Maastrichtian stratigraphy

One of the most expanded upper CampanianeMaastrichtian successions worldwide has been cored in a series of boreholes in eastern Denmark. A high-resolution holostratigraphic analysis of this part of the Chalk Group has been undertaken on these cores, notably Stevns-1, in order to provide a record of changes in chalk facies, water depths and sea-water temperatures. Combined lithological data, a suite of petrophysical logs including gamma ray (GR) logs, nannofossil and dinoflagellate palaeontology, stable carbon isotopes, seismic reflection and refraction sections form the basis for the definition of two new formations and six members, three of which are new, and for recognition of Boreal nannofossil subzones UC15e BP to UC20d BP . The upper Campanianelowermost Maastrichtian Mandehoved Formation is subdivided into the Flagbanke and Boesdal Members and the Maastrichtian Møns Klint Formation is subdivided into the Hvidskud, Rørdal, Sigerslev, Kjølby Gaard Marl and Højerup Members. The Boesdal and Rørdal Members show high GR values and a pronounced chalk-marl cyclicity. The Rørdal and the thin Kjølby Gaard Marl Members have a regional distribution and can be traced over most of the Danish Basin, whereas the Højerup Member is restricted to the easternmost part of Sjaelland. The other members consist of rather featureless white chalk.

The study is a qualitative and semi-quantitative analysis of calcareous nannofossils in marlstone and calcareous mudstone beds in a 4.6-m thick section of the Kropivnik Fucoid Marls (Late Campanian–Early Maastrichtian) in the Skole nappe of the Polish Outer Carpathians. This turbiditic succession is conspicuous by its short-term alternation of marlstone-rich and siliciclastic-rich packages, ca. 1 m thick. A model for paleoceanographic control on sedimentation is proposed on the basis of nannofossil assemblages in the studied section. The nannofossils form assemblages of mixed synsedimentary taxa derived from diverse marine environments, differing in trophy, water temperature and distance from land. The mixing occurred due to submarine resedimentation processes. The nannofossils indicate that the siliciclastic-rich packages were deposited during periods of lowered water temperature, decreased calcareous nannoplankton production and oligotrophic to mesotrophic water conditions, which corresponded to the sea-level fall and lowstand. Anti-estuarine circulation and downwelling due to arising shelf-break front are inferred as the factors responsible for oligotrophy. In contrast, in the marlstone-rich packages, the calcareous nannofossils indicate sedimentation during periods of significantly increased calcareous nannoplankton production, which corresponded to the sea-level rise and highstand. The increased nannoplankton production is attributed to estuarine circulation and upwelling. The changes in sea level and water circulation conform to the climate changes postulated independently for the Late Campanian–Early Maastrichtian.

Highlights

• Nannofossils in shelf-sourced turbiditic packages reflect sea-level changes.
• Sea-level falls caused low carbonate production and oligotrophy in shelf zone.
• Sea-level fall and lowstand activated anti-estuarine type of circulation.
• Sea-level rises caused high carbonate production and meso-/eutrophy in shelf zone
• Sea-level rise and highstand activated estuarine type of circulation.""

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.