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

Abstract

ABSTRACT:Wilmsen, M. and Niebuhr, B. 2017. High-resolution Campanian-Maastrichtian carbon and oxygen stable isotopes of bulk-rock and skeletal components: palaeoceanographic and palaeoenvironmental implications for the Boreal shelf sea. Acta Geologica Polonica, 67 (1), 47-74. Warszawa.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) d O 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 d 18O 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.

Stable isotopes and predation marks shed new light on ammonoid habitat depth preferences

“…However, this method excludes from study those specimens that originate from carbonates in which the aragonitic shells were dissolved during fossilisation proces, leaving only natural moulds (steinkerns). This is just the case in the white chalk facies, which predominated in the Boreal Chalk Sea of Europe during the Late Cretaceous [13][14][15] .Absence of original shells does not mean, however, that the European chalk ammonoid faunas 16,17 are completely out of reach where isotope palaeothermometry is concerned. The chalk locally yields aptychi, that is paired calcitic coverings of the lower ammonoid jaws 18,19 .…”

“…However, this method excludes from study those specimens that originate from carbonates in which the aragonitic shells were dissolved during fossilisation proces, leaving only natural moulds (steinkerns). This is just the case in the white chalk facies, which predominated in the Boreal Chalk Sea of Europe during the Late Cretaceous [13][14][15] .…”

Advances and Challenges in Palaeoenvironmental Studies Based on Oxygen Isotope Composition of Skeletal Carbonates and Phosphates

“…[246]) and the Morondava basin of Madagascar (cf. [247]), most elevated belemnite δ 18 O values are derived from the Boreal belemnite groups, i.e., Jurassic Cylindroteuthidae belemnite family (data of Anderson et al [46] and Mettam et al [243]) and Cretaceous Belemnitellidae belemnite family (data of Voigt et al [52] and Wilmsen and Niebuhr [244]). Interestingly, distinctly higher (by 0.8‰) δ 18 O values of uppermost Middle-Upper Jurassic Boreal cylindroteuthid belemnites compared to the oxygen isotope values of co-occurring Tethyan belemnopseid belemnites have been reported by Wierzbowski et al [55] from the Russian Platform.…”

“…1‰ higher δ 18 O values of Cretaceous belemnite rostra compared to the oxygen isotope values of brachiopod shells [52], (6) ca. 1‰ higher δ 18 O values of Cretaceous belemnite rostra compared to the oxygen isotope values of inoceramid and brachiopod shells [244], (7) 0.5 to 2‰ higher δ 18 O values of Jurassic belemnite rostra compared to the values of co-occurring oyster and brachiopod shells [56,245]. Apart from the results of Alberti et al [56,245], which might reflect migratory behaviour of investigated Tethyan Belemnopseidae (=Mesohibolitidae) and Duvalidae belemnites, possibly related to their post-spawning mortality, in the shallow Kachchh basin of India (cf.…”

Introduction to the Principles of δ18O, δ13C, and 87Sr/86Sr in the Palaeosciences.

“…Robin, 1977;Siegenthaler et al, 1988;Hendricks et al, 2000), sediment samples (e.g. Jenkyns and Clayton, 1986;Wilmsen and Niebuhr, 2017) and fossil shells and bones. Oxygen isotope analyses of marine carbonate fossils could substantiate the modelled palaeoclimate evolution by providing information on oceanic palaeotemperatures.…”