Sedimentary Features Research Articles

High-resolution clay mineral and major elemental characterization of a Permian-Triassic terrestrial succession in southwestern China: Diagenetic and paleoclimatic/paleoenvironmental significance

Relatively high-resolution clay mineralogical and chemical index of alteration (CIA) analyses were conducted on the terrestrial Lubei section in southwestern China, to gain a better understanding of the paleoclimatic/paleoenvironmental evolution on land during the Permian-Triassic transition (P-Tr transition). Clay-mineral species include illite-smectite mixed layers (I/S), illite, irregular chlorite-expandable mixed layers (C/E), chlorite, kaolinite, vermiculite, hydroxyl-interlayered mineral (HIM), and corrensite. CIA values are as high as approaching 100 in the Permian and show a gradual and subtle decrease towards the lowermost Triassic, where a sudden decrease to persistently <60 occurs with only periodic positive excursions. Diagenetic alteration is important at the study section and include chloritization, illitization of smectite in the Permian-lowest Triassic, transformation of smectite to corrensite in the upper sampled Triassic and potassium-addition induced decrease of CIA values throughout the section. However, with the integration of climate-sensitive sedimentary features, paleoclimatic/paleoenvironmental information was extracted from both clay-mineral composition and CIA. The dominance of precursor smectite together with the occurrence of kaolinite, Gigantopteris-type flora and coal seams, indicates an overall warm and semi-humid to semi-arid climate for the Permian part, and a general drying-out trend is suggested by the gradual decrease and final disappearance upsection of kaolinite, Gigantopteris-type flora and coal seams, as well as decreasing CIA values. Chemical weathering decrease is minor up to the lowest Triassic, which is mainly manifested by the subtle decrease of CIA values and which is probably partly due to the augmentation by acidification as indicated by the presence of vermiculite and HIM clay minerals. The short-term lingering (preliminarily estimated as <0.08Myr) of relatively intense chemical weathering after the extinction event was followed by an abrupt drop of CIA values to <60, which indicates the onset of a rapid and enhanced dry-out condition unfavorable for chemical weathering. In association with the general drying-out trend is an increase in climate periodicity and/or seasonality, which is manifested by increasingly prominent laminations, lithological alternation and intermittent large excursions of CIA values, suggesting a more complicated climate condition during the Early Triassic than previously recognized. While drying-out rather than acidification is suggested in this study to have been a killer agent to land plant at the Lubei section, the real relationship between environmental deterioration and the end-Permian mass extinction is still enigmatic and needs further investigation. This is the first relative high-resolution clay mineralogical and CIA investigation on a well-preserved and continuous terrestrial Permian-Triassic section.

Evolution of a Pyrenean molassic basin in the Western Mediterranean area: The Eocene–Oligocene Cixerri Formation in Southern Sardinia (Italy)

The sedimentary features of the Cixerri Formation (Eocene–Oligocene) and its evolution in space and time are described through mapping, investigation of all the significant outcrops, and also by analysing the depositional architecture of well‐exposed and laterally extensive outcrops. The Cixerri Formation marks the middle Eocene Pyrenean unconformity and blankets a former structural ridge‐and‐swale morphology. This started by covering the flanks of the ridges with small alluvial fans and ultimately filled the swales with fluvial deposits in braided to meandering stream environments. In this latter sedimentation phase, the depositional environment of the formation evolved both upwards, and from west to east, to gradually lower energy environments, suggesting a transgressive‐type evolution. The Eocene–Oligocene Cixerri Formation was deposited by a fluvial network with a regular flow regime under a humid–warm climate: This network was formed by a main W‐E‐directed trunk and a NW‐SE‐directed minor branch that ultimately joined together. The Cixerri Formation, which was fed by the erosion of a sector of the Pyrenean Chain, passes upwards to coarser deposits that indicate the transition from a quiet tectonic environment to an active transtensional tectonic phase (Apennine phase). A comparison with similar coeval formations in Northern Sardinia, Corsica, and the Western Mediterranean area (Balearic Islands, France) is attempted, before the significance of the formation in the Pyrenean orogeny is then discussed.

How fast are soil-forming processes in Quaternary sediments of a tropical floodplain? A case study in southeast Brazil

Floodplains are depositional features of a channel valley associated with a specific climatic and hydrologic regime of a drainage basin. In tropical conditions, sediments can be quickly weathered by soil-forming processes and tend to obliterate pre-existing sedimentary structures. Therefore, the objective of many studies on floodplains is to identify and discuss such sedimentary features, mostly those related to the morphology of channel deposits. Additionally, a qualitative approach to identify aspects of pedological evolution in these environments has been attempted in few studies. The purpose of this study was to interpret the intensity and the time of alluvial sediment weathering by pedogenetic processes in tropical humid conditions. Soil profiles were analyzed in different environments of deposition in the Pardo River floodplain (southeast Brazil) by accounting for sedimentary facies and pedological features supported by multi proxy data provided from geochemistry, macro- and micromorphology, grain size, total carbon, total nitrogen, 13C isotopic analysis and 14C/OSL (optically stimulated luminescence) dating. Based on the results, we identified that pedogenetic features and soil horizon distributions were closely related to sediment architecture, grain size and position in the floodplain. In the Pardo floodplain, Fluvic Gleysols (Loamic and Clayic) with moderately to strongly developed structures were identified in overbank fine sediments. Fluvic Cambisols (Clayic) were found in abandoned paleomeanders, Fluvic Cambisols (Loamic) in sandy scrollbars, Gleyic Acrisols (Clayic, Cutanic, Differentic) in channel deposits, which presented a 130-cm-thick Bt horizon with illuvial clay coatings, and Histosols (Fluvic) with high contents of total carbon (11.9% and 26.8% in histic horizons) in small-scale avulsive systems. Deposits were dated to between 35,000 and 700years BP. 13C isotopic data revealed a trend toward enriched values in older samples (−14.21‰) in which C4 plants dominated and a relative impoverishment of the values in more recent samples (−26.9‰ to −27.9‰). This result was consistent with the tendency of the distribution of C3 plants to increase over that of C4 plants, favored by the warmer and wetter climate since the Upper Holocene. In this study, a Fluvic Gleysol profile of <1000years and a Fluvic Cambisol of <700years were identified. Nevertheless, our primary contribution is to highlight that soil evolution in this specific situation could be more efficient than expected. Moreover, to provide consistent analyses in future studies, tools from both sedimentology and pedology are essential.

Quantitative interrogation of a fossilized carbonate sand body – The Pleistocene Miami oolite of South Florida

AbstractExposures of the Pleistocene Miami oolite in South Florida provide excellent examples of preserved primary sedimentary features and subsequent diagenetic changes of a ‘fossilized’ ooid sand body that has been subaerially exposed in a tropical climate since its deposition during the last interglacial highstand – Marine Isotope Stage 5e. Using a robust airborne light detection and ranging digital terrain model and select outcrops, a detailed analysis of the morphologies and dimensions of the different portions of the Miami oolite was conducted. The sand body, extending 95 km north to south and approximately 15 km wide, consists of shoals (or bars) separated by tidal channels and is partly bounded on the ocean‐facing side by a prograding barrier bar that collectively cover an area of approximately 1000 sq. km. Results of the quantitative interrogation of the Miami oolite are compared with those of previously published work from modern sand bodies on Great Bahama Bank including the Exumas, Schooners Cays and Tongue of the Ocean. Digital terrain models developed for these modern sand bodies on the Great Bahama Bank and the ancient Miami oolite were used as the basis for the definition of shoals, shoal crests (peaks) and channels which were examined with respect to their size, shape and orientation. The Exumas sand body is the best morphometric match when analysing the bars and the channels, and the Joulter Cays area is an analogue for the formation of the barrier bar and for burrow reworking of cross‐bedding within stabilized sand shoals. The Exumas is a particularly compelling analogue for the Miami oolite with respect to length and overall visual comparison between the morphologies of the sand bodies, shoal (or bar) shape, number of tidal channels, channel length and width, and high areas parallel to the strike trend of the sand body (islands in the Exumas and possible islands as part of the Miami oolite barrier bar). Despite ca 115 kyr of subaerial exposure and meteoric diagenesis including karst, the morphology of the Miami oolite is still relatively intact to the point where it can be easily analysed and meaningful comparisons to modern systems can be made. The Miami oolite serves as a key reference example for comparison to Holocene sand units in the Bahamas – it validates the concept of comparative sedimentology and in particular emphasizes how results from the modern can improve the interpretation of a fossilized example.

On the purported presence of fossilized collagen fibres in an ichthyosaur and a theropod dinosaur

AbstractSince the discovery of exceptionally preserved theropod dinosaurs with soft tissues in China in the 1990s, there has been much debate about the nature of filamentous structures observed in some specimens. Sinosauropteryx was the first non‐avian theropod to be described with these structures, and remains one of the most studied examples. Despite a general consensus that the structures represent feathers or feather homologues, a few identify them as degraded collagen fibres derived from the skin. This latter view has been based on observations of low‐quality images of Sinosauropteryx, as well as the suggestion that because superficially similar structures are seen in Jurassic ichthyosaurs they cannot represent feathers. Here, we highlight issues with the evidence put forward in support of this view, showing that integumentary structures have been misinterpreted based on sedimentary features and preparation marks, and that these errors have led to incorrect conclusions being drawn about the existence of collagen in Sinosauropteryx and the ichthyosaur Stenopterygius. We find that there is no evidence to support the idea that the integumentary structures seen in the two taxa are collagen fibres, and confirm that the most parsimonious interpretation of fossilized structures that look like feather homologues in Sinosauropteryx is that they are indeed the remains of feather homologues.

Sedimentary features reveal transport paths for Holocene sediments on the Kristianstad coastal plain, SE Sweden

We have investigated coastal and aeolian deposits on the Kristianstad plain in southernmost Sweden by a combination of methods that has yielded data on sedimentary features such as grain-size variations, shape and character of quartz grain surfaces (determined in light microscope and scanning electron microscope), and mineralogical composition. Such sedimentary techniques have been not applied to coastal deposits in this part of the Baltic Sea region before. The littoral, foredune and parabolic dune sands are sedimentologically similar, only a slight grain-size transformation by aeolian processes in the foredune was observed. Sand in straight-crested dunes, on the other hand, originates from immature glaciolacustrine sediments, seen e.g. through the increase in mineral maturity during active aeolian transport. Finally, a palaeosol, occuring below an aeolian cover, carries both aeolian and glaciolacustrine sedimentary signals.

Insights Into Marls From Optical and Back-Scattered Electron Petrography: An Example From the Outer Carpathians (Poland)

Abstract: This paper is a study of grain provenance, depositional processes, and the relationship of those processes to composition and diagenesis of fine-grained rocks, based on high-resolution petrography. The marly successions deposited in siliciclastic flysch and related to the paleotectonics of the northern domain of the Tethys Ocean (Outer Carpathian Basin) were examined. The following marls were studied: Upper Jurassic marls from the Vendryně Formation (Goleszow Marls); Upper Cretaceous Siliceous-Fucoid, Wegierka, Weglowka, Frydek, Jasienica, and Żegocina Marls; Eocene Łącko, Budzow, Zembrzyce, and Leluchow Marls; and Oligocene Sub-Cergowa and Grybow Marls. These marls are products of the redeposition of shelf sediments into deeper parts of the basin. Knowledge of their diagenetic history can contribute to the evaluation of the petroleum potential of the Polish Outer Carpathians. Thin-section analysis by optical and electron back-scattered microscopy (FESEM-BSE) highlights the similarity of all these marls with respect to composition, grain size, sedimentary features, and diagenetic changes. They differ only in the quantitative proportion of constituents, the relative extent of key microfacies, and diagenetic effects. The diagenetic modifications recognized in the rocks studied are characteristic of the processes operating in the sedimentary environment and during burial diagenesis. Thin-section petrography of the marls reveals fine, mostly silt-size siliciclastic material and bioclasts supported by matrix. Siliciclastic particles comprise mostly quartz, micas, feldspars, glauconitic nodules, and lithoclasts. Calcareous and siliceous bioclasts, mostly microfossils (foram and sponge spicules, and a few radiolarians and diatoms) and coccospheres, are variably preserved; they may occur as calcite, silica, and clay pseudomorphs. Additional components include peloids and stringers of brown organic matter. Millimeter-scale fabric analysis provides detailed insight into the processes of transport and deposition. Five microfacies are identified: parallel-laminated, wavy and lenticular-laminated, homogeneous exhibiting preferred orientation of elongated components, bioturbated, and bioclast-bearing. The range of microfacies suggests that the marl sediment was deposited while currents were active. The depositional settings identified range from traction, reworking by bottom currents, supply by nepheloid flow (indistinctly bounded laminae), possible eolian input (laminae a few grains thick), and biogenic reworking of sediments. Back-scattered electron images reveal that the matrix consists of coccolithophorid remains with varying abundances of clay, silica, and carbonate cements. Five varieties of matrix are distinguished: 1) carbonate–clay–silica bearing, 2) carbonate–clay supported, 3) carbonate–silica supported, 4) clay–silica supported, and 5) clay dominated. Clay appears as rosette and lamellar aggregates, silica as nanoquartz (microspheres, clusters, coatings), quartz overgrowths, and occasionally opal CT as lepispheres and aggregates moss-like in appearance, and calcite as overgrown coccoliths, pseudomicrite, micrite, and microspar. Pyrite framboids are present in some samples. Intrabiotic and intergranular cements are developed. Also present are partially dissolved coccolith placoliths, silica- and clay-replaced micarb, and grains similar in appearance to volcanic glass shards that now consist of calcite and quartz. Bioclasts may have been a source for calcite and silica cements. Volcanic glass may have been a source for authigenic silica and clay minerals; this is suggested by the close spatial juxtaposition of silica microspheres and authigenic clay (cauliflower-like aggregates). The authigenic origin of the clay in these marls is also suggested by the presence of overgrown coccoliths because recrystallization of shields is reduced when clay is present, so that the overgrowths must have been formed in an environment where clay minerals were scarce initially. Despite diagenetic changes, the presence of pyroclasts is still recognizable. There are quartz crystal chips, shard-shaped grains, volcanic rock fragments, and minerals (biotite, apatite, zircon). The marls studied could be described as impure fine-grained detrital limestones chalky in type, with evidence of redeposition and possible volcanic-ash input. The marl depositional system within the Outer Carpathian Basin was associated with tectonic movements which initiated chalk-type facies, and this was particularly widespread in the Upper Cretaceous and Paleocene.

Methods for Investigating Sediment Flux under High-Energy Conditions on the Southeast Florida Continental Shelf using Laser Airborne Depth Sounding (LADS) in a Geographic Information System (GIS) Dataframe

ABSTRACT Finkl, C.W. and Vollmer, H.M., 2017. Methods for investigating sediment flux under high-energy conditions on the southeast Florida continental shelf using Laser Airborne Depth Sounding (LADS) in a Geographic Information System (GIS) dataframe. Laser Airborne Depth Sounding (LADS) bathymetric surveys conducted in 2001 and 2008 bracket two hurricane landfalls (Hurricane Ivan in 2004 and Hurricane Katrina in 2005) in Broward County, southeast Florida, thus providing an opportunity to investigate changes in bottom topography as a result of wave and current action. The seafloor in this region is characterized by a wide range of sedimentary features that are normally stabilized (held in place) by outcrops of carbonate bedrock and coral reefs. During high-energy events, however, the sedimentary deposits are partially mobilized by waves and currents. This methodological study used the two LADS bathymetric surveys to construct triangulated irregular networks (TINs, which are a digital means of representin...

MICROBIAL MAT SANDWICHES AND OTHER ANACTUALISTIC SEDIMENTARY FEATURES OF THE EDIACARA MEMBER (RAWNSLEY QUARTZITE, SOUTH AUSTRALIA): IMPLICATIONS FOR INTERPRETATION OF THE EDIACARAN SEDIMENTARY RECORD

Abstract: The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota—Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systematic excavation and reassembly of bedding planes has resulted in reconstruction of over 400 square meters of Ediacaran seafloor, permitting detailed and sequential sedimentary, paleoecological and taphonomic assessment of Ediacara fossilized communities and the shallow marine settings in which these ecosystems lived. Sedimentological investigation reveals that the Ediacara Member consists of successions of sandstone event beds and a paucity of other lithologies. Moreover, these Ediacara sandstones are characterized by a suite of sedimentary features and style of stratigraphic packaging uncharacteristic of Phanerozoic sandstone successions considered to ha...

Sedimentologia e estratigrafia de um depósito deltaico gerado por modelagem física empregando amostragem tipo testemunho

A análise de testemunhos de depósitos sedimentares é um método rotineiramente utilizado nos estudos sedimentológicos e estratigráficos. Propõe-se neste trabalho um método inédito para amostrar depósitos sedimentares gerados por de modelagem física em escala reduzida, adaptando o método de testemunhagem para descrever e interpretar depósitos deltaicos e, posteriormente, determinar o quão representativa é a simulação do ponto de vista geológico. O processo de amostragem inicialmente consiste na perfuração vertical do depósito, ou seja retirada do material sedimentar, e posterior preenchimento da cavidade por resina. A resina penetra horizontalmente alguns centímetros nas camadas sedimentares e, após a secagem, permite a retirada de um testemunho bastante preservado. No total foram descritos 30 testemunhos, gerando perfis verticais de fácies que posteriormente foram interpretados e correlacionados, usando modelos e conceitos de sedimentologia e estratigrafia. Nos testemunhos foram identificadas características sedimentoló- gicas e geométricas similares àquelas encontradas em deltas naturais, o que permitiu interpretar as associações de fácies deltaicas e, juntamente com a correlação lateral dos perfis, mostrar a evolução estratigráfica do depósito.

Sedimentary constraints on the development of a narrow deep strait (São Sebastião Channel, SE Brazil)

The Sao Sebastiao Channel (SSC), which separates Sao Sebastiao Island from the continent, is a deep elongated strait on the inner shelf of the Sao Paulo Bight (SE Brazil). The aim of this study is to explain why it is presently sediment starved, instead of forming a tombolo. Wave data were obtained from both a WW3 model database and buoy records, and wave propagation patterns from the SWAN numerical model. Grain size trend analysis of 579 surficial sediment samples from the strait and the surrounding region served to estimate the residual transport directions. Bedload sediment transport was computed considering in situ currents and bottom sediment grain size. Moreover, six seismic profiles and one gravity core were obtained in the strait in order to evaluate the hickness of the sedimentary deposits. The geometry of the SSC (X/B=0.3, where B is the breakwater or island diameter and X is its cross-shore distance to the mainland) predicts that a tombolo should be formed, and wave patterns confirm that it is a zone sheltered from both S and NE waves. Previous studies have shown that the hydrodynamics of the SSC is controlled by wind-driven currents, which are more intense in the eastern and central sectors of the strait. The western sector is currently covered by sandy mud, whereas very coarse to fine sand prevails in the deeper eastern sector. Sediment patterns show a trend to deposition of fine sediment in the western sector of the SSC and two main depocentres located at the northern limit of the study area and at the southern mouth of the strait. Sandy mud in the western sector forms a 40-m-thick deposit close to the outer limit of Araca Bay, whereas the remainder of the SSC is covered by a very thin layer of sandy sediments. Dominance of mud in the depositional western sector suggests low availability of sand in the area. Therefore, despite the geometry and wave patterns of the SSC favouring the formation of a tombolo, the dominance of wind-driven currents and the low availability of sand determine that such a sedimentary feature cannot be formed, resulting in a deep strait.

The preservation potential of environmentally diagnostic sedimentary structures from a coastal sabkha

The Abu Dhabi sabkha constitutes the landward portion of the shallow-sloping carbonate ramp situated on the northwestern coast of the United Arab Emirates (UAE). The sabkha in this region is composed of a complex assortment of carbonate, organic, and evaporitic facies that constitute a regressive sabkha sequence. The surface features of the sabkha can be grouped into distinct, laterally continuous facies associations that are directly correlatable with elevation above present-day sea level. Previous investigations have suggested the employment of the Abu Dhabi sabkha as a modern depositional analogue to ancient carbonate-evaporite formations; however, a quantitative analysis of the relationship between sabkha surface and subsurface characteristics has not previously been undertaken. This study describes in detail the sedimentary structures and textures seen at the sabkha surface and compares them to the Holocene-age facies retained in the shallow subsurface. Of the 36 sedimentary structures observed at the sabkha surface, only seven (19%) are still identifiable in the early burial realm. The majority of the surface structures were lost during early burial as a result of microbial mat decomposition, destructive evaporite precipitation, and compaction. The loss of diagnostic sedimentary features during early burial as a result of fabric-destructive processes has considerable implications for the recognition and interpretation of ancient sabkha sequences. Documenting these processes from a range of modern sedimentary environments will aid in the identification of those diagnostic features that may be reliably employed during paleoenvironmental reconstructions.

Contrasting storm- versus tsunami-related shell beds in shallow-water ramps

Shell beds are sedimentary features that can potentially provide significant palaeoenvironmental and sequence stratigraphic information. High-energy events, such as storms/hurricanes and tsunamis, might originate sedimentary shell beds due to either landward-incoming waves or basinward backwash flows. Many papers have dealt with the taphonomic characterization of storm shell beds (=tempestites) along palaeobathymetric gradients. On the contrary, only a few taphonomic studies have examined the skeletal remains deposited in tsunami shell beds (=tsunamiites). These studies seek to differentiate taphonomic traits of skeletal remains in tempestites and tsunamiites. These assessments are restricted to tsunamiites deposited inland in connection with historically well-known tsunami events. To date, no studies of tsunami shell beds deposited offshore are available in the literature and, consequently, whether taphonomic attributes can be used to separate storm and tsunami shell beds deposited along the shelf remain to be demonstrated. In the Sorbas Basin (SE Spain), uppermost Tortonian-lowermost Messinian temperate-water carbonate ramp deposits record shell beds attributed to storm events and one thick shell bed interpreted as a tsunamiite. A quantitative taphonomic study allows the differentiation of bioclastic tempestites and tsunamiites deposited on the ramp: 1) tsunamiites are characterized by a mixture of organisms coming from different parts along the ramp (from inner to outer ramp), while tempestites include closely spaced organisms; 2) fragmentation is higher in tempestites than in tsunamiites; 3) shell fragments are predominantly rounded in tempestites but preferentially sharp in tsunamiites; 4) skeletal remains are preferentially oriented horizontally (<30° with respect to stratification) in tempestites, while obliquely (between 30° and 60°) and perpendicularly (>60°) in tsunamiites; 5) concave shells tend to be concave-up stacked in tempestites but chaotically arranged in tsunamiites; and 6) encrustation and borings are more abundant in tempestites than in tsunamiites. The intensity and scale of the depositional mechanisms associated with high-energy events, storms vs. tsunamis, account for the different preservation styles of shells. The key taphonomic features identified in this study help to discriminate offshore shell beds originated either by storms or tsunamis in other geological contexts regardless of the age and the geography, and contributes to the understanding of the scarce examples of fully marine shelly tsunami deposits.

Fluid escape structures as possible indicators of past gas hydrate dissociation during the deposition of the Barremian sediments in the Recôncavo Basin, NE, Brazil

ABSTRACT: Empty elliptical vesicles are observed in outcrops of Barremian very fine clayey sandstone to siltstone lacustrine slurry deposits of the Pitanga Member (Maracangalha Formation), exposed in the Maré Island, Southern Recôncavo Basin, Brazil. These sedimentary features have been traditionally interpreted as water escape structures triggered by the diapirism of the underlying shales of the Candeias Formation. This work proposes that vesicles were generated during massive gas hydrate dissociation as a result of tectonic activity in a paleolake system. Tectonic uplift would have triggered both the reduction of the confining pressure as well as an increase in lake bottom temperature, resulting in the instability of gas hydrate and causing intense release of both methane - or carbon dioxide (CO2) - and water. On one hand, this proposal has a strong impact on paleoenvironmental interpretations, giving support to the current hypothesis that rocks related to the Pitanga Member would have been deposited under water columns deep enough for gas hydrate formation and subsequent dissociation. On the other hand, it provides new insights on the genesis of fluid escape structures in sedimentary rocks, both lacustrine and marine, providing a paleobathymetric indicator.

Industrial Mercury Pollution in a Mountain Valley: A Combined Geophysical and Geochemical Study

Many alpine valleys have inherited strong industrial remnants. Chemical and metallurgical companies were set up in these narrow glacial valleys at the beginning of the industrial era to benefit from cheap labor and hydroelectricity. Regulations concerning solid and liquid waste handling did not exist, and contaminated sediments were often used as soil amendment to improve soil texture, spreading the contamination, which local Authorities have now to deal with.In the present study we report on mercury contamination in the narrow alpine valley known as canton of Valais valley. Waste materials and contaminated sediments were deposited in the valley for many years. An electromagnetic conductivity survey allowed a definitive mapping of the extent of such practices because an EM conductivity contrast was clearly detectable between the added silty-clay material and the natural silty-sand soil. High EM conductivity correlates quite well with high Hg surface soil content. Cores drilled at hotspots and along the canal were analyzed for total mercury, methyl mercury, and core sedimentary features recorded. While up to 70cm thick, dredged, Hg-contaminated material was found to lay above the original sandy soil in housing areas, the mercury contamination extends down to 1.5 m depth, i.e. down to the water table, probably caused by the high sediment material organic content (OC), and OC-Hg enhanced transport. Methylation reductive conditions were observed, together with high MeHg relative abundance ([MeHg]/ [HgT]> 0.1%), in two environments, namely the zone of fluctuating water table and the canal water/sediment interface. Groundwater quality was not impacted, because of large groundwater fluxes observed in these glacial alpine valleys.

Depositional architecture and peculiar sedimentary features of late Cretaceous Utrillas Formation at Tamajón (Guadalajara, Spain)

The Utrillas Formation represents clastic wedges that accumulated in relation to continental-coastal areas of Iberian Basin during the worldwide late Cretaceous sea-level rise. At the Tamajon outcrop the late Cenomanian Utrillas wedges are composed of four facies associations (FA1 to FA4), which unconformable overlay Triassic deposits. Basal sediments (FA1) are interpreted as high energy, braided fluvial deposits, characterized by coarse-grained (conglomerate–sandstone) facies; which grade upwards to tide-influenced, estuarine sedimentation (sandstones and mudstones with inclined heterolithic stratification, FA2), and then to high-energy, coastal sheet and channelled sandstones with different tidal features (FA3); and finally, to fine-grained (mudstones and minor burrowed sandstones) of an offshore marine associations (FA4). The depositional architecture based in the presence and hierarchy of several ranks of bounding surfaces and the overall upward-fining succession show the long term retrogradational trend of these facies associations. Peculiar sedimentary features of these sediments are 1) the presence of large-scale, single sets of cross beds infilling large erosive channels, which are tidal (not aeolian) in origin. 2) The size and length of the cross-bedding defined by couplets of different grain size; here interpreted as originated by flow unsteadiness in relation to changing tides. And 3) an unusual association of ironstones, wrinkle structures and vertebrate tracks with microbial mats and penecontemporaneous iron encrusting allowing track preservation in the sedimentary record.

First Lower Jurassic vertebrate burrow from southern Africa (upper Elliot Formation, Karoo Basin, South Africa)

Vertebrate burrows are common ichnofossils in the Permo-Triassic of the main Karoo Basin in South Africa. They are generally attributable to one of several lineages of therapsid, including the derived clade known as cynodonts. Despite the presence of cynodont species in the Upper Triassic and Lower Jurassic of the Karoo Supergroup, vertebrate burrows have never been reported from this part of the succession. Recent fieldwork recovered a semi-elliptical burrow cast in the Lower Jurassic upper Elliot Formation (Stormberg Group) on the farm Edelweiss 698 (Free State). The horizontal and vertical diameters of the burrow cast are ~18 and ~7cm, respectively. This semi-horizontal, straight to slightly sinuous tunnel is ~50cm long with a ramp angle of <5°. The tunnel lacks branching, terminal chambers, and associated fossil bones. The burrow cast consists of medium, massive sandstone and very rare, faint, horizontal to slightly inclined lamination. The burrow cast is hosted in fine-grained, palaeo-pedogenically altered, crevasse splay sandstone that is 10–20cm thick and is under- and overlain by a massive, red, bioturbated floodplain mudstone unit with large-scale (>20cm deep) desiccation cracks, invertebrate trace fossils, calcareous rhizoconcretions, and spherical-to-elongated carbonate nodules. These and other associated sedimentary features provide evidence for a semi-arid, fluvio-lacustrine palaeoenvironment during the burrowing activity. Based on comparisons to fossil and modern burrows, this burrow cast is interpreted as a vertebrate burrow, and is the first record of vertebrate fossorial activity within the Lower Jurassic of southern Africa. The ancient burrow architect has yet to be positively identified. However, given the size and morphology of the burrow and the occurrence of similar sized fossil cynodont therapsids that inhabited the main Karoo Basin in the earliest Jurassic, the potential burrow-maker may be tentatively linked to the Cynodontia (e.g., Pachygenelus - an advanced tritheledontid).

Regression-transgression cycles of paleolakes in the Fen River Graben Basin during the mid to late Quaternary and their tectonic implication

An investigation into lake terraces and their sedimentary features in the Fen River Graben Basin shows that several paleolake regression-transgression cycles took place during the mid to late Quaternary. The horizontal distribution of the lowest loess/paleosol unit overlying each lake terrace indicates the occurrence of four rapid lake regressions when paleosols S8, S5, S2, and S1 began to develop. The horizontal distribution of the topmost loess/ paleosol unit underlying the lacustrine sediment in each transition zone between two adjacent terraces indicates that following a lake regression, a very slow lake transgression occurred. The durations of three lake transgressions correspond to those of the deposition or development of loess/paleosols L8 to L6, L5 to L3, and L2. It is thereby inferred that regional tectonic movement is likely the primary factor resulting in the cyclical process of paleolake regressions and transgressions. Taking these findings along with published geophysical research results regarding the upper mantle movements underneath the graben basin into account, this paper deduces that a cause and effect relationship may exist between the paleolake regression-transgression cycles and the tectonic activity in the upper mantle. The occurrence of a rapid lake regression implies that the upwelling of the upper mantle underneath the graben basin may be dominant and resulting in a rapid uplifting of the basin floor. The subsequent slow lake transgression implies that the thinning of the crust and cooling of the warm mantle material underneath the graben basin may become dominant causing the basin floor to subside slowly. Four rapid paleolake regressions indicate that four episodic tectonic movements took place in the graben basin during the mid to late Quaternary.

Benthic foraminiferal response to sedimentary disturbance in the Capbreton canyon (Bay of Biscay, NE Atlantic)

Living (Rose Bengal stained) and dead benthic foraminifera were investigated at 6 deep-sea sites sampled in the Capbreton canyon area (Bay of Biscay, France). Three sites were located along the canyon axis at 301m, 983m and 1478m and 3 stations were positioned on adjacent terraces at 251m, 894m and 1454m. Sedimentary features indicate that frequent sedimentary disturbances of different magnitudes occur along the Capbreton canyon axis and adjacent terraces. Such environmental conditions cause the presence of very particular benthic environments. Along the 6 studied sites, different foraminiferal responses to various sedimentary patterns are observed revealing the complexity of this canyon environment. Some sites (Gitan 3 (canyon axis), Gitan 5 (canyon axis) and Gitan 6 (terrace)) are characterized by moderate to low standing stocks and low diversity and are mainly dominated by pioneer taxa such as Fursenkoina brady, Reophax dentaliniformis and Technitella melo suggesting a recent response to turbidite deposits recorded at these sites. Others sites (Gitan 1 and Gitan 2) show extremely high standing stocks and are mainly dominated by the opportunistic Bolivina subaenariensis and Bulimina marginata. Such faunal characteristics belonging to a more advanced stage of ecosystem colonization indicates strongly food-enriched sediment but extremely unstable conditions. Moderate standing stocks and diverse assemblage composed of species such as Uvigerina mediterranea and U. peregrina has only been observed at the terrace site Gitan 4. More stable sedimentary conditions recorded at this terrace seem to be suitable to the development of a dense and diverse foraminiferal community. Numerous neritic allochtonous species were observed in the dead foraminiferal fauna. These allochthonous species mainly originate from shelf areas (<60m).

Growth pattern research on the modern deposition of Ganjiang delta in Poyang lake basin by spatio-temporal remote sensing images

It is of great importance for petroleum exploration to study the sedimentary features and the growth pattern of shoal water deltas in lake basins. Taking spatio-temporal remote sensing images as the principal data source, combined with field sedimentation survey, a quantitative research on the modern deposition of Ganjiang delta in the Poyang Lake Basin is described in this paper. Using 76 multi-temporal and multi-type remote sensing images acquired from 1973 to 2015, combined with field sedimentation survey, remote sensing interpretation analysis was conducted on the sedimentary facies of the Ganjiang delta. It is found that that the current Poyang Lake mainly consists of three types of sand body deposits including deltaic deposit, overflow channel deposit, and aeolian deposit, and the distribution of sand bodies was affected by the above three types of depositions jointly. The mid-branch channels of the Ganjiang delta increased on an exponential growth rhythm. The main growth pattern of the Ganjiang delta is dendritic and reticular, and the distributary channel mostly arborizes at lake inlet and was reworked to be reticulatus at late stage.