Sedimentological Characteristics Research Articles

Analysis of the Impact Area of the 2022 El Tejado Ravine Mudflow (Quito, Ecuador) from the Sedimentological and the Published Multimedia Documents Approach

Quito (Ecuador) has a history of mudflow events from ravines that pose significant risks to its urban areas. Located close to the Pichincha Volcanic Complex, on 31 January 2022, the northwest and central parts of the city were hit by a mudflow triggered by unusual rainfall in the upper part of the drainage, with 28 fatalities and several properties affected. This research focuses on the affected area from collector overflow to the end, considering sedimentological characteristics and behavior through various urban elements. This study integrates the analysis of videos, images, and sediment deposits to understand the dynamics and impacts of the mudflow using a multidisciplinary approach. The methodology includes verifying multimedia materials using free software alongside the Large-Scale Particle Image Velocimetry (LSPIV) to estimate the kinematic parameters of the mudflow. The affected area, reaching a maximum distance of 3.2 km from the overflow point, was divided into four zones for a detailed analysis, each characterized by its impact level and sediment distribution. Results indicate significant variations in mudflow behavior across different urban areas, influenced by topographical and anthropogenic factors. Multimedia analysis provided insights into the mudflow’s velocity and evolution as it entered urban areas. The study also highlights the role of urban planning and infrastructure in modifying the mudflow’s distribution, particularly in the Northern and Southern Axes of its path, compared with a similar 1975 event, seven times larger than this. It also contributes to understanding urban mudflow events in Quito, offering valuable insights for disaster risk management in similar contexts.

Palynological study of some Afowo bituminous sediments in parts of Southwestern Nigeria

The tar sand and shale sequences of the Afowo Formation exposed at Lore, Shagbon, and Gbegude areas in parts of southwestern Nigeria has been palynologically investigated to unravel the depositional history. The lithofacies assemblage of the studied section comprising of shale, siltstone, claystone, lignites and ferruginised facies and their peculiar sedimentological features indicate low energy quiet setting, ranging from fresh water to nearshore marine swamps. Recovered palynomorph assemblage include marine dinoflagellate cyst such as Paleocystodinium golzowenses, Lycopodium spp. of Maastrichtian age. The pollen and spore (Retidiporites magdalenensis, Echimonocolpites, Echitriporites trianguliformis and C-cristatus) indicate terrestrial fresh water environment. The abundance of palmea pollen (Echitriporites and Longapertites) and the pteridophyte suggest that the vegetation developed under a predominant humid climate.

Sedimentologic characteristics and correlations of coastal plain sand and alluvium deposits within Lagos environs southwestern Nigeria

Sedimentologic characteristics and correlations of coastal plain sand and alluvium deposits within Lagos environs southwestern Nigeria

An integrated stratigraphic re-evaluation of key Central Atlantic DSDP sites

Re-sampling and new analysis of DSDP core from key Central Atlantic sites, drilled over 30 years ago, has allowed an updated stratigraphic framework to be developed. This study refines the timing and nature of key unconformities that have previously been documented to occur elsewhere in the oceanic domain of the Central Atlantic during the drilling of many DSDP legs. Biostratigraphic dating using calcareous nannofossils and palynology has been performed on 168 samples. This higher biostratigraphic resolution improves regional correlation and has allowed identification of major hiati previously unrecognised within the oceanic domain stratigraphy.This work builds on the pioneering work of the DSDP cruises, and utilises the valuable data collected for new age dating, supplemented with new organic geochemistry analysis and sedimentological characterisation to improve documentation of the Mesozoic strata. Results are extrapolated along the continental margin of northwest Africa and the conjugate in South America, using regional two-dimensional seismic sections, providing a correlation between the oceanic domain stratigraphy and shelfal depositional systems penetrated by hydrocarbon exploration wells.At DSDP Site 367, a middle Berriasian unconformity is recognised for the first time in Core 33, where middle Berriasian white pelagic limestones (Blake-Bahama Formation) sit unconformably on Early Tithonian red argillaceous limestones (Cat Gap Formation). Faunal dating indicates a ca. 5 Myr hiatus at the Jurassic-Cretaceous boundary. Marl interbeds within the pelagic limestones increase in occurrence through the Barremian, reflecting increased terrigenous input, with associated total organic content (TOC) averaging 5%.A second major lithological break is identified at DSDP Site 367, interpreted as a base Albian unconformity, between the Blake-Bahama and overlying Hatteras Formations. Sediments above are intra late Albian variegated claystones with abundant terrestrial detritus and distal turbidites. Seismic data that intersects the well location show onlapping reflections of early-middle Albian strata landward of DSDP Site 367, indicating paleo-topography prior to Albian deposition. These sediments are contemporaneous with a major progradational phase on the shelf and a sedimentary wedge observed at the base of the carbonate escarpment. Early Albian sediments sit above the interpreted base Albian unconformity at DSDP Site 534 A on the conjugate US Atlantic margin, suggesting the super-regional nature of this event. The refined dating provides age calibration of a basin-wide unconformity, previously known from seismo-stratigraphic studies as Reflector β.In addition to the revised stratigraphic framework, evidence is presented for the occurrence of seaward dipping reflectors (SDRs) northwest of the Guinea Plateau. SDRs have not been reported along this section of the African margin, demonstrating volcanic addition during early seafloor spreading and extending the occurrence of volcanics associated with the African Blake Spur magnetic anomaly further south beyond the Cap Vert fracture zone previously mapped. At DSDP Site 368 we also note that the late Albian to late Cenomanian strata (Hatteras Formation) is composed of a 164 m thick organic-rich interval, containing up to 37% TOC, with facies and organic geochemical heterogeneity. This transgressive sequence is associated with a flooding of the shelf.This revised stratigraphic framework provides a solid foundation for future Central Atlantic studies intending to use these sites as calibration of the oceanic domain stratigraphy.

Sedimentological characterization of earthquake-generated turbidites in fault-proximal glacial lakes: a case study from Jenny Lake, Teton range, Wyoming

Lakes in seismically active regions preserve valuable sedimentary archives of paleoseismic activity within their catchment and beyond. A series of glacially-excavated lakes positioned directly along the surface trace of the Teton normal fault at the base of the Teton Range, WY, are ideally situated to record past fault activity since their formation approximately 15,000 years ago. Here, we focus on the sediment fill contained in Jenny Lake (5 km2; approximately 73 m max depth) located at the bottom of Cascade Canyon, in the central Tetons, where postglacial slip rates are greatest. Past earthquakes that generated slope failures in and around Jenny Lake are expressed stratigraphically as coseismic turbidite deposits. These deposits were previously identified and dated in sub-bottom profiles and in sediment cores taken from multiple locations around the basin. In this study, we focus on the six thickest turbidites (ranging from 6 to 34 cm thick) present in multiple cores recovered from the central depositional basin and analyze them at sub-centimeter resolution for changes in physical, biological, and geochemical parameters, including sediment density, magnetic susceptibility, grain size distributions, organic content, and elemental composition. Results reveal each deposit contains a well-defined, three-component sedimentary sequence composed of a relatively homogenous and thick basal sandy unit with a sharp bottom contact, a similarly thick silt-rich middle unit, and a thin top unit of very fine-grained sediments. The characteristics of these components and their similarity between individual deposits suggest consistent sediment sources and transport pathways during successive earthquake events. Based on our analyses and the unique local geomorphic setting, we create a mechanistic model of coseismic turbidite formation in Jenny Lake, which may provide an improved framework for identifying, characterizing, and correlating earthquake-generated disturbance deposits in other Teton lakes and lakes in similar tectonic-geomorphological settings, for example, in the Basin and Range Province, USA or beyond.

Geophysical and Sedimentological Characterization of Oil Sand Deposit in Part of Eastern Dahomey Basin Southwestern Nigeria

Unconventional oil is the group name given to unconventional petroleum deposits such as oil sands and heavy oils. Oil sand, commonly referred to as tar sand or bituminous sand is a sandstone formation impregnated with viscous bitumen. This study utilized the two-dimensional electrical resistivity imaging technique to characterize oil sand and validate its true resistivity value and sedimentological analysis to evaluate the physical properties of the oil sand deposit. The two-dimension electrical resistivity imaging data acquisition was done along seven profiles systematically in a grid format using dipole-dipole electrode configuration and processed using the RES2DINV software. Fresh samples were collected from three points within the study area for grain sizes and textural properties analysis. The result of the 2-D ERI in the study area showed two to three geoelectric layers and the oil sand being the second layer as evident in the 3-D model obtained from the systemic data acquisition procedure. The resistivity obtained for oil sand in the study area range between 2,500 Ωm to 105 Ωm which validates the report of high resistivity value of oil sand in the study area. The sedimentological analysis showed that the sediments in the study area are of medium sand moderately sorted sand grain and leptokurtic to mesokurtic sand suggesting unimodal and bimodal parent source.

Littoral landforms of Lake Hulun and Lake Buir (China and Mongolia): Wind-driven hydro-sedimentary dynamics and resulting clastics distribution

Two rectangular-shaped lakes, Lake Hulun and Lake Buir, located at the boundary between China and Mongolia, only c. 75 km apart and therefore experiencing similar wind fields, have been studied based on satellite images and field surveys in order to compare their geomorphological and sedimentological characteristics. The wind-driven hydrodynamics, which have a significant effect on the development of littoral landforms and on sediment distribution, have been discussed for the two similar lakes that experienced a prevailing wind perpendicular to their long axis. A conceptual model related to wind-driven water bodies and sediment distribution is proposed. Wave-influenced to wave-dominated deltas, beaches, spits, and eolian dune deposits develop around these two lakes, with a strikingly similar distribution pattern. These features locally inform the longshore drift and help reconstruct the water circulation induced by wind forcing. Under the NW prevailing wind regime, the spits developed on the SW coast with a NW–SE extension, which was influenced by the NW–SE longshore currents. The same influence was observed in the delta extension in the NE area. The differences lie in the presence of fan deltas in the NW region of Lake Hulun, but not in Lake Buir. Additionally, the width of the beach and eolian deposits on the downwind coast of Lake Hulun is three times greater than that of Lake Buir which were caused by the differences in sediment supply and wind fetch between the two lakes. Lake Hulun and Lake Buir provide two reliable examples to understand the relationship among the wind field, provenance, hydrodynamics, landforms, and asymmetrical distribution of clastics in elongated lakes. They also represent relevant modern analogs, which may also be of guiding significance to wind-driven sand body prediction in lacustrine basins.

A Cretaceous siliceous sinter in NE China: Sedimentological and geochemical constraints on its genesis

Phanerozoic sinter deposits have been reported globally, with their identification mainly based on sedimentological, petrological, and mineralogical studies. In this study, a detailed geochemical investigation, combined with sedimentological characterization, was conducted on the Wugonglilu siliceous deposit, a Cretaceous (106 Ma) sinter in NE China, to examine its genesis. The deposit is inferred as a siliceous hot spring deposit (sinter) owing to its geological setting in an epithermal gold-mining district, its morphologically variable microbial textures typical of subaerial sinters, and nearly pure silica composition. Three lithofacies were recognized in this study, including laminated to thinly bedded sinter, silica-cemented breccia, and epithermal vein, which represent deposits from three contrasting hydrothermal environments. The 87Sr/86Sr ratios of the sinter are similar to the bedrock through which the geothermal fluids passed, namely the Upper Triassic Dajiahe Formation (T3dj), a marine siliceous rock unit, and the Lower Cretaceous Datashanlinchang Formation (K1d), a rhyolite unit. Results indicate that both underlying units are possible Sr sources of the silica in the Wugonglilu sinter. The REE + Y (rare-earth elements and yttrium) patterns of the sinter exhibit significant variability, primarily due to terrestrial detrital contamination. Differential REE + Y contamination by terrestrial detritus was striking in the white and dark laminae/beds of the laminated to thinly bedded sinter. The white laminae/beds, generally less contaminated, were probably formed during the dry season, whereas the dark laminae/beds exhibiting greater detrital contamination were likely formed during the wet season. When excluding the samples strongly contaminated by detritus, the sinter exhibits Y anomalies comparable to Post-Archean Australian Shale (PAAS), and to the adjacent underlying K1d rhyolite and T3dj siliceous rock samples, indicating that these anomalies were not inherited from rocks dominating the reservoirs. Furthermore, the sinter shows a (Ce/Ce*)N range close to that of the underlying marine siliceous rock and rhyolite samples, reflecting that the (Ce/Ce*)N of the sinter is largely inherited from the reservoir rock(s). The overall REE + Y patterns of the sinter range from nearly flat to LREE-depleted, similar to some samples of the K1d rhyolite and T3dj siliceous rock units. However, most samples of the K1d rhyolite and T3dj siliceous rock display (Pr/Tb)N and (Pr/Yb)N higher than many studied sinter samples. This is likely because of the formation of strong HREE–carbonate complexes during groundwater migration. Based on these results, a generalized formation model of the studied sinter system was constructed. This study suggests that integrated sedimentological and geochemical investigations can aid in interpreting the genesis of sinter deposits, in particular the link between sinter deposits and corresponding reservoir rocks.

Nature-based solutions for coastal protection in sheltered and exposed coastal waters: integrated monitoring program for baseline ecological structure and functioning assessment

Nature-based solutions, such as shellfish reefs, can support natural coastal defence and be a potential solution for climate-resilient shorelines in the future. In the Belgian Part of the North Sea, the “Coastbusters” projects aim to develop nature-based coastal protection by favouring subtidal mussel bed establishment on the seafloor through typical longline aquaculture techniques. Mussel beds are dependent on environmental conditions, and both influence the physical and biogeochemical features in a soft-sediment environment. Therefore, a comprehensive ecological monitoring program is essential to assess the success of future mussel bed development and its influence on the surrounding ecosystem. For establishing a monitoring baseline of the two experimental areas, a combination of conventional benthic assessment methods (grab sampling and granulometry) and non-invasive techniques (sediment profile imaging and transect diving video surveys) were utilised. Although mussel reefs did not yet develop by the time of this study, clear differences in ecological and sedimentological characteristics were found between two experimental areas (sheltered and exposed), subjected to slightly different hydrodynamic conditions. The one sheltered by coastal sandbanks was dominated by fine-muddy sand, higher species richness, biomass, and higher biological activity (burrows, fauna, and biological beds) as observed by all methods in one or another way. Moreover, functional diversity indices revealed a higher partitioning of the total available resources, suggesting more complex ecological processes in the sheltered area. Conversely, the area more exposed to the open sea was dominated by more sandy sediments, and fewer organisms were found. The combination of those different monitoring tools provides an integrated, complementary view, from different perspectives, on the biological, physical and functional characteristics of the study areas.

Intrasediment gypsum in subtidal offshore carbonates as a witness of basin-wide evaporitic precipitation. The case of the southern Variscan foreland basin (mid-Carboniferous)

Widespread calcite and quartz pseudomorphs, interpreted as originally gypsum crystals, occur within hemipelagic calci-mudstone accumulated in subtidal offshore environments in the broad marine foreland basin developed on the southern flank of the Ouachita–Alleghanian–Variscan Orogen during mid-Carboniferous times, which acted as a marine corridor connecting the Panthalassa and Palaeo-Tethys Oceans during the Mississippian, and progressively narrowed during the assembly of Pangea. In this study, 67 outcrops of radiolaria-bearing calci-mudstone deposits that contain calcite and quartz pseudomorphs located in northern Spain and southern France were studied to constrain the gypsum spatial distribution and sedimentological features. The recognised microfacies indicate intrasediment gypsum precipitation, accompanied by less abundant bottom-grown precipitates and gypsum cumulates, in extensive offshore, probably several ten to a few hundred metres deep, basinal environments. Gypsum precipitation took place during a short-lived temporal episode during the early Bashkirian time (Voznesenkian), which can be correlated, on the basis of benthic foraminifera, with the coastal (inter- to supratidal) gypsum evaporites identified in NW Africa (Tindouf and Reggan successions in Morocco and Algeria) that would represent the shallow-water counterparts. The occurrence of gypsum precipitates both in offshore hemipelagic calci-mudstones of the Variscan foreland basin and in inter- to supratidal environments of the epeiric Sahara Platform indicates that hypersaline conditions affected vast marine areas, roughly coinciding with the estimated age of closure of the Panthalassa and Palaeo-Tethys marine connection. Therefore, the studied succession represents the trace of a basin-wide evaporitic episode extending for hundreds of kilometres driven by foreland basin restriction, mid-Carboniferous sea-level fall and arid climate. This study provides new insights for the interpretation of gypsum precipitates in offshore marine environments encountered in the Phanerozoic and whose genesis is poorly understood.

Interpreted depositional conditions of balanced-fill lake basin strata incorporating vertebrate and invertebrate trace fossils, Triassic Santa Clara sub-basin, Cuyana rift basin, Argentina

ABSTRACT The Santa Clara Abajo and Santa Clara Arriba formations host a diverse assemblage of trace fossils that record a wide range of behaviors and a broad array of ecological niches during the Middle Triassic—a critical period in the evolution of continental fauna with the diversification of both synapsids (cynodont and dicynodont) and archosauromorphs (dinosaurs, pterosaurs, and crocodilians) that represent post-Permian faunal recovery. The Santa Clara formations are part of the continental infill of the Cuyana rift basin in Argentina and represent a lacustrine system with fluvial input and delta development. Sedimentological characteristics of these units as well as their stacking patterns characterize a “fluctuating profundal” facies association typical of a balanced-fill lake basin. The lacustrine and associated terrestrial environments preserve a rich record of invertebrate traces with 26 ichnogenera from ethological classes of fodichnia, domichnia, repichnia, pascichnia, and cubichnia occupying all continental tiers (subaerial and subaqueous, surficial, and/or very shallow, shallow, mid, and deeper) and ecological niches (epiterraphilic, terraphilic, hygrophilic, and hydrophilic). In association with invertebrate traces, two taphonomic modes of tetrapod footprints have been found: a moderate-fidelity mode and a high-fidelity mode. Physical sedimentary features, burrows, trails, and tracks, and their stratigraphic positions are integrated to interpret the main factors involved in footprint preservation in these subsettings. The most significant and variable preservational factor found is water-table fluctuation controlled by the paleohydrology of a balanced-fill lake system. These data show that in balanced-fill lake systems, diverse trace assemblages occur in the lake and associated subsettings such as delta plains and lake-margin settings, whereas trace fossils can be totally absent in coeval lake-center strata, particularly if anoxic lake-bottom conditions occur, as probably occurred in the meromictic Santa Clara lake system.

The Jurassic ophiolitic mélanges in Serbia: a review and new insights

In Serbia ophiolitic mélanges widely occur below ophiolites. These ophiolites are interpreted to derive from different oceanic domains and are therefore attributed to different tectonic units. We revisited all existing data on matrix ages and blocks in the mélanges, studied the relict sedimentological features and dated new sections and blocks from various ophiolitic mélanges. On the basis of these results we can distinguish three types of ophiolitic mélanges: (1) intra-oceanic ophiolitic mélanges (OM1); (2) ophiolitic mélanges formed during ophiolite obduction with continental blocks (OM2); (3) ophiolitic mélanges with fluviatile transported sedimentary rocks or tectonically incorporated much younger blocks at the base (OM3). These three types of ophiolitic mélanges resemble the polyphase history of shortening and ophiolite emplacement on the wider Adria plate of Serbia. All ophiolitic mélanges contain the same Triassic component spectrum of oceanic sedimentary cover rocks and have similar matrix ages. It can be concluded that all of the ophiolites and ophiolitic mélanges derive from the same Triassic–Jurassic oceanic domain, the Neotethys Ocean, the western part of which obducted during Middle–Late Jurassic time on wider Adria. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management

AbstractElevated fine sediment accumulation in a river system's gravel bed is known to cause detrimental ecological impacts. Current sediment targets and approaches to mitigation have failed due to the oversimplification of geomorphological processes controlling fine sediment accumulation and the lack of relevant scientific knowledge underpinning them. This is particularly apparent in chalk streams (groundwater‐dominated systems) which regularly exhibit high rates of sediment accumulation despite low suspended sediment yields. A necessary first step is to better characterise their sedimentology; thus, the novelty of this study was to determine the sedimentological characteristics of chalk stream gravel beds, specifically the quantity and distribution of fine sediment with depth. We collated published and unpublished freeze‐core data, encompassing 90 sites across 11 UK chalk streams. Results showed average quantities of fine sediment (<2 mm) in chalk stream gravel beds were 25% by weight, with >75% of beds exceeding thresholds for ecological degradation. Quantities of fine sediment increased with increasing depth into the bed, with an average increase between surface and subsurface layers of 54%, and 89% of the gravel bed over‐saturated with fine sediment. Regional differences were attributed to differences in stream power and local sediment sources, including surficial geology and catchment land use. Additionally, a major contrast was identified between experimental conditions in flume studies used to establish models describing interactions/mechanisms of fine sediment infiltration into immobile gravel beds and the natural conditions observed in chalk streams. As such, the use of such models as a basis to explore sediment management scenarios is unlikely to predict the outcome of such management techniques correctly in a real‐world situation.

Linking archaeology and paleoenvironment: Mid‐Holocene occupational sequences in the Varamin Plain (Iran)

AbstractEarly human habitation of the arid to semiarid Central Iranian Plateau was strongly connected to the availability of water and associated natural hazards, such as flooding and drought events. In this geoarchaeological study, we focus on the occupation at the prehistoric site of Ajor Pazi within the formerly active fluvial environment of the Varamin Plain. Through radiocarbon and luminescence‐dated sediment cross‐sections, we apply multivariate statistics to sedimentological characteristics of bulk samples collected during a rescue excavation in 2018. Based on facies interpretations, we differentiate depositional processes and present their implications for the environs of Ajor Pazi. Our results show evidence of settlement activities between 6.4 and 5.6 ka cal B.P. (4.4–3.6 ka cal. B.C.E.). Phases of reduced geomorphodynamics can be distinguished when soil‐forming processes take place. Our findings provide insights into the hitherto scarcely explored Transitional Chalcolithic II period during which the site of Ajor Pazi emerged and began to shape its environs.

A preliminary geochemical study of the archaeological site of the Battle of Jenipapo (Piauí state, Brazil)

AbstractThis paper presents, for the first time, geochemical data related to the Battle of Jenipapo, a significant event that occurred on March 13, 1823, marking a political activity favorable to Brazil's independence. The present work aimed to analyze the contents of lead and copper as markers of historical armaments in sediments for geochemical prospecting of the archaeological area in which the Battle of Jenipapo probably occurred. Nine sediment samples were collected: seven from the prospect area and two control samples. Sedimentological characteristics were evaluated, such as pH (6.1–6.9), acidity (0.19–3.00 mmol L−1), organic matter (0.86–3.37% w/w), and granulometric classification (sandy predominance). The metals (lead and copper) were determined by inductively coupled plasma mass spectrometry (ICP‐MS) after acid digestion of the sediments. Lead content ranged from 7.9 to 14.9 mg kg−1 for samples and 5.4 mg kg−1 for control samples. Copper content ranged from 14.2 to 29.3 mg kg−1. The results showed that only lead could be used for the geochemical prospecting of the area that presented strong evidence of anthropic intervention allowing the carrying out of excavation steps.

Sedimentary and stratigraphic architecture in the geoarchaeological context of Late-Holocene deposits in the eastern coastal plain of Belgium: Zwin region – Hoeke

A sedimentary investigation was carried out into the rise and fall of mediaeval Bruges’ maritime access. Because the mediaeval metropolis had no direct connection with the North Sea, its maritime connectivity during the High- and Late-Middle Ages depended on a tidal channel, known as the ‘Zwin’. In order to reconstruct the mediaeval physical environmental situation correctly, the entire Holocene sedimentary record was studied through undisturbed mechanically-drilled cores and electrical cone penetration tests (CPT-e). A detailed sedimentary analysis was complemented with radiocarbon dating and datable archaeological finds to resolve a timeframe for the sedimentary evolution. Tidal channel systems with diverse morphologic and sedimentologic characteristics prevail and cover a period from at least the Roman period till the Late-Middle Ages. The presence of a single peat layer directly on top of the Pleistocene substrate and the stratigraphic position of the tidal channel deposits relative to this peat layer, proves that no seawater entered this part of the Belgian coastal plain before the Late-Holocene. The tidal channel system that was active during the heydays of Bruges (the Zwin) was the last natural one. It silted up due to a further reduction of the accommodation space as a consequence of new embankments, possibly expedited by storms.

Estuaries House Earth’s oldest known non-marine eukaryotes

Some of the oldest postulated non-marine eukaryotic microfossils occur in the 1.1–1.0 Ga Poll a’Mhuillt, Loch na Dal, and Diabaig formations in NW Scotland. These sedimentary strata have traditionally been interpreted as lacustrine. Here we report new trace element, sulfur isotope and metal abundance data and sedimentological observations for the latter two units. The geochemical data imply low salinity, oxic conditions whereas sedimentological features indicate marine tide and storm processes. Interpreting their depositional settings as estuaries, rather than lakes, with seawater-freshwater mixing fronts reconciles the contrasting datasets. Thus, whist these microbial habitats likely experienced frequent seawater input, they appear to have experienced the lowest salinity conditions of all known in situ fossil assemblages in the Precambrian. The Torridonian may in fact be representative of the low-salinity habitats predicted for ancestral eukaryotes based on phylogenetic reconstructions. Estuarine settings with gradients in water chemistry over space and time may have facilitated the transition of eukaryotic life from land to sea.

The effects of the rock stratigraphy on TPH/PAH absorption and transmission in some sections of the Gokana and Khana Local Government Areas

Concentration of TPH/PAH in soils in parts of Gokana and Khana local government areas of Rivers state were examined using samples from 30 shallow wells drilled with hand auger. The core intervals penetrated, ranged between 0 on the surface to 100cm at total depth and was composited into two sections corresponding to upper 0 – 0.5m and lower 0.51 – 0.1m sections respectively. The samples were described to determine their sedimentological characteristics and effect on absorption and transmission of fluids. The total hydrocarbon content in samples of the study area were determined following the EPA 1664 Hexane Method (Method No: EPA 418.1/413.2 & EPA 1664). Individual concentrations of identified PAH congeners were noted and combined to generate the PAH concentrations in each of the two composited sections of the 30 sampled locations. The sedimentology of the logged sections consists mostly of peaty clay, clayey sands and organic clay in the upper section and clayey silt and clayey sand in the lower section. TPH in the study area ranged between 20612mg/kg at Location 15 to 37.09mg/kg at Location 11 for the upper (0 – 0.5m) sections and 14731mg/kg at Location 12 to 14.67mg/kg at Location 17 for the lower (0.51 – 1m) section. PAH ranged from 9.55mg/kg at Location 12 to <0.01mg/kg at several other Locations for the upper (0 – 0.5m) sections and 5.71mg/kg at Location 11 to <0.01mg/kg at several other Locations for the lower (0.51 – 1m) section. Correlation of sedimentology descriptions with the geochemical analysis indicates high concentrations of total petroleum hydrocarbon (TPH) and polycyclic aromatic hydrocarbon (PAH) within the upper (0 – 0.5m) sections than in the lower (0.51 – 0.1m) sections in consonant with the stratigraphy of the logged section.

Lithofacies and paleoenvironmental analysis of the Upper Cretaceous successions: Yagaan Khovil fossil locality, central Gobi region, Mongolia

The Upper Cretaceous successions are exposed at the Yagaan Khovil fossil locality in the central Gobi region, Mongolia. The successions comprise fluvial deposits that are divided into two units based on the lithological characteristics of the floodplain deposits. The lower unit (Unit 1) is characterized by eolian-influenced environments, whereas the upper unit (Unit 2) is composed predominantly of meandering river systems with lateral accretionary channel fill deposits that show concretion at the top of the bed. The shift in depositional processes from the lower to the upper unit can be hypothesized as the result of the change in the proximity of the eolian-affected area to the study area. The successions preserving the similar paleoenvironmental transition are also present in the Nemegt Basin, where the successions shift from reddish mud beds affected by eolian processes to meandering fluvial successions. Additionally, to the similar sedimentological features, similarities in vertebrate fossils between Yagaan Khovil and the formations in the Nemegt Basin imply the close relationship between the two areas in terms of environmental conditions, ages, and stratigraphic positions. To enhance the stratigraphic framework of the Upper Cretaceous strata in Mongolia, future work should integrate the findings of this study with new radiometric dating techniques.

Identification of three stages of paleochannels and main source analysis beginning in the middle Pleistocene in the western Bohai sea in north China

Significant global sea transgressions–regressions have occurred under the influence of glacial–interglacial climatic change during the Quaternary period. Various types of paleochannels developed on the continental shelf of the western Bohai Sea as a result of sea level decline. Currently, the source of the paleochannels and the sedimentary environment and evolutionary pattern of the paleochannels are disputed. This study interprets high-resolution single-channel seismic data using a chronological framework based on accelerator mass spectrometry 14C (AMS14C) dating and optically stimulated luminescence (OSL) dating of core DZQ01. Furthermore, this research correlates this data with the cores of TJC-1 and H6 in the Western Bohai Sea and analyzes sedimentological characteristics based on grain size and clay mineral analyses. The results indicate that (1) three stages of paleochannels, namely Seismic Unit 6 (SU6), SU4, and SU2 are identified from bottom to top during Marine Isotope Stage 8 (MIS 8), MIS 6, and MIS 4, respectively; (2) from 300 to 243 cal. ka B.P., the SU6 paleochannel has four pathways, with the Yellow River serving as a primary source; from 191 to 130 cal ka B.P., the SU4 paleochannel has three pathways, and the main sources are the Yellow River, the Liao River, and the Luan River; from 74 to 14 cal. ka B.P., the SU2 paleochannels have two large tributaries, with the principal sources being the Yellow River and the Luan River. We, therefore, it can be inferred that the uplift of the Tibetan Plateau and glacial–interglacial climatic change constitute the formation mechanism for the paleochannels.