Cyclostratigraphy

An integrated study of magnetic mass susceptibility (MS), bulk stable isotopes and calcareous nannofossil paleoecological changes is undertaken on the late Maastrichtian of the Elles section, Tunisia, spanning the last ca. 1 Myr of the Cretaceous. A cyclostratigraphic analysis reveals the presence of Milankovitch frequencies and is used for proposal of two distinct orbital age-models and to provide ages of important stratigraphic horizons, relative to the age of the Cretaceous-Paleogene boundary (K-PgB). Principal Component Analysis (PCA) performed on the nannofossil assemblage reveal two main factors, PCA1, mostly representing fluctuations of D. rotatorius, P. stoveri, Lithraphidites spp., Retecapsa spp., Staurolithites spp., Micula spp., and PCA2, mostly representing fluctuations of A. regularis, C. ehrenbergii, Micula spp., Rhagodiscus spp., W. barnesiae and
Zeugrhabdotus spp. Variations in PCA1 and PCA2 match changes in bulk δ13C and δ18O, respectively, and suggest changes in surface-water fertility and temperatures and associated stress. The variations in abundances of high-latitude taxa and the warm-water species Micula murus, and in bulk δ18O delineate fast changes in sea-surface paleotemperatures. As in many other sites, an end-Maastrichtian greenhouse warming is highlighted, followed by a short cooling and an additional warm pulse in the last 30 kyr of the Maastrichtian which has rarely been documented so far. Orbital tuning of the delineated climatic events is proposed following the two different age-models. Calcareous nannofossil assemblages
34 highlight a decrease in surface-water nutriency but their species richness remain high through the latest Maastrichtian, indicating, in Tunisia, a weak impact of Deccan volcanism on calcareous nannoplankton diversity before the mass extinction.

The Dales Gorge Member (DGM) of the Brockman Iron Formation (Hamersley Basin, Western Australia) is a classic banded iron formation (BIF) that was deposited during the Archean-Proterozoic transition just prior to the Great Oxidation Event. The goal of this study is to apply modern cyclostratigraphic principles to investigate the possible origins of the characteristic stratigraphic banding in this BIF, which indicates the influence of quasiregular cyclic processes in the deposition of iron-rich and chert-rich lithologies. A grayscale scan series of the DGM ‘type section’ 47A* drillcore photographs from three cores drilled in the Wittenoon Gorge vicinity is examined using well established methods of time series analysis. Complex banding patterns suggest that
Milankovitch forcing may have taken place with orbital-rotational parameters that were significantly modified from the present-day due to continuous planetary tidal dissipation over the past 2.5 billion years. The banding patterns change systematically and dramatically within the member in response to slowly varying environmental conditions, which are interpreted to be related to low-frequency sea level changes and/or tectonic evolution of the Hamersley Basin.

Following votes by the Hauterivian Working Group, the Cretaceous Subcommission and the International Commission on Stratigraphy, in December 2019 the Executive Committee of the International Union of Geological Sciences unanimously approved the proposal that the Global
Stratotype Section and Point (GSSP) for the base of the Hauterivian Stage of the Lower Cretaceous be placed at the base of bed no 189 of the La Charce section, Drôme, southeast France (Vocontian Basin). This level is marked by the first appearance of the ammonite genus Acanthodiscus, which defines the base of the Acanthodiscus radiatus
ammonite Zone. Complementary data include 13 ammonite and nannofossil events, and magnetostratigraphic and carbon isotope events.

The results bio-, magnetostratigraphic, cyclostratigraphic, lithological and mineralogic studies of the  upper part of Sultanovskaya formation and Zelenogorskaya formation near v. Alexeevka (Belogorskiy
region of Crimea) were presented in current work. The results of lithological and mineralogic analysis argues for the stratigraphic break between “Sultanovskaya” formation and “Zelenogorskaya” formation and implicitly indicate the age of the sediments as late berriasian. The analogue of magnetic chron M16n and probable analogue of M15n chron, were established in the section. With help of spectral analysis of petromagnetic variations along the section, there were detected 4 short
eccentricity cycles (~100 kyr) and 11 obliquity cycles (40 kyr) within M16n.

The Friulian-Venetian Basin (FVB) is the northeastern portion of the wider Po Plain-Adriatic foreland, which bounds the whole Italian peninsula to the East, and is the place where most of the Italian hydrocarbon fields occur. The present-day architecture of the FVB is the result of the inherited Mesozoic sea-bottom topography which evolved during Cenozoic in the foreland basin shared by three different collisional systems: the Dinarides, the Southern Alps and the Northern Apennines. This work provides a high-resolution chronostratigraphic framework for the upper Neogene subsurface succession of the VFB since the early Zanclean regional transgressive surface to the latest Pleistocene, using a 2D reflection seismic lines grid and well log correlations (by spontaneous potential and resistivity signals) from Eni E&P dataset. The detailed sequence-stratigraphy analysis was based on the allogroups, (i.e. major stratigraphic units bounded at base and top by regional tectonically-induced unconformities, related to the Northern Apennines foredeep northeast migration), and on their lower rank units of climate and tectonic origin, recognized by Ghielmi et al. (2013). The almost absent deformation of the FVB sedimentary succession after Messinian well preserved the succession and allows handling the subsequent 3D basin scale interpretation. To get a high chronostratigraphic resolution we have performed a complete biostratigraphic revision of the ca. 1km-long continuously cored Venezia 1 well, integrated with near, correlatable onshore and offshore hydrocarbon wells to cover the entire Plio-Pleistocene sedimentary record. During Middle-Late Pleistocene, glaciations affected the whole Po Plain-Adriatic basin consequently suffered long periods of sea-level lowstand with large siliciclastic sediment supply followed by smaller transgressive events due to the shorter interglacials. This basin-wide short-term cyclicity is still not fully defined, but some geometries of the transgressive-regressive cyclothems are visible in seismic. In detail, into the Venetian shelf, cross-correlation panels show how the cycles can be correlated each other by well-log signals and linked to Global Eustatic sea-level curve. The resulting new age model, obtained merging biostratigraphy, seismics, direct (bottom cores) and indirect (well log) sedimentological data like electric logs, provides a new high-resolution subsurface chronostratigraphic frame for the Venetian-Friulian and Northern Adriatic basin, especially useful to date the uppermost part of the FVB Pleistocene clastic sediments, made by Milankovitch-type cyclothemes. Ghielmi M., Minervini M., Nini C., Rogledi S. & Rossi M. 2013. Late Miocene-Middle Pleistocene sequences in the Po Plain-Northern Adriatic Sea (Italy): The stratigraphic record of modification phases affecting a complex foreland basin. Marine and Petroleum Geology, 42, 50-81.

Cyclostratigraphic analysis of the Maastrichtian limestone–marl alternations of Bidart (SW France) allows the hypothesis of orbital control on lithological cycles to be evaluated. Magnetic susceptibility (MS), oxygen and carbon isotope measurements, sampled at a high resolution, are analyzed using various cyclostratigraphic tools. A statistically significant orbital signal is detected, with a remarkable record of the precession corresponding to the limestone–marl couplets. This well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the MS and δ13C records based on the 100 kyr eccentricity cycle. The total duration of the section is estimated at 1.44 ± 0.22 Myr. Correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled Bidart δ13C record to the astronomically calibrated δ13C signal of ODP Hole 762C shows that the studied section extends from − 71.5 to − 70 Ma, covering the upper part of Chron C32n.1n and 2/3 of Chron C31r. Oxygen isotope data suggest a 2 °C cooling of sea-surface temperatures during the studied interval. When placed on the long-term δ18O trend of the Bidart section, this interval is here recognized as the onset of the early Maastrichtian cooling event. With its excellent record of the precessional forcing, the Bidart section, along with other sections of the Basque Country, is a useful tool for the refinement of the Maastrichtian timescale.