Restricted Marine Conditions Research Articles

Paleoceanographic evolution in the South Atlantic Ocean (Kwanza Basin, Angola) during its post-salt foundering

Calcareous nannofossil distribution, environmental magnetism, and geochemical data provide stratigraphic evidence concerning the paleoceanographic changes across the lower/middle Albian and the Oceanic Anoxic Event 1b (OAE1b, Kilian Level) at South Atlantic Ocean. In this study, we analyzed samples from the sedimentary records at Deep Sea Drilling Project (DSDP) Site 364, Kwanza Basin, Angola. This section is associated with the initial phases of evolution of the South Atlantic Ocean, characterized by the deposition of extensive evaporite layers under restricted marine conditions, which were preserved in many sedimentary basins of the Brazilian and African continental margins. The open marine conditions that followed this period are recorded in the sequences of limestones interbedded with organic matter-rich black shales. In the Kwanza Basin, Site 364 contains a well-preserved sedimentary record of these post-salt sequences. In this study, we address the Lower Cretaceous sedimentary records at Site 364 from a paleoceanographic perspective, investigating the influence of OAE1b and local paleoenvironmental conditions. Our data analysis indicates a progressive reduction in hypersaline conditions during the lower/middle Albian. In these conditions, five paleoceanographic intervals (PIs) were described, which show different evidence of dysoxia/anoxia and salinity fluctuations, euxinic intervals, surface-water temperature changes, and hydrothermal activity signals, as well as possible ocean acidification episodes. These paleoceanographic conditions at Site 364 are associated with a stratified thermocline composed of warm surface-water from the North Atlantic (Western Tethys) and cool deep-water incursions from the Austral Atlantic, which strongly affected the composition of the calcareous nannofossil assemblages. We propose that the lower/middle Albian paleogeographic and paleoceanographic conditions observed in the Kwanza Basin were likely related not only to local events linked to the early development of the South Atlantic, but also to the OAE1b - Kilian Level recognized in several basins from around the world.

Palaeocene to Miocene southern Tethyan carbonate factories: A meta‐analysis of the successions of South‐western and Western Central Asia

AbstractOne hundred and forty‐four published successions of shallow‐water carbonates, deposited between the Palaeocene and the Miocene, from the Levant to the Himalayas, have been re‐analysed using a standardised approach to investigate the distribution of carbonate facies and carbonate‐producing organisms. Large benthic foraminifera were found to be the volumetrically most important group of carbonate producers during the whole period, with a peak in abundance during the Eocene. Colonial corals are relatively abundant during the Palaeocene and Miocene, their abundance peaks during the Oligocene and has a minimum during the Eocene. Red calcareous algae have a similar pattern although their peak in abundance covers both the Oligocene and Miocene. Green calcareous algae decrease from the Palaeocene onward. Facies related to very shallow and/or restricted marine conditions peak during the Miocene and in particular during the Aquitanian. Both the pattern of large benthic foraminifera and of colonial corals seems to be related to temperature, with warm periods favouring the former group and cool periods the latter group. Red calcareous algae display a pattern similar to that of colonial corals suggesting that the periods favourable for one group are, on a large scale, also favourable for the other. The progressive decrease of green calcareous alga could be tentatively related to a preservation bias connected to the transition from Palaeogene assemblages that included presumably calcitic taxa of green algae to Neogene assemblages entirely constituted by aragonitic taxa with limited preservation potential. The Aquitanian peak in facies related to very shallow and/or restricted marine conditions is most likely connected to the progressive narrowing of the Tethys related to the collision between Arabia and Eurasia. These results denote an overall agreement between the abundance of the various types of shallow‐water carbonate facies and large‐scale environmental and geological processes, highlighting the potential for palaeoenvironmental reconstruction locked in the shallow‐water record.

Structural analysis of layered evaporites using internal deformation patterns: Examples from Santos and Campos basins, Brazil

The Santos and Campos basins, offshore southeastern Brazil, contain layered evaporite sequences (LES) deposited during the Late Aptian, marking the end of lacustrine and beginning of restricted marine conditions. Density and velocity differences between evaporite minerals such as halite, anhydrite, carnalite, tachyhydrite and other bittern salts result in strong seismic impedance contrasts and therefore enable excellent stratal imaging of internal salt deformation. Different acoustic responses allow a detailed analysis of the internal deformation of evaporites, with the corresponding mechanical properties providing constraints on regional salt flow in the Santos and Campos basins. Detailed mapping and analysis of deformed LES support conclusions from cross-section restorations and provide insight on local salt flow and deformation mechanisms. This study utilizes kinematically restored regional sections to characterize overall basin-wide salt flow, while leveraging salt facies and their control on internal salt fold styles to demonstrate localized salt deformation. The important results from this study are the following. a) Santos and Campos basins are linked extension-contraction systems, however pre-existing basin-wide changes in paleo-topography represents a fundamental control in the overall salt flow, accounting for much of the downdip contraction in the middle of the basins rather than the toe of the system. b) Salt mobilization due to gravity initiated early and there is evidence that it was contemporaneous with evaporite deposition in many parts of the basins. Intrasalt unconformities and stratigraphic features are presented to support this conclusion. c) Mechanical stratigraphy within the LES play an important role in controlling intra-salt structural styles, and their fold interference patterns can be used to understand salt deformation in great detail. These results can be applied to better investigate a spectrum of salt tectonic problems in the basins and elsewhere, such as regional and localized salt flow, sub-regional prediction of weld kinematics and local prediction of weak salt units for drilling hazard analysis.

Biostratigraphic ages and depositional environments of the upper Oligocene to lower Miocene Veldhoven Formation in the central Roer Valley Rift System (SE Netherlands-NE Belgium)

Abstract Discussions on the age and the depositional environments of the Veldhoven Formation and its members are persistent in Belgium and the Netherlands. Uncertainties on stratigraphy and the constructive process of sediment accumulation continue today as a result of lack of data on this succession within the Roer Valley Rift System. The present study provides new information on the bio- and lithostratigraphy and facies from two boreholes based on dinoflagellate cyst taxa. The results were correlated by gamma-ray logs towards other key boreholes in the region and show a good consistency for stratigraphy and depositional environments for the members of the Veldhoven Formation. After marginal to restricted marine conditions in the latest Rupelian (early Oligocene), the start of deposition of the Veldhoven Formation marked the transition towards a higher sea level, expressed by increased glauconite contents and gamma-ray values. The Voort Member in the lower part of the Veldhoven Formation has an early to late Chattian (Late Oligocene) age and comprises predominantly shallow marine (fluctuating restricted to open marine) conditions. The lithology in the lower part of this unit is often very clayey but is coarsening upward into sands. The superjacent Wintelre Member has a latest Chattian to early Aquitanian (early Miocene) age. This member is distinct by its clayey nature which is expressed by relatively high gamma-ray values. Earlier studies suggest a deeper marine facies for the Wintelre Member compared to the Someren and Voort members. However, the dinoflagellate cyst assemblages in this unit are mostly dominated by a single genus indicating a restricted marine setting, including salinities that deviate from normal marine conditions, most probably due to minor ventilation by narrow or lack of connection to the Atlantic Ocean. A glacio-eustatic sea-level fall around the Oligocene/Miocene boundary limited the sea coverage to the strongest subsiding areas, where deposition of the Wintelre Member is recorded, while non-deposition or erosion occurred in the surrounding highs, hence creating an isolated (sub)basin. The superjacent Someren Member was deposited during the late Aquitanian to middle Burdigalian and consists of shallow to open marine clayey fine sands. Increasing clay contents indicate a gradual development towards a higher sea level, which coincide with upward increasing gamma-ray values. The biostratigraphic results of this study suggest that no major hiatuses are present in the differentially subsiding blocks of the Roer Valley Rift System during the late Oligocene to early Miocene.

Zircon (U-Th)/He thermochronology reveals pre-Great Unconformity paleotopography in the Grand Canyon region, USA

Abstract The Great Unconformity is an iconic geologic feature that coincides with an enigmatic period of Earth's history that spans the assembly and breakup of the supercontinent Rodinia and the Snowball Earth glaciations. We use zircon (U-Th)/He thermochronology (ZHe) to explore the erosion history below the Great Unconformity at its classic Grand Canyon locality in Arizona, United States. ZHe dates are as old as 809 ± 25 Ma with data patterns that differ across both long (∼100 km) and short (tens of kilometers) spatial wavelengths. The spatially variable thermal histories implied by these data are best explained by Proterozoic syn-depositional normal faulting that induced differences in exhumation and burial across the region. The data, geologic relationships, and thermal history models suggest Neoproterozoic rock exhumation and the presence of a basement paleo high at the present-day Lower Granite Gorge synchronous with Grand Canyon Supergroup deposition at the present-day Upper Granite Gorge. The paleo high created a topographic barrier that may have limited deposition to restricted marine or nonmarine conditions. This paleotopographic evolution reflects protracted, multiphase tectonic activity during Rodinia assembly and breakup that induced multiple events that formed unconformities over hundreds of millions of years, all with claim to the title of a “Great Unconformity.”

The evolution of the Carpathian Foredeep Basin during the latest Badenian and Sarmatian (Middle Miocene): inferences from micropalaeontological data

Seven Middle Miocene (Upper Badenian to Lower Sarmatian) sedimentary sections of the Central Paratethys, two from the Polish Carpathian Foredeep Basin (PCFB) and five from the Eastern Carpathian Foreland Basin (ECFB) of Romania and the Republic of Moldova have been analysed micropalaeontologically to better constrain the Badenian-Sarmatian Extinction Event, characterized by significant taxonomic impoverishment of both foraminifers and ostracods. Our studies show significant palaeoenvironmental changes in the basin including depth, salinity, oxygenation, and organic matter flux. The occurrence of moderately diverse planktonic foraminifera (Globigerina, Globigerinita, Globorotalia, Trilobatus, Orbulina, Velapertina) in the Upper Badenian deposits of the PCFB as well as in the ECFB and their rarity in the lowermost Sarmatian indicate an almost fully marine environment during the latest Badenian, followed by a significant regression and possible appearance of much more restricted marine conditions across the boundary. The taxonomic composition of the Sarmatian foraminifera, ostracoda and calcareous nannofossils indicate that during this interval the salinity fluctuated strongly, with the water regime varying from brackish to normal marine. In addition, the identified micropalaeontological assemblages identified show palaeoenvironmental similarity across different basins of the Central Paratethys. This supports a hypothesis of possible connections during the latest Badenian between different areas of the Central Paratethys, as well as of the existence of a gateway between the Central Paratethys and the Mediterranean realm

Integrated stratigraphy and paleontology of the lower Miocene Monte León Formation, southeastern Patagonia, Argentina: Unraveling paleoenvironmental changes and factors controlling sedimentation

Marine sedimentary rocks of the lower Miocene Monte León Formation of southeastern Patagonia (Austral Basin), Argentina are important geological archives for better understanding regional tectonics, paleoenvironments, oceanography, and climate. In this paper, we describe assemblages of invertebrates, palynomorphs, foraminifera, ostracods and calcareous nannofossils in a stratigraphical and sedimentological framework, which suggest deposition during a transgressive-regressive cycle. From base to top, the lowermost outcropping deposits of the Punta Entrada Member represent an inner shelf environment, formed during a transgressive phase. The zone of maximum flooding is marked by a high diversity of protoperidiniaceans (heterotrophic) and offshore dinoflagellate cysts, an increase in the percentage and size of planktonic foraminifera, and a decrease in shallow water benthic foraminifera. Regressive deposits in the upper part of the Punta Entrada Member exhibit a progradational stratal stacking pattern and are characterized by an upward decrease in bioturbation and in the content of marine invertebrates; the dinoflagellate cyst assemblages point toward shallower and more restricted marine conditions than in underlying deposits. The cycle ends with the Monte Observación Member, which contains an impoverished and mostly reworked fauna of invertebrates. The presence of monospecific reefs of Crassostrea orbignyi, the decrease in dinoflagellate cysts and calcareous microfossils diversity, and the increase of continental palynomorphs suggest progressively shallower conditions and increasing influence of freshwater discharge. Although eustatic controls could have contributed to the sedimentary evolution of the Monte León Formation, the upward regressive trend is interpreted as the result of tectonism linked to the Andean orogeny, which led to the uplift, exhumation, and erosion of the highlands in the west. This is supported by the abundance of pyroclastic material, together with reworked specimens of Upper Cretaceous forams and Upper Cretaceous and middle Eocene dinoflagellate cysts in the upper part of the Punta Entrada Member and in the Monte Observación Member.

Tracing paleoredox conditions across the Devonian–Carboniferous boundary event: A case study from carbonate-dominated settings of Belgium, the Czech Republic, and northern France

The Devonian–Carboniferous boundary was coeval with the Hangenberg Crisis, which is regarded as a first-order mass extinction event related with large sea-level changes and widespread anoxia. This study aims to trace the geochemical paleoproductivity and paleoredox proxies across the Devonian–Carboniferous carbonate-dominated successions of the Namur-Dinant Basin (Belgium, northern France) and the Moravo-Silesian Basin (Czech Republic), located in the Variscan Rhenohercynian Zone. The research was focused on the distribution of oxides (SiO2, Al2O3, Fe2O3, CaO, Na2O, K2O, TiO2, MnO) and trace elements (Th, U, V, Zr, Mo, Zn, Pb, Ni, Cu) measured by ICP-OES and ICP-MS, respectively. The enrichment factors of Mo and U and their ratios were used as the main paleoredox proxies, whereas the enrichment factors of Zn, Cu, Pb, and Ni were employed to trace the paleoproductivity changes. High values of Zr/Al2O3 (>0.001), TiO2/Al2O3 (>0.06), and Fe/Ti (>20) and low values of Al/(Al + Fe + Mn) (<0.35) coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients, related to Late Devonian and Early Carboniferous extensional magmatism in the Rhenohercynian domain, although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded. The studied Devonian–Carboniferous boundary sections from the Namur-Dinant Basin (Gendron-Celles, Ardennes quarry) reveal three levels with similar vectors of Mo and U enrichments. The pre-crisis Famennian pattern is typical for weakly restricted basins with Fe-Mn redox cycling accompanying vertical fluctuations of the oxic/anoxic chemocline close to the sediment/water interface with the influence of particulate shuttle. The MoEF and UEF patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive Hangenberg Black Shale Event. The lower Tournaisian MoEF and UEF patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions. In the Moravo-Silesian Basin (Lesní lom section), the pre-crisis Famennian MoEF and UEF vector indicates an unrestricted marine trend which converges with that of restricted systems. Redox conditions range from suboxic to euxinic. In the Tournaisian, MoEF and UEF oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions. Increased isolation of both studied basins in the Early Tournaisian is regarded as a reflection of a significant eustatic fall during the Hangenberg Crisis, linked to a severe episode of the Gondwana glaciation. These paleohydrographic patterns have correlative potential that should be considered for a revised Devonian-Carboniferous Boundary definition.

Microbial-mediated pre-salt carbonate deposition during the Messinian salinity crisis (Calcare di Base fm., Southern Italy)

A multi-scale analysis of sedimentary carbonate facies and post-sedimentary diagenetic features of the Calcare di Base Formation, the precursor to evaporites in Upper Messinian successions of Northern Calabria and Central Sicily, has revealed their microbial bio-mediated origin. Massive to laminated microbial boundstones represent the most common sedimentary facies forming flat to low relief cm to m scale stromatolitic and thrombolitic bodies. The fabric of the micrite varies from peloidal to aphanitic, and almost always preserves filamentous bacteria which characterized the original microbial mat. The mat was dominated by sulphur-oxidizing bacteria belonging to the Thiotrichaceae, but there is evidence for a more complex community with sulphate- and/or nitrate-reducing bacteria, all being responsible for the mediation of the carbonate precipitation. Microbial boundstones are rich in pseudomorphs of Ca-sulphate and halite, which formed during the deposition of the microbial carbonate. Layers of primary gypsum are interbedded locally with carbonates suggesting the presence of restricted marine conditions. The stable O and C isotopic composition of the carbonates, that vary from dolomite to aragonite and calcite, suggests a complex interplay between arid to humid climatic changes, expressed cyclic interbedding of the carbonate with marl-marlstone. Later diagenetic events mainly consist of phreatic meteoric recrystallization and cementation. Although considered as diachronous, the microbial carbonates can be mapped out over a distance of more than 500 km across southern Italy; this indicates near-constant environmental conditions upon the central Mediterranean shelf at the beginning of the salinity crisis. Deposition of the extensive subaqueous microbial deposit that largely comprises the Calcare di Base is envisaged to have taken place across a shallow to moderate depth platform with local slopes into deeper water areas, where some resedimentation occurred.

Local paleoenvironmental controls on the carbon-isotope record defining the Bitter Springs Anomaly.

Large magnitude (>10‰) carbon-isotope (δ13 C) excursions recorded in carbonate-bearing sediments are increasingly used to monitor environmental change and constrain the chronology of the critical interval in the Neoproterozoic stratigraphic record that is timed with the first appearance and radiation of metazoan life. The ~10‰ Bitter Springs Anomaly preserved in Tonian-aged (1000-720Ma) carbonate rocks in the Amadeus Basin of central Australia has been offered as one of the best preserved examples of a primary marine δ13 C excursion because it is regionally reproducible and δ13 C values covary in organic and carbonate carbon arguing against diagenetic exchange. However, here we show that δ13 C values defining the excursion coincide with abrupt lithofacies changes between regularly cyclic grainstone and microbial carbonates, and desiccated red bed mudstones with interbedded evaporite and dolomite deposits, recording local environmental shifts from restricted marine conditions to alkaline lacustrine and playa settings that preserve negative (-4‰) and positive (+6‰) δ13 C values, respectively. The stratigraphic δ13 C pattern in both organic and carbonate carbon recurs within the basin in a similar way to associated sedimentary facies, reflecting the linkage of local paleoenvironmental conditions and δ13 C values. These local excursions may be time transgressive or record a relative sea-level influence manifest through exposure of sub-basins isolated by sea-level fall below shallow sills, but are independent of secular seawater variation. As the shallow intracratonic setting of the Bitter Springs Formation is typical of other Neoproterozoic carbonate successions used to construct the present δ13 C seawater record, it identifies the potential for local influences on δ13 C excursions that are neither diagenetic nor representative of the global exogenic cycle.

Microfacies and depositional environments of Jurassic (Callovian) Tuwaiq Mountain Formation in central Saudi Arabia

Three stratigraphic sections of the Callovian Tuwaiq Mountain Formation at Shaib El-Hisyan, Khashm Al-Giddayah and Dirab, near Riyadh City, central Saudi Arabia have been studied to distinguish their microfacies features and the equivalent probable depositional environments. Lithostratigraphically, the Tuwaiq Mountain Formation is subdivided into two lower and upper Tuwaiq members. The part that informally is known as upper Tuwaiq Member is subdivided from base to top into T1, T2, and T3 members, respectively. The microfacies analysis of the Tuwaiq Mountain Formation led to the recognition of 12 microfacies types (FT1–FT12) that are grouped into three associations: (1) open platform facies association (FT1–FT5); (2) high-energy shoals of ooids and patch reefs facies association (FT6–FT9); and (3) restricted carbonate platform facies association (FT10, FT12). The lower part of the Tuwaiq Mountain Formation is characterized by relative abundance of wackestone and wacke/packstone facies that are capped by thin peloidal molluscan floatstone facies. The former indicates a quiet open platform environment with periodic agitation, while the later indicates deposition in a sand shoal environment. The facies of basal unit of the upper Tuwaiq Mountain Formation, T1, are enriched with dense micrite matrix and shell fragments of epifaunal and deep infaunal organisms (e.g., Pholadomya spp.). The microfacies pattern of Baladiyah Member (T1) indicates a quiet open platform with low and sometimes high water circulation. The Maysiah Member (T2) is composed of hard limestone with abundance of coralline microfacies in framestone, grainstone, and packstone textures suggesting a high-energy shallow reefal environment with periods of quiet open platform conditions. This shallow reefal environment becomes more restricted southward, where shales and algal dolomitic grainstones were formed. The Daddiyah Member (T3) that made up of chalky limestone with chert intercalations is predominated by matrix-support lime mudstone, wackestone, and packstone facies. These microfacies reflect open platform with slightly low circulation below fair-weather wave base with period of restricted marine conditions forming rudstone microfacies. Southward, these environments became shallower and subjected to considerable quartz influx in an agitated sand shoal.

Dinoflagellate cysts and palynofacies from the upper Badenian (Middle Miocene) of the Roztocze area at Józefów and Żelebsko (Carpathian Foredeep Basin, Poland): palaeoenvironmental implications

The post-evaporitic upper Badenian (Middle Miocene) succession of the Roztocze (marginal zone of the Carpathian Foredeep Basin) consists of shallow-marine sands and organodetrital deposits. The latter, although predominantly coarse-grained, include very rare and usually very thin intercalations of fine-grained, loamy material. A few such clay layers were sampled for their palynological content in quarries at Jozefow (Jozefow and Pardysowka) and Żelebsko. The clay samples yielded palynological organic matter, in contrast to organodetrital limestone samples, which were barren. The palynofacies composition, both presence/absence of land-derived material and the specific composition of aquatic material, are useful for the palaeoenvironmental reconstructions of sedimentary settings. During late Badenian time, the sedimentary setting of the deposits studied was characteri- zed by proximity to the shoreline, which, however, supplied limited input of terrestrial matter, and by restricted marine conditions caused by increased salinity. During the latest Badenian, water salinity presumably underwent a further increase, leading to the collapse of the dinoflagellate floras. The frequent occurrence of reworked Palaeogene dinoflagellate cysts in upper Badenian samples and their absence from the uppermost Badenian indicate variable intensity of erosion of the epicontinental Palaeogene strata during the Middle Miocene at Roztocze.

Palynostratigraphy and palaeoenvironments of the Eagle Ford Group (Upper Cretaceous) at the Lozier Canyon outcrop reference section, west Texas, USA

This study describes the detailed palynology of the Eagle Ford Group at Lozier Canyon, its principal outcrop reference section in west Texas. Prominent marine phytoplankton assemblages are consistent with a proposed depositional setting for Lozier Canyon on a submarine platform within the Cretaceous Western Interior Seaway (KWIS) of the USA. The Lower Eagle Ford Formation (middle to upper Cenomanian) was deposited under restricted marine conditions with oxygen-deficient, probably anoxic bottom waters, as indicated by the black, organic-rich (ca. 1 to > 6% total organic carbon) shale lithology. The formation comprises two fourth-order stratigraphical sequences, each showing sedimentary evidence of increasing water depth during deposition. Palynomorph assemblages from the sequences are dominated by green algal prasinophyte phycomata in the lower parts and peridinioid dinoflagellate cysts in the upper parts. The productivity of these marine phytoplankton groups may have been stimulated by availability of ammonium (prasinophytes) and nitrite (peridinioids) from upwelling, or vertical expansion of the oxygen-minimum zone. The transition from prasinophyte- to peridinioid-dominated assemblages may reflect elevation of the photic zone to a level less regularly encroached by deeper, ammonium-enriched waters of the denitrification zone. The overlying Upper Eagle Ford Formation (upper Cenomanian to upper Turonian or Coniacian) was deposited under deeper, relatively open marine conditions, as indicated by a decrease in organic carbon content and an increase in carbonate content. This is supported by the presence of diversified dinoflagellate cyst assemblages, including inter-regional (high- to mid-latitude) marker events; in the upper Cenomanian, base and acme Cyclonephelium compactum-membraniphorum, top consistent and frequent Litosphaeridium siphoniphorum, and top Adnatosphaeridium tutulosum; in the middle to upper Turonian, range bases of Heterosphaeridium difficile and Senoniasphaera rotundata. The stratigraphical resolution offered by palynology indicates potential application to wellsite ‘geosteering’ of commercial shale oil and shale gas wells drilled in the Eagle Ford Group.

Depositional history of the Upper Triassic Kapp Toscana Group on Svalbard, Norway, inferred from palynofacies analysis and organic geochemistry

Upper Triassic sediments in the Svalbard Archipelago were deposited in several transgressive-regressive cycles. Understanding their deposition and distribution is of vital importance because of their potential as hydrocarbon reservoir rocks. In this study we integrate palynofacies with organic geochemistry in order to reconstruct the depositional environment of the upper Botneheia Fm up to the lower the Knorringfjellet Fm from two sections located in central Spitsbergen, for which distinctive palynofacies zones have been distinguished. These are mainly terrestrially dominated but occasionally contain amorphous organic matter and marine palynomorphs. Rock-Eval pyrolysis reveals overall mature kerogen type III/IV samples. Our results indicate that at least partially restricted marine conditions prevailed during deposition of the Botneheia Fm. The Botneheia Fm is overlain by a regressive cycle from the lower part of the Tschermakfjellet Fm up to the top of the De Geerdalen Fm with terrestrially dominated palynofacies assemblages. The Knorringfjellet Fm contains increased marine palynofacies and marine dinoflagellate cysts, which is in accordance with a transgression at the base of this unit. This study integrates for the first time in the Spitsbergen area quantitative palynofacies and sedimentary organic matter characterization, and shows the generally accepted paleo-environmental development for the Svalbard Archipelago.

Replacement of benthic communities in two Neoproterozoic–Cambrian subtropical-to-temperate rift basins, High Atlas and Anti-Atlas, Morocco

The ‘Cambrian explosion’ is often introduced as a major shift in benthic marine communities with a coeval decline of microbial consortia related to the diversification of metazoans and development of bioturbation (‘Agronomic Revolution’). Successive community replacements have been reported along with ecosystem diversification and increase in guild complexity from Neoproterozoic to Cambrian times. This process is recorded worldwide but with regional diachroneities, some of them directly controlled by the geodynamic conditions of sedimentary basins.The southern High Atlas and Anti-Atlas of Morocco record development of two rifts, Tonian (?) – early Cryogenian and latest Ediacarian–Cambrian in age, separated by the onset of the Pan-African Orogeny. This tectonically controlled, regional geodynamic change played a primary control on pattern and timing of benthic ecosystem replacements. Benthic communities include microbial consortia, archaeocyathan–thromboid reefal complexes, chancelloriid–echinoderm–sponge meadows, and deeper offshore echinoderm-dominated communities. Microbial consortia appeared in deeper parts of the Tonian (?) – early Cryogenian fluvio-deltaic progradational rift sequences, lacustrine environments of the Ediacaran Volcanic Atlasic Chain (Ouarzazate Supergroup) and the Ediacaran–Cambrian boundary interval, characterized by the peritidal-dominated Tifnout Member (Adoudou Formation). They persisted and were largely significant until Cambrian Age 3, as previous restricted marine conditions precluded the immigration of shelly metazoans in the relatively shallow epeiric parts of the Cambrian Atlas Rift. Successive Cambrian benthic communities were replaced as a result of distinct hydrodynamic and substrate conditions, which allow identification of biotic (e.g., antagonistic relationships between microbial consortia and echinoderms, and taphonomic feedback patterns in chancelloriid–echinoderm–sponge meadows) and abiotic (e.g., rifting, associated volcanism and drastic platform drowning events, and substrate) factors that controlled ecosystem diversification in the Atlas Rift.

Terrestrial vertebrates from the Sarmatian (late Serravallian) of the Central Paratethys – the fossil site of Gratkorn (Styrian Basin, Austria)

The Paratethys Sea represents a huge landlocked water body of western Eurasia, which evolved during the Cenozoic era from open to restricted marine conditions towards brackish and lacustrine basins (Rogl and Steininger 1983). Due to the endemic evolution of Paratethyan biota and the tectonics of the Alpine orogeny, chronostratigraphic correlations and basin evolution are still partly a matter of debate and a subject of intense scientific research. Despite the mainly marine or lacustrine sedimentation (Steininger et al. 1985), fossils of continental biota are not rare in deposits in the Paratethyan realm. Notably, terrestrial vertebrates have been known for a long time (e.g. Eichwald 1835), but well-documented excavations and faunas are rare or absent from many stratigraphic stages and basins. This is especially true for the Sarmatian regional stage when the Paratethys was becoming isolated from the world oceans (Piller et al. 2007). This chronostratigraphic stage is crucial, because the Sarmatian sensu stricto (=Volhynian and early Bessarabian) represents the last period with a uniform marine biofacies in the entire Paratethys, extending from the Styrian Basin in the west to the Lake Aral in the east (Steininger and Wessely 2000). While the deposits cover a huge area, terrestrial biota are still a rarity, and those from the early to late Sarmatian transition (Volhynian–Bessarabian transition) virtually unknown. The discovery of the Gratkorn fossil site due to geologic mapping in 2005 gives a unique opportunity to study continental ecosystems of this specific time horizon (12.2– 12.0 Ma, early to late Sarmatian transition). Systematic palaeontologic excavations starting in 2006 have been carried out in a cooperation between the Universalmuseum Joanneum (Graz), the Ludwig Maximillians Universitat Munchen, and the Eberhard Karls Universitat Tubingen. Besides abundant fossils of plants (leafand carpoflora), molluscs (gastropods and mussels), and arthropods (insects, ostracodes, and crabs), more than 1,500 specimens of vertebrates have so far been excavated. These fossils cover all major groups of vertebrates, namely fishes, amphibians, reptiles, birds, and mammals, rendering Gratkorn a benchmark locality for continental biota from the Sarmatian of the Central Paratethys. This special issue is dedicated to Prof. Dr. Friedrich Franz Steininger on the occasion of his 75th birthday in 2014, and in honour of his noteworthy scientific contributions to chronostratigraphy, palaeogeography, and biofacies of the Paratethys Sea. Twelve publications have been brought together summarising the first nearly 10 years of research at Gratkorn. They deal with the geology of the Gratkorn locality, the vertebrate taphonomy, and selected aspects of vertebrate taxonomy and ecology. Further scientific contributions to Gratkorn, e.g. the macro-flora and the carnivore mammals, are in preparation and will shortly be published in a forthcoming issue of Palaeobiodiversity and Palaeoenvironments. This article is a contribution to the special issue “The Sarmatian vertebrate locality Gratkorn, Styrian Basin.”

The Tethyan Seaway Iranian Plate Oligo-Miocene deposits (the Qom Formation): distribution of Rupelian (Early Oligocene) and evaporate deposits as evidences for timing and trending of opening and closure of the Tethyan Seaway

The aim of this research is to shed light on the distribution of Rupelian (Early Oligocene) and evaporate deposits as evidences for timing and trending of opening and closure of the Tethyan Seaway. To accomplish these goals, four sets of data were scrutinized: (1) two stratigraphic sections (Ghohroud and Vidoja) of the Qom Formation in the southern and southwestern Kashan (to determine the age of their lower deposits), (2) results of the study of more than 100 stratigraphic sections of the Qom Formation, (3) Geological maps of Iran Sheets and (4) more than 30 geological maps of different parts of Iran. Consideration of four sets of data led to the following conclusions. Deposition of the Qom Formation (with Rupelian–Burdigalian range) took place in three NW–SE-trending basins: Sanandaj–Sirjan (fore-arc basin), Urumieh–Dokhtar magmatic arc (intra-arc basin) and Central Iran (back-arc basin). Marine conditions in the low latitudes of these three basins started in the Rupelian. Rupelian deposits are vastly distributed in the intra-arc and fore-arc basins but in the back-arc basin Rupelian deposits are deposited only in a few places in close proximity of the magmatic arc. It is remarkable that mostly all of the intra-arc Rupelian deposits-bearing sections are underlain by Eocene volcanic rocks. Latitudinally, the Rupelian deposits of the Qom Formatiom are deposited below 34°2′N, the Chattian deposits continue to 35°N, but above 35°N the Qom Formation is deposited during the Miocene, based on previous age dating; therefore, transgression of the Tethyan Seaway on the Iranian Plate started from the southeast and continued northwestward gradually. The last true Nummulites spp. became extinct at the top of Late Rupelian and all of the in situ Nummulites-bearing layers of the Qom Formation are Rupelian in age. According to the presence of Nummulites spp. (Nummulites fichteli, Nummulites vascus, Nummulites sp.), the lower 185 m of the Ghohroud section and whole deposits of the Vidoja section are attributed to the Rupelian. Evaporate deposits of the Qom Formation are deposited in a rather small area of Central Iran back-arc basin and are deposited totally in the Early Miocene (Aquitanian–Burdigalian). This indicates that due to the compressive tectonic regime in the Central Iran back-arc basin, the gates to the open ocean became restricted in the Early Miocene gradually. During the Aquitanain and Burdigalian, restricted marine conditions prevailed and episodic precipitation of evaporate deposits occurred. In the Qom area near the depocentre of the Qom basin, evaporates were precipitated episodically. Deposition of evaporate deposits took place along the concave side of an assumptive curved line crossing from SE of Anarak, Nain, Navab Anticline (SE of Kashan), Shourab (SE of Qom), immediate S, SW and W of Qom, N of Howz Soltan Lake, SW of Tehran, SW, W and SE of Varamin, NE of Garmsar and NW, N and NE of Semnan. Distribution of the Qom Formation, evaporate deposits and Rupelian deposits are illustrated on new maps shown herein as figures.

Clay mineralogy and calcareous nannofossils from Jagüel and Roca formations in the eastern sector of Pellegrini Lake, Neuquen Basin, República Argentina.

This study presents new mineralogical, sedimentological,&nbsp;and micropaleontological data from the Jag&uuml;el (Late Maastrichtian-Early Danian) and Roca (Danian) formations,&nbsp;located in the eastern sector of Pellegrini Lake, R&iacute;o Negro province, Rep&uacute;blica Argentina. According to the physical&nbsp;characteristics and the age of the sediments that conform these formations, two siliciclastic lithofacies and a carbonate&nbsp;one were recognized, they are named: Maastrichtian grayish yellow calcareous mudstones, Danian olive gray calcareous&nbsp;mudstones, and Danian carbonates. The rocks which constitutes siliciclastic lithofacies were classified as allochemical&nbsp;mudstones and the mineralogy is characterized by high proportions of clay minerals and, to a lesser extent, calcite. The&nbsp;clay mineral association is dominated by a random (R0) I/S mixed-layers (70-90% Sm) accompanied by lower proportions of illite and kaolinite. The mineralogy and the microfabric of the mudstones reflect that these sediments have not&nbsp;been affected significantly by diagenesis. Clay minerals would be of detrital origin and the predominance of the highly&nbsp;smectitic I/S along all sections would be associated with an active volcanism coming from the western magmatic arc,&nbsp;located in the Neuqu&eacute;n Basin during the Late Cretaceous and Paleocene. Micropalaeontological analyses confirmed&nbsp;the presence of Cretaceous-Paleogene transition in the Jag&uuml;el Formation beds. The calcareous nannofossils allowed to&nbsp;relate changes in the the mineralogical associations along the K/P transition. In this way, it was possible to detect an&nbsp;increase in kaolinite content close to the K/P boundary (&gt;10%), that decreases towards higher positions of the Danian,&nbsp;which could indicate a warmer and wetter climate during this interval, that it would tend to be drier with seasonal conditions in the late Danian. The Maastrichtian calcareous nannofossil assemblages suggest oligotrophic environments&nbsp;and a well stratified photic zone, nevertheless, in some horizons, the nannoflora is abundant with lower richness which&nbsp;would indicate more restricted marine conditions.

The impact of conjugate margins analysis on play fairway evaluation – an analysis of the hydrocarbon potential of Nova Scotia

An analysis of the rifting history of the Central Atlantic focused on Nova Scotia and Morocco reveals new plays potentially charged from an Early Jurassic source system. The revised rift model is based on newly acquired seismic refraction data, reprocessing of existing refraction and multi-channel seismic data, and integration of potential fields data from the conjugate margins. We infer from the geophysical evidence that there was volcanic rifting from south-west Nova Scotia to the Newfoundland fracture zone during the Early Jurassic, with a restricted, shallow marine environment for sediment deposition. We have integrated plate tectonics, geochemistry, and sequence stratigraphic interpretation with the aim of identifying new plays. Analysis and integration of geochemical evidence has led to a new paradigm for the exploration potential offshore Nova Scotia. In particular, there is now good evidence for deposition of a source rock in restricted marine conditions during the Early Jurassic. This source rock is capable of providing charge to an oil play in the south-western half of the Scotian margin, which is a new concept for this area.

Late quaternary ecological turnover in high arctic lake einstaken, nordaustlandet, svalbard (80° n)

Luoto, T.P., Nevalainen, L., Kubischta, F., Kultti, S., Knudsen, K.L. and Salonen, V.‐P., 2011: Late Quaternary ecological turnover in high arctic Lake Einstaken, Nordaustlandet, Svalbard (80° N). Geografiska Annaler: Series A, Physical Geography, 93, 337–354. DOI:10.1111/j.1468‐0459.2011.00435.xMultiproxy palaeolimnological analyses of a sediment core record from Lake Einstaken, Nordaustlandet, give insight into long‐term ecological and environmental dynamics in the High Arctic Svalbard during the last c. 13-000 cal yr bp. Fossil remains of foraminifera, chironomidae, cladocera and diatoms (Bacillariophyta) revealed several distinct ecological turnovers during the late Quaternary. The foraminiferal assemblages in a marine interval in the lower part of the core indicated one distinct faunal turnover and two subsequent minor changes. The foraminiferal assemblages reflected high‐arctic, shallow‐water conditions in an area of changing salinity conditions. A development of gradually more restricted marine conditions, presumably related to a decrease in water depth during the isostatic uplift, was evident from the foraminiferal assemblages. The Holocene was characterized by a freshwater environment in the isolated Lake Einstaken. The cladoceran assemblages experienced two complete faunal turnovers in the early part of the lacustrine sediment sequence, most likely related to inlake processes. The chironomid assemblages went through five distinct Holocene faunal changes that were probably mostly related to climate development and changes in nutrient conditions. The freshwater diatoms revealed four distinct episodes of change in their assemblages that could be related to their sensitivity to pH and nutrient status. The most distinct common feature in the Holocene faunal and floral assemblages was the pioneer phase during the early Holocene. The recent environmental changes, which were most visibly reflected in the chironomid records, are possibly related to a coupled effect of elevated nutrient conditions and increased temperatures.