1,766,830 research outputs found
Stable isotope stratigraphy of the early Quaternary of borehole Noordwijk, southern North Sea
Full text linkBetween 2.58Ma and 2.4Ma, most of the present onshore sector of the Netherlands was an epicontinental sea. Previous studies suggest the occurrence of multiple cold and warm phases in shallow marine successions of the Maassluis Formation in conjunction with the first prominent Northern Hemisphere ice sheet expansions. Nevertheless, correlation with deep marine isotope stages is tentative and relies on relative dating as absolute dating techniques are difficult to apply. Here, we present for the first time an early Quaternary, high-resolution benthic stable isotope record from the onshore sector of the Netherlands, taken from borehole Noordwijk. We tune our record to MIS 100-94 using the characteristic δ18O signature and complementary biostratigraphic data. This new high resolution isotope chronology is providing important insights on stratigraphy and palaeoenvironmental development of the southern North Sea area during the early Quaternary
Chronology with a pinch of salt:Integrated stratigraphy of Messinian evaporites in the deep Eastern Mediterranean reveals long-lasting halite deposition during Atlantic connectivity
Full text linkThe Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is considered an extreme environmental event driven by changes in climate and tectonics, which affected global ocean salinity and shaped the biogeochemical composition of the Mediterranean Sea. Yet, after more than 50 years of research, MSC stratigraphy remains controversial. Recent studies agree that the transition from the underlying pre-evaporite sediments to thick halite deposits is conformal in the deep Eastern Mediterranean Basin. However, the age of the base and the duration of halite deposition are still unclear. Also disputed is the nature of the intermediate and upper MSC units, which are characterized as periods of increased clastic deposition into the Eastern Mediterranean based on marginal outcrops and seismic data. We provide a multidisciplinary study of sedimentary, geochemical, and geophysical data from industrial offshore wells in the Levant Basin, which recovered a sedimentary record of deep-basin Mediterranean evaporites deposited during the MSC. In combination with previous observations of the MSC throughout the Mediterranean Basin, our results promote the need for a new chronological model. Remarkably, the one-kilometer-thick lower part of the evaporitic unit is composed of essentially pure halite, except for a thin transitional anhydrite layer at its base. The halite is undisturbed and homogeneous, lacking diverse features apparent in more proximal sections, indicating a deep-sea depositional environment. We find that distinct, meters-thick non-evaporitic intervals interbedded with the halite, previously thought to be clastic layers, are diatomites. While XRD analysis confirms an increase in clastic components in these sediments, they are composed primarily of well-preserved marine and freshwater planktonic diatoms. The occurrence of marine planktonic diatoms in these intervals indicates the input of Atlantic waters into the Mediterranean Basin during the deposition of the massive halite unit. Seismic stratigraphy and well-log cyclostratigraphy further support deep basin halite deposition, which started about 300 kyr earlier than widely assumed (~5.97 Ma). We propose that halite deposition in the deep Mediterranean took place during stage 1 of the MSC, rather than being limited to the short 50 kyr MSC acme when sea level was presumably at its lowest. Thus, brine formation, salt precipitation, and faunal extinction occurred at least in part in a deep, non-desiccated basin, with a restricted yet open Mediterranean-Atlantic connection that allowed inflow of oceanic water. We observe an increase in heavy minerals and reworked fauna within the clastic-evaporitic, Interbedded Evaporites of the basinal MSC section, and argue that these settings correspond in the deep basins with a significant sea-level drawdown during stage 2 of the MSC, as observed in the marginal sections. This correlation is corroborated by astrochronology and chemostratigraphic markers, such as the distribution of n-alkanes and biomarker-based thermal maturity indices. The Levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep-basin deep-water halite, while sea-level drawdown promoted deposition of reworked and transported material from the margins into deep Mediterranean basins. This study modifies the current understanding of the mechanisms governing salt deposition throughout the MSC with implications for other evaporitic events in the geologic record.</p
Stratigraphy and Geochemistry of the Vossenveld Formation
Full text linkThe Winterswijkse Steengroeve quarry complex in the east of the Netherlands exposes a ~ 40 m thick sedimentary sequence of intertidal and shallow marine deposits of the Vossenveld Formation dated as Anisian (early Middle Triassic). Here, we present a detailed stratigraphic and sedimentological description combined with geochemical data (carbonate content, spectral gamma ray, magnetic susceptibility, stable isotopes) of the sedimentary sequence in the Winterswijkse Steengroeve. Stable isotope ratios point to paleotemperatures in the range of 25 to 35 °C. These high temperatures in combination with the shallow enclosed character and proximity to the equator made the environment particularly susceptible to substantial evaporation and likely very saline. The concentration of predominantly isolated skeletal fossils resulted from storm activity. Unexpected is the overall increasing salinity in combination with the occurrence of larger sauropterygians in the top 10 m, accompanied by the halophytic bivalve Neoschizodus orbicularis. A subsequent literature study of the distribution of the sauropterygian genera described from the Vossenveld Formation sheds light on their deposition and burial conditions. The combined isotopic, geochemical, and sedimentological study on the Vossenveld Formation elucidates the depositional environment in which the rich fossil assemblage of Winterswijk is preserved. The obtained information on the preservation and paleoenvironment is pivotal in understanding the mode and pacing of the biotic recovery after the end-Permian mass extinction
The El Masnou Infralittoral sedimentary environment (Barcelona province, NW Mediterranean Sea): morphology and Holocene seismic stratigraphy
Full text linkA detailed analysis of the morphology and the Holocene seismic and sequence stratigraphy and architecture of the infralittoral sedimentary environment of the El Masnou coast (Catalonia, NW Mediterranean Sea) was carried out using multibeam bathymetry and GeoPulse seismic data. This environment extends down to 26-30 m water depth, and is defined morphologically by two depositional wedges whose seafloor is affected by erosive furrows, slides, fields of large- and small-scale wavy bedforms, and dredging trenches and pits. Erosive terraces are also identified in the transition domain toward the inner continental shelf. The Holocene stratigraphy of the infralittoral environment is defined by two major seismic sequences (lower and upper), each one formed by internal seismic units. The sequences and units are characterised by downlapping surfaces made up of deposits formed by progradation of coastal lithosomes. The stratigraphy and stratal architecture, displaying a retrogradational arrangement with progradational patterns of minor order, were controlled by different sea-level positions. The stratigraphic division represents the coastal response to the last fourth-order transgressive and highstand conditions, modulated by small-scale sea-level oscillations (≈1-2 m) of fith to sixth order. This study also highlights the advantage of an integrated analysis using acoustic/seismic methods for practical assessment of the anthropogenic effects on infralittoral domains based on the association of marine geological observations
Klimaatextremen
No full textOns menselijk besef van klimaatextremen beperkt zich in grote mate tot kortstondige periode van excessieve weersomstandigheden. Door de wereldwijde opwarming van de aarde is er een toenemende ongerustheid dat deze extremen vaker zullen voorkomen. Maar hoe verontrustend is die opwarming van de aarde nu eigenlijk? Of is er toch een nieuwe ijstijd in het vooruitzicht? In zijn oratie ‘Klimaatextremen’ plaatst Lucas Lourens de huidige opwarming van de aarde in een geologisch perspectief, waarbij wordt ingegaan op extreme broeikasperioden, die de aarde 56-50 miljoen jaar geleden teisterden en de invloed van astronomische cycli op het klimaat. Het vakgebied paleoklimatologie bestudeert klimaatveranderingen die in het verleden hebben plaatsgevonden op basis van reconstructies en modelstudies. Voor de reconstructies worden verschillende indicatoren gebruikt, zoals de stabiele isotopensamenstelling van foraminiferen. Dit zijn eencellige micro-organismen, die een kalkschaaltje maken dat in grote aantallen als gefossiliseerd materiaal in diepzee sedimenten wordt aangetroffen. Mede door de ontwikkeling van hoge resolutie astronomische dateringtechnieken worden er steeds nauwkeuriger klimaatreconstructies gemaakt, die kunnen worden gebruikt om de uitkomsten van lange tijdexperimenten met geavanceerde klimaatmodellen te toetsen. Door de vraag naar steeds betrouwbaardere modellen om toekomstscenario’s beter te kunnen voorspellen zal dit multidisciplinaire vakgebied zich blijven ontwikkelen
The asbian to arnsbergian conodonts and sequence stratigraphy of the Northumberland trough
Full text linkYoredale sequences are excellent exemplars of the sequence stratigraphy model; the spacial and temporal variation of these complex shallow marine/fluvio-deltaic/ coastal plain cycles, exhibit all the uiternal facies architecture that would be expected of a shelf succession. The detailed analysis of Yoredale successions has led to the designation of 15 sequences during the Namurian, which have true chronostratigraphic value. The stacking pattern of Yoredale sequences shows that deposition during the Asbian-Arnsbergian was influenced by three orders of eustatic sea-level change (high, medium and low frequency), which produced three orders of sequence stratigraphic unit (sequences, sequence sets and mega-sequences). Though all three orders of eustatic sea-level change had an influence on deposition, it was the interference of the cycles that produced the major sequence stratigraphic events. Almost two hundred conodont samples, contammg 1039 identifiable elements, representing eleven species, have been used m this study. The multielement species described in the systematic palaeontology and the extensive synonymy lists are a useful addition to British mid-Carboniferous conodont taxonomy. Five biozones have been erected based upon the first appearance of conodont species. The three Brigantian biozones can each be confidently related to a significant rise in sea level caused by the constructive interference of all three frequencies of sea-level cycle. Whatsmore, each successive biozone is related to a deeper water species which corresponds to the long-term rise in the low-frequency sea-level cycle during this period. The palaeoecology of the Great Lunestone was studied using constrained serration. This proved a clear shallo wing-up ward trend and was used to define four biofacies. A comparison between biofacies distribution and sequence stratigraphy proved an intimate relation between sea-level change and the resulting distribution of nekto- benthonic biofacies
Rodents from the Upper Miocene Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey)
No full textThe upper Miocene assemblages of rodents collected from two layers of the type section of the Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey) are described. The assemblage from the lower level is considerably less diverse than that from the upper level. It contains Progonomys together with Megacricetodon, which is a very unusual association. The assemblage from the upper layer shows a relatively high diversity with four species of Gliridae instead of only one in the lower layer. Apart from the more diverse Gliridae, Byzantinia sp., Spermophilinus, Keramidomys and Myocricetodon appear in the upper layer. The absence of Murinae in the assemblage from the upper layer is very unexpected, because they usually become dominant soon after their arrival. Their unusual subsequent absence may be either due to a significant change from an open and humid environment to a more dry and wooded environment or to taphonomic bias. Both rodent faunas are assigned to local zone I, which is correlated to the lower Vallesian (MN9)
Linking Diagenesis to Sequence Stratigraphy: An Integrated Tool for Understanding and Predicting Reservoir Quality Distribution
No full textSequence stratigraphy is a useful tool for the prediction of primary (depositional) porosity and permeability. However, these primary characteristics are modified to variable extents by diverse diagenetic processes. This chapter demonstrates that integration of sequence stratigraphy and diagenesis is possible because the parameters controlling the sequence stratigraphic framework may have a profound impact on early diagenetic processes. The latter processes play a decisive role in the burial diagenetic and related reservoir-quality evolution pathways. Therefore, the integration of sequence stratigraphy and diagenesis allows a proper understanding and prediction of the spatial and temporal distribution of diagenetic alterations and, consequently, of reservoir quality in sedimentary successions.</p
A specimen of Canis cf. C. etruscus (Mammalia, Carnivora) from the Middle Villafranchian of the Oosterschelde
Full text linkA recent find of a Middle Villafranchian (c. 2.35–2.10 Ma) Canis cf. C. etruscus in the trawlings from the Oosterschelde concerns the oldest dog known from the Netherlands and is the first appearance record of this canid in the North Sea Basin. It shows that the tribe Canini was dispersed beyond south central Europe up to the northwestern edge of the continent. The find confirms the lack of synchroneity and usefulness of the so-called ‘Wolf Event’
- …
