay. The core, named the HMD Core, was divided into seven lithological layers with clay and silt as the main lithological components. The sporopollen assemblages of this core combined with TOC/TN and stable organic carbon isotope (δ13CTOC) analysis revealed the sedimentary environmental changes since the later part of the Late Pleistocene in the Ningshao plain. The study area changed from terrestrial fluvial-flood plain facies before Marine Isotope Stage (MIS) 3 to shore plain during transgression in MIS3, and became a freshwater lake during regression at the time of the Last Glacial Maximum (LGM). The area started to become a semi-salt lake influenced by sea water during 15,900–5000 cal. BP, in which time period the lake was deeper and the climate became gradually warmer. Later the seawater withdrew, the lake began desalinating, and then became swampy and accumulated peat until 1000 cal. BP. After that, the area became dry land. The results also indicate that the sediments of the core are of endogenous organic origin and the δ13CTOC value was controlled by change in the concentration of atmospheric CO2, and thus was a response to global changes.

Charophytes from the Upper Berriasian of the Western Interior Basin of the United States

A charophyte flora from the Upper Berriasian is described from the Lakota (Black Hills, South Dakota) and Cedar Mountain formations (San Rafael Swell, Utah) of the Western Interior Basin, United States of America. Whereas the latter is dominated by monotonous assemblages of the clavatoracean Nodosoclavator bradleyi (Harris, 1939), found in temporary lakes within palustrine facies, the flora of the Lakota Formation consists of more varied assemblages of the clavatoraceans N. bradleyi (Harris, 1939), Clavator grovesii grovesiiHarris 1939, C. bilateralisPeck 1957 and early characeans (Mesochara sp. or Tolypella sp.). This flora was found in deposits related to permanent lakes in fluvial floodplains, i.e. lacustrine marls and limestones that do not show any evidence of subaerial exposure. To date, little is known about C. bilateralis, we provide a new definition on the basis of its particular structure, which shows lateral bract-cell units with a pinnate arrangement. This species appears to be endemic to North America and stratigraphically limited to the earliest Cretaceous. C. grovesii grovesii is part of a long-lasting charophyte lineage, which until now was considered to have originated in the Central Tethyan Archipelago (Europe) during the Early Berriasian, about 145 Ma, and limited to Eurasia until most of the Early Cretaceous. The new data presented here suggest that during the Berriasian this species was very broadly distributed, comprising North America, Europe and China.

Sub-layer Correlation of Quantou IV Formation of the Lower Cretaceous in Haituozi Area of Songliao Basin

Fluvial-flood plain facies are developed at lower-mid Quantou Ⅳ Formation, and delta front - shallow lake facies are developed at the upper formation in Haituozi area of Southern Songliao Basin. Channel sand bodies are good oil and gas reservoirs, but the distribution of sand is not clear, which has become a key factor restricting oil and gas development. No less than 100 wells data of logging, some data of drilling, cores and testing are collected and used in correlation, firstly 5 roughly provenance direction and 5 crosscutting provenance direction sections were selected in the area, with high resolution sequence stratigraphic analysis, Quantou Ⅳ Formation is subdivided into 4 sequences (corresponding to the fifth order cycle sequence, are respectively called cycle A, B, C and D), sequence stratigraphic framework were established. Then the similarity of facies association characteristics in base level change, consistency of reservoir fluid properties, isochronous maximum flooding surface in a certain area, different stages of overlay channels are took full account in the operation of sub-layer correlation. In the end 3 sub-layers are divided from cycle A , 3 sub-layers divided from cycle B, 5 sub-layers from cycle C, and cycles D corresponds to a sub-layer, Quantou Ⅳ Formation is divided into 12 sub-layers, which lays good foundation for the production and development. Key words : High resolution sequence stratigraphy; Sub-layer correlation; Songliao basin; Haituozi area; Quantou Ⅳ Formation

Periphytic algae colonization driven by variable environmental components in a temperate floodplain lake

The colonization of periphytic algae in a temperate floodplain was studied in Lake Sakadas, a part of a fluvial floodplain along the Danube River. An in situ investigation, using artificial substrata, was started after extremely high spring flooding and was carried out during long-lasting summer floods (July–August 2010). The physical and chemical environment was variable and large stands of metaphyton, submersed and floating macrophytes were spread along the lake. The periphyton development was initiated on the first day of exposition and algal abundance increased exponentially till day 27. Directional changes in the relative abundance of algal species, shown by the results of the non-metric multidimensional scaling, indicate a pattern of short-term sequences in algal colonization. The initial attachment of planktonic cyanobacteria and unicellular diatoms (initial phase, days 1–3) to the biofilm matrix was followed by the development of the filamentous chlorophytes, Cladophora glomerata and Oedogonium spp. (intermediate phase, days 6–15) and then by stalk-forming diatoms particularly Gomphonema spp . (late phase, days 18–33). According to the redundancy analyses, water temperature and oscillations of Danube water level that define the flooding pattern had the most significant influence on algal colonization. Flood-induced spreading of metaphyton firstly supported the rapid progress of algal colonization towards a climax community, while later, metaphyton together with macrophytes disrupted algal community by increasing the mechanical injuries, shading and grazing pressure. Consequently, algal abundance and community structure were returned to the intermediate phase of colonization.

Paleogene high elevations in the Qiangtang Terrane, central Tibetan Plateau

The timing of uplift of the Tibetan Plateau remains controversial, with estimates varying from Eocene to more recent than Pliocene. In particular, the paleoaltimetry of the Qiangtang terrane, on the central Tibetan Plateau, is completely unknown. Here, we present new stable isotope results of fluvial/lacustrine carbonate cement, pedogenic carbonate and marl from the Kangtuo and Suonahu formations deposited between ∼51 and ∼28Ma in the Heihuling–Bamaoqiongzong area of the northern Qiangtang terrane. The lithofacies associations indicate that the Kangtuo formation was deposited in alluvial fan and fluvial floodplain environments, and the Suonahu formation was deposited in near shore lacustrine, playa-lake and channelized fluvial environments. Carbon and oxygen isotope values, coupled with the sedimentary facies interpretations, point to evaporation and low respiration rates in the Eocene–Oligocene paleosols, suggesting an arid climate in the high Qiangtang area at the time. The δ18Opsw values of paleo-surface water reconstructed from the lowest (i.e. the least evaporated) δ18Oc (PDB) values of the unaltered authigenic carbonates are used to make the minimum estimates of the average paleoelevation of the drainage basin. The paleoelevation of the northern Qiangtang terrane is reconstructed as above 5000m by at least the middle Oligocene (28Ma), similar to the present elevation in this area. The aridity and the positive shift in oxygen isotope values of surface waters in our study area may suggest that the high Lhasa terrane established by the middle Oligocene blocked the northward transport of tropical moisture. Maintenance of high elevation (>5000m) from at least the Oligocene to the present suggests that the Qiangtang crust was already thickened by that time, and that underthrusting of India beneath Asia since then has continued to provide additional material while at the same time driving Asian lower crust eastward by crustal flow.

Late Holocene flooding records from the floodplain deposits of the Yugu River, South Korea

Predicting responses of regional hydrological cycles to global warming requires an understanding of past hydrological events on various timescales. This study investigated the variability of flooding as recorded in fluvial floodplain deposits. The percentage of sand-sized material in two cores collected from the floodplain of the Yugu River, one of the tributaries of the Keum River, central South Korea, has been tested as a proxy for the occurrence and magnitude of past flooding. The sand fraction of the floodplain deposits in cores KL28 and KL29, which record deposition over the last 3500years, varied on multicentury timescales and suggests several past episodes of higher frequency large floods. These clusters of large floods seem to correlate well with Northern Hemisphere temperature anomalies and suggest that more frequent large floods occurred during the Medieval Warm Period (MWP) than during the Little Ice Age (LIA). The occurrence of more frequent large floods on the Keum River tributary may have been driven by intensified northerly winds over East Asia and resultant moisture convergence over Korea and/or a weakened thermal gradient between the tropical ocean and Asian continent. Furthermore, the centennial-scale changes in the sand fraction of the floodplain deposits were partly similar to remote El Niño–Southern Oscillation (ENSO) activity, implying a possible link between flooding in central South Korea and ENSO activity. This study has demonstrated that floodplain deposits have much potential for recording paleofloods though floodplains can be, and quite often are, very complex places in terms of their depositional history. In regions where natural lakes suitable for the study of paleohydrology and paleoclimate are lacking, well-controlled time-series data for the sand content at multiple sites in fluvial floodplains may be used to understand paleoflooding and extreme precipitation variability in the past.

Sequence stratigraphic analysis of Cenomanian greenhouse palaeosols: A case study from southern Patagonia, Argentina

The aim of this contribution is to analyse extrinsic (i.e., tectonics, climate and eustasy) and intrinsic (i.e., palaeotopography, palaeodrainage and relative sedimentation rates) factors that controlled palaeosol development in the Cenomanian Mata Amarilla Formation (Austral foreland basin, southwestern Patagonia, Argentina). Detailed sedimentological logs, facies analysis, pedofeatures and palaeosol horizon identification led to the definition of six pedotypes, which represent Histosols, acid sulphate Histosols, Vertisols, hydromorphic Vertisols, Inceptisols and vertic Alfisols.Small- and large-scale changes in palaeosol development were recognised throughout the units. Small-scale or high-frequency variations, identified within the middle section are represented by the lateral and vertical superimposition of Inceptisols, Vertisols and hydromorphic Vertisols. Lateral changes are interpreted as the result of intrinsic factors to the depositional systems, such as the relative position within the floodplain and the distance from the main channels, that condition the nature of parent material, the sedimentation rate and eventually the palaeotopographic position. Vertical stacking of different soil types is linked to avulsion processes and the relatively abrupt change in the distance to main channels as the system aggraded.The large-scale or low-frequency vertical variations in palaeosol type occurring in the Mata Amarilla Formation are related to long-term changes in depositional environments. The lower and upper sections of the studied logs are characterised by Histosols and acid sulphate Histosols, and few hydromorphic Vertisols associated with low-gradient coastal environments (i.e., lagoons, estuaries and distal fluvial systems). At the lower boundary of the middle section, a thick palaeosol succession composed of vertic Alfisols occurs. The rest of the middle section is characterised by Vertisols, hydromorphic Vertisols and Inceptisols occurring on distal and proximal fluvial floodplains, respectively.The palaeosol succession for the Mata Amarilla Formation can be analysed within a sequence stratigraphic scheme considering changes in depositional environments in relation to accommodation/supply conditions. The results contrast with classical models, mainly in that the palaeosols of the Mata Amarilla Formation are relatively well-developed throughout the whole sequence, including transgressive periods of relatively high aggradation rate. Also, even when during regressive episodes, when a thick palaeosol succession that marks the sequence boundary is developed in the classical models, the lack of incised valleys in this succession led to the preservation of thick palaeosol successions during lowstand conditions. The vertical and lateral palaeosol distribution identified in the Mata Amarilla Formation could be eventually extrapolated to other sequences deposited during climate optimums.

A polar dinosaur-track assemblage from the Eumeralla Formation (Albian), Victoria, Australia

Martin, A.J., Rich, T.H., Hall, M., Vickers-Rich, P. & Vazquez-Prokopec, G., June 2012. A polar dinosaur-track assemblage from the Eumeralla Formation (Albian), Victoria, Australia. Alcheringa 36, 171–188. ISSN 0311-5518. The Eumeralla Formation (Aptian–Albian) of the Otway Group in Victoria, Australia, has yielded a significant amount of dinosaur skeletal material since the late 1970s, which, when combined with finds from the Wonthaggi Formation (Aptian) of the upper Strzelecki Group, constitute the best-documented polar-dinosaur assemblage in the Southern Hemisphere. In contrast, dinosaur tracks have barely augmented this body fossil record; up to now, only one ornithopod track had been documented in any detail from the Otway Group. In this study, we report a new find of at least 24 dinosaur tracks preserved on two ripple-bedded sandstone blocks of the Eumeralla Formation, discovered at Milanesia Beach, Victoria. This dinosaur-track assemblage is the best in terms of numbers and quality found thus far in formerly polar environments of the Southern Hemisphere. One block includes the first known dinosaur trackway from the Cretaceous of Victoria, consisting of three consecutive footprints made by a small theropod. The assemblage indicates three differently sized theropods, thus providing new insights on dinosaur diversity and activity not indicated previously by body fossils in the Eumeralla Formation. Tracks are preserved in fluvial floodplain deposits and were possibly imprinted on emergent floodplain surfaces following seasonal flooding during a polar summer. The abundant tracks at this site suggest more such finds are likely in floodplain deposits of the Otway Group, although behavioural and preservational conditions unique to polar environments may have limited their formation. Anthony J. Martin and Gonzalo Vazquez-Prokopec [geoam@learnlink.emory.edu, gmvazqu@emory.edu] Department of Environmental Studies, Emory University, Atlanta, GA 30322, USA; Thomas H. Rich [trich@museum.vic.gov.au] Museum Victoria, Melbourne, Victoria, Australia; Michael Hall, Patricia Vickers-Rich and secondary address of Anthony J. Martin [mike.hall@monash.edu, pat.rich@monash.edu] School of Geosciences, Monash University, Clayton, Victoria 3800, Australia. Received 15.4.2011; revised 6.6.2011; accepted 14.6.2011.

Differential transportation and deposition of terrestrial biomarkers in middle Eocene fluvial to estuarine environments, Hokkaido, Japan

Abstract Higher plants constitute a significant portion of sedimentary organic matter in middle Eocene fluvial–floodplain–estuarine sedimentary rocks exposed in the Bibai region of central Hokkaido, Japan. The differential transportation and deposition of terrestrial biomarkers were studied in this area. The distribution of higher plant and fungal biomarkers in the Bibai non-marine sedimentary rocks was constrained by sedimentary facies and lithology. Claystones and siltstones lacking coaly fragments tended to be rich in angiosperm biomarkers, whereas coal and coaly mudstones were comparatively rich in gymnosperm biomarkers. Perylene, a possible fungal biomarker, was detected in fine-grained floodplain deposits. Facies and lithologic controls on terrestrial biomarker distribution can be attributed to the differential transportation and deposition of organic debris and degradation products derived from higher plants and fungi. Redox potential of the depositional environment is another important factor for the formation and preservation of terrestrial aromatic biomarkers. Reconstruction of land-based paleovegetation from terrestrial biomarkers in non-marine sediments requires careful consideration of the differential transportation and preservation of precursory terrestrial organic compounds.

Evaluation of a coastal flood inundation model using hard and soft data

Observed data of coastal inundation are very rare, yet are essential for testing the performance of simulation models for this significant natural hazard. In this paper we therefore examine the extent to which observed data can constrain predictions of a typical flood inundation model for a coastal flood event that affected the Somerset Levels in the UK on 13th December 1981. In doing so, a detailed reconstruction is made of the flooding that occurred along a 20 km stretch of the North Somerset coast, potentially providing a benchmark data set for comparative model analysis. Information on the extent of flooding was gathered from photographs taken on the day following the storm (‘hard’ or quantitative data), and contemporary newspaper reports and interviews with a number of people who had first hand experience of the storm and the consequent flooding (‘soft’ or qualitative data). Data on tidal levels and wave overtopping rates were collated from contemporary reports. Information on the topography of the study area and the configuration and heights of the sea defences at the time was determined from a variety of sources. Across the whole domain the model correctly predicted 85% of the flooded area; a level of performance comparable to fluvial applications of inundation models. The performance of the model in areas where flooding was dominated by wave overtopping was shown to be very sensitive to relatively small changes (±50%) in the specified flux rate, yet this parameter can plausibly vary by as much as ±300%. The overtopping flux rate was shown to be a much more sensitive control on the model performance than friction parameters. Finally, the study shows that 2D hydraulic models with relatively simple physics can closely simulate real coastal flood events given the availability of high resolution, high accuracy terrain data such as LiDAR. These conclusions mirror those arrived at over the last decade for fluvial flooding and suggest that the hydrodynamics of coastal and fluvial floodplain inundation are similar, if not identical.

Numerical investigation of long-term planform dynamics and stability of river meandering on fluvial floodplains

A mathematical model for river meandering and floodplain development is presented under the assumption of constant channel width, which combined Johanneson and Parker (1989) linear theory for flows in river bends and a conceptual depositional model from Howard (1992). A new bank erosion model is also developed, which takes into consideration of the nonlinearity in near-bank velocity and the outer bank height. Simulations reproduce the long-term behavior of river meandering and floodplain evolution in a way very similar to their natural processes. Based on the simulation results, stability of river meandering dynamics is discussed and the concept of filtration effect is introduced to highlight meandering rivers’ capability to filter out arbitrarily applied planform disturbance. Simulations are also carried out to investigate the influence of the velocity nonlinearity and the outer bank height in bank erosion model, as well as their combinations. Results show that the consideration of velocity nonlinearity in bank erosion model leads to highly upstream-skewing geometry of fully developed river meanders, as well as a slower downstream migration of meander trains. The influence of nonlinearity in bank erosion model is much smaller than the influence of bank height, which reduces the bank migration rate exponentially in the newly introduced bank erosion model. The outer bank height consideration tends to decelerate the downstream migration rate of river meanders and accelerate lateral expansion of the floodplain as well. Consequently, a broader floodplain is generated compared with simulations without bank height considerations.

Palaeoenvironmental reconstruction at an oxbow lake situated at the lower Nottawasaga River, southern Ontario, Canada

The purpose of this investigation at the lower Nottawasaga River in southern Ontario, Canada, was to reconstruct the impact of base level on fluvial stability and human occupation during the Holocene in a topographically confined section, where the river cuts through the Edenvale Moraine. Three cores were extracted from an oxbow lake (Doran Lake) and a ground-penetrating radar survey was executed in its vicinity to study wider subsurface alluvial architecture. Radiocarbon dating suggests that the Nottawasaga River became entrenched in the Edenvale Moraine early in the Holocene, with base-level lowering in the Lake Huron basin, and that Doran Lake formed towards the middle Holocene as a meander cutoff when water levels in the Lake Huron basin increased, leading to a period of fluvial instability, enhanced flow and floodplain aggradation. Fluctuating lake levels would have affected human settlement as well as the preservation and visibility of archaeological remains predominantly through vertical accretion.

Contrasting Pliocene fluvial depositional systems within the rapidly subsiding South Caspian Basin; a case study of the palaeo-Volga and palaeo-Kura river systems in the Surakhany Suite, Upper Productive Series, onshore Azerbaijan

The South Caspian Basin contains major hydrocarbon reservoirs within the largely Early Pliocene Productive Series. This paper describes and contrasts outcrops of the uppermost ∼500 m of the series (the Surakhany Suite) deposited by two of the main fluvial systems that supplied the Azeri margin of the basin. Sedimentary facies and, for the first time from the Productive Series, palynological analyses document fluvial channel belt complexes, sheetflood overbank and flood plain to flood plain lake environments. The Productive Series on the Apsheron Peninsula, Azerbaijan, was supplied predominantly from the north by the palaeo-Volga river system. It displays an overall fining-upward trend, such that the Surakhany Suite at Lokbatan is dominated by mudstone. Siltstone and coarser-grained sediments make up 28% of the section. Channel bodies are on average 1.5 m thick and form 13% of the succession. In the sub-surface of the Apsheron Peninsula, ratty wireline log responses also indicate that siltstone and sandstone bodies are predominantly thin bedded, with SP-derived net-to-gross sand ratios of ∼0.35–0.40. The succession in the Kura Basin was sourced predominantly from the west by the palaeo-Kura river system. It displays a coarsening-upward trend, such that in the middle and upper Surakhany Suite at Babazanan siltstone and coarser sediments make up 52% of the section. It is characterised by numerous stacked and laterally continuous channel sandstone bodies that are on average 5.8 m thick and comprise 42% of the outcrop. In the sub-surface of the Kura Basin, wireline log responses of the Surakhany Suite have a blocky character and indicate SP-derived net-to-gross sand ratios of 0.26–0.38. These values are similar to calculated sandstone volumes at outcrop (44%). The palynological data, including multivariate analyses, show that the main controls on palynomorph distribution are the degree of fluvial or lacustrine influence, subaerial exposure and salinity. Despite their more lithic nature, Surakhany Suite sandstones derived from the palaeo-Kura river system along the Kurovdag-Babazanan-Neftchala trend have similar or better petrophysical properties than those derived from the palaeo-Volga river on the Apsheron Peninsula and its offshore continuation. This is probably due to their coarser-grain size. This, combined with their greater sandstone body thickness, would suggest that the axis of the Kura Basin forms the most promising part of the Azeri sector of the South Caspian Basin for exploration within the uppermost part of the Productive Series.

Origin of ferricretes in fluvial-marine deposits of the Lower Cenomanian Bahariya Formation, Bahariya Oasis, Western Desert, Egypt

The type section of the Lower Cenomanian Bahariya Formation at Gebel El-Dist (Bahariya Oasis, Western Desert), Egypt, comprises claystones, mudstones, siltstones and sandstones deposited in fluvial-deltaic coastal plain, lagoonal, estuarine and shallow marine environments. The formation is characterized by an abundance of ferruginous sandstones that locally weather to form prominent iron crusts. These centimeter to decimeter-scale ferruginous horizons display a continuum of features ranging from unaltered sandstone with a pervasive ferruginous matrix to distinct ironstone beds with massive, nodular, vesicular and pisolitic textures. Ferruginous sandstone typically occurs at the tops of sandstone beds, or bracketing the base and top of beds, in the fining-upward cycles of deltaic plain deposits in the lower part of the formation and on a low-energy fluvial floodplain in the middle of the formation. Indurated ironstone beds occur mainly as the caps of coarsening-upward cycles of prograding shoreface sediments through much of the formation. We interpret the ironstone crusts as ferricretes, formed by iron accumulation that resulted from the oxidation and precipitation of soluble iron or colloids transported in the sediment load or by groundwater. This accumulation possibly took place at the water table or possibly below the water table at the fresh water/saline water interface. However, base-level fall and subsequent subaerial exposure of the sediments resulted in reworking and pedogenic modification of some of the iron-impregnated horizons.

Fluxes of Heavy Metals from a Highly Polluted Watershed During Flood Events: A Case Study of the Litavka River, Czech Republic

The Litavka River (length 56 km, watershed area 630 km2, average flow at the outlet to the Berounka River 2.57 m3 s−1) drains the historical mining, ore processing, and smelting region of Přibram. This Ag–Pb–Zn±Sb ore district (production from the thirteenth century to 1978, locally to 1980) is known for extensive heavy metal contamination. Recent contamination of the Litavka River system is mostly related to the erosion of contaminated soils and fluvial floodplains sediments, especially from a low-gradient river section located immediately below the ore district, where the fine-grained floodplain sediments are from 1.0 to 1.7 m thick. Radiocarbon accelerator mass spectrometry dating of charcoal fragments separated from one floodplain profile showed calibrated 14C age in the range AD 1220–1284 at a depth of 1.2 m below the surface, while depths of 0.4 and 0.8 m yielded ages in the range AD 1680–1939. Formation of this floodplain was related to disturbance of the river equilibrium resulting from deforestation and the influx of fine-grained material from ore processing, including historical failures of settling ponds. Fluxes of heavy metals during flood events in the Litavka River were studied 35 km downstream below the ore district. Metals are transported here mostly (more than 99% for Pb) in the form of suspended particulate matter (SPM), which at the outlet of the Litavka River contains 2,016 mg kg−1 Zn, 918 mg kg−1 Pb, and 25.5 mg kg−1 Cd on average. During a snowmelt-related minor flood event between March 25 and 29, 2006 (peak flow 36.6 m3 s−1), the river transported 2,400 tonnes of SPM during 4 days, containing 74 kg of Cd, 2,954 kg of Pb, and 5,811 kg of Zn. During larger floods (water flows above 55 m3 s−1 have occurred here 27 times during the last 77 years), the contamination is more diluted by material eroded in the floodplain along the middle and lower river course.

Age Controls on the Tanqua and Laingsburg Deep-Water Systems: New Insights on the Evolution and Sedimentary Fill of the Karoo Basin, South Africa

Abstract Improved constraints on the timing of Permian clastic sedimentation in the Karoo basin of South Africa have been revealed by new U-Pb single-grain zircon ages determined using the Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG). Analyses were performed on 180 zircon grains recovered from six ash beds exposed in the southwestern part of the Karoo basin. Samples were collected from two distinct loci of deep-water basin-floor and submarine-slope deposition within the Permian Ecca Group: the Tanqua and Laingsburg depocenters. Previous work constrained depositional ages of the 1800-m-thick deep-water to fluvial succession to 270–255 Ma. This poor chronostratigraphic resolution precluded robust stratigraphic correlation between the depocenters and impeded interpretation of basin evolution. The new data suggest that deep-water siliciclastic deposition began ~ 275 Ma (the lower Permian Collingham Formation), while the youngest ages are latest Permian. The Tanqua and Laingsburg depocenters began sand deposition at different times. Sandstone deposition in the Laingsburg depocenter started sometime after 275 Ma, and deposition of the first thick turbidite-dominated succession (Fan A) is bracketed into a period of less than 20 My. The Tanqua depocenter was sand starved during this interval. Both the uppermost sample from the Laingsburg depocenter and the lowermost from the Tanqua depocenter yield similar maximum depositional ages. This indicates, within the resolution of the age data, synchronous submarine sandstone deposition in the two loci at this time (~ 255 Ma). These data indicate that submarine deposition was still ongoing at a time when fluvial floodplain conditions are interpreted elsewhere in the Karoo basin. All the ash samples contain late Paleozoic zircon-grain age populations, while three samples contain small numbers of early Paleozoic, Proterozoic, and Archean zircon grains. Paleozoic zircon-grain age populations are interpreted as a record of arc activity linked to subduction. Increasing numbers of Precambrian zircons stratigraphically upward provide insight into changing source terranes during deposition into the Karoo basin.

Estuarine–fluvial floodplain formation in the Holocene Lower Tagus valley (Central Portugal) and implications for Quaternary fluvial system evolution

We present a brief synthesis of the Quaternary fluvial record in the Lower Tagus Basin (central Portugal), concentrating on factors controlling infill and incision. The Holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established Quaternary fluvial evolution model, in particular the link between sea-level change and fluvial incision-deposition. We suggest that several incision-aggradation phases may have occurred during glacial periods. Major aggradation events may overlap with cold episodes, while incision appears to concentrate on the warming limb of climate transitions. The complex stratigraphy of the Quaternary record in the Lower Tagus valley is influenced by repeated base-level and climate changes.This paper submits the first chronostratigraphic framework for valley fill deposits in the Lower Tagus area. Sea-level rise forced aggradation and controlled deposition of the fine-grained sedimentary wedge underlying the low-gradient Lower Tagus floodplain. Investigations have focused on the lower Muge tributary, where rapidly aggrading estuarine and fluvial environments were abruptly established (∼8150calBP) as sea level rose. Base level at the valley mouth controlled the upstream extent of the fine-grained backfill. Tidal environments disappeared abruptly (∼5800calBP) when the open estuary at the Muge confluence was infilled by the Tagus River. The decrease and final still stand of sea-level rise led to floodplain stabilisation with peat (∼6400–5200calBP) and soil formation (∼5200–2200calBP). Localised renewed sedimentation (∼2200–200calBP) is linked to human activity.

Evaluasi awal kerentanan pelulukan/likuefaksi daerah Kendal dan sekitarnya, Jawa Tengah

http://dx.doi.org/10.17014/ijog.vol2no3.20074The investigated area is a region prone to liquefaction hazards since it consists of loose, saturated Quaternary deposits. The Quaternary deposits were deposited in several sediment environments such as swamp, estuary, near shore, off shore, and fluvial (flood plain, flood basin and paleo channel). Among those Quaternary deposits, the paleo channel and estuary deposits which mainly consist of fine - to medium - sand have high susceptibility to liquefaction. An earthquake-source zone which is able to trigger earthquake and to cause liquefaction hazards is known to be thrust fault and subduction zones. Earthquakes produced by thrust fault activities are classified as shallow earthquakes while earthquakes produced by a subduction zone are deep earthquakes. The investigated area is divided into low liquefaction susceptibility, moderate susceptibility and high liquefaction susceptibility zones. This division has been made based on physical characteristic of the sand deposits, grain size, thickness of sand and its position to groundwater level as well as the physical character of overburden layer.