Brackish Conditions Research Articles

EVALUATING GROWTH AND NUTRIENT COMPOSITION OF AFRICAN CATFISH UNDER DIFFERENT SALINITIES

An investigation was carried out to explore the effect of salinity on the growth and flesh quality of African catfish (Clarias gariepinus), a significant species in global aquaculture. Fifty juvenile catfish of weight 24.25±0.4g were collected from the Chenab River in Pakistan and acclimatized in controlled aquaculture conditions at different salinity levels NaCl (T1; 0, T2; 2, T3; 4; T4; 6, and T5; 8 ppt) over 60 days. Growth performance indicators, including final weights, weight gain, growth rate, and feed conversion ratio (FCR), were measured. The statistical result indicated that the fish in lower salinity environments (0-2 ppt) exhibited significant (p < 0.05) final weights, weight gain, and growth rates, with performance declining significantly as salinity increased. The best FCR 1.2±0.01 was indicated at 0 ppt, while the highest salinity (8 ppt) was revealed in the FCR 1.7±0.04. Proximate composition analysis indicated that crude protein and moisture content elevated with salinity while crude fat and ash content decreased. These results suggest that C. gariepinus thrives in slightly brackish conditions, with optimal growth at low salinity levels. However, higher salinities adversely impact physiological health and growth performance.

Biomineralization and biomechanical trade-offs under heterogeneous environments in the eastern oyster Crassostrea virginica

ABSTRACT Accurate biological models are critical to reliably predict vulnerability of marine organisms and ecosystems to rapid environmental changes. Current predictions on the biological impacts of climate change and human-caused disturbances primarily stem from controlled experiments but lack assessments of the mechanisms underlying biotic variations in natural systems, especially for habitat-forming, climate-sensitive species with key ecological roles. This study aimed to characterize and quantify spatial patterns of shell biomineralization and biomechanical properties in a key reef-building oyster, Crassostrea virginica, collected from restored reefs along natural estuarine gradients in the Hudson River Estuary (NY, USA). We characterized patterns of oyster shell deposition, structure, composition and mechanical performance at the macro- and microscale. Eastern oysters show a strong capacity for adjustments in shell biomineralization and biomechanics to maintain shell production and protective functions. We reveal salinity as a key predictor of oyster shell structure, mechanical integrity and resistance to dissolution, and describe the functional role of chalky calcite in shaping shell mechanical performance. Changes in shell production along salinity gradients indicate formation of shells with (1) high mechanical resistance but increased vulnerability to dissolution under marine conditions and (2) lower structural integrity but higher protection from dissolution under brackish conditions. Our work illustrates that biomineralization and biomechanical trade-offs may act as mechanisms in eastern oysters to maintain overall performance under heterogeneous estuarine environments and could represent a cornerstone for calcifying organisms to acclimate and maintain their ecological functions in a rapidly changing climate.

Climatic-hydrologic influence on redox condition in the Cryogenian interglacial Nanhua Basin: Insights from the Datangpo Formation in the northwestern Yangtze Block, South China

Tracking climatic and oceanic redox changes throughout the Neoproterozoic Cryogenian is crucial to a better understanding of the coevolution of life and environment in geological history. However, the processes and driven mechanisms of redox evolution in the Cryogenian interglacial ocean still remain uncertain. Here, we present a combined study of geochemical proxies, such as paleoclimatic proxies (CIA and Zr/Al) and paleosalinity proxies (B/Ga and Sr/Ba), from the interglacial Datangpo Formation in the shallow-water Zuojiawan section exposed in the northwestern Yangtze Block, to constrain climatic and hydrologic changes on redox conditions. Our data indicate that two apparently climatic cycles from warming to cooling occurred during the deposition of the Datangpo Formation, supplementing the monotonous climatic warming in previous research during the Cryogenian interglaciation. The low B/Ga and Sr/Ba ratios throughout Datangpo Formation suggest a continuous freshwater condition, which is in contrast to a transition of marine condition to brackish condition in relatively deep-water sections. Compiled salinity reconstructions at different paleo-depths imply the salinity gradient in the Nanhua Basin with a density stratification like modern Baltic Sea, at least during the early Cryogenian interglacial period. We find that the climate-driven local riverine freshwater input may be a significant driver for maintaining long-term freshwater condition in the Zuojiawan section. Accompanied by synchronously climatic warming, the progressive desalinization with declining B/Ga and Sr/Ba ratios in the middle to upper deposition of the Datangpo Formation are probably attributed to the persistent freshwater input to a nearshore shallow-water paleogeographic setting. Combined the improving oceanic oxygenation backdrop with the elevating seawater sulfate concentration in the Nanhua Basin in this period, we conclude that the continuous dilution of seawater in the restrict (semi-) Nanhua Basin could attenuate the density stratification and enhance the vertical mixing of watermass, favoring the ventilation of deepwater and penetration of sulfate. This contribution provides a new insight for the study of salinity changes on redox conditions in the Yangtze Block during the Cryogenian interglacial period, and provides new data for supporting a systematic understanding of the evolutional mechanism of oceanic redox state.

Reconstructing the South American Miocene puzzle: An integrated analysis of the Paraná Formation (Argentina)

In recent decades, Miocene marine transgressions in South America have sparked ongoing debates concerning their boundaries, number of events, regional connectivity, and the existence of an epicontinental sea formed during the Andean orogeny. The bed-by-bed analysis of the Late Miocene Paraná Formation deposits in Entre Ríos Province (Argentina) allow defining six facies associations: (i) beach ridge, (ii) tidal inlet channel and washover fan, (iii) outer estuarine bioherms, (iv) central estuary, (v) tidal bar and sandflat, and (vi) tidal mudflat and creek deposits. Architectural and stacking pattern analyses reveal transgressive-regressive sequences typical of the coastal strip, encompassing shallow marine to estuarine sub-environments. The analysis identified diverse ecological guilds, including bivalve and gastropod assemblages in bioherms, and crustacean traces in tidal flats. Regressive units are characterized by wave-dominated shoreface deposits, while transgressive units comprise fine-grained estuarine deposits interbedded with bioclastic sandstones and storm deposits. The paleoenvironmental and paleoecological data indicate normal salinity marine environments with macroinvertebrates and estuarine components and suggesting tropical brackish conditions. Plant remains point to a range of vegetative communities, including mangroves, palm forests, grasslands, humid riparian forests, and dry upland forests, reflecting tropical to subtropical and humid to semiarid environments. This study concludes that the Paraná Formation correspond to a third-order transgressive system tract influenced by the Miocene Paranaense Sea. The basin-scale implications suggest that the distal Chaco-Paraná basin was affected by eustatic changes due to its low accommodation and topographic relief. The Chaco-Paraná foreland basin's evolution was driven by interactions between tectonic, climatic, and eustatic processes. The comprehensive analysis of sedimentary and fossil records provides a detailed paleogeographic reconstruction of the Miocene marine transgression in southern South America.

Paleosedimentary environmental reconstruction and mechanisms of the response to the Toarcian OAE in a lacustrine shale system

The Lower Jurassic Ziliujing Formation in China’s Sichuan Basin is a significant shale target for exploration; however, the strong heterogeneity of the properties of organic matter (OM) in shale makes it challenging to identify the target area for exploration, and the mechanism of OM enrichment is still unclear. Furthermore, the mechanisms of the response of the Da’anzhai member to the Toarcian Oceanic Anoxic Event (T-OAE) are controversial. Previous studies have focused on sedimentary facies analysis based on mineralogy and elemental abundances and have provided minimal information about organic geochemistry, which adds to the challenge of deeply understanding the influence of the T-OAE on the molecular geochemical characteristics of the Da’anzhai member. In this study, the Da’anzhai member of the Lower Jurassic Ziliujing Formation in the Langzhong area, Sichuan Basin, is studied via X-ray diffraction, total organic carbon, gas chromatography–mass spectrometry, organic carbon isotope, organic petrographical and pyrolysis analyses. To accurately identify the trend of the paleosedimentary environmental proxies, the Mann‒Kendall test is utilized to identify the trend of the data. Our results show that the Da’anzhai shale was deposited in a dysoxic transitional environment to an intermittent reducing environment with freshwater to brackish conditions. The response to the T-OAE can be identified in the middle and upper parts of the middle submember and the bottom of the upper submember of the Da’anzhai member. The T-OAE influenced the redox conditions, salinity, and OM origins during deposition in the middle of the Da’anzhai member, which resulted in the enrichment of OM. The abnormally high C30 diahopane/C30 hopane (C30D/C30H) ratio can be considered a potential proxy for locating the section of strata that responded to the T-OAE in the Da’anzhai member. In the study area, the mechanism of the response of the Da’anzhai shale to the T-OAE manifested as an improvement in hydrological cycling rather than a marine incursion. Our study provides new information that deepens the understanding of the mechanisms of the response of lacustrine shales to oceanic anoxic events from the perspective of molecular organic geochemistry.

Groundwater in the coastal areas of Ghana: Quality and associated health risks

Self-supply water sources, particularly groundwater sources, play key roles in the water supply ecosystem of developing countries. Recent studies indicate that groundwater sources in coastal communities in Ghana are under threat from improper waste management practices, seawater intrusion and atmospheric aerosol deposition. In this study, Water Quality Index (WQI) and Nemerow's Pollution Index (NPI) were employed to assess groundwater quality in four coastal communities of Ghana. The health risks associated with metal pollution of groundwater were investigated using incremental life cancer risk and hazard quotient. pH of groundwater in all the studied communities were acidic during the rainy season. Electrical conductivity ranged from 0.44 to 2.61 mS/cm in the rainy season and from 0.43 to 2.45 mS/cm in the dry season for the four studied locations. Results also showed brackish conditions and mineralization of groundwater in Winneba, Accra, and Keta. Mean nitrate concentrations in Winneba and Accra were higher than the WHO standards for both the rainy and the dry season. Arsenic was higher than the acceptable level in Accra and Keta during the dry season, while iron was higher than the acceptable levels in Accra in both the rainy and dry seasons. Principal Component Analyses showed that Pb, As, and Fe had the highest loading in the first component in Essiama, while PO43-and Pb had the highest loading in the second component in Accra. WQI showed that the quality of groundwater in all the studied communities ranged from marginal to poor indicating that groundwater in the coastal communities often or usually departs from desirable quality. NPI revealed that NO3- , As, and Fe contribute to groundwater deterioration. Health risk assessment showed that As posed a high cancer risk in Accra and potential cancer risk in Essiama, Winneba, and Keta during the dry season. As also posed potential cancer risk in Accra during the rainy season. Non-cancer health risk was observed for As in Accra and Keta. The findings of this study suggest urgent regulations and monitoring strategies to improve groundwater quality in the coastal communities of Ghana.

Mid-Holocene marine faunas from the Bangkok Clay deposits in Nakhon Nayok, the Central Plain of Thailand.

Based on several field investigations, many molluscan shells and chondrichthyan teeth, together with other invertebrate and actinopterygian remains were found from the marine Bangkok Clay deposits in Ongkharak, Nakhon Nayok, at a depth of ~ 5-7 m below the topsoil surface. Animal macrofossils recovered from these Holocene marine deposits were identified and their chronological context was investigated in order to reconstruct the paleoenvironments of the area at that time. The majority of marine fossils recovered from the site consist of molluscs, with a total of 63 species identified. Other invertebrate species include a stony coral, a mud lobster, barnacles, and a sea urchin. The vertebrates are represented by fish remains, including carcharhinid shark teeth from at least nine species, stingray and trichiurid teeth, and one sciaenid otolith. The molluscan fauna indicates that the paleoenvironments of the area corresponded to intertidal to sublittoral zones, where some areas were mangrove forests and intertidal mudflats. The fish fauna is dominated by the river shark Glyphis, indicating freshwater influences and possibly occasional brackish conditions. The carbon-14 analysis of mollusc and charcoal remains shows that deposition of the marine sediment sequence began during the mid-Holocene, spanning approximately from 8,800 to 5,300 cal yr BP. This study provides in-depth insights into the diversity of fishes, marine molluscs, and other invertebrates from the Bangkok Clay deposits, supporting the existence of a marine transgression onto the Lower Central Plain of Thailand during the mid-Holocene.

Characterization of a novel root-associated diazotrophic rare PGPR taxa, Aquabacter pokkalii sp. nov., isolated from pokkali rice: new insights into the plant-associated lifestyle and brackish adaptation

Salinity impacts crop growth and productivity and lowers the activities of rhizosphere microbiota. The identification and utilization of habitat-specific salinity-adapted plant growth-promoting rhizobacteria (PGPR) are considered alternative strategies to improve the growth and yields of crops in salinity-affected coastal agricultural fields. In this study, we characterize strain L1I39T, the first Aquabacter species with PGPR traits isolated from a salt-tolerant pokkali rice cultivated in brackish environments. L1I39T is positive for 1-aminocyclopropane-1-carboxylate deaminase activity and nitrogen fixation and can promote pokkali rice growth by supplying fixed nitrogen under a nitrogen-deficient seawater condition. Importantly, enhanced plant growth and efficient root colonization were evident in L1I39T-inoculated plants grown under 20% seawater but not in zero-seawater conditions, identifying brackish conditions as a key local environmental factor critical for L1I39T-pokkali rice symbiosis. Detailed physiological studies revealed that L1I39T is well-adapted to brackish environments. In-depth genome analysis of L1I39T identified multiple gene systems contributing to its plant-associated lifestyle and brackish adaptations. The 16S rRNA-based metagenomic study identified L1I39T as an important rare PGPR taxon. Based on the polyphasic taxonomy analysis, we established strain L1I39T as a novel Aquabacter species and proposed Aquabacter pokkalii sp nov. Overall, this study provides a better understanding of a marine-adapted PGPR strain L1I39T that may perform a substantial role in host growth and health in nitrogen-poor brackish environments.

Climatic controls on water-mass chemistry in a Paleocene lacustrine setting, Subei Basin, eastern China

The Paleocene epoch was characterized by global climate fluctuations and major carbon-cycle perturbations. During the greenhouse climate that characterized the early Cenozoic, a short-lived late Paleocene global cooling event has been recognized from marine records. However, the response of the terrestrial system to this climate cooling event is poorly understood. Here, we present major- and trace-element analyses, iron speciation systematics, carbonate carbon isotope data, and mineralogical observations from lacustrine sediments in Member II of the Paleocene Funing Formation (E1f2), utilizing well-preserved drill core from the Subei Basin, eastern China. Both chemical (chemical index of alteration [CIA], Al/K ratios) and mineralogical (mineralogical index of alteration, clay/feldspar ratios) proxies yield consistent weathering and paleoclimatic interpretations, suggesting a transition from cool and arid climatic conditions to warmer and more humid climatic conditions. Correlation of carbon isotopes between the Subei Basin and deep-sea records implies that this terrestrial setting records the short-lived Paleocene climate cooling event. The combination of climate records and paleosalinity proxies (B/Ga and S/total organic carbon [TOC]) indicates a relatively high-salinity water column (brackish to saline) under cool and arid climatic conditions in the Subei Basin, suggesting that elevated salinity was likely produced via net-evaporative conditions, rather than marine incursions. A shift toward less saline brackish conditions up section reflects an increase in precipitation and freshwater runoff under warmer and more humid climatic conditions. Iron speciation and redox-sensitive trace-metal systematics reveal fluctuating redox conditions, from oxic through to anoxic ferruginous, but with the distinct development of better ventilated conditions as freshwater inputs increased under more humid conditions. Our findings demonstrate the sensitivity of terrestrial climate to the late Paleocene climate cooling event and further reveal the chemical response of a lacustrine setting to a cooling episode in a greenhouse world.

Foraminiferal and Palynological Records of an Abrupt Environmental Change at the Badenian/Sarmatian Boundary (Middle Miocene): A Case Study in Northeastern Central Paratethys

The Badenian/Sarmatian boundary in the Central Paratethyan basins is characterised by a change from open marine conditions during the late Badenian to the assumed brackish conditions during the early Sarmatian. The foraminiferal and palynological results of the Badenian/Sarmatian boundary interval in the Babczyn 2 borehole (in SE Poland) showed that the studied interval accumulated under variable, unstable sedimentary conditions. The Badenian/Sarmatian boundary, as correlated with a sudden extinction of stenohaline foraminifera, is interpreted as being due to the shallowing of the basin. The lack of foraminifera and marine palynomorphs just above the Badenian/Sarmatian boundary can reflect short-term anoxia. The composition of the euryhaline assemblages, characteristic for the lower Sarmatian part of the studied succession, indicates from marine to hypersaline conditions.

Heavy Metals Bioaccumulation in Mytilus galloprovincialis and Tapes decussatus from Faro Lake (Messina), Italy.

The aim of this study was to evaluate the potential bioaccumulation of arsenic (As), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb) and mercury (Hg) in the haemolymph and corpus of Mytilus galloprovincialis and Tapes decussatus from Lake Faro. The lake is particularly prone to the accumulation of substances that are potentially toxic to aquatic organisms, due to the input of pollutants from urban and agricultural sources and the low rate of water exchange. The combination of saltwater from the Tyrrhenian Sea, the Strait of Messina and freshwater from hilly aquifers has created brackish conditions in the lake, resulting in an area of high commercial shellfish productivity. As, Cd, Cu, Pb and Zn were determined using a single quadrupole inductively coupled plasma mass spectrometer; Hg was determined using a direct mercury analyser (DMA-80). Physicochemical parameters of the water from Lake Faro were also performed. Statistical analysis was carried out using GraphPad Prism 9.0 (GraphPad Software, Inc., Boston, MA, USA) and Shapiro-Wilk normality was applied. Concentrations of Cd, Hg and Pb below the permitted MRLs in Mytilus galloprovincialis and Tapes decussatus used as ''biological indicators'' show that Lake Faro is not at risk of contamination by these pollutants and, moreover, is free of health problems for the consumer based on regulatory limits.

A new species of lamprey from Cretaceous semisaline environment in China

ABSTRACT A new fossil species of lamprey, Caeruleum gracilis sp. nov. is described from the Early Cretaceous Jiufotang Formation in China Hebei province, North China. Caeruleum gracilis sp. nov. is characterised by a slender body shape and a dorsal fin originating above the second branchial pouch. Given the intricate life history of lampreys, their presence in saltwater and freshwater, and their convoluted and ambiguous evolutionary trajectory, it is imperative to investigate whether the living environment of fossil lamprey species encompassed varying levels of salinity. This inquiry will facilitate our understanding and tracing of the earliest adaptations of lampreys to freshwater and saltwater environments. Based on salinity analysis, the environment of the Jiufotang Formation may be attributed to brackish conditions. Therefore, the lampreys Caeruleum gracilis sp. nov. and Caeruleum miraculum from the Jiufotang Formation may represent the one of earliest lampreys records that acquired adaptations to freshwater environments.

Reshaping the understanding of the paratethys using paleogeographic reconstructions and geochronology studies

The history of the Paratethys and its inhabiting organisms was profoundly influenced by its connections with the Global Ocean. As the sea?straits linking Paratethys with the ocean expanded, they integrated the Paratethys with the global ocean, causing its water level to mirror the global eustatic fluctuations. These intervals of increased ocean connectivity existed during most part of the Oligocene?Early Miocene, in the Early Badenian?Tarkhanian, and in the Late Badenian?Konkian, when also fostered favourable environments for marine life to flourish in the Paratethys. When the marine connections became unstable and the sea?straits closed (e.g., in the second half of Rupelian?Solenovian time, late Ottnangian?Kozakhurian, middle Badenian?Karaganian and from the onset of the Sarmatian up to the Pliocene), transformed into vast lacustrine waterbodies where water levels and salinities were controlled by the balance between river runoff and precipitation versus evaporation. Excess of water led to the basin expansion and brackish conditions, while deficits caused contraction and fragmentation. This resulted in hypersaline basins and lagoons co?existing with freshwater lakes, creating diverse environments and faunas that hindered effective biostratigraphic correlations. These fluctuations caused the decline of the marine biota, leaving behind only euribiontic organisms capable of enduring drastic shifts in salinity, ion composition, and oxygen levels. Over time, these survivors diversified and gave rise to endemic faunal communities adapted to the brackish environments. The history of the faunistic and phytoplankton composition of the Carpathian part of the basin (Central Paratethys) became noticeably different from the Euxine?Caspian ones from the beginning of the Neogene, which led to different stratigraphic schemes of these parts of the Paratethys. In recent decades, our focus has centred on refining our understanding of the Eastern Paratethys paleogeography. While the periods of high base levels in the Eastern Paratethys are well?documented, the significant base?level drops during isolation phases have often been overlooked. This was primarily because, until recently, there were no effective methods for reconstructing the paleogeography and geo ? chronology of Paratethys during these episodes of base?level drops. However, with the advancements in seismic stratigraphy and the utilization of integrated magneto?bio?stratigraphy, we now possess the means to explore the scale and spatial distribution of paleogeographic changes, particularly during the substantial basin reductions in partial desiccation periods. Large regressions (during second part of the Rupelian, terminal Tarkhanian, and Sarmatian in the Eastern Paratethys and during early Pliocene in the Caspian basin) erode parts of sedimentary layers, forming surfaces of inconsistency between geological bodies accumulated before and after the sea?level drop, which can be traced on seismic profiles as erosion boundaries. By deciphering such surfaces and the depth of river incisions flowing into the basin, it is now possible to reconstruct the relief picture resulting from these erosions and quantify the depth of baselevel drops in the Paratethys during the largest regressions.

Ineffective artificial mouth-breaching practices and altered hydrology confound eutrophic symptoms in a temporarily closed estuary

Context Artificial breaching of intermittently closed estuaries has become more frequent in the face of global-change pressures. Aims This study aimed to determine whether the ecological health of the Great Brak Estuary has been affected by the prolonged loss of marine connectivity arising from below-average inflow and failed breaching attempts. Methods We characterised primary eutrophic symptoms (inorganic nutrients, dissolved oxygen, microalgae) typical of the various mouth states, i.e. open, closed and semi-closed. Key results Initially, low inflow and closed mouth conditions facilitated the widespread occurrence of macroalgal blooms (Cladophora glomerata). Phytoplankton bloom conditions (>20 μg Chl-a L−1) ensued only in response to favourable hydrodynamic conditions (e.g. increased water residency, halocline formation) and increased nutrient availability from fluvial sources and macroalgal dieback. These blooms occurred in brackish conditions and comprised numerous taxa, including Cyclotella atomus var. marina, Cryptomonas sp. and Prorocentrum cordatum. Widespread hypoxia (<2 mg L−1) occurred during the semi-closed mouth phase because of the reduced flushing potential associated with the preceding high flow conditions. Conclusions Global-change pressures and ineffective breaching practices will promote eutrophic conditions in intermittently closed estuaries in the future. Implications Allocating sufficient environmental flows is key to preventing ecosystem degradation.

Holocene climate and catchment change inferred from the geochemistry of Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia

We present a continuous ∼7000-year sedimentary record from Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia, a region heavily impacted by drought and bushfires in recent decades. Records such as this are vital to contextualise current climatic and environmental shifts, particularly regarding the interplay between hydroclimate and fire-related disturbances in this ecologically sensitive area. We use high-resolution μX-ray fluorescence core scanning, complemented by bulk organic geochemistry and X-ray diffraction mineralogy of catchment soil and lake sediments to reconstruct past climate and catchment processes. Phases of elevated sediment organic matter content (inferred from high Br and total organic carbon) suggest increased lake freshening and productivity, and coincide with increased chemical weathering (inferred from high Al/K and kaolinite/illite and feldspars), likely reflecting the influence of wetter climates. Conversely, periods of high Ca correlate with biogenic carbonate inputs typical of brackish conditions, which we attribute to drier climates or a marine influence. From 7.0 ka, at the mid-Holocene sea level highstand, until 5.7 ka, we suspect Lashmars Lagoon was under virtually continuous influence from the sea. At 5.7 ka, we interpret the abrupt increase in sediment total organic carbon to reflect the severance of the connection to the sea, allowing organic material to accumulate. This, coupled with evidence of high inferred chemical weathering, suggests the climate was relatively wet at the time. After 5.4 ka, our data point to the establishment of drier conditions until the commencement of wetter climates again at 4.5 ka. From 2.5 ka, however, drier climates prevailed again until present. Notably, the climate changes recorded in the sedimentary sequence at Lashmars Lagoon seem to be linked to the strength of the Leeuwin Current, a current that brings warm tropical waters to southern Australia and demonstrates a teleconnection with the El Niño Southern Oscillation, and may well have been an important driver of rainfall on Kangaroo Island (Karti/Karta) over the past ∼7000 years.

Sediment Record of the Earliest Stage of the Evolution of Lake Kanozero (Sw Kola Peninsula): New Data for Regional Deglaciation Reconstructions and Relative Sea-Level Studies

The multi-proxy study of the lowermost part of the sediment sequence of Lake Kanozero (south-western part of the Kola Peninsula, ca. 53 m a.s.l.) revealed the evidences for marine waters penetration into the basin during the earliest stage of its evolution. The diatom analysis inferred the conditions of a large brackish-water basin. Sediments composition and very low organic content also supported large-basin and low-productivity environments. Based on the pollen study, this stage covers a cooling period preceding the Allerød (tentatively assigned to the Older Dryas) and the onset of the Allerød. Periglacial vegetation typical of the cold and dry climate prevailed in the area for the most of the period. The subsequent transition to the freshwater conditions inferred from the diatom study took place in the Allerød, according to the pollen data. Except for a minor decrease in the fine sand fraction, no other corresponding changes were observed in the sediment record suggesting no major shifts in sedimentary environments. In the late Allerød and throughout the Younger Dryas, Lake Kanozero remained a large, low-productive freshwater basin. Our results indicate that ice-free conditions with aquatic sedimentation in the Kanozero depression had already existed in the Older Dryas. This assumes earlier deglaciation of the study area than it was previously thought. The study also suggests that brackish conditions in the White Sea basin established earlier than reported before. While the previous studies found no signals of marine transgression above ca. 41 m a.s.l., our results indicate that the local marine limit in the study area exceeds ca. 53 m a.s.l.

Anaerobic methanotrophy is stimulated by graphene oxide in a brackish urban canal sediment.

Anthropogenic activities are influencing aquatic environments through increased chemical pollution and thus are greatly affecting the biogeochemical cycling of elements. This has increased greenhouse gas emissions, particularly methane, from lakes, wetlands, and canals. Most of the methane produced in anoxic sediments is converted into carbon dioxide by methanotrophs before it reaches the atmosphere. Anaerobic oxidation of methane requires an electron acceptor such as sulphate, nitrate, or metal oxides. Here, we explore the anaerobic methanotrophy in sediments of three urban canals in Amsterdam, covering a gradient from freshwater to brackish conditions. Biogeochemical analysis showed the presence of a shallow sulphate-methane transition zone in sediments of the most brackish canal, suggesting that sulphate could be a relevant electron acceptor for anaerobic methanotrophy in this setting. However, sediment incubations amended with sulphate or iron oxides (ferrihydrite) did not lead to detectable rates of methanotrophy. Despite the presence of known nitrate-dependent anaerobic methanotrophs (Methanoperedenaceae), no nitrate-driven methanotrophy was observed in any of the investigated sediments either. Interestingly, graphene oxide stimulated anaerobic methanotrophy in incubations of brackish canal sediment, possibly catalysed by anaerobic methanotrophs of the ANME-2a/b clade. We propose that natural organic matter serving as electron acceptor drives anaerobic methanotrophy in brackish sediments.

Calibration of redox thresholds in black shale: Insight from a stratified Mississippian basin with warm saline bottom waters

Depositional models for black shale formation rely on a detailed understanding of redox conditions and how they relate to basin development. Here, we calibrate multiple redox proxies (Fe speciation, U and Mo systematics, and pyrite framboid distributions) in the Bowland Shale, a major hydrocarbon unit in the Mississippian basin of northern England, and develop a depositional model for black shale deposition in basins adjacent to extensive carbonate platforms. The transition from deep ramp carbonates to basinal mudrocks initially occurred under oxic conditions before anoxic conditions began to expand from basin-center locations. By the end of Bowland Shale deposition, ∼10 m.y. later, black shale deposition extended from the basin, where platform-edge carbonates were deposited, into shallow-water settings. By this stage, euxinic conditions were widespread throughout the Bowland Shale. The prolonged persistence of euxinia during younger Bowland Shale deposition, and the sharp transition to fully oxygenated facies at the basin margin, suggest there was a well-developed water-column pycnocline. Black shale development in silled basins is traditionally interpreted to form beneath a halocline with a positive water balance caused by freshwater run-off (estuarine circulation). This model is not considered appropriate in this case. Bowland Shale deposition was terminated by the onset of turbidite deposition supplied by a major deltaic system; but for most of its history, the basin was surrounded by carbonate platforms that are unlikely to have experienced brackish conditions. The encroachment of the clastic system saw the rapid improvement of basinal oxygenation in the uppermost Bowland Shale, and even minor turbidite sandstones within the black shales coincided with a weakening in the intensity of euxinia, which suggests that fresher, sediment-laden waters flushed out and oxygenated the basin. We therefore suggest a warm saline bottom-water model for black shale deposition, with basinal waters generated on the adjacent carbonate platforms due to evaporation. Such a scenario is likely more broadly applicable to basinal black shales that developed adjacent to shallow-water carbonate successions.

Implications of a geochemical approach to reconstruct the Maastrichtian–Danian seaways of central India: The planktic foraminifera-bearing Jhilmili intertrappean revisited

Maastrichtian–Danian sedimentary sequences associated with Deccan volcanism are commonly interpreted to be deposited in fluviatile-lacustrine environments, except for the nearshore marine outcrops in Razol province (Rajahmundry). Discovery of Danian zone-P1a planktic-foraminifera, from a thin-horizon of an otherwise entirely lacustrine-palustrine Jhilmili intertrappean section in central India, makes this section unique, with reliable age-constraints. The presence of this foraminifera-bearing unit was used to postulate the existence of an ∼800 km marine-seaway from the west up to central India. Occurrences of non-marine biota in the foraminifera-bearing horizon and the absence of associated lithotopes and biotopes characteristic of marine transgressive events in this section is noteworthy. This study focuses on trace-element geochemistry and clay-mineralogy of the Jhilmili section to explore changes in depositional conditions along this section and obtain insights on the ambient waters from which Unit 3 was deposited. High-resolution sampling has been conducted and geochemical proxies such as Sr/Ba, Y/Ho (whole-rock, clay-fractions) and REE+Y (carbonates) have been utilized. Geochemical parameters suggest a non-marine environment for the entire section except the middle-unit showing brackish conditions because of storm/tsunami induced seawater mixing into freshwater depositional settings. Lithofacies, fossil-assemblage and variations in geochemical ratios indicate short-term episodic mixing of marine elements, possibly through storm/tsunami related activity in the lacustrine-palustrine freshwater ecosystem. Previous palaeobiological records from outcrops in the Godavari Rift indicate that seawater possibly entered through the Godavari rift. This study provides additional insights for the Maastrichtian–Danian paleogeography of central India.

New stratigraphic and paleoenvironmental constraints on the Paleogene paleogeography of Western Amazonia

The rise of the Andes and the associated propagation of the retroarc foreland basin during the Mesozoic Cenozoic in western South America shaped the paleogeography and paleoenvironmental settings of Western Amazonia. Much attention has been paid to the Neogene evolution of the Amazonian Basin, but few studies have investigated in detail the paleoenvironments of Western Amazonia during the Paleogene. We present a multi-proxy study that includes new biostratigraphic and paleontologic data, the interpretation of depositional environments and zircon U–Pb data from the Upper Cretaceous-Paleogene sedimentary sequence exposed in the Huallaga Basin (northern Peru). The biostratigraphic dating suggests that the lower part of the sequence is Maastrichtian in age. The maximum depositional age and maximum likelihood age according to the U–Pb zircon dating of Paleogene sedimentary rocks indicate Lutetian to Bartonian ages (from 43.5 ± 0.64 Ma to 37.6 ± 0.85 Ma). These results reveal a hiatus in the depositional record during Paleocene time. Two depositional systems can be distinguished: a lacustrine system composed of red mudrocks interbedded with thick sandstone layers and carbonate beds, and a siliciclastic tide-dominated system composed of fine-to medium-grained sandstones associated with tidal bundles, reactivation surfaces and heterolithic stratifications. However, the carbon and oxygen stable isotope values in carbonates tend to characterize a freshwater system, with a transition to brackish conditions toward the upper part of the section (Bartonian), thereby suggesting the presence of an estuary system. Finally, we suggest that the Bartonian shallow marine incursion recorded in the Huallaga Basin occurred from the north through the Caribbean Sea, and that it might have played a role in regional biodiversity patterns in the Paleogene.