PICO
PICO: Wed, 30 Apr | PICO spot 2
The Slovenian Basin (the eastern Southern Alps, Slovenia) formed during the Middle Triassic and lasted until the end of the Mesozoic. The oldest succession belongs to the Ladinian volcanic- and clastics-dominated Pseudozilian Formation, followed by the Carnian Amphiclina Formation, composed of shale, sandstone, subordinately conglomerate and bedded limestone. Several sections were documented by Skaberne et al. (2024) in the southern part of the Tolmin Nappe (subunit of the Southern Alps), but only one succession was logged from more northern parts of the Tolmin Nappe (Gale et al., 2017). Consequently, little is known about Carnian paleotopography of the basin. To augment current knowledge on the lateral differences within the Amphiclina Formation, a succession was logged on the Martinj Vrh hill, structurally situated in the middle part of the Tolmin Nappe. The entire succession is 47.3 m long and ends at the transition to the Norian-Rhaetian Bača Dolomite Formation. According to conodont data, this stratigraphic boundary corresponds to the Carnian-Norian boundary. The rocks were analysed using optical microscopy, XRD, and μ-EDRF. The outcrop consists of bedded fine-, medium- and coarse-grained sandstone, marlstone, mud-supported conglomeratic breccia, conglomeratic breccia with carbonate cement, and bedded limestone with occasional occurrences of dolomite. Parallel and cross-lamination, load casts, ball and flame structures, scour structures, slumps and synsedimentary faults are present. Limestone is mudstone-wackestone with radiolaria, filament and bioclastic wackestone, echinoderm-intraclastic packstone, filament-peloidal packstone-grainstone, intraclastic-peloid packstone-grainstone, peloidal grainstone, and rudstone. Position within the basinal area cannot be directly determined, although the sedimentary structures suggest that sedimentation took place on the basin slope. Comparison with previously published logs shows that sedimentation within the basin greatly varied and that no clear distinction can be drawn between different parts of the Tolmin Nappe. This is probably due to complex internal topography of the basin.
Gale et. al. 2017: Characterization of silicified fossil assemblage from upper Carnian "Amphiclina beds" at Crngrob (central Slovenia). Geologija, No. 60/1, pp. 61–75.
Skaberne et. al. 2024: Middle Triassic deeper-marine volcano-sedimentary successions in western Slovenia. Geologija, No. 67/1, pp. 71–103.
How to cite: Pristavec, M., Rožič, B., and Gale, L.: Carnian clastic-carbonate succession from the Slovenian Basin (Southern Alps), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8136, https://doi.org/10.5194/egusphere-egu25-8136, 2025.
The polar oceans are critical in regulating atmospheric CO2 concentrations (pCO2) during Pleistocene glacial cycles. However, the role of the subarctic Pacific, despite being the largest reservoir of respired carbon in the modern ocean, remains underexplored due to limited data. This study presents high-resolution export productivity records, normalized using 230Th, from the subarctic northwestern Pacific spanning the last five glacial cycles. These records reveal distinct glacial-interglacial patterns overlaid with variability driven by precession. Warm interglacial climates, coupled with high boreal summer insolation, facilitated the upwelling of nutrient-rich subsurface waters, leading to increased export productivity. Transient model simulations demonstrate that ice sheet dynamics and, to a lesser extent, precession significantly influence the strength and latitudinal shifts of the westerlies. Intensified and poleward-shifting northern westerlies during warmer intervals likely enhanced the upwelling of carbon- and nutrient-rich waters, releasing previously stored CO2 from the subarctic Pacific into the atmosphere. These findings underscore the substantial influence of the subarctic Pacific in regulating pCO2 variations during Pleistocene climate cycles, particularly on the precessional timescale (~20 kyr).
How to cite: Yao, Z., Shi, X., and Yin, Q.: Productivity and upwelling changes in the Subarctic Pacific over the past five glacial cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8165, https://doi.org/10.5194/egusphere-egu25-8165, 2025.
Upper Cretaceous Blackhawk Formation of the Western Interior Seaway of the North America was used to develop the models for shoreface and wave dominated delta in the stratigraphic record. The hundred of meters thick continuous outcrops also served as a model for development of sequence stratigraphy and many geoscientists continue to train using delta deposits in the Book Cliffs area of Utah. However, the existing deltaic facies models do not consider the delta double-clinoform morphology, shoreline and subaqueous-delta components, that is now widely documented in modern delta systems.
River deltas prograding into a basin are reworked by waves and tidal currents and this causes the double clinoforms geometry as observed in modern delts (e.g., Mekong, Huanghe, Yangtze, Amazon, Atchafalaya). The directly river derived sediments form prograding mouth bars and reworked shorelines/interdistributary bays and these form the shoreline or subaerial delta clinoforms. The high energy around wave-dominated shorelines causes especially the large-volume finer grained portion of the sediment budget to bypass further onto the shelf, producing the subaqueous delta with a very gentle rollover from platform to subaqueous foreset in tens of meters water depth.
Fifteen published and 6 new measured sections in outcrops of Book Cliffs north of Green River, together with tens of well logs allow observation of the facies and architecture of the Kenilowrth Mbr. of the Blackhawk Fm. along depositional strike and dip. Kenilworth Mbr. has multiple parasequences tens of meters thick that coarsen and thicken up from cm thick silts to cm to dm thick parallel laminated and ripple cross-strata very fine sandstones within otherwise quite muddy successions. Thin sandstone beds have sharp to erosive bases suggesting emplacement as “event-beds” on the subaqueous-delta clinothems. Bioturbation is overall low to moderate but locally, in the mud intervals between very fine sandstones can be intense. The fine-grained coarsening-up units are capped by a few dm thick beds with ripple cross-lamination, low angle lamination and thin sets of hummocky strata. The total thickness of these deposits varies between 0.5m to 2m and are then overlain by structureless or cm thick laminated silts and very fine sandstones. Stacking of 2 to 3 coarsening upward parasequences in a subaqueous delta unit can total 90m thick deposits. The overlying 10 to 15 m coarsening upward sandstone dominated unit with dm to m thick rippled and trough or hummocky stratified fine to medium grained sandstone is interpreted as the delta front or shoreline clinothem.
The proposed model of double-delta clinoforms triggered by observations on modern delta systems and numerical models has had a significant impact and allows us the reinterpretation of stratigraphy. A subaqueous platform that is kilometers to tens of kilometers wide allowed the transport of fine and very fine sands further into the basin. The generation of the subaqueous platform changes the conventional architecture of the delta deposits with multiple subaqueous lobes in addition to the “subaerial” delta lobes that define the shoreline. Coeval progradation of the shoreline and subaqueous delta clinoforms produces two coarsening upward successions to the compound delta.
How to cite: Olariu, C. and Steel, R.: Delta double clinoforms facies model for sequences of the Upper Cretaceous Blackhawk Formation in the Western Interior Seaway, Utah, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14638, https://doi.org/10.5194/egusphere-egu25-14638, 2025.
During much of the Mesozoic, deposition on the eastern part of the Adria microplate contrasted between two major paleogeographic domains: the deep-water realm of its subsided margin flanking the Neotethys Ocean and the shallow-water carbonate platform environments of its interior. Since the late Jurassic tectonic processes related to Europe-Adria convergence progressively affected both of these regions. Ophiolite obduction and continued nappe propagation involving Adria basement caused local uplift and subsidence related to lithosphere flexure and migration of foreland basin depocenters. The area of Gacko in Bosnia and Herzegovina offers a well exposed sedimentary record of initial foreland basin encroachment onto the margin of the long standing Adriatic Carbonate Platform.
Along a transect north of the town of Gacko, Lower Cretaceous shallow marine deposits are overlain by massive bioclastic floatstone - rudstone interpreted as deposited in a ramp environment, marking an early stage of foreland basin formation. Upwards the succession changes into a well-bedded Santonian-Campanian sequence of alternating pelagic wackestones, carbonate turbidites, hyperconcentrated density flows, and slumps deposited in a slope environment. Clast composition includes various bioclasts (benthic foraminifera, rudists), intraclasts of pelagic wackestone-packstones hosting Late Cretaceous foraminifera, and extraclasts of Cretaceous limestones. A dominance of pelagic sedimentation suggests continued relative deepening during the Campanian. Further in the succession sedimentation shifts to coarse grained carbonate breccias and calcarenites possibly indicating coeval tectonic influence along the basin flank. In the Maastrichtian and Paleocene, deposits are characterized by an alternation of marls, sandstones, calcarenites, and carbonate breccias. Thick (>10 m) megabeds consist of poorly sorted, clast-supported, angular carbonate clasts (up to 40 cm in size) in their lower segments, topped by several meter thick massive calcarenite upper segments. Their clast composition includes various carbonate lithoclasts, which together with E-NE-directed paleocurrent orientations suggest a dominant derivation of material from the carbonate platform realm to the SW. The siliciclastic component in the sandstones is largely composed of quartz and foliated quartz-mica lithoclasts, while the heavy mineral fraction includes Cr-spinel, zircon, garnet, rutile, and tourmaline, indicating contribution of material from units exposed in the advancing orogenic wedge.
How to cite: Lužar-Oberiter, B., Petrinjak, K., Kukoč, D., Banak, A., Kocjančič, A., Bjelogrlić, M., Šamarija, R., Aščić, Š., Šuica, S., Olić, I., Mezga, A., and Moro, A.: Initial stages of foreland basin formation along the Adriatic carbonate platform margin of the Dinarides (Gacko, Bosnia and Herzegovina), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14856, https://doi.org/10.5194/egusphere-egu25-14856, 2025.
The Fram Strait, located between Svalbard and Northeast Greenland, is the only deep oceanic passage linking the Arctic and Atlantic Oceans. Water exchange through the strait is crucial for the Atlantic Meridional Overturning Circulation, controlling global climate. Increased water exchange between the Arctic and Atlantic Oceans might have been one of the main factors driving global climate into an icehouse state at the Eocene-Oligocene Transition, around 34 million years ago. However, proxy evidence is scarce due to limited sedimentary archives from the region.
The <20 km-wide Forlandsundet Graben located on the western Svalbard margin is a pull-apart basin formed during the early Paleogene. It may represent a precursor to the Fram Strait, potentially allowing water exchange already during the Paleogene. The thickness and age of the graben fill are poorly constrained, necessitating a better stratigraphic framework to understand the events leading to the seaway’s opening and deep-water connection between the Atlantic to the Arctic Ocean.
Vintage 2D seismic data suggest the sedimentary succession in the graben may exceed 4 km. A petroleum exploration well (7811/5-1) drilled onshore at Sarstangen in 1974 reached metamorphic basement rocks at a depth of 1046 m, penetrating over 1 km of mostly marine mudstones and sandstones, initially dated as possibly Eocene and Oligocene.
To refine the stratigraphy and estimate paleo-environments and maturity of the sedimentary succession, we investigated three cored intervals of the 7811/5-1 well. Combined dinocyst and foraminifera assemblages suggest a middle Eocene age for the lowermost core interval and an upper Eocene to early Oligocene age for the uppermost core interval. Foraminifera indicate outer neritic to upper bathyal water depths (100-500 m) in the Eocene. Pollen and spores are more common than marine dinocysts, and the uppermost core yields coal fragments. TOC, Tmax, and HI suggest inert kerogen of mixed origin, classified as type III/IV.
These findings enhance our understanding of the Forlandsundet Graben's stratigraphy and its role in Arctic-Atlantic water exchange during the Paleogene, providing crucial insights into the geological history and paleo-environments of the region.
How to cite: Sliwinska, K. K., Sheldon, E., Bojesen-Koefoed, J., Grundvåg, S.-A., Jones, M., Knutsen, S.-M., Weber, M., Senger, K., and Laberg, J. S.: Deciphering the geological history of the Forlandsundet Graben and its implications for Arctic-Atlantic connectivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17246, https://doi.org/10.5194/egusphere-egu25-17246, 2025.
Prograding clinoforms of different scales usually occur in special carbonate sedimentary systems. Since carbonates are mainly generated in situ by biochemical processes within the basin, prograding clinoform sediments are less common than terrigenous clastic sedimentary systems. Carbonate prograding clinoforms have not received much attention in research, resulting in a lack of investigation into their sedimentary process, genetic mechanism and controlling factors. The investigation utilized integrated analysis of cores, thin sections, 3-D seismic and well logging data to explain the sedimentary process, genetic mechanism, controlling factors of carbonate clinoforms and its relationship with the development of favorable reservoirs. The result shows that there are five vertically overlapped clinoforms advancing from WWS to NNE. which occurs as S-shaped lens, with thick middle parts and thin ends. Well logging and seismic characteristics have provided the basis for establishing a sequence-stratigraphic framework. Two regionally third-order sequences (Sq1-Sq2) are developed in the Stage-3 succession, Sq1 incorporates three clinoforms (C1-C3); Sq2 incorporates two clinoforms (C4-C5). In the Sq1, the vertically aggradational thickness of the clinoforms were large, about 70~160 m, and the study area was dominated by the outer middle-ramp deposits. In the Sq2, the vertically aggradational thickness of the clinoforms were small, about 3~40 m, and shallow shoal deposits were developed in the edge of the clinoforms. The clinoforms can be further divided into 21 2rd-clinoforms. Four main types of clinoform architecture were recognized: falling (progradational pattern), flat (progradational pattern), rising (progradational and aggradational pattern) and backstepping (retrogradational pattern) edge trajectories. The present study revealed that the formation of clinoforms were controlled by the change of eustasy. Due to the broad ramp sedimentary background and sea-level fall, the sedimentary accommodation space continued to decrease, which ultimately lead to the formation of the prograding clinoforms. Reservoirs dominated by high-energy shoal are developed at the edge of the clinoforms.
How to cite: He, Q., Shi, K., Liu, B., Wu, C., Adam, M., and Mountney, N.: Stratigraphic evolution of Stage-3 clinoforms from northern Tarim Basin: Evaluating controlling factors on a distal steepening carbonate ramp growth and shallow-water sedimentation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20201, https://doi.org/10.5194/egusphere-egu25-20201, 2025.
In the year 2014 the so far oldest Bavarian fossil (a typical archaeocyathid hollow horn formed sponge) with an age of ~520 ma was identified near Schwarzenbach/Wald (north-east Bavaria-Germany).
Recently, the Bavarian Environment Agency started the hunt for a new oldest Bavarian. In 1988 Reitz and Höll described one specimen of Acritarcha with moderately bad preservation of the Prasinit-Phyllit-Series (PPS) of north eastern Bavaria and claimed a pre-Cambrian age for the deposit. Nevertheless, recent studies show that a continuative pre-Cambrian or even Cambrian age of the PPS cannot be provided and therefore the biostratigraphic dating has to be checked intensely.
Therefore, analyses of three different outcrops (Sparneck and Schwarzenbach/Saale outcrop 1 and 2) have been conducted to test and/or verify the pre-Cambrian age.
If a pre-Cambrian age can be confirmed and suitable Acritarcha of the PPS can be found and identified, this will not only be the oldest Bavarian but also the oldest confirmed German (fossil) ever found.
How to cite: Kranner, M.: The hunt for the oldest Bavarian – Acritarcha of the Prasinit-Phyllit-Series (Münchberg Massif), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8210, https://doi.org/10.5194/egusphere-egu25-8210, 2025.
Fusulinids, the earliest recorded group of larger benthic foraminifera, first appeared in the Early Carboniferous and flourished from the Late Carboniferous to the end of the Middle Permian. Their most notable diversification occurred during the Late Carboniferous to the earliest Permian, coinciding with the peak of the Late Paleozoic Ice Age (LPIA). Understanding in more detail the link between fusulinid diversification and climate changes could provide a unique perspective on evolutionary responses to climatic variability. Here, based on newly established patterns of high-temporal-resolution species richness and factor analysis, we recognize four evolutionary faunas akin Sepkoski’s evolutionary faunas. The four evolutionary faunas are pre-LPIA, early-LPIA, late-LPIA, and post-LPIA. These evolutionary faunas are characterized by long decline patterns (pre-LPIA and early-LPIA faunas), and extinction patterns with sudden eliminations of the whole fauna (late-LPIA and post-LPIA faunas). Further analyses revealed that the magnitude of climatic changes played a key role in shaping different diversity trajectories of fusulinid evolutionary faunas and the succession of faunas. Our findings offer insights into how different levels of climatic changes would influence global biodiversity over geological timescales.
How to cite: Zhang, S., Shi, Y., Shen, S., and Kiessling, W.: Fusulinid Evolutionary Faunas of the late Paleozoic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1925, https://doi.org/10.5194/egusphere-egu25-1925, 2025.
The Konzentrat-Lagerstätteof ‘Lo Hueco’ in Central Spain represents an extremely rich and diverse upper Campanian-lower Maastrichtian fossil assemblage comprising more than 10,000 fossil remains: This has made it, in recent years, one of the most relevant European fossil sites for the study of continental vertebrate faunas. The stratigraphic succession in ‘Lo Hueco’ is primarily characterized by six levels separated by transitional boundaries of green (V), grey (G1), red (R1), grey (G2), red (R2) and brown (M) beds of marly mudstones. The sample of microvertebrates remains analysed here was obtained from the screenwashing and sorting of the sediments from the G2 bed, as it corresponds to one of the richest lithosomes in terms of abundance and diversity of vertebrate microfossils from the site. Among these fossil materials, the most prevailing are the fish, especially the conical teeth and ganoid scales from Lepisosteidae. Other fish remain, though less abundant, include lanceolate teeth attributed to Amiidae and two types of molariform teeth. The first type consists of oval and flattened teeth from Pycnodontidae, while the second type correspond to circular dome-shaped teeth similar to those of Paralbulinae. The Lissamphibia material is represented by appendicular elements such as humeri, radioulnae and tibiofibulae assigned to Anura. However, one humerus probably belongs to discoglosids due to some similarities. One small fragment with a pleurodont tooth is attributed to a scincomorph lizard. Crocodiles remain correspond to at least six tooth morphotypes that can be assigned to Allodaposuchidae teeth and Atoposauridae-like teeth. Allodaposuchids are represented by cf. “Agaresuchus” sp. and others. The atoposauridae teeth are considered as to cf. “Theriosuchus” sp. Theropod tooth specimens, despite being among the least abundant fossil remains, constitute an important part of the diversity reported here, pointing out the presence of cf. Dromeosaurinae, cf. Velociraptorinae, cf. Troodontidae and cf. Richardoestesia sp. This vertebrate assemblage is consistent with upper Campanian-lower Maastrichtian coastal shallow flooded muddy plains, which also provides a unique set of fauna that distinguishes it from other Iberian Peninsula localities.
How to cite: Cabrera Hernández, J. S., Ortega, F., and Torices, A.: Microvertebrate assemblage from the Upper Cretaceous site of Lo Hueco (Cuenca, Spain): A preliminary approach., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19127, https://doi.org/10.5194/egusphere-egu25-19127, 2025.
The Central Anatolian Plateau (CAP) has played a dynamic role in the Africa-Eurasia convergence system since the mid-Mesozoic. It has been influenced by various geological processes, including lithospheric delamination, slab segmentation (specifically the Cyprus and Antalya slabs), tilting, and slab break-off. The southern margin of the CAP, marked by the Central Taurides, is unconformably overlain by Neogene marine sedimentary deposits from the Mut and Antalya basins. To better understand the mechanisms driving the Middle Pleistocene uplift, we present new evidence from a marine succession (Tol-1 section) of the Mut Basin, located at 1171 m a.s.l. Tol-1 section is approximately 71 m thick and consists of marls, clayey marls, and occasional calcarenite layers, indicating a shallowing-upward sequence. The calcareous nannofossil analysis revealed two key bioevents: the Last Occurrence (LO) of Pseudoemiliania lacunosa (0.46 Ma), in the midsection, and the First Occurrence (FO) of Emiliania huxleyi (0.26 Ma), near the top. Although the abundant reworked specimens, these taxa provide reliable chronological markers. The FO of E. huxleyi and the estimated sedimentation rate for the top of the Tol-1 section point to an age of ca. 0.21 Ma (Marine Isotope Stage, MIS 7) for the youngest marine deposits of the Mut Basin. Ostracod taphonomy suggests paleobathymetric conditions ranging from littoral to upper epibathyal environments (depths not exceeding 400 m). Paleomagnetic analysis confirms Brunhes' normal polarity, supporting a late Middle Pleistocene age for the Tol-1 section. So far, this section is identified as the youngest marine deposits reported at this elevation along the southern margin of the CAP. By combining our age constraints, the paleobathymetry of the top section (50 m b.s.l.), and the eustatic sea level during the late Middle Pleistocene (~-18.5 m), we estimate an uplift rate of ~5.9 m/kyr for the southern margin of the CAP. This uplift may be induced by the upwelling of low-density asthenospheric mantle following slab break-off as suggested in previous studies (Faccenna et al., 2006; Keskin, 2003; Cosentino et al., 2012; Schildgen et al., 2014; Öğretmen et al., 2018; Racano et al., 2020; 2021).
How to cite: Sari, S., Cipollari, P., Cosentino, D., Gliozzi, E., Lirer, F., Kanbur, S., Öğretmen, N., Mattei, M., Cifelli, F., and Faranda, C.: The Middle Pleistocene uplift of the Central Anatolian Plateau (CAP) southern margin: New evidence from the Mut Basin (South Turkey) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10350, https://doi.org/10.5194/egusphere-egu25-10350, 2025.
Mollusc shells are composite structures built of calcium carbonate crystals (calcite and/or aragonite) and biopolymers (protein, polysaccharides and lipids). These two classes of materials create a great variety of microstructures characterised by complex architectures and unique material properties. The formation of shell microstructures is controlled by environmental and physiological factors and the variety of microstructures is believed to be of phylogenetic and adaptive biomechanical significance. Here, through SEM and XRD analyses, we provide for the first time a detailed characterisation, description and illustration of the shell microstructure and mineralogy of three mollusc species: the bivalves Anadara uropigimelana (Bory de Saint-Vincent, 1827) and Tivela stefaninii (Nardini, 1933), and the gastropod Oliva bulbosa (Röding, 1798). The specimens were collected in the Upper Holocene HAS1 settlement and in a shell midden in the Khor Rori Archaeological Park (Oman). These species frequently occur in archaeological assemblages and show clear growth lines and increments in their shells, making them excellent tools to be used for high resolution palaeoclimatic and palaeoenvironmental studies. However, data on their shell microstructure and mineralogy, that are fundamental for fossil shell preservation analyses, are lacking. Our results show that shells of Anadara uropigimelana are aragonitic with an outer crossed lamellar layer, an inner complex crossed lamellar layer and an irregular simple prismatic pallial myostracum; periodic bands of dendritic nondenticular composite prisms occur in the outer part of the outer layer, reflecting seasonal changes in water temperatures and growth rates. Tivela stefaninii shells are aragonitic and show an outer composite prismatic layer, a middle crossed lamellar layer, and an inner complex crossed lamellar layer. Shells of Oliva bulbosa are composed of an irregular alternation of aragonitic crossed lamellar layers; a transitional layer characterised by the occurrence of tidally controlled growth lines, a crossed lamellar callus and a myostracal layer are also described in Oliva bulbosa specimens. With this analysis, we are able to provide novel microstructural and mineralogical data on three poorly known mollusc species, which are useful for crystallographic, phylogenetic, evolutionary and palaeoenvironmental studies.
How to cite: Chiari, A., Dapiaggi, M., and Crippa, G.: Investigating the shell microstructure and mineralogy of three Upper Holocene mollusc species from the Khor Rori Archaeological Park (Dhofar, Oman), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3699, https://doi.org/10.5194/egusphere-egu25-3699, 2025.
During the Miocene (c. 23–10 Ma), climatic and tectonic changes led to the development of a large wetland with shallow lakes and swamps in Western Amazonia (Hoorn et al. 2010). These new aquatic environments of the “Pebas” system were colonized by rapidly evolving endemic invertebrate faunas composed of mollusks and ostracods (Wesselingh, 2006; Purper, 1979; Sheppard & Bate, 1980, among others). The ‘Pebasian’ ostracods hold a highly endemic and diverse fauna, which led to the description of several new genera and species.
The goals of this study are to review the taxonomy of Amazonian Perissocytheridea species, analyze their intraspecific variability and ontogenetic development, and to identify evolutionary pathways.
We studied samples from eight localities in the Iquitos region (Peru) covering the Middle Miocene mollusk biozones MZ4–MZ9 (Wesselingh et al., 2006).
We identified two species: Perissocytheridea sp. 1 and Perissocytheridea sp. 2, both of which appear to be endemic to the Pebas system. Remarkably, the specimens belonging to Perissocytheridea sp. 2 display ‘inverse’ hinges. The two species co-occur in different stratigraphic sections, with Perissocytheridea sp. 2 being less abundant in all samples. Both species exhibit a kind of premature sexual dimorphism from the juvenile stages A-1 to A-3. Additionally, polymorphism was found in specimens of Perissocytheridea sp. 1, manifested in variations in surface ornamentation, in size and shape of the alar and caudal process.
So far, no chronological trend has been established and other features remain to be compared (e.g., inner lamella, pores).
Although there are many references to ‘Pebasian’ ostracods with ‘inverse’ hinges, all of them were documented in the genus Cyprideis (Purper & Pinto, 1983, 1985; Whatley et al. 1998; Gross et al. 2013, 2014). Here, ‘inverse’ Perissocytheridea is reported for the first time. The presence of these ‘inverse’ forms could explain reproductive isolation and therefore, sympatric speciation, as suggested for the ‘Cyprideis species flock’ (Gross et al. 2014). In any case, the trigger for the occurrence of these ‘inverse’ forms in ‘Pebasian’ ostracods is still unknown.
Finally, we prefer not to assign the specimens to already described Perissocytheridea species from the Pebas system, as potential synonyms are still under study.
How to cite: Zamudio, M. B., Gross, M., Salazar Rios, A., and Piller, W.: Perissocytheridea (Ostracoda, Crustacea) from Western Amazonia (Middle Miocene), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1570, https://doi.org/10.5194/egusphere-egu25-1570, 2025.
The Siwalik strata of the Indian subcontinent are renowned for their rich vertebrate fossil assemblages, particularly mammals, spanning approximately 18 to 0.22 million years ago. However, squamate reptiles well known for their diverse morphology and ecological adaptations, remain underexplored in this region, reflecting a significant gap in our knowledge of Miocene herpetofauna. A comprehensive study of Miocene squamate vertebral morphology in India has yet to be undertaken. This research examined the vertebral morphology of squamate fossil remains from Siwalik localities, including the Middle Miocene Ramnagar (Jammu) and Late Miocene Haritalyangar (Himachal Pradesh), for taxonomic identification and ecological insights through comparisons with extant taxa. The collected specimens were analysed using a micro-CT and a Stereozoom microscope (10X). Identification and examination were conducted based on key morphological characteristics, including overall size and shape, cotyle and condyle dimensions, the presence or absence of zygosphene and zygantrum, the number and arrangement of ventral keels, the presence of foramina, the shape of the neural canal, and the occurrence of hypapophyses. The examined samples reveal the presence of various taxa, including Acrochordus, Anguimorpha, Colubridae, Constrictores, Python, and Varanus. Notably, the presence of fully aquatic piscivore Acrochordus from Late Miocene Haritalyangar (10–8.5 Ma), based on a single probably surface-collected specimen, appears to be artifactual and requires further investigation. However, the high diversity of thermophilic lizards and snakes dominated by Python and colubrids during the Miocene period indicates elevated mean annual temperatures. The coexistence of terrestrial and semi-aquatic squamates suggests a seasonally wet, sub-humid to semi-arid climate.
How to cite: Deep, S.: A Comparative Analysis of Vertebral Morphology of Middle to Late Miocene Squamates from the Siwaliks of India: Paleoenvironmental Implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-261, https://doi.org/10.5194/egusphere-egu25-261, 2025.
Mesophotic (30–150 m) and deep reef (> 150 m) paleo-communities are significantly less studied in the Central Mediterranean, limiting our understanding of their development across this region. The Terrible and Nameless Banks in the Sicily Channel present a valuable opportunity to investigate these ancient ecosystems, offering insights into the processes that shaped deeper reef communities around these structures.
Here, we examined carbonate rocks collected from mesophotic to deeper settings on the Terrible and Nameless Banks. We aimed to describe the carbonate bioconstruction surrounding these structures and to understand the processes that led to their evolution. Carbonate rocks and fossil samples have been collected using rectangular chain bag dredges during the R/V Meteor expedition M191. A total of 50 carbonate samples, including well-lithified carbonate crusts and dead benthic organisms, have been described, of which 20 have been cut and prepared for thin-section analysis.
Samples recovered from mesophotic depths of both Terrible and Nameless Banks show that paleo-reefs associated with these depths are mainly associated with coralline algae-rich facies. Highly bioeroded coralline boundstone is associated with fragments of corals, bryozoans, and serpulids. The free-living form of coralline algae, rhodoliths, are also significant contributors to mesophotic ecosystems. Rhodoliths are 2 to 5 cm in size, showing spheroidal to ellipsoidal morphologies, with growth forms ranging from encrusting, warty to fruticose, lumpy. Coralline algae typically encrust various lithified rocks, including sedimentary and volcanic rocks, which can serve as nuclei for their growth. These encrusted rocks are often further covered by fenestrate bryozoans and encrusting foraminifers. Coral species at this depth are represented by Corallium rubrum (red coral) and Dendrophyllia sp. In the deeper regions of the banks, down to a depth of 655 meters, the carbonate samples consist primarily of lithified, hard rocks, and no coralline algae have been observed. The paleo-communities are mainly represented by cold-water coral species such as Lophelia pertusa, Desmophyllum dianthus, and Dendrophyllia alternata. Additionally, colonies of deep-water oyster-coral framestone, possibly Neopycnodonte zibrowii-Desmophyllum association, are present.
Our initial results show that the presence of sufficient light in the mesophotic zone is an important factor for the thriving of coralline algae-related facies. The specific topography of the Terrible and Nameless Banks creates moderate to strong currents around these structures, prevents sediment burial, and promotes the rolling and shaping of rhodoliths into rounded forms. These currents also produce local upwelling around banks, bringing cool, nutrient-rich water from deeper depths to the mesophotic zone and enhancing the development of corals and bryozoans. In deeper waters, internal waves can play a significant role in nutrient delivery, sustaining the biogenic communities such as coral and oyster assemblages.
How to cite: Kiani Harchegani, F., Coletti, G., Bialik, O., Micallef, A., and Geldmacher, J.: Paleo-communities across the mesophotic to deep zones of the Terrible and Nameless Banks, The Sicily Channel, Central Mediterranean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6926, https://doi.org/10.5194/egusphere-egu25-6926, 2025.
The Herbert Schaffer fossil collection, acquired in 2024 by the Upper Austrian State Cultural Organization (OÖ Landes-Kultur GmbH), represents the most significant private paleontological collection in Austria. By early 2025, the staggering amount of approximately 60 tons of fossil material had been recovered from Würting Castle in Upper Austria. This remarkable collection is unique not only for its size and unusual history but also because nearly all objects remain scientifically unstudied and undescribed. The collection’s breadth and quality offer unparalleled opportunities for paleontological research, making it a treasure of national importance for understanding the geological and biological history of Austria.
Among the most noteworthy objects are the fossils from the site of Traun-Pucking, comprising remains of multiple odontocete individuals. More than 5,000 boxes containing primarily Syngnathidae, Labridae, and other Percomorphaceae from the site of St. Margarethen, Burgenland, were retrieved from the upper floors of Würting Castle in Offenhausen. Also stored in the halls of the castle’s second floor was an unprepared Jurassic crocodile from the clays near Peterborough, UK, as well as a ca. 3.5-meter-long Ichthyosaurus from the world-famous Lagerstätte of Holzmaden, Germany. Furthermore, the Schaffer collection includes fossils from the following localities in vast quantities: Eggenburg, Lower Austria; Nefgraben near Rußbach, Upper Austria; Bad Adelholzen, Germany; Schlaifhausen, Germany; and Weistal near Hallein, Salzburg. A complete list of all fossil sites recorded can be provided by the authors.
Efforts to preserve, catalog, and digitize the collection are currently underway, ensuring its accessibility for scientific study and public engagement. This initiative not only honors Herbert Schaffer’s legacy but also seeks to establish a foundation for interdisciplinary research in paleontology and paleoecology at the Biodiversity Research Center Linz of the OÖLKG. By presenting an overview of the collection and its immense scientific potential, this contribution seeks to highlight its value, raise awareness within the scientific community, and attract researchers to contribute to the study and comprehensive analysis of this extraordinary paleontological treasure.
How to cite: Wöger, J., zucali, K., and reiter, E.: The Exceptional Fossil Collection of Herbert Schaffer from Würting Castle: Conservation, Digitalization, and Identification of Fossil from Europe and Northern Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21901, https://doi.org/10.5194/egusphere-egu25-21901, 2025.
The Tilioideae (Malvacae) contains about 50 extant species assigned to the three genera, Craigia, Mortoniodendron, and Tilia. The pollen morphology and ultrastructure of Tilioideae is characteristic and pollen of this subfamily is relatively easy to recognize during routine light microscopy (LM) investigations. Tilioideae pollen is small to medium sized, circular to convex-triangular in outline, oblate, brevi(3)colporate with thickened nexine surrounding the endopori (costae), and has reticulate ornamentation that can range from perforate to reticulate. To assign fossil Tilioideae type pollen to extant genera, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) has to be employed. Mortoniodendron pollen grains are small (20-33 µm in LM) and with a coarse reticulum in SEM with psilate or crested muri. The lumina are filled with free-standing columellae which form an internal tectum in TEM. Craigia pollen is medium sized (29-37 µm in LM) and has nano- to microreticulate ornamentation with psilate or striate muri and psilate to perforated lumina. In TEM, Craigia pollen has an indistinct internal tectum. Tilia pollen is large (30–52 µm in LM) and has a microreticulate ornamentation and lumina that are irregularly polygonal and funnel shaped. An internal tectum is rare in Tilia. The costae at the apertures in Mortoniodendron and Craigia pollen are of similar thickness and width. The costae in pollen of Mortoniodendron usually form acute angles to the interapertural wall, but the costae in Craigia pollen consistently form right to obtuse angles to the interapertural wall. Tilia has the most massive and widest costae, and in pollen of some Tilia species the sexine bulges outwards, which adds to the thickening of the aperture. The importance of accurately affiliating fossil Tilioideae pollen to extant genera (or to exclude them) lies in their climate preferences. Mortoniodendron occurs in fully humid to monsoonal tropical rainforest climate and biomes. Craigia grows in subtropical winter dry forests with warm to hot summers. Tilia thrives in temperate broadleaf to mixed deciduous and conifer forests in subtropical, warm temperate, and boreal climates, it is cold resistant but prefers abundant humidity. Using combined LM, SEM, and especially TEM, to investigate fossil Tilioideae type pollen makes it possible to correctly identify Craigia, Mortoniodendron, and Tilia pollen, and to exclude similar pollen from extinct taxa of the subfamily as well as other closely related fossil or extant Malvaceae.
How to cite: Geier, C., Bouchal, J. M., Ulrich, S., and Grímsson, F.: Identifying Tilioideae pollen in the fossil record using electron microscopy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17212, https://doi.org/10.5194/egusphere-egu25-17212, 2025.
One of the important hydrocarbon reservoir targets in the Midyan Basin, Northwest of Saudi Arabia along the Red Sea is the deep-sea sandstone turbidites of the Miocene Burqan Formation. This study leverages well-exposed outcrops to comprehensively assess the reservoir characteristics of this formation. A multi-faceted approach integrating field observations (sedimentology, stratigraphy, structural geology) with detailed measurements and advanced techniques (photomosaics, LiDAR) was employed to characterize reservoir heterogeneity, quality, and architecture. Fieldwork encompassed vertical and lateral outcrop profiling across a 25 km transect, capturing the spatial distribution and geometry of sandstone bodies. LiDAR facilitated high-resolution documentation of sedimentological, stratigraphic, and structural features, including strata geometry, fault networks, and fracture distributions. Laboratory analyses complemented field observations, examining lithofacies textures, composition, and petrophysical properties. Results demonstrate significant lateral and vertical variability in reservoir characteristics. Sandstone body thicknesses decrease from proximal (1.5-5 m) to distal zones (0.4-1 m), accompanied by an increasing shale-to-sandstone ratio. Sandstone bodies exhibit lateral extents ranging from 80 to over 130 meters. Lithofacies include conglomerates, pebbly sandstones, and coarse- to medium-grained sandstones, interbedded with finer-grained units. Proximal regions display well-developed stacked sand bodies, while distal areas exhibit greater shale and mudstone interbedding, potentially forming baffles. The tectonically active setting, characterized by rifting and faulting, has significantly impacted reservoir architecture, influencing seal relationships, continuity, and the distribution of internal barriers. This outcrop-based study provides a valuable framework for understanding the impact of geological heterogeneities on reservoir quality and architecture within the Burqan Formation. The findings have critical implications for exploration and development activities in the geologically complex Red Sea region and analogous hydrocarbon provinces.
How to cite: Osman, M. and Abdullatif, O.: Characterization of the Miocene Turbidite Sandstone Reservoirs in the Burqan Formation, Red Sea Region: Insights from Outcrop and Structural Analyses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19835, https://doi.org/10.5194/egusphere-egu25-19835, 2025.
The determination of sedimentary facies and the fine division of sedimentary microfacies are of great significance for oil and gas exploration, it not only helps to find new blocks of oil and gas potential, but also points out the direction for the fine development of old oilfields. Taking the Shahejie Formation in Huanghua Depression as an example, the sedimentary environment and sedimentary model were studied by comprehensive utilization of core data, logging, seismic and analytical test data, and the following research results were obtained :
(1) Using core data to identify the development of fan delta facies deposits in the study area, and according to the type of lithofacies, the hydrodynamic conditions of the reduction fan deposition period are divided. Eight lithofacies types are identified in the study area, which are massive bedding pebbly sandstone facies, massive bedding sandstone facies, parallel bedding sandstone facies and wavy bedding sandstone facies formed under strong hydrodynamic conditions. Horizontal bedding siltstone facies, lenticular bedding siltstone facies, massive argillaceous siltstone facies and massive mudstone facies formed under weak hydrodynamic conditions ;
(2) Four types of sedimentary microfacies were identified by well-seismic combination method, and the spatial distribution characteristics of sedimentary microfacies were quantitatively characterized. That is, the source direction has the characteristics of contiguous distribution of fan delta sand bodies close to the source and dendritic distribution of sand bodies far from the source ; in the direction of vertical provenance, the lateral migration of fan delta sand bodies leads to the superposition of sand bodies. The cross-well sections along the source and vertical source reveal that the fan delta sand body is retrograded to the source area;
(3) The difference of reservoir quality is characterized by comprehensive utilization of logging and analysis test data. The study shows that there are five reservoir types in the retrograde fan delta facies, and the difference of reservoir quality is closely related to the type of sedimentary microfacies. There are also significant differences in reservoir quality within the same microfacies;
(4) Through comprehensive analysis, the development characteristics of retrograde fan delta facies sand bodies under ' model constraint and well-seismic combination ' are clarified. This kind of sedimentary model is helpful to better describe the reservoir, determine the potential block through the dominant facies, and lay a foundation for tapping the potential of remaining oil.
How to cite: Yang, Y. and Wei, T.: Study on sedimentary evolution characteristics and sand body distribution law of regressive fan delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4733, https://doi.org/10.5194/egusphere-egu25-4733, 2025.
Fan deltas are usually constructed through episodic flood event with debris flow transforming to hyper-concentrated flow during sediments proceeding. However, the role of topography in controlling the flow transformation and sediments aggradation has been less studied. This constrains studies of sediment distribution and understanding of graded profile. For lake basin sequences, geomorphological control is much stronger than lake level rise and fall. Under extreme conditions, sediments can still prograde when the lake level rises. Therefore, describing the influence of geomorphology on the flow transformation and stacking pattern of the lobes can provide a deeper understanding of the controlling factors of the lake basin stratigraphy sequence. Xiligou lake (XLG) fan delta from Xisai Basin provides an optimal case for addressing this issue. Three lobes developed on the XLG fan delta with significant differences in their morphologies, architectures, lithofacies, sediment distributions and topographies. Through trenching, drone photography, and satellite data, we analyzed the structure of the sediments and the distribution of sedimentary facies. Based on the analysis of debris flow and hyper-concentrated flow deposits, two transformation models corresponding to different topographies were established. Sediment unloading is caused by a frictional reduction or a sudden momentum loss in the sediments flow's carrying capacity, allowing the debris flow transforms to hyper-concentrated flow and then to stream flow during the movement. The role of topography in controlling sediment flow transformation and sediment distribution is clarified through forces analysis of sediment grain. The topographic gradient of the linear slope is constant, so the direction of fluid movement is consistent with the topographic direction. Therefore, sediment flows move on linear slope without collision with the bed and there is no sudden loss of momentum. The gradual or sudden reduction in topographic gradient of concave slopes forces a constant or sudden change in the direction of fluid movement, which facilitates the unloading of sediments and the transformation of flow. The sudden change of topography forces unloading of viscous component, and the non-viscous component pass over to form hyper-concentrated flow, often accompanied by remobilized large gravels. The graded profile was an equilibrium between the dynamics and resistance of sediment transport. Changes in lake level affect the graded profile by changing the elevation of sediment transport, which is the total gravitational potential energy. The instantaneous graded profile and temporary graded profile are different scales of equilibrium corresponding to hydrodynamic equilibrium and depositional trend respectively. This study reveals the role of geomorphological dynamics in controlling sedimentary body progradation, thus providing a new perspective on the analysis of lake basin stratigraphy sequence.
How to cite: Li, S., Sun, H., and Li, P.: Morpho-dynamics in fan deltas: Effect of topography on flow transformation, facies distribution and graded profile evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4143, https://doi.org/10.5194/egusphere-egu25-4143, 2025.
The architecture of sedimentary basins is shaped by the interplay between relative sea-level changes and sediment supply combined with sediment transport processes. Relative sea-level changes are controlled by both eustatic sea-level variations and tectonics. While the effects of these factors on stratal stacking patterns have been a focus of extensive research, their distinct contributions remain incompletely understood.
In this study, we interpreted high-resolution seismic profiles together with deep well data from the South Adriatic Foredeep (SAF), focusing on tectonic and sedimentary processes and sea-level fluctuations over the last 5.3 Ma. The SAF is an active basin, bounded by the Dinaric/Albanian thrust front and Apennine thrust/Apulian platform. Furthermore, the sedimentary system was further analysed by the means of 3D stratigraphic numerical modelling with DionisosFlow that accounts for the variability of the sediment and water flux combined with climatic and sea level variations, and sediment compaction. A series of models were conducted testing different subsidence, sediment supply and water discharge values, eustatic curves and sediment compaction parameters on the overall basin morphology.
Based on the joint interpretation of the observational and model data, we propose a new stratigraphic model for the Miocene to Recent sedimentary evolution of the South Adriatic Foredeep. The basin is characterized by the variable length of the shelf around the basin margin with deposits of the deep-water gravity flow and bottom-currents on the slopes. The progradation of the shelf in NW reached up to 55 km, on top of the Apulian platform around 50 km, while at the footwall of the Dinaric thrust belt varies from 15 km to 30 km, with different thicknesses. The rate of the progradation at some places increased three times during Pleistocene, e.g. from 5,5 to 16 m/kry. Calculated subsidence also varies around the basin affecting the lateral change in accommodation space. Finally, the sedimentary architecture on the shelf is overprinted by compaction effects, which are most pronounced over basin confinements, sometimes causing significant deformation and subsequent aggradation.
A key characteristic is the pronounced variability in sediment deposition along basin margins, driven by local tectonic and climatic forcing, as well as variation in autogenic processes. We conclude that the overall progradation was shaped by variable long-term (> 100 kyr) versus short-term (<100 kry) forcing factors. In the long run, i.e. from the beginning of the Pleistocene, repeated glaciations led to greater water fluxes and sediment supply, resulting in higher progradation rates. The tectonic influence on the rates of accommodation space do not show abrupt changes over time. Short-term factors influencing the water flow and sediment discharge in combination with the fall and rise of sea level lead to high-frequency changes in stratigraphy and are responsible for the formation of clinoforms on the basin slopes.
Beicip-Franlab is acknowledged for providing an academic license for DionisosFlow. This study was supported by the Croatian Science Foundation as part of the Outgoing Mobility Program.
How to cite: Rukavina, D. and Balázs, A.: Tectonic and climatic forcing on shelf margin slope progradation in the Adriatic Sea: inferences from seismic and well data and 3D numerical forward modelling , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12577, https://doi.org/10.5194/egusphere-egu25-12577, 2025.
The Belgica Mound Drift, located in the Porcupine Seabight offshore west Ireland, is a small (~30 km²) contourite drift situated between the Irish Shelf to the east and cold-water coral mounds to the west. These contourite deposits are shaped by the dynamic interaction of the Mediterranean Outflow Water and the complex seabed topography. Despite significant advances in marine research, identifying and characterising contourites within the sedimentary record remains poorly understood. The relatively small size of the Belgica Mound Drift presents a unique opportunity to examine spatial and temporal sedimentological variability within a contourite drift. During the 2023-13 RV Belgica campaign, new sediment 3 m long cores were collected from the crest and the flanks of the drift, estimated to cover the last deglaciation. The cores were used for sedimentological and compositional analysis. The results of the medical CT scans and line-scan imaging, reveal that the cores from both locations exhibit similar sedimentary characteristics. Sedimentological analyses, including grain size, and magnetic susceptibility measurements (MS), coupled with compositional analysis via Itrax XRF scanning, suggest that the cores can be subdivided into two primary units. The top layer of unimodal fine sand has a mean grain size of 185 µm and relatively low MS values. The bottom part of the cores consists of bimodal sandy silt to silt with a mean grain size of 15 µm and relatively high MS. Additionally, the lower unit is heavily bioturbated, obscuring many primary sedimentary structures. The two distinct sedimentary layers indicate a clear change in depositional settings and the current regime of the Mediterranean Outflow Water in the Porcupine Seabight during the last deglaciation.
How to cite: Reyniers, P., Vander Cruyssen, P., Vander Haeghen, N., and Van Rooij, D.: Spatiotemporal sediment dynamics within the Belgica Mound Drift during the last deglaciation, offshore Ireland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17160, https://doi.org/10.5194/egusphere-egu25-17160, 2025.
We present heavy minerals, detrital zircon data and U-Pb tuff ages from the sedimentary units of the Yukon-Koyukuk Basin (YKB) in Alaska, to investigate and understand its evolution within a tectonic framework. Two basins in Southeast Asia, with similar tectonic settings, serve as modern analogues for comparison. The YKB started to form in middle to late Jurassic after the collision between an intraoceanic volcanic arc and the Arctic Alaska margin, which eventually led to the thrusting of the oceanic basement over the passive continental margin. The basin is flanked by the metamorphic rocks of the Seward Peninsula to the west, the Brooks Range to the north and the Ruby Terrane to the east.
Our results are from the whole stratigraphic column of the basin, from the lowermost Kv unit to the uppermost Ks unit:
- Kv unit: basaltic and andesitic lava flows interbedded with volcanogenic sediments. K-Ar ages vary from 134 Ma and 118 Ma. A single U-Pb zircon age from a tuff is about 138 Ma.
- Kvg unit: volcaniclastic greywacke with Albian molluscs are interbedded with tuffaceous layers. Two of these are dated at 112 Ma and 110 Ma (Albian).
- Kmc unit: conglomerate and greywacke with a strong mafic and calcareous imprint. Cretaceous molluscs are widespread.
- Kqc unit: quartz rich deposits with plant fossils of Cretaceous age.
- Ks+Kms units: late Cretaceous fluvial to shallow marine and deep marine sandstone and shale layers.
We use QEMSCAN® (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) for heavy mineral (HM) analysis, which, along with point counting, petrographic description, paleocurrent data and sedimentary features analysis, helps to constrain sediment provenance. Kv is the only unit reflecting a volcanic source, while the others display the progressive unroofing of the deeper and higher-grade metamorphic rocks surrounding the basin. U-Pb SIMS dating of tuffs and detrital zircons provide, for the first time, an absolute chronology for basin evolution.
The combined data indicate the YKB formed in a forearc/backarc setting prior to 138 Ma (deposition of the volcanic-rich Kv unit). With the progressive denudation of the Brooks Range, sedimentation shifted towards greater metamorphic input, leading to the deposition of the Kvg unit at 110 Ma. Ultimately, after the Late Cretaceous uplift of the Ruby Terrane, the main sediment source changed again, and the stratigraphically higher units were deposited from the Cenomanian to at least the Maastrichtian. The Savu Sea and the Taiwan margin in Southeast Asia show similarities in structure, metamorphic grade, sediment composition and tectonic setting, suggesting these are effective modern analogues that can enhance our understanding of both ancient and modern arc-continent collisional systems.
How to cite: Seminara, S., Pease, V., Toro, J., and Omma, J.: Provenance analyses: a tool to constrain tectonic changes. Parallelism between the ancient Yukon-Koyukuk Basin (Alaska) and modern Southeast Asia., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12028, https://doi.org/10.5194/egusphere-egu25-12028, 2025.
The Aptian-Albian deposits of the Anglo-Paris Basin consist of terrigenous sediments formed in shallow continental and coastal environments within an extensional intracratonic basin. The Aptian-Albian interval is rarely exposed, except in the Wessex Basin, where subsiding sub-basins developed during the Early Cretaceous and were later exposed due to tectonic inversion (Chadwick, 1993). Outcrops in southern England, Cap de la Hève (Normandy), and Burgundy quarries complement subsurface data from Paris Basin drill cores. Stratigraphic correlations from wireline logs and outcrops at the basin's margins have highlighted nine transgressive/regressive cycles constrained by biostratigraphy, showing subsidence variations between the Paris and Wessex Basins.
The Lower Aptian deposits are affected by the sub-Aptian discordance. In the Paris Basin, many ammonite-bearing zones are absent due to significant erosion, and the Lower Aptian deposits consist of marine shales. This interpretation is supported by signs of reworking, attributed to localized tidal influences, ruling out offshore deposition. In contrast, the Lower Aptian in the Wessex Basin is unaffected by the sub-Aptian unconformity and records thick sand layers resulting from deltaic progradation eastward, with significant subsidence located in the Isle of Wight (Channel Basin).
During the Upper Aptian, southern England and the English Channel are marked by lower subsidence and are characterized by estuarine deposits of the Sandrock Formation. In the Paris Basin, Late Aptian subsidence was also significant and accompanied by major hiatuses in ammonite’s zones, with the Sables Verts deposited in estuarine and tidal-dominated environments overlying an unconformity. The Wessex and Paris basins were separated by the "Hampshire-Dieppe” structural High (Jollivet-Castelot 2018), forming the northern boundary of the Paris Basin.
The onset of the Albian marks a shift in dynamics between the Paris and Wessex Basins. In the Wessex, reduced subsidence led to continental sedimentation (Monk’s Bay Sandstone Formation) over an erosion surface. Meanwhile, increased subsidence in the Paris Basin resulted in the deposition of the Sables des Drillons, indicating a shift from transgressive tidal-dominatedsands to regressive shoreface deposits. Structural highs in the northern basin continued to limit communication between the basins.
The Middle Albian is characterized by diachronous subsidence between the Paris and Wessex Basins. In Wessex, the Gault Clay Formation was deposited due to significant subsidence, while in the Paris Basin, this period corresponds to the deposition of the Sables de Frécambault, indicating littoral sands progradation followed by offshore clay deposits with Gault facies at the top of the Middle Albian. This marks the first communication between sub-basins, forming the Anglo-Paris Basin. The top of the Middle Albian is marked by a significant regression, with incised valleys filled with fluvio-estuarine deposits, preceding the major Late Albian transgression marked by shale sedimentation with Gault facies, heralding the major Cenomanian transgression.
The Upper Albian is marked by homogeneous subsidence in both basins, strengthening communication with marine domains such as the North Atlantic and North Sea (Amédro and Matrion, 2014). In the Wessex, tidal-dominated shallow marine deposits (Upper Greensand Formation) transition eastward into outer platform deposits (Rawson, 2006), while in the Paris Basin, the Late Albian corresponds to outer platform deposits (Gault Formation).
How to cite: Seguin, F., Deschamps, R., Patrier, P., Lasseur, E., Briais, J., and Souque, C.: Sedimentary dynamics of the Anglo-Paris Basin during the Aptian-Albian period, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9690, https://doi.org/10.5194/egusphere-egu25-9690, 2025.
At present, research on the sedimentary configuration of river facies at sea focuses on the identification and characterization of different levels of interlayers, and there are the following problems: (1) the accuracy of predicting and characterizing the heterogeneity of physical properties within different levels of configuration units in river facies reservoirs is low, and there is a lack of methods and means; (2) The remaining oil distribution pattern controlled by the differences in physical properties of different levels of configuration units in the later stage of ultra-high water content is unclear. After more than 20 years of development, Qinhuangdao 32-6 Oilfield has entered the late stage of ultra-high water cut development, with a comprehensive water cut of 96.8%. After long-term high fold water flooding, the advantageous seepage channels have developed, and the continuous deep tapping of the main sand body faces great challenges.
In response to the above issues, this article uses sedimentary genesis models as constraints to quantitatively characterize and characterize configuration units at different levels. Based on this, the influence of different levels of configuration units in river facies on the distribution of remaining oil is studied, forming a set of multi-level quantitative characterization methods for the internal structure of reservoirs in different levels of configuration units in river facies. The specific steps are: (1) Summarize the quality difference patterns of different levels of configuration units in river facies, as well as the geological knowledge base including lithofacies and configuration unit types, configuration unit structural styles and parameters, reservoir physical property parameters, etc. (2) Establish two-dimensional and three-dimensional prototype geological models of reservoir quality differences in configuration units, and carry out simulation of fluvial facies sedimentation. (3) Based on the prototype geological model, 3D seismic forward simulation is conducted to study the seismic response characteristics of reservoir configuration unit quality differences, and a feature map is established. The quantitative characterization of reservoir configurations based on different levels of configuration units not only enriches the research content of reservoir configurations, but also provides theoretical support for the characterization of heterogeneity in fluvial reservoirs.
How to cite: li, S.: Quantitative characterization of reservoir quality differences in different levels of configuration units: a case study of typical fluvial sand bodies in Qinhuangdao 32-6 oilfield, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3265, https://doi.org/10.5194/egusphere-egu25-3265, 2025.
Sedimentology of coastal carbonate sediments and evaporites of Abu Dhabi has been intensively studied. However, information about deeper subtidal deposits and seasonal variations of water properties is more limited. This investigation explores the sediment composition of six cores and water column properties (temperature, salinity, dissolved oxygen, pH) along a 150 km long SSE-NNW transect in offshore eastern Abu Dhabi, with water depths ranging from 11 to 45 meters. Situated in the southeastern Arabian Gulf, the transect includes diverse oceanographic and sedimentological zones, serving as a crucial benchmark for understanding seasonal variability and regional environmental dynamics.
CTD surveys conducted in August 2024 captured temperature, salinity, pH, and dissolved oxygen profiles during the warmest part of the seasonal cycle. Temperature profiles revealed stratification of the distal water body, with surface temperatures reaching 36°C and a thermocline between 10 and 28 meters. The proximal water body showed no temperature stratification and uniform temperatures from 35-36°C from the coast to 80 km offshore and down to 28m water depth. Salinity ranged from 39 PSU offshore to 45 PSU nearshore, with a uniform surface layer and increasing stratification with depth. Dissolved oxygen peaked at 5 ml/l in surface waters, declining to 2 ml/l at the bottom, indicating significant stratification but no hypoxia in the deep-water body. Surface pH values were high (above 8.45), decreasing gradually to 8.2 in bottom waters.
The grain size distribution of the cores reveals a correlation between core penetration depth and sediment characteristics. Coarse-grained sediments yielded shorter cores (10–20 cm), while muddy sediments at the deepest site produced a 50 cm core. Grain size analysis identified a progression of mean grain size from fine and medium sand in shallower cores to coarse sand further offshore and muddy sediments at greater depths (> 40m), illustrating dynamic sedimentary processes
The sediment composition predominantly includes small bivalves, gastropods, benthic foraminifera, echinoid spines, ostracods, and occasional planktonic components such as pteropods. The high abundance of micromollusks (bivalves and gastropods < 2mm) compared to similar carbonate depositional settings highlights their potential role in carbonate production.
Further analyses include the quantification of sediment compositions across grain-size fractions and stable isotope analyses of bioclasts to determine seasonal carbonate production patterns. Analyses of seawater and sediments provide insights into nutrient dynamics, seawater acidification and oxygenation, enhancing the understanding of the response of already extreme marine environment of the Arabian Gulf to climate change.
How to cite: Rojas-Lequerica, S., Aljaberi, A., Alshehhi, A., Abdelmaksoud, A., Aldhanhani , O., Al Suwaidi, A., Sreenivasan, S., Environmental Agency Abu Dhabi, J., and Steuber, T.: Spatial Variability in Sediment Composition and Seawater Properties along a transect in Eastern Offshore Abu Dhabi, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17749, https://doi.org/10.5194/egusphere-egu25-17749, 2025.
Deep marine gaps are topographical choke-points where constricted bottom currents may interact with down-slope gravitational flows originating from surrounding topographic highs. Such gaps can provide unique insight into processes understudied in abyssal settings: pure contouritic systems and mixed (turbidite-contourite) systems. Here, we present a detailed study of the Theta Gap, a deep marine gap that connects the Biscay Abyssal Plain and the Iberian Abyssal Plain. Previous studies identified significant erosion and deposition of turbidites but only focussed on the area between the Finisterre and A Coruña Seamounts. The processes occurring between the Galicia Bank and the Finisterre Seamount are less defined. Our aim was to compare these two areas within the Theta Gap to determine if the south Theta Gap contributes to the exchange of Lower Deep Water between the abyssal plains and how this affects sediment deposition. To achieve this aim, we used sub-bottom profiles along with a detailed analysis of four sedimentary cores, to study the sedimentary facies across the two areas. Hydrological data was used to assess to what degree Lower Deep Water and associated bottom currents are contributing to sediment distribution in the gap. We found clear differences in turbidite deposition between the north and south Theta Gap. The same event often has thinner and coarser deposits in the north compared to the south. In the south, the turbidite sequences are thicker, more complete and include discontinuous silt laminae and mud/silt couplets. The distribution of iostherms and isopycnals in the Theta Gap suggest that Lower Deep Water flows north-eastwards through the south Theta Gap before recirculating and flowing south-westwards through the north Theta Gap. We hypothesise, the discrepancy in turbidite distribution is greatly controlled by these bottom currents which foster deposition in the south Theta Gap and, at times, prevent deposition in the north Theta Gap. Such bottom current – sediment interactions are understudied in abyssal settings and deep marine gaps, such as the Theta Gap, can provide unique insight into these processes of sediment transport and reworking.
How to cite: Glazkova, T., Llave, E., Maestro, A., Dickson, A. J., Francés, G., and Hernández-Molina, F. J.: Sedimentary Processes in the Theta Gap, NE Atlantic , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9547, https://doi.org/10.5194/egusphere-egu25-9547, 2025.
Glauconites are abundant in Paleocene Alaji Formation and Eocene Jaddala Formation. This study highlights the influence of depositional conditions on mineralogical and chemical composition of Palaeogene glauconites in Iraq. Petrographical, textural, mineralogical, and chemical characterization were done on Paleogene green clays. The green clays were examined in marl and limestone, in proximal (Kirkuk section), medial (B 12/7 and Gharaf sections), and distal (B 15/7 sections) sections of the basin, formed in middle shelf, outer shelf, and upper slope to upper-middle slope conditions, respectively. The green clays are found in an upward fining sequence and condensed sections. The sedimentary aspects indicate a transgressive systems tract and maximum flooding surface condition of formation of the green clays. The green clays appear light to dark green under microscope and are ~30 µm to ~1000 µm long. The green clays occur as pellets, and as infillings in foraminifera, algae, showing radiating cracks. The medium to poor sorting of green clays, showing radiating cracks indicates their authigenic origin. Microstructurally, the green clays show well-developed flaky and rosette structures. The presence of well-developed lamellar texture indicates evolved character of the green clays. The green clays show ~10 Å (001), 4.53 Å (020), 3.32 Å (003) and ~1.511 Å (060) reflections, which are characteristic of glauconite. The distal glauconites show better-developed spectra with narrower and more intense reflections and a 10 Å (001) reflection (FWHM: 0.43 °2θ), compared to the proximal glauconites with a 10.5 Å (001) reflection (FWHM: 1.11 °2θ). Upon glycolation, the distal glauconites show no shift in the d-spacing of (001) reflection (10.02 Å), with hardly any increase in peak width (FWHM: 0.54 °2θ), while the proximal glauconites show some shift in the d-spacing of (001) reflection (10.15 Å) with minor increase in peak width (FWHM: 1.33 °2θ). These mineralogical observations indicate better-ordered crystal structure in the distal glauconites, compared to the proximal glauconites, with lower smectite content in the distal glauconites. Medial and distal glauconites contain > 15% to ~27.5% Fe2O3(total), ~6% to ~10% K2O, ~2.5% to ~12.5% Al2O3, and ~4% to ~6% MgO, while the proximal glauconites show < 15% to ~10% Fe2O3(total), ~7% to ~8% K2O, > 12.5% to ~15% Al2O3, and ~6% to ~8% MgO. The chemical nature of the medial and distal green clays indicates a glauconite affinity, while the proximal green clays are High-Mg, Al-glauconites. The medial and distal glauconites formed in a deeper setting, where sedimentation rates are low and detrital Fe-rich particles are available. While, the proximal glauconites formed in a shallower setting close to the Zagros ophiolite belt, where sedimentation rates are high and Mg-Al-rich detrital particles are available. Lower sedimentation rates favor higher evolution of glauconites. Thus, the medial and distal glauconites formed on a Fe-rich precursor like Fe-Al smectite, while the proximal glauconites formed on an Mg-Al rich precursor like Mg-Al phyllosilicate, with higher evolution of the medial and distal glauconites. The high abundance of the glauconites is attributed to the Paleocene-Eocene thermal maximum, as warm seas favor higher kinetics of the reaction.
How to cite: Sarin, T., Banerjee, S., Zaki, N., Farouk, S., Al-Kahtany, K., and Mohammed, I. Q.: The influence of depositional conditions on the crystallo-chemical characteristics of Paleogene glauconites of Iraq, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3733, https://doi.org/10.5194/egusphere-egu25-3733, 2025.
The PG2 sandstone volatile oil reservoir, located in the Es1 formation of the Nanpu Depression is a lake-bottom fan sedimentary reservoir with significant internal heterogeneity. This heterogeneity is characterized by the development of interlayers and barrier layers, which result in complex seepage characteristics during the process of converting oil reservoirs into gas storage. The transportation and distribution patterns of the reservoir fluid are not well understood. Therefore, it is crucial to study the sedimentary architectural pattern and the distribution characteristics of architectural units to clarify the heterogeneity of the reservoir and the fluid transportation and distribution rules. This would provide theoretical support for the subsequent construction of the gas storage and help identify the favorable reservoir areas. To address these issues, this paper systematically quantifies and characterizes the architectural interfaces and units in a hierarchical order, guided by the sedimentary genetic model. On this basis, a multi-level architectural method is developed for quantitatively characterizing the internal structure of the reservoir. The specific steps are as follows: (1)After establishing that the seventh order consists of composite genetic units formed by multiple single-phase sandy debris flow events, while the eighth order is a single genetic unit formed by a single-phase sandy debris flow event, the architectural interface between the seventh and eighth orders of the reservoir is quantitatively characterized. As there are no horizontal well in the study area at the target interval, empirical formulas for single watercourses and beds in lake-bottom fans, developed by previous scholars, are applied. The structural unit boundaries in areas without wells are determined through a combination of empirical formulas, inter-well comparisons, and data from the geological knowledge base. This process is used to define the scale of the architecture units, and the relevant parameters are then statistical counted. (2)Based on the identification of architectural interfaces, the study focuses on the classification, recognition, and distribution of the seventh and eighth order architectural units. The distribution characteristics of these different architectural orders are depicted in detail, and a developmental model for the eighth-order architectural units is established. Finally, the results of the reservoir architectural characterization are verified using dynamic production data, which confirms that the method accurately characterizes the internal structure of the reservoir and quantitatively describes its internal heterogeneity and fluid transport and distribution patterns. This provides theoretical support for identifying favorable reservoir areas for converting oil reservoirs into gas storage.
How to cite: Li, X. K. and Zhang, X.: Architecture Characteristics of Lake-Bottom Fan Sedimentary Reservoir: A Case Study of the PG2 Oil Reservoir, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3692, https://doi.org/10.5194/egusphere-egu25-3692, 2025.
Accurate lithofacies identification plays a crucial role in the exploration and development of shale oil reservoirs, while existing methods all have their own shortcomings. In this paper, focusing on the shale oil reservoirs in the Weixinan Sag of the Beibu Gulf Basin, a particle swarm optimized random forest (PSO-RF) algorithm was proposed for lithofacies identification. Firstly, based on the core characteristics in the study area, nine lithofacies were classified with mineral composition, grain size, and sedimentary structure as the main factors. After that, principal component analysis method was used to reduce the dimensionality of the logging data and eliminate redundant information among the logging curves. Finally, particle swarm optimization algorithm was employed to search for the optimal hyperparameters of the random forest model, which is the PSO-RF algorithm. Compared with the results of core observations, the lithofacies identification results of cored wells in the study area demonstrated the effectiveness of the PSO-RF algorithm, achieving an overall accuracy of 90% on the test set. In Addition, the PSO-RF model showed excellent adaptability when applied to non-cored wells, with prediction results that outperform traditional machine learning algorithms. This study provides an effective method for lithofacies identification in the Beibu Gulf Basin and similar shale oil reservoirs.
How to cite: Li, Y., Zhao, M., and Wei, X.: Lithofacies Identification by a Particle Swarm Optimized Random Forest Algorithm in Shale Oil Reservoir, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5450, https://doi.org/10.5194/egusphere-egu25-5450, 2025.
Mixed siliciclastic-carbonate deposits accumulated in the passive continental margin of the Arabian plate are commonly found in the Mesozoic stratigraphic interval in southeastern Iraq. As important hydrocarbon reservoirs in the area, the Cretaceous strata have attracted great interests of researchers to study their sedimentary features, depositional processes and petrophysical properties. However, in-depth studies considering the systematic evolution of a mixed siliciclastic-carbonate succession in the context of sequence stratigraphy and its control on the petrophysical properties of the rocks are still rare. In this study, two representative formations (i.e., the Nahr Umr and the Mishrif formations) that constitute a seismic-scale strata mixing (sensu Chiarella et al., 2017) were fully investigated. An integrated dataset, including core and thin section descriptions, well logs, and results from core experiments (e.g., XRD analysis, grain size distribution, porosity, and permeability measurements), was employed to perform a detailed analysis of sedimentary facies, interpret depositional environments, and evaluate petrophysical properties. The Nahr Umr Formation is dominated by siliciclastic sediments with sedimentary facies interpreted as distributary channel, tidal channel, tidal flat, tide-modified mouth bar, bay, lower shoreface, offshore transition and offshore. The assemblage of sedimentary structures observed in this formation, including cross-bedding, ripple cross-lamination, lenticular bedding, and wavy bedding, indicates a tide-influenced deltaic environment. This interpretation is further supported by the bimodal grain size distribution revealed through analysis, reflecting the combined influences of fluvial and tidal processes. The Mishrif Formation is dominated by carbonate sediments deposited in a carbonate platform environment, with sedimentary facies interpreted as high-energy shoal, low-energy shoal, tidal channel, lagoon, subtidal, swamp and incised valley. Local depositional environments transitioned among open platform, semi-restricted platform, and platform margin settings in response to relative sea-level fluctuations. The petrophysical properties of the studied formations are influenced by both sedimentary and diagenetic processes. High-quality reservoirs are typically associated with sedimentary facies such as distributary channels, tidal channels, and bioclastic shoals. Diagenetic dissolution has played an important role in enhancing reservoir quality.
How to cite: Gao, M., Chiarella, D., Han, H., Ning, C., and Lyu, Z.: Reservoir characterization of a mixed siliciclastic-carbonate succession, Middle Cretaceous, southeastern Iraq, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20438, https://doi.org/10.5194/egusphere-egu25-20438, 2025.
Due to the difficulty and high cost of core data, it is very important to use the logging data to continuously identify and divide the longitudinal upper stria structure types of a single well. The conventional logging resolution is mostly decimeter to meter level, while the high-resolution imaging logging resolution can reach 5 mm, and the imaging logging dynamic and static images obtained on the basis of the resistivity scale can clearly reflect the bedding changes of the formation, which is an important means for fine identification and characterization of the streak. However, it takes a lot of work to manually identify the type and thickness of the striae, and the thickness of the striae is difficult to observe intuitively with the naked eye.
This study presents a machine learning and wavelet transform-based method for extracting and recognizing texture layer characteristics and thickness from imaging well logging images. Grayscale images are obtained from well logging slices, and grayscale curves are extracted at the fourth quartile. An average grayscale curve is constructed, and wavelet transform is applied to remove noise, yielding a transformed curve. Grayscale differences between pre- and post-transformation curves are calculated to form a difference curve. These grayscale values and differences serve as clustering features, classifying texture layers into four types. Texture layer thickness is then statistically analyzed based on these types. The method enables automated texture layer and thickness recognition, enhancing accuracy and efficiency in feature extraction.
How to cite: Li, X.: FMI image lamina features and thickness extraction and recognition method basedon machine learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4678, https://doi.org/10.5194/egusphere-egu25-4678, 2025.
