Over the past 30 years, our knowledge of Cretaceous stratigraphy and timescale has expanded exponentially. This has been based partly on the greater refinement of biostratigraphy, including the utilisation of groups of fossils previously poorly known or ignored (microcrinoids, inoceramid bivalves, diverse microfossil groups) and also the development of geochemical and geophysical stratigraphies, most notably stable carbon isotope- and magnetostratigraphy. These two methodologies have enabled previously impossible correlations to be made, independent of facies and sometimes in the absence of biostratigraphical evidence. The identification of orbital cycles in Cretaceous sediments, integrated with new radiometric dates, now provides a high-resolution timescale for intervals of the Cretaceous. Work continues apace to extend and refine the timescale and integrate this with new stratigraphical data. Additionally, data generated primarily for the purpose of correlation, such as stable carbon isotope curves, provide direct evidence of the Cretaceous carbon cycle and allow a better understanding of palaeoenvironmental changes.

Until very recently, it was generally assumed that the marine flooding of the Saxonian Cretaceous Basin (SCB) was largely related to the naviculare Transgression of the early Late Cenomanian. However, based on the detailed investigation of 39 Cenomanian sites at surface and subsurface, and considering new macrobiostratigraphic data and existing palynological facts, a completely revised integrated stratigraphic framework and palaeogeographic reconstructions of the lower Elbtal Group are presented (Niebuhr & Wilmsen 2023, ZDGG 174, DOI: 10.1127/zdgg/2023/0376). Demonstrably, Cretaceous sedimentation started already in the early Early Cenomanian, indicated by the contemporaneous onlap of non-marine (Niederschöna Formation) and marine strata (Oberhäslich Formation). The Cenomanian transgressions advanced from the north, at first following the course of roughly south–north-discharging palaeovalleys of a fluvial palaeodrainage system. Sequence stratigraphic analyses demonstrate the presence of four complete, unconformity-bounded Cenomanian depositional sequences (DS) and a fifth one, DS Ce-Tu 1, which started in the mid-Late Cenomanian and lasted into the Early Turonian. The depositional sequences comprise five major transgressive phases that overstepped each other, culminating in an earliest Turonian climax of the 2^nd-order Cenomanian transgressive hemicycle. The maximum thickness (100–120 m) equates to the accommodation generated by eustasy and regional subsidence during the entire 6-myr-long Cenomanian age (sedimentation rate ≤20 m/myr). Thickness changes within the lower Elbtal Group can quite simply be related to pre-transgression topography and sequence stratigraphic onlap patterns. Thus, the new stratigraphic and palaeogeographic framework of the lower Elbtal Group also demonstrates that tectonic inversion in the SCB was essentially a post-Cenomanian process.

The Oxfordian period is characterized by a long-term (ca. 6 Myrs) trend of increasing stable carbon isotope values, punctuated by three short-lived (ca. <1 Myrs) carbon isotope excursions (CIEs) at the Callovian/Oxfordian boundary, in the lower Oxfordian (Quenstedtoceras mariae ammonite zone), and in the middle Oxfordian (Gregoryceras transversarium ammonite zone), also known as the MOxE. This pattern is evident worldwide in both organic and inorganic carbon (δ¹³C_org and δ¹³C_carb) in terrestrial and shallow marine environments, indicating recurrent global carbon cycle disturbances affecting the entire ocean-atmosphere system. However, previous sedimentological and chemostratigraphic studies on Oxfordian strata in the Lower Saxony Basin (LSB) of northern Germany, have failed to identify the three CIEs cited above, hindering their correlation with the global carbon isotope record. In this study, we provide, for the first time, a high-resolution δ¹³C_carb record revealing the MOxE expressed in a positive CIE of 3.8‰. We collected data from drilling core samples of the Korallenoolith Formation in the Konrad 101 borehole, located in the southwestern part of the LSB. This exploration drilling is biostratigraphically well constrained, unlike many other sections in the LSB that are characteristic of shallow tropical marine depositional settings. This particularity enables us to compare the Konrad 101 δ¹³C_carb pattern with other localities distributed worldwide incl. Europe, western Asia, and the Gulf of Mexico. Our high-resolution δ¹³C_carb reflects a major synchronous change in the exogenic carbon cycle, with no satisfying explanation so far for the triggering mechanisms, in the context of already published datasets.

The biostratigraphy of the Jurassic system has made many advances in recent years. We can distinguish over 50 successive faunal horizons in the Callovian, which corresponds to a resolution of perhaps 75,000 to 100,000 years. The distribution of the ammonite genus Kepplerites in space and time has been extensively studied. This example illustrates the importance of a precise stratigraphy for paleontological and sequence-stratigraphic questions.

The beginnings of the ammonite genus Kepplerites can be traced back to the Subboreal sea of NW Canada in the late Bathonian (Middle Jurassic). Thereafter the evolution can be followed over Greenland, the Russian platform over the Caucasus to Central Europe, up to its abrupt extinction at the beginning of the Callovian. Only a small population survived, probably in what is now the Caucasus. From here, a few specimens reached Central Europe and the Russian platform, where new species emerged (genetic drift). At the beginning of the Koenigi Zone, a species migrated from Russia via the Caucasus to Central Europe, where they mixed again. From this, separate lines developed in England and Central Europe (gradualism), the seas of Greenland were also settled again. At the end of the Koenigi Zone, Russian species immigrated again and replaced the weakened populations in Central Europe and England. By the end of the Early Callovian, all sea straits were open and a unified Subboreal faunal province of NW Europe, Greenland and the Russian Platform was established. This scenario was controlled by sea level rises and falls and short-term climatic changes.