Episodes Of Deposition Research Articles

Benthic response to event deposition and environmental disturbance in a shoreface to subaqueous delta system: Ichnology of the Silurian-Devonian Furada Formation of Asturias, Spain

The Furada Formation of Asturias, Spain, represents a clastic shallow-marine unit deposited during the middle Silurian to the Early Devonian. This formation contains abundant evidence of event deposition and non-uniform distribution of bioturbation structures representing a benthic response to multiple stressors. The 170-m-thick succession was measured and described, and the ichnotaxa were recorded and associated with five sedimentary facies. Most shallow-marine environments are characterized by periodic events of environmental disturbance, mainly by episodic deposition, which may be recorded by a change in both the degree of bioturbation and ichnodiversity. The general depositional setting for this formation has been previously interpreted as a wave-dominated and storm-influenced shallow-marine environment. However, sedimentologic features described in this study, such as anomalous heterolithic and mudstone units, representing fluid mud layers, hyperpycnal flow deposits and plume collapse accumulations, suggest the influence of fluvial discharge, making it a more complex depositional setting. The proposed model comprises an inner sandy shoreface belt flanked seawards by a muddy subaqueous delta platform. The trace-fossil assemblages of this formation reflect environmental stress factors introduced by the interplay of storms and fluvial input (e.g., high sedimentation rate, fluctuating hydrodynamic energy, decreased substrate consolidation), resulting in reduced ichnodiversity and low abundance. From an ichnofacies perspective, the shoreface complex is characterized by the Cruziana Ichnofacies, whereas the subaqueous delta platform is represented by the Phycosiphon Ichnofacies. Integration of sedimentologic and ichnologic datasets allows for a refined depositional interpretation of the formation and greater understanding of the environmental diversity of wave-and river-influenced shallow-marine clastic systems, including the responses of the middle Paleozoic shallow-marine benthos to event sedimentation and environmental disturbance. This study is one of the first detailed documentations of the ichnology of subaqueous deltas.

From the Northern Hajar Foothills to the Batinah Coast – a Geoarchaeological Survey at Saham and Dahwa (Northern Oman)

This geoarchaeological survey was dedicated to (i) the Umm an-Nar (2700–2000 BCE) settlement site of Dahwa and surrounding areas in the foothills of the Hajar Mountains as well as (ii) the coastal area near Saham on the Batinah coastal plain in northern Oman, the latter without focus on a specific cultural epoch. Stratigraphic sections from the proximal coastal plain provide insights into highly dynamic episodic sedimentation patterns with thick units of variable grain sizes and sorting. In one of the stratigraphic profiles in the town of Saham, a small anthropogenic pit or channel was found, interpreted as a pit hearth used by the Samad culture (300 BCE–100/200 CE) based on granulometry, thin-section analysis, clustered macro-charcoals, amorphous organic remains, as well as luminescence and 14C dating. Our coincidental discovery of this site indicates that there might be abundant traces of the Samad culture buried in the thick alluvium, from a period of hydrologically favourable conditions c. 50–300 CE. The Umm an-Nar dating of the Dahwa archaeological site in the foothills of the Hajar Mountains was confirmed for the first time by luminescence dating, although the low dose rate and high scatter of equivalent doses pose substantial challenges to the regional application of this method.

Quantifying paleoecological impact of the OAE1a on shallow marine ecosystems from southeastern France

Climate and environmental instability during the early Aptian culminated with the unfolding of the Oceanic Anoxic Event (OAE) 1a, which resulted in the deposition of black shales in deep marine settings and a typical negative spike followed by a positive excursion in δ13C values. In Vercors (southern France) the Urgonian platform developed prior to and coeval to the OAE1a, but the impact of this paleoenvironmental crisis on the ecology of benthic ecosystems is yet to be quantified. We gathered field and petrographic data to identify sequence boundaries and maximum flooding surfaces that are biostratigraphically dated and correlated between four localities within the study area. A composite δ13C curve is built where the C3 to C7 isotope segments from the literature are identified, pinpointing the onset of the OAE1a above the last episode of deposition of Urgonian facies rich in rudist bivalves. Furthermore, thin section point counting data are used to quantify the proportion of allochems in samples and to trace changes in the ecology of ecosystems. The principal component analysis of point counting data helps define ecological tiers: a diversified, photozoan association with rudists, green algae, and benthic foraminifera dominated ecosystems before the OAE1a and up to the C7 segment, while a less diversified heterozoan association with bryozoans and crinoids developed after the OAE1a. To explore the triggers for this change, the principal component analysis of elemental geochemical data highlights an increased nutrient and detrital input as major triggering mechanisms for ecological adjustments and changes in the biodiversity of ecosystems. In particular after the OAE1a, an increase in detrital and nutrient input leads to the replacement of photozoan by heterozoan assemblages more adapted to these stressful conditions. This research directly links paleoenvironmental deterioration to paleoecological changes and quantifies the amount of adaptation of ecosystems.

Linha São Luiz Geosite, Rio Grande do Sul State: 25 years of discoveries, and a unique window to the Brazilian Mesozoic

The Linha São Luiz Geosite is one of the most remarkable outcrops from the central region of Rio Grande do Sul state, southern Brazil. With more than 20 meters of vertical exposure, the locality preserves records of distinct sedimentary episodes, and one of the richest fossil assemblages known in southern Brazil. After a quarter of a century from the first expeditions to the site, the Linha São Luiz still yields new discoveries, registering exquisitely preserved fossils from micro and macrovertebrates, invertebrates, and plants, as well as trace fossils generated by these groups. In this contribution, we assembled representatives from distinct fields of paleontological study to provide a summary of the fossil assemblage from this site. We also briefly discuss the history of research and report geoconservation strategies, which are being implemented at the locality, in order to preserve this important window to the Brazilian Mesozoic.

Pre-Choiyoi volcanism at Cordillera del Viento, southwestern margin of Gondwana (∼37° S): Geological characterisation, geochronology and regional implications

This contribution provides a comprehensive description and classification of fifteen lithofacies within the Carboniferous rocks attributed to the Arroyo del Torreón Formation and Sofía Dacite in order to understand the eruptive dynamics and the evolution of volcanism associated with the onset of the Gondwanan Orogenic Cycle at the Cordillera del Viento (Argentina). The outcrops of Carboniferous volcanic and volcaniclastic rocks linked to this cycle are restricted to the Cordilllera del Viento range. In consequence, they offer a valuable opportunity to research the volcanic arc products of the pre-Choiyoi magmatism.The Arroyo del Torreón Formation lithofacies interpretation and its distribution indicate that the volcanism commenced with local andesitic lava flows followed by a volcano-sedimentary sequence formed by multiple pumice-rich quasi-steady concentrated pyroclastic density currents alternating with episodes of epiclastic sedimentation. The latter are covered ignimbrites developed by boiling over eruptions. Crystal-rich tuffs overlie the ignimbrites and represent a transition to a plinian eruption. This eruption style continued, developing concentrated pyroclastic density currents with highly unsteadiness conditions and scarce fall-out deposits. Conversely, the Sofía Dacite, represent a notable shift in the volcanism style, characterized by dacitic to rhyolitic lava flows with minor pyroclastic beds. Zircon dating of a pumice-rich lapilli-tuff from the Arroyo del Torreón Formation yielded a minimum age of 327.77 ± 1.79 Ma that was interpreted as the maximum depositional age for this unit. Similarly, zircons from a porphyritic dacite representing the Sofía Dacite provided a Concordia age of 329.11 ± 1.31 Ma that was interpreted as the crystallisation age of this rock.Consequently, we propose a new stratigraphic division of the Arroyo del Torreón Formation into two members. The Cerro San Pedro Member will comprise the pyroclastic rocks at the base of the sequence, while the Sofía Member will include the upper lava-dominated portion of the unit. In this sense, the whole lithostratigraphic unit represents a distinctive Carboniferous basin associated with arc-related volcanism representative from the pre-Choiyoi magmatism.

Desert-oasis evolutionary process in the Tarim Basin since ∼ 2.2 ka B.P. during the late Holocene and their environmental implications

Oases, serving as ideal locations for human settlements in arid regions, exhibit extreme sensitivity to regional climatic fluctuations. Consequently, the oasis deposition sediments play a pivotal role in the study of regional paleoenvironmental changes and the exploration of prehistoric human-environment interactions. The YSD and STM sections, both typical aeolian-lacustrine sections located at the edge of the Tarim Basin, were investigated in this study. By analyzing optically stimulated luminescence (OSL) dating results and grain-size proxy indicators, the environmental evolution patterns in the Tarim Basin since approximately 2.2 ka BP were reconstructed. Additionally, the parametric end-member analysis on the grain-size data was conducted to explore the environmental significance revealed by each end-member. The research findings indicate that: (1) ∼ 2.2–1.8 ka B.P., sediment morphology and grain-size parameters indicate that the climate in the Tarim Basin recorded by the STM section was relatively dry, with rivers gradually receding and frequent sand-drift activities. During the development of the YSD section (∼1.67–1.5 ka B.P.), the environmental conditions in the Tarim Basin transitioned to a relatively humid phase, with the Yarkand River experienced multiple episodes of natural diluvial deposition. The grain-size data of two sections both comprise five sedimentary dynamic components, serving as sensitive indicators of regional humidity conditions and winter monsoon intensity. (2) The oasis development in the Tarim Basin during the late Holocene (particularly refers to between ∼ 2.2 ka B.P. and ∼ 1.4 ka B.P.) exhibits a significant positive correlation with temperature records. (3) Environmental changes and human activities jointly regulate the spatial and temporal distribution and number of archeological sites during the development of both sections. However, the dominance of the two factors varied across different historical periods.

Strong Saharan Dust Deposition Events Alter Microbial Diversity and Composition in Sediments of High-Mountain Lakes of Sierra Nevada (Spain)

Mediterranean high-mountain lakes are being increasingly affected by strong Saharan dust deposition events. However, the ecological impacts of these severe atmospheric episodes remain largely unknown. We examined the effects of a strong Saharan dust intrusion to the Iberian Peninsula in 2022 on the physicochemical parameters and prokaryotic communities in sediments of nine high-mountain lakes of Sierra Nevada (Spain) located above 2800 m.a.s.l and in different orientations (north vs. south). A previous year (2021), with lower Saharan dust deposition with respect to 2022, was used for interannual comparisons. The strong dust deposition to the high-mountain lakes resulted in a significant increase in sediment nutrient availability which was linked to changes in the composition of prokaryotic communities. Decreases in alpha diversity and changes in beta diversity of prokaryotic communities were mainly observed in lakes located in the south compared to the north orientation likely because the former was more affected by the atmospheric dust deposition episode. Dust intrusion to the high-mountain lakes resulted in significant changes in the relative abundance of specific genera involved in important nutrient cycling processes such as phosphate solubilization, nitrogen fixation, nitrification, and denitrification. Saharan dust deposition also increased predicted microbial functionality in all lakes. Our findings show that severe atmospheric dust inputs to remote high-mountain lakes of Sierra Nevada can have significant biogeochemical and biodiversity consequences through changes in nutrient availability and prokaryotic communities in sediments of these freshwater ecosystems. This information contributes to understanding how Mediterranean high-mountain lakes of Sierra Nevada face strong intrusions of Saharan dust and their ecological consequences.

Carbonate‐rich megabeds within a Triassic siliciclastic deep‐water system, West Qinling orogenic belt, Central China: Character, processes and implications

AbstractDeep‐water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep‐water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep‐marine systems. Less documented are carbonate‐rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep‐water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate‐rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow‐water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast‐supported conglomeratic division (Division I), an intermediate matrix‐supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep‐water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally‐supplied carbonate‐rich megaflows that eroded and incorporated the substrate during transport.

The first documented and characterized Norwegian acid sulfate soils

AbstractAcid sulfate soils (ASS) containing hypersulfidic material (pH >4) can, when drained, transform to ASS with a thionic horizon (pH <4), which can cause environmental effects due to the formation of sulfuric acid and the consequent mobilization and leaching of metals and acid into waterways, as well as cause geotechnical problems. Yet, the occurrence of ASS has till now not been a topic of research in Norway. The present pilot study was carried out on an area along the northern coast of Norway. Thirty‐nine localities were sampled and analysed near Alta. Of these, six were classified as ASS with either hypersulfidic or parahypersulfidic material. ASS is not as widespread as within the Baltic Sea area, but the analyses document the occurrence of ASS with hypersulfidic material with high acidifying potential in certain areas if oxidized. This pilot study shows that ASS occurs in specific areas. Three localities with documented ASS were studied in greater detail. Here, sections were excavated and analysed to help with the understanding of the geological context of these occurrences. In this way, the geological prerequisites considered of importance of soils with ASS with hypersulfidic material are outlined. The prerequisites for ASS occurrence that evolved during this study include young, marine, fine‐grained deposits and a low relief environment subjected to episodic sedimentation but otherwise calm water and little water exchange. The results are a starting point for further studies of ASS occurrences along the Norwegian coast.

Sediment resuspension and transport in the offshore subaqueous Yangtze Delta during winter storms

Storm-induced episodic sediment redistribution in coastal systems can reshape geomorphic bodies, disrupt ecosystems, and cause economic damage. However, cold-wave-storm-induced hydrodynamic changes and residual sediment transport in large, exposed subaqueous deltas, such as the Yangtze Delta, are poorly understood because it is typically expensive and difficult to obtain systematic field data in open coast settings during storm events. We conducted a successful field survey of waves, currents, changes in water depth, and turbidity at a station (time-averaged water depth of 20 m) in the offshore subaqueous Yangtze Delta over 10 days during winter, covering two storms and two fair-weather periods. During the storm events, strong northerly winds drove southward longshore currents (~0.2 m/s) and resulted in increased wave height and sediment resuspension, thereby leading to massive southward sediment transport. In contrast, both southward and northward transports were limited during the fair-weather periods. A better understanding of the storm-induced sediment transport can be obtained by using an approximately half-day lag in sediment transport behind wind force, given the time needed to form waves and longshore drift, the inertia of water motion, and the slow settling velocity of fine-grained sediment. Our results directly support previous findings of southward sediment transport from the Yangtze Delta during winter, which is deposited in the Zhejiang–Fujian mud belt in the inner shelf of the East China Sea. In addition, the southward sediment transport from the Yangtze Delta occurs mainly during episodic storm events, rather than during the winter monsoon, and winter storms dominate over typhoons in driving southward sediment transport from the delta. This study highlights the importance of storms, especially during winter storms, in coastal sediment redistribution, which is of particular significance when considering the projected increase in storm intensity with global warming.

High-resolution seismic record of the Quaternary palaeoenvironments along a Dalmatian-type coast (Lošinj Channel, Adriatic Sea)

Coastal systems have changed considerably in response to Quaternary glacial–interglacial variability. Here, we offer the first detailed assessment of geomorphic features and late Quaternary sedimentation dynamics in the Lošinj Channel in the Adriatic Sea. The present study attempts to resolve the complex evolution of the environments by applying high-resolution seismic records that build upon sediment core data. Within this coastal karst basin, a significant amount of sediment accumulated during the Quaternary. Notably, the existence of several prominent erosional and depositional environments was revealed. We distinguished recurrent episodes of fluvio-lacustrine and marine sedimentation that probably occurred since Marine Isotope Stage (MIS) 6. The preserved record consists of erosional features and subparallel and oblique reflectors attributed to glacial periods (Seismic Units SU-II, SU-IV, and SU-V). Interglacial units are acoustically semitransparent and generally reflection-free (Seismic Units SU-I and SU-III). The mutual influence of sea level and climate change, sill depth, and karst hydrology enabled environmental changes in the Lošinj Channel. The area proves to be important for Quaternary studies because it contains a long sediment succession spanning at least the middle and late Pleistocene and Holocene. Our study has implications for the assessment of the long-term palaeoenvironmental evolution of similar coastal settings and reconstruction of the regional palaeogeography which is in turn crucial for understanding prehistoric human occupation and/or dispersal. This is one of the few well-preserved records in the Adriatic Sea that provides insight into submerged landscapes and sea levels since the penultimate glacial.

Source rock assessment and organic matter characterization of the Oligocene upper Shahejie and Dongying formations in the Nanpu depression of the saline lacustrine Bohai Bay basin, China: Geochemical, palynological, and mineralogical perspectives

The Bohai Bay Basin, located in eastern China, is a significant petroliferous, non-marine rift basin, underwent intricate tectonic activities throughout the Cenozoic. The Nanpu Depression in the Huanghua sub-basin in the northern part of the basin was controlled by Paleogene rifting and increased subsidence. These geological processes resulted in the deposition of the Shahejie and Dongying formations, which exhibited varying quantities and qualities of organic matter. Eighty drill cuttings samples of the Paleogene First Member (Es1) and the overlying Third (Ed3) and Second (Ed2) members of the Shahejie and Dongying formations, respectively, were investigated. An integrated approach including organic and inorganic geochemistry, palynology, and mineralogy was employed to assess the paleoredox and marine incursion conditions, source rock quality and levels of thermal maturity, and factors that governed organic matter accumulation. Results indicated that the Es1 Member was deposited under anoxic conditions, resulting in the accumulation of organic matter-rich mudstones in the Nanpu Depression. Abundant pollen grains and acritarchs were found in the Es1 Member yielded along with minor occurrences of dinoflagellate cysts, freshwater algae, and spores. Terrestrial palynomorph composition provided evidence of increased terrestrial runoff, while the high abundance of acritarchs, accompanied by some dinoflagellate cysts, confirmed episodes of marine incursion and deposition under hypersaline conditions in the lacustrine Bohai Bay Basin. The Ed2 Member exhibited poor to fair amounts of organic matter and a limited potential of hydrocarbon generation with a variety of kerogen Types, including IV, III, II/III, and II. The Ed3 Member shows fair to good organic matter richness and hydrocarbon potential of kerogen Types III, II/III, and II. The Es1 Member emerged as the most promising source rock within the studied interval, boasting good to excellent organic matter richness, and fair to good hydrocarbon generation potential of kerogen Types III and II/III. Evaluating the thermal maturity of organic matter, based on Tmax and VRo-Eq% and related cross-plots, revealed that the Shahejie and Dongying formations are still in the immature to the early stage of the oil window. The mineralogical composition of the Es1 Member primarily consists of clay and quartz with some carbonate and accessory minerals, such as epigenetic halite, dolomite, and plagioclase. Weak correlations observed between the total organic carbon (TOC) and mineral components indicated that the availability of organic matter was primarily controlled by enhanced production and preservation rather than limited dilution under saline lacustrine, oxygen-deprived, and well-stratified water column conditions. Regional investigations of the Es1 Member confirmed the widespread anoxia and deposition of organic-rich source rocks in the Bohai Bay Basin during the Oligocene.

Tracking the tempo of a continental margin arc: Insights from a forearc succession in West Antarctica

Abstract The Fossil Bluff Group of eastern Alexander Island records the exceptional preservation of more than 8 km of Mesozoic sedimentary rocks deposited into an accretionary forearc basin that developed unconformably above a late Paleozoic accretionary complex, and in proximity to a continental margin arc during a prolonged phase of enhanced magmatism. Through the Mesozoic, the Fossil Bluff Group evolved from a trench-slope environment to a forearc basin sourced from the continental margin arc. During this period, the Antarctic Peninsula’s convergent margin was characterized by episodes of magmatic flare-ups that developed during tectonic compression, crustal thickening, extension, and uplift. U-Pb and Lu-Hf detrital zircon data are used to determine the provenance of the forearc succession and as a monitor of arc magmatic tempos during the late Mesozoic. The magmatic record in the adjacent arc is poorly preserved or partially absent, but the sedimentary record of the forearc basin preserves a largely uninterrupted record of arc magmatism that can be studied with detrital zircon geochronology and geochemistry. The basal succession of the Fossil Bluff Group is sourced from the adjacent accretionary complex, but thereafter it is strongly controlled by the proximal arc in western Palmer Land and is characterized by a mixed arc/recycled signature during episodes of renewed sedimentation. However, the main phases of deposition during the Early Jurassic (ca. 180 Ma), Early Cretaceous (141–131 Ma), and mid-Cretaceous (125–102 Ma) are dominated by arc-only sources. The Lu-Hf isotopic record supports a transition from convergence to extension and a return to convergence during the Mesozoic, which is consistent with accretionary orogens from elsewhere along the West Gondwanan margin. The provenance record during the depositional history of the basin points overwhelmingly to an autochthonous origin; as such, models for parts of the western province of the Antarctic Peninsula being allochthonous are unsupported.

Oligocene to Miocene magmatic and hydrothermal evolution in the Maricunga belt (Región de Copiapó, Chile): A new look to a long known metallogenic belt

The Maricunga metallogenic belt, herein defined to encompass the region from 25° S to 28° S along the Cordillera Frontal of northern Chile, is known for hosting a series of gold-copper and lesser copper-molybdenum porphyries and gold-silver epithermal systems that are hosted in a segment of the late Oligocene-Miocene Andean calc-alkaline magmatic arc. Based on an up-to-date geochronological database, four episodes of magmatism and related hydrothermal deposits are proposed to characterize intensity and style of volcanism and hypabyssal intrusive rocks over time. The late Oligocene episode (26-21 Ma) is characterized by stratovolcanoes, dome complexes, pyroclastic sequences, and hypabyssal intrusives of andesitic to dacitic composition that host gold-rich porphyry systems such as Caspiche, Maricunga, and La Pepa. The early Miocene episode (21–17 Ma) has similar rock types but is volumetrically reduced, hosting epithermal and porphyry deposits like La Coipa and Caserones, respectively. A reinvigoration of volcanism occurred during the third stage between 17 and 11 Ma, giving rise to large volcanic complexes and intra-to extra-caldera ignimbritic deposits that host several gold-rich porphyry deposits such as Lobo-Marte, Luciano, and Cerro Casale; as well as epithermal deposits such as Fenix. Some of the 17 to 11 Ma and younger igneous rock belong to the high-K calc-alkaline series, showing a higher alkali content compared to previous periods. The last magmatic episode, from 11 to 5 Ma, coincides with the shallowing of the subduction angle and is characterized by an eastward migration of volcanism, and more heterogeneous rocks including trachytic compositions. During this period mineralization was emplaced at the Salares Norte epithermal deposit and El Volcan porphyry Au–Cu deposit.Porphyry and epithermal systems formed throughout the evolution of the Maricunga belt. Overprint of advanced argillic alteration on porphyry style alteration is widespread albeit commonly devoid of significant addition of epithermal Au–Ag mineralization. The Au-rich nature of the majority of the porphyry systems is attributed to the shallow crustal depths of emplacement compared to Cu- and Mo-rich porphyry systems. Conversely, high-sulfidation epithermal Au–Ag deposits such as La Coipa and Nueva Esperanza are not known to be telescoped on coeval porphyry gold deposits.The location of the mineralized centers was favored by crustal weaknesses expressed by intersection of oblique- and parallel-to arc structures, the former inherited from the construction of the continent before to the formation of the Andean range. The arc oblique structures also segment the Maricunga belt into domains with unique magmatic and hydrothermal styles.

Deltaic marsh accretion under episodic sediment supply controlled by river regulations and storms: Implications for coastal wetlands restoration in the Yellow River Delta

Sediment supply has long been recognized as a critical factor affecting salt marsh evolutions. Subject to fluctuating river discharges and coastal hydrodynamics, sediment supply to deltaic marshes are episodic rather than continuous. To evaluate the impacts of episodic sediment delivery under river regulations and storm events on deltaic marsh accretion, a 5-month (April 18th to September 4th, 2021) field campaign was conducted at a Spartina alterniflora marsh of the Yellow River Delta, China. Nine storm events and the Water-Sediment Regulation Scheme (WSRS) coinciding with a freshwater diversion were captured. It was found that the two phases of the WSRS differed greatly in their contribution to marsh accretion. During the Water-Regulation Phase (WRP), marsh accretion rates showed little difference with pre-WRP periods. However, the subsequent Sediment-Regulation Phase (SRP) contributed to ∼15 % of annual accretion within only 4 days, suggesting the SRP was more effective in nourishing deltaic marshes with sediment. Further analyses indicated that the higher accretion during SRP was attributed to both higher sediment concentrations and more favorable sediment pathways, influenced by delta-scale river-tide interactions. Observations also showed that storm events contributed to half of the marsh accretion during the non-WSRS period when the fluvial sediment supply was very low. During storms, wave-induced intertidal resuspension acted as the major sediment sources. Under favorable conditions (onshore wind, high water levels, high waves), tidal-averaged sediment delivery to marshes underwent as much as fifty-fold increase compared with the calm period. The observed marsh dynamics suggested that marsh sedimentations depended on not only the seaward sediment concentrations, but also the sediment transport pathways. For deltaic marsh restoration practices, we proposed that marsh-orientated schemes which align river regulations with favorable meteorological and hydrodynamic conditions, could potentially make better use of fluvial sediment for deltaic marsh nourishment.

Episodic sediment accumulation linked to global change in the endorheic Qaidam Basin of the Tibetan Plateau revealed by feldspar luminescence dating

Given its high accumulation rate in sediments, the endorheic basin in arid regions plays a crucial role in reconstructing paleo-environment. However, it would not provide high-resolution climatic records if significant wind-eroded depositional hiatuses were inevitable within a severe wind environment. Unconformable contacts have been found during field survey in the top part of the stratigraphy in the Qaidam Basin, a prototypical endorheic basin in central Asia. To elucidate whether the sediment is continuous, we employed luminescence dating methods of feldspar pIR200IR250 and quartz OSL to date sediments, including lacustrine sediments and salt crusts, from the Qarhan Playa that is the Quaternary depositional center of the Qaidam Basin. Various experiment tests, including preheat plateau, dose recovery, and residual dose, were conducted. The dating results show that the feldspar pIR200IR250 can provide dependable ages with negligible residual doses. The pIR200IR250 dating ages within the last glacial cycle reveal several environmental shifts. A Qarhan paleolake in Marine Isotope Stage (MIS) 5 was demonstrated by the cluster ages of ∼140–80 ka of lacustrine sediments. The salt crust ages of 136 ± 10 ka and 97 ± 6 ka indicate that, before completely disappeared, the paleolake with shallow dish-shape depression had been dried up more than once, illustrating “shallow——dry——shallow” cycles. The playa in the eastern Qaidam Basin evolved mainly in warm periods, such as MIS 5 and MIS 1, supported by the salt crust ages of MIS 5 (136 ± 10 ka and 97 ± 6 ka) and MIS 1 (10 ± 1 ka and 0.6 ± 0.1 ka). Depositional hiatus in the last glacial cycle were identified by unconformable contacts in three sections between the lacustrine strata and their overlying playa strata, with corresponding age gaps of 158 ± 20–97 ± 6 ka, 131 ± 10–10 ± 1 ka, and 84 ± 7–0.6 ± 0.1 ka, respectively. In all the three sections the sediments for the whole of the last glacial period is missing, eroded by wind. This process should have occurred periodically during the glacial-interglacial cycles of the orbital global climatic changes. The results also show that hiatuses are common for endorheic basins on the Earth with age gaps of up to ∼100 ka, suggesting that robust chronology should be established before any climatic correlation due to severe wind erosion leading to episodic sediment accumulation.

Tectono-stratigraphic and sedimentological analysis of the Early to Middle Devonian Floresta Formation: Insights from the Floresta Massif, Northern Andes, Colombia

A comprehensive tectono-stratigraphic and sedimentological investigation of Early to Middle Devonian rocks was conducted in the southern Floresta Massif and adjacent regions in the Northern Andes of Colombia. A substantially reduced thickness of the Floresta Formation compared to prior studies is suggested here, attributable to pronounced stratal deformation and the prevalence of recumbent folds throughout the area. The deformation in the Floresta Formation manifests as atypical recumbent folds, diverging from the structural behavior observed in the underlying and overlying strata of the El Tibet and Cuche formations respectively, which exhibit minimal deformation. Our findings also reveal that the Floresta Formation accumulated under shallow-water platform conditions, subject to eustatic sea-level fluctuations. This resulted in distinct episodes of carbonate and siliciclastic deposition, with terrigenous sediments sourced from continental origins, potentially encompassing a combination of cratonic areas and uplifted blocks. The identification of a plausible stage of carbonate silicification signifies a post-diagenetic transformation. The sedimentary rocks of the Floresta Formation reached the upper epizone conditions, in proximity to the transition between the epizone and the upper anchizone, which suggests a maximum depth and temperature of ~5-7 km and ~300 °C, respectively. This contribution provides new insights into the geological history of the region, emphasizing the importance of scrutinizing Early to Middle Devonian rocks within the broader geological context of the Northern Andes.

A unique subseafloor microbiosphere in the Mariana Trench driven by episodic sedimentation.

The online version contains supplementary material available at 10.1007/s42995-023-00212-y.

Investigation of the last two centuries sedimentation dynamics in high-altitude lakes of Southern Carpathians, Romania

This study investigates the last two centuries sedimentation dynamics in four high-altitude lakes located in Southern Carpathians, Romania. Furthermore, a novel approach is proposed for identifying the anthropic or natural underlying causes, by comparison of the acceleration of the change in sedimentation rate with a baseline growth rate trend provided by an isolated peat bog. The high-resolution chronologies were developed using the 210Pb dating technique and the CRS model. 137Cs alternative time-marker validated the age-depth models and reassured the quality of the results. The results indicated several short-interval high sedimentation events within the lake cores, yielding up to five times the average rate for the investigated period. The cause of the high sedimentation episodes was generally attributed to anthropic activities (primarily road construction) and extreme natural events. A first-order derivative equation was employed to plot the acceleration in the sedimentation rate of the lakes with the peat bog baseline. The discrepancies between the acceleration trends highlighted significant deviations from the natural variation tendencies and provided preliminary data regarding the underlying causes of the intense sedimentation periods.

A 50 year record for perfluoroalkyl acids in the high arctic: implications for global and local transport.

Perfluoroalkyl acids (PFAAs) are persistent compounds that are ubiquitous globally, though some uncertainties remain in the understanding of their long-range transport mechanisms. They are frequently detected in remote locations, where local sources may be unimportant. We collected a 16.5 metre ice core on northern Ellesmere Island, Nunavut, Canada to investigate PFAA deposition trends and transport mechanisms. The dated core represents fifty years of deposition (1967-2016), which accounts for the longest deposition record of perfluoroalkylcarboxylic acids (PFCAs) in the Arctic and the longest record of perfluoroalkylsulfonic acids (PFSAs) globally. PFCAs were detected frequently after the 1990s and have been increasing since. Homologue pair correlations, molar concentration ratios, and model comparisons suggest that PFCAs are primarily formed through oxidation of volatile precursors. PFSAs showed no discernible trend, with concentrations at least an order of magnitude lower than PFCAs. We observed episodic deposition of some PFAAs, notably perfluorooctane sulfonic acid (PFOS) and perfluorobutane sulfonic acid (PFBS) before the 1990s, which may be linked to Arctic military activities. Tracer analysis suggests that marine aerosols and mineral dust are relevant as transport vectors for selected PFAAs during specific time periods. These observations highlight the complex mechanisms responsible for the transport and deposition of PFAAs in the High Arctic.