Fluvial geomorphic elements in modern sedimentary basins and their potential preservation in the rock record : A review

We appreciate very helpful reviews by Dr. Martin Stokes and three anonymous reviewers and editor Dr. Richard Marston. We also appreciate the encouragement for writing this paper from Dr. Timothy Horscroft. We acknowledge support of the sponsors of the Fluvial Systems Research Group consortium, BP, BG, Chevron, ConocoPhillips and Total.

Vertical trends within the prograding Salt Wash distributive fluvial system, SW USA

Peer reviewed

Uranium distribution as a proxy for basin-scale fluid flow in distributive fluvial systems

This work was supported by the Fluvial Systems Research Group sponsors BG Group, BP, Chevron, ConocoPhilips, and Total. We thank reviews from Martin Stokes, an anonymous reviewer and Editor Stuart Jones.

Importance relative des producteurs primaires sur la production globale du lac Saint-Pierre, un grand lac fluvial du Saint-Laurent

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Importance relative des producteurs primaires sur la production globale du lac Saint-Pierre, un grand lac fluvial du Saint-Laurent

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Strontium isotopes and sedimentology of a marine Triassic succession (upper Ladinian) of the westernmost Tethys, Spain

Chemical Stratigraphy, or the study of the variation of chemical elements within sedimentary sequences, has gradually become an experienced tool in the research and correlation of global geologic events. In this paper 87Sr/ 86Sr ratios of the Triassic marine carbonates (Muschelkalk facies) of southeast Iberian Ranges, Iberian Peninsula, are presented and the representative Sr-isotopic curve constructed for the upper Ladinian interval. The studied stratigraphic succession is 102 meters thick, continuous, and well preserved. Previous paleontological data from macro and micro, ammonites, bivalves, foraminifera, conodonts and palynological assemblages, suggest a Fassanian-Longobardian age (Late Ladinian). Although diagenetic minerals are present in small amounts, the elemental data content of bulk carbonate samples, especially Sr contents, show a major variation that probably reflects palaeoenvironmental changes. The 87Sr/86Sr ratios curve shows a rise from 0.707649 near the base of the section to 0.707741 and then declines rapidly to 0.707624, with a final values rise up to 0.70787 in the upper part. The data up to meter 80 in the studied succession is broadly concurrent with 87Sr/86Sr ratios of sequences of similar age and complements these data. Moreover, the sequence stratigraphic framework and its key surfaces, which are difficult to be recognised just based in the facies analysis, are characterised by combining variations of the Ca, Mg, Mn, Sr and CaCO3 contents

Upper-Pleistocene terrace deposits in Mediterranean climate: geomorphological and source-rock control on mineral and geochemical signatures (Betic Cordillera, SE Spain)

Mineral and chemical composition of alluvial Upper-Pleistocene deposits from the Alto Guadalquivir Basin (SE Spain) were studied as a tool to identify sedimentary and geomorphological processes controlling its formation. Sediments located upstream, in the north-eastern sector of the basin, are rich in dolomite, illite, MgO and KB2BO. Downstream, sediments at the sequence base are enriched in calcite, smectite and CaO, whereas the upper sediments have similar features to those from upstream. Elevated rare-earth elements (REE) values can be related to low carbonate content in the sediments and the increase of silicate material produced and concentrated during soil formation processes in the neighbouring source areas. Two mineralogical and geochemical signatures related to different sediment source areas were identified. Basal levels were deposited during a predominantly erosive initial stage, and are mainly composed of calcite and smectite materials enriched in REE coming from Neogene marls and limestones. Then the deposition of the upper levels of the alluvial sequences, made of dolomite and illitic materials depleted in REE coming from the surrounding Sierra de Cazorla area took place during a less erosive later stage of the fluvial system. Such modification was responsible of the change in the mineralogical and geochemical composition of the alluvial sediments.

Incisión fluvial del río Darro durante el periodo 1890-2010 en el sector urbano de Granada (Alambra-Valparaíso, España) determinada a partir de fotografías históricas

En este trabajo se calcula la tasa media de incisión fluvial del río Darro (Granada, España) durante el periodo 1890-2010 en su tramo urbano (sector Alhambra-Valparaíso). Para ello se han utilizado fotografías históricas en las que aparece dicho río, a partir de las cuales se ha podido determinar la posición del cauce en el momento en el que se realizaron las fotografías. La comparación con los escenarios actuales de tales imágenes ha permitido determinar la diferencia de altura del cauce a través de medidas de cotas absolutas realizadas mediante teodolito. Esta metodología ha permitido estimar de modo cuantitativo un índice de encajamiento vertical medio del río de 1,05 cm/año para el periodo histórico considerado.

Geoquímica dos eclogitos do Maciço de Bragança: origem dos "veios dioríticos" e implicações geocronológicas

A análise dos perfis de elementos incompatíveis imóveis em eclogitos do Maciço de Bragança permitiu dividir estas rochas em três grupos (A, B e C). As rochas dos grupos B e C correspondem a eclogitos granulitizados que, frequentemente, contêm veios "dioríticos". Os dados geoquímicos disponíveis revelam que os materiais dos veios e os eclogitos hospedeiros têm concentrações muito semelhantes de elementos incompatíveis "imóveis", enquanto há diferenças significativas no que se refere a elementos móveis. Assim, é improvável que os veios possam representar magmas dioríticos gerados por fusão parcial dos eclogitos hospedeiros. Os veios "dioríticos" são interpretados neste trabalho como produtos de actividade metassomática que afectou os eclogitos; o metassomatismo terá sido induzido por fluidos que terão emanado dos gnaisses encaixantes duranto o metamorfismo prógrado da descompressão. Este episódio metasomático terá causado reajustamentos isotópicos, o que explicaria as contradições aparentes entre os dados geocronológicos obtidos nos eclogitos.

Geoquímica dos filões máficos de Lagoa (Maciço de Morais, Trás-os-Montes, NE Portugal)

No Maciço de Morais, os gnaisses de Lagoa são intruídos por filões máficos, de idade precâmbrica-câmbrica, que cortam um "fabric" metamórfico precoce naqueles gnaisses. Os filões máficos de Lagoa têm características geoquímicas de toleítos continentais e testemunham processos ACF. A actividade magmática em que esses filões se inserem reflecte ascenção astenosférica subsequente ao sobre-espessamento crustal precâmbrico, correspondendo a uma manifestação precoce do regime tectónico/magmático que irá caracterizar, durante o Paleozóico inferior, o ciclo varisco ibérico.

The estuarine geochemical reactivity of Zn isotopes and its relevance for the biomonitoring of anthropogenic Zn and Cd contaminations from metallurgical activities: Example of the Gironde fluvial-estuarine system, France

Zinc stable isotopes measurements by MC-ICP-MS, validated by laboratory intercalibrations, were performed on wild oysters, suspended particles and filtered river/estuarine water samples to provide new constraints for the use of Zn isotopes as environmental tracers. The samples selected were representative of the long range (400 km) transport of metal (Zn, Cd, etc.) contamination from former Zn-refining activities at Decazeville (i.e. δ66Zn > 1 ‰) and its phasing out, recorded during 30 years in wild oysters from the Gironde Estuary mouth (RNO/ROCCH sample bank). The study also addresses additional anthropogenic sources (urban and viticulture) and focuses on geochemical reactivity of Zn in the turbidity gradient and the maximum turbidity zone (MTZ) of the fluvial Gironde Estuary. In this area, dissolved Zn showed a strong removal onto suspended particulate matter (SPM) and progressive enrichment in heavy isotopes with increasing SPM concentrations varying from δ66Zn = -0.02 ‰ at 2 mg/L to +0.90 ‰ at 1310 mg/L. These signatures were attributed to kinetically driven adsorption due to strongly increasing sorption sites in the turbidity gradient and MTZ of the estuary. Oysters from the estuary mouth, contaminated sediments from the Lot River and SPM entering the estuary showed parallel historical evolutions (1979-2010) for Zn/Cd ratios but not for δ66Zn values. Oysters had signatures varying from δ66Zn = 1.43 ‰ in 1983 to 1.18 ‰ in 2010 and were offset by δ66Zn = 0.6 - 0.7 ‰ compared to past (1988) and present SPM from the salinity gradient. Isotopic signatures in river-borne particles entering the Gironde Estuary under contrasting freshwater discharge regimes during 2003-2011 showed similar values (δ66Zn ≈ 0.35 ± 0.03 ‰; 1SD, n=15), i.e. they were neither related to former metal refining activities at least for the past decade nor clearly affected by other anthropogenic sources. Therefore, the Zn isotopic signatures in Gironde oysters reflect the geochemical reactivity of Zn in the estuary rather than signatures of past metallurgical contaminations in the watershed as recorded in contaminated river sediments. The study also shows that the isotopic composition of Zn is strongly fractionated by its geochemical reactivity in the Gironde Estuary, representative of meso-macrotidal estuarine systems.