Displays

Accurate stable isotope stratigraphies are essential for understanding how past climates are influenced by orbital forcing. Deep-sea benthic foraminiferal δ¹⁸O and δ¹³C stratigraphies can provide precise astronomical age control and record changes in past deep-sea ocean temperatures, global ice volume and the carbon cycle. Our understanding of Plio-Pleistocene climate dynamics has improved through the development of global (LR04; Lisiecki & Raymo, 2005) and regional stacks (Ceara Rise; Wilkens et al., 2017). However, the late Miocene climate system remains poorly understood, in part because the late Miocene benthic foraminiferal δ¹⁸O stratigraphy is notoriously low amplitude.

Here, we present the first global late Miocene global benthic foraminiferal δ¹⁸O compilation spanning 8.00-5.33 Ma. We formed a “Base Stack” using six continuous benthic stratigraphies from the Atlantic (ODP Sites 982 (N), 926 (E) and 1264 (S)) and Pacific Oceans (IODP Sites U1337 and U1338 (E), ODP Site 1146 (W)). To avoid misidentification of individual excursions between sites, we verified existing splices, generated isotope data where necessary and established independent astrochronologies. To accompany the “Base Stack”, we compiled a “Comprehensive Stack”, which incorporates single-hole benthic δ¹⁸O stratigraphies to optimise global coverage.

The new global late Miocene benthic foraminiferal δ¹⁸O stack represents a stratigraphic reference section back to 8.00 Ma. The stack is accurately tied to the Geomagnetic Polarity Time Scale between Chrons C3r and C4n.2n using the magnetostratigraphy from IODP Site U1337. We recognise 68 new δ¹⁸O Marine Isotope Stages (MIS) between 7.7 and 6.5 Ma. An exceptional global response is imprinted on the dispersed sites between 7.7-6.9 & 6.4-5.4 Ma, when a strong 40 kyr heartbeat dominates the climate system. The origin of these cycles remains unclear. The influence of deep-sea temperature on the benthic δ¹⁸O stack is explored at IODP Site U1337 using Mg/Ca data. The dominant 40-kyr δ¹⁸O cycles are asymmetric, suggesting at least a partial ice volume imprint and raising the possibility that these cycles relate to early signs of northern hemisphere glaciation.

How to cite: Drury, A. J., Westerhold, T., Hodell, D., White, S., Ravelo, A. C., and Wilkens, R.: Constraints on late Miocene ice volume variability from a global benthic δ18O compilation (8.0-5.0 Ma), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16771, https://doi.org/10.5194/egusphere-egu2020-16771, 2020.

Numerous boreholes of the OMV oil company penetrate the northern Vienna Basin (VB) and several detailed analyses have been conducted on these drilling for years. Despite the effort of decades, the distribution and correlation of Neogene sediments throughout the basin remained ambiguous, due to the complex fault system of the VB. To resolve remaining issues of the Neogene deposits of the area OMV initiated detailed integrative stratigraphic analyses, combining biostratigraphical, lithological, modern 3D seismic- and geophysical data.

Paleontological analysis with main focus on micropaleontology, especially foraminifers, of 46 wells (more than 650 samples) of the northern Vienna Basin have been conducted and help to create a well resolved stratigraphic north – south cross-section of the Neogene units. Of particular interest were lower and middle Miocene (Ottnangian, Karpatian, Badenian and Sarmatian) units. Hardly known and described were the patchy lower Badenian deposits and the much more complex, than previously expected, middle Badenian units. Foraminiferal analysis revealed about 50.000 specimens belonging to 228 species and an allocation to local ecozones, biostratigraphic zonations and ecological reconstructions were established.

Additionally, 50 samples have been analyzed for calcareous nannoplankton which showed extreme reworking throughout all successions.

Some samples displayed the underlying Mesozoic limestones and cutting samples of one well brought insights into the Cenozoic underling Rhenodanubian Flysch units of the Vienna Basin This huge and stratigraphic long ranging set of data did not just reveal major sedimentation gaps during the formation of the modern pull-apart basin, but also provided the opportunity to create a framework for a modern sequence stratigraphy re-assessment of the Vienna Basin.

Furthermore, a formalization of widely used formations in literature will be established in later steps of this project.

This project was financed by the OMV-AG.

How to cite: Kranner, M., Harzhauser, M., Mandic, O., Piller, W. E., Ćorić, S., Strauss, P., and Siedl, W.: Biostratigraphic correlation of Miocene drillings in the Vienna Basin (Austria) - Integrated Neogene stratigraphy of the largest onshore petroleum province in Central Europe (Vienna Basin, Austria), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13410, https://doi.org/10.5194/egusphere-egu2020-13410, 2020.

The Cretaceous Normal Polarity Superchron (CNPS, chron C34n, Aptian–Santonian, ~83–118 Ma in CK95 GPTS) is followed in the Campanian by two relatively long chrons (chron C33r, 3.925 My duration and then the normal chron C33n, 5.456 My duration) straddling most of the Campanian stage. The analysis of the geomagnetic reversal history has classically determined two nearly linear segments for the late Cretaceous–Cenozoic interval divided at chron C12r. The length of chrons in the younger interval has no systematic trend and henceforth is considered stationary for statistical analysis with a mean chron length of 0.248–0.219 My while the older segment has 0.749 My mean chron length. The stationarity for this latter interval is attained, however, when the two long polarity chrons C33r and C33n adjacent to the CNPS are omitted. Studies in the weakly magnetized southern England chalk succession and marine Bearpaw Shale in the Canadian Rockies from Alberta have argued about the presence of a number of reversals within C33r and C33n (and C34n). However, all these remain ambiguously established and not incorporated in the standard GPTS despite their significance for theories of geodynamo behavior and potentiality for high-resolution stratigraphic correlations that could notably impact, for instance, the chronostratigraphy of dinosaur-bearing terrestrial Upper Cretaceous of the Western Interior of North America. In any case, no polarity subchrons within C33r or C33n have been reported in any deep-sea record or in the landmark pelagic “scaglia” sections from the Gubbio area in the central Italian Apennines, for which a good integrated biostratigraphy and a thorough paleomagnetic record exists.

Here, we report on a new reverse subchron in the lower part of C33n, informally named the Postalm Fall Subchron (PFS), retrieved in the Postalm section (Gosau Group, Northern Calcareous Alps of Austria). The Postalm section shows a deepening trend from upper Santonian conglomerates and grey shelf marls to pelagic bathyal red marly limestones of Campanian age. The section has previously been studied in the frame of an integrated multi-proxy stratigraphic study that includes high-resolution calcareous plankton biostratigraphy, magnetostratigraphy, stable isotopes, strontium stratigraphy and Fe content. Robust paleomagnetic data has pinpointed the top of C34n that defines the Santonian-Campanian boundary together with key biostratigraphic markers in the lower part of the red unit. The integrated study extents upwards for about 170 m up to calcareous nannofossil zone UC16 in chron C32 in the late Campanian. The cyclic nature of the pelagic sequence has been studied by means of spectral analysis on the limestone/marl couplet thickness data and geochemical proxies that allows identifying the short and long eccentricity cycles and to establish a cyclostratigraphic framework. From 33 new tightly collected samples in this study, 23 display unambiguous reverse polarity and conform the PFS subchron that straddles 3–4 precession cycles (~70 ky duration) within the UC15b calcareous nannofossil biozone. The average sediment accumulation rate at Postalm (~2 cm/ky compared to ~0.6–1 cm/ky at Gubbio) and the high-quality paleomagnetic signal have favored this discovery. The absolute age calibration and related geomagnetic and chronostratigraphic implications would be discussed.

How to cite: Dinarès-Turell, J., Wolfgring, E., and Wagreich, M.: A new reverse subchron (C33n.1r) in the Campanian: astronomical duration estimate and geomagnetic/chronostratigraphic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1677, https://doi.org/10.5194/egusphere-egu2020-1677, 2020.

The Barents Sea Shelf on the north-western corner of the Eurasian plate has a complex geological history, comprising large-scale processes controlled by plate movements, climatic variations and changing depositional environments. During the last decades, as the search for hydrocarbons within the area gained increased interest, Triassic sequences have been the target of comprehensive investigations. In our project, we test the potential of improving the correlation of Triassic strata using X-ray fluorescence (XRF) core scanning of siliciclastic drill cores.

XRF core scanning is a frequently used method on soft sediment cores, e.g. within marine geology and palaeo-climate studies. However, the applicability of this method on drill cores from exploration wells from the hydrocarbon industry has not been tested so far. We use this method to establish geochemical stratigraphic parameters, as well as to contribute to the identification of provenances, reconstruct palaeo-envrionments, and support the correlation of drill cores. This provides a novel, fast, inexpensive, and non-destructive method to be applied in hydrocarbon exploration, as well as in studies of lithified siliciclastic sediments in general.

Triassic intervals from 24 shallow drill cores from the southern Barents Sea (Finnmark Platform, Nordkapp Basin, Svalis Dome, Maud Basin and Bjarmeland Platform) provide the basis for this study. The cores have previously been comprehensively studied and described by IKU (the Norwegian Continental Shelf Institute; today SINTEF Petroleum Research), and studies of provenance and palaeo-environment have also been performed (e.g. Vigran et al., 1986). This data makes it possible to compare the geochemical units established in this study with other stratigraphic information.

We present preliminary results of establishing geochemical units from XRF core scanning, and the use of these for correlation within known stratigraphic frameworks and between geographic areas, as well as to increase the understanding of changes in provenance and palaeo-environments within these successions in the Barents Sea.

References:
Vigran, J.O., G. Elvebakk, T.L. Leith, T. Bugge, V. Fjerdingstad, R.M. Goll, R. Konieczny, and A. Mørk. 1986. 'Dia-Structure Shallow Drilling 1986. Main data report. IKU Rep. No. 21.3420.00/04/86, 242 pp'.

How to cite: Kvendbø Hegstad, S. M., Ahokas, J., Forwick, M., and Grundvåg, S.-A.: Chemostratigraphy of Triassic successions on the southern Barents Sea Shelf – preliminary results from XRF Core Scanning., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10299, https://doi.org/10.5194/egusphere-egu2020-10299, 2020.

            The rise of animals occurred during an interval of Earth history that witnessed highly dynamic atmosphere-ocean redox conditions; regional, transient glaciations; extraordinarily low magnetic field intensities potentially related to inner core formation; and perturbations to the global carbon cycle of a size not seen before or since. The largest of these, the Shuram carbon isotope excursion, has been invoked as a driving mechanism for, or consequence of, various biological and geological events during the Ediacaran Period. However, there are a number of major controversies regarding the Shuram, including its timing. Without age constraints on its onset or duration, it is impossible to confidently connect the Shuram Event with any biological or geological upheavals.

Here, we apply multiple methods, including Re-Os on black shales and U-Pb LA-ICP-MS dating on carbonates, to well-preserved Ediacaran stratigraphy from Oman, deriving new age controls in previously undated parts of the stratigraphy. Our new data show that paired Re-Os shale and U-Pb carbonate analyses constrain the onset and duration of the Shuram excursion in Oman. The results—which are consistent with recent age constraints on Shuram-bearing stratigraphy from Northwest Canada (Rooney et al. 2019, Goldschmidt)—demonstrate the utility of leveraging multiple geochronological techniques within a single basin to constrain deposition in deep to shallow depositional environments. The results also provide key absolute age constraints on the onset of the Shuram excursion in the stratigraphy where it was first defined, critical for testing global correlation schemes, constructing a temporal framework for the Ediacaran period, and identifying causal mechanisms during this interval of geobiological and geodynamic dynamism.

How to cite: Cantine, M., Rooney, A., Linneman, U., Hofmann, M., Albert, R., Gomez Perez, I., Baloushi, B., Gerdes, A., and Bergmann, K.: Geochronologic constraints on the Shuram excursion in Oman, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10839, https://doi.org/10.5194/egusphere-egu2020-10839, 2020.

Cyclostratigraphy is increasingly used to improve the Geologic Time Scale and our understanding of past climatic systems. However, except in a few existing methodologies, the quality of the results is often not evaluated.

We propose a new methodology to document this quality, through a decomposition of a signal into a set of narrow band components from which instantaneous frequency and amplitude can be computed, using the Hilbert transform. The components can be obtained by Empirical Mode Decomposition (EMD), but also by filtering a signal (be it tuned or not) in any relevant way, and by subsequently performing EMD on the signal minus its filtered parts.

From that decomposition, verification is performed to estimate the pertinence of the results, based on different concepts that we introduce:

•  Integrity quantifies to what extent the sum of the components is equal to the signal. It is defined as the cumulated difference between (1) the signal, and (2) the summed components of the decomposition. EMD fulfils integrity by design, except for errors caused by floating-decimal arithmetic. Ensemble Empirical Mode Decomposition (EEMD) may fail to satisfy integrity unless noisy realisations are carefully chosen in the algorithm to cancel each other when averaging the realisations. We present such an algorithm implemented in R: “extricate”, which performs EEMD in a few seconds.
•  Parsimony checks that the decomposition does not generate components that heavily cancel out. We propose to quantify it as the ratio between (1) the cumulated absolute values of each component (except the trend), and (2) the cumulated absolute values of the signal (minus the trend). The trend should be ignored in the calculation, because an added trend decreases the parsimony estimation of a similar decomposition.
•  IMF departure (IMFD) quantifies the departure of each component to the definition of intrinsic mode functions (IMF), from which instantaneous frequency can reliably be computed. We define it as the mean of the absolute differences of the base 2 logarithms of frequencies obtained using (1) a robust generalized zero-crossing method (GZC, which simplifies the components into extrema separated by zero-crossings) and (2) a more local method such as the Hilbert Transform.
•  Reversibility is the concept that all initial data points are preserved, even after linear interpolation and tuning. This allows to revert back to the original signal and discuss the significance of each data point. To facilitate reversibility we introduce the concept of quanta (smallest depth or time interval having significance for a given sampling) and an algorithm computing the highest rational common divisor of given values in R: “divisor”.

This new methodology allows to check the final result of cyclostratigraphic analysis independently of how it was performed (i.e. a posteriori). Once the above-mentioned concepts are taken into account, the instantaneous frequencies, ratios of frequencies and amplitudes of the components can be computed and used to interpret the pertinence of the analysis in a geologically meaningful way. The instantaneity and independence of frequency and amplitude so obtained open a new way of performing time-series analysis.

How to cite: Wouters, S., Crucifix, M., Sinnesael, M., Da Silva, A.-C., Zeeden, C., Zivanovic, M., Boulvain, F., and Devleeschouwer, X.: A posteriori verification methodology for astrochronology: a step further to improve the falsifiability of cyclostratigraphy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10874, https://doi.org/10.5194/egusphere-egu2020-10874, 2020.

The origin of carbonatic rhythmically alternating lithologies, called limestone-marl alternations (LMA), is a lively debated topic. LMA are commonly used as high-resolution cyclostratigraphic record, but diagenetic studies indicate that not all LMA reflect genuine differences in the original composition driven by environmental changes. LMA with a clear difference between limestones and marls in their ratios of diagenetically inert elements such as Al₂O₃/TiO₂ can be identified as the product of primary sedimentary differences, i.e. variation affecting the terrigenous compound of the precursor sediment. In contrast, LMA without these differences could be the product of (1) variations in the carbonate compounds of the precursor sediment, i.e. aragonite and calcite input, or of (2) the distortion of the latter by diagenetic carbonate redistribution, or of (3) diagenetic carbonate redistribution in a homogenous precursor sediment. The problem of differentiating these three cases is known as the diagenetic dilemma. The question is, how can the composition in the original CaCO₃ compound (aragonite, calcite) of the precursor sediment be reconstructed? This study provides a new approach to tackle the diagenetic dilemma. According to the model of differential diagenesis, the concentration of trace elements is inversely proportional to the amount of diagenetically redistributed carbonate. Consequently, the difference between the ratios of diagenetically inert elements from two adjacent beds is a measure for carbonate redistribution between them. This is quantifiable by calculating the vector length between these ratios for two adjacent beds. The new approach is illustrated here by evaluating 75 contiguous limestone and marl beds from the Högklint Formation (Silurian) on Gotland, Sweden. To test the new method, trace elements in these beds were compared according to their relative solubility during diagenesis. All elements which are either bound to clay minerals or fit into the calcite lattice show the same pattern of vector lengths (

How to cite: Nohl, T., Steinbauer, M., Sinnesael, M., and Jarochowska, E.: Detecting original variations in calcite and aragonite input in limestone-marl alternations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1531, https://doi.org/10.5194/egusphere-egu2020-1531, 2020.

Assessing the rift to sag evolution of Parnaíba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance

Rodrigo I. Cerri¹; Lucas V. Warren¹; Mario L. Assine^1
1 São Paulo State University (UNESP), Institute of Geosciences and Exact Sciences, Rio Claro, Brazil.

Nowadays one of the most prolific topics in the geological sciences is the origin of intracratonic basins. Despite many Paleozoic examples in which rift systems occur under these basins, there is no consensus about how these mechanical subsidence basins influenced the origin of continental-scale intracratonic basins. Due to its inherent complexity, the understanding of this problem only comes from integrated studies based in multi-proxy analysis, placing it on the frontier of modern science. In the northeast part of Brazil, the Late-Precambrian to Early-Cambrian Jaibaras Basin is interpreted as the precursor rift of the Parnaíba intracratonic Basin, following a simple model of mechanical-to-thermal subsidence evolution. In order to assess the provenance patterns and maximum depositional ages (MDA) between the rift and cratonic phases of these basins, we present a novel detrital zircon U-Pb ages of rocks from the Aprazível and Ipu formations. The main goals of this approach is to identify provenance changes (or similarities) between the last rift related sedimentary unit of the Jaibaras Basin and the first intracratonic related sedimentary unit form the Parnaíba Basin, thus allowing to test the rift-to-sag hypothesis. The MDA for the Aprazível Formation (ca. 499 ± 5 Ma, Furongian to Miaolingian) indicates a Late Cambrian age for the upper part of the Jaibaras Basin. The Ipu Formation records a MDA of ca. 528 ± 11 Ma (Terreneuvian to Series 2, Early Cambrian). However, due to its stratigraphic position relative to the lower Aprazível (499 ± 5 Ma) and upper Tianguá (Early Silurian, Llandovery) formations, the depositional age of this unit is probably younger (Late-Cambrian to Early-Ordovician). Thus, the successions deposited in the end of the rift and the beginning of the sag phase are clearly separated by a regional unconformity (10 to 30 Ma). We also identify the complete absence of Cambrian zircons followed by a significant increase in Paleoproterozoic ones in the Ipu Formation. Although these units were significantly sourced by Neoproterozoic terrains (especially Ediacaran), this modification indicates an interesting change in provenance between the rift to sag basins. The detrital zircon provenance, helped by a consistent paleocurrent analysis, reveal local source areas for the Aprazível Formation and a consistent distal sedimentary transport towards NW for the Ipu Formation. This suggests that the primary sources for the first cratonic unit of Parnaíba Basin were located at the orogenic areas related with the Neoproterozoic Brasiliano/Pan-African Orogeny at the south/southern of Borborema Province (e.g. Rio Preto, Riacho do Pontal and Rio Grande do Norte metamorphic belts). Unlike the alluvial-related Aprazível Formation, the Ipu Formation characterizes a huge fluvial system that flowed towards NW, probably following a homoclinal ramp-like tilted and opened to the paleomargins of Gondwana.

How to cite: Cerri, R. I., Warren, L. V., and Assine, M. L.: Assessing the rift to sag evolution of Parnaiba Basin, NE Brazil, through U-Pb detrital zircon geochronology and provenance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-141, https://doi.org/10.5194/egusphere-egu2020-141, 2020.

The Late Paleozoic Ice Age (LPIA), one of the best known and prolonged glaciation events in Earth's history, resulted in the deposition of glacial sediments over Gondwana. The terminal deglaciation, a diachronic event starting earlier at the western and later in the eastern part of the continent, caused sea level rise and the widespread deposition of transgressive sedimentary successions. The Paraná Basin is one of these basins recording both glacial influenced (Itararé Group) and post-glacial (Guatá Group) deposits. However, the absence of Carboniferous and Permian guide fossils has motivated a chronostratigraphic approach based on plants and palynomorphs, which associated with sparse radioisotopic ages have suggested that transition between the glacial-influenced and the post-glacial succession would have occurred in the Sakmarian, early Permian (Holz et al., 2010).  These results are in conflict with recent studies that indicate LPIA glacial deposits are constrained to the Carboniferous (Cagliari et al., 2016; Griffis et al., 2019). Therefore, in this study we present new high-precision single-crystal CA-ID-TIMS U-Pb radioisotopic ages for the glacial influenced (one samples) and post-glacial (six samples) deposits in the southern Paraná Basin. Along with these new radioisotopic ages, a Bayesian age-depth model was applied to constrain the age of the LPIA demise in the southern Paraná Basin, which also represents the icehouse-greenhouse transition. The resulting age for the Rio do Sul Formation, topmost unit of the Itararé Group, is Ghzelian (Carboniferous). For the Rio Bonito Formation, basal Guatá Group, all samples are Asselian (Permian). The results reinforce that glacial-influenced deposits in the southern Paraná Basin are constrained to the Carboniferous. Based upon the depth-age model, the icehouse to greenhouse transition likely occurred in the Late Carboníferous. The integration between our results and recent published high-resolution U-Pb ages allowed us to detail the Carboniferous-Permian chronostratigraphic framework of the southern Paraná Basin.

References:

Holz, M., França, A.B., Souza, P.A., Iannuzzi, R., Rohn, R. (2010). A stratigraphic chart of the Late Carboniferous/Permian succession of the eastern border of the Paraná Basin, Brazil, South America. Journal of South American Earth Sciences 29, 381–399.

Cagliari, J., Philipp, R.P., Buso, V.V., Netto, R.G., Hillebrand, P.K., Lopes, R.C.L., Basei, M.A.S., Faccini, U.F. (2016). Age constraints of the glaciation in the Paraná basin: Evidence from new U–Pb dates. Journal of the Geological Society 173, 871–874.

Griffis, N.P., Montañez, I.P., Mundil, R., Richey, J., Isbell, J., Fedorchuk, N., Linol, B., Iannuzzi, R., Vesely, F., Mottin, T., Rosa, E., Keller, B., Yin, Q. (2019). Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana. Geology 47, 1146–1150.

How to cite: Cagliari, J., Schmitz, M. D., C. Lavina, E. L., and G. Netto, R.: U-Pb CA-IDTIMS geochronology of the Late Paleozoic glacial and post-glacial deposits in southern Paraná Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12101, https://doi.org/10.5194/egusphere-egu2020-12101, 2020.

The Ladinian/Carnian boundary (LCB) is defined at Prati di Stuores (GSSP of the Carnian Stage) with the First Appearance Datum (FAD) of ammonoid Daxatina canadensis and approximated by the FAD of conodont Paragondolella polygnathiformis. The age of the Carnian is currently estimated at ca. 237 Ma using the composite magnetostratigraphy of the main late Ladinian basinal sequences from literature, calibrated with a U-Pb radiometric age of 237.77±0.14 Ma from the Rio Nigra section in Alpe di Siusi (Dolomites, NE Italy). In the attempt to improve the precision of the Geomagnetic Polarity Time Scale (GPTS) around the LCB we investigated for magnetostratigraphy the Punta Grohmann section in the Dolomites. The Punta Grohmann section is calibrated with ammonoids (the FAD of Zestoceras cf. lorigae is considered a proxy of the LCB) and is chronologically constrained by two U-Pb radiometric ages from zircons (237.58±0.04 Ma; 237.68±0.05 Ma). The magnetostratigraphy of the Punta Grohmann section has been successfully correlated to other Ladinian-Carnian magnetostratigraphic sections (Prati di Stuores, Mayerling, Rio Nigra) and compared to the most recent version of the Triassic Geomagnetic Polarity Time Scale (GPTS). The LCB at Prati di Stuores is calibrated through magnetostratigraphy with the U-Pb radiometric datings of Punta Grohmann, obtaining an age of the LCB of ca. 237.4 Ma. Therefore, the Ladinian should be ca. 4 Myr long and the Carnian ca. 10.4 Myr long.

How to cite: Maron, M., Muttoni, G., Ghezzi, M., Rigo, M., and Gianolla, P.: New magnetostratigraphy from the Punta Grohmann section (Dolomites, NE Italy): an improvement of the Geomagnetic Polarity Time Scale around the Ladinian/Carnian boundary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11836, https://doi.org/10.5194/egusphere-egu2020-11836, 2020.

This project examines organic rich black shales from the Upper Jurassic on the Norwegian shelf. The aim is to investigate the relationship between the depositional environment as determined from facies descriptions and the magnetic properties of the black shale. An additional aim is to relate cyclicity in the magnetic measurements to the Milankovitch cycles using time series analysis techniques. Cores from four different location on the Norwegian shelf were investigated using sedimentological description, facies analysis, and measuring of bulk magnetic susceptibility. The cores were drilled in the Skagerrak Region in the North Sea (core 13/01-U-01), Møre-Trøndelag Region of the Norwegian Sea (core 6307/07-U-03 A), Lofoten Region of the Norwegian Sea (core 6814/04-U-02), and the Nordkapp Basin in the NE Barents Sea (core 7230/05-U-02).

Based on preliminary results from the sedimentological description and facies analysis, the sediments were separated into facies: (1) massive black mudstone, (2) siderite cemented mudstone, (3) lenticular laminated sandy mudstone, (4) flaser laminated muddy sandstone with silt clasts, (5) heavily bioturbated silty sandstone, and (6) sandstone. Deposits like high-density turbidites, debrites and slump deposits, as well as post depositional processes like bioturbation, pyrite- and siderite-cementation were found in the cores. Deposits from mass movements can be thick, but they are deposited over a short time interval. It is therefore important to remove the mass movement deposits in the cyclostratigraphic analysis. The high iron content in the siderite and pyrite cemented deposits must be taken into account in regard to the magnetic susceptibility measurements. The magnetic susceptibility data will be used to correlate the cores in the homogeneous black shale sections.

How to cite: Kimerud, J. K. and Felix, M.: Environmental controls on the magnetic properties of Upper Jurassic black shales on the Norwegian shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10406, https://doi.org/10.5194/egusphere-egu2020-10406, 2020.

A new δ¹³C reference curve for the Mesozoic is presented. This has been constructed using in excess of 10,000 published analyses of bulk carbonate sediments extracted from published literature.  Available data from sections world-wide were compiled for each stage and the stratigraphic trends visually compared.  Data sets used to construct the composite reference curve were those offering patterns that are consistent with other sections and offer the highest stratigraphic resolution (close sample spacing), constrained by biostratigraphic first appearance (FAD) and last appearance datum (LAD) levels, magnetostratigraphy, radiometric dates and cyclostratigraphy.  Preference was given to time series that showed the least scatter.  Pelagic carbonates proved most suitable for these purposes but data from hemipelagic and shallow-water carbonate sections were included where necessary. 

Age calibration was achieved using stage boundary ages, biostratigraphic FAD and LAD datums levels, and chron boundary ages derived from the new GTS2020 timescale.  Where possible, data from multiple authors and/or multiple stratigraphic sections were age-calibrated and interleaved to generate composite profiles for each time interval.  Data from individual stages were spliced together with offsets being avoided wherever possible; minor offsets in values were corrected where necessary to generate a continuous smooth time series.  The uneven geographical spread of published data and suitable lithofacies has resulted in source information being derived from different regions for different time intervals.  For example, the Early – Middle Triassic curve is constructed from eastern Paleotethys sections (South China), the Jurassic and Early Cretaceous curves principally from Tethyan areas of Europe and North Africa (Morocco, Portugal, southern France, Switzerland, northern Italy), and the Late Cretaceous curve from the Boreal Sea of northern Europe (England, Denmark).  The global significance of the resulting curves requires further testing.

The stratigraphic positions and recalibrated ages of positive and negative δ¹³C excursions that define carbon isotope events (CIEs) are presented.  These reflect major perturbation in the global carbon cycle.  Changes in the production and burial of organic matter on land and in the oceans, plus the balance between carbonate versus organic carbon deposition, are the principal mechanisms driving the observed long-term stratigraphic trends and short-term excursions.  These are linked to palaeogeographic and palaeoceanographic change, with climate and sea-level fluctuations driven by orbital forcing, tectonics, and volcanic events.  The emplacement of large igneous plateaus (LIPs) and associated volcanism likely played a major role in driving many of the palaeoenvironmental perturbations reflected in the carbon isotope stratigraphy. 

The most prominent CIEs characterise the Early Triassic with amplitudes exceeding 5‰ δ¹³C_carb (VPDB), with other notable excursions in the mid-Carnian, mid-Norian and Rhaetian.  The Toarcian negative CIEs are the stand-out feature of the Jurassic, but multiple lower amplitude CIEs occur throughout, notably in the Hettangian, Bajocian Callovian and Oxfordian.  The most prominent Cretaceous CIEs in the Valanginian, Aptian and at the Cenomanian/Turonian boundary are linked to Oceanic Anoxic Events.

How to cite: Jarvis, I.: Secular variation in the global carbon cycle during the Mesozoic: a new composite carbonate δ13C reference curve calibrated to GTS2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13553, https://doi.org/10.5194/egusphere-egu2020-13553, 2020.

The youngest time interval of the Cretaceous Period is known as the Maastrichtian, a reference to the marine strata exposed in the area surrounding the city of Maastricht, in the Netherlands-Belgium border region. The stratigraphic succession at the original type-locality of the Maastrichtian (ENCI quarry, NL) only covers the upper part of the Maastrichtian Stage as it is nowadays defined. However, in combination with similar rock sequences in several other quarries (e.g. Hallembaye, Curfs) in the region, a substantial part of the Maastrichtian Stage is represented.

While the type-Maastrichtian strata have provided a wealth of paleontological data, comparatively little geochemical work has been carried out on this succession. So far, the age assessment of, and stratigraphic correlation with, the type-Maastrichtian has been largely based on biostratigraphy and preliminary attempts at cyclostratigraphy, techniques that are hampered by bioprovincialism and the presence of stratigraphic gaps in the succession. In recent years, stable carbon isotope stratigraphy has been proven to be a powerful tool for correlating Upper Cretaceous strata on a global scale. When calibrated with biostratigraphic events, carbon isotope stratigraphy can be used to test the synchroneity of bio-events and reconcile inter-regional biostratigraphic schemes. Therefore, we have generated the first high-resolution stable carbon isotope stratigraphy for the type-Maastrichtian, using the extensive sample set acquired in the context of the Maastrichtian Geoheritage Project. In combination with elemental data generated using µXRF (e.g. Ca, Si, Al, Ti, Fe wt%), our record presents the first high-resolution chemostratigraphy for the type-Maastrichtian. This new chemostratigraphic framework enables us to refine the age-model for studied strata, and allows a better regional and global correlation with the type-Maastrichtian successions, placing the paleontological records from the type-Maastrichtian in a global context.  

How to cite: Vellekoop, J., Kaskes, P., Matthias, S., Jagt, J. W. M., Speijer, R. P., and Claeys, P.: A chemostratigraphic framework for the type-Maastrichtian, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13863, https://doi.org/10.5194/egusphere-egu2020-13863, 2020.

The Istria basin, situated in the NW Black Sea, is composed of Mesozoic to Cenozoic successions. The opening of the Western Black Sea, including the Istria basin, initiated in the late Early Cretaceous. Rifting and expansion continued in the Late Cretaceous, while in the Late Paleogene a compressional regime settled. In the Middle Eocene, the Western Black Sea basin margin inverted, due to the collision of Pontides and Taurides belts (Okay and Tüysüz, 1999; Dinu et al., 2005). The continuing compression shaped this basin until the Middle Miocene (Ionescu et al., 2002).

Tens of wells for hydrocarbon exploration were drilled in the Istria basin (Romanian offshore) since the 70’s. In this study, we have interpreted the acquired core reports containing litho- and biostratigraphic data. Based on identified calcareous nannofossil biozones, a continuous deposition was found in the Cenomanian-Maastrichtian interval. Lithologically, the Upper Cretaceous is composed of carbonatic rocks, such as limestones and marlstones, with intercalations of calcareous sandstones. The Eocene deposits are unconformably lying on Upper Cretaceous ones. Lithologically, the Eocene is characterized by alternating calcareous and siliciclastic sandstones. Biostratigraphy on planktonic and benthic foraminifers, as well as calcareous nannofossils, indicate a late Early Eocene to Middle Eocene age (i.e., late Ypresian to Bartonian).

The observed large thickness variation, from W towards E in the Istria Basin, is a consequence of various tectonic settings. The western part (i.e., the Sinoe area) is situated in the hanging-wall of an inverted normal fault filled with Early Eocene deposits and was inverted by high angle thrust fault during the Late Eocene-Oligocene interval. In the E (i.e., the Lebǎda area), there is an uplifted normal fault foot-wall, showing a reduced thickness in comparison with the W (Munteanu et al., 2011). The erosion level increased eastward, removing the entire Upper Eocene and the top of the Middle Eocene. This feature may be linked to a large sea level drop towards the Eocene top, with subaerial erosion and development of large-scale canyons system at the self to slope transition, like the Plio-Quaternary Viteaz Canyon of the NW Black Sea.

The financial support for this paper was provided by the Romanian Ministry of Research and Innovation, through the Programme Development of the National System of Research – Institutional Performance, Project of Excellence for Rivers-Deltas-Sea Systems No. 8PFE/2018.

References

Dinu, C., Wong, H.K., Țambrea, D., Mațenco, L., 2005. Stratigraphic and structural characteristics of the Romanian Black Sea shelf. Tectonophysics, 410, 417-435.

Ionescu, G., Sisman, M., Cataraiani, R., 2002. Source and reservoir rocks and trapping mechanism on the Romanian Black Sea shelf. In: Dinu, C., Mocanu, V. (Eds.) Geology and Tectonics of the Romanian Black Sea Shelf and its Hydrocarbon Potential. BGF Special Volume, 2, 67–83.

Munteanu, I., Maţenco, L., Dinu, C., Cloetingh, S., 2011. Kinematics of back-arc inversion of the western Black Sea basin. Tectonics, 30, TC5004.

Okay, A.I., Tüysüz, O., 1999. Tethyan sutures of northern Turkey. Geological Society, London, Special Publications, 156, 475-515.

How to cite: Anton, M. E., Munteanu, I., Dinu, C., and Melinte-Dobrinescu, M. C.: Upper Cretaceous and Eocene litho- and biostratigraphy of the Istria Basin (NW Black Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5033, https://doi.org/10.5194/egusphere-egu2020-5033, 2020.

A recent biostratigraphic re-evaluation of Ocean Drilling Program (ODP) Site 722 (Bialik et al., accepted, Paleoceanogr. and Paleocl.) provides new insights into the history of monsoon driven upwelling in the Arabian Sea between 15 and 8.5 Ma. They suggest the modern monsoon was only established after tectonic preconditioning, linked to the uplift of the Himalayas, closure of the Tethyan Seaway, and the inception of Indonesian Throughflow restriction. But the requisite topography for the Indian monsoon was already in place by at least the late early Miocene which suggests another driver. However, as northern hemisphere latitudinal heat gradients continued to be shallower than modern throughout the Miocene, steepening southern hemisphere gradients during the middle Miocene glaciation of Antarctica ~14.8 Ma (Pound et al., 2012, Earth-Sci. Rev., 112) may have played an important role in pacing the monsoon system during the middle to late Miocene.

Here we further explore these findings by using recently acquired X-ray fluorescence (XRF) core scanning data from two additional ODP sites located in the central (Site 707) and southern (Site 752) Indian Ocean. We trace the timing and pacing of these environmental changes along a cross hemispheric transect within key areas of the larger Indian Ocean-Atmospheric system: (1) the monsoonal upwelling regions along the Oman Margin (Site 722); (2) the Somali/Findlater jets (Site 707); and (3) the high-pressure zone in the southern horse latitudes (Site 752).

Using updated age constraints at all sites, we show that the intensification of upwelling at Site 722 is tightly linked to climatic and oceanographic changes in the southern high latitudes (e.g., Groeneveld et al., 2017; Sci. Adv.). This close co-evolution of southern hemisphere climatic shifts and monsoon dynamics hints at a strong contribution of increasing southern hemisphere thermal gradients on the middle to late Miocene evolution of the Indian Ocean circulation system and Indian monsoon dynamics. Our findings thus re-emphasize the Indian summer monsoon as the result of a complex cross-hemispheric ocean-atmospheric system spanning the Indo-Pacific (e.g., Gadgil, 2018, J. Earth Syst. Sci., 127). We postulate that the Indian Ocean-Atmospheric system experienced a gradual intensification that began after the Middle Miocene Climatic Optimum with Antarctic Ice Sheet expansion. These changes then culminated in a synchronous shift ~11 Ma during the Ser4/Tor1 sea level lowstand (Haq et al., 1987; Science, 235). Future chrono-, chemo- and cyclostratigraphic work at ODP Sites 707 and 752 will further help to constrain the timing of these events, and fully place them in the context of the global climatic evolution during the Miocene.

How to cite: Auer, G., Christensen, B., Bialik, O., Ogawa, N., Yamaoka, R., Antoulas, M.-E., De Vleeschouwer, D., Kroon, D., Ohkouchi, N., and Piller, W.: Timing and pacing of middle to late Miocene intensification of the Indian Ocean-Atmospheric circulation system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22410, https://doi.org/10.5194/egusphere-egu2020-22410, 2020.

StratigrapheR is an open-source integrated stratigraphy package. It is available in the free software environment R (https://CRAN.R-project.org/package=StratigrapheR) and is designed to generate lithologs in a semi-automated way, to process stratigraphical information, and to visualize any plot along the lithologs in the R environment.

The basic graphical principle behind StratigrapheR is the incremental addition of elements to a drawing: a plot is opened, and graphical elements are successively added. This allows compartmentalisation of the drawing process, as well as the superposition of different plots for comparison. For instance a litholog of a single section can be written as a single function including all the drawing sub-functions, and be integrated in a larger plot, for instance to be correlated to other sections or to show proxy data.

The StratigrapheR package is designed for efficient work, and minimum coding, while still allowing versatility. The lithological information of beds (upper and lower boundary, hardness, lithology, etc.) is converted into polygons. All polygons are drawn together using a single function, and each polygon can have its personalised symbology allowing to distinguish lithologies. A similar workflow can be used for plotting proxies while distinguishing each sample by their lithology. Vector graphics can be imported as SVG files, and precisely drawn with the lithologs to serve as symbols or complex elements. Every type of symbol is plotted by calling one single function which repeats the drawing for each occurrence of the represented feature. This illustrates that the amount of work invested to make lithologs using StratigrapheR is related to their complexity rather than their length: a long but monotonous litholog (e.g. of marl-limestone alternations) only takes a few lines of code to generate.

The StratigrapheR package also provides a set of functions to deal with selected stratigraphic intervals (for instance in the [0,1[ form): they allow simplification, merging, inversion and visualisation of intervals, as well as identifying the samples included in the given intervals, and characterising the relation of the intervals with each other (overlap, neighbouring, etc.). StratigrapheR includes PDF and SVG generation of plots, of any dimension. The generated PDF can even store multiple plots in a single file (each plot on a different page) to document data processing comprehensively.

How to cite: Devleeschouwer, X., Da Silva, A.-C., Boulvain, F., and Wouters, S.: StratigrapheR: making and using lithologs in R, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4700, https://doi.org/10.5194/egusphere-egu2020-4700, 2020.

Carbonate-fluorapatite (CFA) is a common early diagenetic component of marine sedimentary sequences. Nodules, laminae and shell overgrowths or infills composed of CFA are relatively common features in phosphorites, carbonates and other marine sediments (e.g., Datillo et al., 2016). CFA U-Pb dating thus has potential application as a chronometer in a wide variety of ancient marine sediments, particularly in those marine sections lacking diagnostic faunal and/or floral assemblages, or well-dated volcanogenic horizons.

In order to test empirically whether accurate and precise U-Pb ages can be obtained from CFA using LA-ICPMS we have analysed CFA from a several marine sediment samples. These include samples of Cretaceous phosphatic chalk from southern England, phosphatic nodules from the Cretaceous of northern Ireland and western Scotland, and a sample from a laterally extensive Carboniferous phosphorite in western Ireland. Ages obtained from CFA in these rocks can be precise (as low as c. 0.55% 2SE error in one sample), and are all unimodal. U-Pb ages of CFA, however, range from stratigraphically-consistent ages to ages that record much younger events than their host rock stratigraphic ages.

While ‘ages’ obtained from CFA may be precise, what each of these ages represents geologically requires further study. The genetic relationship between phosphate and its host rock must be petrographically studied to understand the correspondence between the phosphatic and other components of these rocks in terms of their depositional and diagenetic histories. It is apparent that in some cases CFA will record deposition or early diagenesis, but that the U-Pb system in CFA can be overprinted by later tectonic events in other cases. In addition, whilst LA-ICPMS U-Pb dating of apatite (i.e. fluorapatite and chlorapatite) in crystalline rocks is now routine, the crystal structure and composition of CFA differs from apatite derived from igneous and metamorphic rocks, including the established fluorapatite U-Pb standards (e.g. Madagascar apatite, Thomson et al., 2012). Thus, assessment of matrix-matching effects will have to be undertaken to fully establish the CFA U-Pb chronometer.

Dattilo, B.F., Freeman, R.L., Peters, W.S., Heimbrock, W.P., Deline, B., Martin, A.J., Kallmeyer, J.W., Reeder, J. and Argast, A., 2016. Giants among micromorphs: were Cincinnatian (Ordovician, Katian) small shelly phosphatic faunas dwarfed?. Palaios, 31(3), pp.55-70.

Thomson, S.N., Gehrels, G.E., Ruiz, J., Buchwaldt, R., 2012. Routine low-damage apatite U-Pb dating using laser ablation-multicollector- ICPMS. Geochemistry, Geophys. Geosystems 13, 1–23. doi:10.1029/2011GC003928

How to cite: O'Sullivan, G., Mortimore, R., Chew, D., and Daly, S.: U-Pb dating of carbonate-fluorapatite: a potential chronological tool for ancient marine sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20017, https://doi.org/10.5194/egusphere-egu2020-20017, 2020.

Paleomagnetic data are used in different data formats, adapted to data output of a variety of devices and specific analysis software. This includes widely used openly available software, e.g. PMag.py/MagIC, AGICO/.jr6 & .ged, and PuffinPlot/.ppl. Besides these, individual software and data formats have been established by individual laboratories.

Here we compare different data formats, identify similarities and create a common and interchangeable data basis. We introduce the idea of a paleomagnetic object (pmob), a simple data table that can include any and all data that would be relevant to the user. We propose a basic nomenclature of abbreviations for the most common paleomagnetic data to merge different data formats. For this purpose, we introduce a set of automatization routines for paleomagnetic data conversion. Our routines bring several data formats into a common data format (pmob), and also allow reversion into selected formats. We propose creating similar routines for all existing paleomagnetic data formats; our suite of computation tools will provide the basis to facilitate the inclusion of further data formats. Furthermore, automatized data processing allows quality assessment of data.

How to cite: Zeeden, C., Laag, C., Camps, P., Guyodo, Y., Hambach, U., Just, J., Lurcock, P., Rolf, C., Satolli, S., Scheidt, S., and Wouters, S.: Towards data interchangeability in paleomagnetism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10627, https://doi.org/10.5194/egusphere-egu2020-10627, 2020.