Hydraulic Sorting Research Articles

Mechanistic controls on diverse fates of terrestrial organic components in the East China Sea

Terrestrial carbon transferred from the land to sea is a critical component of the global carbon cycle. A range of geochemical proxies has been developed to fingerprint the fate of terrestrial organic matter (TOM) in marine sediments. However, discrepancies among different proxies limit our ability to quantify and interpret the terrestrial signals in marine sediments, with consequences for the investigation of both the modern carbon cycle and past environmental change. To mechanistically understand these discrepancies, we examined the distributions of a range of terrestrial proxies and their aquatic counterparts (i.e. marine proxies) in the Yangtze river-East China Sea (YR-ECS) shelf system, where TOM experiences extensive modification during transport and burial. TOM proxies in the YR-ECS system collectively fit a power-law model but with distinct attenuation rates (the a∗ values) for individual molecular proxy groups. Among a range of TOM proxies, the modeled a∗ values decrease in the order: soil-marker BHPs>triterpenols>lignin>HMW n-alkanols>branched GDGTs>HMW n-alkanes for biomarkers; and Rsoil>BIT>%TOMiso for proxies tracing %TOM. Rapid loss of TOM components through dissociation in the narrow estuary, followed by oxidation over the wide open shelf, are best described by power curves. Inherent chemical reactivity (i.e. the number of functional groups), responses to hydraulic sorting, and in situ production regulate the individual attenuation rates. Of them, chemical reactivity plays the most important role on proxy behavior, supported by a strong correlation between a∗ values and standard molal Gibbs energies. Both, physical protection and chemical reactivity fundamentally control the overall behavior of TOM components, with the relative importance being setting-dependant: The former is relatively important in the estuary, whereas the later is the primary control over the open shelf. Moreover, regional variation of different marine-counterparts is also significant over the river-ECS shelf system, seemingly regulated by regional nutrient distributions. Therefore, for %TOM estimates using molecular ratio approaches, the specific behavior of individual terrestrial components and marine-counterparts and the physical, biological and chemical characteristics of depositional settings all need to be considered.

Robust assessment of moderate heavy metal contamination levels in floodplain sediments: A case study on the Jizera River, Czech Republic

Enrichment factors for Cr, Cu, Ni, Pb and Zn in floodplain fines from the middle and the lower courses of the Jizera River (a tributary of the Elbe River in the Czech Republic) were evaluated to compare the original contamination profiles with post-depositional and pedogenic changes. Background concentrations of heavy metals were assessed from uncontaminated sediments (soils) in the study area that belong to the same sedimentary facies and were not affected by reductimorphic processes. Facies assignment is accessible by geophysical imaging combined with core analysis. Sediments from point bars and channel banks in direct contact with riverine water are more heavily polluted than overbank fines from the distal floodplain. The point pollution source, a century-old battery and car production facility in the city of Mladá Boleslav, has certainly been responsible for Ni and Cr pollution, contributed substantially to Cu and Pb pollution, and had a less significant effect on the Zn enrichment factor. Although the use of soil enrichment factors has been criticized, these factors help to manage hydraulic sorting and recognition of post-depositional migration in soil profiles of floodplain sediments. When moderate pollution (enrichment factor about 1.5 for Cu, Pb and Zn) is found, background concentrations must be carefully evaluated and natural enrichment must be taken into account. Studies of such small enrichment factors contribute to the understanding of the dispersal and fates of pollutants in floodplains.

Weathering geochemistry and Sr‐Nd fingerprints of equatorial upper Nile and Congo muds

AbstractThis study investigates processes of sediment generation in equatorial central Africa. An original, complete and integrated mineralogical‐geochemical database on silt‐sized sediments derived from different parent rocks (basalt, granite, gneiss, metapsammite, sandstone) along the East African Rift from 5°S in Tanzania to 5°N in Sudan is presented and used to assess the incidence of diverse factors controlling sediment composition (source‐rock lithology, geomorphology, hydraulic sorting, grain size, recycling), with particular emphasis on chemical weathering.

The Paleoenvironment and Lithic Taphonomy of Shi’Bat Dihya 1, a Middle Paleolithic Site in Wadi Surdud, Yemen

The Shi'bat Dihya 1 site in western Yemen, dated by optically stimulated luminescence to 55 ka, provides insight into the Middle Paleolithic peopling of the Arabian Peninsula. The archaeological layer is interstratified within thick, sandy silt floodplain deposits filling a piedmont basin. Luminescence dates, lack of soil development, and gypsum precipitation indicate a high accretion rate of the floodplain during Marine Isotope Stage 3, in connection with a (semi)‐arid environment. Rapid overbank sedimentation was likely a result of the remobilization of loess material deposited on the Yemeni Great Escarpment at the periphery of the adjacent Tihama coastal sand desert or of other sources. Fabric and size analyses of the lithic artifacts, together with spatial projections, indicate site modifications by floods. Primary modifications include (1) selective accumulation of medium‐sized lithic pieces as a result of hydraulic sorting, (2) bimodal orientation of artifacts, and (3) ripple‐like arrangement of lithics and bone/tooth fragments. The overrepresentation of teeth may also be a consequence of sorting. Although floods have distorted the original site patterning, long‐distance transport of artifacts by water can be excluded, as indicated by relatively high refitting rate, close proximity of artifacts derived from the same block of raw material, and lack of abrasion of the pieces. Therefore, the site is considered “geologically” in situ because its remobilization by water occurred shortly after human abandonment. This study also stresses that the effective preservation of a site cannot be assessed without careful taphonomic study, even in a potentially favorable depositional context such as silty alluvium.

Geochemistry of beach sands along the western Gulf of Mexico, Mexico: Implication for provenance

This paper contributes to understanding the intractable problems in provenance study due to hydraulic sorting and geochemical heterogeneity in medium, fine, and very fine sands. For this purpose, detrital modes, major, trace, and rare earth element (REE) compositions of recent sands from the Playa Azul, Tecolutla, and Nautla beach areas of the western Gulf of Mexico have been investigated. Marked geochemical and petrographic differences occur among the three beach sands, even though they are separated just by 45km. The average quartz-feldspar-lithic fragment (QtFL) ratios for the Playa Azul, Tecolutla, and Nautla sands are respectively Qt69–F10–L21, Qt57–F11–L32, and Qt37–F5–L58. The volcanic lithic fragment (Lv)−sedimentary lithic fragment (Ls)−[plutonic lithic (Lp)+metamorphic lithic fragments (Lm)] ternary diagram indicates that the Nautla sands are dominated by volcanic detritus, while the Tecolutla sands are dominated by sedimentary and volcanic detritus. The Playa Azul sands are dominated largely by sedimentary detritus. Geochemically, the three beach sands are quite distinctive from each other. The Playa Azul sands are higher in SiO2 content (∼64–84wt.%) than in the Tecolutla sands (SiO2=∼47–69wt.%). The Nautla sands are very low in SiO2 content (<46wt.%). The contrasting geochemical compositions among the three beach areas are also confirmed by significant variations in Al2O3/TiO2, Na2O/K2O, K2O/Al2O3, Rb/Al2O3, and Cr/Ni ratios. The CIA values (∼39–69; chemical index of alteration) for the three beach areas suggest low to moderate weathering nature.In the three beach sands studied, the decrease in grain size is accompanied by a gradual decrease in SiO2 content and an increase in TiO2, Al2O3, Fe2O3, MgO, Zr, Hf, Cr, and V contents. Similarly, the ∑REE content increases with decreasing grain size. However, very fine sands in the Playa Azul and Nautla beaches are different in ∑REE content. This observation suggests that the provenance is more important in controlling the geochemical composition of beach sands than the grain size. The zirconium concentration in beach sands, however, is not related to the grain size.The comparison of REE patterns of beach sands with those of source rocks located relatively close to the study areas suggests that the Playa Azul sands were derived from felsic rocks, whereas a mixed provenance with contributions from felsic and intermediate rocks is more likely for the Tecolutla sands. In contrast, the REE distribution patterns of Nautla sands resemble those derived from basalt and basaltic andesite. However, selective concentration of magnetite grains in beach sands increases the LREE content and fractionates Eu resulting in a europium anomaly that is more negative than that displayed by Nautla sands. All of the above observations suggest that rivers delivering sands to the beaches are the important factors in controlling the composition of beach sands and that longshore currents play a less significant role.

Influence of granitoid textural parameters on sediment composition: Implications for sediment generation

The aim of this study is to determine and characterise the control exerted by parent rock texture on sand composition as a function of grain size. The sands investigated were generated from granitoid parent rocks by the Rhone, Damma and Sidelen glaciers, which drain the Aar Massif in the Central Alps (Switzerland), and were deposited in glacial and fluvio-glacial settings. Mechanical erosion, comminution (crystal breakdown and abrasion) and hydraulic sorting are the most important processes controlling the generation of sediments in this environment, whereas chemical and/or biochemical weathering plays a negligible role. By using a GIS-based Microscopic Information System (MIS), five samples from the glacier-drained portions of the Aar basement have been analysed to determine textural parameters such as modal composition, crystal size distribution and mineral interfaces (types and lengths). Petrographic data of analysed sands include traditional point counts (Gazzi-Dickinson method, minimum of 300 points) as well as textural counts to determine interface types, frequency, and polycrystallinity in phaneritic rock fragments. According to Pettijohn's classification, grain‐size dependent compositions vary from feldspathic litharenite (0φ fraction) via lithic arkose (1φ and 2φ) to arkose (3φ and 4φ). Compositional differences among our data set were compared to modern plutoniclastic sands from the Iberian Massif (Spain) and the St. Gabriel Mts. (California, USA), which allowed us to assess the role exerted by glaciers in generating sediments. By combining data from the MIS with those from petrographic analysis, we outlined the evolution of mineral interfaces from the parent rocks to the sediments.

Coarse sediment and lower Yellow River siltation

Trap sediment by reservoirs has been effective in protecting the Lower Yellow River (LYR) but it can hard be sustainable. After reviewing the nature of sediment and siltation, the effect of coarse sediment (d > 0.08–0.1 mm) (CS) on LYR siltation is studied. It is basically proved that the CS was apt to aggregate in special reach in the upmost fluctuating backwater of reservoirs due to the effect of hydraulic sorting; persistent dredging here in a fixed dredging basin (FDB) can remove most CS and prevent it from entering the LYR. It is thus possible to ease or to cease LYR siltation. Removing CS has also proved to be able to save reservoir capacity (Zhou et al., 2010). Therefore, previously projected temporary trapping storages as the Xiaolangdi reservoir (XLDR) immediately upstream of LYR can be adjusted with new role to screen CS. The LYR can be protected without needing more dams.

Chromium and nickel as indicators of source-to-sink sediment transfer in a Holocene alluvial and coastal system (Po Plain, Italy)

A reliable quantitative estimate of changes in source-to-sink sediment transfer requires that high-resolution stratigraphic studies be coupled with accurate reconstructions of spatial and temporal variability of the sediment-routing system through time. Source-to-sink patterns from the contributing upland river catchments to the deltaic and coastal system are reconstructed from the Holocene succession of the Po Plain on the basis of selected geochemical indicators. Sediment supplied to the delta area by the major trunk river (the Po) exhibits naturally high Cr and Ni values, which invariably exceed the maximum permissible concentrations for unpolluted sites. This ‘anomaly’ reflects remarkable sediment contribution from ultramafic (ophiolitic) parent rocks cropping out in the Po drainage basin (Western Alps and NW Apennines). In contrast, alluvial and coastal plain deposits supplied by ophiolite-free, Apenninic catchments invariably display lower Cr and Ni contents. For constant sediment provenance domain, Cr and Ni distribution is observed to be controlled primarily by hydraulic sorting. Clay-silt deposits (floodplain, swamp and lagoon/bay facies associations) invariably show higher metal concentrations than their sandy counterparts (fluvial-channel, distributary-channel and beach-ridge facies associations). From a stratigraphic perspective, in sedimentary basins characterized by strong differences in sediment composition geochemical fingerprinting of individual facies associations framed by surfaces of chronostratigraphic significance is proposed as an invaluable approach towards an accurate quantitative assessment of sediment storage in alluvial and coastal depositional systems as opposed to volumetric reconstructions based on lithologic or geometric criteria alone.

Modal and Geochemical Compositions of the Lower Silurian Clastic Rocks In North Qilian, Nw China: Implications For Provenance, Chemical Weathering, and Tectonic Setting

Abstract The North Qilian orogenic belt records the transition from Ordovician marine back-arc basin to Early Devonian terrestrial molasse basin as the Central Qilian Block was sutured to the North China Craton. The detrital framework and geochemical composition of Lower Silurian sedimentary rocks within the North Qilian Belt record the provenance, tectonic setting, and a variety of sedimentary processes that operated during transport from source to sink. The petrological and geochemical characteristics of sandstones, siltstones, and shales in the western segment of the North Qilian Belt indicate a generally low degree of chemical weathering of source area(s) and limited sorting prior to deposition. These characteristics suggest an active tectonic setting. In contrast, samples studied from the eastern part of the North Qilian Belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting. Such characteristics imply a more stable tectonic setting. Geochemical data including Eu/Eu*, Ti/Nb, Th/Sc, and Co/Th ratios suggest contrasting source regions for the western and eastern segments of the North Qilian Belt. Sources in the west included basement rocks of the Central Qilian Block and the North China Craton. In addition, western sources may have included mafic rocks located within the North Qilian arc. In contrast, data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the Central Qilian Block and the North China Craton. Overall, detrital and geochemical data, combined with the regional geology, suggest a foreland basin setting that formed during collision of the Central Qilian Block with the North China Craton.

Grain size distribution and age population of detrital zircons from the Changjiang (Yangtze) River system, China

This study investigated the correlation of the size of detrital zircons with their age populations in a fluvial environment. From 31 floodplain sediments that were isolated from the mainstream and ten major tributaries of the Changjiang River, 3526 detrital zircon grains were selected for size examination, and 1358 were chosen for U–Pb age measurements. The Equivalent Spherical Diameter (ESD) of most zircon grains falls within the range of 32–250μm, and the dominant size is 63–125μm. Small-sized zircons with ESDs of <63μm are found in higher proportions in the mid-lower mainstream than in the upper reaches. An overall decrease in the average ESD size of detrital zircons towards the mid-lower reaches reflects the hydraulic sorting effect of different river flow regimes along this river. Overall, the age populations of zircons between the different tributaries and mainstream are similar, and several age groups correspond well with major tectonic–magmatic events that happened in the river basin. This study confirms the notion that younger zircons have coarser and more variable sizes than the older zircons, indicating the potential influence of hydrodynamic fractionation on zircon size and ages. The problem of grain-size bias on age-data acquisition and interpretation of detrital zircons from large rivers is not negligible and deserves more attention when using zircon geochronology to decipher sediment provenance and tectonic evolution. Although the zircons with an ESD of 63–125μm dominate the Changjiang sediment and have similar age populations as the bulk zircons, whether this narrow-sized window can accurately represent the bulk zircon geochronology of the weathered and heterogeneous rocks in the large catchment awaits additional investigations.

Visualization and analysis of temporal trends of sand infiltration into a gravel bed

Sand infiltration into gravel frameworks affects a wide range of ecological, geomorphic, and engineering processes. Four flume experiments were conducted with tracer materials to examine how a sand pulse infiltrates into a gravel bed. These experiments were primarily designed to test two hypotheses: (1) that vertical gradational trends of interstitial deposits are due to differential transport of finer sand in suspended load (hydraulic sorting) and (2) that the formation of a bridge layer (a thin layer of infiltrated sediments that become lodged in shallow pore throats) precludes subsequent infiltration into a gravel framework. Several sand colors were sequentially introduced into a flume containing a gravel substrate. After the experiments were conducted bed cores were collected and separated into vertical layers including surface layers composed primarily of sand that was transporting as bed load before the experiment was terminated and interstitial deposits in the gravel framework. Sand from each layer was sieved and measured. The color distribution of each grain class of each vertical layer of each core was measured to determine the temporal provenance of the interstitial deposits. Results supported the occurrence of hydraulic sorting. Older (finer) sand particles were disproportionately prevalent in interstitial deposits when compared to bed load samples. The experiments did not support the second hypothesis. Substantial secondary infiltration occurred after the initial formation of a bridge layer. More secondary infiltration was measured for systems with higher d15Gravel/d85Sand ratios and when bed shear was sufficient to mobilize the gravel.

The effects of depositional processes on benthic foraminiferal taphonomy in the Southeastern Yellow Sea of Korea

To understand the role of depositional processes on the distribution of benthic foraminifera, grain size analysis, paleontological statistics and textural analysis were conducted on three piston cores (Core Nos. 3, 7, 9) from the southeastern Yellow Sea of Korea. Two foraminiferal assemblages were defined by cluster analysis. The Cibicides lobatulus-Ammonia ketienziensis assemblage has low P.F/B.F, species diversity and evenness and high number of benthic foram. individuals/20 ml, and is interpreted as representing relict benthic foraminiferal assemblage comprising the upper layer of Core No. 7 and No. 9. The deposit of well sorted alternation layers of muddy sand and sandy mud in Core No. 9. is interpreted as being influenced by hydraulic sorting processes of higher wave and current especially during storm periods. The preservation of 13 Pseudorotalia gaimardii extracted from Core No. 7 confirmed that bed load transport was responsible for its heavily abraded and broken thick-walled tests. The Pseudoparrellan araensis assemblage is a recent benthic foraminiferal assemblage found in the modern homogeneous fine-grained mud facies corresponding to the uppermost part of HMB. It seemed that the apparent sorting phenomena and bed load transport of the benthic foraminifera are the result of turbidity currents which promulgated by rapid tidal currents formed during the last postglacial period in the southeastern Yellow Sea of Korea.

Depositional versus ecological control on the conodont distribution in the Lower Frasnian fore-reef facies, Holy Cross Mountains, Poland

Lithofacies and conodont biofacies of reef-slope deposits of the Wietrznia Beds (Lower Frasnian Palmatolepis transitans Zone) were studied in three measured sections at the Wietrznia quarry (Holy Cross Mts. Poland). The diverse reef-derived grained deposits interrupted the background sedimentation that included lime mudstones, deposited largely at 50 to 90m depths in oxygen-depleted middle slope to toe of slope settings. The mainly storm-controlled proximal gradient is laterally marked by gradual changes from coarse-grained tempestites, represented by flat-pebble conglomerate fabric, to diluted muddy tempestites. The mostly sparse polygnathid and mesotaxid–polygnathid biofacies characterize the hemipelagic facies, whilst polygnathid–ancyrodellid biofacies dominates in the event layers. Three-step taphofacies scheme is proposed, distinguishing settled (parautochthonous), residual (winnowed) and displaced (settled from waning currents and/or transported in sediment-gravity flows) conodont element accumulations. The primary ecological signals are still partly preserved in most of the tempestite-derived assemblages, indicating scarcity of truly residual, lag-like taphofacies. The hydraulic sorting was most effective in the middle-slope setting affected by unidirectional and/or oscillatory flows. Syndepositional mixing was strengthened upslope by an importation of off-reef mesotaxid faunas due to storm surge onto the reef. This reworking pattern as a key factor in biofacies interpretation may be applicable only on a local scale. However, similarly biased conodont signature is probably common in other hurricane-affected carbonate complexes, even if without a disrupting impact on major biofacies belts.

Varietal heavy mineral analysis of sediment provenance, Lower Cretaceous Scotian Basin, eastern Canada

The origin of a major increase in sand supply in the Early Cretaceous of the Scotian Basin, offshore eastern Canada, has been investigated by analysis of heavy mineral varieties. The chemistry of detrital minerals from the Scotian Basin was compared with that of minerals from potential source rocks, sampled from older sedimentary successions, river sands and glacial tills on land. Heavy mineral varieties were established based on > 1000 high quality electron microprobe (EMP) analyses and used to classify heavy mineral types by Mineral Liberation Analysis (MLA), which uses a rapid scanning electron microscope particle analyser. Heavy mineral varieties were compared between the Cretaceous quartz arenites and subarkoses and samples from potential source areas. Different chemical varieties of the same mineral group have different grain size distributions, so that their relative modal abundances may be influenced by hydraulic sorting, but modal abundance of different varieties of tourmaline, garnet and spinel provides useful information. Widely used provenance-sensitive mineral ratios are difficult to interpret because of the abundance of polycyclic sources. Comparisons of the shape parameters of the individual mineral types are also useful for provenance identification. Aspect ratio in elongate grains, such as tourmaline and zircon, is a measure of polycyclic reworking, but is influenced by the initial shapes of minerals from different source rocks. Uniformity of varietal heavy minerals over a large area and stratigraphic range, and the covariance of spinel and zircon with quite different crystalline sources, indicate predominance of polycyclic sources to the Central Scotian Basin, probably principally from Carboniferous and Lower Paleozoic sandstones, in part sourced from western Newfoundland ophiolites. Heavy mineral varieties in the West Scotian Basin can be closely matched to sources in the adjacent Meguma Terrane of the Appalachians. All the data show that the sands of the Scotian Basin were derived from reworking of crystalline basement of the Appalachian orogen and its Paleozoic sandstone cover, uplifted during rifting of Iberia from the Grand Banks. There is no evidence of a significant supply of sand to the Scotian Basin from a proto-St Lawrence River.

Geochemical signatures for the grain size variation in the siliciclastics of Kaimur Group, Vindhyan Supergroup from Markundi ghat, Sonbhadra district, (U.P.), India

The chemical composition of siliciclastics from Mesoproterozoic Kaimur Group, Vindhyan Supergroup have been investigated to determine and appraise the influence of the weathering, hydraulic sorting and recycling processes upon source rock signature. The studies pertaining to the relationship between major, trace and REE and the grain size variation were carried out along Markundi ghat section, Sonbhadra district, Son valley. Upper Kaimur Group has been divided into three principal formations-the uppermost-Dhandraul quartzites, Scarp sandstone and Bijaigarh shales. Petrographically, they range from quartz arenite, sublitharenite, subfeldspathic arenite to pyritiferous shale. The elemental enrichment, except for SiO2, is in the following order-Bijaigarh Shale > Scarp Sandstone ≫ Dhandraul Sandstone.

Geochemical reconstruction of the provenance, weathering and deposition of detrital-dominated sediments in the Perth Basin: The Cretaceous Leederville Formation, south-west Australia

The deep (> 10 km) Permian to present day Perth Basin in southwest Western Australia is composed of sedimentary successions of continental to shallow marine origin. This study examines the compositional variation, weathering and provenance of the early Cretaceous Leederville Formation within the Perth Basin. Over 200 sediment samples were retrieved from two deep boreholes of ~ 350 to 530 m in depth encompassing the Leederville Formation, and analysed for major and trace element geochemistry and mineralogy. The Leederville Formation is composed of subarkosic sands, predominantly composed of quartz (64%) and K-feldspars (27%); silts and clays composed of kaolinite (24–54%), K-feldspars (20–29%) and quartz (18–40%), with their compositional variation reflecting weathering, hydraulic sorting during transport, mostly subaqueous deposition and subsequent diagenesis. Most trace elements are associated with fine grained lithologies due to their occurrence within clays, sulphide or zircon. Major and trace element geochemistry suggests a typical passive margin origin with minimal intrabasinal sediment recycling. The regionally extensive Yilgarn Craton, appears to be the main sediment source for the Leederville Formation within the study area.

Empirical modelling of large scale patterns in river bed surface grain size

The large-scale management of river resources requires an understanding of the spatial distribution of bed surface grain size. According to Sternberg's law, bed surface grain size at basin scales (i.e., 10 2–10 4 km), reduces in the downstream direction. We tested if such patterns were consistent across multiple large basins, and inferred their potential explanatory variables. Specifically , we fitted random forest regression models to mean grain size estimates (Φ units) derived from visual observations on several occasions in 677 stream and river reaches throughout France. Model predictors included the distance from the headwaters, variables describing rainfall, topography and geology of the upstream watershed and the slope of the valley segment on which the reach was located. We made three sets of independent predictions of mean grain size by 1) withholding each observation reach in turn during model-fitting and making a prediction for the withheld reach, 2) withholding reaches in six subsets defined by large drainage basins during model-fitting and making predictions for the withheld reaches in turn and 3) making predictions for 106 hydraulic habitat survey sites where grain size had been measured using protocols that differed from the fitting data. We also evaluated model consistency by fitting it to the six subsets defined by large drainage basins. Regression of the observed ( y) vs. predicted ( x) mean grain size generated from our three sets of independent predictions had r 2 of 52%, 47%, and 38%, respectively; and were unbiased. The characteristic model error, as defined by root mean squared deviation was 2.9 (Φ units), however, the tests indicated that the model uncertainties for the finer size classes were larger. Contrary to expectations, we found consistently weak relationships between mean grain size and distance from the headwaters. The most important contributors to modelled grain size were (consistently across the 6 large basins) watershed slope, segment slope and watershed variables describing rainfall and geological hardness. This suggests that grain size distribution at the scale of multiple basins is mainly governed by patterns associated with sediment sources and hydraulic sorting. Though uncertain at the reach scale, the high generality of our model supports the research of empirical or simplified physically based models of bed surface grain size distribution in multiple basins.

Taphonomy of Late Pleistocene micromammalian fauna of Narmada valley, Central India

Taphonomical investigations of a micromammalian assemblage were undertaken in the vicinity of a prominent Homo erectus site around Jabalpur and Devakachar, Central India. The sediments consist of thin bedded floodplain deposits and the fauna contains micromammalian remains (teeth, jaws, and bones) in addition to numerous fossils of invertebrate genera. The taphonomical investigations were carried out only on the micromammalian remains by studying breakage pattern, digestion, weathering, gnawing marks, and charring traces. The breakage pattern of skeletal elements, intact small bone elements such as tarsals and metatarsals, and higher proportional representation of limb bones suggest that the fossil assemblage was initially accumulated by a predator and had gone through a significant amount of hydraulic sorting as well. Our results, although based on limited fossil material, may provide a baseline for recognition of owls as agents of accumulation of Narmada micromammal fossils.

Controls of heavy minerals and grain size in a holocene regressive barrier (Ilha Comprida, southeastern Brazil)

Ilha Comprida is a regressive barrier island located in southeastern Brazil that was formed essentially by Quaternary sandy sediments. Ilha Comprida sediments were analyzed to assess heavy mineral indices and grain size variables. The spatial variation of heavy minerals and grain size was interpreted in terms of the present barrier dynamics and the barrier’s evolution since the Middle Holocene. These analyses allowed for the identification of the main factors and processes that control the variation of heavy minerals and grain size on the barrier. Rutile and zircon (RZi) and tourmaline and hornblende (THi) are significantly sensitive to provenance and exhibit the contributions of the Ribeira de Iguape River sediments, which reach the coast next to the northeastern end of Ilha Comprida. In addition to the influence of provenance, TZi responds mainly to hydraulic sorting processes. This agrees with a sediment transport pattern characterized by a divergence of two resultant net alongshore drifts southwest of the barrier. The sediments from the Ribeira de Iguape River reach the barrier directly through the river mouth and indirectly after temporary storage in the inner shelf. The combination of grain size and heavy mineral analyses is a reliable method for determining sediment transport patterns and provenance.

Stratigraphy, sedimentology, and taphonomy of the Albertosaurus bonebed (upper Horseshoe Canyon Formation; Maastrichtian), southern Alberta, CanadaThis article is one of a series of papers published in this Special Issue on the theme Albertosaurus.

The Albertosaurus bonebed provides evidence for the mass-mortality of at least 12 Albertosaurus . Albertosaurus, other vertebrates, and trees are concentrated on upper point bar surfaces of a small meandering paleochannel. Throughout the field area, Albertosaurus, other vertebrates, and coalified plants are also preserved patchily in overbank mudstones at the same horizon. Although the bonebed is dominated by Albertosaurus, there are also sparse macrofossil remains of Hypacrosaurus and Albertonykus . The basal lag yields vertebrate microfossils containing at least 19 additional taxa. Freshwater invertebrates are preserved at and below the base of the paleochannel. Large elements are over represented at the site, whereas smaller elements are under represented, suggesting hydraulic sorting. The taphonomic signature of the site suggests that death, disarticulation, and burial took place within one year. We conclude that one or more storms of large intensity downed trees and temporarily drowned the paleolandscape, ultimately killing the tyrannosaurids directly or indirectly. Logs and carcasses were reworked on a point bar during the waning stages of the storm and over subsequent years. Scavenging and breakage of remains by large carnivores was probably inhibited by the mixed log and bone jam. Remains of smaller scavengers (small theropods and snails) are plentiful suggesting these forms were more successful at accessing remains. Juvenile Albertosaurus are under represented at the site suggesting the possibility of age segregation. Because the group of Albertosaurus may have been forced together by rising floodwaters, it is not possible to assess the degree to which the taxon was gregarious from these data alone.