Search Results (6)

The Badenian/Sarmatian boundary in the Central Paratethyan basins is characterised by a change from open marine conditions during the late Badenian to the assumed brackish conditions during the early Sarmatian. The foraminiferal and palynological results of the Badenian/Sarmatian boundary interval in the Babczyn 2 borehole (in SE Poland) showed that the studied interval accumulated under variable, unstable sedimentary conditions. The Badenian/Sarmatian boundary, as correlated with a sudden extinction of stenohaline foraminifera, is interpreted as being due to the shallowing of the basin. The lack of foraminifera and marine palynomorphs just above the Badenian/Sarmatian boundary can reflect short-term anoxia. The composition of the euryhaline assemblages, characteristic for the lower Sarmatian part of the studied succession, indicates from marine to hypersaline conditions. Full article

The Middle Jurassic in the north Western Desert, Egypt, was a time of complex tectonics and increased environmental perturbations attributed to the predominant sedimentation of organic carbon-rich fine siliciclastic and carbonate deposits of the Khatatba Formation. Although some studies have addressed the hydrocarbon potential and source rock characteristics of the Khatatba Formation, a regional-scale investigation of the prevalent paleoenvironmental conditions and organic matter characteristics is still necessary. In this study, the Khatatba Formation is investigated for detailed palynofacies analysis and palynomorph composition to assess organic matter kerogen types and reconstruct the depositional paleoenvironmental patterns on a regional scale. For this purpose, 116 drill cuttings were collected from five wells in the Matruh, Shushan, and Dahab-Mireir Basins. Moderately diverse assemblages of spores, pollen, and dinoflagellate cysts are reported. Age-diagnostic dinoflagellate cysts, including Adnatosphaeridium caulleryi, Dichadogonyaulax sellwoodii, Korystocysta gochtii, Wanaea acollaris, and Pareodinia ceratophora, along with occasional records of Systematophora areolate and Systematophora penicillate, defined a Bajocian–Callovian age. Based on particulate organic matter (POM) composition, four palynofacies assemblages (PFAs) are identified. PFA-1 is the most common within the Khatatba Formation in the five studied wells. It contains high proportions of phytoclast fragments versus low contents of amorphous organic matter (AOM) and palynomorphs and is defined by a gas-prone kerogen Type III. PFA-2 is comprised of moderate abundances of AOM and phytoclast characteristics of oil-prone kerogen Type II. PFA-3 is dominated by phytoclasts and moderate to low proportions of AOM and palynomorphs of kerogen Type III, whereas PFA-4 consists of AOM and palynomorphs defining kerogen Type II. PFA-1 indicates predominant deposition in proximal active fluvio-deltaic sources to marginal marine conditions with enhanced contributions of terrestrial/riverine influx. PFA-2 and PFA-3 reveal deposition under an enhanced dysoxic to anoxic proximal inner neritic shelf due to the abundant occurrences of spores and coastal to shallow marine dinoflagellate cysts. PFA-4 suggests deposition under enhanced suboxic to anoxic distal inner neritic conditions because of enhanced AOM and abundant proximate and some chorate dinoflagellate cysts. Thus, the Middle Jurassic experienced a predominantly marginal to shallow water column in this part of the southern margin of the Tethyan Ocean where the Matruh, Shushan, and Dahab-Mireir Basins were located. Full article

This paper presents the diatom and palynomorph data from a sediment trap deployed in the northern part of the East Barents Sea for an annual cycle from August 2017 to August 2018. The average monthly fluxes of diatoms and dinoflagellate cysts in the photic layer of the northeastern part of the Barents Sea varies from 10.4 × 10³ to 640.8 × 10³ valves m⁻² day⁻¹ and from 0.3 × 10³ to 90.0 × 10³ cysts m⁻² day⁻¹, respectively. Their fluxes are related to the low irradiance of the photic layer during the sea-ice cover period, dominance of southward currents, modern climate, and nepheloid layer conditions. Based on redundancy analysis of the relationship between the fluxes of diatoms and dinoflagellate cysts and organic carbon fluxes, sea-ice covers, and the seasonal cycle of light availability we determined the following. First, sea-ice-associated diatoms and dinocysts are exported to the sediment trap from the melting sea ice with a two-week delay. Second, the appearance of freshwater diatoms and green algae in the sinking material accumulating from March 2018 to July 2018 is also related to the melting of sea ice. And third, the presence of Coscinodiscus radiatus, C. perforatus, Shionodiscus oestrupii and Operculodinium centrocarpum in the diatoms and dinocysts species composition throughout the year indicates the advection of Atlantic waters into the Barents Sea up to 80° N. Full article

The Eocene-Miocene successions recovered at DSDP sites on the Jan Mayen Ridge (NE Atlantic) and on the adjacent East Greenland margin provide a sedimentary record of the rifting and separation of the Jan Mayen Microcontinent from East Greenland. A combination of palynology, conventional heavy mineral analysis, single-grain major and trace element geochemistry and radiometric dating of amphibole and zircon has revealed a major change in sediment provenance took place at the Early/Late Oligocene boundary corresponding to a prominent seismic reflector termed JA. During the Eocene and Early Oligocene, lateral variations in provenance character indicate multiple, small-scale transport systems. Site 349 and Kap Brewster were predominantly supplied from magmatic sources (Kap Brewster having a stronger subalkaline signature compared with Site 349), whereas Site 346 received almost exclusively metasedimentary detritus. By contrast, Late Oligocene provenance characteristics are closely comparable at the two Jan Mayen sites, the most distinctive feature being the abundance of reworked Carboniferous, Jurassic, Cretaceous and Eocene palynomorphs. The Site 349 succession documents an evolution in the nature of the magmatic provenance component. Supply from evolved alkaline magmatic rocks, such as syenites, was important in the Middle Eocene and lower part of the Early Oligocene, but was superseded in the later Early Oligocene by mafic magmatic sources. In the latest Early Oligocene, the presence of evolved clinopyroxenes provides evidence for prolonged magmatic fractionation. Initial low degrees of partial melting led to generation of alkaline (syenitic) magmas. The extent of partial melting increased during the Early Oligocene, generating basaltic rocks with both subalkaline and alkaline compositions. Towards the end of the Early Oligocene, the amount of partial melting and magma supply rates decreased. In the Late Oligocene, there is no evidence for contemporaneous igneous activity, with scarce magmatic indicator minerals. The provenance change suggests that the hiatus at the Early/Late Oligocene boundary represents the initiation of the proto-Kolbeinsey Ridge and separation of the Jan Mayen Microcontinent from East Greenland. Full article

Widespread deposition of pelagic-hemipelagic sediments provide an archive for the Late Cretaceous greenhouse that triggered sea level oscillations. Global distribution of dinoflagellate cysts (dinocysts) exhibited a comparable pattern to the eustatic sea level, and thus, considered reliable indicators for sea level and sequence stratigraphic reconstructions. Highly diverse assemblage of marine palynomorphs along with elemental proxies that relate to carbonates and siliciclastics and bulk carbonate δ¹³C and δ¹⁸O from the Upper Cretaceous Abu Roash A Member were used to reconstruct short-term sea level oscillations in the Abu Gharadig Basin, southern Tethys. Additionally, we investigated the relationship between various palynological, elemental, and isotope geochemistry parameters and their response to sea level changes and examined the link between these sea level changes and Late Cretaceous climate. This multiproxy approach revealed that a long-term sea-level rise, interrupted by minor short-term fall, was prevalent during the Coniacian-earliest Campanian in the southern Tethys, which allowed to divide the studied succession into four complete and two incomplete 3^rd order transgressive-regressive sequences. Carbon and oxygen isotopes of bulk hemipelagic carbonates were calibrated with gonyaulacoids and freshwater algae (FWA)-pteridophyte spores and results showed that positive δ¹³C_carb trends were consistent, in part, with excess gonyaulacoid dinocysts and reduced FWA-spores, reinforcing a rising sea level and vice versa. A reverse pattern was shown between the δ¹⁸O_carb and gonyaulacoid dinocysts, where negative δ¹⁸O_carb trends were slightly consistent with enhanced gonyaulacoid content, indicating a rising sea level and vice versa. However, stable isotope trends were not in agreement with palynological calibrations at some intervals. Therefore, the isotope records can be used as reliable indicators for reconstructing changes in long-term sea level rather than short-term oscillations. Full article

We present analyses of macroscopic and microscopic remains as a tool to characterise sedge fen peats. We use it to describe peat composition and stages of peat decomposition, to assess the success of rewetting of a formerly drained fen, and to understand the workings of these novel ecosystems. We studied two percolation fen sites, one drained and one drained and rewetted 20 years ago. Years of deep drainage have resulted in a layer of strongly decomposed peat which lacks recognizable macro-remains. We could associate micro-remains with macro-remains, and thus still characterise the peat and the plants that once formed it. We show that the strongly decomposed peat is of the same origin as the slightly decomposed peat below, and that is was ploughed. We present descriptions of eight types of the main constituent of sedge peat: plant roots, including Carex rostrata type, C. lasiocarpa/rostrata type, C. limosa type, C. acutiformis type, C. echinata type, Phragmites australis type, Cladium type, Equisetum type. We describe three new non-pollen palynomorph types (microscopic remains) and five new subtypes. The rewetted fen provides insights into plant succession after rewetting and the formation of peat that predominantly consists of roots. Results indicate that leaf sheaths may be a consistent component of the peat. Full article