Fluvial Influence Research Articles

Holocene paleoenvironmental reconstructions in western Brittany (Bay of Brest): Part II – A 7 kyr human-environment story with a focus on the Neolithic-Bronze Age transition

The Bay of Brest (BB, NW France) is a semi-enclosed basin of 180 km² subject to macro-tidal dynamics and to the fluvial influences of the rivers Aulne and Elorn, which combined drain watersheds of 2600 km². This coastal environment is subject to natural climate oscillations overlaid on the long-term landscape transformations inherited from the post-glacial sea level rise and increasing anthropogenic forcing since the Neolithic (6.9 ka BP), and especially from the Bronze Age (4.2 ka BP) onwards. The BB therefore appears suitable for the reconstruction of the interactions between climate, environment and human dynamics across the Holocene. In this study, a palynological stack was created based on five cores (including two new cores PALM-KS05 and PALM-KS06 from the Brest harbour), allowing us to discuss vegetation dynamics over the last 7 kyrs. Since the Neolithic period, the forest cover has decreased in favour of open and agro-pastoral landscapes. This trend is not uniform, however: forest cover first declined slowly around 4 ka BP, then strongly decreased at the end of the Iron Age, before experiencing a revival of about five centuries at the end of the Roman period (1.7–1.2 ka BP). Finally, a drastic fall of tree pollen taxa is recorded at the start of the Middle Ages. This study is the first on long-term Holocene trends that allows discussion of both climatic and anthropogenic forcing at an unprecedent average study resolution of 35 years. We also place this local evolution in a wider context to detail interactions between natural and anthropic forcings over the last 7 kyrs BP at a regional-scale and we discuss paleoenvironments and human dynamics thanks to the incorporation of an up-to-date corpus of archaeological data.

Investigating relationships between shoreline process regime, shelf-margin architecture, and deep-water sand delivery: Insights from the early post-rift Hammerhead shelf margin (Bight Basin, southern Australia)

Shelf margins represent a crucial area along source-to-sink systems where sediments are partitioned from the shelf to slope and basin-floor areas. Reconstructing the evolution of these depositional systems is key for interpreting the interplay between past accommodation and sediment supply, and sediment dispersal mechanisms into deep water. In the Bight Basin, on the southern margin of Australia, the Hammerhead shelf margin prograded during the Late Cretaceous following break-up between Australia and Antarctica. This understudied interval offers important insights into source-to-sink processes in a post-rift, greenhouse, high sediment supply setting. A dynamic stratigraphic approach using high-resolution 3D seismic data across the Hammerhead shelf margin has been used to quantitatively characterise 28 clinothems developed over ∼ 1.9 Myrs each with an average duration of ∼ 67,000 years. By applying a shallow-marine process-based classification to shorelines, alongside quantitative analysis of the architecture of their coeval deep-water deposits downdip, statistical relationships and clear links between shallow-marine processes, stratigraphic architecture, and deep-water sand delivery are revealed. A statistically significant relationship between fluvial dominated shorelines, high slope gradients, and mass-transport deposit development is demonstrated, as is a requirement for fluvial influence at the shoreline for the initiation of long run-out turbidite systems. These long run-out turbidite systems are interpreted to have been formed by repeated density flows which lead to greater sediment transfer efficiency and increased sediment supply. This research has direct application to improve prediction of reservoir locations within the Bight Basin for resource exploration and/or carbon sequestration and may also be applied to improve deep-water sediment predictability in other basins worldwide developed in similar tectonic and climatic settings.

Latest Pleistocene-Holocene sedimentary evolution from sediment records of the Tam Giang-Cau Hai coastal lagoon system, central Vietnam

The latest Pleistocene-Holocene sedimentary evolution was reconstructed from two boreholes collected in the Tam Giang-Cau Hai coastal lagoon region of central Vietnam. This research was based on analyzing radiocarbon dating, grain size, sedimentary structure, petrological components, and diatom assemblages. Besides, some high-resolution seismic data from the lagoon water body were interpreted to estimate Holocene sediment thickness. Sedimentary records of two boreholes revealed various sedimentary facies under the sea-level change since the Last Glacial Maximum (LGM): Fluvial channel facies, fluvial-lagoonal transition facies, lagoon facies, lagoonal-to-fluvial facies, and flood plain facies. Radiocarbon dating indicated that the coastal lagoon system possibly initiated around 8.8–8.5 cal kyr BP, corresponding to the meltwater pulse 1 C when saltwater intruded into the lagoon system. The borehole-sediment data combined with the high-resolution seismic data shows the thickness of Holocene sediments is approximately 20–35 m in the lagoon region. The study also suggested that the sandy barrier complex along the coast between the lagoon system and the open sea has been likely built during the transgression since 10–8.8 cal kyr BP. Additionally, five ecological zones were identified based on diatom assemblages in borehole HK02 indicating variations in marine and fluvial influence in the coastal lagoon system during the past 8.8 kyr: Dia-HK02–1 indicates a low presence of diatoms, suggesting a weak marine influence in the coastal lagoon system; Dia-HK02–02 shows the strongest marine influence and stable ecological conditions in the coastal lagoon system; Dia-HK02–03 demonstrates a partial decrease in marine influence; Dia-HK02–4 shows an increasing fluvial influence; and Dia-HK02–5 developed under completely dominated fluvial conditions on land.

Spatial patterns of organic matter content in the surface soil of the salt marshes of the Venice Lagoon (Italy)

Abstract. Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity.

Recent environmental and morphosedimentary evolution of the mining-impacted Nalón Estuary (Asturias, N Spain): Disentangling natural and anthropogenic processes

Distinguishing between natural and anthropogenic processes in sedimentary records from estuaries with legacy pollutants is an essential task, as it provides baselines to predict future environmental trajectories of coastal areas. Here, we have addressed the recent transformation history of the mining-impacted Nalón Estuary (Asturias, N Spain). Surface and core sediment records from marshes and tidal flats were examined through a broad multidisciplinary approach, involving micropaleontological (benthic foraminifera), sedimentological (grain-size), geochemical (trace metals, major element Al and total organic carbon), physical (magnetic susceptibility, frequency-dependent magnetic susceptibility and large microplastics) and radioisotopic (210Pb, 137Cs and 239+240Pu) proxies. Results suggest that the interplay between natural (high fluvial influence and extreme hydrological events) and anthropogenic (coal and mercury mining disposals) factors induced strong sedimentation-erosion processes, further shaping the recent evolution of the estuary. Short-time scale and intense sedimentation processes were revealed by overall high sediment accumulation rates, the dilution of some geological signatures and the rapid formation of a marsh in the lower estuary bay. The increasing mining fingerprints during the 20th century were shortly interrupted by the catastrophic riverine flooding of 1938. Conversely, current erosional processes by fluvial influence led to the remobilization of contaminated sedimentary materials and exposure of mining-legacy Hg levels in tidal flats from the middle sector. Fluvial activity, floodings and taphonomic biases exerted a major control on benthic foraminifera since the 19th century, although Hg ecotoxicological effects on modern assemblages at certain areas within the estuary cannot be discarded. These findings, along with the documented enhanced erosion of marshes with ‘trapped’ pollutants (Hg, coal microparticles and microplastics), highlight the importance of monitoring the environmental and geomorphic processes taking place in historically-contaminated estuaries.

Tectonically induced travertine deposition in the Middle Miocene Levač intramountain basin (Central Serbia)

ABSTRACTTravertines are terrestrial carbonates that are commonly associated with fault activity in extensional and transtensional basins. The faults serve as conduits for the rising and mixing of carbonate‐enriched fluids with thermal and meteoric CO2 inputs promoting travertine precipitation at the surface. Therefore, travertine successions provide key constraint on the faulting, depositional environments, fluid flow and climate. This work focuses on the travertine succession in the Miocene Levač Basin, the marginal basin of the Morava Corridor situated at the junction of the Dinarides and the southernmost Carpathians. Detailed sedimentological, geochronological (U–Pb age, laser ablation – inductively coupled plasma – mass spectrometry) and structural analyses of the travertines are used to reconstruct the evolution of the feeding geoothermal system. Furthermore, these data were used to understand the controlling factors governing alternation of fluid flows enriched in thermally generated and meteoric CO2, and precipitation of travertines in Levač Basin, and finally to elucidate the late stage of basin evolution. Four facies associations are distinguished within the succession, i.e. travertine slope, ridge, flat, and travertine flat under the fluvial influence. The results demonstrated that travertine deposition was controlled by north‐west/south‐west and north‐east/south‐east normal fault arrays. Stable isotope data show positive δ13C values (with δ18O being negative) shifting to negative in the distal and stratigraphically younger deposits implying dilution of deep hydrothermal fluids by mixing with meteoric waters. Finally, travertine deposits yielded a new U–Pb age of ca 14 Ma indicating that the Middle Miocene extensional phase known from other intermountain basins in the Dinarides reached as far east as the Levač Basin and Morava Corridor.

Non-marine ostracod fauna from the Cretaceous Xiagou Formation (Jiuquan Basin, NW China): Taxonomy, biostratigraphy, palaeogeography and palaeoenvironment

The non-marine ostracod fauna of the Xiagou Formation of the Chijinpu Group in the Jiuquan Basin of northwestern China includes Bisulcocypridea astuta, Cypridea koskulensis, C. yumenensis, C. latiovata, C. cf. elegantula, Limnocypridea? diwopuensis, Candona sp., Lycopterocypris debilis, Mongolianella gigantea, Rhinocypris jurassica, Ziziphocypris costata, Alicenula? leguminella, Limnocythere xiagouensis and L. fragilis. Comparison of the Xiagou Formation ostracod fauna with those from Northeast China, Mongolia, Central Asia and Russia indicates that the Xiagou Formation is Aptian in age. The stratigraphic ranges of the Cypridea valdensis–parallela group, R. jurassica and L. fragilis are extended to the Aptian. The known distributions of ostracod taxa—especially the Cypridea valdensis–parallela group, Bisulcocypridea and L. fragilis—in ostracod faunas of Europe, Asia and North America provides evidence that intercontinental and continental ostracod faunal exchanges were active during the Early Cretaceous. Dispersal of these ostracods occurred alongside known dispersal events of non-marine vertebrates between Asia and Europe as well as between Asia and North America, which may imply that large animals (i.e., dinosaurs) played an important role in intercontinental invertebrate faunal interchange. In addition, Aptian palaeolakes/ponds in northwestern China were important in forming isolated environments for the explosive radiation of the superfamilies Cypridoidea and Cytheroidea, and they also provided non-marine habitats for the migration of ostracod species from other continents. The ostracod fauna indicates that the Xiagou Formation represents a fresh to slightly saline shallow to littoral-marginal lacustrine environment with a fluvial influence that may have included shallow temporary waterbodies (e.g., ponds).

At the Sources of the Sacred: Evoking Nature and its Cults by Listening to the Rivers

Zones of fluvial influence, which were the cradles of many human societies both past and present, are key in today’s discourse on how to manage water, culture and heritage in ways that are compatible with sustainable development. Water/river customs have served environmental/cultural practices. This article discusses the interdependence or dissociation between “nature/water” and “culture,” which has forged a more or less strict dualism depending on specific religious frameworks. This dualism can be critically analyzed by sociology, phenomenology and political ecology. The relationship between the reverence accorded to the “sacred” and “nature” and how humans have maintained this respect is however not enough when addressing environmental crises. Could a new approach involve exploiting religious history to restore practical and moral meaning to contemporary challenges, including water-related environmental issues? Very few research programs or development projects really consider transdisciplinary and transcultural perspectives. A suggestion would be to combine the history of science, the comparative history of religious beliefs, the political sciences and cultural studies to define a “global history of religious ecology.” This would aid understanding of the multiplicity of religious conceptions of nature.

Gastrochaenolites as Palaeoenvironmental Information Traps: The Case of the Tholos of La Pastora (Valencina de la Concepción, SW Spain)

ABSTRACT In the Mio-Pliocene calcareous sandstone slabs used as capstones at La Pastora tholos in the Copper Age megasite of Valencina de la Concepción-Castilleja de Guzmán (SW Spain), marine bioerosion structures produced in the 3rd millennium BCE were recognised. In this work, we focus on the perforations made by the lithophage bivalve Petricola lithophaga, called Gastrochaenolites, specifically on its functionality as a ‘trap’ of sediment of the environment where they were produced and of which there are no observable outcrops. The microfaunal content consisting of planktonic and benthic foraminifera as well as ostracods was studied. It was possible to infer the palaeoenvironmental conditions of the place where the slabs were quarried, c. 4700–4600 years ago, which correspond to a wide marine bay. The presence of benthic foraminifera like Astrononium stelligerum, Elphidum crispum, Ammonia beccarii and ostracods like Loxoconcha elliptica and Cytherois fischeri implies that the sector of the bay had a water temperature of no more than 20°C, a bathymetry between 0 and 25 m of depth. Also, episodes of fluvial influence caused a variation in water salinity between 30 and 35‰, attested by the presence of euryhaline species of ostracods from low energy environments and clay substrates, thus confirming estuarine conditions.

A paleo-bioclimatological study on gondwana coal deposits in northwestern Bangladesh and the associated environment reflected by pollen and geochemical analysis

To comprehend the realistic paleo-bioclimate and depositional environment, we need to clearly grasp the methods that can be used to track paleoclimate in the past. The present research has focused on palynological investigation, X-ray Diffraction analysis, and elemental analysis of the core coal samples of the Gondwana coal of the Barapukuria Basin. The palynological study identifies two Palynoassemblage zones (Zone I and Zone II). A non-striate desiccate Scheuringipollenite, Crucisaccites, Parasaccites palynoassemblages are identified as Zone I and denotes as Lower Barakar Palynozone in the Early Permian where Zone II is dominated by striate desiccate Barakarites, Faunipollenites, Callumispora Palynoassemblages in the Late Permian. The Glossopterid plant family ruled the botanical affinity of Zone I and Zone II. It rendered the Gymnosperm group of plants as the rapid deglaciation assisted dissemination of Glossopteris flora. Higher percentages of clay minerals in X-ray diffraction (XRD) analysis and higher amounts of carbon content, lower sulfur, and higher C/S>10 ratio in the elemental analysis have been identified. All evidence from the research suggests that coals were deposited when glaciers retreated in the Early Permian, and the Gymnosperm group of plants prevailed and accumulated in the warm and humid climatic conditions under the braided fluvial influence in the terrestrial environment. J. Asiat. Soc. Bangladesh, Sci. 49(1): 101-119, June 2023

Sedimentological and palynological records since 10 ka BP along a proximal-distal gradient on the Armorican shelf (NW France)

New findings acquired in Armorican shelf (core MD08-3204 CQ: Bay of Quiberon and core VK03-58bis: South Glénan islands) depict Holocene paleoenvironmental changes since 10 ka BP through a multi-proxy dataset including sedimentological and palynological data. First, grain-size analyses and AMS-14C dates show a common sedimentary history for both study cores. The slowdown of the relative sea level (RSL) rise was accompanied by a drop of the sedimentation rates between ∼8.3 and 5.7 ka BP; the rates had been relatively higher at the onset of the Holocene. This interval led to the establishment of a shell-condensed level, identified in core VK03-58bis by the “Turritella layer” and interpreted as a marker for the Maximum Flooding Surface. Palynological data (pollen and dinoflagellate cyst assemblages) acquired in core MD08-3204 CQ argue for an amplification of the fluvial influence since 5.7 ka BP; the establishment of the Highstand System Tract (i.e., mixed marine and fluviatile influences on the platform) then accompanied the slowdown of the RSL rise rates. On the shelf, the amplification of Anthropogenic Pollen Indicators (API) has been better detected since 4.2 ka BP, due not only to the increase of human impact but also due to a stronger fluvial influence on the shelf during the Late Holocene. Palynological data, recorded on the 8.5–8.3 ka BP interval along an inshore-offshore gradient, also demonstrate the complexity of the palynological signals such as i) the fluvial influence that promotes some pollen taxa (Alnus and Corylus) from proximal areas and ii) the macro-regionalization of palynomorph sources in distal cores. In addition, the comparison of palynological tracers, including API, over the last 7 kyrs BP, with South Brittany coastal and mid-shelf sites subject to northern vs. southern Loire catchment areas, shows a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre (SPG) dynamics, combined with recurrent positive North Atlantic Oscillation (NAO) configurations, appear responsible for increased winter precipitation and fluvial discharge over northern Europe, as in Brittany. Conversely, weakened SPG intervals, associated with recurrent negative NAO-like modes, are characterized by intensified winter fluvial discharge over southern Europe. Interestingly, at an infra-orbital timescale, we record major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites subject to detritic-organic matter inputs from Brittany (/Loire) watersheds.

Sedimentary facies and textural characteristics of Cretaceous sandstones in the southern Bida Basin, Nigeria: Implication for reservoir potential and depositional environment

A study of sedimentary facies, mineral and textural characteristics of sections of conglomerates/pebbles and sandstone facies found within the Lokoja and Patti Formations in southern Bida Basin, Nigeria, is carried out to evaluate the paleo-environment and reservoir quality of the sandstones of the formations through field observations and textural and mineralogical (using X-Ray Diffractogram) analyses. Nine lithofacies are identified and grouped into three main facies associations. These sedimentary facies suggest deposition in both foreshore and estuaries. The mineral analysis (XRD) shows that the quartz content in sandstone facies of the Lokoja Formation ranges between 49% and 67%, and that of the Patti Sandstone between 43% and 56%, indicating a quartz dominance. The granulometric studies reveal that the Lokoja Formation comprises coarse-to medium-grained (−0.63 to 1.30 φ) sandstone with moderate-poor sorting of 0.72–1.82 φ. On the other hand, medium to fine-grained sandstones dominate the Patti Formation, which is averagely poorly sorted (1.29–1.54 φ). The sandstones are coarsely skewed to finely skewed, with the kurtosis ranging from very platykurtic to leptokurtic. Morphological results of the pebbles from both Lokoja and Patti Formations indicate that the study areas are mainly characterized by the interplay of both wave and fluvial processes, which suggests that the environment of deposition of sandstone facies is predominantly of the fluvial to the shallow marine environment with the indication of tidal influence.Integrating sedimentary facies and textural results suggests subtidal sand ridge/foreshore, estuarine mudflat, and estuarine delta environments with fluvial influences. Evidence from the textural and mineral characteristics indicate that the sandstone facies of the Lokoja and Patti Formations are fairly matured and can act as potential hydrocarbon reservoirs in the formations. The facies, XRD mineral, and textural results have revealed potential hydrocarbon reservoir areas and paleo-depositional features of the Lokoja and Patti Formations.

Diatom-based paleoenvironmental reconstruction from the coast of Northern Patagonia, Argentina

Estuaries and deltas are common along modern coasts and are well represented in the geologic record because of the high preservation of their deposits. Worldwide, estuaries are more abundant than deltas because of the relatively short time available for Holocene coastal sedimentation due to sea level variations. The evolution of estuaries and deltas during the recent geological past can be reliably reconstructed. Among others, paleostudies in estuaries aim to reconstruct sea level and freshwater input variations, and the timing and frequency of extreme events (e.g., tsunamis). A significant number of studies have been published in the past 20 years, which used preserved remains of microorganisms accumulated during long intervals in sediments. The preserved record of fossil remains evidences the response of microorganisms to environmental changes at the time of their deposition. Among the proxies preserved in sediments, diatoms are one of the most reliable bioindicators to trace environmental changes. Due to rapid reproduction rate under favourable conditions and their siliceous frustule, they are abundant in recent and older sediments from estuaries and deltas. In this manuscript, results from previous studies were reviewed, integrated and statistically analyzed with the aim to reconstruct Holocene coastal changes in relation to sea level curves. These studies were conducted along a latitudinal transect on four estuarine mesotidal systems from Northern Patagonia, Argentina: Colorado River delta (39°40′S; 62°08′W), San Blas Bay (40°33′S; 62°13′W), Negro River (40°57′S; 62°49′W) and Chubut River estuaries (43°22′S; 65°03′W). The focus is on the preserved diatom assemblages and the paleoecological information they represent. Seven coastal sedimentary cores were correlated. Based on multivariate analysis (NMDS), fossil and modern diatom assemblages were integrated and compared. These estuary systems are dominated by littoral drift, where the plains became flooded by the sea about 7000 14C years BP ago. When the sea transgression occupied the area, Colorado delta and San Blas Bay evolved from tidal channels flooded to tidal flats, sand flats and marshes during the late Holocene regression. At Colorado River, the gradually increase of the fluvial influence is associated with the eastward progradation of the deltaic lobe during the last ca. 7000 14C years BP. At the Negro River estuary, a shallow vegetated brackish/freshwater environment evolved into marine conditions, tidal channels and marshes during the last 2000 14C years BP. A marine coastal environment (estuary) at ca. 4400 14C years BP that evolved into a salt marsh was inferred at the inlet of the Chubut River. Diatom salinity-preferences showed how connections between the wetland and the sea varied over time with sea level changes and gradual infilling. Diatom-inferred paleoenvironments and radiocarbon dates allowed reconstruction of the coastline position to the east in the Early Holocene and to the west during transgressive-regressive events.

Channel, dune and sand sheet architectures of a strait-adjacent delta, Rifian Corridor, Morocco

Abstract Sea straits are elongated zones where geographical constriction can amplify marine currents. Sediment deposits that formed in sea straits are relatively well studied and robust models of tidal strait depositional systems have been developed. However, models of strait-adjacent systems remain uncommon. In this study, we present such a model which is based on detailed outcrop descriptions of Miocene deposits that formed adjacent to the Rifian Corridor, an ancient sea strait that existed in what is now northern Morocco. The kilometre-scale outcrops at the Ben Allou locality (30 km north of Fez, Morocco) contain a succession of claystones, siltstones and sandstones that formed under a sea strait-adjacent process regime characterized by marine current constriction, tidal amplification and reduced wave activity. Detailed descriptions of the sandstone's sedimentary architectures reflect a development from mud drape-bearing sand sheets in the proximal regions of the system to stacked cross-strata and channel forms nearer to the basin depocentre. In the deep, distal reaches of this system, sediment grain sizes are generally fine (silt and clay) and are sparsely interbedded with sandy turbidites. These results confirm existing models which show that proximal strait-adjacent deposits tend to be tide dominated, and wave and fluvial influence can be overprinted by tidal processes. Some insights into the formation of tidal dunes are discussed. For example, it is shown that compound tidal dunes may not be preserved differently than simple tidal dunes, which is relevant for predicting sedimentary architectures and fluid flow properties of ancient tide-dominated successions.

Mud lobster Thalassina Latreille, 1806 (Decapoda: Gebiidea: Thalassinidae), its Cenozoic occurrences in Italy and palaeobiogeography

Two specimens of Thalassina sp. are reported from the lower Oligocene sediments cropping out at Salcedo, Italy. Although the material is not sufficiently preserved to be identified below the genus level, it represents an important addition to the known fossil record of the genus. Thalassina sp. from Salcedo is considered the oldest and the only fossil occurrence of the genus from Europe; indeed, the previous reports on Thalassina grandidactylus Robineau Desvoidy, 1849 from the Cretaceous of France and Thalassina sp. from the Pliocene of Italy are disputed herein. Thalassina is today known only from the Indo-West Pacific region; however, unequivocal evidence of Thalassina in the Oligocene strata of Europe suggests the origin of the genus in the west Tethyan (modern circum-Mediterranean area). Alternatively, the geographic distribution of the genus might be wider in the Oligocene than it is today. The Italian material presented herein comes from marine settings with strong fluvial influence, suggesting that the environmental preferences of Thalassina have not changed since the Oligocene.

Distribution, morphology and composition of mesophotic ‘reefs’ on the Amazon Continental Margin

The geomorphology of the Amazon Continental Margin (ACM) is highly heterogeneous and includes a variety of reef-like formations found in deep-water along the shelf-slope transition. The ACM has been divided into three Sectors (Northern, Central and Southern) according to the distribution of the carbonate producers and the ‘reefs’, influenced by the Amazon River plume. Here, we characterize these structures that were sampled with a manned submersible and multibeam surveys to depths of up to 230 m, exploring their relationship with the Amazon river plume and changing sea level following the Last Glacial Maximum (LGM). The shelf-slope transition and a deeper shelf break in the Northern Sector of the Brazilian portion of the ACM carry a series of prominent high-relief structures (HRS) that experience a strong fluvial influence. The tops of these features are between 110 and 165 m depths and seem to have originated during lowstands, through erosion of Pleistocene sandstones. Siliciclastic and carbonate deposits accumulated on the tops of these features in shallow waters during the LGM and early deglaciation and were gradually submerged by rising sea level and subsidence. A thin layer of encrusting organisms, coralline algae, sponges, bryozoans and serpulids presently colonizes most of these surfaces at the sites sampled and contributes to the aggregation of thin fine-grained siliciclastic deposits. The Central Sector, off the river mouth, is associated with long-term sediment accumulation and lacks a shelf break. Nevertheless, living benthic communities occur on rock outcrops. The Southern Sector is less influenced by the river plume and includes a shallower shelf-break and a prominent canyon. The surveyed outcrops of Pleistocene carbonate and siliciclastic rocks at 180 m carry thin covers of a benthic community dominated by sponges and coralline algae, which is responsible for the accumulation of a thin (up to a few centimeters) deposit of carbonate bioclasts, quartz sand and mud on the rocky substrate. Thus, the ‘reefs’ of the outer shelf and mesophotic Amazon margin are typically eroded older rocks, colonized by encrusting organisms during the LGM and deglaciation forming a carbonate veneer, which now support a mesophotic community.

Flora of Ceará State, Brazil: Caryocaraceae, Hypericaceae, and Rhizophoraceae

Abstract We examined the diversity and distribution of Caryocaraceae, Hypericaceae, and Rhizophoraceae in Ceará State, Brazil. Floristic treatments were carried out based on comparative analyses of the morphological characters of specimens from several Brazilian herbaria (ALCB, EAC, HCDAL, HST, HUEFS, HVASF, IAN, MBM, MOSS, SP, UEC and UFMT), the scientific literature, and photographs of type collections. Each family is represented here by a single species. Caryocar coriaceum occurs predominantly in the southern portion of Ceará State in typical open (cerrado) and forested savannas (cerradão). Vismia guianensis is widely distributed and occurs in several vegetation types, but mainly ombrophilous forests and savannas. Rhizophora mangle has a narrow distribution range, being recorded in coastal vegetation with fluvial and/or lacustrine influences (mangrove swamps). All three species were recorded in designated Conservation Areas. An identification key for the species, morphological descriptions, commentaries on their conservation, habitats and phenologies, as well as photographs and illustrations are provided.

Deglacial Land-Ocean Linkages at the Alaskan Continental Margin in the Bering Sea

A marine sediment record from the central Bering Sea, spanning the last 20 thousand years (ka), was studied to unravel the depositional history with regard to terrigenous sediment supply and biogenic sedimentation. Methodic approaches comprised the inference of accumulation rates of siliciclastic and biogenic components, grain-size analysis, and (clay) mineralogy, as well as paleoclimatic modelling. Changes in the depositional history provides insight into land-ocean linkages of paleoenvironmental changes. During the finale of the Last Glacial Maximum, the depositional environment was characterized by hemipelagic background sedimentation. A marked change in the terrigenous sediment provenance during the late Heinrich 1 Stadial (15.7–14.5 ka), indicated by increases in kaolinite and a high glaciofluvial influx of clay, gives evidence of the deglaciation of the Brooks Range in the hinterland of Alaska. This meltwater pulse also stimulated the postglacial onset of biological productivity. Glacial melt implies regional climate warming during a time of widespread cooling on the northern hemisphere. Our simulation experiment with a coupled climate model suggests atmospheric teleconnections to the North Atlantic, with impacts on the dynamics of the Aleutian Low system that gave rise to warmer winters and an early onset of spring during that time. The late deglacial period between 14.5 and 11.0 ka was characterized by enhanced fluvial runoff and biological productivity in the course of climate amelioration, sea-level rise, seasonal sea-ice retreat, and permafrost thaw in the hinterland. The latter processes temporarily stalled during the Younger Dryas stadial (12.9-11.7 ka) and commenced again during the Preboreal (earliest Holocene), after 11.7 ka. High river runoff might have fertilized the Bering Sea and contributed to enhanced upper ocean stratification. Since 11.0 ka, advanced transgression has shifted the coast line and fluvial influence of the Yukon River away from the study site. The opening of the Bering Strait strengthened contour currents along the continental slope, leaving behind winnowed sand-rich sediments through the early to mid-Holocene, with non-deposition occurring since about 6.0 ka.

Origin and distribution of grain-coating and pore-filling chlorite in deltaic sandstones for reservoir quality assessment

Grain-coating chlorite preserves porosity and permeability through the inhibition of quartz cement whereas pore-filling chlorite blocks pore-throats and diminishes reservoir quality. The aim of this study is to determine the origin and principal mechanisms which govern the distribution of grain-coating and pore-filling chlorite in Jurassic deltaic sandstones (Tilje Formation, Smørbukk field, Mid Norwegian Shelf). The study focussed on very high-density sampling for petrographic analysis, from three sections of sandstone core from the same well with contrasting reservoir quality, rather than the low-density sampling approach typically employed. The aim was to gain new understanding of specific controls on porosity and permeability based on core description, core analysis measurements and a suite of petrographic techniques. Results of this study show grain-coating chlorite originated from the thermally-driven recrystallisation of detrital clay coats and/or clay mineral precursors. Pore-filling chlorite has principally derived from the ductile deformation of chlorite-rich Fe-ooids, that were possibly reworked from a proximal evaporitic setting. The distribution of chlorite precursor material, detrital clay coats, and subsequently the distribution of grain-coating and pore-filling chlorite, were controlled by the relative dominance of tidal and fluvial processes active during sediment deposition. Optimum grain-coating chlorite is found in tidal-fluvial sandstones with moderate fluvial influence. Pore-filling chlorite is pervasive in tidal-fluvial channel sandstones deposited during periods of high fluvial discharge, or proximal to the central turbidity maximum zone; marked by an abundance of fluid mud. Tidal channel sandstones with no fluvial influence are pervasively quartz cemented due to an absence of grain-coating chlorite. Grain-coating chlorite and good reservoir quality occurs in heterolithic distributary mouth bar sandstones, however mixing of mud- and sand-prone facies due to intense bioturbation has reduced permeability. Results from this study can be used to predict reservoir quality in the Smørbukk field and in analogous shallow-marine sandstones worldwide.

Holocene vegetation and hydroclimate changes in the Kansk forest steppe, Yenisei River Basin, East Siberia

Our study focuses on the Holocene hydroclimate long‐term trends in southern East Siberia and places them in the context of the adjacent areas of the Siberian taiga in the north and the arid central Asia in the south. We present a new record from the eutrophic mire, in the forest‐steppe region, covering the last 9000 years. Our multi‐proxy approach includes physiochemical (ash content, grain size, micro‐charcoal, peat decomposition) and biological indicators (pollen, non‐pollen palynomorphs, plant macrofossils, testate amoebae, molluscs). The record indicates increased humidity during the Holocene Thermal Maximum at 8150–7400 cal. a BP, and drier conditions with evidence for fires at 7400–5100 cal. a BP. Next, wetter conditions occurred at the coring site at 5100–1400 cal. a BP based on evidence of fluvial influence, which is consistent with other records in the wider region. A short‐term dry episode occurred at 1400–1300 cal. a BP, followed by a wet Medieval Warm Period (1300–650 cal. a BP) and Little Ice Age (450–300 cal. a BP) and a moderately wet environment from 300 cal. a BP to the present day. These results are consistent with the previously published palaeoenvironmental reconstructions from the steppe and forest‐steppe regions in the south of East and West Siberia and taken together reveal a common trend towards wetter conditions with a maximum wetness between 4500 and 3000 cal. a BP. This differs from the taiga region further north and from the Altai‐Sayan Mountains and Kazakhstan Hills further south, which show the trend from dry to wet and then to drier conditions in the Holocene, and from the Trans‐Baikal region where the Holocene trend is to drier conditions. This study supports the predominant influence of the North Atlantic on the regional palaeoclimate changes in the forest‐steppe region of East Siberia during the Holocene.