Estuarine Channel Research Articles

Characterizing the Middle–Upper Miocene Reservoir Intervals of a Producing Field in the Niger Delta Basin: An Application of Facies, Sequence Stratigraphic and Petrophysical Analyses

Well log and core data were used to carry out detailed facies, sequence stratigraphic, and petrophysical analyses of the “Iota field” in the onshore Niger Delta Basin. The aim was to recognize facies distribution, environments of deposition, stratigraphic framework, reservoir continuity, and property distribution for better understanding of reservoir characteristics across the field. Sedimentological evidence reveals the occurrence of fifteen lithofacies, which were further classified into eight facies associations. The facies associations depict deposition in the offshore, offshore transition, lower shoreface, upper shoreface, estuarine channel, tidal channel, and fluvial channel environments. Sequence stratigraphic analysis reveals the occurrence of three maximum flooding surfaces and three sequence boundaries, which reflect series of transgressive and regressive episodes during the Serravallian–Tortonian age. Two depositional sequences comprising lowstand system tract, transgressive system tract, and highstand system tract packages were recognized. The sand and shale of the fluvial, tidal, estuarine, shoreface and offshore deposits, constitute the reservoir and seal/source rock packages. Correlation indicates that the reservoir packages have good lateral continuity, except where channel incision has occurred. Petrophysical analysis shows that the reservoir units have fair-to-good porosity and good- to-excellent net-to-gross qualities. Dominance of oil-bearing zones were detected at shallow to deeper interval at the northern section of the study area, with few gas-bearing intervals occurring at the intermediate intervals of the southern section. Overall, integrated analytical approach has provided more insight into the facies and reservoir quality distribution, thus reducing subsurface reservoir uncertainties.

Nitrogen attenuation, dilution and recycling in the intertidal hyporheic zone of a subtropical estuary

Abstract. Tidal estuarine channels have complex and dynamic interfaces controlled by upland groundwater discharge, waves, tides and channel velocities that also control biogeochemical processes within adjacent sediments. In an Australian subtropical estuary, discharging groundwater with elevated (> 300 mg N L−1) NH4+ and NO3- concentrations had 80 % of the N attenuated at this interface, one of the highest N removal rates (> 100 mmol m−2 day−1) measured for intertidal sediments. The remaining N was also diluted by a factor of 2 or more by mixing with surface water before being discharged to the estuary. Most of the mixing occurred in a hyporheic zone in the upper 50 cm of the channel bed. However, groundwater entering this zone was already partially mixed (12 %–60 %) with surface water via tide-induced circulation. Below the hyporheic zone (50–125 cm below the channel bed), NO3- concentrations declined slightly faster than NH4+ concentrations and δ15NNO3 and δ18ONO3 gradually increased, suggesting a co-occurrence of anammox and denitrification. In the hyporheic zone, δ15NNO3 continued to become enriched (consistent with either denitrification or anammox) but δ18ONO3 became more depleted (indicating some nitrification). A high δ15NNO3 (23 ‰–35 ‰) and a low δ18ONO3 (1.2 ‰–8.2 ‰) in all porewater samples indicated that the original synthetic nitrate pool (industrial NH4NO3; δ15N ∼ 0 ‰; δ18O ∼ 18 ‰–20 ‰) had turned over completely during transport in the aquifer before reaching the channel bed. Whilst porewater NO3- was more δ18O depleted than its synthetic source, porewater δ18OH2O (−3.2 ‰ to −1.8 ‰) was enriched by 1 ‰–4 ‰ relative to rainfall-derived groundwater mixed with seawater. Isotopic fractionation from H2O uptake during the N cycle and H2O production during synthetic NO3- reduction are the probable causes for this δ18OH2O enrichment. Whilst occurring at a smaller spatial scale than tide-induced circulation, hyporheic exchange can provide a similar magnitude of mixing and biogeochemical transformations for groundwater solutes discharging through intertidal zones.

Suspended sediment dynamics in a well-mixed estuary: The role of high suspended sediment concentration (SSC) from the adjacent sea area

Understanding the sediment transport processes, especially the formation and maintenance of the estuarine turbidity maximum (ETM) in estuaries is essential for dealing with harbour siltation and the related estuarine environmental issues. To gain insight into the mechanism of sediment dynamics and ETM formation in the Yongjiang estuary (YE), which is well-mixed and features abundant suspended sediment sourced from the adjacent sea area, field observations were conducted in June 2015. The flow velocity, salinity, and suspended sediment concentration (SSC) were synchronously measured over a 25-h tidal cycle along the YE and its adjacent sea area. Observations showed that there was abundant suspended sediment exchanging between the YE and its adjacent sea area. In particular, there existed an obvious difference in the single or twin peak SSC signals in different stations during a semi-diurnal tidal cycle, especially between the inner-estuary and outer-estuary regions. Detailed analyses on the processes of sediment transport showed that, in the outer sea area, the tidal-driven advection of suspended sediment was dominant to the temporal distribution of SSC, which was featured by a single peak signal in a semi-diurnal tidal cycle. For the estuarine channel, the landward transport of high-concentration suspended sediment by the flood current from the sea region was the major inducement of peak SSC signals in the lower reach of the YE, while the effect of bed sediment resuspension was mainly responsible for the peak signals during the ebb period. Unlike the formation of ETM in highly stratified or partially mixed estuaries, the ETM in the YE, which is located approximately 7 km upstream from the estuary mouth, was mainly controlled by the effect of tidal asymmetry, together with the contributions made by local resuspension of bed sediment and possible fluid mud. Some other possible factors, such as deflocculation, may also impact the formation and maintenance of the ETM in the YE, but further study is needed in the future.

Sedimentological Sectorization Model In An Amazonian Estuary

ABSTRACT Peixoto, H.J.C.; Baia, L.P.; Pereira, D.R.; Rollnic, M., and Monteiro, S.M., 2018. Sedimentological Sectorization Model in an Amazonian Estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 91–95. Coconut Creek (Florida), ISSN 0749-0208. The aim of this study is to check whether a macro tide-dominated Amazonian estuary might be separated in sectors according to recent sediment distribution, considering local hydrodynamics. The case study was conducted in the river Mojuim estuary (−0.72° and −48.00°), situated between the Para River mouth and the Atlantic Ocean, northeastern Para, Brazil. A total of 117 superficial sediment samples were collected using a Van Veen dredge in the lower estuary (16 km). Stations are equidistant and encompass margins and estuarine channel. We performed a sieving granulometric analysis and a calcination analysis of total ...

Impact of Channel Deepening on Tidal and Gravitational Circulation in a Highly Engineered Estuarine Basin

Deepening of estuarine channels is a common practice to ensure navigation. Here, we investigate whether such deepening impacts physical processes such as the strength of the estuarine exchange flow, the horizontal salinity gradient, and tidal dynamics. We analyze recent and historical hydrodynamic observations in Newark Bay, New Jersey, to assess the effect of channel deepening on tides, circulation, and salinity. The Bay’s navigational channel has undergone significant deepening, from 3 to 10 m in the nineteenth century to ~16 m today. Observations presented here include sea-level data from the nineteenth, twentieth, and twenty-first century, and moored Doppler current data and bottom salinity measurements made over the past 20 years. Results show a doubling of the estuarine exchange flow, a slight increase in salinity and in the horizontal salinity gradient, a decrease in tidal current amplitude, and a spatially variable change in the tidal range. The doubling of the exchange flow is consistent with the Hansen and Rattray scaling provided that the horizontal salinity gradient is unable to fully adjust landward because the dredging is limited to a short reach of the estuary. However, uncertainty in channel depth leaves open the possibility that the exchange flow is also augmented by an increase in the horizontal salinity gradient and/or a reduction in vertical mixing. Nevertheless, results demonstrate that a relatively small (15%) increase in depth appears to have doubled the exchange flow. We believe that this result is relevant to other systems where dredging is limited to a short reach of an estuary.

Allogenic and autogenic effects on mangrove dynamics from the Ceará Mirim River, north‐eastern Brazil, during the middle and late Holocene

AbstractIt is possible that climate changes and sea level fluctuations (allogenic processes) are and will cause major changes in mangrove dynamics. However, other driving forces may be significantly affecting this system. Distinguishing allogenic and autogenic influence on mangroves is a challenging question, because mechanisms related to the natural dynamics of depositional environments (autogenic processes) have strong influences on the establishment and degradation of mangroves. Thus, impacts on mangroves caused by autogenic processes may be erroneously attributed to allogenic mechanisms. Therefore, it is imperative to identify the ‘fingerprint’ of global changes in modern mangrove dynamics. In order to characterize the influence of these forces on mangroves, this work has used geomorphology and vegetation maps integrated with sedimentological and palynological data, radiocarbon dating, as well as δ13C, δ15N and C/N from sedimentary organic matter. The inter‐proxy analyses reveal an estuarine influence with mangrove development along the Ceará Mirim River, north‐eastern Brazil, since ~6920 cal yr bp, after the post‐glacial sea level rise. Relative sea level (RSL) has been stable during the middle and late Holocene. Mangrove establishment along this fluvial valley begins at about 6920 cal yr bp, caused by the sea‐level stabilization, an allogenic influence. However, after its establishment, wetland dynamics were mainly controlled by autogenic factors, related to channel migrations, instead of allogenic process. Some influence of sea‐level and climate changes on mangrove dynamics in this estuarine channel have been weakened by more intense tidal channels activities. Therefore, the expansion and contraction of mangrove areas along the estuary of the Ceará Mirim River since 6920 cal yr bp has been mainly influenced by channel dynamics that regulate the accretion and erosion of mangrove substrates. Copyright © 2018 John Wiley & Sons, Ltd.

An analysis on half century morphological changes in the Changjiang Estuary: Spatial variability under natural processes and human intervention

Abstract Examination of large scale, alluvial estuarine morphology and associated time evolution is of particular importance regarding management of channel navigability, ecosystem, etc. In this work, we analyze morphological evolution and changes of the channel-shoal system in the Changjiang Estuary, a river- and tide-controlled coastal plain estuary, based on bathymetric data between 1958 and 2016. We see that its channel-shoal pattern is featured by meandering and bifurcated channels persisting over decades. In the vertical direction, hypsometry curves show that the sand bars and shoals are continuously accreted while the deep channels are eroded, leading to narrower and deeper estuarine channels. Intensive human activities in terms of reclamation, embankment, and dredging play a profound role in controlling the decadal morphological evolution by stabilizing coastlines and narrowing channels. Even though, the present Changjiang Estuary is still a pretty wide and shallow system with channel width-to-depth ratios >1000, much larger than usual fluvial rivers and small estuaries. In-depth analysis suggests that the Changjiang Estuary as a whole exhibited an overall deposition trend over 59 years, i.e., a net deposition volume of 8.3 × 108 m3. Spatially, the pan-South Branch was net eroded by 9.7 × 108 m3 whereas the mouth bar zone was net deposited by 18 × 108 m3, suggesting that the mouth bar zone is a major sediment sink. Over time there is no directional deposition or erosion trend in the interval though riverine sediment supply has decreased by 2/3 since the mid-1980s. We infer that the pan-South Branch is more fluvial-controlled therefore its morphology responds to riverine sediment load reduction fast while the mouth bar zone is more controlled by both river and tides that its morphological response lags to riverine sediment supply changes at a time scale >10 years, which is an issue largely ignored in previous studies. We argue that the time lag effect needs particular consideration in projecting future estuarine morphological changes under a low sediment supply regime and sea-level rise. Overall, the findings in this work can have implications on management of estuarine ecosystem, navigation channel and coastal flooding in general.

Sediment transport and fluid mud layer formation in the macro-tidal Chikugo river estuary during a fortnightly tidal cycle

The erosion and deposition dynamics of fine sediment in a highly turbid estuarine channel were successfully surveyed during the period from August 29 to September 12, 2009 using an echo sounder in combination with a high-resolution acoustic Doppler current profiler. Field measurements were conducted focusing on the tide driven dynamics of suspended sediment concentration (SSC), and fluid mud at the upstream of the macrotidal Chikugo river estuary during semidiurnal and fortnightly tidal cycles. Morphological evolution was observed especially during the spring tide over a period of two weeks. The elevation of the channel bed was stable during neap tide, but it underwent fluctuations when the spring tide occurred owing to the increase in the velocity and shear stress. Two days of time lag were observed between the maximum SSC and peak tidal flow, which resulted in the asymmetry between neap-to-spring and spring-to-neap transitions. During the spring tide, a hysteresis loop was observed between shear stress and SSC, and its direction was different during flood and ebb tides. Although both fine sediments and flocs were dominant during flood tides, only fine sediments were noticed during ebb tides. Hence, the net elevation change in the bed was positive, and sedimentation took place during the semilunar tidal cycle. Finally, a bed of consolidated mud was deposited on the initial bed, and the height of the channel bed increased by 0.9 m during the two-week period. The observed hysteretic effect between shear stress and SSC during the spring tides, and the asymmetrical neap-spring-neap tidal cycle influenced the near-bed sediment dynamics of the channel, and led to the formation of a fluid mud layer at the bottom of the river.

Climate affects fish-kill events in subtropical estuaries of eastern Australia

Fish kills following austral summer flood events (November–March) occur episodically in estuarine channels in Australia. We examined the climatic conditions associated with the historic record of such events in a subtropical region in eastern Australia to determine the effect of antecedent weather conditions on the probability of post-flood fish-kill events. Records, including regional county council logs, newspapers and New South Wales Fisheries annual reports, were analysed for reports of floods and fish kills following these events. Daily rainfall patterns preceding floods with fish-kill events tended to be drier than rainfall patterns preceding floods when a fish kill did not occur. Based on these observations, it is proposed that estuarine hypoxia resulting in a fish kill is increased by prolonged dry periods followed by rapid and intensive rainfall preceding the flood peak. This is most likely due to (i) accumulation of organic material on the floodplain due to vegetation stress and reduced decomposition processes in drier conditions; (ii) upstream migration of the salt wedge, allowing some estuarine fish species to maintain an optimum environment, followed by flooding with (iii) rapid consumption of dissolved oxygen during decomposition of accumulated organic material sourced from senescent vegetation; and (iv) fish becoming trapped upstream in discharging hypoxic floodwater during the flood recession phase.

Estuarine Channel Evolution in Response to Closure of Secondary Basins: An Observational and Morphodynamic Modeling Study of the Western Scheldt Estuary

The fringes of estuaries are often characterized by the presence of side embayments (secondary basins), with dimensions in the order of hundreds of meters to tens of kilometers. The presence of secondary basins significantly alters the hydrodynamic and sediment characteristics in the main estuary, implying that loss of secondary basin area due to human interventions might affect the estuarine morphodynamics. Analysis of historical bathymetric data of the Western Scheldt Estuary (Netherlands) suggests that closure of its secondary basins has triggered the observed lateral displacement of the nearby channels. This analysis motivated investigation of the impact of secondary basins on decadal evolution of estuarine channels, using the numerical model Delft3D. Model results show that channels that form near a secondary basin are located farther away from the bank of the estuary with respect to their positions in the case without a basin. Overall, results in cases with two or three basins are similar to those in case with one single basin. The wider the basin, the farther away the nearby channel forms. Removing a secondary basin causes a lateral displacement of the nearby channel toward the bank, indicating that the observed lateral displacement of channels in the Western Scheldt is triggered by closure of its secondary basins. The physical explanation is that tidal currents in the main estuary are weaker and more rotary near secondary basins, favoring sediment deposition and shoal development at these locations. Model results are particularly relevant for estuaries with moderate to high friction and converging width.

Efecto del dragado de un canal de comunicación al mar (estero) sobre la asociación de peces en la Laguna Larga, Cayo Coco, Cuba

En este trabajo se caracterizaron el hábitat y la comunidad de peces en el canal de comunicación al mar de Laguna Larga, antes y después de un proceso de dragado realizado en el año 2012. Para ello el canal se dividió en cuatro secciones, dos iniciales cercanas al mar y dos finales cercanas a la laguna. Se realizaron 112 censos visuales mediante buceo libre. Para caracterizar el hábitat se midieron el área de refugio, sombra, temperatura del agua, salinidad, profundidad y velocidad de la corriente. Se determinaron la distribución espacio-temporal de los peces, riqueza de especies, densidad y frecuencia relativa en cada sección y se relacionaron con las características del hábitat. Se registraron 22 especies de peces distribuidas en 14 familias. Las especies Abudefduf saxatilis, Halichoeres bivittatus, Stegastes leucostictus y Lutjanus griseus fueron dominantes. Se encontró que las densidades y riquezas de peces en el inicio del canal eran más altas que en el extremo, particularmente la especie Lutjanus griseus, la cual cambió sus preferencias de nichos, desde el final del canal hacia el inicio. Se encontró que las comunidades de peces variaron espacial y temporalmente. El proceso de restauración produjo una disminución en la disponibilidad de refugios y, en consecuencia determinó la disminución de la densidad y riqueza de especies solo en el canal de entrada a la laguna. Los cambios más drásticos en el patrón espacial y temporal de los peces estuvieron asociados a las secciones finales del canal, las cuales sufrieron las mayores alteraciones de hábitat.

Source to sink sandstone-mudstone proportion and facies distribution across a third-order clastic wedge, Cretaceous Western Interior Seaway

The Iles Clastic Wedge is a 500 m thick, 3 My duration, third-order sequence that built out eastward in the Cretaceous Western Interior Seaway. The wedge also contains high-frequency regressive-to-transgressive sequences that are irregularly stacked in a basinward-stepping pattern (lower limb) and in a landward-stepping pattern (upper limb). The entire wedge and the component cycles were analyzed in terms of vertically monitored sandstone-mudstone proportion, thickness, and facies distribution. The measured profiles through the Iles Clastic Wedge form a 300 km long, source-to-sink transect from southeast Rock Springs uplift, Wyoming to Kremmling, Colorado. The sandstone proportion in the entire wedge (and also in the basinward-stepping half of the wedge) attains a maximum in the proximal reaches (fluvial and tidal-fluvial/estuarine channels) of the study transect and decreases unsteadily toward the medial and distal zone. A slight secondary increase in sand proportion also appears irregularly in the medial shoreline zone. On the other hand, the sandstone proportion in the landward-stepping half of the wedge reaches a maximum in the medial (tidal-fluvial and estuarine channels and delta-front) to distal zone (basinal regressive delta) of the wedge and decreases slightly sourceward. Along individual fourth-order sequences, the sandstones and mudstones indicate a more nuanced partitioning, with three marked sandstone maxima (proximal, medial, and distal zones), separated by zones with abundant mudstone. These sandstone peaks are produced by the presence of fluvial and tidal-fluvial/estuarine channel sandstones in the most proximal zone, delta front/shoreface in the medial reaches, and basinal regressive delta front in the distal zone. The mudstone peaks represent the muddy, coal-bearing coastal plain and the prodelta area. This accentuated sandstone and mudstone partitioning at shorter time scales (few 100 Ky) becomes blurred at the longer time scale (3 My) because of the progressive basinward, then landward, offset of successive high-frequency sequences that form the larger clastic wedge.

Impact of intertidal area characteristics on estuarine tidal hydrodynamics: A modelling study for the Scheldt Estuary

Marsh restoration projects are nowadays being implemented as ecosystem-based strategies to reduce flood risks and to restore intertidal habitat along estuaries. Changes in estuarine tidal hydrodynamics are expected along with such intertidal area changes. A validated hydrodynamic model of the Scheldt Estuary is used to gain fundamental insights in the role of intertidal area characteristics on tidal hydrodynamics and tidal asymmetry in particular through several geomorphological scenarios in which intertidal area elevation and location along the estuary is varied. Model results indicate that the location of intertidal areas and their storage volume relative to the local tidal prism determine the intensity and reach along the estuary over which tidal hydrodynamics are affected. Our model results also suggest that intertidal storage areas that are located within the main estuarine channel system, and hence are part of the flow-carrying part of the estuary, may affect tidal hydrodynamics differently than intertidal areas that are side-basins of the main estuarine channel, and hence only contribute little to the flow-carrying cross-section of the estuary. If tidal flats contribute to the channel cross-section and exert frictional effects on the tidal propagation, the elevation of intertidal flats influences the magnitude and direction of tidal asymmetry along estuarine channels. Ebb-dominance is most strongly enhanced if tidal flats are around mean sea level or slightly above. Conversely, flood-dominance is enhanced if the tidal flats are situated low in the tidal frame. For intertidal storage areas at specific locations besides the main channel, flood-dominance in the estuary channel peaks in the vicinity of those areas and generally reduces upstream and downstream compared to a reference scenario. Finally, the model results indicate an along-estuary varying impact on the tidal prism as a result of adding intertidal storage at a specific location. In addition to known effects of tidal prism decrease upstream and tidal prism increase downstream of additional storage areas, our model results indicate a reduction in tidal prism far downstream of intertidal storage areas as a result of a decreasing tidal range. This study may assist estuarine managers in assessing the impact of marsh restoration and managed shoreline realignment projects, as well as with the morphological management of estuaries through dredging and disposal of sediment on intertidal areas.

Stratification and salt-wedge in the Seomjin river estuary under the idealized tidal influence

Advection, straining, and vertical mixing play primary roles in the process of estuarine stratification. Estuaries can be classified as salt-wedge, partially-mixed or well-mixed depending on the vertical density structure determined by the balancing of advection, mixing and straining. In particular, straining plays a major role in the stratification of the estuarine water body along the estuarine channel. Also, the behavior of a salt wedge with a halocline shape in a stratified channel can be controlled by the competition between straining and mixing induced by buoyancy from the riverine source and tidal forcing. The present study uses Finite Volume Coastal Ocean Model (FVCOM) to show that straining and vertical mixing play major roles in controlling along-channel flow and stratification structures in the Seomjin river estuary (SRE) under idealized conditions. The Potential Energy Anomaly (PEA) dynamic equation quantifies the governing processes thereby enabling the determination of the stratification type. By comparing terms in the equation, we examined how the relative strengths of straining and mixing alter the stratification types in the SRE due to changes in river discharge and the depth resulting from dredging activities. SRE under idealized tidal forcing tends to be partially-mixed based on an analysis of the balance between terms and the vertical structure of salinity, and the morphological and hydrological change in SRE results in the shift of stratification type. While the depth affects the mixing, the freshwater discharge mainly controls the straining, and the balance between mixing and straining determines the final state of the stratification in an estuarine channel. As a result, the development and location of a salt wedge along the channel in a partially mixed and highly stratified condition is also determined by the ratio of straining to mixing. Finally, our findings confirm that the contributions of mixing and straining can be assessed by using the conventional non-dimensional parameters with respect to salt-wedge behavior.

A Miocene wave-dominated estuarine system in the Paraíba Basin, northeastern Brazil

A number of publications have documented the effect of the Miocene transgression on several coasts of the world. However, this event is incompletely documented along the Brazilian margin, despite the existence of an impressive record of Miocene deposits exposed mostly as several coastal cliffs along more than 5000 km of distance. The transgressive nature of Miocene deposits, so far recognized only in a few localities of northeastern Brazil, needs to be amplified in order to better characterize the impact of the Miocene transgression in eastern South America. In this work, we provide facies analysis of early/middle Miocene strata exposed in the Paraíba Basin, northeastern Brazil, aiming reconstruct the depositional paleoenvironments and analyze their evolution within the context of relative sea-level fluctuations data. The results revealed deposits characterized by several features that were related to the action of tidal currents, such as alternating thicker/thinner forest packages, abundant reactivation surfaces, mud drapes and oppositely-dipping (herringbone) cross sets. These sedimentary structures were associated with an ichnological assemblage indicative of marine-influenced and brackish water, best represented by Ophiomorpha, Planolites-Palaeophycus-Thalassinoides and Thallassinoides-Planolites-Palaeophycus ichnofabrics. Sedimentation occurred in environments consisting of estuarine channel, estuarine central basin, tidal inlet/tidal channel, tidal delta/washover, tidal flat/shoal and foreshore, which were related to an estuarine setting, at least in part of a wave-dominated type. Analysis of facies stratal patterns led to suggest that the estuarine deposits of the Paraíba Basin reflect a rise in relative sea level probably during the transgressive and/or highstand stage of a depositional sequence formed directly overlying Cretaceous rocks. This rise can be correlated with the worldwide early/mid Miocene marine transgression. However, while the eustatic sea level remained rising through the middle Miocene, the estuarine sedimentation in the study area was cut off, being replaced by a regional unconformity marked by lateritic paleosols. Thus, a relative sea-level fall is recorded in the Paraíba Basin while the eustatic sea level remained rising through the middle Miocene, before its fall in the Tortonian. It follows that other factors, such as tectonics, is proposed to explain the mid-Miocene fall in sea level along the Paraíba coast, while the eustatic sea level was rising.

A new species of Deltamys Thomas, 1917 (Rodentia: Cricetidae) endemic to the southern Brazilian Araucaria Forest and notes on the expanded phylogeographic scenario of D. kempi

Deltamys is a monotypic sigmodontine rodent from the Pampas of South America. In addition to the formally recognized D. kempi that inhabits lowlands, an undescribed form Deltamys sp. 2n=40 was recently found in the highlands of southeastern Brazil. In the present study, we perform a phylogeographic reassessment of Deltamys and describe a third form of the genus, endemic to the Brazilian Araucaria Forest. We describe this new species based on an integrative analysis, using complete cytochrome b DNA sequences, karyology and morphology. Bayesian tree recovered two allopatric clades (lowlands vs. highlands) and three lineages: (i) the lowland D. kempi, (ii) the highland Deltamys sp. 2n=40, and (iii) Deltamys araucaria sp. n. Deltamys araucaria sp. n. is karyotypically (2n=34) and morphologically distinguishable from D. kempi (2n=37-38), showing a tawnier dorsum/flank pelage, presence of a protostyle, M1 alveolus positioned anteriorly to the posterior margin of the zygomatic plate, and several other distinguishing characteristics. A phylogeographic assessment of D. kempi recovered two haplogroups with significant differences in skull measurements. This phylogeographic break seems to have been shaped by the Patos Lagoon estuarine channel. The diversification in Deltamys might have been triggered by dispersal of older lineages over different altitudinal ranges in the Paraná geological basin.

Prevention of infectious complications in predicted severe acute pancreatitis (SAP) – a single center randomized controlled trial

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

From freshwater to fully marine: Exploring animal-substrate interactions along a salinity gradient (Miocene Oficina Formation of Venezuela)

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

Thirty years of scintillating acoustic data in diverse ocean environments, thanks to David Farmer

The acoustic scintillation method was first applied in a coastal tidal channel in the early 1980s by David Farmer and this laid the foundation for studies of estuarine channel flows, bottom boundary layer dynamics, deep-sea hydrothermal plumes, and now more recently hydrocarbon seeps. Over short distances, using high frequencies and high transmission rates, amplitude and phase fluctuations measured over transmitter and receiver arrays have been used to infer horizontal (or vertical) flows and turbulent motions, all averaged along the acoustic path over the range separating transmitters and receivers. Autonomous and cabled instrumentation have provided measurements of temporally and spatially averaged quantities, continuously in time. This ability to make long-term continuous measurements has shown major advances in our understanding of acoustic forward scatter from velocity and temperature fluctuations in moving random media and for identifying strong turbulence levels in a variety of ocean settings. Much of the measurements described here would not have been possible without the generous contributions of David Farmer.

Mineralogical and geochemical characterisation of warm-water, shallow-marine glaucony from the Tertiary of the London Basin

AbstractGlaucony is present in the Palaeocene sediments of the London Basin, from the Thanet Sand Formation to the gravel beds at the base of the Lower Mottled Beds of the Reading Formation. The Upnor Formation glaucony is a rare example of formation in warm, shallow, brackish water and this, combined with the ready availability of fresh material from boreholes, make this study important in developing our understanding of this mineral. Glaucony comprises up to 50% of the Upnor Formation, a grey to green sandstone, of variable thickness and composition, which was deposited in awarm, shallow, marine to estuarine environment, ∼55.6–56.2 Ma. Using morphological criteria, X-ray diffraction data and K+abundance, the Upnor glaucony may be defined as evolved. The underlying shallow marine Thanet Sand contains <5% of nascent to slightly evolved glaucony. The rare earth element (REE) data for the Upnor Formation suggest more than one source for the sediment from which the Upnor glaucony formed, while the ThanetREEdata are consistent with a large detrital clay component.In the Upnor Formation, the large proportion of glaucony that occurs as granule fragments rather than whole granules, and the high-energy estuarine to shallow-marine environment of deposition, are indicative of reworking. The Upnor glaucony is inferred to be intraformationally reworked, rather than derived from the Thanet Sand Formation. The glaucony may have formed in sediments deposited away from the main estuarine channel, and been subsequently reworked into higher-energy sediments.Warm seas with freshwater mixing are more typically characteristic of verdine formation than of glaucony. The shallow, brackish environment of deposition suggests that there is not a clear distinction between the environmental requirements of verdine (or odinite) and glaucony (or glauconite), as is often proposed. The highly fractured, delicate nature of some granules indicates that they have experienced somematurationin situ, after reworking.The oxygen and hydrogen isotopic compositions of Upnor Formation shark teeth and glaucony point to formation in low-salinity water at ∼23 ± 3°C, also consistent with formation in the Upnor Formation, rather than in a fully marine sediment and subsequent reworking. A higher than normal temperature of formation may have increased the rate of evolution of glaucony.Our multidisciplinary study considers many of the factors relating to depositional environment that must be considered when glaucony-rich facies are encountered in comparable palaeo-environmental settings elsewhere in the geological record.