Shallow Epicontinental Sea Research Articles

Hidden Depths: A Unique Biodiversity Oasis in the Persian Gulf in Need of Further Exploration and Conservation

The Persian Gulf, a young and shallow epicontinental sea, is known for its unique geological and oceanographic characteristics that foster its diverse and productive marine ecosystems. A substantial portion of the Gulf’s seafloor consists of unconsolidated soft sediments, making it unsuitable for colonization by many sessile organisms. Consequently, relatively few hard grounds and submerged banks provide suitable habitats for benthic and substrate dwellers. This study documents a unique marine habitat on an offshore submerged bank, likely a raised salt dome, south of Qeshm Island, Iran. This area is home to a high concentration of ahermatypic coral species and remains relatively sheltered from human activities. The bank’s geographic location allows inflow currents from the Strait of Hormuz to transport larvae and nutrients, providing suitable substrates for various sessile invertebrates. Moreover, it causes the formation of Taylor columns, which affect fluid dynamics and circulation patterns, indirectly enhancing biodiversity. Despite facing risks from large-scale regional and localized threats, the bank’s remoteness from the main coast and its depth provide some protection. This study emphasizes the need for continued exploration and the implementation of effective conservation measures in the region, along with additional research to clarify the ecological and physical parameters supporting its diversity. It also presents the first in situ photographic evidence for the occurrence of some octocoral genera in the Gulf. Future research should investigate how the species compositions of hidden banks and shoals contribute to the overall biodiversity of the Persian Gulf.

Shaking and splashing—A case study of far‐field effects of the Mjølnir asteroid impact on depositional environments in the Barents Sea

AbstractThe Mjølnir impact crater in the Norwegian Barents Sea features among the 20 largest impact craters listed in the Earth Impact Database. The impact is dated to 142 ± 2.6 Ma, corresponding closely to the Jurassic/Cretaceous boundary in the Boreal stratigraphy. Multidisciplinary studies carried out over the last three decades have suggested that the up to 40 km wide crater was created by a 1–3 km diameter impactor colliding with a shallow epicontinental sea, causing regional havoc and a regional ecological crisis that followed in its wake. Only minor evidence for the consequences of the impact for the surrounding depositional basins has been documented so far. This study describes a large submarine slump penetrated by hydrocarbon exploration well 7121/9‐1, located in the southern Hammerfest Basin and approximately 350 km away from the impact site. The slump is dated by a black shale drape, which contains characteristic impact‐related biotic assemblages and potential ejecta material. This precise dating enables us to associate the slump with large‐scale fault movements and footwall collapse along the basin‐bounding Troms‐Finnmark Fault Complex, which we conclude were caused by shock waves from the Mjølnir impact and the passage of associated tsunami trains. The draping black shale is interpreted to represent significant reworking of material from the contemporary seabed by tsunamis and currents set up by the impact.

Latest Miocene ostracods from the Bookpurnong Formation in the Murray Basin of southeastern Australia: shallow marine migrants into an epicontinental sea

The uppermost Miocene Bookpurnong Formation within the Murray Basin of southeastern Australia overlies a regionally extensive subaerial unconformity formed by relatively low late Miocene eustatic sea levels, and the initial phase of the Kosciuszko Uplift tectonic event. A diverse marine fossil ostracod fauna has been recovered from the Bookpurnong Formation, and is associated with a marine transgression that flooded inland regions of southeastern Australia to form a shallow epicontinental sea. Many of the Bookpurnong Formation ostracods represent immigrant taxa, with species such as Puriana lubbockiana, evidencing a subtropical range expansion of thermophilic warm water forms into southern mid-latitudes. We attribute this to warm plumes from the East Australian Current, which would have impacted southeastern Australia at that time. In general, the Bookpurnong Formation ostracod assemblages indicate low to moderate energy shallow offshore palaeoenvironments subject to warm-temperate and subtropical conditions. One new genus and five new species are described: Fortistriginglymus gen. nov., Bradyleberis praecristatella sp. nov., Callistocythere bookpurnongensis sp. nov., Callistocythere mchenryi sp. nov., Callistocythere zigzaga sp. nov., and Parakeijia notoreticularis sp. nov.

Biostratigraphy and conditions of formation of Albian and Cenomanian deposits on the south-western slope of the Ukrainian Shield (Middle Dnister region)

Data from a comprehensive study into the lithological composition and lateral distribution of Albian and Cenomanian deposits in the Middle Dnister region (Ukraine), in the watersheds of the Smotrych–Tarnava–Studenytsia–Ushytsia–Kalyus–Zhvan–Lyadova–Nemiya–Murafa–Rusava–Markovka rivers, are presented in the paper. Cretaceous deposits of Volyn-Podillia are part of the terrigenous-carbonate subformation of the Jurassic-Cretaceous carbonate formation (J3–K1) and the glauconite Cretaceous formation (K1al3–K2), which includes gaizeous (K1al3–K2s1), siliceous-chalk (K2s2–K2k) and marl-gaizeous (K2sn–K2m) subformations. Cretaceous deposits of the Middle Dnister region are represented by the lower (Albian stage) and upper parts (Cenomanian stage).The study is focused on the distribution of micro- and macrofauna (e.g. molluscs, calcareous nannoplankton) in the Albian and Cenomanian deposits and their facies affiliation, as well as on the quantitative analysis of organic remains and palaeoecological conditions. Differences in homogeneous conditions of sedimentation within the epicontinental sea basin of the modern Middle Dnister region at the Early-Late Cretaceous boundary were insignificant. Due to a study of Cretaceous macro- and microfauna, its facies distribution, quantitative analysis, and palaeoecological conditions, it is possible to trace slight differences between close homogeneous conditions of sedimentation within the relatively homogeneous sea basin of the Middle Dnister region on the verge of the Early and Late Cretaceous. This shallow epicontinental sea was characterized by normal salinity and well-aerated warm waters with temporary strong bottom currents within shallow water and with maximum depths up to 150–200 m in some areas and soft muddy bottom of deep-water areas. Phosphatisation of the early-middle Cenomanian fauna is evidence for the important role of the Carpathian upwelling at that time. Geochemically active phosphorus is concentrated on shelf due to changes in salinity, temperature, pH, CO2 content and other parameters of the aquatic environment, which were characteristic for this region of Volyn-Podillia.

Deciphering Late Cretaceous palaeo‐river catchments in eastern Australia: Recognition of distinct northern and southern drainage basins

AbstractDuring the Early Cretaceous, Australia was flooded by the epicontinental Eromanga Sea, deposits of which occur across the Great Australian Superbasin. However, the mid‐Cretaceous retreat of this shallow sea, and the resultant palaeogeographic and sediment distribution patterns, are poorly understood. This study chronicles the Eromanga Sea's northward regression through the Carpentaria Basin as captured in the sedimentary record of the Normanton Formation. We achieve this by integrating sedimentary facies analysis of cores from across the Carpentaria Basin with palynology, sandstone petrography and U‐Pb detrital zircon geochronology. Results indicate that the Normanton Formation was deposited between ca. 100 and 96 Ma, and that it represents a large, northward‐prograding, likely river‐dominated delta system. The unit's volcanoclastic nature is exhibited through abundant lithic volcanics and devitrified glass, with a prominent, near‐depositional detrital zircon population attributed to a proximal continental magmatic arc‐derived source hypothesised to parallel the eastern seaboard of Australia at this time. The Normanton Formation is temporally correlative with the lower‐middle portions of the similarly volcanoclastic Winton Formation in the Eromanga Basin, which drained southwards into the Cenomanian‐Santonian Ceduna River Delta system. However, Normanton Formation strata display subtly different provenance signatures and drainage patterns, indicating input from similar, but likely more northern source terrains than much of the contemporaneous Winton Formation. These sediments were unlikely recycled southwards into the Ceduna Delta like those of the Winton Formation; rather they drained northward following the retreat of the Eromanga Sea through the Carpentaria Basin, indicating a Cretaceous drainage divide between two river systems, with distinct northern and southern drainage catchments. The mid‐Cretaceous palaeogeography of eastern Australia is analogous to that of the Late Cretaceous Western Interior Seaway of North America, in which the retreat of a shallow epicontinental sea is marked by the rapid deposition and progradation of multiple large, geographically distinct clastic wedges.

Hyperpycnal littoral deltas: A case of study from the Lower Cretaceous Agrio Formation in the Neuquén Basin, Argentina

Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental seas. After the introduction of sequence stratigraphic concepts, meter-scale coarsening and thickening upward successions have been considered as “parasequences” originated by high-frequency sea-level changes. Nevertheless, recent studies enhanced the importance of wave-aided low-dense hyperpycnal flows in transporting fine-grained sediments in shallow shelfal areas. These poorly-known (and at the same time very common) types of delta, known as hyperpycnal littoral deltas (HLD), develop very low gradient progradational units, controlled by changes in the sediment supply instead of sea level changes. These small-scale progradational units are very common in shallow epicontinental seas like the Lower Cretaceous Agrio Formation in the Neuquén Basin. This study provides a first detailed analysis of hyperpycnal littoral deltas from the Agua de la Mula Member (upper Hauterivian–lower Barremian) of the Agrio Formation. This unit has been studied in three locations near Bajada del Agrio locality in the central part of the Neuquén Basin, Argentina. Six sandy facies, three heterolithic facies, three muddy facies and four calcareous facies were recognized. From facies analysis, three facies associations could be determined, corresponding to offshore/prodelta, distal ramp delta and proximal ramp delta. The three stratigraphic sections discussed in this study are internally composed of several small-scale sequences showing a coarsening and thickening upward pattern, transitionally going from muddy to sandy wave-dominated facies, and ending with calcareous bioclastics levels on top. These small-scale sequences are interpreted as delta front deposits of wave-influenced hyperpycnal littoral deltas, punctuated by calcareous intervals accumulated during periods of low sediment supply. It is interpreted that the development of hyperpycnal littoral deltas could have been facilitated by a decrease in sea water salinity related to an increasing runoff.

Extensive non-marine depositional setting evidenced by carbonate minerals in the Ediacaran clastic series of the western East European Craton

The Ediacaran sedimentary rocks on the East European Craton (EEC) comprise chiefly siliciclastic deposits of the Volyn and Valdai series that have commonly been regarded as deposits in a shallow epicontinental sea on Baltica. However, an intermittent fresh-water sedimentary setting was also indicated for some part of the paleocontinent. Surprisingly, although Baltica was positioned in low latitudes during the Ediacaran period, no carbonate sequences have formed on the EEC. Systematic and detailed mineralogical, petrographic and stable isotope evaluation of carbonate minerals occurring in the Ediacaran sedimentary rocks of the western EEC stretching from the Arkhangelsk area at the White Sea to the Ukraine-Moldova borderland near the Black Sea show that continuously marine or sea water-influenced depositional conditions existed only in the marginal parts of the area: Podillya, Moldova, and the Arkhangelsk area. In contrast, a fully continental depositional setting stretched in the central part (St. Petersburg area, Lithuania, E Belarus) with intermittent periods of marine or brackish-water conditions only in E Belarus. SW Belarus and Volyn were influenced by marine or brackish environments.Highly 13C-enriched early-diagenetic calcite from Poddillya and pedogenic siderite from the St. Petersburg area attest for bacterial methanogenesis operating during the Kotlinian period both in marine and continental environments, respectively. This shows that not only marine, but also terrestrial biosphere was already very productive at the end of the Ediacaran. The δ18O composition of meteoric, marine hypersaline, burial, and hydrothermal fluids was reconstructed by integration of mineralogical, petrographic and stable isotope data for various types of Ediacaran carbonates from the western EEC. Moreover, the range of δ18O values for Ediacaran marine carbonate was constrained by setting the lower limit at −5‰, which is the maximum value for pedogenic siderite, and the upper limit at +2‰, which is the minimum value for carbonates associated with saline fluids.

Plasticity of trophic interactions in fish assemblages results in temporal stability of benthic-pelagic couplings

This study addresses the temporal variability of couplings between pelagic and benthic habitats for fish assemblages at five periods in a shallow epicontinental sea, the Eastern English Channel (EEC). Organic matter fluxes fueling fish assemblages and the relative contribution of their different sources were assessed using stable isotope analysis and associated isotopic functional metrics. Couplings between benthic and pelagic realms appeared to be a permanent feature in the EEC, potentially favored by shallow depth and driven by the combination of two trophic processes. First, trophic interactions exhibited plasticity and revealed resource partitioning. Second, changes in the composition of fish assemblages did not impact benthic-pelagic couplings, as most dominant species were generalists during at least one time period, allowing complete use of available resources. Examining both unweighted and biomass-weighted indices was complementary and permitted a better understanding of trophic interactions and energy fluxes.

Trace fossils and depositional environments of the middle Turonian sandstones in the Upper Nysa Kłodzka Graben (Sudetes, Poland) revisited

We provide the first reports of some rare trace fossils from the middle Turonian (Upper Cretaceous) of the Sudety Mountains (SW Poland, Upper Nysa Kłodzka Graben, Długopole Górne Quarry). These include burrows ? Ancorichnus isp., Asterosoma cf. ludwigae Schlirf, 2000, Asterosoma isp., cf. Phycodes isp., Dactyloidites ottoi (Geinitz, 1849), Funalichnus strangulatus (Fritsch, 1883), Phycodes cf. palmatus Hall, 1852, cf. Phycodes , Phycosiphon incertum Fischer-Ooster, 1858, ? Phycosiphon isp., Planolites beverleyensis (Billings, 1862) and borings Entobia isp. Some body fossils, bivalves ? Brachidontes sp., Lima canalifera Goldfuss, 1836, Pinna ( Pinna ) cretacea (Schlotheim, 1813) and Rhynchostreon suborbiculatum (Lamarck, 1801) are also reported. The trace fossil assemblage indicates a distal Skolithos ichnofacies and proximal Cruziana ichnofacies, which characterize a proximal and distal lower shoreface setting respectively. Sedimentation of the middle Turonian sandstones took place in a shallow epicontinental sea of normal salinity and a soft substrate, which was well-oxygenated under low-moderate hydrodynamic conditions. The presence of the oyster Rhynchostreon in the deposits studied suggests the influence of a warm Tethys Ocean.

Permian mixed carbonate–siliciclastic lagoon coastal system in West-Central Gondwana

Although in recent years mixed carbonate–siliciclastic platforms have been increasingly recognized in the Permian of Western Gondwana, there is no detailed description of these mixed systems in West-Central Gondwana. This study focuses on the Permian of the Sergipe–Alagoas Basin (NE Brazil), with the aim of filling this knowledge gap. Based on sedimentological data and microfacies analysis, six facies associations (FA) were identified: FA1 is an eolian–fluvial system, composed of stratified sandstones, FA2 and FA3 represent a mixed tidal flat–lagoon system composed of microbialites, pelitic/micritic sediments and intraclastic packstones, FA4 represents shoreface wave deposits composed of laminated sandstones and silicified grainstones, and FA5 and FA6 are interpreted as a barrier–tidal inlet system, composed of oolitic/intraclastic grainstones, subtidal microbialites, and mixed rudstones. Facies associations reflect the paleoenvironmental conditions of a coastal environment, with dunes and small rivers adjacent to a mixed carbonate–siliciclastic ramp. This is defined as a lagoon system associated with tidal flats protected from the high-energy region by carbonate shoals and microbial constructions. These deposits represent the eastern portion of a shallow epicontinental sea that covered lowlands in West-Central Gondwana within the arid–semiarid belt, whose climate characteristics are reflected in eolian deposits, desiccation structures, mixed carbonate–siliciclastic facies, and fossil records. The main diagenetic feature observed in petrographic analyses was an early diagenetic silicification. Although the absence of spiculites and shelf configuration did not allow a correlation with the Permian glass ramp model, similarities were observed with Eocene glass ramps of Australia, and a relationship with the Permian Chert Event is suggested.

EARLIEST PETROXESTES BORINGS FROM SANDBIAN (EARLIEST LATE ORDOVICIAN) BRYOZOANS OF NORTHERN ESTONIA

ABSTRACT The earliest Petroxestes borings were excavated in large trepostome bryozoans in the Sandbian (earliest Late Ordovician) of Estonia. The Estonian specimens are morphologically similar to the type material from the later Katian of North America. Petroxestes pera is rare in the Sandbian of Estonia and occurs only in biogenic hard substrates. Petroxestes borings occur in muddy environments that were preferred by macroborers in the Hirnantian and early Silurian of North America. It is possible that muddy environments supported higher bioerosion intensities and higher diversity of bioerosional traces in the shallow epicontinental seas of the Late Ordovician. The discovery of Petroxestes in the Sandbian of Estonia supports the idea that there was an earliest Late Ordovician peak in the diversification of borings in Baltica. It is possible that there was a migration of bioerosional trace makers from Baltica to Laurentia in the Late Ordovician.

Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space – A geophysical approach

Carbonate mud mounds developed within the Baltoscandian Basin, an epicratonic basin on the Baltica palaeocontinent, during the Ordovician. In the Upper Ordovician succession of the Baltoscandian Basin, a large number of mud mounds are present at three stratigraphic levels namely, the Kullsbergs mounds (late Sandbian-early Katian), Nabala and Rakvere mounds (middle Katian), and the Boda mounds (late Katian). These formed in a subtropical-tropical carbonate platform environment, covered by a shallow epicontinental sea. The mud mounds at these stratigraphic levels beneath and around Gotland have been characterized using a comprehensive seismic and well dataset acquired during a period of hydrocarbon exploration and exploitation which began more than 30 years ago. Interpretation of the largely unpublished seismic data in this study provides details on the distribution of mound complexes in the basin and constraints on the geometry of the mounds. Detailed structure contour maps of the top and the base of the Ordovician succession beneath Gotland based on the seismic interpretation are presented. The results give a comprehensive characterization of carbonate mud mound generation on Gotland which may help in understanding the distribution patterns of similar mound complexes in other parts of the Ordovician world formed in similar environments.

Dynamic climate-driven controls on the deposition of the Kimmeridge Clay Formation in the Cleveland Basin, Yorkshire, UK

Abstract. The Kimmeridge Clay Formation (KCF) is a laterally extensive, total-organic-carbon-rich succession deposited throughout northwest Europe during the Kimmeridgian–Tithonian (Late Jurassic). It has recently been postulated that an expanded Hadley cell, with an intensified but alternating hydrological cycle, heavily influenced sedimentation and total organic carbon (TOC) enrichment by promoting primary productivity and organic matter burial in the UK sectors of the Boreal Seaway. Consistent with such climate boundary conditions, petrographic observations, total organic carbon and carbonate contents, and major and trace element data presented here indicate that the KCF of the Cleveland Basin was deposited in the Laurasian Seaway under the influence of these conditions. Depositional conditions alternated between three states that produced a distinct cyclicity in the lithological and geochemical records: lower-variability mudstone intervals (LVMIs) which comprise clay-rich mudstone and higher-variability mudstone intervals (HVMIs) which comprise TOC-rich sedimentation and carbonate-rich sedimentation. The lower-variability mudstone intervals dominate the studied interval but are punctuated by three ∼ 2–4 m thick intervals of alternating TOC-rich and carbonate-rich sedimentation (HVMIs). During the lower-variability mudstone intervals, conditions were quiescent with oxic to suboxic bottom water conditions. During the higher-variability mudstone intervals, highly dynamic conditions resulted in repeated switching of the redox system in a way similar to the modern deep basins of the Baltic Sea. During carbonate-rich sedimentation, oxic conditions prevailed, most likely due to elevated depositional energies at the seafloor by current–wave action. During TOC-rich sedimentation, intermittent anoxic–euxinic conditions led to an enrichment of redox-sensitive and sulfide-forming trace metals at the seafloor and a preservation of organic matter, and an active Mn–Fe particulate shuttle delivered redox-sensitive and sulfide-forming trace metals to the seafloor. In addition, based on TOC–S–Fe relationships, organic matter sulfurization appears to have increased organic material preservation in about half of the analysed samples throughout the core, while the remaining samples were either dominated by excess Fe input into the system or experienced pyrite oxidation and sulfur loss during oxygenation events. New Hg∕TOC data do not provide evidence of increased volcanism during this time, consistent with previous work. Set in the context of recent climate modelling, our study provides a comprehensive example of the dynamic climate-driven depositional and redox conditions that can control TOC and metal accumulations in a shallow epicontinental sea, and it is therefore key to understanding the formation of similar deposits throughout Earth's history.

Predicting the Distribution of the Extinct Sea Bird Hesperornis

In the Late Cretaceous, North America was divided by a shallow epicontinental sea known as the Western Interior Seaway. Native life included various marine reptiles, fish, ammonites, and seabirds such as Hesperornis . Previous research has applied ecological niche modeling to discuss competition among large vertebrates in the seaway (mosasaurs and predatory fish) but ignored small vertebrates. The present study combined localities of Hesperornis fossils with sea surface temperature estimates to characterize the distribution of Hesperornis in the upper Great Plains. Temperature interpolation in ArcGIS and niche analysis in Maxent predicted that Hesperornis preferred warmer marine waters (highest suitability values) and may support the hypothesis that Hesperornis migrated between the paleo Arctic and the lower Western Interior Seaway. Most of the study area, however, is homogenous in suitability, indicating the results are largely inconclusive. Additional ecosystem variables (e.g., biological interactions and rock type) will be applied in future analyses to describe the distribution of Hesperornis

The Silurian climatic transition recorded in the epicontinental Baltica Sea

The transition from the Middle to Late Ordovician cold climate to the Silurian greenhouse phase was marked by major climatic and oceanographic changes. The vast epereic sea that during the early Paleozoic extended over the Baltic Plate for hundreds of kilometres recorded the dynamic processes that characterized this important climatic evolution. This shallow epicontinental sea experienced phases of hypoxic conditions for millions of years during the Silurian favouring the sedimentation of organic-rich deposits. A continuous core drilled in the Silurian fine-grained succession of the Baltic Basin was studied integrating sedimentological, palynological and geochemical data. The succession, deposited in a restricted environment in low-energy settings, recorded three long-term variations in bottom-water redox conditions. Our data highlight a direct control of long-term climatic changes on oceanic redox cycles. Phases of cool and dry climate with reduced runoff alternated with periods of warmer and humid conditions with higher runoff and fluvial discharge. During warmer and more humid climatic phases, the presence of a stable pycnocline hampered deep-water renewal efficiency, and together with increased nutrients led by enhanced weathering and runoff favoured the onset of anoxic bottom-water conditions. Cooler and drier intervals favoured instead a weaker and less stable pycnocline that, coupled with more oligotrophic conditions, drove the formation of oxic bottom-waters. The variation through time in water salinity and temperature influenced both the type of organic matter in the surface waters as well as its preservation along the water column. In fact, the extended residence time at the stable pycnocline during the anoxic phases led to the degradation of the organic matter and limited its accumulation at the sediment-water interface. The waning of the latest Ordovician cooling to the Silurian greenhouse climate was characterized by the progressive alternation of cool phases and warmer periods. The effect of this dynamic climatic instability on the redox state of the Baltica epicontinental sea protracted over millions of years up to the middle Silurian.

Cenozoic record of δ34S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial

Understanding the changes in, and drivers of, isotopic variability of sulfur in seawater sulfate (δ34SSO4-sw) over geological time remains a long-standing goal, particularly because of the coupling between the biogeochemical sulfur and carbon cycles. The early Cenozoic has remained enigmatic in this regard, as the existing seawater sulfate isotopic records appear to be decoupled from the well-defined carbon isotope composition of the ocean. Here, we present a new Cenozoic record of sulfur isotopes, using carbonate-associated sulfate hosted in the calcite lattice of single-species foraminifera. The vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles, as recorded by their isotopes, are not fully decoupled in the early Cenozoic. With a model driven by partial coupling of the carbon and sulfur cycles, we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in δ34SSO4-sw ~53 million years ago (Ma) and the subsequent long steady state. We suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open-ocean sediments around 53 Ma. Loss of extensive shelf environments corresponds to Cretaceous–Palaeogene sea-level changes and tectonic reorganization, occurring as the Himalayan arc first collided with Asia. A Cenozoic reconstruction of the δ34S of marine sulfate suggests a shift in the locus of pyrite burial from shallow seas to the open ocean during the early Eocene.

Coniacian sandstones from the North Sudetic Synclinorium revisited: palaeoenvironmental and palaeogeographical reconstructions based on trace fossil analysis and associated body fossils

AbstractThe Coniacian quartz sandstones (Żerkowice Member, Rakowice Wielkie Formation) that crop out at quarries near Czaple-Nowa Wieś Grodziska (North Sudetic Synclinorium) contain a low-diversity assemblage of trace fossils:Gyrochorteisp.,Ophiomorpha nodosaLundgren, 1891,Ophiomorphaisp.,Phycodescf.curvipalmatum(Pollard, 1981), ?Phycodesisp.,Planolitescf.beverleyensis(Billings, 1862),Thalassinoides paradoxicusWoodward, 1830 and ?Thalassinoidesisp. Moreover, interesting compound burrow systems, here referred to asThalassinoides-Phycodescf.palmatusand ?Thalassinoides-Phycodes, were recognised at the Czaple Quarry. Additionally, ?Gyrochorteisp.,Phycodescf.flabellum(Miller and Dyer, 1878) and ?Treptichnusisp. were encountered at correlative levels in the Rakowice Małe Quarry. Some of these ichnotaxa have not been recorded previously from Coniacian sandstones of the Żerkowice Member. Additionally, in slabs of these sandstones, the gastropodNerinea bicinctaBronn, 1836 and the bivalveLima haidingeriZittel, 1866 were found. These interesting finds, in particular the gastropods, were already noted from the study area in the first half of the twentieth century by Scupin (1912–1913). Ethologically, the trace fossil assemblage is represented by domichnia or domichnia/fodinichnia (Ophiomorpha,Thalassinoides), fodinichnia (Phycodes) and pascichnia (Gyrochorte,Planolites). The compound burrow systems (Thalassinoides-Phycodes) are interpreted as dwelling/feeding structures. The possible tracemakers are crustaceans (Ophiomorpha,Thalassinoides) or worm-like animals (annelids and other) (Planolites, ?Phycodes,Gyrochorteand ?Treptichnus). The assemblage of trace fossils is characteristic of theSkolithosichnofacies andCruzianaichnofacies, typical of shallow-marine settings. Ichnological studies, as well as the presence of accompanying fossils (bivalves, gastropods), confirm the palaeoenvironmental reconstruction of the Żerkowice Member sandstones by Leszczyński (2010). That author interpreted the Coniacian sandstones as bar and storm deposits laid down in a shallow epicontinental sea (mainly the foreshore-upper shoreface; up to the middle shoreface) under normal oxygenation and salinity, in soft substrate, above fair-weather wave base. The deposition of the Żerkowice Member sandstones is linked to a regression that started after uplift of the southeastern part of the North Sudetic Synclinorium.

Depositional history of a condensed shallow marine reservoir succession: stratigraphy and detrital zircon geochronology of the Jurassic Stø Formation, Barents Sea

The Early to Middle Jurassic Stø Formation (Toarcian to Bajocian) was deposited in a relatively shallow (10 s of meter deep) epicontinental sea in northern Pangea and represents one of the most prolific reservoir intervals in the Barents Sea basin. It comprises a condensed, predominantly shallow marine succession characterized by long hiatuses and erosional reworking with several horizons of extraformational pebble grade conglomerate. Six distinct facies associations describe sedimentological environments ranging from transgressive, tidal, fluvial and regressive shoreface. Deposits are interpreted and correlated within three sequence stratigraphic units (SI to SIII) which reflect variations in relative sea-level during an overall transgression of the basin. Interpreted depositional systems show subtle variations in petrographic character, but provenance analyses reveal different sedimentary sources. Thirteen core samples distributed geographically and stratigraphically were analysed for detrital zircon U-Pb geochronology. Data show that the Southwestern Barents Sea Basin (SWBSB) was dominated by mixing of reworked material and coarse grained sediment supply from extrabasinal source areas including a Caledonian provenance in the southwest and a Fennoscandian provenance to the southeast. Intra-basinal erosion of underlying strata with Triassic zircon grains dominate in northern parts of the basin. Supplementary material : Supporting information relating to the analysis of different dataset and the interpretations presented in the paper are available at https://doi.org/10.6084/m9.figshare.c.3841282 .

Pyritization of dinoflagellate cysts: A case study from the Polish Middle Jurassic (Bathonian)

Bathonian mudstones and claystones were deposited in a shallow epicontinental sea of the Polish Basin (the Ore-Bearing Częstochowa Clay Formation). They are represented by two units, differing in stratigraphical and facies development. Dinoflagellate cyst taxa are dominated by Ctenidodinium. The effects of the environment and sedimentation rate on pyritization intensity were compared using two locations. Where the sedimentation rate was probably faster and grey mudstones were deposited under dysoxic conditions, the extent of cyst pyritization was relatively minor. In contrast, where the deposition of black claystones was slower with deposition under more suboxic conditions, very intense pyritization led to complete infilling of cysts by pyrite. Pyritization required transport of iron, probably from microbial iron reduction, and sulphide, from bacterial sulphate reduction, from the surrounding sediment into the open dinoflagellate cysts. The supply of sulphur was the limiting factor. Controls on pyrite crystal habit by the organic composition of the dinoflagellate cysts walls and cells are inferred by the observation that dinoflagellate cysts uniquely contain mainly cuboid pyrite crystals.

The comparative osteology of Plesiochelys bigleri n. sp., a new coastal marine turtle from the Late Jurassic of Porrentruy (Switzerland).

BackgroundDuring the Late Jurassic, several groups of eucryptodiran turtles inhabited the shallow epicontinental seas of Western Europe. Plesiochelyidae are an important part of this first radiation of crown-group turtles into coastal marine ecosystems. Fossils of Plesiochelyidae occur in many European localities, and are especially abundant in the Kimmeridgian layers of the Swiss Jura Mountains (Solothurn and Porrentruy). In the mid-19th century, the quarries of Solothurn (NW Switzerland) already provided a large amount of fossil turtles, most notably Plesiochelys etalloni, the best-known plesiochelyid species. Recent excavations in the Porrentruy area (NW Switzerland) revealed new fossils of Plesiochelys, including numerous well-preserved shells with associated cranial and postcranial material.Methods/resultsOut of 80 shells referred to Plesiochelys, 41 are assigned to a new species, Plesiochelys bigleri n. sp., including a skull–shell association. We furthermore refer 15 shells to Plesiochelys etalloni, and 24 shells to Plesiochelys sp. Anatomical comparisons show that Plesiochelys bigleri can clearly be differentiated from Plesiochelys etalloni by cranial features. The shell anatomy and the appendicular skeleton of Plesiochelys bigleri and Plesiochelys etalloni are very similar. However, a statistical analysis demonstrates that the thickness of neural bones allows to separate the two species based on incomplete material. This study furthermore illustrates the extent of intraspecific variation in the shell anatomy of Plesiochelys bigleri and Plesiochelys etalloni.