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A marker band folgen stratigraphy for the Cenomanian Chalk of England and its extension to northen Germany and France

Jeans Christopher Vincent

Acta Geologica Polonica

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2023

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Vol. 73, no. 2

135--180

EN

A novel stratigraphical scheme within the Folge Concept is described for the Cenomanian Chalk of England that is particularly suitable for investigating the regional changes in the lithofacies, diagenesis, geochemistry, and mineralogy of the sediments of the Chalk Sea leading up to the Cenomanian–Turonian Oceanic Anoxic Event. It is based on “isochronous” marker bands defined largely by calcitic macrofossil assemblages, and it avoids problems caused by the poor or non-preservation of ammonite assemblages and lateral changes in chalk lithofacies. Eight folgen are based on one, two, or more marker bands. Their sequences, lithologies and calcitic macrofossil assemblages are described from 33 exposures in the Northern Chalk Province of England. The folgen are named, in ascending order, the Belchford, Stenigot, Dalby, Bigby, Candlesby, Nettleton, Louth and Flixton, after villages in Lincolnshire and Yorkshire, England. The folgen are traced throughout the Transitional and Southern Chalk provinces of England. They are present in the Cenomanian chalk of northern Germany and northwest France. Regionally, an individual folge may display considerable vertical and lateral variation in general lithology and lithofacies whilst still maintaining their defining marker bands. The possibility of further refinement to the scheme is discussed.

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High-resolution Campanian-Maastrichtian carbon and oxygen stable isotopes of bulk-rock and skeletal components: palaeoceanographic and palaeoenviron-mental implications for the Boreal shelf sea

Wilmsen M., Niebuhr B.

Acta Geologica Polonica

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2017

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Vol. 67, no. 1

47--74

EN

A high-resolution latest Early Campanian to Early Maastrichtian carbon and oxygen stable isotope record from the northern German Boreal shelf sea based on 537 analyses of co-occurring belemnites, brachiopods, inoceramids, oysters, and bulk rock samples is presented. All samples are precisely related to their stratigraphic, systematic and facies backgrounds and form an integrated, nearly 10-myr-long dataset with considerable palaeoenvironmental and palaeoceanographical implications. Petrographic studies indicate that low-magnesium calcitic coccoliths and calcispheres (i.e., planktic carbonate) predominate the bulk-rock data (marl-limestone rhythmites and chalks), thus representing a sea-surface water signal, and that only minor diagenetic alteration of the carbonate muds took place. Based on TL and CL microscopy, the investigated belemnites are extraordinarily well preserved, which may in part be explained by their early diagenetic surficial silicification (container effect), while the other macroinvertebrate groups are all less well preserved. The (plankton-dominated) δ13C values of the marl-limestone rhythmites and chalks (+1.1 to +2.5‰), recording a surface water signal, compare well with the δ13C data of inoceramids while δ13C brach.values (+1.5 to +3.0‰) are heavier than the bulk rock data. The large variation in the δ13Cbel. (-0.1 to +3.6‰) is attributed to isotopic disequilibrium of the biogenic carbonate formed by the belemnite animal. The bulk rock δ18O values show a remarkable low scatter, supporting petrographic observation of only minor diagenetic stabilisation/cementation, and can be approximated with northern German shelf sea-surface temperatures of ca. 20°C for the Late Campanian (ca. -2‰ δ18O), being slightly cooler during the Early Maastrichtian. The δ18O values of the belemnite rostra are even less variable and quite rich in heavier 18O (-0.7 to +0.6 with a mean of -0.1‰ δ18Obel.) in comparison to bulk rock and other skeletal components. Based on their excellent microstructural preservation and non-luminescence, we conclude that the belemnite rostra are diagenetically unaltered and have preserved the primary δ18O signal of ambient seawater (12±2°C). In the absence of any indication for migration from cooler water masses and evidence for authochtonous populations we assume that the belemnites of the genera Belemnitella and Belemnella lived as nektobenthos near the sea-floor and thus record the temperature of the bottom mixed layer of the seasonally weakly stratified north German shelf sea at water depths of 100 to 150 m; the temperature gradient was thus 12.5–18.75 m/1°C. A conspicuous latest Campanian cooling event is evident in both sea-surface and bottom-water temperatures. The δ18O values of nearly all investigated benthic fossils lie between the isotope values of pristine belemnites and bulk rock, and, therefore, should be used for palaeotemperature reconstructions only with great care.

3

The benthic macrofauna from the Lower Maastrichtian chalk of Kronsmoor (northern Germany, Saturn quarry): taxonomic outline and palaeoecologic implications

Engelke J., Esser K. J. K., Linnert C., Mutterlose J., Wilmsen M.

Acta Geologica Polonica

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2016

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Vol. 66, no. 4

671--694

EN

The benthic macroinvertebrates of the Lower Maastrichtian chalk of Saturn quarry at Kronsmoor (northern Germany)been studied taxonomically based on more than 1,000 specimens. Two successive benthic macrofossil assemblages were recognised: the lower interval in the upper part of the Kronsmoor Formation (Belemnella obtusa Zone) is characterized by low abundances of macroinvertebrates while the upper interval in the uppermost Kronsmoor and lowermost Hemmoor formations (lower to middle Belemnella sumensis Zone) shows a high macroinvertebrate abundance (eight times more than in the B. obtusa Zone) and a conspicuous dominance of brachiopods. The palaeoecological analysis of these two assemblages indicates the presence of eight different guilds, of which epifaunal suspension feeders (fixo-sessile and libero-sessile guilds), comprising approximately half of the trophic nucleus of the lower interval, increased to a dominant 86% in the upper interval, including a considerable proportion of rhynchonelliform brachiopods. It is tempting to relate this shift from the lower to the upper interval to an increase in nutrient supply and/or a shallowing of the depositional environment but further data including geochemical proxies are needed to fully understand the macrofossil distribution patterns in the Lower Maastrichtian of Kronsmoor.

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Integrated stratigraphy of the Kronsmoor section (northern Germany), a reference point for the base of the Maastrichtian in the Boreal Realm

Niebuhr B., Hampton M., Gallagher L., Remin Z.

Acta Geologica Polonica

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2011

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Vol. 61, no. 2

193-214

EN

Results of detailed multistratigraphic analyses of the Campanian.Maastrichtian boundary section at Kronsmoor in northern Germany are summarised and calibrated with the GSSP at Tercis les Bains, southwest France. Additional markers for the definition of the boundary in the Boreal Realm are proposed, and a detailed carbon isotope curve around the Campanian.Maastrichtian boundary in the chalk facies of the Boreal epicontinental sea is presented. The C isotopic GSSP marker for global correlation is the markedly abrupt decrease of c. 0.7 [per mil] [delta^13]C directly at the Campanian.Maastrichtian boundary as dated by ammonites. In electronic borehole measurements the Kronsmoor section covers the SP peaks 53 to 64 and the base of the Maastrichtian being situated just below SP peak 60. The first occurrence (FO) of the ammonite Pachydiscus neubergicus, which corresponds to biohorizon 1 at Tercis, falls in the upper part of nannofossil Zone UC15, at both localities. Biohorizon 3 is the FO of the ammonite Diplomoceras cylindraceum, which first appears in the Upper Campanian of Tercis and at Kronsmoor enters significantly above the FO of Belemnella lanceolata, the conventional Boreal belemnite marker for the base of the Maastrichtian Stage. Based on ammonite evidence, the internationally accepted base of the Maastrichtian at Kronsmoor is located between the FOs of Diplomoceras cylindraceum (Upper Campanian) and Pachydiscus neubergicus (Lower Maastrichtian) c. 11 m above flint layer F 600, at which the first representatives of the belemnite genus Belemnella, in particular Bn. lanceolata occur. The latter thus is a Late Campanian species, appearing c. 450 ky prior to the ammonite-based boundary. The FOs of Belemnella pseudobtusa (sensu Schulz) resp. Belemnella obtusa (sensu Remin) directly at the boundary can be use as the coleoid proxy for the definition of the base of the Maastrichtian in the Boreal Realm. To define the boundary by benthic foraminifera the last occurrence (LO) of Neoflabellina praereticulata is suitable. Biohorizon 12, as defined at Tercis, involves the nannofossil Uniplanarius trifidus, however, at Kronsmoor this species is rare, occurs only sporadically and also significantly lower in comparison to Tercis. It is possible though to compare and correlate nannofossil events between Kronsmoor and Tercis using cosmopolitan taxa such as Broinsonia parca constricta and Eiffellithus eximius. The LO of the latter appears to be situated just above the boundary in both sections; it follows from this that the top of nannofossil Zone UC15 is of Early Maastrichtian age.