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Since the publication of 40Ar/39Ar dates from Cretaceous bentonites in the Western Interior Basin by J.D. Obradovich in 1993 and in Japan by J.D. Obradovich and colleagues in 2002, improvements in the 40Ar/39Ar method have included a shift to astronomically calibrated ages for standard minerals and development of a new generation of multi-collector mass spectrometers. Thus, the 40Ar/39Ar chronometer can yield results that are synchronous with U-Pb zircon dates and astrochronologic age models for Cretaceous strata. Ages determined by Obradovich have ± 2σ analytical uncertainties of ± 400 ka (excluding J value or systematic contributions) that have been used to discriminate stratigraphic events at ca. 1 Ma resolution. From among several dozen sanidine samples, 32 of which were dated by Obradovich in 1993, we present new multi-collector 40Ar/39Ar ages that reduce the average analytical uncertainties by nearly an order of magnitude. These new ages (where the uncertainties also include the contribution of the neutron fluence J value) include: Topmost Bentonite, Mowry Shale, Kaycee, Wyoming, USA, 97.52 ± 0.09 Ma Clay Spur Bentonite, Mowry Shale, Casper, Wyoming, 98.17 ± 0.11 Ma Arrow Creek Bentonite, Colorado Shale, Montana, USA, 99.12 ± 0.14 Ma Upper Newcastle Sandstone, Black Hills, Wyoming, 99.49 ± 0.07 Ma Middle Newcastle Sandstone, Black Hills, Wyoming, 99.58 ± 0.12 Ma Shell Creek Shale, Bighorn Basin, Crow Reservation, Wyoming, 99.62 ± 0.07 Ma Shell Creek Shale, Bighorn Basin, Greybull, Wyoming, 99.67 ± 0.13 Ma Shell Creek Shale, Bighorn Basin, Lander, Montana, 100.07 ± 0.07 Ma Muddy Sandstone, Wind River Basin, Wyoming, 101.23 ± 0.09 Ma Thermopolis Shale, Bighorn Basin, Wyoming, 101.36 ± 0.11 Ma Vaughn Member, Blackleaf Formation, Sweetgrass Arch, Montana, 102.68 ± 0.07 Ma Taft Hill Member, Blackleaf Formation, Sweetgrass Arch, Montana, 103.08 ± 0.11 Ma Base of the Skull Creek Shale, Black Hills, Wyoming, 104.87 ± 0.10 Ma Thermopolis Shale, Bighorn Basin, Wyoming, 106.37 ± 0.11 Ma A new U-Pb zircon age of 104.69 ± 0.07 Ma from the Skull Creek Shale at Dinosaur Ridge, Colorado, USA, is close to the new 40Ar/39Ar age of the Skull Creek Shale in the Black Hills, Wyoming, but 5 m.y. is missing in the unconformity between the Skull Creek Shale of the Black Hills and the overlying Newcastle Sandstone. Considering the average total uncertainties that include decay constant and standard age or tracer composition for the 40Ar/39Ar (± 0.19 Ma) and the U-Pb (± 0.13 Ma) ages does not alter this finding. Moreover, the lower Thermopolis Shale in the Bighorn Basin is 1.5 Ma older than the Skull Creek Shale in the Black Hills. The 100.07 ± 0.07 Ma Shell Creek Bentonite in Montana is close to the Albian–Cenomanian boundary age of 100.2 ± 0.2 Ma of Obradovich and colleagues from Hokkaido, Japan, and 100.5 ± 0.5 Ma adopted in the 2012 geological time scale of J.G. Ogg and L.A. Hinnov. Our findings indicate that correlations based on similarity of lithology, without independent radioisotopic ages or detailed biostratigraphic constraints, can be problematic or invalid. There is much more time missing in unconformities than has been previously recognized in these important, petroleum-bearing reservoir strata.

New belemnite finds from the Lower Cretaceous (Berriasian – Hauterivian) of Arctic Canada and North-East Greenland provide insight into the spatial distribution patterns of belemnites at northern high latitudes. The belemnite faunas of both areas can be attributed to the Boreal-Arctic Province of the Boreal Realm. The stratigraphic patchiness of the recorded belemnites makes palaeobiogeographic interpretations problematic. The few specimens from Arctic Canada, which are assigned to Arctoteuthis, suggest a faunal isolation of this area. The belemnite assemblages of North-East Greenland are much richer and more diverse. The Valanginian is here characterized by Arctoteuthis, Pachyteuthis, Acroteuthis, Lagonibelus and Simobelus with Acroteuthis being most common. Genera well known from the Tethys (Hibolithes, Pseudobelus, Duvalia) document immigration from the south. The abundance of Tethyan taxa increases in the Hauterivian.

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The original description of the large and characteristic belemnite species Arctoteuthis bluethgeni Doyle was based on fragmentary material from a relatively uncertain stratigraphic interval in Kong Karls Land, Svalbard. Recent collection of a belemnite assemblage in the Lower Cretaceous Rurikfjellet Formation on Spitsbergen include numerous complete specimens, allowing a detailed description of the species. With the exception of a specimen reported from Arctic Canada, its distribution is restricted to Svalbard. Its stratigraphic range appears to be restricted to the upper Valanginian – lower Hauterivian from ages obtained from palynostratigraphy. A. bluethgeni is therefore considered to be a useful Lower Cretaceous guide fossil in the Boreal High Arctic.

The upper Campanian–lower Maastrichtian interval from the white chalk of the Kronsmoor section (northern Germany) has been a target of various studies on benthic foraminifera and benthic macroinvertebrates. The results of these studies are in part contradictory, as foraminifera suggest decreasing fertility throughout the early Maastrichtian, whereas macroinvertebrates imply increasing food supply. In order to elucidate this discrepancy, we re-studied benthic foraminiferal assemblages from Kronsmoor. This section provides a continuous upper Campanian–lower Maastrichtian succession with well-preserved foraminifera. Benthic assemblages are highly diverse and abundant. Common foraminifer species include Bolivina incrassata, Cibicidoides voltzianus, Gyroidinoides umbilicatus, Osangularia cordieriana, Sitella laevis and Stensioeina pommerana. Only a few variations in diversity or in morphogroup composition have been observed throughout the studied interval. Some individual taxa (e.g., B. incrassata, Cibicidoides spp.), show a trend of decreasing abundances, whereas others (Cibicides beaumontianus, G. umbilicatus) increase. The relatively stable composition of benthic morphogroups suggests that there were no severe palaeoenvironmental disruptions in the western Chalk Sea such as excess eutrophication or oxygen depletion. Modest palaeoecological shifts are indicated by the variation patterns of individual taxa such as G. umbilicus (increasing organic influx), C. beaumontianus (bottom water circulation) and Bolivinoides spp. (cooling).

Calcareous nannofossils and stable isotope data (δ13Ccarb) from a pelagic section of the Zagros Basin (west Iran) were used for an integrated oceanographic analysis of the Barremian – Aptian interval. The study aims at analyzing various oceanographic shifts recorded from this period, including the Oceanic Anoxic Event 1a (OAE 1a), in an expanded carbonate rich mudstone sequence of the eastern Tethys. The extreme thickness (510 m) of the succession allows us to study the environmental changes known from the Barremian and Aptian interval in much more detail than previously done. By looking at closely spaced samples it is possible to better understand the onset, the course and the aftermath of the OAE 1a event. Calcareous nannofossils suggest an early Barremian (nannofossil zone CC5/NC5C) to late Aptian age (nannofossil zone CC7b/NC7B) for the studied sequence. The biostratigraphic zonation is based on the last occurrence of Calcicalathina oblongata, the first occurrences of Rucinolithus irregularis and Eprolithus floralis and the last occurrence of Micrantholithus hoschulzii. A total of 98 species has been encountered in the studied interval with good to moderate, in few cases poor preservation. Based on the calcareous nannofossil assemblages, signals for a warming event in the mid-Barremian are characterized by high relative abundances of warm water specie (e.g., Rhagodiscus asper) along with neritic taxa (Micrantholithus spp., Nannoconus spp.) The OAE 1a was identified via calcareous nannofossil biostratigraphy in combination with the δ13Ccarb record. For the OAE 1a (early Aptian), warm and eutroph conditions were likely, as suggested by high relative abundances of R. asper, Diazomatolithus lehmanii, small Zeugrhabdotus spp. and Lithraphidites carniolensis. The late Aptian is characterized by cool surface water conditions.

The Jurassic–Cretaceous boundary interval of northern Germany is characterised by non-marine deposits attributed to the Purbeck and Wealden facies. These organic-rich sediments were deposited under restricted, brackish-lacustrine conditions in a palaeogeographically isolated basin (Lower Saxony Basin). Rock-Eval and δ13Corg measurements were performed to characterise the composition and distribution of the organic matter, to determine the kerogen type chemically, and to define the quantity and maturity of the organic matter. A strong correlation between the optical characteristics, documented by the palynofacies analysis, and the chemical kerogen analyses have led to a better understanding of the palaeoenvironment and the processes which caused the organic matter enrichment. The samples studied from the basin center show a high petroleum generation potential, their estimated maturity is close to the onset of oil generation. Total organic carbon (TOC) concentrations of up to 18% have been measured, hydrogen index values reach up to 1185 mg HC/g TOC. The kerogen assemblages in two basinal successions are dominated by granular amorphous organic material (AOM), dinoflagellate cysts, and Botryococcus algae. In a more marginal succession continent-derived debris (phytoclasts, pollen and spores) is dominant. The AOM is interpreted to have originated either from phytoplankton (probably dinoflagellate cysts and Botryococcus), or its bacterial/archaeal degradation products formed under anoxic conditions. TOC-rich samples which are dominated by these amorphous kerogens show the highest petroleum potential, the AOM therefore plays a key role for the petroleum generation. The long-term climatic and hydrological evolution of the Lower Saxony Basin, which is based on palynomorphs, ostracods, and benthic foraminifera, is here interpreted by a five-stage model. Fluctuations in the salinity of the water bodies are directly reflected by the ratio between different freshwater and brackish-marine organisms as well dinoflagellate cyst diversity; five different cyst morphogroups are used for palaeoenvironmental interpretations. The deposition of TOC-rich beds in the German Wealden can be best explained by both high primary productivity and the establishment of prolonged phases of bottom water anoxia in a brackish-lacustrine depositional environment. Ecological conditions supporting enhanced productivity and preservation of the algal/bacterial-derived organic matter were most favourable during the mid–late Berriasian (Wealden 1–4).

The δ18O(PO4) of shark teeth can be used as a geochemical proxy for the palaeoenvironment during tooth mineralization. A well-preserved state of the teeth is necessary for this approach. We used polarization, cathodoluminescence (CL) and scanning electron microscopy to investigate two fossil shark teeth (Sphenodus nitidus) from the Late Jurassic Nusplingen Plattenkalk. The data are compared with those for two recent shark teeth (Hemipristis elongata, Lamiopsis temminckii). δ18O(PO4) of six further Jurassic shark teeth was measured and is compared with δ18O data from co-occurring belemnite rostra and carbonate sediments. The enameloid of both the fossil and the recent shark teeth shows orange–red CL, which is due to incorporation of Mn during biomineralization. The δ18O(PO4) values of the fossil enameloid are constant around 21.50‰ V-SMOW whereas those of the fossil dentine are more negative with values around 20‰ V-SMOW, which indicates that the enameloid is well preserved. Palaeotemperatures calculated from the enameloid are like those derived from belemnites. We demonstrate that CL microscopy should only be used cautiously as a diagenesis-screening method for fossil biophosphates. Geochemical and microstructural analyses of tissue types with different susceptibility to diagenetic alteration on the other hand provide an effective way to identify well-preserved tissues. Supplementary material: Polarization microscopy images, energy-dispersive X-ray data and cathodoluminescence spectra are available at https://doi.org/10.6084/m9.figshare.c.4373720

An integrative multi proxy approach based on lithology, microfacies, bulk rock composition, total organic carbon (TOC), and δ13Ccarb was used to estimate southeastern Tethys sea level fluctuations during the deposition of the Maastrichtian-Danian oil shales in Jordan. Clay mineral assemblages were used as proxies to determine climatic variation induced sediment supply during the Cretaceous/Paleogene boundary (K/Pg) interval. The results from two cores (OS-02, Jafr Basin, southeast Jordan; OS-28 Azraq-Hamza Basin, central-east Jordan) reveal four major intervals of distinctive bulk rock composition reflecting sea level changes. Interval I (earliest Maastrichtian) with a low sea level and the formation of dolomites and a high detrital quartz input predates the oil shales. Intervals II and III in core OS-02 and interval II in core OS-28 represent the highest relative sea level following the Early Maastrichtian sea level rise on the Arabian Platform. Intervals III (core OS-02) and II (core OS-28) coincide with the highest organic matter deposition. Interval IV (core OS-02) and intervals III and IV (core OS-28) relate to the sea level regression-transgression cycle in the latest Maastrichtian through Danian and are marked by a large drop in the TOC content. Increased terrestrial influx during sea level lows is evident from two peaks/intervals of major negative δ13Ccarb values in core OS-28. Based on clay mineralogy it can be differentiated between warm/humid, warm/cool seasonally alternating, and cool/arid climates. When bulk rock composition is used as a sea level proxy, clay mineral assemblages from both cores reveal the dominance of warm and humid climate or, alternatively, warm/cool seasonal alternations during high sea levels (II and III core OS-02; II and IV core OS-28), while periods of arid and cool climate correspond to lower sea levels. The sea level changes and climatic variations deduced from the Jordanian oil shale successions are in agreement with the long term variations from the Egyptian Western Desert sections (southeastern Tethys), and the Tunisian El-Kef section (southweastern Tethys). Moreover, the sea level changes identified relate to the regional changes on the Arabian platform during the Maastrichtian-Danian.

This study is based on Maastrichtian and Danian oil shales of a cored well located in the Jafr Basin in central Jordan. Studied sedimentary rocks consist of alternations of monotonous bituminous marls, phosphatized marls, occasional dolomite, black chert, and limestone concretions. The main characteristics of these deposits are the high values of the total organic carbon (TOC) which fluctuate between 2.8 and 32.1 wt%. Benthic foraminifera were studied quantitatively in order to reconstruct environmental changes across the Maastrichtian and early Danian. Three clusters of benthic foraminifera, showing different assemblage compositions on the species level, were distinguished. Each of these assemblages is characterized by changes of diversity indices and abundances, indicating fluctuations of the bottom water oxygenation and organic matter fluxes. Water-depth preferences based on three associations and marker species of benthic foraminifera indicate an estimated paleodepth from middle to outer neritic (∼50–200 m) during the Maastrichtian and Danian. During the Maastrichtian, Anomalinoides praeacutus is the dominant benthic foraminifera species characterized by high abundances. A short decline of A. praeacutus, observed in calcareous nannofossil biozone UC18/19 (lower Maastrichtian), is compensated by an increase of Anomalinoides umboniferus. Abundance fluctuations of benthic foraminifera included in the Buliminacea (Sitella fabilis, Elhasaella alanwoodi, Neobulimina canadensis, Reussella aegyptiaca) are recorded from the assemblages. The taxonomic composition of the assemblages and the varying TOC values indicate low oxygen bottom-water conditions under high organic flux across the Maastrichtian. A moderate change is documented for the Danian, where A. praeacutus continues to dominate the assemblages, but Siphogenerinoides eleganta and Uvigerinella spp. are less common. These benthic associations along with a decrease of the TOC content suggest a gentle increase of the bottom water oxygenation with moderate organic fluxes.

The Early–mid Cretaceous Garau and Kazhdumi Formations of the Zagros Basin (western and southwestern Iran) have been studied for calcareous nannofossils and their assemblage composition. The 722 m thick Garau Formation was investigated in the Kabir-Kuh section (northwestern Zagros), the 197 m thick Kazhdumi Formation was studied in the Maghar section (southwestern Zagros). Based on the calcareous nannofossil assemblages, the Garau Formation can be attributed to the Valanginian to Lower Aptian. The sequence yields moderately diverse nannofossil assemblages which are closely related to those of the western Tethys. The assemblages encountered in the current study differ by the absence or rarity of several taxa, which are otherwise common in the western Tethys. On the other hand, some taxa (e.g., Rhagodiscus asper, Lithraphidites carniolensis and small Zeugrhabdotus spp.) are more common than elsewhere in Tethys. Two phases of decline of nannoconids, observed in other parts of the Tethys as well, are reported for the late Barremian and early Aptian. Warm water species like R. asper are quite common, while taxa preferring cool to temperate water like Repagulum parvidentatum are entirely absent. The Kazhdumi Formation spans the interval from the upper Lower Aptian to the Lower Cenomanian. In the Kazhdumi Formation the index taxa Prediscosphaera columnata and Corollithion kennedyi, which are quite rare, are used to define the Aptian–Albian and the Albian–Cenomanian boundary. The Nannoconus truitti acme, known from various sites around the globe (South Atlantic, western Tethys, Boreal Realm), is recorded from the late Aptian.

Many aspects of the paleobiology and biomineralization of belemnites, the most common fossil coleoid cephalopods of the Mesozoic, are still unclear. Here, we describe a pearl from an Early Cretaceous belemnite rostrum (Duvalia emerici) using high-resolution micro-CT imaging. After initial formation of a free pearl within the soft tissue, the pearl was fused to the rostrum and later overgrown by rostrum increments, thereby forming a blister pearl. The contact zone of the pearl with the rostrum shows resorption and deformation of earlier rostrum increments. Formation of a free pearl inside the soft tissue of the belemnite demonstrates a relatively thick (min. 5.6 mm) tissue layer surrounding the rostrum in this species. Our data show that classification of paleopathologies based on external features alone might lead to false inferences of formation mechanisms.

Organic matter (OM) rich marls were deposited in several intrashelf basins in Jordan (e.g. Yarmouk Basin, Lajjun Basin, Azraq-Hamza Basin, Jafr Basin, Eshidiyya Basin) on the southeastern Tethyan margin during the Maastrichtian to middle Eocene . Factors like surface water productivity fueled by upwelling and sea level changes affected their deposition. Potential effects of climatic changes have not been determined yet. We present the first stable carbon and oxygen isotope records of Maastrichtian-Danian oil shales from the Azraq-Hamza and Jafr Basins in south- and central-east Jordan. The δ 13Ccarb curves were time-calibrated based on calcareous nannofossil biostratigraphy . Eight notable excursions were identified in the Jordanian Maastrichtian sections. These were correlated with the documented Maastrichtian δ 13Ccarb events in the (sub) tropical sections of Italy and the western Pacific: the Campanian-Maastrichtian boundary Events 4 and 5 (CMBE-4, CMBE-5), the Middle Maastrichtian Events 1 to 3 (MME-1 to MME-3) and the Cretaceous-Paleogene boundary Events 1 to 3 (KPgE-1 to KPgE-3). Signs of the Latest Danian Event (LDE) were recognized as well. Total organic carbon (TOC) data exhibit a complex relationship with the δ 13Ccarb proxy record. The δ13Ccarb signals are repeatedly dampened due to the OM oxidation and subsequent 12 C release. The effect of short term climate changes is observed, but is not always straight forward. Long term climate changes had indirect effects on bottom water oxygenation and OM preservation via sea level changes. The δ 18Ocarb data from both sections reveal minor temperature changes in the Maastrichtian. Slight warming is observed in the MME interval. A potential increase of the paleotemperature is reported from the Azraq-Hamza section occurring in the latest Maastrichtian to earliest Danian.

The Late Cretaceous global sea level maximum is documented by the widespread occurrence of chalks and marls. These carbonates, which contain rich and diverse calcareous nannofossil assemblages, were deposited in pelagic to hemipelagic environments. Previous studies of the biostratigraphy and ecology of calcareous nannofossils have therefore often focused on sections from open oceanic settings, including DSDP and ODP sites. Marine nearshore sediments of Late Cretaceous age have recently been cored by drilling activities in the western part of the Munsterland. Six wells, positioned about 5–20 km north of the former coastline, penetrated Cenomanian to Campanian sedimentary rocks. Lithologically these strata are composed of sand-rich, glauconitic marls and glauconitic limestones, which unexpectedly yielded well-preserved and diverse calcareous nannofossil assemblages. The light-microscopic analysis of 330 rock samples provided the following results: 1) A detailed, biostratigraphic zonation based on calcareous nannofossils has been established for shallow-water successions. The interval studied covers biozones UC0-1a (lowermost Cenomanian) to UC14a (lower Campanian). 2) The δ13C bulk carbonate curve obtained from one of the cores correlates well with the standard curve of the English Chalk facies. The following isotope events were observed: CTBE (late Cenomanian), White Fall (middle Coniacian), Haven Brow and Horseshoe Bay (middle Santonian), Buckle (middle to upper Santonian), Hawks Brow (upper Santonian) and SCBE (lower Campanian). 3) The biostratigraphic data suggest a heterochronous onset of the Late Cretaceous transgression in the study area, related to local variations in topography. 4) By correlating the six cores stratigraphically, we recognise that certain sedimentation patterns are controlled by eustasy and others by local tectonics. The Cenomanian to lower Turonian successions suggest a gradual flooding, where cores with condensation and hiatuses reflect local topographic highs. For the northernmost core, positioned furthest from the palaeocoast, an early to middle Turonian phase of tectonic uplift has been identified.

The non-marine Purbeck- and Wealden-type sediments of latest Jurassic (Tithonian) and earliest Cretaceous (Berriasian) age in northern Germany were deposited in a restricted intercontinental basin. They mark an interval of strong faunal and floral provincialism which makes correlation of the non-marine strata across northwest Europe difficult. The position of the Jurassic–Cretaceous boundary has therefore been debated for decades. Our integrated stratigraphy of four sections in northern Germany, based on palynology (spores, pollen, dinoflagellate cysts) and ostracods, provides new evidence for a precise correlation with contemporaneous strata of other non-marine basins in northwest Europe. Correlation with the marine Boreal Realm and the Tethys is achieved via the Purbeck type section in England. A stratigraphic subdivision of the non-marine Berriasian succession in Germany is possible by using seven short-lived marine flooding events, which are documented by ceratioid dinoflagellate cysts and foraminifera. Our data suggest that a first major transgression took place close to the base of the Boreal Surites stenomphalus ammonite Zone. This level corresponds to a contemporaneous flooding event in southern England (Scallop Beds, Purbeck Group) and in southern Sweden (Annero Formation), thereby providing an excellent marker horizon for interbasinal correlation.

© 2018 Cushman Foundation. All rights reserved. This study presents benthic foraminiferal data from two sedimentary successions across the Paleocene-Eocene Thermal Maximum (PETM) from Jordan. Calcareous nannofossil biozones NP9a, NP9b, and NP10 of latest Paleocene and earliest Eocene age were encountered in proximal (core OS-01) and distal (core OS-28) sites. Lithologically, the investigated sequence consists of marls, shales, and limestones attributed to the Muwaqqar Chalk-Marl Formation and the Urn Rijam Chert Limestone Formation. The δ 13 C org curve records the typical carbon isotope excursion (CIE) and shows four distinctive intervals (pre-CIE, CIE-"core", CIE "recovery", post-CIE) over the entire PETM interval in both cores. In the pre-CIE interval, the more proximal site (OS-01) shows high abundances of Neoeponides duwi co-occurring with an outer neritic Midway-type fauna. The fauna indicates mesoto eutrophic conditions in a middle to outerneritic setting. The more distal site (OS-28) is characterized by outer-neritic to upper-bathyal taxa (e.g., Cibicides pseudoacutus, Gavelinella beccariiformis, Nuttallides truempyî) suggesting well-ventilated, oligo-to mesotrophic seafloor conditions. The earliest Eocene corresponds to the CIE-"core" interval and is marked by a negative δ 13 C org signal, high TOC, low CaCO 3 contents, and near absence of benthic foraminifera. Oxygen deficiency in bottom waters with increased organic flux is the most likely scenario to explain the elevated organic content at the seafloor. The subsequent CIE-"recovery" interval of early Eocene age is marked by a restoration of oxygenated seafloor conditions. The proximal site is characterized by a relatively elevated TOC content and high abundance of Lenticulina spp., Valvulineria scrobiculata and common Anomalinoides zitteli, suggesting moderate oxygen conditions and mesotrophic bottom waters. The distal site is characterized by low TOC content and the presence of Lenticulina spp., Valvulineria scrobiculata, Anomalinoides zitteli and Oridorsalis plummerae, indicating a normalization of the organic flux and moderate oxygen concentrations near the seafloor. The post-CIE interval is marked by low TOC content in both cores. Benthic foraminifera include abundant Anomalinoides zitteli and common Lenticulina spp., Valvulineria scrobiculata, Oridorsalis plummerae, Cibicidoides rigidus, Cibici-doides pharaonis, and Anomalinoides praeacutus in the proximal setting. Mesotrophic conditions and a better ventilation of bottom waters are suggested for this interval. Lenticulina spp., Valvulineria scrobiculata, and Oridorsalis plummerae are also associated with the post-CIE interval in the distal site, suggesting similar mesotrophic conditions with renewed oxygenation in bottom waters. ispartof: JOURNAL OF FORAMINIFERAL RESEARCH vol:48 issue:2 pages:100-120 status: published

This high-resolution study (210 samples/44 m) of the uppermost Campanian–lower Maastrichtian chalk at Kronsmoor (northern Germany) intends to define the inorganic depositional setting of Late Cretaceous chalk deposition as well as to reconstruct contemporaneous sea-level fluctuations and palaeoenvironmental changes. A latest Campanian event associated with significantly decreased carbonate contents and palaeotemperatures is reflected in most geochemical palaeoproductivity proxies and indicates reduced marine fertility across the Campanian–Maastrichtian boundary. Sr/Ca and δ13C remain low afterwards while other productivity proxies show a significant rebound, indicating recovery and a potential qualitative change in marine productivity during the early Maastrichtian. Redox-sensitive proxies indicate overall well oxygenated conditions. The %terrigenous proxy tracks an argillaceous chalk depositional event related to an inferred glacio-eustatic latest Campanian sea-level fall followed by a low sea-level stand until the earliest Maastrichtian. It decreases and stays low up-section, reflecting an early Maastrichtian sea-level rise and highstand, parallelled by increasing and consistently high carbonate contents. However, the concomitant conspicuous variability and increase in other terrigenous input proxies indicate more strongly fluctuating and higher aeolian supply. Time-series analysis of selected geochemical proxies demonstrates the presence of the obliquity (∼40 kyr) the long-eccentricity (∼400 kyr) cycles of the Milankovitch Band. The covariance of productivity proxies and indicators of aeolian input suggests that obliquity forcing of dust input exerted control on (surface) water productivity, CaCO3 flux and the end-Cretaceous carbon cycle.

Core OS-28 located in central Jordan offers an expanded record of calcareous nannofossils and benthic foraminifera for the early Eocene of the southern Tethys. The oil shale succession of the studied interval covers calcareous nannofossil biozones NP10, NP11, NP12 and NP13. Microfossils document the biotic response of calcareous nannofossils and benthic foraminifera to short and long term warming trends of the early Eocene following the Paleocene-Eocene Thermal Maximum (PETM). On a global scale, two early Eocene short term shifts to higher atmospheric CO 2 concentration are recorded by negative δ 13 C excursions. These are known as Eocene Thermal Maximum 2 and 3 (ETM2, ETM3). Stable isotope records (δ 13 C org , δ 13 C carb , δ 18 O carb ) from the study area do not show these negative excursions, which elsewhere can be correlated with the two hyperthermal events known from early Eocene successions. The absence of negative δ 13 C signals otherwise typical for ETM2 and ETM3 is explained by a diagenetic alteration of the isotope signal after deposition. High abundances of the nannofossil taxon Sphenolithus spp. in biozone NP10 indicate less fertile conditions for this interval than for the overlying biozone NP11. Throughout biozones NP11 to NP13 Coccolithus pelagicus and Toweius spp. are the dominant taxa of the assemblages, suggesting a mesotrophic environment. Surface waters experienced a temperature change from warm to moderate-warm. The benthic foraminifera in calcareous nannofossils biozone NP10 and in the lower part of NP11 reflect oligo-mesotrophic and moderate to well oxygenated bottom water conditions. Throughout the upper part of biozones NP11, NP12 and NP13, the benthic foraminifera are characterized by an increasing abundance of Anomalinoides zitteli , Lenticulina spp. and Valvulineria scrobiculata . This coincides with enriched total organic matter content (TOC), indicating a shift to mesotrophic conditions and a moderate oxygen supply of the bottom waters. Based on the micropaleontological observations made in core OS-28 the early Eocene is first characterized by an increase and subsequently by a decrease of nutrients and oxygen. The composition of both, benthic and planktic communities was rather controlled by variations of regional environmental parameters than by global ones. These include strong runoff, climatic variability and the architecture of the basin.

Lower Maastrichtian strata (Belemnella obtusa and lower–middle B elemnella sumensis cephalopod biozones) at the Saturn quarry near Kronsmoor (northern Germany) were logged and sampled in detail (33 bulk samples of about 6 kg each) for high-resolution quantitative palaeoecological analysis of the benthic fauna. Following standardised preparation, the size fractions 500 μm–1 mm and >1 mm were considered, documenting a diverse benthic assemblage of bryozoans, brachiopods, bivalves, various echinoid taxa, asteroids, ophiuroids, crinoids, sponges, small-sized sabellids and serpulids, cirripedes and foraminifera. A general, gradual up-section increase in the abundance of benthic faunas was recognised. Furthermore, from the lower to the upper part of the section, epifaunal suspension feeders became more dominant as the mobile guilds (epifaunal and shallow infaunal) saw a reduction in numbers. These observations parallel results obtained from low-resolution macrofossil analyses of this interval that documented an impoverished lower and a rich upper assemblage, the latter clearly dominated by epifaunal suspension feeders. Palaeoecological data of benthic community relicts at Kronsmoor are indicative of increased nutrient availability during the early Maastrichtian. However, in the absence of any evidence of increased productivity in the overlying photic zone (calcareous nannofossil data), a lateral input (upwelling) of nutrient-rich waters onto the shelf to fuel the benthic ecosystem has to be considered. This view is supported by records of contemporaneous changes in latest Cretaceous ocean circulation that followed the latest Campanian cooling event, inclusive of a southward spread of waters of intermediate depth from high latitudes.

Belemnites, a group of extinct coleoid cephalopods, were important components of Mesozoic marine ecosystems. Their calcitic rostra are extensively used in biostratigraphy and geochemistry. The preservation state of the rostra is a crucial factor for the interpretation of their geochemical data. However, their preservation is difficult to assess, since no modern cephalopod forms calcitic rostra. The biomineralization process of the rostrum, which functioned as an internal skeleton, is poorly understood for most species. This also applies for the epirostrum, a late ontogenetic extension of the rostrum which is only present in some belemnite species. The primary structure and function of this character are still being debated controversially. We have investigated the microstructure, stable isotope (δ 13 C, δ 18 O), and elemental composition (Mg/Ca, Sr/Ca, Fe/Ca, Mn/Ca) of both, ortho- and epirostra of the belemnite species Neohibolites minimus (Early Cretaceous, Albian). For comparison, we studied argonauts ( Argonauta argo ). These recent octopuses build a calcitic shell. Ortho- and epirostra of N . minimus show microstructural and geochemical differences. Cathodoluminescence-microscopy and the microstructures of belemnites and argonauts indicate that blue/orange luminescent growth lines in the studied belemnites are largely a primary biomineralization phenomenon and not solely due to diagenesis. Based in part on analogy to argonaut shell, we suggest that the inner part of the belemnite epirostrum is a continuation of an originally organic apical line. The development and evolution of the epirostrum as a potential sexually selected character is discussed. Well-preserved epirostrum calcite has higher element/Ca ratios than the calcite of the orthorostrum, suggesting a vital effect affecting these values. We further found evidence for vital effects on the stable isotope signatures due to metabolic and kinetic fractionation. Our findings suggest a complex mineralization process of the studied rostra. Different microstructures with distinctive geochemical signatures occur in a single belemnite species. Vital effects played an important role in the rostrum geochemistry, complicating the application of the rostra as paleoclimatic archives.

The benthic macroinvertebrates of the Lower Maastrichtian chalk of Saturn quarry at Kronsmoor (northern Germany) have 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 obtusaZone) is characterized by low abundances of macroinvertebrates while the upper interval in the uppermost Kronsmoor and lowermost Hemmoor formations (lower to middleBelemnella sumensisZone) shows a high macroinvertebrate abundance (eight times more than in theB. obtusaZone) 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.

We integrate previously published data from geochemistry, clay mineralogy, and benthic foraminifera with new findings from calcareous nannofossils and the sulfur content to reconstruct the variations of bottom and surface water conditions resulting from climate changes in the Jafr Sub-basin (Jordan). The fluctuation of the organic matter content recorded from Maastrichtian and Danian oil shales of a cored section, is seen as a response to nutrient fluxes, inducing changes in primary productivity. Bacterial workover and enrichment played a secondary role. The benthic foraminifera and calcareous nannofossils reflect oxygen depleted bottom waters and ecologically stressful surface waters. The preservation of organic matter and organic matter bound sulfur, which dominates almost throughout the entire Maastrichtian, is linked to warm-humid climatic conditions. A slight increase of the oxygen content of bottom and surface waters, which has been recorded for the latest Maastrichtian and Danian, is associated with warm-arid conditions. The biota response to these changes is documented by the extinction of most calcareous nannofossil species across the Cretaceous-Paleogene boundary, while benthic foraminifera were less affected. The short- and long-term climatic variations during the Maastrichtian-Danian interval suggest the following scenario. Riverine influx in combination with an upwelling system provided the nutrient input fueling the primary productivity of the southeastern Tethyan surface waters during the late phase of extended shelf flooding.

The Paleocene-Eocene Thermal Maximum (PETM) is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean-atmosphere system. These include a negative carbon isotope excursion, intense carbonate dissolution and biotic changes of marine floras and faunas. The current study reports the response of calcareous nannofossils across the Paleocene-Eocene boundary in a paleoshelf setting in Jordan (core OS-28), clearly marked by a negative δ 13 C org excursion and the occurrence of characteristic “excursion taxa” (e.g., Discoaster araneus , Rhomboaster spp., Coccolithus bownii ). While this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion, it retains well-preserved, diverse nannofossil assemblages from the pre-PETM, PETM recovery and post-PETM intervals. These assemblages are dominated by two taxa of inferred mesotrophic affinities ( Coccolithus pelagicus , Toweius spp.) and show only low abundances of oligotrophic taxa ( Discoaster spp., Fasciculithus spp., Sphenolithus spp.). Overall, there appear to be only relatively low-level changes in the general assemblage composition across the PETM. During the post-PETM, however, there was a gradual decrease in relative abundance of C. pelagicus and Toweius spp. This decline co-coccured with a relative increase of Coccolithus bownii and Coccolithus foraminis , and in its later phase was accompanied by an increase in the relative abundance of Sphenolithus spp. These changes, indicate a possible shift towards less fertile conditions following the hyperthermal event. The relatively muted signal of biotic change associated with the PETM interval at this site was partly a consequence of poor preservation within the key sequence of the studied core. On the other hand, the low signal may also be indicative for local environment processes, such as variations in riverine sourced nutrients, salinity, turbidity. Operating on a regional scale, these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the PETM in open ocean sites. Finally, the assemblages from the Jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the PETM interval. These heterogeneities have been observed in shelf assemblages from Tanzania, New Jersey and the Tethyan margins, which again points to the strong influence of regional controls like river input in more marginal settings.

The early Aptian Oceanic Anoxic Event 1a (OAE 1a; ∼120 Ma) was caused by a global perturbation of the Early Cretaceous climate. It supposedly affected the composition of the marine biosphere, including the primary producers. This study aims at using the size evolution of three species of coccolithophores ( Biscutum constans , Zeugrhabdotus erectus and Watznaueria barnesiae ) for better understanding the impact of the OAE 1a on primary producers. A total of 30 samples derived from three sites, which cover the upper Barremian–lower Aptian interval, have been analyzed from the North Sea and the Lower Saxony Basin. The sections expose near-shore and shallow marine sediments. The measured data of B. constans and Z. erectus are characterized by a size decrease synchronous to the negative carbon isotope excursion. This size reduction marks the early phase of the OAE 1a, more precisely the carbon isotope segment C3. Coccolith sizes recover to pre-OAE 1a values in the aftermath of this brief interval. The short termed size reduction is seen as a reaction of specific nannofossil taxa to an increase in humidity during the early phase of OAE 1a. Due to high weathering rates and a substantial run-off, the amount of detrital material transported into the marine system increased significantly. Consequently light availability diminished in the surface waters, causing habitat changes for the photoautotrophic primary producers. Light-sensitive species like B. constans and Z. erectus adjusted by forming smaller skeletons, thereby reducing their size. This strategy allowed for dwelling in shallower water depth and thus compensated for the decrease in sun light. The sizes of W. barnesiae in contrast remain stable throughout the entire OAE 1a interval. W. barnesiae was not affected by these environmental shifts and is thus interpreted as being robust with respect to changes of the sun light.

The Rollrock Section in the Sverdrup Basin of Arctic Canada is one of the northernmost outcrops where the Jurassic-Cretaceous transition is accessible. The over 500 m thick sedimentary succession exposes the Oxfordian to Valanginian Ringnes and Deer Bay formations. Macrofauna from 15 discrete horizons includes ammonites, Buchia bivalves and belemnites. These fossils improve the biostratigraphy of the Tithonian and Berriasian in the Sverdrup Basin, provide correlation to the remainder of the Boreal Realm and set reliable calibration points. The occurrence of Buchia rugosa in the Ringnes Formation moves the upper formation boundary from the top of the Kimmeridgian into the lower Tithonian. Dorsoplanites maximus and D. sachsi document the middle Tithonian Dorsoplanites maximus Zone in Arctic Canada for the first time. The late Tithonian to early Berriasian Buchia terebratuloides is considered to be the best approximate indicator of the Jurassic-Cretaceous transition in the Rollrock Section. The middle early Berriasian Praetollia maynci and the late early Berriasian Borealites fedorovi tie the respective horizons to the successive Chetaites sibiricus and Hectoroceras kochi zones. Two species of the belemnite Arctoteuthis, collected from an interval with common glendonites, suggest a Valanginian age for the upper Deer Bay Formation. The dearth of Late Jurassic to earliest Cretaceous macrofossils in the Sverdrup Basin is inferred to be predominantly a function of diagenetic carbonate loss. Abundant dropstones and glendonites in the middle Tithonian to middle Valanginian interval suggest cold climatic conditions, and make the Rollrock Section a prime candidate for studying the Arctic environmental perturbations of this time.

The argonauts (genus Argonauta) are enigmatic cephalopods. They have a cosmopolitan distribution in subtropical and tropical seas, where they inhabit the epipelagic zone. Their biology, ecology, and life cycle are poorly understood. It is for the first time that stable isotope (δ13C, δ18O) and element ratios (Mg/Ca, Sr/Ca, Ba/Ca) from three argonaut shells have been analyzed in order to test whether their life cycle and habitat are reflected in these data. The three studied shells have been collected in October 2012 from a mass stranding in Yoichi Bay, Hokkaido, Japan. The specimens were sampled along the keel of the shells to acquire ontogenetic records and along growth-sections of the shells to obtain synchronous data of differing shell growth rates. Carbon and oxygen isotope values as well as Mg/Ca ratios are in part controlled by the shell growth rate. Sr/Ca values show similar ontogenetic trends in the three shells. Comparison with measured sea surface temperature data indicates a temperature control on δ18O, Mg/Ca, and Sr/Ca, and a fast growth of the argonaut shell. Ba/Ca ratios of the shells might record environmental parameters. These new data highlight the influence of vital effects, but they also demonstrate that argonaut shell isotopic and elemental records can be used to understand the life cycle of these animals better.

Nutrients and sea-surface temperature were likely the most important paleoecological parameters that controlled the composition of Late Cretaceous calcareous nannofossil assemblages. The extinct nannofossil taxa Biscutum spp., Tranolithus orionatus and Zeugrhabdotus spp. are commonly thought to have preferred nutrient-rich surface waters. In order to test this hypothesis, calcareous nannofossils from two lower Turonian nearshore sections (Bochum, Herne; northwest Germany) were studied. These sections, which reflect a mesotrophic and perhaps cool paleoenvironment, contain well-preserved and highly diverse calcareous nannofossil assemblages yielding 92 species. Based on the first occurrences of Eprolithus eptapetalus, Quadrum gartneri, and Eiffellithus eximius, both sections have been assigned an early Turonian age. The most common taxa are Watznaueria barnesiae, Zeugrhabdotus spp., Biscutum constans, Prediscosphaera cretacea, and Tranolithus orionatus. In combination with previously published data...

There is an abundance of evidence for short intervals of cold climatic conditions during the Early Cretaceous. However, the lack of a high-resolution, long-term Early Cretaceous paleotemperature record hampers a full-scale synthesis of these putative “cold snap” episodes, as well as a more holistic approach to Early Cretaceous climate changes. We present an extended compilation of belemnite-based oxygen, carbon and strontium isotope records covering the Berriasian–middle Albian from the Vocontian Basin (SE France). This dataset clearly demonstrates three intervals of cold climatic conditions during the Early Cretaceous (late Valanginian–earliest Hauterivian, late early Aptian, latest Aptian–earliest Albian). Each of these intervals is associated with rapid and high amplitude sea-level fluctuations, supporting the hypothesis of transient growth of polar ice caps during the Early Cretaceous. As evidenced by positive carbon isotope excursions, each cold episode is associated with enhanced burial of organic matter on a global scale. Moreover, there is a relatively good match between the timing and size of large igneous province eruptions and the amplitude of Early Cretaceous warming episodes. Altogether, these observations confirm the instrumental role of atmospheric CO2 variations in driving Early Cretaceous climate change. From a long-term perspective, the coupling of global paleotemperature and seawater strontium isotopic ratio during the Early Cretaceous is best explained by temperature-controlled changes of continental crust weathering rates.

Biometric studies of coccoliths, the remains of coccolithophores, offer the opportunity to survey single species instead of entire assemblages. We obtained and analyzed size data of three common species (Biscutum constans, Zeugrhabdotus erectus and Watznaueria barnesiae) in a stratigraphically very well-defined interval of early Aptian age (~ 126 Ma; Cretaceous). Material is derived from four sites (Lower Saxony Basin, North Sea, western Tethys, Mid-Pacific) covering nearshore to open-oceanic paleosettings. Length and width measurements of 1986 specimens were evaluated. The recorded size patterns show a larger data spread for B. constans and W. barnesiae in the western Tethys and the Mid-Pacific than in the North Sea and the Lower Saxony Basin. The latter two sites are dominated by small coccoliths of B. constans while coccoliths of W. barnesiae show similar sizes at all four sites. Solely small specimens of Z. erectus characterize the samples from the North Sea and the Lower Saxony Basin while only large ones are present in the samples of the western Tethys and Mid-Pacific. For explaining the recorded size patterns, three theories are discussed in detail; these include (1) preservation of nannofossils, (2) genetics and (3) paleoecology. (1) Intense dissolution or overgrowth of the nannofossils may have altered the original coccolith sizes particularly when biometric data from different sites with potentially varying states of preservation are compared. Due to its delicate morphology, Z. erectus appears most prone to dissolution, probably explaining its size pattern. (2) If the recorded size data of the remaining two species represent original patterns, these can be interpreted by new findings in recent coccolithophore genetics. It has been shown that size variations within a single cryptic species are only minor. Shifts of coccolith sizes, both in recent and fossil taxa, can be related to genotypic variation. The varying size ranges recorded for B. constans and W. barnesiae may therefore reflect diversity changes of cryptic species at the different sites. (3) These cryptic species may have preferred different depth habitats depending on geographically-controlled factors such as sea-surface temperatures, light availability or trophic load.

Large distance correlation of sedimentary organic rich facies units in Jordan has been established by means of calcareous nannofossil biostratigraphy. Based on a biostratigraphic framework, a better understanding of the deposition and distribution of Maastrichtian to Eocene oil shales is obtained. A total of 812 samples representing 29 wells located across Jordan were studied for calcareous nannofossil biostratigraphy. The results reveal major regional changes in paleogeography leading to a change in oil shales distribution in time. The tectonic settings have been determined for four different oil shale sequences of Maastrichtian, Paleocene, Early Eocene and Middle Eocene age. Large variations in thickness over short distances indicate syndepositional subsidence control in several fault bound sedimentary sub-basins. During the Early Maastrichtian transgression, a thick oil shale dominated succession was accumulated in the south of Jordan. This transgression continued into the Paleocene as represented by a thick sequence of oil shales in nannofossil Zone NP 3. In the Late Paleocene, the gradual progradation of the oil shale facies from south to north coincided with an uplift of the Sirhan Sub-basin in east Jordan. Accordingly, the oil shale distribution varies locally and shows a scattered geographic distribution in the Late Paleocene. An up to 60 m thick succession of Early Eocene oil shales was found in central Jordan. Localized restricted conditions, which prevailed during the Ypresian–Lutetian transition (nannofossil Zone NP 14), were caused by the subsidence of the Azraq-Hamza and Sirhan sub-basins. These movements resulted in thick oil shale accumulation in the southeastern and central parts of Jordan. A gradual relative sea level fall during the Bartonian resulted in a prograding and thinning of the oil shale facies from west to east in central Jordan.

Oil-shale beds formed under anoxic conditions that were controlled by various local, regional and global factors. The Jordanian oil shales, which were deposited during the Late Cretaceous to Eocene, are considered as an example for the interplay of these factors. Two cores of organic-rich marls were investigated and analyzed with respect to their lithology, ichnofabrics and carbonate microfacies. The first core (OS-01, 183.3 m; South Jordan) is of Late Cretaceous age, the second one (OS-23, 256.3 m; Central Jordan) is of Eocene age. Our studies revealed that the Upper Cretaceous oil shales were deposited in a shallow-water carbonate shelf. Oyster bioherms acted as physical barriers that reduced the water circulation with the open shelf, thereby causing anoxic conditions. The Eocene oil shales also accumulated on a shallow-water carbonate shelf. In this case, however, synsedimentary tectonics caused subsiding grabens and half grabens, which in turn gave way to anoxic conditions. Both deposition and richness of the Jordanian oil shales were affected by regional sea-level fluctuations and global climatic changes.

The accurate habitats of the extinct ammonites and belemnites are largely unknown. Most ammonites are thought to have had a pelagic lifestyle, while belemnites are often considered to have dwelled in deeper, colder waters. Stable isotope analysis (δ18O, δ13C) provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods, but is at the same time limited by various unknowns, including the isotopic composition of the past seawater, ‘vital’ effects and diagenesis. In this paper, stable isotope data from 12 ammonite shells (Simbirskites spp.) from the upper Hauterivian of the Lower Saxony Basin (northwest Germany) are presented. Ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime. These new ammonite data are combined with published stable isotope data from belemnites (Hibolithes jaculoides) and TEX86 palaeotemperature-estimates from the same section. The combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other. Calculated palaeotemperatures of the two groups differ by 5–10 °C, with belemnites always showing the colder temperatures. All juvenile shells show an increase of the δ13Camm to more positive values throughout their ontogeny; they are stable in an adult shell-fragment. The incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects, probably linked to the shell growth rate. The isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites, indicating that the δ13Camm values might record a combination of environmental and metabolic signals. Taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells, a similar pelagic habitat is proposed here for both, ammonites and belemnites.

Biometric measurements of Mesozoic coccoliths (coccolith length and width) have been used in short-term biostratigraphic, taxonomic and palaeoecologic studies, but until now, not over longer time scales. Here, we present a long time-series study (∼ 30 million years) for the Upper Cretaceous, which aims to identify broad trends in coccolith size and to understand the factors governing coccolith size change over long time scales. We have generated biometric data for the dominant Upper Cretaceous coccolith groups, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa and Watznaueria, from 36 Cenomanian–Maastrichtian (100.5–66 Ma) samples from Goban Spur in the northeast Atlantic (DSDP Site 549). These data show that the coccolith sizes within Prediscosphaera, Retecapsa and Watznaueria were relatively stable through the Late Cretaceous, with mean size variation less than 0.7 μm. Within the Broinsonia/Arkhangelskiella group there was more pronounced variation, with a mean size increase from ∼ 6 μm in the Cenomanian to ∼ 10 μm in the Campanian. This significant change in mean size was largely driven by evolutionary turnover (species origination and extinctions), and, in particular, the appearance of larger species/subspecies (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) in the early Campanian, replacing smaller species, such as Broinsonia signata and Broinsonia enormis. Shorter-term size fluctuations within Broinsonia/Arkhangelskiella, observed across the Late Cenomanian–Turonian and Late Campanian–Maastrichtian intervals, may, however, reflect changing palaeoenvironmental conditions, such as sea surface temperature and nutrient availability. / Les dimensions des coccolithes du Mesozoique (longueur et largeur) ont ete utilisees dans des etudes biostratigraphiques, taxonomiques et paleoecologiques sur le court-terme mais jusqu’a present, jamais sur le long-terme. Ici, nous presentons l’etude d’une serie chronologique a echelle de temps longue (∼ 30 millions d’annees) du Cretace superieur, visant a identifier les tendances generales de leur taille et de comprendre les facteurs gouvernant les changements de taille des coccolithes sur une echelle de temps longue. Nous avons genere des donnees biometriques pour les groupes de coccolithes dominants au Cretace superieur, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa et Watznaueria, sur 36 echantillons du Cenomanien–Maastrichtien (100,5–66 Ma) provenant du Goban Spur dans l’Atlantique Nord-Est (DSDP Site 549). Ces donnees montrent que la taille des coccolithes appartenant aux groupes Prediscosphaera, Retecapsa et Watznaueria fut relativement stable durant tout le Cretace superieur, avec une variation de la taille moyenne inferieure a 0,7 μm. Au sein du groupe Broinsonia/Arkhangelskiella, les variations furent plus prononcees, avec une augmentation de la taille moyenne de ∼ 6 μm au Cenomanien jusqu’a ∼ 10 μm au Campanien. Ce changement significatif de la taille moyenne fut largement du aux processus evolutifs (speciations et extinctions), et en particulier a l’apparition d’especes/sous-especes plus larges (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) au Campanien inferieur, remplacant des especes plus petites, telles que Broinsonia signata et Broinsonia enormis. Cependant, les fluctuations a court-terme au sein du groupe Broinsonia/Arkhangelskiella, observees aux transitions Cenomanien–Turonien et Campanien–Maastrichtien, pourraient refleter un changement des conditions paleoenvironnementales, telles que la temperature superficielle des eaux oceaniques et la disponibilite en nutriment.