Dinoflagellate Cysts Research Articles

Dinoflagellate cyst and pollen assemblages as tracers for marine productivity and river input in the northern Gulf of Mexico

Abstract. Both marine dinoflagellate cysts and terrestrially derived pollen and spores are abundant in coastal sediments close to river mouths, making sediment records from such settings ideal to simultaneously study land–ocean climate interactions, marine productivity patterns and freshwater input over time. However, few studies consider the combined calibration of these palynological proxies in modern coastal sediments offshore from rivers, which is needed to strengthen the interpretation of paleoreconstructions. Here, we analyze the palynological content of marine surface sediments along land–sea transects off the Mississippi and Atchafalaya river mouths in the northern Gulf of Mexico (GoM) and test three palynological indices which are often employed in the paleo-domain: (i) the abundance of cysts of heterotrophic and autotrophic dinoflagellates (dinocysts) as a tracer for primary productivity (H/A ratio) and (ii) the ratio between non-bisaccate pollen and bisaccates (P/B) as well as (iii) the ratio between pollen (excluding bisaccates) and dinocysts (P/D), which are both tracers for river input and distance to the coast. Our results show that dinoflagellate cysts are most abundant on the shelf, where heterotrophic dinocyst species dominate coastal assemblages in reach of the river plume, while autotrophic taxa are more present in the oligotrophic open ocean. This is clearly reflected in decreasing H/A values further offshore. Individual dinocyst taxa also seem to inhabit specific niches along an onshore–offshore transect, linked to nutrient availability and proximity to the turbid river plume. The highest pollen concentrations are found close to the Mississippi river mouth and mostly represent a mixture of local coastal and upstream vegetation, whereas bisaccate pollen was most abundant further offshore of the Mississippi river. Multivariate redundancy analysis (RDA) performed on both pollen and dinocyst assemblages, a set of environmental parameters, and the three palynological ratios showed that net primary productivity was the most important variable influencing the dinocyst assemblages, likely as the result of nutrient input. Additionally, the RDA confirmed that the H/A ratio indeed seems to track primary productivity, while the P/B ratio results in a robust indicator for distance to the coast, and the P/D ratio better reflects river input. Together, our data confirm and further specify the suitability of these three palynological ratios in river-dominated coastal margins as proxies for (past) marine productivity and distance to the coast and river.

New Tithonian-Berriasian morphospecies of the genus Stomiosphaera Wanner (calcareous dinoflagellate cysts) from the Vaca Muerta Formation, Neuquén Basin, Argentina

Five new morphospecies of calcareous dinoflagellate cysts belonging to the genus Stomiosphaera Wanner, are described from the Tithonian–Berriasian Vaca Muerta Formation, in the Neuquén Basin, Western Argentina: Stomiosphaera triangulata sp. nov., Stomiosphaera quadrata sp. nov., Stomiosphaera subechinata sp. nov., Stomiosphaera subspinosa sp. nov., and Stomiosphaera gracilis sp. nov. Their stratigraphic distribution is discussed, particularly that of Stomiosphaera subechinata sp. nov. (Tithonian – lower Berriasian), which was previously assigned to Stomiosphaera echinata Nowak, a species that in the Tethys domain appears for the first time in the upper Valanginian. Likewise, possible assignments to the genera defined from three-dimensional observations are proposed, and eutrophic neritic conditions are interpreted for the time in which these species appear in the Neuquén Basin.

Reconciling Southern Ocean fronts equatorward migration with minor Antarctic ice volume change during Miocene cooling

Gradual climate cooling and CO2 decline in the Miocene were recently shown not to be associated with major ice volume expansion, challenging a fundamental paradigm in the functioning of the Antarctic cryosphere. Here, we explore Miocene ice-ocean-climate interactions by presenting a multi-proxy reconstruction of subtropical front migration, bottom water temperature and global ice volume change, using dinoflagellate cyst biogeography, benthic foraminiferal clumped isotopes from offshore Tasmania. We report an equatorward frontal migration and strengthening, concurrent with surface and deep ocean cooling but absence of ice volume change in the mid–late-Miocene. To reconcile these counterintuitive findings, we argue based on new ice sheet modelling that the Antarctic ice sheet progressively lowered in height while expanding seawards, to maintain a stable volume. This can be achieved with rigorous intervention in model precipitation regimes on Antarctica and ice-induced ocean cooling and requires rethinking the interactions between ice, ocean and climate.

Plankton assemblages from microplastics of tropical coastal environments reveal high diversity and evidence of toxic species

Microplastics are a major constituent of plastic waste and are of an increasing global concern. Although microplastics are prevalent in marine ecosystems, the characterisation of plankton communities has been largely neglected in this aspect, especially in tropical ecosystems. To better understand the role of microplastics as a carrier of harmful plankton in marine ecosystems, epiplastic plankton communities in tropical marine ecosystems were studied from beach sediments along the Johor and Singapore Straits. Complementary analysis of microscopy and high throughput sequencing of the 16S rRNA (V3–V4) and 18S (V4) rRNA regions provided evidence that the plastisphere provided an appropriate environment to host a wide range of planktonic organisms. An average of 781 OTUs were identified across the three sampling sites. The structures of plankton communities were distinct across the sampling sites and were generally dominated by dinoflagellates, fungi and chlorophytes. We demonstrate that marine microplastics serve as microhabitats that are a host to harmful phytoplankton species, including viable resting cysts of dinoflagellates. Furthermore, plastics isolated from the location with the greatest anthropogenic influence demonstrated the greatest plankton diversity. This study presents evidence of diverse toxic plankton species present on the plastisphere and highlights its importance as a vector of the transport of harmful opportunistic species in relation to anthropogenic influence, in the marine environment.

The Age and the Accumulation Conditions of the Upper Paleogene–Lower Neogene Kurshskaya Formation Stratotype (Kaliningrad Oblast) by Palynological Data

The results of the palinologycal study of the Kurshskaya Formation stratotype (Primorsky quarry, Kaliningrad Oblast) are presented. In the lower part of the Kurshskaya Formation (Member of “chocolate” clays), a complex of dinoflagellate cysts with Areosphaeridium diktyoplokum, Glaphyrocysta semitecta, and Cordosphaeridium funiculatum of latest Eocene age was found. The formation is characterized by four spore-pollen assemblages: (1) Pinuspollenites–Inaperturopollenites–Sciadopityspollenites assemblage of latest Eocene age in the “chocolate” clays and in the lower part of brown sands; (2) Sequoiapollenites–Betulaepollenites betuloides assemblage of early Oligocene age in the lower part of the brown sands member; (3) Boehlensipollis hohli–Carpinipites carpinoides assemblage of early Oligocene age in the middle part of brown sands member; (4) Alnipollenites–Corylopollis assemblage of late Oligocene–early Miocene age in the upper part of the brown sands of the Kurshskaya Formation. The general age of the Kurshskaya Formation is terminal Eocene–early Miocene. In the lower parts of the Zamland Formation, which overlies the Kurshskaya Formation, the Pinuspollenites–Tricolporopollenites pseudocingulum–T. euphorii assemblage presumably of middle Miocene age was found. Based on the obtained palynological data, the conditions of sedimentation at the end of the Eocene–Oligocene–early Miocene in the South Baltic region are reconstructed. The regression of the sea basin began as early as the end of the Priabonian, the climate was still quite warm and humid, close to subtropical. Mesophytic mixed coniferous-broad-leaved forests grew along the shores of the strait, low-lying areas of land were occupied by marsh vegetation. Cooling at the Eocene/Oligocene boundary resulted in the appearance of hemlock in plant communities and an increase in the proportion of catkins (alder, birch, hornbeam). Presumably, in the late Oligocene–early Miocene, the proportion of small-leaved trees, especially alder and hazel, sharply increased in mesophytic forests, while the number of pine trees decreased. Wetter and warmer climatic conditions are assumed for the early Miocene: this time is characterized by an increase in the number of walnut, cypress, and Cyrillaceae. In the middle Miocene, the climate was still quite warm, but drier, and such moisture-loving species as podocarpus, spruce, glyptostrobus, and swamp cypress disappeared from plant communities.

Palynostratigraphical review of the K–Pg boundary from the Ibero-Armorican Island: New data from the Maastrichtian dinosaur outcrop Veracruz 1 (Pyrenees, NE Iberian Peninsula)

The palynostratigraphy of the K–Pg boundary interval in SW Europe has been a subject of ongoing debate, despite numerous palynological studies in the region. To address this, we review previous publications and conduct analysis of new deposits to establish a palynostratigraphical chart. A total of 40 palynological studies within the Normapolles palynological province were reexamined to elucidate key taxa restricted to the Cretaceous (K-taxa), to the Maastrichtian–Danian interval (KPg-taxa) and those restricted to the Paleogene (Pg-taxa). Eventually, we propose 18 key taxa to differentiate a Maastrichtian from a Danian palynological assemblage within the Normapolles Province. Afterward, a palynostratigraphical analysis was carried out in Veracruz 1 (Aragonese Pyrenees), one of the more modern dinosaur-bearing sites of Europe. The palynological assemblage corresponded to an upper Maastrichtian age and was composed by pteridophyte spores, gymnosperms, angiosperms, dinoflagellate cysts, algae, and fungal spores. It was predominated by angiosperm pollen (Liliaceae, post-Normapolles, and triporate pollen). The plant communities in Veracruz 1 seem to be characterized by plants from an open coastal forest prevailed by Liliaceae flowering herbs and Juglandaceae/Myricaceae dicotyledonous trees and shrubs thriving in temperate-warm paleoclimate. The Gondwanan botanical influence was also supported by the presence of Bacumorphomonocolpites sp., as this taxon was previously recorded in other upper Maastrichtian deposits from Europe.

Dinoflagellate cyst distribution over the past 9 kyrs BP from offshore east Tasmania, southeast Australia

Southeastern Australia’s marine waters are notably warming, surpassing global averages. This region has emerged as a strategic location for researching planktic microfossils, particularly dinoflagellate cysts, in modern and Late Quaternary sediments, offering crucial insights into the biophysical properties of mid-latitude waters. This study examined cyst distribution in marine sediment cores near Maria Island, Tasmania, southeastern Australia, up to 9000 years before present (kyrs BP). Dominant cysts included Protoceratium reticulatum, Protoperidinium spp. (P. avellana, P. conicum, P. oblongum, P. subinerme, P. shanghaiense), and Spiniferites spp. (S. bulloideus, S. hyperacanthus, S. membranaceus, S. mirabilis, S. pachydermus, and S. ramosus). Inshore, Spiniferites spp. constituted a higher proportion (up to 61%), while offshore was dominated by P. reticulatum (up to 80%). Impagidinium spp. and Nematosphaeropsis labyrinthus were exclusively found offshore and displayed increased abundance from ∼6 kyrs BP, suggesting a shift from a shallow to a deep-water habitat. Alexandrium tamarense species complex cysts were present over 140 years inshore and approaching 9 kyrs BP offshore, indicating a longstanding endemic presence. Gymnodinium catenatum cysts were detected exclusively inshore from ∼50 years ago, indicating a relatively recent bloom phenomenon. The East Australian Current’s limited southward reach is suggested by the absence of the warm-water cyst-producing taxon Lingulodinium polyedra. Similarly, the non-detection of the cold-water species Spiniferites antarctica and Impagidinium pallidum reflects Subtropical Front boundaries against subantarctic incursions from the south. In contrast to coccolithophores in the same core, no noticeable shift from cold to warm-water dinoflagellate cyst species was observed. This documentation of dinoflagellate cysts aids in predicting environmental impacts on local communities and beyond.

Disentangling environmental drivers of subarctic dinocyst assemblage compositional change during the Holocene

Abstract. Analysis of compositional changes in fossil organic-walled dinoflagellate cyst (dinocysts) assemblages is a widely used tool for the quantitative reconstruction of past environmental parameters. This approach assumes that the assemblage composition is significantly related to the reconstructed environmental parameter, which requires an independent correlation between the assemblage and the variable, meaning that the variable explains a dimension of the assemblage variance that is not also explained by other parameters. Theoretically, dinocyst assemblages can be used to reconstruct multiple environmental variables. However, there is evidence that primary and subordinate drivers for assemblage compositions regionally differ, and it remains unclear whether a significant relationship to specific parameters in the present ocean always implies that this relationship is significant in fossil assemblages, questioning if past changes in these multiple parameters can be reconstructed simultaneously from fossil assemblages. Here, we analysed a local subset of the Northern Hemisphere dinocyst calibration dataset (n=1968), including samples from the Baffin Bay area (n=421), and evaluated the benefits of a local versus a more regional or global calibration for the environmental reconstruction of Baffin Bay oceanography during the Holocene. We determined the dimensionality of the dinocyst ecological response and identified environmental drivers in the Baffin Bay area for the modern dataset. We analysed four existing Holocene records along a north–south transect in the area and evaluated the statistical significance of downcore reconstructions by applying the local and global datasets with different techniques: the modern analogue technique (MAT), the weighted average partial least square (WA-PLS) and maximum likelihood (ML). We evaluated reconstructions tested as significant in light of the existing state of knowledge about West Greenland's Holocene palaeoceanography. Our analyses imply that present-day and Holocene dinocyst assemblages in the Baffin Bay area are primarily driven by salinity changes; other parameters were less important in driving assemblage compositions, and their contribution differed among the studied records. We show that the objectively occurring and temporally coherent shifts in dinocyst assemblages in the Holocene of Baffin Bay can be robustly interpreted only by transfer functions that are locally calibrated. Transfer functions based on the broad Northern Hemisphere calibration yielded many insignificant environmental reconstructions. At the same time, we show that even in the local calibration, not all parameters that appear to significantly affect dinocyst assemblages in the calibration dataset can be meaningfully reconstructed in the fossil record. A thorough evaluation of the calibration dataset and the significance of downcore applications is necessary to reveal the region-specific information contained in dinocyst assemblage composition.

Single-cell DNA from West Greenland marine sediments suggests presence of Protoperidinium tricingulatum in the Arctic.

Spiny brown dinoflagellate cysts are commonly used as sea-ice indicators in the Arctic, but their biological affinities are not well known. We present the first indication of hitherto temperate Protoperidinium tricingulatum in the Arctic based on single-cell LSU rDNA sequencing from sediments of the Disko Bay-Vaigat Sound, West Greenland. The morphological similarity of the sequenced cyst morphotype to the sea-ice indicator Islandinium? cezare morphotype 1 is striking. The morphology of the isolated cysts, as well as those observed in the total cyst assemblage following standard palynological preparation, both resemble either I.? cezare morphotype 1 or P. tricingulatum, suggesting that the specimens may in fact be close morphological variants of the same species. In addition, nine LSU rDNA sequences were obtained from morphological variants assigned to Islandinium minutum s.l.: including both subspecies minutum and subspecies barbatum. The two subspecies could not be differentiated based on partial LSU rDNA sequencing. Overall, Arctic spiny brown dinoflagellate cyst species may be morphologically more diverse and taxonomically more complex than shown earlier and further genetic and morphological studies are needed. Importantly, the value of cysts as palaeoecological indicators depends on a sound understanding of their biological affinity and taxonomy.

New dinoflagellate cyst species from the Middle Eocene of the Volgograd–Volga region, south-west Russia

The Keresta Formation, located in the Volgograd–Volga region (the Volga–Caspian subregion of south-west Russia) has been dated as Middle Eocene, Lutetian, based on dinoflagellate cysts of the Enneadocysta arcuata Zone and nannofossils from the Lutetian subzones CP13c–CP14a. Within this interval, four new species of dinoflagellate cysts are described: Spiniferella grigorovichiae sp. nov., Impagidinium tuberculatum sp. nov., Hystrichostrogylon crassitunicatum sp. nov. and Hystrichosphaeropsis tenerum sp. nov. The new species present a high correlation potential for Middle Eocene stratigraphy over the southern part of the Russian Platform. Also, the assemblage of organic-walled microphytoplankton from the Keresta Formation indicates warm-water marine environments within the marginal part of the Paratethys Basin.

Calcareous dinoflagellate blooms during the Late Cretaceous 'greenhouse' world-a case study from western Ukraine.

The Late Cretaceous was a unique period in the history of the Earth characterized by elevated sea levels, reduced land area, and significantly high concentrations of atmospheric CO2 resulting in increased temperatures across the globe-a 'Greenhouse World'. During this period, calcareous dinoflagellate cysts (c-dinocysts) flourished and became a ubiquitous constituent of calcifying plankton around the world. An acme in calcareous dinocysts during the Albian to the Turonian coincided with the highest recorded seawater surface temperatures and was possibly linked to conditions that favored calcification and a highly oligotrophic system in European shelf seas. This study examines the potential applicability of c-dinocysts as a proxy for paleoenvironmental conditions based on their assemblage changes plotted against foraminiferal occurrences and microfacies analysis. The material was extracted from the upper Turonian chalk of the Dubivtsi region in western Ukraine. An inverse correlation was observed between species diversity and the number of c-dinocyst specimens. Nutrient availability gradients apparently determined important changes in the calcareous dinocysts distribution. These trophic changes were likely caused by the interplay of eustatic sea-level fluctuations and Subhercynian tectonic activity leading to changeable nutrient inputs from the nearby land.

Fecal Pellet‐Like Gyrodinium Species in Sinking Particles: Newly Found Potential Contributors for Carbon Export in the Antarctic Seasonal Ice Zone

AbstractFecal pellets (FPs) are generated by various species and have gained attention as contributors to the biological carbon pump. Metazoans and protozoans are known as FP and minipellet‐producers, respectively. Herein, we discovered fecal pellet‐like dinoflagellates (FLDs) in the seasonal sea ice zone in the Southern Ocean. The size and form of these FLDs were similar to those of zooplankton oval FPs. However, due to their appearance, they have been misclassified as FPs rather than dinoflagellates, leading to potential oversight of their role in the carbon cycle. Thus, we aimed to identify FLD cells at the species level and examine the impact of FLDs on flux estimation of particulate organic carbon (POC). Our findings are as follows: first, FLD cells were identified as Gyrodinium rubrum and Gyrodinium heterogrammum through 18S rRNA gene sequencing. Second, FLDs can potentially excrete larger FPs than minipellets. Third, the sinking rate of FLDs is higher than that of other protozoa and dinoflagellate cysts. Finally, a maximum of 12 mgC m−2 day−1 of the POC flux can be attributed to FLDs (representing 32% of POC flux). These results suggest that FLDs are important drivers not only for the microbial loop but also for the biological carbon pump. In future projections of carbon sequestration, the contribution of metazoans to carbon export must be considered, but not that of FLDs. Their unknown physiological and ecological characteristics, especially including the responses to climate changes, must be urgently investigated for future projections of carbon sequestration in the Southern Ocean.

The first record of Permo-Triassic palynomorphs and palynological change across the Triassic-Jurassic transition in the onshore Ruvu Basin, Tanzania

The Ruvu Basin in northeastern coastal Tanzania is one of the least studied basins in the country. It likely contains a record of the pre-and post-breakup sequences of the Gondwana supercontinent. In this study, the first comprehensive palynological investigation on drill-cuttings samples from the Makarawe-1 well in the Ruvu Basin was conducted. In the lower section of this well, four distinct palynologic intervals are recorded: Aratrisporites spp.-Klausipollenites schaubergeri interval (Upper Permian); Reduviasporonites spp. interval (Permo-Triassic transition); Extinction Interval (Permo-Triassic extinction) and Alisporites-Falcisporites Interval (Upper Triassic). This implies that the Ruvu Basin heralds a succession across the Permian-Triassic boundary and its associated extinction. We also record substantial palynological change across the transition to the upper portion of the Makarawe-1 well, where marine dinoflagellate cysts and abundant Classopollis pollen dominate the assemblage. Based on the ranges of dinoflagellate cysts supplemented by pollen-spore ranges, two main palynological intervals (the Classopollis-Nannoceratopsis interval and the Wanaea clathrata interval) are here established. These intervals are of late Middle Jurassic and Late Jurassic (Bajocian - Kimmeridgian) age. This suggests possible correlations with the Lugoba, Msata, Msolwa, Magindu and Malivundo formations of the Ruvu Basin. The findings presented herein suggest a downhole extension of the Wanaea clathrata interval (Oxfordian-Kimmeridgian) sensu [Msaky 2007] to 1215–1235 m. In addition, the Nannoceratopsis-dominated assemblage is indicative of an Early Jurassic association that developed during immediate post-break-up phase, with low-salinities and basinal restriction. With similarity to the Ngerengere dinocyst assemblage reported in previous studies, these results further suggest that the Ngerengere beds are not a so-called Karoo equivalent, but rather a syn- or post-breakup sequence. The recorded intervals are highly similar to other palynostratigraphic units of Africa, Australia, Europe and South America. The data collected in this study add important insights for the general stratigraphic framework within this poorly constrained coastal basin, while also providing a perspective on more distant correlations using palynology.

Eocene paleoceanographic and paleoclimatic events recognized by assemblages of dinoflagellate cysts in the Southwest Atlantic Ocean

Variations in the relative frequencies between cosmopolitan dinoflagellate cysts and Antarctic assemblage species indicate temperature changes and variations of ocean currents during the Paleogene. This study is based on the analysis of 23 samples from two stratigraphic intervals from the Well BP-01 (Imbé Formation), drilled by in the Pelotas Basin offshore. We identified 66 dinoflagellate cyst taxa, 47 of them belong to the Order Gonyaulacales and 19 to the Order Peridiniales. The relative abundance data highlight two different dinoflagellate ecogroups represented by Apectodinium and Enneadocysta in the intervals A and B, respectively. The level with the highest percentages of Apectodinium recorded in the Calcareous Nannofossil Zone N-410 (Ypresian), suggest that the Apectodinium maximum represents the Early Eocene Maximum Thermal Event (EMT-2). Enneadocysta Acmes registered near the Bartonian/Priabonian boundary, can be correlated with a drop in sea surface temperature that occurred after the Mid-Eocene Climatic Optimum. Dinoflagellate occurrences suggest deposition in open sea conditions during the transgressive phase. The P/G ratio does not reach significant values in the analyzed intervals, indicating low dissolved nutrient concentrations.

Valvaeodinium hymenosynypha (Morbey) comb. nov., a dinoflagellate cyst from the uppermost Triassic and lowermost Jurassic (Rhaetian and Hettangian) of Europe

Cymatiosphaera hymenosynypha Morbey 1975, previously recorded from the Rhaetian Westbury Formation in the United Kingdom, occurs in Triassic–Jurassic boundary strata from Denmark. From the present study it is clear that this small, finely reticulate, ellipsoidal, two-layered palynomorph is not a prasinophyte, but a dinoflagellate cyst with a combination apical/intercalary archaeopyle (type tAtI) which involves three apical plates plus one intercalary plate. This cavate cyst is morphologically similar but not identical to Valvaeodinium hanneae Piasecki 2001 from the uppermost Bathonian to lower Callovian of East Greenland, and it is therefore here transferred to Valvaeodinium, as Valvaeodinium hymenosynypha (Morbey) Lindström comb. nov. The appearance of Valvaeodinium hymenosynypha in Rhaetian strata in the Danish Basin suggests that the lineage of cavate Valvaeodinium cysts originated in the Late Triassic alongside a chorate species of the genus. Valvaeodinium hymenosynypha seems to have survived just barely past the end-Triassic mass extinction as it is also present in the earliest Hettangian.

Organic petrography and palynofacies of the Upper Cretaceous (Campanian-Maastrichtian) organic rich strata of the Quseir-Safaga Region, Eastern Egypt

The Campanian-Maastrichtian organic-rich rocks in the Quseir – Safaga Region in the Eastern Desert of Egypt have growing economic importance. This economic importance is discussed in many of previous studies by many of different geological tools that lacked the petrographic examination of organic matter occurrence modes. The organic petrography provides the essential tools for microscopic analysis to study the organic matter that are applied for the first time in the present study. The palynofacies and organic petrography are used in the present study to investigate the nature of the organic matter and the paleoenvironmental settings that controlled their distribution in the Duwi and Dakhla formations in the Younis and Mohamed Rabah areas (Egypt). The study of dinoflagellate cysts allowed the identification of the biostratigraphically characteristic assemblages of the Campanian – Maastrichtian in the Eastern Desert including Assemblage II/I (in Duwi Formation) and Assemblage III (in Dakhla Formation) that were identified in Egyptian oil shales of this time range. The identified assemblages are correlated with local and regional studies to delineating the formal biozonation. The organic matter in the Duwi Formation comprises rich fluorescent amorphous organic matter, prasinophytes, sporomorphs, dinocysts as well as a minor terrigenous component of phytoclasts. In the Dakhla Formation, the fluorescent AOM is found to be highly mixed with Botryococcus in addition to prasinophytes and marine palynomorphs. The paleoenvironmental analysis indicates deposition in distal anoxic to proximal suboxic marine conditions with high paleoproductivity. The results are confirmed with the inorganic geochemical composition of redox sensitive elements. The analysis reveals that the Younis section is differentiated into two palynofacies types (proximal, suboxic high productivity in the Duwi Formation and distal anoxic in the Dakhla Formation). The Mohamed Rabah section, one palynofacies type is recognized that is proximal, suboxic high productivity. The principal component analysis is used to interpret the distribution of organic matter abundances. The kerogen types are distinguished based on the area percentages of the fluorescent organic matter and application of kerogen plots. The samples of both formations fall within oil prone kerogen type II. The spore coloration and measured vitrinite reflectance indicate immature kerogen in the studied sections. The organic matter in the studied rocks comprises hydrogen rich compounds that can be treated for direct composition or retorted to extract shale oil. The heavy metals concentrations are significant and present technology will increase its economic value.

Sequence stratigraphy of a wave-dominated, tidally influenced delta in the Danian of Seymour Island, Antarctica: An integrated sedimentological–palaeoecological approach

Lower Paleocene marine siliciclastics of the Sobral Formation (Seymour Island, Antarctica) form an important component of a key southern high latitude reference section for the Maastrichtian–Eocene. The formation comprises a coarsening-upward, regressive succession (270 m thick), shallowing from prodeltaic, mud-rich to sandy nearshore sediments. Sedimentary facies analysis, integrated with macrofaunal and microfloral palaeoecological studies, indicate a wave-dominated, tidally influenced deltaic environment. Four depositional sequences (1–4) record the role of relative sea-level changes in controlling the stepwise progradation of the system. Prodeltaic and distal delta-front deposits (Sequences 1, 2), comprise coarsening-upward parasequences of mud-rich heteroliths and bioturbated fine-grained muddy sands displaying draped slump scars. The overlying erosional sequence boundary is marked by incised valleys filled with fluvio-estuarine sediments; succeeding sand-rich facies (Sequences 3, 4) represent the proximal delta front and delta platform. The macro-invertebrate and palynological datasets display contrasting responses to the regressive history of the formation. The macrofaunal record in the distal deltaic sediments reflects the marine influence, though a stratigraphic increase in diversity was controlled both by ecological factors and biotic recovery following the K–Pg event. The associated palynological assemblage also displays a strong marine signal and includes typical outer neritic – oceanic dinoflagellate cyst taxa. A sharp decline in macrofossil diversity and abundance in Sequences 3, 4 is compatible with ecological stress in shallow-water, restricted inshore settings. Though the palynological record at this level is terrestrially dominated, the marine component reflects the cosmopolitan nature of dinoflagellates, displaying the highest diversities in the formation. The regressive Sobral Formation ended a protracted c. 60 Myr history of regional subsidence and marine sedimentation; although amplified by two Danian sea-level falls of probable eustatic origin, the regressive trend heralded mid-Paleocene basin inversion potentially linked to the onset of regional tectonic reorganization that ultimately led to opening of the Scotia Sea.

Upper Cretaceous dinoflagellate cysts events from the sub-tropical northern hemisphere

Recognizing the ranking optime sequence of fossil dinoflagellate cysts can be a challenge for qualitative biostratigraphy. For this reason, we present the result of a quantitative stratigraphic study through probabilistic analysis of six wells from Baja California (Mexico) and six from the Gulf of Suez and the Mediterranean Sea (Egypt), which allows us to recognize 22 species of dinoflagellate cysts in an optimal sequence with 95% probability for the Upper Cretaceous in subtropical areas of the Northern Hemisphere. Photoautotrophic species represent the largest number in the database (159 species), indicating that they are the main producers, while heterotrophic species are in the minority (74 species). Spiniferites and Florentinia are the most abundant and diverse taxa, which, together with the absence of the genus Impagidinium, indicates a shallow marine depositional environment. The quantitative analysis estimates an optimal classified succession that allows the Upper Cretaceous to be divided into five groups (G1 to G5) of species communities with similar ages. The greatest species diversity is found in group G4, associated with the Maastrichtian, and the least in group G1, associated with the early Cenomanian to early Turonian. These results and comparison with previous studies using the same method of quantitative biostratigraphy suggest a similarity of paleoenvironmental conditions in subtropical regions of the Northern Hemisphere and tropical regions during the Upper Cretaceous.

Integrated biostratigraphy (orbitolinids, calcareous nannofossils, and palynomorphs) of the Lower Cretaceous Sarcheshmeh Formation, western Koppeh-Dagh Basin, NE Iran

An integrated biostratigraphy using orbitolinids, calcareous nannofossils, and dinoflagellate cysts was conducted on the Lower Cretaceous Sarcheshmeh Formation in two stratigraphic sections from the western Koppeh-Dagh Basin (NE Iran). The analyzed successions consist mainly of deep-marine shales and marlstones with intercalations of thin-bedded orbitolinid-bearing limestones. These strata yielded common to abundant and fairly well to well-preserved calcareous nannofossil assemblages. The aforementioned assemblages led to the identification of parts of the NC6 and NC7a biozones that can be correlated with parts of the CC7a and CC7b zones. The organic-walled dinoflagellate cysts also show well-preserved and relatively diverse assemblages in the studied sections that corresponded to the Odontochitina operculata Zone. Additionally, within the limestone intercalations of the Sarcheshmeh Formation, two index species of orbitolinids, Praeorbitolina cormyi Schroeder, and P. wienandsi Schroeder, were recorded, indicating the presence of the Praeorbitolina cormyi Zone. According to the literature, these recognized biozones are compatible with the ammonite zones of Deshayesites forbesi, Deshayesites deshayesi, and Dufrenoyia furcata, as well as the Globigerinelloides blowi and Leupoldina cabri planktonic foraminiferal zones. By the compilation of all acquired data, an age of late early Aptian (late Bedoulian) is deduced for the Sarcheshmeh Formation in the studied sections.

Organic matter preservation conditions in the third member of the Shahejie Formation (Dongpu Depression, China)

The third member of the Paleogene Shahejie Formation (Es3) in the Dongpu Depression, China, was studied to interpret its paleoenvironment through a series of trace element proxies, to reveal paleosalinity conditions, to elucidate on the hydrological conditions of the paleolake using carbon and oxygen stable isotopes, and to investigate the effects of paleoredox conditions on organic matter preservation. Most of the redox-sensitive proxies, such as U/Th, V/Cr, Ni/Co, Uauth, (Cu + Mo)/Zn, Cu/Zn, Th/U, and V/Sc, indicate that the Es3 was deposited under predominantly oxic and oxic/suboxic conditions, while V/(V + Ni) and δU and previous studies suggested that the formation was deposited under mainly anoxic conditions. Oxygen levels agreed with the trace element ratios and showed a decrease from the lower to the upper part of the Es3 and an increase in paleoproductivity in the same direction. Salt rocks interbedded within the formation were shown to have overall lower oxygen levels than their neighboring organic-rich layers, black shale, and mudstone intervals, thus have likely altered the paleoredox proxies to oxygen consumption. Although Sr/Ba values point to a saline lake environment, the relative fluctuations seen suggest that the above ratio is not an appropriate indicator of paleosalinity in salt-bearing strata and that the variations in paleoredox conditions in the formation are not a function of paleosalinity. Based on the negative δ13C and δ18O stable isotopic values, it is inferred that the shales in the Es3 were deposited in a hydrologically open lake environment. However, the presence of palynomorphs such as dinoflagellate cysts that are typically found in middle to outer neritic and open marine environments reinforces the assumption of a sea level transgression and inundation of the lake basin and mixing with freshwater algae and rare terrigenous phytoclasts such as cuticles, wood fragments, and suberin. The higher paleoproductivity and lower oxygen levels in the upper Es3 have contributed to greater OM preservation conditions in the absence of any variations in salinity or freshwater influx. The study also demonstrates that many of the paleoredox proxies and thresholds established are not valid to properly characterize certain formations deposited in lacustrine lake paleoenvironments such as the Shahejie, thus their applicability in certain situations must be re-evaluated.