Indicators of biosiliceous production offer unique insights into the silica cycle at dynamic marine-continental interfaces, where seasonal discharges interact with a nutrient-depleted tropical ocean. This study reconstructs variations in siliceous paleoproductivity in the southwestern Gulf of Mexico (SW GoM) over the last 33.0 cal ka BP, investigating the complex interplay between oceanic circulation and continental nutrient forcing. Using a multiproxy approach, we integrated siliceous microfossils (diatoms, radiolarians, silicoflagellates, and sponge spicules) with bulk geochemical indicators (Corg, CaCO3, and Siopal %wt) and total planktonic foraminifera. Our results reveal that while the SW GoM remained predominantly resource-limited, biogenic production exhibited significant variability across established Quaternary periods, with CONISS analysis delineating three distinct paleoceanographic stages over the Pleistocene-Holocene transition: (1) Last Glacial (33.0–19.0 cal ka BP), characterised by minimal biogenic accumulation across all microfossil groups due to enhanced stratification and reduced fluvial input relative to the current interglacial. (2) Deglaciation or Termination I (19.0–11.7 cal ka BP) was marked by a rise in diatom and sponge spicule abundance alongside peak planktonic foraminifera, indicating a carbonate-dominated system during marine transgression. (3) The interglacial (the last 11.7 cal ka BP) recorded the maximum biosiliceous accumulation, reflected in maximum Corg and Siopal values, driven by sea-level stability and increased river discharge relative to the glacial. Our findings demonstrate that the siliceous fraction, although a minor component of total biogenic production, tracks the coupling between the silicon and carbon cycles. This study underscores the sensitivity of siliceous microfossils to land-sea interactions, demonstrating their crucial role in understanding the long-term evolution of tropical ecosystems.
Conodont Alteration Index (CAI) is widely used to evaluate the alteration history of conodont elements and is commonly employed in studies of thermal maturity. This study investigates the relationships among CAI, surface microtextures, petrographic features, and elemental composition in Pennsylvanian conodonts from the Río Nevado Formation at the Totumo section, Chibcha Terrane, Colombia. Petrographic analyses reveal an extensive diagenetic overprint characterized by ferruginous coatings, pressure-solution seams, stylolites, neomorphic cements, and recrystallized micritic textures, with no evidence of hydrothermal alteration or low-grade metamorphism. Conodont elements exhibit heterogeneous CAI values ranging from 5 to 8, with most specimens corresponding to CAI 6. Scanning electron microscopy reveals a continuum of surface modification from partially preserved smooth surfaces to dense sugary textures composed of hexagonal networks, microcrystalline coatings, corrosion features, and localized crystal growth. No consistent relationship was observed between the degree of microtextural modification and CAI values. EDS analyses indicate that smooth and altered surfaces share similar major-element compositions dominated by Ca, P, and F, whereas euhedral crystals developed on conodont surfaces correspond to authigenic quartz and calcite. The compositional similarity among the different microtextures suggests that significant surface modification may occur without substantial changes in the primary elemental composition of the conodont elements. The integration of petrographic, CAI, SEM, and EDS data indicates that elevated CAI values may develop in successions dominated by diagenetic processes and should therefore be interpreted cautiously when used as indicators of thermal conditions.
The analysis of δ13C and δ18O isotopes from Lenticulina shells and bulk carbonate in the La Cerradura section (External Subbetic, South-Iberian Palaeomargin) indicates the occurrence of a negative carbon isotope excursion (CIE) associated with the Jenkyns Event. Lenticulina incorporates sediment pore-water dissolved inorganic carbon in to their calcitic tests, recording the global negative CIE. The δ13CLenticulina values are lower compared to bulk carbonate, which includes calcareous nannofossils and uncertain micrite origins from carbonate-mud export, and scarce biocalcifier benthic remains. The fluctuations in δ13CLenticulina may correlate with (1) the microhabitat depth of Lenticulina, ranging from epifaunal to deep infaunal environments, with the lowest values corresponding to deeper habitats and (2) periods of increased organic matter accumulation. A notable decrease in δ13CLenticulina during the Jenkyns Event coincides with the lowest δ13Cbulk and occurs in a context of changing facies, enhanced total organic carbon levels, and oxygen-depleted conditions.The decrease in the difference between δ13CLenticulina and δ13Cbulk (Δδ13C) during the CIE presents challenges for explanation, potentially linked to a crisis of carbonate productivity and oceanographic shifts as indicated by calcareous nannofossil assemblages. Conversely, δ18OLenticulina values trend differently from δ18Obulk, typically being higher in the upper Pliensbachian and similar in the Polymorphum Zone (lowermost Toarcian). During the onset of dark marls, marking the negative CIE, δ18Obulk values exceed those of δ18OLenticulina, while negative Δδ18Obulk-Lenticulina values during marl-limestone alternations suggest significant oceanographic changes facilitated by high evaporation rates affecting the South-Iberian Palaeomargin.Post-Jenkyns Event, a decrease in Δδ18Obulk-Lenticulina corresponds with the recovery of carbonate productivity and increases in deep-dwelling calcareous nannofossils. This recovery aligns with a return to more positive C-isotope values (for Lenticulina and bulk carbonate), indicating a recovery of productivity in the photic zone of the water column and the adjacent carbonate platform. Overall, the isotopic analyses of the carbonates deposited in the hemipelagic context reflect significant changes in palaeoenvironmental conditions, including variations in water salinity and temperature of the surrounding Prebetic shallow platform.Therefore, the integration of C and O isotopic composition from Lenticulina and bulk carbonate with analysis of calcareous nannofossils allows to identify oceanographic changes affecting the carbonate productivity in the Western Tethys associated with the Jenkyns Event and the subsequent recovery.
This study summarizes the conodont record from the marine portion of the Piaui Formation in the Parnaiba Basin, Northeast Brazil, western Gondwana. New data on conodont occurrences throughout the stratigraphic succession are presented, together with a taxonomic revision of previously described specimens and a taphonomic analysis based on statistical data. A total of 12 conodont species belonging to eight genera were identified, including Idiognathodus (I. saelansae, I. obstipus, Idiognathodus sp.), Diplognathodus (D. ellesmerensis, D. orphanus), Declinognathodus (D. marginodosus), Neognathodus (N. bothrops, N. uralicus), Hindeodus (H. minutus), Adetognathodus (A. lautus), Idioprioniodus (Idioprioniodus sp.), and Streptognathodus (Streptognathodus sp.). The occurrence of Idiognathodus saelensae, Idiognathodus obstipus, Neognathodus bothrops, and Neognathodus uralicus, previously reported from the Amazonas Basin, North America, Russia, and South China, supports a lower Moscovian age for the studied succession. The analysis of 255 conodont elements, classified according to four previously established taphonomic alteration parameters, indicates that the deposits were subjected to significant mechanical reworking under moderate- to high-energy marine conditions. The combined taxonomic and taphonomic data indicate that the Piaui Formation preserves a mechanically reworked but biostratigraphically reliable lower Moscovian conodont fauna, offering important insights for both regional and global correlations of Pennsylvanian marine successions.
Planktonic foraminifera are widely used as tracers of upper-ocean thermal structure due to their sensitivity to ambient temperature; however, accurate paleoceanographic reconstructions require robust constraints on their depth habitats. Here, we determine the apparent calcification depths (ACD) of four key planktonic foraminifera species from a modern sediment core recovered from the Soledad Basin (Baja California Peninsula, eastern tropical North Pacific). ACD were estimated by matching measured oxygen isotopic compositions of foraminiferal calcite (δ18Oc) with depth-resolved equilibrium calcite values (δ18Oe) derived for the upper 200 m of the water column. Our results reveal a clear and consistent vertical habitat partitioning: Globigerinoides ruber and Trilobatus sacculifer calcify within the mixed layer (∼0–30 m), Globigerina bulloides occupies subsurface waters near the chlorophyll maximum, and Neogloboquadrina dutertrei is constrained to the thermocline. While ACD estimates show some sensitivity to paleotemperature calibration and seasonal flux biases, the relative depth structure among species remains robust. These findings provide the first regional calibration of foraminiferal ACDs in the eastern tropical North Pacific and demonstrate that a multi-species approach offers a reliable framework for reconstructing past changes in upper-ocean thermal stratification in dynamic upwelling systems.
High diatom blooms occur on the Crozet and Kerguelen Plateaus of the Southern Ocean (SO) due to natural iron fertilization, despite iron and light co-limitation in the Polar Front Zone (PFZ). However, glacial-interglacial records of diatom productivity and the biological carbon pump are limited. We present a diatom productivity record for the past ∼40 ka from sediment core SN2 (47°S, 57°30′E), located between the Crozet and Kerguelen Plateaus. Our results show the highest diatom productivity during early Marine Isotope Stage (MIS) 2, the lowest during the deglacial-Holocene, and intermediate during late MIS3 and the Last Glacial Maximum (LGM). The abundances of the permanent open ocean zone (POOZ) group diatoms co-varied with diatom productivity and were inversely correlated with coastal planktonic group diatoms. Neither diatom productivity nor POOZ diatoms correlated with dust and iron fluxes. An inverse relationship was also observed between the PFZ and Antarctic zone diatoms. We suggest that higher diatom productivity during early MIS 2 likely resulted from nutrient-rich southern waters resulting from SO upwelling, driven by the northward migration of the Antarctic Polar Front (APF). Conversely, reduced southern nutrient-rich waters led to lower diatom productivity during late MIS 3 and the deglacial-Holocene. Although the APF was present near the core site during the LGM, lower diatom productivity may have resulted from increased stratification. We propose that APF migration and upwelling intensity may have controlled diatom productivity and the biological carbon pump through deep-water nutrients (iron and silicate).
Planktonic foraminifera are valuable paleoceanographic indicators because their shell assemblages reflect ocean surface conditions. However, studies examining relationship with environmental factors in the subtropical Northwest Pacific remain limited. Herein, we investigated seasonal changes in foraminiferal fluxes and assemblages using bi-weekly sediment-trap samples collected from October 2019 to August 2020 in the North Pacific Subtropical Gyre (NPSG). Fluxes and assemblages showed significant seasonal variation, and cluster analysis grouped species into three clusters. Group A (symbiont-bearing warm-water species) was regulated primarily by SST (sea surface temperature) (similar to 28.5 degrees C), likely due to photosymbiosis. Group B (deep-dwelling species) appeared to be driven by annual reproduction cycles and food availability. Group C (Globigerinella siphonifera) showed no clear seasonality. We also report, for the first time, three morphotypes of Orbulina universa (Type I-III) with distinct seasonal variations in the North Pacific. Notably, Type II exhibited a flux pattern similar to Group A, suggesting a preference for warm, stratified waters. By integrating 18 sediment-trap records from the North Pacific, we found that assemblage composition was primarily determined by SST, whereas the magnitude of total foraminiferal fluxes (TFFs) was closely associated with primary productivity and organic carbon (OC) flux. OC and TFFs were particularly low in the NPSG, reflecting its strongly stratified oligotrophic conditions. Although no major assemblage shift was detected over the past two decades, long-term SST records revealed significant warming, particularly in winter, suggesting enhanced stratification. These results imply that future warming may expand subtropical waters, potentially reducing foraminiferal fluxes and affecting the marine carbon cycle.
Pteropods, owing to their fragile aragonitic shells and sensitivity to upper-ocean carbonate chemistry, represent promising yet underutilized archives of past ocean conditions. This study investigates the stable oxygen and carbon isotopic composition (518O and 513C) of the aragonitic pteropod Heliconoides inflatus and the calcitic planktonic foraminifera Globigerinoides ruber from core-top samples and Late Holocene sediment cores (SSK-98 SPC13 and SPC09) from the Bay of Bengal and Andaman Sea. Consistent inter-species isotopic offsets are observed, with H. inflatus exhibiting higher 518O and lower 513C values than G. ruber, reflecting differences in mineralogy, calcification depth, and habitat ecology. 518O-derived depth estimates indicate that G. ruber calcifies within the upper mixed layer (20-50 m), recording near-surface hydrographic conditions, whereas H. inflatus forms its shell within the upper thermocline (ca. 60-110 m), capturing subsurface water properties. Downcore 518O and temperature reconstructions reveal contrasting Late Holocene responses to monsoon variability, with relatively stable surface temperatures inferred from G. ruber and enhanced thermocline variability recorded by H. inflatus, indicating increased upper-ocean stratification during weaker monsoon phases. The weak correlation between H. inflatus isotopic values and the Limacina Dissolution Index (LDX) suggests minimal diagenetic alteration, implying that the observed variability reflects hydrographic changes from the surface to 260 m. Strong agreement between pteropod-based proxies, carbonate ion estimates, and foraminiferal records demonstrates that H. inflatus is a reliable archive of past thermocline conditions, underscoring the value of pteropods in multi-proxy reconstructions of monsoon and carbonate system variability in the tropical Indian Ocean.
The world's oldest encrusting calcareous Foraminifera are here described from the Sheinwoodian of Saaremaa Island, Estonia. The encrusting Foraminifera represents a new species of the genus Earlandia, and E. giga n.sp. is characterized by a slightly conical and huge bilocular test. The foraminifera encrust gastropod shells in a gregarious manner. The Estonian material suggests that early calcareous Foraminifera had already experimented with a range of life strategies, including large body size and attachment to hard substrates. Our findings challenge the traditional narrative of early calcareous Foraminifera as exclusively soft-substrate dwellers, indicating a more complex ecological differentiation during the early Palaeozoic.
Conodont distribution patterns from the Rio Nevado Formation (Totumo section), Chibcha Terrane, northern Andean Cordillera of Colombia, are analyzed using quantitative methods within a stratigraphic framework. The aim is to evaluate paleoecological differentiation and paleobiogeographic affinity during the early to middle Moscovian. Variations in taxonomic composition and relative abundance define consistent trends along the stratigraphic succession. These trends reflect changes in assemblage structure across a shallow-marine carbonate platform. Assemblages dominated by Adetognathus are associated with reduced diversity and lower abundance. In contrast, assemblages dominated by Idiognathodus and Neognathodus show higher abundance and moderate diversity. Multivariate analyses, including non-metric multidimensional scaling and constrained ordination, reveal a compositional gradient consistent with a facies-related environmental trend, suggesting a proximal-distal organization of assemblages across the carbonate platform. Paleobiogeographic relationships were evaluated using presence-absence data from multiple sections across the Chibcha Terrane, combined with coeval datasets from other regions. Similarity-based clustering and ordination reveal a strong faunal affinity between the Chibcha Terrane and the North American Midcontinent, supported by the prevalence of Idiognathodus and Neognathodus. In contrast, Tethyan regions such as South China and eastern Europe are characterized by taxa such as Declinognathodus, Idiognathoides, and Swadelina, which define a distinct assemblage structure. Western Gondwana occupies an intermediate position and includes taxa from both domains. These results are consistent with a Panthalassic paleobiogeographic affinity for the Chibcha Terrane prior to its accretion to Gondwana. They also highlight the value of conodont assemblages for integrating paleoecological and paleobiogeographic signals.
An integrated molecular, morphometric, and biogeographic investigation of the benthic foraminiferal genus Ammonia was conducted along the Indian coastline, encompassing selected marginal marine localities spanning both the Arabian Sea and Bay of Bengal. Living specimens were sampled from 22 locations between 2021 and 2025. A total of 120 specimens were imaged using a Scanning Electron Microscope (SEM), and 46 specimens were sequenced using partial small subunit (SSU) rRNA gene fragment. Phylogenetic analyses of the SSU rDNA sequences resolved four genetically distinct, fully supported (100% bootstrap) monophyletic lineages: A. veneta/T1, A. arabica/T26, A. nigami/T27, and the newly described A. saraswatii sp. nov./T28. Multivariate statistical analysis of 40 significant test characters, demonstrated that all four species are morphologically distinct. Our results show that the use of following key diagnostic morphological characters: in profile view (gsd, gsd/height, spiral side concavity/convexity, peripheral structure), umbilical view (sutural notches, beads/grooves along sutures, peripheral spines), and spiral view (sutural relief in central test region) enable sufficient discrimination using stereo zoom microscope. The four species exhibit contrasting biogeographic distributions directly interpretable in terms of the oceanographic and ecological differences between the Arabian Sea and the Bay of Bengal: A. veneta/T1 is cosmopolitan; A. arabica/T26 and A. saraswatii/T28 show distributional affinities to the northern Indian Ocean; and A. nigami/T27 is endemic to the low-salinity northern Bay of Bengal. This integrated morphological and molecular framework links biogeographic patterns to measurable test-architectural differences, enabling confident phylotype recognition in modern and fossil assemblages and improving paleoenvironmental reconstructions across the Indian subcontinent.
The formation and evolution of the Taihu Plain during the Holocene have significantly influenced the development of Neolithic cultures in the region. Based on AMS 14C dating, lithological analyses of cores SZ24 and SZ50, and pollen analyses of core SZ24, and supplemented with previous results from cores SE2 and JLQ, this study reconstructs the Holocene depositional history of the southern Taihu coastal zone. The Late Pleistocene surface represented an ancient plain incised by palaeo-valleys near the Qiantang River. Holocene sediments overlie this substrate and record a transgressive estuarine environment during the early Holocene, followed by plain progradation during a relatively slow rise and gradual stabilization of mid-Holocene sea-level. After-7.0-5.7 cal kyr BP, the southern Taihu Plain gradually emerged, forming the modern landscape. The sedimentary processes differ from those of larger estuaries in East Asia during the middle to late Holocene, possibly due to the absence of a large river discharging into the palaeo-estuary.
We present Paleocene-Eocene calcareous nannofossil biostratigraphy and paleoecology for the Surprise Hill core, U.S. Atlantic Coastal Plain, Virginia. Calcareous nannofossil datums ranging from Zone NP3 to NP14 were identified. The Danian-aged Brightseat Formation rests unconformably atop the Lower Cretaceous Potomac Group at 211.4 m and disconformably underlies the Aquia Formation at 208.8 m. The absence of Zone NP7 suggests a hiatus is present in the Aquia Formation (Zones NP5-NP9a). The contact between the Marlboro Clay and the overlying Nanjemoy Formation (Zones NP10-NP14) at 189.5 m is truncated. The Paleocene-Eocene transition is marked by a shift from glauconitic sands of the Aquia Formation to pelitic muds of the Marlboro Clay at 202.7 m. A 3-3.5%o negative delta 13C excursion of benthic foraminifer and a thin dissolution interval (201.6-202.5 m) are recorded in the basal Marlboro Clay. Nannofossil response to the Paleocene-Eocene Thermal Maximum (PETM) include (1) a bloom in taxa with affinities for changing salinity conditions just prior to the PETM basin wide (Hornibrookina australis arca), (2) a decline in taxa with ecological affinities for cool, eutrophic waters (Chiasmolithus bidens) during PETM, (3) fluctuations in mesotrophic to eutrophic, opportunistic taxa (e.g., Neochiastozygus junctus) during PETM, (4) successive turnovers in species of Toweius spp. during core-PETM and its recovery. Our findings suggest that overall nannofossil assemblages in the southernmost portion of the Salisbury Embayment responded similarly to assemblages from South Dover Bridge, but had differing response to local changes in nearshore paleoecology.
The relative warmth of different interglacial periods provides crucial insights into climate system sensitivity under varying boundary conditions. While global proxy records indicate that the Last Interglacial (MIS 5, specifically MIS 5e) was warmer than the present Holocene (MIS 1), quantitative terrestrial evidence from temperature-sensitive proxies in East Asia remains scarce. In this study we present a new high-resolution palynological record from core LYK-1 in the western South Yellow Sea (SYS), spanning from MIS 5 to the present, to quantitatively assess the relative warmth of these two interglacials. We utilize the pollen of Liquidambar, a thermophilous genus with stringent climatic requirements, as a key temperature proxy. By integrating pollen data with robust lithological, foraminiferal, and chronological controls, we first disentangle the influences of sea-level change and depositional environment on the pollen assemblages to isolate the climatic signal. By further comparison with the surrounding records, the results reveal a striking contrast: Liquidambar pollen is significantly more abundant during MIS 5 than MIS 1. This indicates that the MIS 5e climate along the SYS coast was substantially warmer and more humid than the Holocene, allowing for a notable northward expansion of subtropical flora. The herbaceous pollen dominance throughout the core is interpreted as a signature of fluvial transport dynamics in this inner-shelf setting rather than a purely open landscape. This well-dated record provides robust terrestrial evidence for a significantly warmer MIS 5 in East Asia, underscoring the region's sensitivity to interglacial intensity and offering a valuable paleo-analogue for understanding future warming scenarios.
This study aims to present the foraminiferal biostratigraphy of the uppermost Cretaceous phosphatic intervals in the Paraiba and Potiguar onshore basins. Based on the occurrence of typical assemblages and the first occurrences of marker species, including Globotruncana aegyptiaca, Gansserina gansseri and Pseudoguembelina palpebra, three upper Campanian-lower Maastrichtian planktic foraminifera zones were recognized: the G. aegyptiaca-G. gansseri Zone, the G. gansseri Zone, and the P. palpebra-Contusotruncana contusa Zone. In the Paraiba Basin (Itamaraca Formation), the phosphatic interval that spans the G. aegyptiaca-G. gansseri and the G. gansseri zones contains a benthic assemblage comprising Epistomina supracretacea, Orthokarstenia ewaldi, Siphogenerinoides bramletti, Gavelinella spp., and Quinqueloculina spp. In the Potiguar Basin (Jandaira Formation), the phosphatic interval within the G. gansseri Zone yields Afrobolivina afra, Gavelinella spp., and Lenticulina spp. The depositional environment of the study area is characterized by paleobathymetries ranging from inner-middle neritic to middle-outer neritic. These results are consistent with studies from Morocco, Jordan, Iraq, Israel, Syria, Colombia, the subtropical North Atlantic, and Brazil, particularly regarding the age of the phosphatic intervals and their foraminiferal assemblages. The similarities among these assemblages highlight the widespread geographic distribution of phosphogenic deposits during the Late Cretaceous.
Diatom frustules and dinoflagellate cysts preserved in sedimentary archives are routinely utilized as indicators of past climate and environmental change. However, fragile or lightly silicified diatom frustules can be prone to fragmentation and dissolution, and indicator species are often rare or not preserved at all. For dinoflagellates, only a fraction of species are known to form fossilizable organic-walled cysts, thus the large majority remains unaccounted for in the microfossil record. Sedimentary ancient DNA (sedaDNA) can potentially fill this gap due to its ability to trace biota even in the absence of physical remains, yet direct comparisons of microfossil records with marine sedaDNA are still limited. Here, we present a comparative analysis of marine sedaDNA metabarcoding with microfossil records of diatoms and dinoflagellates in a marine sediment core taken off North-West Greenland spanning the past similar to 8300 years. Our results show that the microfossil and sedaDNA records are complementary, both with regard to uncovering past diversity and describing temporal changes. Incongruencies between data types were due to database incompleteness, primer biases, and marker resolution for sedaDNA, while the microfossil records were affected by low abundance or differential preservation potentials. For dinoflagellates, unknown cyst-theca relationships and differential preservation potentials additionally limited comparability. Community efforts are needed to generate reference DNA sequences through culturing and to determine cyst-theca relationships via life-cycle studies. Our study highlights the importance of combining sedaDNA with classical approaches to gain a better understanding of long-term climate and marine ecosystem changes in the Arctic and for marine biodiversity assessments and monitoring.
Foraminifera assemblages from seafloor deposits can serve as bioindicators for environmental conditions. Ideally, baseline catalogues of foraminifer communities nearest to a geographical location of interest are used to identify and compare findings. Such databases, however, do not exist for many geographic locations. This study examines the previously undocumented foraminiferal communities of three southern Maldives atolls and an island; Huvadhu, Addu, and Fuvahmulah covering 26 distinct sites. Sediment samples, collected during the Pristine Seas Program survey of these atolls, aimed to better understand the atolls' biodiversity, ecology and environmental health amid increasing anthropogenic pressures and climate change. A total of 320 species across 118 genera were identified. Results reveal distinct assemblage patterns influenced by substrate type, reef morphology, and depth. Assemblages were dominated by symbiont-bearing rotaliids and planktonic forams accompanied by diverse miliolids and diversity indices indicate overall high ecological stability. Huvadhu, with fewer species but higher dominance by stable, reef-associated taxa, suggests a pristine environment, while Fuvahmulah and Addu show signs of localized stress, likely due in part to tourism and development. Statistical analyses demonstrate significant community differences among atolls, with high heterogeneity within Addu reflecting varied habitat conditions, substrate types, and depth being the principal drivers of assemblage composition. Compared with the central and northern Maldives, the southern atolls exhibit greater species richness and evenness, suggesting more pristine reef environments. As tourism expands, baseline biodiversity assessments like this help in future ecological monitoring and provide new insights into biogeographic gradients and environmental stability within the Indian Ocean reef systems.
Biostratigraphy is a fundamental tool for age-calibrating marine sediments and enabling palaeoceanographic reconstructions. However, establishing age control in marine sediments of the Arctic Ocean is challenging, due to low micro- and nannofossil abundances, discontinuous occurrences across glacial and interglacial periods, as well as spatial and temporal variations in carbonate preservation. Gephyrocapsa huxleyi is a globally distributed coccolithophore whose first occurrence at ca 290 ka is widely used to date Quaternary marine sediments. Yet, its initial appearance and stratigraphic range in the Arctic Ocean are debated. Here, we present the first combined sedaDNA-nannofossil approach to trace the occurrence of G. huxleyi throughout three sediment cores from the Lomonosov Ridge recovered during the Arctic Ocean 2016 expedition on icebreaker Oden. SedaDNA was extracted from 87 samples spanning key lithological boundaries. Following shotgun sequencing, the presence of G. huxleyi was assessed using three independent bioinformatic tools Kraken2, BWA and BLAST. These results were integrated with lithological data and Gephyrocapsa nannofossil assemblages to evaluate the potential of palaeogenomics as a biostratigraphic tool in the Arctic that could potentially overcome the limitations of conventional nannofossil-based approaches. Although we found broadly overlapping sedaDNA and nannofossil results, key discrepancies and methodological limitations do not allow us to confidently identify the first occurrence of G. huxleyi in the studied sequences. We discuss both the potential and the challenges of sedaDNA as a complementary biostratigraphic tool to improve age control of Arctic marine sediments.
The ostracod assemblages from the Bonares-Casa del Pino section in the Lower Guadalquivir Basin, part of the lower Pliocene Arenas de Huelva Formation, have been analysed for palaeoenvironmental purposes. These assemblages form part of a subtropical/tropical biota, consistent with findings from earlier studies on fossil remains within the Zanclean deposits in the Southwestern Iberian Peninsula.The present study marks the first application of the Specific Population Species index Method, originally developed to distinguish autochthonous from allochthonous species in Recent assemblages, to fossil ostracods. Through both quantitative and statistical analyses, the autochthonous nature of both dominant and characteristic species was recognized. The succession was deposited in the northernmost sector of the East Atlantic lower Pliocene tropical palaeo-ecoregion (also known as Atlantic Andalusian Pliocene Mollusc Unit 1), within shallow waters. The attribution to the offshore transition zone, close to the boundary between infralittoral and circalittoral zones, prompted clarification of vertical zonation terminology for both the Atlantic and Mediterranean, in Recent and Pliocene marine environments.
