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A cyclic marl–limestone succession of Middle–Late Campanian age has been investigated with respect to a Milankovitch-controlled origin of geochemical data. In general, the major element geochemistry of the marl–limestone rhythmites can be explained by a simple two-component mixing model with the end-members calcium carbonate and ‘average shale’-like material. Carbonate content varies from 55 to 90%. Non-carbonate components are clay minerals (illite, smectite) and biogenic silica from sponge spicules, as well as authigenically formed zeolites (strontian heulandite) and quartz. The redox potential suggests oxidizing conditions throughout the section. Trace element and stable isotopic data as well as SEM investigations show that the carbonate mud is mostly composed of low-magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts (calcispheres). Diagenetic overprint results in a decrease of 2% δ18O and an increase in Mn of up to 250 ppm. However, the sediment seems to preserve most of its high Sr content compared to the primary low-magnesium calcite of co-occurring belemnite rostra. The periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22.5 ka, attributable to orbital forcing. Accumulation rates within these cycles vary between 40 and 50 m/Ma. The resulting cyclic sedimentary sequence is the product of (a) changes in primary production of low-magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession, demonstrated by the CaCO3 content and the Mg/Al, Mn/Al and Sr/Al ratios, and (b) fluctuations in climate and continental weathering, which changed the quality of supplied clay minerals (the illite/smectite ratio), demonstrated by the K/Al ratio. High carbonate productivity correlates with smectite-favouring weathering (semi-arid conditions, conspicuously dry and moist seasonal changes in warmer climates). Ti as the proxy indicator for the detrital terrigenous influx, as well as Rb, Si, Zr and Na, shows only low frequency signals, indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long-lasting third-order Middle–Upper Campanian sedimentary cycle.

Geological magazine, 2005, Vol.142 (1), p.31-55

Geochemistry and time-series analyses of orbitally forced Upper Cretaceous marl–limestone rhythmites (Lehrte West Syncline, northern Germany)

The Upper Cenomanian–Lower Turonian litho-stratigraphic units of the Danubian Cretaceous Group of the proximal Bodenwöhrer Senke (Regensburg, Eibrunn and Winzerberg formations, the latter consisting of a lower Reinhausen Member and an upper Knollensand Member), have been investigated with a focus on facies analysis and sequence stratigraphy. Analyses of litho-, bio-, and microfacies resulted in the recognition of 12 predominantly marine facies types for the Eibrunn and Winzerberg formations. Petrographic and paleontological properties as well as gradual transitions in the sections suggest that their depositional environment was a texturally graded, predominantly siliciclastic, storm-dominated shelf. The muddy–siliceous facies types FT 1–3 have been deposited below the storm wave-base in an outer shelf setting. Mid-shelf deposits are represented by fine- to medium-grained, bioturbated, partly glauconitic sandstones (FT 4–6). Coarse-grained, gravelly and/or shell-bearing sandstones (FT 7–10) developed in the inner shelf zone. Highly immature, arkosic coarse-grained sandstones and conglomerates (FT 11 and 12) characterize an incised, high-gradient braided river system. The Winzerberg Formation with its general coarsening- and thickening-upward trend reflects a regressive cycle culminating in a subaerial unconformity associated with a coarse-grained, gravelly unit of marine to fluvial origin known as the “Hornsand” which is demonstrably diachronous. The overlying Altenkreith Member of the Roding Formation signifies the onset of a new transgressive cycle in the early Middle Turonian. The sequence stratigraphic analysis suggests that the deposition of the Upper Cenomanian and Lower Turonian strata of the Bodenwöhrer Senke took place in a single cycle of third-order eustatic sea-level change between the major sequence boundaries SB Ce 5 (mid-Late Cenomanian) and SB Tu 1 (Early–Middle Turonian boundary interval). The southeastern part of the Bodenwöhrer Senke was flooded in the mid-Late Cenomanian (
Praeactinocamax plenus
transgression) and a second transgressive event occurred in the earliest Turonian. In the central and northwestern parts of the Bodenwöhrer Senke, however, the initial transgression occurred during the earliest Turonian, related to pre-transgression topography. Thus, the Regensburg and Eibrunn formations are increasingly condensed here and cannot be separated anymore. Following an earliest Turonian maximum flooding, the Lower Turonian Winzerberg Formation filled the available accommodation space, explaining its constant thickness of 35–40 m across the Bodenwöhrer Senke and excluding tectonic activity during this interval. Rapid sea-level fall at SB Tu 1 terminated this depositional sequence. This study shows that Late Cenomanian–Early Turonian deposition in the Bodenwöhrer Senke was governed by eustatic sea-level changes.

Facies, 2013, Vol.59 (4), p.803-827

Late Cenomanian–Early Turonian facies development and sea-level changes in the Bodenwöhrer Senke (Danubian Cretaceous Group, Bavaria, Germany)

Integrated stratigraphic (litho-, bio-, event, chemo-, gamma ray, and sequence stratigraphy) and sedimentologic analyses of two new core sections greatly improved the understanding of facies development, sea-level changes and correlation of the lower Upper Cretaceous in the south-eastern Münsterland Cretaceous Basin, Germany. A large-scale second-order sea-level cycle is mirrored by the increasing importance of offshore facies and thicknesses of depositional sequences, reflecting the rise of accommodation during the Cenomanian to Early Turonian. In the Middle Turonian, this trend started to become reversed and the cycle ends with a major unconformity at the base of the Soest Grünsand Member in the mid-Upper Turonian. Condensation of the mid- and uppermost Turonian reflects the lack of accommodation during a phase of second-order lowstand, followed by a retrogradational trend during the Early Coniacian that marks the transgressive part of a new second-order cycle. Sedimentary unconformities in the Cenomanian–Turonian successions provide evidence for third-order sea-level changes superimposed onto the first early Late Cretaceous second-order cycle. They correspond to sequence boundaries SB Ce 1–5 and SB Tu 1–4 that have been identified in Central European basins and elsewhere, supporting their eustatic origin. The sea-level fall expressed by Upper Turonian unconformity SB Tu 4 is of major magnitude. The overlying Soest Grünsand Member is the only level of greensands in the Upper Turonian of the south-eastern Münsterland: the Alme Grünsand, introduced for another, allegedly uppermost Turonian greensand level, does not exist. Carbon stable isotopes from the mid-Upper Cenomanian to Lower Coniacian allowed calibrating the successions on intra- and interbasinal scales. A conspicuous mid-Middle Turonian positive isotope event has been newly named, i.e., the Niederntudorf Event. Sequence boundaries, marker beds (marl layers) and bentonites turned out to be isochronous within the chemostratigraphic framework. The identification of Turonian bentonites greatly improved the understanding of the stratigraphic relationships, especially in the Upper Turonian while natural gamma radiation logs turned out as a valuable method for intrabasinal correlation. In conclusion, the new sections provide a high-quality standard succession for the lower Upper Cretaceous in the south-eastern Münsterland Cretaceous Basin.

Facies, 2019, Vol.65 (2), p.1-29

The lower Upper Cretaceous of the south-eastern Münsterland Cretaceous Basin, Germany: facies, integrated stratigraphy and inter-basinal correlation

The facies development and onlap pattern of the lower Danubian Cretaceous Group (Bavaria, southern Germany) have been evaluated based on detailed logging, subdivision, and correlation of four key sections using an integrated stratigraphic approach as well as litho-, bio-, and microfacies analyses. Contrary to statements in the literature, the transgressive onlap of the Regensburg Formation started in the Regensburg–Kelheim area already in the early Early Cenomanian
Mantelliceras mantelli
ammonite Zone and not in the Late Cenomanian. In the Early Cenomanian, nearshore glauconitic-bioclastic sandstones prevailed (Saal Member), followed by Middle to lower Upper Cenomanian mid-shelf siliceous carbonates intercalated with fine-sandy to silty marls (Bad Abbach Member). Starting in the mid-Late Cenomanian (
Metoicoceras geslinianum
ammonite Zone), a considerable deepening pulse during the Cenomanian–Turonian Boundary Event (CTBE) initiated the deposition of the deeper shelf silty marls of the Eibrunn Formation, which range into the early Early Turonian. During the CTBE transgression, also the proximal Bodenwöhrer Senke (ca. 40 km NE of Regensburg) was flooded, indicated by the onlap of the Regensburg Formation onto Variscan granites of the Bohemian Massif, overlain by a thin tongue of lowermost Turonian Eibrunn Formation. A detailed record of the positive δ
13
C excursion of the global Oceanic Anoxic Event (OAE) 2 has been retrieved from this shallow-water setting. An integrated approach of bio-, event-, carbon stable isotope and sequence stratigraphy was applied to correlate the sections and to decipher the dynamics of this overall transgressive depositional system. The Cenomanian successions show five prominent unconformities, which correlate with those being known from basins in Europe and elsewhere, indicating their eustatic origin. The rate of sea-level rise during the CTBE suggests glacio-eustasy as a driving mechanism for Late Cenomanian sea-level changes. The Regensburg and Eibrunn formations of the lower Danubian Cretaceous Group are highly diachronous lithostratigraphic units. Their regional distribution and northeast-directed onlap pattern onto the southwestern margin of the Bohemian Massif can readily be explained by the lateral movements of roughly coast-parallel (i.e., NW/SE-trending) facies belts of a graded shelf system transgressing on a northeastward-rising substrate. It took the Cenomanian coastline ca. 6 Ma to transgress from southwest of Regensburg to the topographically elevated granite cliffs southeast of Roding in the Bodenwöhrer Senke (=60 km distance).

Facies, 2010, Vol.56 (4), p.483-507

Facies pattern and sea-level dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria, southern Germany)

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