Conference Agenda

During the mid-Early Cretaceous, the Lower Saxony Basin expanded onto the Central German, Pompeckj and Altmark swells. At the turn of the Valanginian/Hauterivian, the Braunschweig embayment was formed in what is now SE Lower Saxony between the Harz Mountains in the south and the Flechtingen-Roßlau Thrust in the north-east, expanding into the Subhercynian Basin in the course of the subsequent Cretaceous transgressions. The deposits of the Hauterivian transgression were analysed in terms of stratigraphy, bio- and microfacies on the western and southern margins of the Elm, a halokinetic uplift structure east of Braunschweig, and its corresponding marginal depressions, the western Schandelah and the southern Schöppenstedt synclines. The strata reflect a coarse-grained bioclastic carbonate facies (Hilsconglomerate facies = Grenzlerburg Member of the Salzgitter Formation) while different degrees of subsurface salt migration and synsedimentary tectonics differentiated the depositional environments. On the shallow-water shelf of the Elm, patch reefs developed with highly diverse habitats, documented by fossils from around ten classes, representing a range from calcareous sponge and bryozoan reefs to oyster and brachiopod beds. In front of the western margin of this platform, mainly clays were deposited in the basins, intercalated by highly diverse allochthonous bioclastic rud- and floatstones. Despite their fragmentation, the microstructural preservation of the components is excellent due to rapid embedding in an argillaceous matrix. The biofacies with a dominance of bryozoans, brachiopods, echinoderms and oysters characterises the Hilsconglomerate facies as a temperate, moderately productive echino-bryomol carbonate factory, characterised by the absence of significant amounts of micrite (periplatform muds).

The early Albian succession in the Jebel Serdj-Bargou mega-anticline (Northern Atlas, Central Tunisia) is characterized by well-developed carbonate platforms, representing a significant component of the last carbonate unit (Cu5) stratigraphic interval of the Serdj Formation. This study investigates the paleoenvironmental evolution of these platforms, addressing a key knowledge gap in the southern Tethys.

Thirteen microfacies (MF1 to MF13) and seven facies associations (FA1–FA7) were identified, primarily based on fossil assemblages (corals, rudists, benthic foraminifera), texture, and fabric. These facies associations reflect a biogenic composition typical of an inner to outer ramp environment within a warm tropical climate.

The succession vertically evolves from an open marine basinal setting (T4) to moderate to high-energy shallow marine carbonates (Cu5), with high productivity evolving laterally from inner platform to marginal settings. Two distinct domains of high carbonate production are recognized: Jebel Bargou in the south and Jebel Cheirich in the north. In contrast, the Drija area, situated between these zones, is characterized by reduced carbonate production (50% lower) and reworked mixed facies suggesting an local intrashelf graben.

A well-developed coralline platform is observed in the northern Cheirich area, indicating favorable conditions for coral growth. This platform displays diverse biogenic components, including porcelaneous larger benthic foraminifera (alveolinids and soritids), which indicate euphotic, shallow marine conditions.

These findings enhance understanding of the early Albian carbonate platform dynamics in Central Tunisia, providing insights into facies distribution, carbonate production, and paleoenvironmental evolution, offering a valuable reference for similar Tethyan settings.

The Sergipe-Alagoas Basin, located in northeastern Brazil, is a key area for geological and paleontological research, as it hosts some of the most complete Cretaceous stratigraphic successions among Brazilian sedimentary basins. These successions record all tectono-sedimentary stages related to the initial opening of the South Atlantic Ocean during the Early Cretaceous, associated with the f Gondwana breakup. Within this context, the Riachuelo Formation stands out, representing a transitional restricted environment that grades into shallow to deep marine settings. Globally the Early Cretaceous was marked by the widespread development of carbonate platforms, with significant oceanic records. Microfacies analysis is a powerful tool for identifying such records, reconstructing depositional systems, and characterizing associated marine biota. Despite its importance, microfacies-based studies of the Riachuelo Formation remain limited. This study analyzes petrographic thin sections from three onshore cores (SER-01, SER-03, and SER-04) in the Sergipe-Alagoas Basin. The successions represent a mixed carbonate–siliciclastic shelf system, including quartz-bearing sandstones and packstones deposited in a transitional zone protected by carbonate banks. These evolve from sand-bar and shelf-margin facies (packstones, grainstones, and rudstones) to deeper outer shelf environments dominated by mudstones and wackestones. The fossil assemblage is predominantly composed of planktonic and benthic foraminifera, echinoderms, and mollusks, along with local occurrences of cadosinids, green and red algae, microcrinoids, inoceramids, and microbial fragments. As a result, six distinct microfacies were identified, indicating a transition from shallow, high-energy marine environments to deeper, as well as low-energy settings typical of the outer shelf. [Acknowledgements: CNPq project: 405679/2022-0]

The present study is focused on the upper Campanian–Maastrichtian sequence of the Bazov Dyal Formation in the Central Balkan Mts (Central Balkan Zone) that is outcropped in four sections (Mountaineers’ Memorial, Polenitsi South, Polenitsi and Starna Reka) and one locality (Polenitsi North). The succession is characterized by variable thickness and ranges from a few centimetres up to 12 m. The lower part is composed of light grey limestones, which rapidly grade upwards into grey sandy bioclastic limestones. Scattered coarse-sand to granule-sized grains of quartz and lithic frag­ments also occur and are locally abundant in separate beds.

Four microfacies types (MFT 1–4) have been distinguished and described: MFT 1 Echinoderm packstone/grainstone; MFT 2 Bioclastic grainstone with coralline red algae; MFT 3 Sandy bioclastic grainstone/rudstone; and MFT 4 Sandy bioclastic-intraclastic packestone/grainstone. The observed fossil association (mainly echinoderms, bryozoans, coralline red algae, brachiopods) indicate normal salinity and open-water circulation. Grain-supported limestone varieties (packstones, grainstones and rudstones) characterise agitated hydrodynamic conditions. Commonly presented well-rounded quartz and feldspar clastic grains, as well as lithic fragments with various sizes and composition (different volcanic, igneous, metamorphic and sedimentary rocks), suggest possible fluvial terrigenous supply.

Based on the obtained preliminary data, it can be assumed that the carbonate deposits of the Bazov Dyal Formation have been formed in a high-energy open-marine setting with locally important fluvial terrigenous supply.

Acknowledgements. The Bulgarian National Science Fund of the Ministry of Education and Sci­ence, Grant KP-06-N74/3, supported this study.

Stylolites, pressure-solution features common in carbonate rocks, significantly influence fluid flow and permeability in reservoir systems. However, the role of clay accumulations along stylolite seams remains poorly understood. This study investigates the relationship between stylolite morphology, associated clay mineralogy, and their influence on permeability and fluid circulation. We present preliminary results from the first study area in southern Italy (Apulia), based on scanning electron microscopy (SEM) combined with micro-XRD and micro-XRF analyses.

The data reveal systematic variations in clay mineral assemblages and their distribution along stylolites, suggesting a potential sealing effect and anisotropic control on fluid pathways, which may influence proto-karst development. Preliminary findings also indicate a correlation between the orientation of major cave systems (under investigation) and dominant stylolite families in the area. Additional SEM and micro-XRD analyses help refine the characterization of mineralogical textures and controls on fluid behavior.

Ongoing work aims to better quantify clay content and evaluate its spatial correlation with fluid migration, porosity evolution, and early-stage karstification. Future research will extend karst-related analysis to two additional areas in Slovenia and the Czech Republic to test the broader relevance of these observations.

The Cenomanian/Turonian Boundary was a period of extreme environmental conditions, marked by hyperthermic climate, high sea-levels, and the Oceanic Anoxic Event 2 (OAE2). During this period, huge portions of the continental margins of North Africa were flooded, with the emplacement of an epicontinental carbonate platform known as North Saharian Platform.

The Akrabou Formation in Southeastern Morocco provides an intriguing window into the dynamics of this shallow-marine carbonate system. This formation, up to 100 m thick, is dominated by low-energy, shallow-water facies with fine-grained wackestone/packstone rich in micrite and oligotypic assemblage of small benthic foraminifera, alternated to oyster-rich beds. A temporary shutdown of the benthic community and the deepening of the platform is testified by a fast and short transition to laminated lime-mudstones with planktonic foraminifera. After the return to shallow-water benthic-dominated facies, an increase in energy is observed before the emersion of the platform.

Stable isotope analysis (δ13C) shows a positive excursion of +3‰ VPDB, aligning with global OAE2 signatures. Interestingly, the platform's maximum deepening occurs with a delay relative to the OAE2 isotopic peak, suggesting a complex interplay between global and local factors in platform evolution.

Despite the stress induced by OAE2, evidenced by the temporary shift to deeper environments, the shallow benthic carbonate community demonstrated resilience, quickly re-establishing after the crisis. This study highlights the Akrabou Formation as a valuable archive of epicontinental carbonate platform dynamics during extreme environmental changes, offering insights into the interplay between global events and local responses in shallow-marine carbonate systems.

The Gorgo a Cerbara section (Piobbico, Italy), a Global Stratotype Section and Point (GSSP) candidate for the Barremian/Aptian boundary, was investigated through rock magnetic analyses to characterize its magnetic proxies and paleoenvironment. The section documents the transition between the Maiolica Formation (Tithonian–early Aptian) and the Marne a Fucoidi Formation (Aptian–Albian), with the OAE 1a anoxic event (Selli Level) preserved as laminated organic-rich shales in the upper unit. Paleomagnetic analyses, such as hysteresis, isothermal remanent magnetization acquisition (IRM), magnetic susceptibility measurements, thermomagnetic curves, and anisotropy of magnetic susceptibility (AMS) analysis, were performed on section samples. The paleomagnetic results identified magnetite as the primary magnetic carrier, evidenced by low-coercivity hysteresis, rapid IRM saturation below 300 mT, and corroborated by thermomagnetic curves. The presence of maghemite in some samples along the section suggests partial oxidation of the primary magnetite. This oxidation is reflected in the Day plot by a slight shift of some data points toward the multidomain field, potentially indicating grain size reduction or surface alteration. While maghemite formation may introduce minor complexities in magnetic signal interpretation, the dominance of magnetite and its pseudo-single-domain behavior in most samples suggests these sediments remain generally reliable for magnetostratigraphic studies. Post-anoxic intervals exhibit increased high-coercivity components (possibly hematite), which may reflect changing redox conditions. The presence of both minerals provides valuable information about post-depositional oxidation processes that affected the section. AMS parameters are being analyzed to reveal depositional magnetic fabric and paleocurrent directions, enhancing the paleoenvironmental understanding of this Early Cretaceous section.

Understanding the mechanisms that control dolomite distribution within Cretaceous coastal sedimentary sequences remains limited. This study presents an integrated assessment of dolomite occurrence and potential dolomitization processes based on five stratigraphic sections from lithologically heterogeneous coastal successions in the southern sector of the Lusitanian Basin (Ericeira, Portugal). These sections encompass approximately 40 million years of sedimentary record, spanning from the late Valanginian to the late Barremian (São Lourenço to Regatão Formations) and from the early Albian to the early Cenomanian (Rodízio and Galé Formations).

Mineralogical and petrographic datasets were combined to characterize dolomite presence, associated mineralogical assemblages and infer the underlying dolomitization mechanisms. Mineralogical analysis was performed using X-ray diffraction (XRD), and due to the large dataset (N=276), statistical tools were applied to discern compositional trends. These findings were further validated through petrographic and elemental analyses (SEM-EDS), and detailed examination of dolomite crystal structure based on diagnostic XRD peaks.

Dolomite was detected in all studied sections, with its presence ranging from 12% to 68% of the total sampled stratigraphic horizons. Relative abundance estimation indicates that dolomite is the dominant mineral phase (>50%) in 25 samples, typically co-occurring with quartz and calcite. Stratigraphic distribution pattern analysis showed that dolomite-bearing horizons preferentially occur interbedded with siliciclastic levels of mixed mineralogy (quartz and calcite), suggesting a significant control exerted by porosity and/or permeability on dolomitization processes.

Magnetostratigraphy is essential to calibrate sedimentary sequences, particularly in continental settings of the Lower Cretaceous. In Brazil, the rift-type Recôncavo Basin preserves key tectono-sedimentary events linked to the opening of the South Atlantic. Our study focuses on the Gameleira section of the Maracangalha Formation, composed predominantly of fine sandstones and mudstones deposited in lacustrine–fluvial environments. Magnetic mineralogy analyses indicate low-coercivity carriers (magnetite) dominate the natural remanent magnetization of these sediments. The prevalence of pseudo-single-domain minerals and maximum angular deviations below 10° attest to the stability of the paleomagnetic directions. Anisotropy of magnetic susceptibility parameters reveal a imbricate magnetic planar fabric characteristic of calm lacustrine deposition. Three well-defined magnetozones were identified: N1 (0–9 m, Normal), R1 (9–10 m, Reversed), and N2 (10–16 m, Normal) after paleomagnetic analises. The occurrence of ostracode assemblages including Paracypridea brasiliensis, Cypridea ventronodata, Cypridea vulgaris, and Theriosynoecum isoplektum anchors the magnetostratigraphic dating with biostratigraphic control, and correlation with the GPTS assigns the Gameleira section to the Valanginian (Chrons M11–M11A; 134.2–133.3 Ma).

While the Cretaceous Normal Polarity Superchron (CNPS) has documented instances of rapid geomagnetic reversals, the lack of precise age determinations for these abrupt shifts complicates their use as reliable reference tiepoints. This study presents a cyclostratigraphic analysis of gamma-ray data from DSDP Site 402A. By identifying Milankovitch cycles, we developed a 405-kyr astronomically-tuned age model for two geomagnetic reversal events during the Aptian. Our results estimate ages of 117.03 ± 0.14 Ma for the ISEA and 116.17 ± 0.14 Ma for reversal "2", with durations of approximately 20 kyr and 10 kyr, respectively. Sedimentation patterns, influenced by orbital eccentricity cycles, show an average sedimentation rate of 5 cm/kyr. The short durations of these reversals highlight the challenges in detecting them through paleomagnetic analysis in cores, as well as in deep-tow survey

Here we present a tectonic and seismostratigraphic study of the Cretaceous succession from the archetypal East African transform continental margin. This region underwent significant tectonic reconfiguration during the break-up of Gondwana, which began in the Early Jurassic (~183–177 Ma). As a result, Madagascar separated from eastern Africa and drifted southeastward along the Davie Transform Zone (DFZ), reaching its present-day position in the Early Cretaceous (~120.8 Ma). Transform faulting along the studied segment of the East African continental margin was associated with volcanic activity. The post-drift phase was dominated by tectonic and depositional processes related to passive margin development. Cretaceous sedimentation above the oceanic crust was dominated by shales, sandstones, and carbonates.

High-resolution regional 2D reflection seismic data of the East AfricaSPAN™ survey acquired by ION Geophysical has been used to decipher depositional architecture of the Cretaceous succession. The data reveal both regional and local unconformities, numerous erosional incision, and stratigraphic pinch-outs. These seismic features have been interpreted as being related to: (1) syn-depositional volcanic activity, (2) Late Cretaceous uplift of the northern DFZ, (3) bottom currents flowing along bathymetric highs, and (4) terrigenous sediment input from the African mainland, including gravity-driven mass flows. We propose that the observed depositional architecture was likely influenced by pronounced Late Cretaceous exhumation of the eastern Africa hinterland recorded by thermochronological data.

This study was funded by NCN (2024/08/X/ST10/00218), the NAWA Bekker Programme (BPN/BEK/2024/1/00102) and Exxon Mobil. Seismic data was provided by ION Geophysical; academic access to IHS Markit Kingdom software was granted by S&P Global.

A 49-m-thick succession from a drill core of Early to early Late Aptian age from Garbsen, a small city 6 km northwest of Hannover, has been studied with respect to sedimentology, bulk organic geochemistry and biostratigraphy. During Early Cretaceous times the Hannover area represented paleogeographically the eastern-central part and, thus, the depocenter of the Lower Saxony Basin.

The basal 14 m cover a paper shale-mudstone sequence (topmost Hoheneggelsen Formation) with a 2.3-m-thick “Fischschiefer” bed at the top. It is overlain by partly reddish-colored hemipelagic marlstones representing lithostratigraphically the Sarstedt Member (= Hedbergella Marls). The “Fischschiefer” represents the local expression of the global Oceanic Anoxic Event 1a in northern Germany.

In addition to lithological data, we present high-resolution δ¹³C_org, CaCO₃ and TOC data as well as a calcareous nannofossil biostratigraphy for this succession. This new core complements other records in the western part of the basin (Alstätte, Bottini et al., 2012) as well as southeast of Hannover (Hoheneggelsen KB9, Heldt et al., 2012) and, due to its completeness, provides new insights in the transition from the “Fischschiefer” deposit to the hemipelagic marlstones.

References:

Bottini, C., Mutterlose, J., 2012. Integrated stratigraphy of Early Aptian black shales in the Boreal Realm: calcareous nannofossil and stable isotope evidence for global and regional processes. Newsl Stratigr 45, doi:10.1127/0078-0421/2012/0017.

Heldt, M., Mutterlose, J., Berner, U., Erbacher, J., 2012. First high-resolution δ13C-records across black shales of the Early Aptian Oceanic Anoxic Event 1a within the mid-latitudes of northwest Europe (Germany, Lower Saxony Basin). Newsl Stratigr 45, doi:10.1127/0078-0421/2012/0019.

During the Late Turonian, the Bohemian Cretaceous Basin was affected by increased rates of subsidence as well as long-term clastic supply rates, as the tectonic inversion of Central Europe intensified. At the same time, signs of both long- and short-term, transgressive-regressive cyclicity are present in nearshore through hemipelagic facies. The present study focuses on reconstructing the depositional system and stratigraphic geometries along a proximal-distal transect in west-central Bohemian Cretaceous Basin, with the aim to address the relative roles of subsidence, sea level, hydrodynamic conditions, and climate-driven supply variations in the depositional patterns. Detailed correlation of c. 100 outcrop and about 130 well-log/core sections made it possible to revise the existing sequence-stratigraphic scheme in the region and construct isopach maps of newly defined genetic sequence units. The results show migration of the principal depocentre through time, likely driven by along-strike changes in flexural subsidence reflecting varying thrusting activity along the marginal fault system. Superimposed on this process were relative sea-level changes of 400-kyr long-eccentricity timescale and shorter. Higher subsidence rates in the basin centre made it possible to preserve record of falling-stage to lowstand interval that is missing in shallower parts of the basin.

This research resulted from a Master’s Thesis by JB, supervised by DU and SČ.

The Kreibitz-Zittau area (northern margin of the Bohemian Massif, Czech-German border region) exposes a ~1000-m-thick Cenomanian–middle Coniacian succession of quartz arenites with high compositional but low textural maturity. Translucent heavy minerals are almost exclusively composed of zircon, tourmaline and rutile (Ø-ZTR maturity index of 91) with tourmaline predominating (average of 60 %). Zr-in-rutile temperatures document upper amphibolite-eclogite to granulite facies between 700–930°C. Cr/Nb discrimination of rutile and geochemistry of tourmaline indicate that >95 % of these grains originate from Al-rich and Fe-Mg-poor metapelites. U-Pb-ages of detrital rutile show a distinct peak at 320–330 Ma. If present, garnets of the almandine–pyrope series are dominant. The 95 % predominance of Variscan ages in all samples and the high/ultrahigh temperatures of metamorphism exclude the Neoproterozoic greywackes and granitoids of the Lusatian Massif and the granitoids of the Jizera–Krkonoše Massif in the northeast as sources. Potential proto source rocks were high-grade metamorphic rocks similar to those today exposed within the gneissic-migmatitic Góry Sowie Massif, ca. 120 km east of the depositional area. Since the late Devonian, this massif was uplifted, reaching the surface in late Carboniferous times. Consequently, the widespread Permo–Carboniferous Variscan molasse is the major sediment source for the Cretaceous sandstones, which thus were deposited during at least their 2^nd sedimentary cycle. The study shows that integrated approaches combining careful petrography, heavy mineral analyses, mineral-specific geochemistry and thermometry as well as U-Pb age dating with high-resolution stratigraphy are suited to solve complex deep-time provenance puzzles.

Taxonomic studies of foraminifera in thin sections have known limitations. Micro-Computed Tomography (Micro-CT) offers an alternative to study the internal and external structures of foraminifera but suffers from long acquisition time. We have, therefore, designed a vertical holder which stacks up to 15 foraminiferal specimens for each circular scan. Our goal is to create a reference library of accurate 3D foraminiferal models to highlight morphological differences and similarities between different genera and enhance taxonomic identification. We generated digital models of many Cretaceous specimens including Omphalocyclus macroporous, Fissoelphidium operculiferum, Chrysalidina hensoni, and Fallotia sp. and produced cross sections at a variety of orientations. The combined database of 3D models and cross sections will assist micropaleontologists in the study and identification of foraminifera in thin section and eliminate ambiguities.

Holographic projection can be an even more effective tool for morphological studies of foraminifera, so we developed a workflow to optimize foraminiferal models for holographic displays. This workflow not only enables the holographic visualization of 3D foraminifera but also the intuitive interaction and creation of real-time cross-sections at any orientation. Finally, we started the development of a classification tool using Artificial Intelligence to match thin section images to best-fit digital slices from our database of 3D foraminifera. These developments aim to help future specialists identify foraminifera, communicate good taxonomic practices and educate audiences about foraminiferal studies.

Despite forming a distinctive diverse and sometimes abundant element of the preserved fossil assemblages of mid-Cretaceous Neotethyan and central American carbonate platforms, there is no generally accepted and well-defined bioevent/biozonation scheme for larger benthic foraminifera (LBF), which limits their utility as biostratigraphic tools. To achieve this requires, in turn, a review of the identity of the taxa involved and a critical review of published reports of their stratigraphic ranges. We have reviewed the published occurrences of almost 200 taxa to establish their stratigraphic ranges. Once misidentifications are discounted, it is apparent that the inceptions and extinctions of some taxa (e.g., the alveolinids) provides a useful basis for recognising Cenomanian substages and occasionally events at higher resolution. Endemic forms and facies control on stratigraphic distribution means that the choice and timing of some key bioevents differs between regions within the Neotethyan – central American realm. Intriguingly, some taxa are truly long-ranging and survive the end-Cenomanian extinction event, sometimes reappearing after an apparent absence of several million years. The reasons for this remain unknown but may include survival in refugia or homeomorphy of forms well-adapted to specific environmental niches. In summary, we present a draft biozonation for Cenomanian LBF, calibrated where possible to other fossil groups and the carbon isotope chronostratigraphic proxy, thereby increasing the biostratigraphic utility of this important fossil group.

Modern nautiloids are fore-reef slope dwelling cephalopods with distinct morphological and phylogenetic characteristics. We examined their habitat and trophic ecology across the Pacific Ocean regions where they live, using stable isotope analyses (SIA) of tissue samples from multiple populations. Unlike many cephalopods, Nautilus species exhibit scavenging behavior rather than active predation, with δ¹⁵N and δ¹³C values reflecting their unique ecological niches. But of relevance to understanding Cretaceous cephalopods is our finding that nitrogen isotopic values from shell and tissue are identical, and not just for bulk δ¹⁵N and δ¹³C; we show that nitrogen isotopic values of individual amino acids are the same for shell and tissue. Using this tool we have analyzed shells of exquisitely preserved Cretaceous ammonites and nautiloids and obtained not only values for individuals, but values for those individuals through ontogeny. Coupled with the use of the new C_meta estimations of the amount of dietary carbon individual species used, a proxy for relative energetics, we present a comparative graph of planispiral vs heteromorphic ammonite trophic levels.

Fossiliferous Cenomanian strata are superbly exposed in the North Cantabrian Basin (NCB) of Cantabria (northern Spain), yielding rich and diverse Cenomanian ammonite faunas. However, a systematic revision of the faunas is still lacking. The NCB is a relatively small, E–W-elongated extensional basin (~50 x 100 km), developing as an independent structural unit on the rifted North Iberian margin as a result of Valanginian distensional movements. During the Cenomanian, the basin formed a gulf-like embayment in subtropical palaeo-latitudes of ca. 30°N, opening to the deeper marine Basque Basin/Navarro-Cantabrian Ramp in the east and shallowing into the peri-Asturian domain towards the west. The successions yielded diverse Cenomanian ammonite faunas consisting of almost 40 taxa, dominated by representatives of the subfamily Acanthoceratinae. Based on the ammonites, the early Cenomanian Mantelliceras-mantelli and M.-dixoni, the middle Cenomanian Cunningtoniceras-inerme, Acanthoceras-rhotomagense and A.-jukesbrownei, and the late Cenomanian Eucalycoceras-pentagonum and Metoicoceras-geslinianum zones have been identified. There is no record of the latest Cenomanian Neocardioceras juddii Zone. Palaeobiogeographically, the NCB belongs to the "Northern Transitional Subprovince", located between the Tethyan and Boreal realms. The Cenomanian ammonoid faunas of the NCB are entirely dominated by cosmopolitan taxa, associated by some Tethyan forms; true Boreal taxa are absent. The ammonoid faunas are relatively diverse and compare well to Cenomanian ammonite assemblages known from other European localities mediating between the Boreal and Tethyan realms (e.g., Cassis, Bouches-du-Rhône, southern France). The Cenomanian ammonite record of the NCB, thus, provides an important piece in the complex palaeobiogeographic jigsaw puzzle of mid-Cretaceous ammonite faunas.

The Mid-Maastrichtian Event (MME) was related with significant sea level-rise (50–100 m) and anomalously high mercury concentrations in several European Chalk Seas, associated with changes in climate and deep-water circulations. Most probably, the MME was caused by intense volcanic-tectonic activity, related with formation of vast oceanic-plateaus (Dubicka et al., 2024). These dramatic changes have been reflected upon marine ecosystem, and having caused the extinction of the Caribbean-Tethyan rudists and “true” inoceramid bivalves.

The studied Bulgarian stratigraphic sections – Moravitsa, Darmantsi and Chelopek that yielded Maastrichtian inoceramid record fall within the Western Fore Balkan Mountains (Western Bulgaria), are having been formed in Peri-Tethyan Basin System. Their lowest strata are mainly composed of glauconitic sandstones, overlaid by varied limestones. The upper lower Maastrichtian inoceramid assemblages are represented by abundant, large to very large-sized Cataceramus barabini, C. subcircularis, C. bebahoensis, C. glendivensis, C. aff. goldfussianus, Platyceramus stephensoni, P. salisburgensis, Trochoceramus radiosus and “Inoceramus” howletti. The lower upper Maastrichtian inoceramids are small-sized and refer to Endocostea coxi, E. jolkicevi and “Inoceramus” ianjonaensis morgani. During late Campanian–Maastrichtian times, the Bulgarian territory was an arena of tectonic activity, accompanied by gradual sea level rising, where the glauconitic sandstones and the following limestones were accumulated. We assumed that the abundant large-sized inoceramids have lived during the begging of the MME and demonstrating the last flourishing episode of the inoceramids, while small-sized Endocostea and “Inoceramus” showed a decline of the group, prior to its extinction.

This study is financed by project No BG-RRP-2.004-0008-C01.

The early evolutionary history of the inoceramid bivalves still remains uncertain. Inoceramus maedae Hayami, 1960, described from the Berriasian Mitarai Formation of the Tetori Group, and newly-discovered inoceramid specimens from the Tithonian Kamihambara Formation both in northern central Japan, possibly represent one of the earliest records of this family. Their external morphology is similar to that of typical Cretaceous forms (e.g., Neocomiceramus and Inoceramus). However, the multivincular ligament of the Kamihambara inoceramid has only seven or eight sets of pits and interspaces; pits are rounded rectangular, interspaces are ridge or rectangular in shape; the width of pits is much broader than that of the interspaces; the ratio of the width of interspace to that of pit varies; the pits in the anterior part are vertically long, and change their shape to laterally long in the posterior part; ligamental area is situated parallel to commissural plane, trapezoid in shape, and its height decreases gradually in the postero-dorsal area. These characters are distinct from those of Inoceramus, but similar to those of Anopaea, another late Jurassic to early Cretaceous inoceramid genus, though the external shell shape is different from each other. Furthermore, the ligaments of I. maedae can be interpreted as an intermediate form between the Kamihambara inoceramid and Inoceramus. Thus, in the evolutionary history of the inoceramids, the external shape of Cretaceous forms had been already established by the latest Jurassic, and the ligament morphology was gradually changed to that of Inoceramus over the latest Jurassic to the early Cretaceous time.

Fossils of the giant, iconic genus Sphenoceramus have been documented from the Cenomanian to early Maastrichtian Kanguk Formation of the Canadian Arctic Sverdrup Basin since the 1960s and assigned to no less than seven species in the literature. They are accompanied by the small oxytomid bivalve Hypoxytoma at several localities, but no additional taxa have been reported from the same horizons. Fieldwork on western Axel Heiberg Island has produced a remarkable, much richer fossil assemblage composed of abundant Sphenoceramus, infaunal bivalves (Astarte, Pholadomya, Mactromya), gastropods (potential Naticopsidae and Aporrhaidae), driftwood and an enigmatic, foliate phosphatic fossil. Zircon U-Pb dating of an overlying volcanic ash layer indicates a stratigraphic age close to the Santonian–Campanian boundary for this assemblage. Curiously, outside this Sphenoceramus interval, which comprises up to five closely spaced sideritic horizons, only a handful of isolated ammonites or bivalves are known from the entire Kanguk Formation. The association of Sphenoceramus and Hypoxytoma occurs in several parts of the Arctic and beyond, including West and East Greenland, the East European Platform and the Polar Urals, and extends as far south as Kazakhstan. In several of these areas, as well as in the Sverdrup Basin, this association forms one of very few notable macrofossil assemblages within the Upper Cretaceous succession. This, together with the extraordinary size of Sphenoceramus, suggests the occurrence of a spatially extensive but stratigraphically restricted ecologic and taphonomic window, which promoted the establishment of the Sphenoceramus association together with its subsequent preservation in otherwise nearly barren strata.

Although it is a predominantly recent genus, Conchoecia Dana, 1853 has had some Cretaceous forms questionably assigned to it since the description of Conchoecia cretacea Pokorný, 1964. More recently, most of these species have been relocated to genus Neorichterina Toth & Cséfán, 2018, considered a Cretaceous representative of the Entomozoidae family. However, there are still taxonomic uncertainties about this genus, and many aspects about their paleoecology, paleobiogeography and biostratigraphic remain unknown. This study revises the taxon based on the available literature on Neorichterina and the Cretaceous forms previously attributed to “Conchoecia”. Faced with several inconsistencies in the taxonomic description of Neorichterina, we suggest its removal from the Entomozoidae family and identify two potential new species, which remain in open nomenclature. The oldest known occurrence of the genus dates to the late Hauterivian-early Barremian in the Haha Basin, Morocco. Later, Neorichterina expanded into the South Atlantic and the oceans of the Tethys region between the end of the Aptian and the end of the Albian, disappearing in the lower Cenomanian. Neorichterina was probably a planktonic genus adapted to warm neritic environments and able to withstand variations in oxygenation levels. It often appeared associated with proliferations of foraminifera from the Favusellidae group and was especially abundant in the South Atlantic. Despite its wide stratigraphic distribution, its presence in the Santos Basin, Brazil, was only recorded for a short period at the end of the Aptian, which suggests its potential as a regional biostratigraphic marker on the southeastern margin of Brazil.

The former ENCI quarry, comprising the type locality of the Maastrichtian Stage, contains around 70 metres of calcareous rocks, including a seagrass horizon in the Gronsveld Member. Seagrasses, fully marine angiosperms, are associated with typical biota such as larger foraminifera, bivalves, gastropods, ammonites and grazing vertebrates (e.g. chelonioid turtles). The ENCI quarry fauna contains all of these, albeit not always in the seagrass horizon. Of foraminifera, a silicified specimen of large benthic foraminifera (Omphalocyclus macroporus) was recovered from the upper Gronsveld Member, lodged between seagrass rootlets.

Our research yields new data on benthic foraminifera and ostracods in this seagrass environment. Epibenthic morphotypes, with a predominance of Cibicidoides and Gavelinella, prevail in the underlying Valkenburg Member and around the seagrass horizon in the Gronsveld Member. Bairdoppilata, an ostracod genus typical of seagrass environments, is recorded from the Lixhe 3 and Lanaye members. Additionally, nanofossil zones UC19 (Lixhe 3 – Valkenburg) and UC20 (Gronsveld Member) were detected.

The occurrence of silicified seagrass remains is interpreted as storm-generated accumulation associated with both washed-in and indigenous macrofossil taxa. The described benthic foraminiferal assemblage contains epibenthic morphotypes as well as infaunal genera (e.g. Gaudryina, Dorothia and Arenobulimina). Moreover, middle-chain n-alkanes (including n-C 21, n-C 23 and n-C 25) confirm the presence of organic matter from the submerged plants, including seagrass, in the studied samples. Our interpretations will result in a more comprehensive model of the Maastrichtian seagrass environment at the former ENCI quarry.

In the mid-1850s, Bosquet provided the first detailed barnacle descriptions from the wider environs of Maastricht. His collections were subsequently revised by Withers in 1935, who added new species from the area. During recent years, a lot of material has been recovered, mostly from bulk samples, resulting in novel records and taxa. Earliest Campanian forms include Cretiscalpellum obtusum, Arcuatoscalpellum dortangsi (comb. nov.), Fallaxlepas fallax and Zeugmatolepas cretae. Late Campanian taxa include mostly long-ranging forms (Cretiscalpellum glabrum, Jagtscalpellum striatum, Regioscalpellum maximum, Diotascalpellum fossula, Virgiscalpellum beisseli, Brachylepas naissanti and Fallaxlepas fallax, Priscoverruca prisca), plus the endemic Proverruca ornata. Early and late Maastrichtian forms include Bosquetlepas darwiniana, Bosquetlepas gracilis, Bosquetlepas (?) bosqueti, Cretiscalpellum paucistriatum, C. glabrum, J. striatum, R. maximum, Regioscalpellum n. sp. (?), D. fossula, D. gracile, ‘Arcoscalpellum’ pulchellum, Arcuatoscalpellum n. sp., Virgiscalpellum hagenowianum, V. darwinianum, V. radiatum, V. ryckholti, V. exsertum, Pycnolepas industriosa, Brachylepas guascoi, Pr. (?) smeetsi, Verruca jagti and P. prisca. Of special note is the find of a piece of driftwood, with > 1,130 dispersed valves of at least six species of pedunculate cirripede and a minimum number of 126 individuals, which allowed a better characterisation of Virgiscalpellum radiatum and the erection of a new species, ‘Arcoscalpellum’ mosense. Particularly during deposition of the Vaals Formation (predominantly during the early Campanian), the upper Gulpen Formation (Lanaye Member) and lowermost Maastricht Formation (Valkenburg and Gronsveld members), there are clear links with the Atlantic seaboard and Gulf Coast of the United States, with a number of sibling species.

During the Early Cretaceous, terrestrial ecosystems underwent a critical transition driven by the emergence and diversification of angiosperms. Amber deposits from this period provide key evidence for understanding the diversity, interactions, and evolution of terrestrial biota. However, such deposits are geographically and stratigraphically limited. Here, we report a new amber Lagerstätte from the Upper Aptian in northern Hokkaido, Japan. The abundant amber occurs within deep-sea deposits and is rich in bio-inclusions, including arthropods, fungi, and plant remains. These inclusions are preserved in three dimensions and exhibit submicron-scale anatomical details. This is the first report of fossiliferous amber-rich deposits from the Aptian in Asia. It is also one of the oldest amber-rich localities with bio-inclusions after those in northeastern Italy (Carnian, Late Triassic), Austria (Hauterivian), the United Kingdom (early Barremian), the Levant (Tithonian, Late Jurassic; Barremian), and southern Congo (late Aptian). This finding fills a paleobiogeographic gap in the fossil record and provides anatomical and ecological insights into a critical interval marked by the rise of modern-type forest ecosystems.

Pattersoncypris is a fossil ostracod genus comprising fourteen species recovered from non-marine, transitional, and marine Cretaceous deposits in Brazil, Argentina, Liberia, Congo, Gabon, Angola, Chad, and the United States. As an abundant and diverse genus in Lower Cretaceous sedimentary basins of Brazil and Africa, regions associated with the opening of the South Atlantic Ocean, the co-occurrence of species across these basins underscores the importance of these ostracods in reconstructing the Brazil–West Africa Gondwana correlation. As it is a key genus in Aptian biostratigraphy, with guide species for biozones and subzones, a morphological, taxonomic and paleozoogeographic study was conducted to identify the most robust diagnostic features that would allow reliable species identification and provide insights into the evolutionary history and paleozoogeographic distribution of the genus. The review results enabled the standardization of morphological terms for Pattersoncypris, enhancing taxonomic identification, minimizing systematic errors, and improving biostratigraphic accuracy. Data also suggested that Pattersoncypris was an euryhaline genus originating in Gondwana continent, in the region that became the African Continent, from an ancestor with the genus Hourcqia, during the early Aptian. The adaptive radiation of the genus peaked during the Aptian, with the diversity center located in Northeast Brazil. From the Albian onwards, there was a reduction in richness, with reduced number of species being recorded only in Africa. An interval with no recorded species occurred during the early–middle Cenomanian. A single species was recorded in the late Cenomanian in United States, and by the end of this age, the genus was extinct.

Although rhabdopleurids are known since the Cambrian, the global Mesozoic fossil record is so far limited to a few sites in Germany, Poland, France and the United Kingdom only. The Cretaceous fossil record to date is limited to chemically isolated material from chalk and flint. Here we present the first in-situ finds of rhabdopleurids (gen. et sp. indet. and Rhabdopleura vistulae) from the Cretaceous. Stolon systems of rhabdopleurid hemichordates with different branching patterns are reported from the Early Maastrichtian chalk of the island of Rügen, north-eastern Germany. These colonised secondary hardgrounds on the chalk seafloor, notably belemnite rostra and echinoid tests. The material comes from the sumensis, cimbrica and fastigata belemnite zones. As these rhabdopleurids have mostly overgrown other organisms such as bryozoans, bivalves and octocoral bases, they appear to be the youngest colonisers of hard substrates within chalk sea habitat islands on the seafloor. Previous chemically isolated pterobranch material are confirmed by these in-situ specimens. In addition, possibilities for preservation and reasons for the absence of Cretaceous Pterobranchia to date are discussed.

The Balve-Beckum site (Sauerland, western Germany), a karstic infill into Devonian limestone bedrock, yielded a diverse assemblage of terrestrial vertebrates of Barremian-Aptian age. Among the microvertebrates recovered by screen washing, lissamphibians and mammals have been studied so far.

The preserved lissamphibians include one undetermined anuran taxon, two new genera and species of salamandroid salamanders, and at least one albanerpetontid.

The mammal fauna comprises at least seven taxa. Two mandibular fragments and several teeth document a new relatively large eutricondontan. Multituberculates are represented by a number of isolated teeth of a pinheirodontid and an eobaatarid, the latter also documented by a mandible fragment with p4 Three spalacotheriid molars are the first record of ”symmetrodontans” from Central Europe. Dryolestids are represented by two taxa, which is the youngest occurrence of this clade in Europe. Most remarkable is a lower tribosphenic molar which is only the sixth record of an Early Cretaceous tribosphenidan from Europe.

The composition of the lissamphibian assemblage shows similarities with other European Lower Cretaceous assemblages. In general, the Late Jurassic and Early Cretaceous fossil record is rather patchy on that continent which also applies to the record of mammals from that time period in Central Europe which also applies to the record of mammals from that time period in Central Europe. The late survival of spalacotheriids and dryolestids is possibly an effect of the subdivision of Europe into an archipelago and the resulting isolation of terrestrial environments.

It has been known since the 1970s that the infilled karst cavities in the Devonian limestone of the Sauerland may contain fossils from the Lower Cretaceous period. At that time, mainly ornithopods were found at the Brilon-Nehden site. In 2000, a similar site was discovered near Balve-Beckum, where excavations have been carried out by the LWL Museum of Natural History ever since. The fossils have been preserved in sediments filling fissures and caves that were formed by meteoric karst processes, augmented by deep hydrothermal karstification, mainly in the Mesozoic era. They originate from the land surface exposed during the Lower Cretaceous period (Barremian-Aptian) and were washed into the cave system.

The mostly isolated remains of the vertebrate fauna show a rich diversity including various cartilaginous and bony fish, as well as remains of amphibians, small reptiles, turtles, crocodiles, various dinosaur groups, pterosaurs and mammals.

The microvertebrate analysis so far revealed a large number of novel lissamphibian and mammal genera. Larger vertebrates, as well as the chondrichthyan fauna, on the other hand, indicate clearer overlaps with other sites in Europe.

The relatively high proportion of endemic microvertebrate taxa is seen in connection with the subdivision of the European area into an island landscape and the resulting geographical barriers in time, as well as with the particular palaeogeographical position of the site, which was not located near the coast but in the upland environment of the hinterland.

The record of pterosaur fossils in Brazil is significant, however, it remains limited to a few sedimentary basins from the Cretaceous period. This study describes an isolated pterosaur tooth assigned to Ornithocheiriformes, collected from the Quiricó Formation, São Francisco Basin, Early Cretaceous (Aptian), of Minas Gerais State. In addition to the description of the tooth, a comprehensive review of pterosaur records in Brazilian basins during the Cretaceous was conducted, aiming to understand the distribution of these animals throughout the period and to highlight the group diversity in Brazilian sedimentary basins. The tooth was found in association with fossil plants and articulate gonorynchiform fishes. The tooth has a narrow elliptical cross-section, which has marked mesial and distal carinae with no denticles. In lateral view, the tooth is triangular in shape, being slightly curved lingually. The enamel is thin with no striations. These features, coupled with the Lower Cretaceous age of the deposits it was found, suggest the tooth belongs to an ornithocheiriform pterosaur. This finding represents the first report of pterosaur material from the São Francisco Basin and fills a geographical gap when previous records of ornithocheiriforms in Brazil are considered (Araripe, Bauru, Grajaú, and Recôncavo basins), suggesting a broader distribution of these flying archosaurs in Brazil. Also, this new ornithocheiriform record in the São Francisco Basin strengthen the similarity of its vertebrate fauna to the vertebrates found in Kem Kem Beds in Morocco.

Fossil fish from the Campanian of the Baumberge region in western Germany have been internationally known since the 19th century, but they remain rare finds in this area. Long before their scientific study, primarily by von der Marck, these fossils gained public attention. The oldest verifiable find dates back to 1550. The stone carver Franz Brabender, son of the renowned master Heinrich Brabender in Münster, bought the sought-after sandstone from the nearby Baumberge and, while splitting it, discovered a very complete fish fossil. Quick-thinking, he had the find officially certified by the church.

He intended to sell the miracle in stone for a profit and embarked on a journey to Amsterdam, but only reached Kampen in the Netherlands, where he was accused of having forged the fish. Threats against him caused Franz to flee Kampen overnight, leaving the fossil behind. Despite his efforts, he was unable to recover the fossil during his lifetime. Therefore, shortly before his death, he gifted it to Countess Waldburg of Bentheim, who demanded the stone from the city council of Kampen and eventually succeeded in obtaining it.

Thus, the fossil ended up in the curiosity cabinet at Bentheim Castle. A photograph shows the piece roughly in the 1920s to 1930s. After World War II, the castle was used to house British officers. After the troops left, the fish could no longer be found. It is hoped that the piece, after being treasured and kept as a curiosity for almost 400 years, will eventually be rediscovered somewhere.

Here we present five micromorphological groups of Aptian pollen grains affiliated with fifteen taxa of Araucariaceae s.l. by using LM and SEM. In addition to well known araucariacean pollen taxa such as Araucariacites spp., Balmeiopsis spp. and Callialasporites spp., we could also assign Exesipollenites scabratus, E. cf. tumulus, and one Inaperturopollenites taxon as araucariacean and could summarize a collection of pollen taxa named as “Araucariaceae” sp. 1 to sp. 4. This collection looks under LM like Araucariacites but displays a transition to different micromorphological features, thus demonstrating the importance of using scanning electron microscopy in palaeopalynology. Pollen characterized by micromorphological features of micromorphological group 4 comprises Callialasporites spp., Inaperturopollenites sp. and Araucariaceae sp. 1 and are suggested to be the dispersed equivalents of previously described eurypalynous pollen cones. These pollen cones and dispersed pollen might represent an ancient group of Araucariaceae with overlapping characters from Podocarpaceae and Araucariaceae. The fifteen Araucariaceae pollen taxa occurring in the Rio da Batateira Formation exceed the diversity of previously described araucaricean macrofossils and pollen of the Araripe basin and indicate that despite the rapid evolution of angiosperms in the Lower Cretaceous, gymnosperms, particularly Araucariaceae, still played an important role in various ancient vegetation habitats.

Here we present with LM and SEM abundantly occurring Eucommiidites pollen (Erdtmanithecales) from deltaic sedimentary rocks of the Rio da Batateira and lowermost Crato formations. Separation of individual Eucommiidites species using LM only is insufficient and application of SEM is necessary to observe the position and shape of main sulcus and lateral furrows, and the sculpture and ornamentation of the ektexine. Of the twelve taxa differentiated (Eucommiidites sp. 1 to sp. 12), Eucommiidites sp. 6 from sample CAS 27 of the lowermost Crato Formation is preserved as pollen clumps and represents the dispersed equivalent of in situ Araripestrobus resiniferous pollen found in the limestone laminites of the Crato Formation. Other Eucommiidites taxa are known only as dispersed taxa of which Eucommiidites sp. 2 and E. sp. 3 occur frequently and generally abundantly in medium percentages (4 to 15%) in the pollen sum throughout the section and are interpreted to be wind pollinated or come from stands with no specific requirements. The less abundant taxa are assumed to grow at some distance from the distributary channels in more specialized stands. Eucommiidites sp. 6 and E. sp. 8 are preserved in clumps and display a more ornamented tectum and are suggested to be animal pollinated. The presence of unusual high percentages of Eucommiidites (max. 8 -15%) in the pollen sums reveal that Eucommiidites taxa constituted a significant portion of ancient vegetation habitats located upriver, but only comprise a few fragments in the macrofossil record of the Araripe Basin.

The two South Bohemian basins are located in the southern part of the Bohemian Massif. Fossil plants of Turonian-Santonian age occur in the basal-most part of the Klikov Formation. The formation is 350 m thick, primarily filled with material of fluvial origin. Fossil leaves, charcoalified mesofossils and large trunks of Paraphyllanthoxylon including roots were recovered there.

Fossil leaves of Ettingshausenia senonensis, Cocculophyllum cinnamomeum, Pandemophyllum sp. were revised. This revision was done exclusively on the collection of Ervin Knobloch, aiming to re-examine the most important leaf macrofossils from his older collections (e.g. Quercophyllum triangulidente, Debeya bohemica), and compare them to newly gathered data, using new methods. Small leaves from bulk-macerations are a few millimetres in size, mostly serrate or dentate; their cuticle is difficult to obtain due to the degree of charcoalification and small size; usually a cuticle without stomata can be observed, occasionally with trichome bases.

This revision enabled a better understanding of the vegetation. While most of the platanoid leaves are assigned to Ettingshausenia senonensis, leaves of Quercophyllum show the same cuticle as Debeya insignis. Lauroids were more diversified. We have recorded trunks of Paraphyllanthoxylon, and leaves of Pandemophyllum and Cocculophyllum. Both platanoids and lauroids are reconstructed as growing on alluvial plains, while plants of the Normapolles complex are reconstructed as growing on slopes. Lagoons in fluvial plain were vegetated by water monocots, their margins with liverwort Ricciopsis and hornwort Notothylacites. Local swamps were dominated by Geinitzia reichenbachii.

Acknowledgements: The study was financially supported by the Czech Science Foundation (GAČR) 23-05142K.

The Albian Khukhteeg Formation is composed mainly of dark greyish coaly mudstone, light greyish sandstones, and conglomerates. It is widespread in the Eastern Mongolia with a characteristic feature of abundant coal seams (Tal bulag,Tukhum and Erdenetsogt localities).The palynology assemblage of Erdenetsogt Govi coal deposit is composed of Pteridophyta spores (68 %) and of Gymnosperm pollen (32%). Spores are represented mostly by different species of Cicatricosisporites, Concavissimisporites, Trilobosporites, Pilosisporites and Aequitriradites. Non-saccate gymnosperm pollen is presented by Cycadopites, Inaperturapollenites and Monosulcites. Bisaccate conifer pollen, most assignable to the Podocarpidites, Piceapollenites, Pinuspollenites and Protopicea.

The palynology of Tal bulag and Tukhum coal deposits is characterized by the abundance of pollen (60-62%) Piceapollenites, Pinuspollenites, Podocarpidites, Cedripites and non-saccite gymnosperm pollen such as Cycadopites, Ginkgocycadopites and Inaperturapollenites. Spores are not numerous, but presented different species of Concavisporites, Cyathidites, Osmundacidites, Cicatricosisporites, Laevigatosporites, Baculatisporites and Biretisporites. Palynoassemblages of Tal bulag and Tukhum deposits are different from the Erdenetsogt palynocomplex, in these assemblages were not occurred any species of spores such as Pilosisporites, Cooksonites and Trilobosporites . There are many different species of spores, and similarity with second assemblage of the Shivee Ovoo and Matad assemblages (Ichinnorov, 2003; Ichinnorov & Hofmann, 2012). The palynological evidence is consistent with a humid and warm palaeoclimate.

This is a contribution of UNESCO-IUGS IGCP 679.

References:

Ichinnorov.N., 2003. Palynocomplex of the Lower Cretaceous sediments of the Easthern Mongolia. Mongolian Geoscientist. N.22, p.12-16.

Ichinnorov Niiden, Christa-Ch. Hofmann. 2012. Palynology studies of the Matad

artea (Tamsag Basin), South-eastern Mongolia. Journal of Geoscience. №21. p. 63-84

Cathodoluminescence (CL) is a light emission phenomenon that occurs when a substance is irradiated by an electron beam. The CL intensity and spectrum vary depending on lattice defects and impurity elements in crystals.Therefore, the CL spectrum of quartz will vary the characteristics of its source rocks. CL has been widely applied for provenance analysis (e.g., Zinkernagel, 1978).

In this study, we analyzed the CL spectrum using peak separation to create an index for discriminating rock types and examined its applicability to Cretaceous clastic detritus. We created the index using 19 rock samples, including volcanic, plutonic, high-temperature, and high-pressure metamorphic rocks. Additionally, 3 Cretaceous clastic detritus samples were used to apply to the index. The CL spectrum was measured using an SEM-CL system in the 250 to 950 nm range.

This study identified three indices after conducting spectral analysis and PCA. These indices enable discrimination of rock types; this suggests that this scheme can be applied to the provenance analyses and we practically applied to the Cretaceous clastics.

By using the above indices, we propose a discrimination diagram, which the 70% confidence regions segregate most of rock types, although there was some overlap. In particular, plutonic and high-temperature metamorphic rocks were difficult to distinguish. In addition, the application to the Cretaceous clastics ended in failure suggesting an incorrect provenance. There are challenges in determining the plutonic and high-temperature metamorphic regions and application to geological records.

The Mesozoic era is known as a greenhouse era with gradual climate elevation from the Triassic to a super-greenhouse condition in the mid-Cretaceous, reaching the warmest climate in the Phanerozoic. There have been many studies on Mesozoic paleoclimate in the interior of the Asian continent. Still, few studies have been conducted in the coastal areas of the Asian continent, where regional paleoclimate change can be more accurate and sensitive monitor of the global paleoclimate changes. However, there is a lack of information on paleoclimate in the continental margins of Asia. This study aims to elucidate the paleoclimatic evolution of the east Asian continental margin during the Early Triassic to the Middle Cretaceous in the Kitakami belt of Northeastern Japan.

This study conducted geochemical and mineralogical analyses of mudstone samples collected from five formations ranging from the Early Triassic to the Middle Cretaceous, and estimated the paleoenvironment of the east Asian continental margin.

The result indicates that northeast Japan was generally temperate during the Mesozoic but reached its climatic optimum in the mid-Cretaceous. This result is concordant with the trend of Mesozoic global paleoclimate change. However, we also identified temporal severe aridification or cooling during the Late Triassic. We are uncertain what this result suggests but consider that the present result detected a regional paleoclimate change at the eastern continental margin of Asia during the Late Triassic.

The Tetori Group is a Jurassic–Cretaceous siliciclastic succession in Japan that records a marine to non-marine transition and preserves diverse fossils from the eastern margin of East Asia, influenced by the Boreal and Tethyan realms. Despite its importance, regional correlation is difficult due to poor exposure and discontinuous sequences.

Carbon isotope stratigraphy was applied across three sections to improve the regional correlation: Itoshirogawa logging road (ILR, type section), Tamodani (continuous stratigraphy), and Shokawa (chronostratigraphically constrained). Paleomagnetic analysis of the ILR and Tamodani was applied. Total organic carbon and δ¹³C_org values were measured at multiple samples on each horizon, and Rock-Eval pyrolysis was conducted on ILR and Tamodani samples.

Rock-Eval pyrolysis indicated that the organic matter was predominantly from terrestrial higher plants. δ¹³C_org fluctuations were consistent with each section, showing a positive excursion and a negative interval. A new U–Pb zircon date of 128.8 ± 1.4 Ma from a tuff sample of the Itsuki Formation acts as an anchor of the δ¹³C_org curve; the positive excursion was likely correlated with the post-OAE1a excursion in the Aptian, while the negative interval aligns with the Hauterivian after the Weissert Event. All paleomagnetic samples show normal polarity, likely due to an overprint.

A combination of carbon isotope stratigraphy and U–Pb chronology proves essential for regional correlation within the Tetori Group and directly to global and East Asian non-marine records. Identifying other isotopic excursions, such as the Weissert Event or Volgian Isotopic Carbon Excursion, will be key to correlating additional horizons.

The Ulsan area belongs to the southeastern part of the Cretaceous Miryang Sub-basin of the Gyeongsang Basin, the largest Cretaceous terrestrial basins in Korea. However, it has been geologically isolated by faults and intrusive rocks, resulting in a stratigraphy distinct from the main distribution of the Miryang Sub-basin. Recently, some paleontological records have been reported from the Cretaceous deposits in Ulsan, gradually revealing the previously unknown paleoenvironment and paleoecology of the southeastern Gyeongsang Basin. Nevertheless, research on stratigraphy, sedimentary geology, and paleoenvironmental interpretation remains insufficient. This study describes the sedimentary features and paleontological records from the lowest part of the Cretaceous Sayeonri Formation in Ulju-gun, Ulsan, Korea, and interprets their paleoenvironmental and paleoecological implications. The Sayeonri Formation at the study site is interpreted to have been deposited in an alluvial plain, lake margin, and shallow lake based on sedimentary facies analysis. Diverse sedimentary features and paleontological records are found in the deposit, including mudcracks, wave ripples, current ripples, teepee structures, traces of evaporite minerals, raindrop imprints, microbially induced sedimentary structures, calcretes, quadrupedal ornithopod dinosaur footprints, sauropod dinosaur footprints, small vertebrate footprints and invertebrate trace fossils. These features indicate that the Sayeonri Formation was formed in an alluvial plain, lake margin, and shallow lake under an arid to semi-arid climate. Moreover, they suggest that microorganisms, invertebrates, and vertebrates coexisted in this depositional environment. The results of this study provide foundational data for establishing the stratigraphy and uncovering of the hidden paleoenvironments of the Korean Peninsula during the Cretaceous.

The shape of clastic grains has been considered as an essential indicator of the depositional environments and hydro-dynamic experience they have undergone. Therefore, many studies have been pursued to quantify the shape of clastic grains.

For example, Suzuki et al. (2015) utilized the elliptic Fourier principal component analysis (EF-PCA) to analyze the shape of sand particles and created two indices: a macroscopic index of the overall shape of grains (REF1) and a microscopic index of surface roughness (SEF).

REF1-SEF indices can be used not only as a quantitative shape indicator but also as a prediction of grains derived from glacial, fluvial, foreshore and aeolian environments. However, previous studies focused on the application of modern sediments, and little research has been done on sand particles from the geological record (sandstones). In this study, we investigate whether this particle shape analysis (EF-PCA) is helpful for the paleoenvironment predictions of sand grains from the geological records.

The sample used in this study is sandstone from the Daerdang Formation, distributed in the Sichuan Basin, China, which was located in the interior of the Asian continent during the Cretaceous Period. Sandstones analyzed are well-sorted quartzite with high-angle cross-bedding and interpreted as Cretaceous aeolian deposits. The EF-PCA analysis was conducted on these sandstones to see if this scheme is valid for paleoenvironment prediction.

Cathodoluminescence (CL) is a light emission phenomenon that occurs when a substance is irradiated by an electron beam. CL intensity and spectra may vary depending on lattice defects and impurity elements inherited in crystals. Since CL spectra of quartz reflect the characteristics of their source rocks, they have been widely used for provenance analysis (e.g., Zinkernagel, 1978). In this study, we evaluated the CL characteristics of quartz using machine learning to develop a source-rock classification model for detrital quartz. This will provide a new scheme to evaluate the source-rock types of the Cretaceous strata.

We analyzed 26 rock samples mainly formed during the Cretaceous period, including volcanic, plutonic, high-temperature metamorphic, and high-pressure metamorphic rocks. Quartz grains were analyzed using a scanning electron microscope equipped with a diffraction grating spectrometer. CL spectra were measured in the 300–800 nm range and transformed using the isometric log-ratio (ilr; Egozcue et al., 2003). A machine learning model was constructed based on spectral differences and evaluated with stratified k-fold cross-validation.

CL spectra of quartz grains are apparently similar and undistinguishable. However the Linear Discriminant Analysis (LDA) and random forest models enabled discrimination of quartz grains from the four source rocks, achieving about 80% accuracy. The present scheme can hopefully be an useful approach to the provenance analysis of Cretaceous sandstones.

References:
Egozcue, J.J., Pawlowsky-Glahn, V., Mateu-Figueras, G., Barceló-Vidal, C., 2003. Isometric logratio transformations for compositional data analysis. Math. Geol. 35, 279–300.
Zinkernagel, U., 1978, Contributions to Sedimentology, 8, 1-69.

The enhancement of continental weathering during the middle Cretaceous has received wide attention because it may have played a crucial role in causing oceanic anoxic events (OAEs). Global warming may enhance continental weathering, leading to outflow of nutrients into the ocean, provoking excessive primary productivity and raising the middle Cretaceous OAEs (weathering hypothesis). To evaluate the role of continental weathering, this study explores the fluctuation of continental paleoweathering during OAE2 in the east Asian continental margin. The extent of hinterland paleoweathering was quantified using the geochemical weathering index (W values) and the grain size variation was estimated by mineral composition (quartz/phyllosilicate) of the mudstones collected from Saku Fm., Yezo Group, exposed in Hokkaido, northern Japan. The W value ranges from 30 to 50, which is equivalent to recent soils that developed under temperate climates. The W value increases before the onset of OAE2 and during OAE2 that ceased simultaneously with the termination of OAE2. Quartz/phyllosilicate increases during the OAE2 interval. These results indicate an increase in sediment flux during OAE2, which is concordant with a numerical model study showing an increase in precipitation at Mid-latitude Eastern Asia, which is the hinterland of the Yezo Group at elevated atmospheric CO₂ levels.

These results are consistent with the weathering hypothesis as a cause of OAE2. Previous studies revealed that continental weathering increased during OAE2 in the Tethys and proto-North Atlantic oceans. Our data suggest that a similar phenomenon also operated in the western margin of the Pacific Ocean.

The Cretaceous period, characterized by elevated temperatures and high atmospheric CO₂ concentrations, is a crucial subject in paleoclimate studies as it may serve as a reference for understanding the Earth system dynamics under greenhouse conditions. Efforts to elucidate the climatic characteristics of different regions on Earth have been reflected in many studies conducted on various research subjects. Severe aridification has been recognized in low-latitude areas of Southeast Asia during the mid-Cretaceous; however, previous studies have mainly focused on continental interior basins, and the continental margin has not been studied precisely. In this study, we investigated the paleoclimate of Vietnam during the Cretaceous by a detailed assessment of geochemical and clay mineralogical characteristics of mudstones collected from northern Vietnam, the Da Lat region, and Phu Quoc island. The results indicate that Northern Vietnam has experienced a temperate climate in the early Cretaceous but shifted to arid conditions in the Late Cretaceous. Central Vietnam remained in arid conditions and Southern Vietnam was sub-humid through the Cretaceous. The geochemical proxies and clay mineral indicators consistently reveal a decrease in chemical weathering intensity during the Late Cretaceous, suggesting a slight aridification from the Early to the Late Cretaceous. Notably, Central Vietnam is recorded as drier than the North and South during the Cretaceous period. These results indicate that the continent's climate characteristics are strongly controlled by global atmospheric circulation and regional geographical and tectonic factors.

Belemnites are an extinct order of the coleoid cephalopods flourishing in the world ocean from the early Triassic to the end of the Cretaceous, and are often considered as useful palaeobiogeographical indicators. The belemnite records in Japan potentially provide useful information to discuss the palaeobiogeography in the Northwest Pacific at that time, and the presence of the Boreal belemnites in the Middle Jurassic and earliest Cretaceous strata in the Inner Zone of the Southwest Japan attracts much attention recently. Although the occurrences of the belemnites from the Outer Zone of the Southwest Japan had been known, most of them have not been formally described yet, and then their palaeobiogeographical values are not fully discussed. In this paper, several specimens of the mesohibolitid belemnite rostra were described from the Tithonian–Berriasian Yatsuji Formation of the Torinosu Group in the Sakawa area, Shikoku Island, Southwest Japan. Single specimen is identified as Hibolithes aff. marwicki marwicki sensu Mutterlose (1986) described from the lower Tithonian in Antarctica. Other five specimens are similar to Pachybelemnopsis aucklandica aucklandica, which was described from the middle to upper Tithonian in New Zealand, though the length of a ventral groove and the shape of transverse section of the rostra of Sakawa Pachybelemnopsis are slightly different from those of this species. These belemnite taxa can be considered as the Tethyan-Pacific elements, suggesting the faunal connection between the southern part of the South Pacific and the Northwest Pacific through the equatorial region around the interval near the Jurassic/Cretaceous boundary.

The Late Jurassic to Early Cretaceous succession exposed in the Thakkhola Graben (central Nepal Himalaya) is regarded to develop on a passive margin of the north-eastern Gondwana. The Early Cretaceous deposits mark a significant change in sedimentation compared to the Jurassic succession. An offshore shales of the Jurassic Nupra Formation were replaced by the deltaic siliciclastics deposits at the beginning of Cretaceous that designate the next stage of Tethys Himalaya development, where after incipient opening of the Indian Ocean in Middle and Late Jurassic, an extensional tectonic phase started that led to upwarping of the Indian margin and erosion of exposed sedimentary rocks, which provided source material for the Lower Cretaceous Chukh Group. We examined facial development and the green clay nature and distribution of the Chukh sequence exposed on the western bank of the Kali Gandaki (Thakkhola Graben). Our findings confirm the previous interpretations of a general change in the depositional regime of these deposits from terrigenous-derived deltaic to open shelf calcareous environment. However, the occurrence of several horizons of wave or hummocky-cross lamination between the deltaic sand bodies is indicative of their wave reworking, while interbedding of green layers composed of glaucony marks episodes of condensation during sedimentation of deltaic deposits. This indicates the highly variable sedimentation conditions of the lower part of the Chukh sequence, probably due to the eustatic sea-level rise and tectonic subsidence of the Indian margin that followed the break-up between India and Australia. This is contribution No.6 of the scientific initiative Himalayan Academy.

The shape of clastic grains contains essential information about their hydrodynamic transport processes and depositional environments. Many studies have been conducted to quantify grain shape. For example, measuring a grain’s longest, intermediate, and shortest axes (three axes) allows the description of its overall shape, such as elongated to rounded forms. However, these axes cannot capture the surface smoothness of grains.

The reverse is also true: conventional surface smoothness indices cannot be used to describe the overall shape of grains.

This study introduces a method to quantify overall shape and surface smoothness texture using elliptic Fourier–principal component analysis (EF-PCA; Suzuki et al., 2015). Elliptic Fourier analysis encodes grain outlines into sinusoidal waves of various frequencies (100 Fourier wave series were used). Principal component analysis was then applied using both the variance–covariance and correlation matrices of Fourier descriptors. The former emphasizes high-amplitude Fourier waves and reflects overall shape (REF1), while the latter emphasizes fine-scale waves and reflects surface roughness (SEF).

Because this method uses only two-dimensional shape information, it can also be applied to thin-section samples (geological records). In this study, EF-PCA was applied to quartz grains in thin-sections of Cretaceous deposits and compared with grains from modern foreshore sands.

Comparative samples included modern foreshore sand and thin section specimens from the Inubozaki Formation of the Cretaceous Choshi Group. Both were analyzed using EF-PCA to compare grain shape characteristics. The results show that thin section analysis can effectively quantify grain shape in ancient deposits and compare them with modern sediments.

A series of rift basins formed along the northern margin of the North China Craton (NCC) during the Early Cretaceous Period, due to the subduction of the paleo-Pacific Plate and the destruction of the NCC. The Baishan Basin (also known as the "Hunjiang Basin") is one of coal-yielding rift basins in the northern margin of the NCC. Cretaceous strata are widely exposed in the Baishan Basin, and consist of five formations: The Guosong, Yingzuilazi, Linzitou, Shiren and Xiaonangou formations, in ascending stratigraphic order. In this study, a new non-marine ostracod fauna from the Xiaonangou Formation in the Baishan Basin has been detailed described and illustrated for the first time. Eight samples from the Guanghuanjie-Yumuqiaozi section were analyzed, and seven taxa were identified, including Cypridea sp., Mongolocypris shai sp. nov., Lycopterocypris sinuolata, Lycopterocypris sp., Candona praevara, Candonidae gen. indet. sp. and Cyclocypris invalida. This comprehensive taxonomic study not only enhances our understanding of Cretaceous non-marine ostracods in China but also provides the first precise age constraint for the Xiaonangou Formation using ostracod biostratigraphic correlation. Based on the ostracod biostratigraphic analysis, the age of the Xiaonangou Formation is early Albian. Additionally, this study supports the hypothesis of invertebrate faunal exchange in northeastern China during the Early Cretaceous.

Acknowledgments. Financial support for this study as received from the National Natural Science Foundation of China (42372022, 42481540217).

The shape of sedimentary grains, such as roundness and surface smoothness were acquired during the transportation and depositional processes that grains underwent. Therefore, the shape of sedimentary grains might possess information to reconstruct the transportation histories and depositional environment that grains underwent. Therefore, numerous studies had been pursued to quantify the shape of sedimentary grains. Among them, Suzuki et al. (2015) proposed two shape parameters to quantitatively evaluate grain shapes by utilizing elliptic Fourier and principal component analyses (EF-PCA), which can quantify macroscopic circularity (REF1) and microscopic smoothness (SEF) of grains. Suzuki et al. (2015) furthermore revealed that on the REF1-SEF cross plot, sand grains derived from glacial, fluvial, foreshore, and aeolian environments form distinct clusters, and therefore the depositional environment can be predicted by the two indices.

While Suzuki et al. (2015) focused solely on sand, this study demonstrates that EF-PCA is also effective in assessing the degree of abrasion of gravels. Furthermore, we developed an index for the three-dimensional shape evaluation of gravels by the extension of conventional EF-PCA method.

However, it is uncertain whether this method would be effective for the paleoenvironmental analyses, since application to the geological gravel records has not been attempted. Therefore, this study applies EF-PCA to gravels in the Choshi Group in Chiba Prefecture, Japan, to evaluate the validity of this method to the geological records and investigate the Cretaceous paleoenvironment of east Japan.