European Basin Research Articles

The Schilfsandstein and its flora; arguments for a humid mid-Carnian episode?

Recently intensified research on the mid-Carnian episode stimulated discussions about the mid-Carnian climate and a supposed humid climate shift. This basin-scale study on the Schilfsandstein, the type-example of the mid-Carnian episode, applied sedimentological, palynological and palaeobotanical proxies of the palaeoclimate to a large dataset of cored wells and outcrops. The results demonstrate the primary control of circum-Tethyan eustatic cycles on the Central European Basin where transgressions contributed to basin-scale facies shifts. The palaeoclimate proxies point to a uniform arid to semi-arid Carnian climate with low chemical weathering and high evaporation. Consequently, transgressions into the Central European Basin led to increased evaporation forcing the hydrological cycle. The increased runoff from source areas resulted in high-groundwater stages on lowlands characterized by hydromorphic palaeosols and intrazonal vegetation with hygrophytic elements. During lowstands, reduced evaporation and runoff led to increased drainage and desiccation of lowlands characterized by formation of vertisols, calcisols and gypsisols and zonal vegetation with xerophytic elements. The proposed model of sea-level control on the hydrological cycle integrates coeval and subsequent occurrences of wet and dry lowlands, hydromorphic and well-drained palaeosols, and intrazonal and zonal vegetations. Thus, the Schilfsandstein does not provide arguments for a humid mid-Carnian episode. Supplementary material: Datasets of Palynomorph Eco Group (PEG) and Macroplant Eco Group (MEG) analyses are available at https://doi.org/10.6084/m9.figshare.c.4182593

The role of biogenic silica in the formation of Upper Cretaceous pelagic carbonates and its palaeoecological implications

During the Late Cretaceous due to high global sea-level the coastlines were shifted far towards the land and pelagic carbonates dominated over siliciclastic sedimentation. In most parts of the epicontinental European Basin, during that time, the huge amounts of pelagic chalk were formed, while in the NE part of the European Basin similar carbonates with biogenic silica (opoka) were deposited. The main mineralogical component of both lithofacies is calcium carbonate, which is derived from coccoliths (skeletal remains of planktonic algae called coccolithophorids). The opoka is harder than chalk and contains a significant amount of biogenic silica. Detailed petrographic studies of the opoka and its comparison with chalk show the role of biogenic silica in the formation of both lithofacies deposited in an epicontinental sea. The studies indicate that the difference between two lithofacies are primary in origin and are triggered by the presence of a significant amount of sponge spicules occurring only in opoka. The spicules contribute in opal-A input to the calcareous-mud-precursor, which during diagenesis recrystallized into more stable opal-CT, responsible for the macroscopic difference between opoka and chalk. A different scenario occurs in chalk lithofacies, where the sponge spicules are rare and opal-A comes from radiolarian skeletons. The primary difference in compositions of the calcareous-precursor of opoka and chalk are discussed in light of palaeoecological factors during deposition (depth, rate of sedimentation and nutrient influx from currents). The calcareous ooze is considered the modern equivalent of the Cretaceous chalk, but its mineralogical composition is more similar to the opoka mud-precursor.

Tracing water masses with <sup>129</sup>I and <sup>236</sup>U in the subpolar North Atlantic along the GEOTRACES GA01 section

Abstract. Pathways and timescales of water mass transport in the subpolar North Atlantic Ocean (SPNA) have been investigated by many studies due to their importance for the meridional overturning circulation and thus for the global ocean. In this sense, observational data on geochemical tracers provide complementary information to improve the current understanding of the circulation in the SPNA. To this end, we present the first simultaneous distribution of artificial 129I and 236U in 14 depth profiles and in surface waters along the GEOVIDE section covering a zonal transect through the SPNA in spring 2014. Our results show that the two tracers are distributed following the water mass structure and that their presence is largely influenced by the global fallout (GF) and liquid effluents discharged to north-western European coastal waters by the Sellafield and La Hague nuclear reprocessing plants (NRPs). As a result, 129I concentrations and 236U∕238U atom ratios and 129I∕236U atom ratios display a wide range of values: (0.2–256) ×107 at kg−1 (40–2350) ×10-12 and 0.5–200, respectively. The signal from NRPs, which is characterised by higher 129I concentrations and 129I∕236U atom ratios compared to GF, is transported by Atlantic Waters (AWs) into the SPNA, notably by the East Greenland Current (EGC)/Labrador Current (LC) at the surface and by waters overflowing the Greenland–Scotland passage at greater depths. Nevertheless, our results show that the effluents from NRPs may also directly enter the surface of the eastern SPNA through the Iceland–Scotland passage or the English Channel/Irish Sea. The use of the 236U∕238U and 129I∕236U dual tracer approach further serves to discern Polar Intermediate Water (PIW) of Canadian origin from that of Atlantic origin, which carries comparably higher tracer levels due to NRPs (particularly 129I). The cascading of these waters appears to modify the water mass composition in the bottom of the Irminger and Labrador seas, which are dominated by Denmark Strait Overflow Water (DSOW). Indeed, PIW–Atlantic, which has a high level of 129I compared to 236U, appears to contribute to the deep Irminger Sea increasing the 129I concentrations in the realm of DSOW. A similar observation can be made for 236U for PIW entering through the Canadian Archipelago into the Labrador Sea. Several depth profiles also show an increase in 129I concentrations in near bottom waters in the Iceland and the West European basins that are very likely associated with the transport of the NRP signal by the Iceland–Scotland Overflow Water (ISOW). This novel result would support current modelling studies indicating the transport of ISOW into the eastern SPNA. Finally, our tracer data from 2014 are combined with published 129I data for the deep central Labrador Sea between 1993 and 2013. The results obtained from comparing simulated and measured 129I concentrations support the previously suggested two major transport pathways for the AWs in the SPNA, i.e. a short loop through the Nordic seas into the SPNA and a longer loop, which includes recirculation of the AWs in the Arctic Ocean before it enters the western SPNA.

Dissolved Pb and Pb isotopes in the North Atlantic from the GEOVIDE transect (GEOTRACES GA-01) and their decadal evolution

Abstract. During the 2014 GEOVIDE transect, seawater samples were collected for dissolved Pb and Pb isotope analysis. These samples provide a high-resolution “snapshot” of the source regions for the present Pb distribution in the North Atlantic Ocean. Some of these stations were previously occupied for Pb from as early as 1981, and we compare the 2014 data with these older data, some of which are reported here for the first time. Lead concentrations were highest in subsurface Mediterranean Water (MW) near the coast of Portugal, which agrees well with other recent observations by the US GEOTRACES program (Noble et al., 2015). The recently formed Labrador Sea Water (LSW) between Greenland and Nova Scotia is much lower in Pb concentration than the older LSW found in the West European Basin due to decreases in Pb emissions into the atmosphere during the past 20 years. Comparison of North Atlantic data from 1989 to 2014 shows decreasing Pb concentrations consistent with decreased anthropogenic inputs, active scavenging, and advection/convection. Although the isotopic composition of northern North Atlantic seawater appears more homogenous compared to previous decades, a clear spatiotemporal trend in isotope ratios is evident over the past 15 years and implies that small changes to atmospheric Pb emissions continue. Emissions data indicate that the relative proportions of US and European Pb sources to the ocean have been relatively uniform during the past 2 decades, while aerosol data may suggest a greater relative proportion of natural mineral Pb. Using our measurements in conjunction with emissions inventories, we support the findings of previous atmospheric analyses that a significant portion of the Pb deposited to the ocean in 2014 was natural, although it is obscured by the much greater solubility of anthropogenic aerosols over natural ones.

A new record of the Weissert episode from the Valanginian succession of Cehegín (Subbetic, SE Spain): Bio- and carbon isotope stratigraphy

A biostratigraphic and geochemical study (C and O isotopes) of one of the most complete Valanginian sections of the External Zones of the Betic Cordillera (Cehegín composite section), together with its correlation with other European basins, is presented in this contribution. Ammonites and calcareous nannofossil biostratigraphy provide a detailed framework to correlate the Cehegín section with reference sections of the Vocontian, Lombardy and Umbria-Marche basins. The carbon isotope profile of the Cehegín section has been subdivided in four segments, C-Va1 to C-Va4, following the same pattern described from the Vocontian basin. The C-Va2 segment, representing the main carbon isotope excursion (CIE sensu stricto), spans from δ13C values of 0.09–0.11‰ in the upper part of the Karakaschiceras inostranzewi ammonite Subzone (NK3A Subzone of calcareous nannofossils) to 2.67‰ in the upper part of the Karakaschiceras pronecostatum Subzone (NK3B Subzone of calcareous nannofossils). The C-Va3 segment corresponds to an isotopic plateau of the δ13C profile, with values oscillating around 2.39‰, in which the maximum (2.68‰), considered as the upper boundary, was recorded within the upper part of the Olcostephanus nicklesi Subzone, being almost coeval with the last record of the calcareous nannofossil Tubodiscus verenae. The C-Va1 and C-Va4 segments represent, respectively, the pre-CIE δ13C lower values (oscillating around 1‰) and the post-CIE slight decreasing trend (2.60‰–2‰). After considering the different proposals among authors as to which part of the carbon isotope profile should be identified as the Weissert episode, a return to the original definition (interval from minimum to climax of δ13C values) is proposed. That includes, in the Cehegín composite section, the C-Va2 and C-Va3 segments. Segment C-Va2 shows in the Cehegín section a rapid change of δ13C towards higher values (CIE), with an amplitude of 2.57‰, higher than that found in marine carbonates of various Valanginian sections and drills. The biostratigraphic data show that the onset of the Weissert episode is practically synchronous in the Subbetic and in the Vocontian basin, but apparently a little earlier than the onset of that episode in the Lombardy and Umbria-Marche basins, although correlation problems cannot be dismissed. Oxygen isotope values are probably affected by the addition of cement during burial diagenesis. They range from −2.91‰ to 1.19‰, and the δ18O curve shows an initially decreasing trend (minimum in the upper part of the Saynoceras verrucosum Subzone) followed by a segment of nearly stable values, which fluctuate ∼2‰ throughout the rest of the section.

North Atlantic Ocean Internal Decadal Variability: Role of the Mean State and Ocean‐Atmosphere Coupling

AbstractThe origin of the decadal variability in the North Atlantic Ocean is investigated in a series of coupled and ocean‐only numerical experiments. Two versions of the IPSL‐CM5A model are considered, differing only by their atmospheric horizontal resolution (3.75° × 1.87° and 2.5° × 1.25°). When the ocean model is forced by the climatological surface fluxes from the low atmospheric resolution coupled model version, a 20‐year variability emerges, similar to the variability found in the coupled simulation. Such decadal variability is consistent with a large‐scale baroclinic instability of the mean flow in the west European basin. Increasing the atmospheric resolution leads to a more intense Icelandic low, which intensifies the western subpolar gyre, and warms the eastern North Atlantic subpolar gyre region. The mean state changes nearly vanish the associated internal oceanic variability under the corresponding climatological surface fluxes. Increasing the atmospheric resolution also produces a slightly weaker atmospheric stochastic forcing. Both the mean state and atmospheric variability changes are consistent with the decreasing amplitude of the variability in the coupled model. For both model versions, the amplitude of the internal oceanic variability is strongly enhanced in the presence of atmospheric stochastic forcing. Air‐sea coupling on the other hand has a moderate influence on the amplitude of the variability only in the low‐resolution model version, where the North Atlantic oceanic variability at 20 years increases by 23% due to coupling. The coupling effect is therefore modest and sensitive to the atmospheric horizontal resolution.

Environmental changes and carbon cycle perturbations at the Triassic–Jurassic boundary in northern Switzerland

The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ13C of the total organic carbon (δ13CTOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ13CTOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ15NTN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.

A RECORD OF SEQUESTRATION OF PLANT MATERIAL BY MARINE BURROWING ANIMALS AS A NEW FEEDING STRATEGY UNDER OLIGOTROPHIC CONDITIONS EVIDENCED BY PYRITE MICROTEXTURES

Abstract Lepidenteron mantelli is a trace fossil produced by a burrowing marine invertebrate (probably a polychaete) that sequestered plant macroremains in Cenomanian–Coniacian marly calcareous sediments of the Central European Basin during transgression events. For more than a century and half, this trace fossil has been mistaken for a fossil plant. In this paper, L. mantelli is described from upper Turonian marly limestones deposited under offshore, oligotrophic conditions in the Opole Trough, Southern Poland and its taxonomy and occurrences are summarized. Based on detailed studies of pyrite microtexture on wood fragments within the burrow and surrounding sediment, the feeding strategy of the L. mantelli trace maker is interpreted.

Sedimentology and stratigraphy of the Amasra coalfield (Pennsylvanian), NW Turkey – New insight from a 1 km thick section

We report on a sedimentological and biostratigraphic evaluation that was carried out on an approximately 1 km thick coal-bearing Pennsylvanian succession encountered in the boreholes Hema 82 and 85 in the Amasra coalfield of the Zonguldak – Amasra Coal Basin, Turkey.Results of the study include a refined interpretation of sedimentary environments of the coal-bearing strata and their cyclic patterns, improved constraints on macrofloral biozones as well as of boundaries and thickness of lithostratigraphic units. A paleosol-based climatic trend is also proposed, and the tectono-sedimentary history of the Amasra coalfield is compared with other coal basins in Europe. Stratigraphically constrained macroflora confirms a recently suggested discontinuous sedimentary record that contrasts with the previously widely accepted opinion that deposition was continuous throughout the Pennsylvanian. Hiatuses were identified between each adjacent formation. An early Asturian hiatus between the Karadon and Kizilli formations has its equivalent in other Variscan basins of Europe, namely in the Dobrudzha, Upper Silesian, Intra-Sudetic and central and western Bohemian basins. It is in agreement with the former paleogeographic position of the Zonguldak – Amasra Basin and its basement in the southern margin of Laurussia, in the eastern continuation of these central European basins. This conclusion is further supported by paleosol morphology-based climatic trend to increasing aridity around the Westphalian/Stephanian boundary observed in the studied boreholes, and identical with a similar trend in the above-mentioned central European basins.

Progress with monitoring and assessment in the WFD implementation in five European river basins: significant differences but similar problems

The river basin approach of the Water Framework Directive (WFD) and the introduction of ecological status represent a shift in the assessment and management of freshwater systems from discipline-specific to more holistic, catchment-based principles. At the core of the WFD’s approach are catchments as highly interconnected systems. Despite strict timetables, progress towards achieving the WFD objectives has been slow, with deterioration in some cases not being halted. In this paper, looking at evidence from five European basins (Adige, Anglian, Ebro, Evrotas and Sava) we identify some of the key implementation challenges faced by each catchment during the development and implementation of the 1st River Basin Management Plans (RBMPs) of 2009. Despite significant differences in socio-ecological conditions, geographic coverage and starting points in the implementation between these river basins, findings highlight some similar key issues. The lack of a common systemic understanding of each river basin and detailed monitoring data to capture pressure-status interactions in order to anticipate how the system will react to interventions; as well as compliance driven implementation efforts were underlying problems in all five study areas. While some improvements to address these problems can be seen in the 2nd River Basin Management Planning Cycle (2015–2016), our findings demonstrate that a more effective approach is to question the deviation of the whole implementation from the directive’s systemic nature and therefore improve the adaptive, collaborative, participatory and interdisciplinary nature of the implementation efforts.

Hydrological impacts of moderate and high-end climate change across European river basins

Study regionTo provide a picture of hydrological impact of climate change across different climatic zones in Europe, this study considers eight river basins: Tagus in Iberian Peninsula; Emån and Lule in Scandinavia; Rhine, Danube and Teteriv in Central and Eastern Europe; Tay on the island of Great Britain and Northern Dvina in North-Eastern Europe. Study focusIn this study the assessment of the impacts of moderate and high-end climate change scenarios on the hydrological patterns in European basins was conducted. To assess the projected changes, the process-based eco-hydrological model SWIM (Soil and Water Integrated Model) was set up, calibrated and validated for the basins. The SWIM was driven by the bias-corrected climate projections obtained from the coupled simulations of the Global Circulation Models and Regional Climate Models. New hydrological insights for the regionThe results show robust decreasing trends in water availability in the most southern river basin (Tagus), an overall increase in discharge in the most northern river basin (Lule), increase in the winter discharge and shift in seasonality in Northern and Central European catchments. The impacts of the high-end climate change scenario RCP 8.5 continue to develop until the end of the century, while those of the moderate climate change scenario RCP 4.5 level-off after the mid-century. The results of this study also confirm trends, found previously with mostly global scale models.

The <sup>226</sup>Ra–Ba relationship in the North Atlantic during GEOTRACES-GA01

Abstract. We report detailed sections of radium-226 (226Ra, T1∕2 = 1602 years) activities and barium (Ba) concentrations determined in the North Atlantic (Portugal–Greenland–Canada) in the framework of the international GEOTRACES program (GA01 section – GEOVIDE project, May–July 2014). Dissolved 226Ra and Ba are strongly correlated along the section, a pattern that may reflect their similar chemical behavior. Because 226Ra and Ba have been widely used as tracers of water masses and ocean mixing, we investigated their behavior more thoroughly in this crucial region for thermohaline circulation, taking advantage of the contrasting biogeochemical patterns existing along the GA01 section. We used an optimum multiparameter (OMP) analysis to distinguish the relative importance of physical transport (water mass mixing) from nonconservative processes (sedimentary, river or hydrothermal inputs, uptake by particles and dissolved–particulate dynamics) on the 226Ra and Ba distributions in the North Atlantic. Results show that the measured 226Ra and Ba concentrations can be explained by conservative mixing for 58 and 65 % of the samples, respectively, notably at intermediate depth, away from the ocean interfaces. 226Ra and Ba can thus be considered conservative tracers of water mass transport in the ocean interior on the space scales considered here, namely, on the order of a few thousand kilometers. However, regions in which 226Ra and Ba displayed nonconservative behavior and in some cases decoupled behaviors were also identified, mostly at the ocean boundaries (seafloor, continental margins and surface waters). Elevated 226Ra and Ba concentrations found in deepwater in the West European Basin suggest that lower Northeast Atlantic Deep Water (NEADWl) accumulates 226Ra and Ba from sediment diffusion and/or particle dissolution during transport. In the upper 1500 m of the West European Basin, deficiencies in 226Ra and Ba are likely explained by their incorporation in planktonic calcareous and siliceous shells, or in barite (BaSO4) by substitution or adsorption mechanisms. Finally, because Ba and 226Ra display different source terms (mostly deep-sea sediments for 226Ra and rivers for Ba), strong decoupling between 226Ra and Ba were observed at the land–ocean boundaries. This is especially true in the shallow stations near the coasts of Greenland and Newfoundland where high 226Ra ∕ Ba ratios at depth reflect the diffusion of 226Ra from sediment and low 226Ra ∕ Ba ratios in the upper water column reflect the input of Ba associated with meteoric waters.

Dipnoan remains from the Lower-Middle Triassic of the Holy Cross Mountains and northeastern Poland, with remarks on dipnoan palaeobiogeography

Here we present a revision of dipnoans from the Middle-Upper Buntsandstein and the Lower Muschelkalk (Lower-Middle Triassic) of the Holy Cross Mountains (southeastern Poland) and from the Middle Buntsandstein of northeastern Poland. Two genera are identified: Arganodus and Ptychoceratodus. Specimens resemble synchronous species from the European part of Russia. It is the first Middle Triassic finding of Arganodus worldwide. Ptychoceratodus is reported for the first time from the Lower Triassic of Poland. It is its oldest known occurrence in Europe. The Holy Cross Mountains stands between the area of European Russia and the Central European Basin which were both inhabited by Arganodus and Ptychoceratodus in the Early-Middle Triassic. Resulting from a summary of palaeobiogeographic data of these two genera their distributional patterns are hypothesized herein. In the Early Triassic both genera often co-occurred in many regions. Starting from the Middle Triassic their ranges split into two almost separate ones. They reflect the palaeolatitudinal belts in the Late Triassic with Arganodus in the northern tropic belt and Ptychoceratodus along the palaeolatitudes 30°.

Океанографические условия в морях Северо-Европейского бассейна и Северной Атлантики в 2017 г. и их влияние на распределение промысловых рыб

Океанографические условия в морях Северо-Европейского бассейна и Северной Атлантики в 2017 г. и их влияние на распределение промысловых рыб

Mesozoic resource potential in the Southern Permian Basin area: the geological key to exploiting remaining hydrocarbons whilst unlocking geothermal potential

It is generally accepted that hydrocarbon exploration in northern Europe has reached a mature stage. A basin’s maturity is defined by the underlying number of new discoveries and the declining production rate of mature fields (SPE 2015). For geoscientists, a mature basin has well-defined characteristics in terms of, for example, reservoir presence or trap formation (e.g. Byrne 2012). It is interesting, therefore, to note how much is still unknown about certain stratigraphic intervals in northern Europe. The Mesozoic overburden of the Southern Permian Basin (sensu Maystrenko et al. 2008; Doornenbal & Stevenson 2010) continues to provide fresh insights into the geological history of an area where, as the name suggests, historical hydrocarbon exploration has focused on the Paleozoic. The aim of this Special Publication is to increase knowledge of the Mesozoic overburden as a driver for further hydrocarbon exploration/production and the development of new geothermal energy sources. The succeeding chapters are introduced by tectonic framework overviews that give a context for the papers that follow. The remaining articles are organized in approximate stratigraphic order, from old to young, and include a variety of examples from semi-regional to localized field or sub-basin studies. An overview of the study area for all the following chapters is given in Figure 1. It is recognized that the overprinting Mesozoic systems have different naming conventions across the study area (e.g. the Central European Basin System sensu Littke et al. 2008; Maystrenko et al. 2008). Here we use the title ‘Southern Permian Basin area’ to emphasize the resource opportunities associated with a region that has, at least in large part, been associated with hydrocarbon exploration, and very large gas fields, in the Permian Rotliegend. For our purposes, this includes part of the Polish Trough, the highs surrounding the basin (e.g. the Ringkobing-Fyn High), and analogous elements of the Danish and Norwegian offshore. In this introduction, an overview of the geological history and resource base of the area is presented as a framework for the chapters that follow. A description of further prospective resources is then offered (oil and gas plus geothermal potential).

Palaeogeographical evolution of the Lower Jurassic: high-resolution biostratigraphy and sequence stratigraphy in the Central European Basin

Abstract Basin-scale stratigraphic correlation is the fundamental base for successful reservoir exploration, and especially when dealing with cross-border areas. Differences in lithostratigraphic and chronostratigraphic nomenclature between sub-basins and countries often result in problematic estimations of reservoir geometries and potential. This study combines available biostratigraphic, biofaunal and lithofacies data, together with sequence-stratigraphical correlations of the Lower Jurassic from the Central European Basin (CEB), to propose a genetic-based framework of transgressive and regressive depositional units. The determination of four major biofacies environments, composed of (I) polyhaline open-marine/offshore environments, (II) upper mesohaline marine–brackish environments, (III) lower mesohaline brackish environments and (IV) low oligohaline to freshwater continental environments comprising very rare marine phytoplankton and terrestrial spores and pollens, were translated into 12 biofacies reconstructions of ammonite (sub-) chronozone levels. Variations of biofacies reconstructions in time and space were supplemented by biostratigraphically constrained large-scale progradational and retrogradational sedimentary architecture. Retrogradation is accompanied by increasing polyhaline environments and pinpoint basinwide third-order flooding events, whereas progradation is accompanied by decreasing polyhaline environments pointing to third-order regressions. The outcomes of this study support exploration of Lower Jurassic deep geothermal reservoirs or CO 2 storage sites in the eastern CEB (especially Germany and Poland).

Quantitative reconstruction of Middle and Late Eocene paleoclimate based on palynological records from the Huadian Basin, northeastern China: Evidence for monsoonal influence on oil shale formation

The Eocene was an interval of climate evolution, when the extreme high temperatures of the earliest Cenozoic gave way to a global cooling trend. Fine-grained lacustrine sediments of Eocene age from northeastern China represent an excellent archive to study long-term environmental and climatic changes at high-resolution. The Huadian Basin is a Cenozoic, fault-bounded basin in Jilin Province, northeastern China. Though small in area, it contains numerous oil shale- and coal-bearing layers, which provide an abundant Middle to Late Eocene palynoflora. Eighty-five palynomorph genera and one hundred palynomorph species were identified in the Huadian Formation, allowing to distinguish 4 palynozones. The nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad-leaved forests during deposition of the Huadian Formation.Using the coexistence approach (CA), we calculated seven paleoclimatic parameters, which indicate a subtropical warm and humid climate with a mean annual temperature above 13.6°C and a mean annual precipitation of at least 887mm. However, the climate became cooler and drier during the transition from the lower Oil Shale Member to the upper Carbonaceous Shale Member. Palaeoclimatic data from the various Middle and Late Eocene basins of northeastern China (i.e., the Huadian, Fushun, Yilan, Hunchun and Jishu basins) were compared with data from North American and European basins. Middle Eocene climate in the Northern Hemisphere was generally warm and humid, and the mean annual temperature and precipitation in northeastern China were similar to those in North America, though slightly lower than those of Europe. Similar trends in temperature and precipitation on different continents support the existence of a global Mid-Eocene cooling event.This paper is the first systematic study of Middle to Late Eocene seasonality in the Huadian Basin. Our results show an apparent differentiation in both temperature and precipitation between summer and winter, supporting the view that the East Asian Monsoon was established in northeastern China already during the Middle to Late Eocene. This Middle and Late Eocene monsoon was likely driven by the development of Pacific trade winds and an alternating, seasonal high- and low-pressure system over Siberia.The climatic changes observed in our dataset, especially the precipitation changes, appear to have played an important role in controlling oil shale formation in the Huadian Basin. A warmer and more humid climate, with abundant precipitation and high subsidence rates, formed a deeper Huadian depositional lake. High productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation.

Zircon size-age sorting and source-area effect: The German Triassic Buntsandstein Group

This study stresses how zircon-grain length versus age correlation significantly can improve provenance interpretations. Hence, taking sedimentary sorting effects into account, we present a detrital-zircon provenance study for continental deposits of the Central European, Lower Triassic Buntsandstein Group in Germany. The Buntsandstein Group was deposited in an extended intracontinental sag basin of Pangea under arid climate conditions. It included several intrabasinal tectonic swells, some of which have been assumed topographic highs acting as detrital source areas. This study of the Lower and Middle Buntsandstein subgroups in Central Germany indicates that particularly the Massif Central and the Bohemian Massif contributed to the basin fill of the central part of the Central European Basin. The Rhenish Massif, an assumed highland, was submerged. This interpretation is based on >1000 zircon grains from 12 sandstone beds. The unbroken grains in seven of the zircon separates have mean lengths of 190–220μm and five are composed 100–140μm long grains in average. All have a main population of 340–320Ma Carboniferous ages, representative of granitic, probably zircon-rich, rocks from the Variscan Orogen of the Massif Central and the Bohemian Massif. This first-cycle detritus was mixed with recycled, abraded zircon grains from Ediacaran to Palaeozoic metasedimentary units feeding the basin with 610–460Ma (Ediacaran to Ordovician) and 2Ga age grains, as is typical for Gondwana-derived material. The Ediacaran to Ordovician age population is common only in five samples with mean grain lengths of 100–140μm. Grains of such ages mainly are <130μm in the east, but equally common in all grain sizes in western sandstone beds. A western group was fed from the Massif Central and an eastern group derived from the Bohemian Massif. However, abrasion, age-population variations for pre-Variscan grains, and dominating wind directions indicate that two different fluvial systems delivered the Bohemian material and that this was combined with aeolian and alongshore lacustrine transport from the south and west. We conclude that interpretation of detrital zircon ages preferably are separately for different size classes, because zircon studies performed on broad grain-size intervals without considering possible size-age correlations may disguise sorting effects that potentially can lead to a misleading source-area interpretation.

Terrestrial Ecology around the Permian–Triassic Boundary

Permian–Triassic event is usually regarded as the greatest mass extinction in the Earth’s history, although detailed studies have shown that it was not very severe. Localities of fossil insects in European Russia, Tunguska and Kuznetsk basins, and Mongolia provide a unique (the best in the world) opportunity to study the preparation, course of the crisis, and restoration of the biota after it. It is generally believed that climatic changes causing the crisis resulted from eruption of the Siberian traps, so that localities of intertrappean deposits were undoubtedly formed during the crisis. Sedimentation conditions of volcanogenic deposits provide the most detailed time resolution, so that the crisis processes can be investigated in detail. The dynamics of insect diversity in the Paleozoic and basal Mesozoic shows that mass extinctions were absent, although many groups disappeared for some time from the taphonomic window. The crisis events in ecosystems appear earlier than events usually considered as the reason for crisis. The analysis of oryctocoenoses from localities of the intertrappean beds has shown that, during the formation of traps on the mountain plateau, rather diverse ecosystems were retained, including those of the forest formations. They are a source of information, allowing restoration of ecosystems at the end of the Early Triassic.

Sedimentology and depositional sequences of a Kimmeridgian carbonate ramp system, Lower Saxony Basin, Northern Germany

Shallow-marine Kimmeridgian (Late Jurassic) deposits in the Lower Saxony Basin (LSB) composed of alternating limestone, marl and claystone attract great palaeontological interest due to their rich invertebrate and vertebrate assemblages. Unfortunately, the absence of open-marine marker fossils and numerous sedimentary gaps in combination with lateral facies changes hamper the precise stratigraphic correlation of these strata on both a local and global scale. Here, an integrated approach combining carbonate microfacies analysis, ostracod biostratigraphy and high-resolution sequence stratigraphy is applied to two Kimmeridgian sections (Langenberg and Bisperode, 60 km apart) in the southeastern LSB. High-resolution carbonate microfacies analysis enables the definition of 19 microfacies types and seven microfacies associations, which can be arranged into facies belts along a carbonate ramp. Vertical microfacies, bed thickness and diagnostic surfaces define stacking patterns that are interpreted as small-, medium- and large-scale sequences. The ostracod biostratigraphic framework established in this study provides the required stratigraphic control. Correlation of the two studied sections reveals a more proximal setting for Bisperode than Langenberg and an overall shallowing-up trend from mid-ramp to proximal inner ramp developed in both sections. Furthermore, the majority of the medium-scale sequence boundaries defined in this study can be found in similar biostratigraphic positions in other European basins. Synsedimentary tectonics combined with high sediment accumulation rates can be identified as important controlling factors for the distribution and composition of the Kimmeridgian deposits in the LSB based on detailed correlation on both a regional and super-regional scale.