Albian-Cenomanian Transition Research Articles

Cenomanian terrestrial paleoenvironments from the Bohemian Cretaceous Basin in Central Europe and their implications for angiosperm paleoecology

In this paper, we reconstruct the vegetation communities of five terrestrial paleoenvironments from the Cretaceous (Cenomanian) Peruc-Korycany Formation of the Bohemian Cretaceous Basin in Czechia. Reconstructions are based on a synthesis of numerous studies of paleobotany, palynology, paleoecology, sedimentology and geochemistry analyses. Ordered in a transect from coastal marine settings to elevated hinterland regions, paleoenvironments and plant assemblages are reconstructed as follows: (1) Saltmarsh vegetation comprising a Frenelopsis-Classopollis assemblage; (2) Coastal freshwater swamp vegetation comprising a Cunninghamites-Taxodiaceaepollenites assemblage; (3) Meandering river floodplain vegetation comprising a Myrtophyllum-Perucipollis assemblage; (4) Braided river floodplain vegetation comprising a Eucalyptolaurus-Mauldinia assemblage; and (5) Vegetation of drier upland areas comprising fern prairies with angiosperms and Bennettitales - a Zamites-Ephedripites assemblage. Our study shows that in Cenomanian times, angiosperms were diversified, particularly in alluvial plains, where lauroid and platanoid angiosperms prevailed. Comparison of these Cenomanian paleoenvironments in Czechia with other Cenomanian paleoenvironments across Europe show a widespread dominance of angiosperms in the vegetation of alluvial plains across much of the continent. This contrasts with Barremian-Albian times when angiosperms occupied only disturbed habitats, and our findings suggest that angiosperm exchanged a ruderal (disturbed) strategy for a competitive strategy during the Albian-Cenomanian transition. Conversely, conifers dominated alluvial plains in Early Cretaceous times, while they rose to dominate saltmarshes and swamps in the Bohemian Cenomanian, exchanging a competitive strategy for a stress-tolerant strategy.

Benthic foraminifera across the Albian–Cenomanian transition and their paleoceanographic significance during OAE1d in the western Tethys (Umbria–Marche Basin, Italy)

The benthic foraminiferal assemblages from the upper Albian-lower Cenomanian interval of the Scaglia Bianca Formation in the Monte Petrano (MP) and Le Brecce (LB) sections (Umbria–Marche Basin; Italy) provide a detailed record of the faunal changes across the Oceanic Anoxic Event 1d (OAE 1d). Fluctuations in abundance, diversity, and species composition reflect variations in bottom-water oxygenation and organic carbon fluxes. Benthic foraminifera are integrated with planktonic foraminifera, calcareous nannofossils, and geochemical proxies to reconstruct the bottom and surface water conditions across the OAE 1d in the Umbria–Marche Basin.The pre-OAE 1d interval was characterized by benthic foraminifera that thrived under stable mesotrophic condition in bottom waters. In surface waters, planktonic foraminifera indicate dominant mesotrophic conditions in agreement with calcareous nannofossil assemblages suggesting a regime of higher fertility under cooler conditions.During the OAE 1d interval, benthic foraminifera display an increase in the abundance of infaunal taxa, suggesting mesotrophic conditions in bottom waters. Nevertheless, within the Pialli Level, the six laminated black-to-dark grey shale horizons (MP1/LB1 to MP6/LB6), benthic foraminifera are absent or highly impoverished (MP1, MP2, MP4, MP6, LB5, LB6), suggesting hypoxic/anoxic conditions in bottom waters. Planktonic foraminifera in this interval reflect mesotrophic to oligotrophic conditions under the presence of an expanded mixed layer and deeper thermocline in the surface waters. Calcareous nannofossils record warm conditions and lower fertility starting just prior to and across the OAE 1d. However, higher values of fertility are recorded in the black-to-dark grey shales MP3/LB3, MP4/LB4 and MP5/LB5 of the Pialli Level.The post-OAE 1d interval is marked by an increase in the diversity of benthic foraminifera, indicating a restoration of the oxygen conditions in a continuous mesotrophic regime in bottom waters. The surface waters experienced oligotrophic conditions based on the planktonic and calcareous nannofossils.A minor discrepancy between benthic foraminifera and geochemical reconstruction of oxygenation levels of bottom waters was recorded, especially in the Pialli Level. The benthic microfaunas appear to be very sensitive to very short-term oxygen depletion at the seafloor when geochemical proxies suggest temporary suboxia. This might indicate that very rapid redox changes are not resolved by bulk elemental data. Otherwise, benthic foraminifera might be much more responsive to very low concentrations of oxygen in bottom waters and temporarily disappear under strong suboxia before reaching fully anoxic conditions.

A first high-resolution carbon isotope stratigraphy from the Boreal (NW Germany) for the Berriasian to Coniacian interval—implications for the timing of the Aptian–Albian boundary

High-amplitude changes in sedimentary δ13C characterize the Cretaceous system and have been proven useful for supra-regional chemostratigraphic correlation. In the Cretaceous, these δ13C perturbations indicate large shifts between the global carbon reservoirs that are usually caused by volcanic activity of large igneous provinces, the widespread deposition of thick organic carbon-rich sequences and/or changes in orbital parameters. Here, we present an upper Berriasian to lower Coniacian (c. 142–88 Ma) composite carbon isotope record based on 14 drill cores, 2 outcrops, and almost 5,000 samples. The total record comprises a composite thickness of more than 1,500 m. All cores and successions are located in the larger Hanover area, which represents the depocenter of the North German Lower Saxony Basin in Early to mid-Cretaceous times. In Northern Germany, Boreal Lower Cretaceous sediments are predominantly represented by CaCO3-poor mud and siltstones of up to 2,000 m thickness, which become more carbonate-rich during the Albian–Cenomanian transition and even chalkier in the upper Cenomanian to Coniacian interval. The carbon isotope record reveals a number of global key events, including the Valanginian Weissert Event, the Oceanic Anoxic Events (OAEs) 1a and d, and the Kilian Event (Aptian–Albian boundary, part of OAE 1b). For the early Late Cretaceous, the Mid-Cenomanian Event, the OAE 2 (Cenomanian–Turonian Boundary Event), and the Navigation Event, among others, have been identified. The Kilian Event represents the Aptian–Albian boundary and has been identified herein for the first time in Northern Europe. Based on the evaluation of its relative position to the Vöhrum boundary tuff, we tentatively propose a slightly older age for the Aptian–Albian boundary of c. 113.65 Ma instead of 113.2 Ma. The observed chemostratigraphic events enable a detailed stratigraphic comparison with Tethyan and other Boreal records and associated paleoenvironmental data. Thus, this new detailed chemostratigraphy provides a unique opportunity to potentially overcome many still existing Boreal–Tethyan correlation issues. The presented record can be considered almost complete, albeit a 2-Myr gap during the early Albian is likely, and condensed intervals occur specifically during the lower Aptian.

Brachiopods from the Albian–Cenomanian transition (Cretaceous) of the Eastern Prebetic (South-Iberian paleomargin)

Brachiopod communities in the Albian–Cenomanian transition from the Eastern Betic Ranges were previously accredited and frequently considered as biochronostratigraphical tools to dating the hemipelagic successions of this timespan by correlation with other neighboring Tethyan basins. However, the knowledge of these mid-Cretaceous assemblages in this part of the South-Iberian paleomargin remained poorly understood so far. Brachiopod communities of this timespan are commonly dominated by homeomorphic terebratulides and asymmetrical multicostate rhynchonellides, these later recurrently attributed to Cyclothyris difformis due to the strong external similarity with their NW-European counterparts, and consequently, the Prebetic deposits were customarily assigned to the Cenomanian stage. In this work, the detailed analysis of the assemblages from the taxonomic and biostratigraphical standpoints allows for the identification of a new brachiopod fauna endemic to the Eastern Prebetic Domain, inhabiting platform environments with frequent terrigenous inputs in transition to the more offshore areas. This analysis has led to the formal description of two new species, Cyclothyris bitririca and Sellithyris binalubensis, together with Cyclothyris ementitum, recently erected as new species, plus Psilothyris hispanica, both endemic to the Prebetic area as well. The successive faunal replacement between two defined assemblages enclosing this fauna is a useful regional biomarker around the Albian–Cenomanian boundary. The bioevents typifying this turnover consist of a rhynchonellide taxa short-term replacement and the burst on diversity and abundance of smooth, nearly homomorphic terebratulides for the levels just underlying the base of the Cenomanian stage.

Stratigraphy of the Albian–Cenomanian (Cretaceous) phosphorite interval in central Poland: a reappraisal

Several closely-spaced phosphorite beds stand out at the Albian–Cenomanian transition in the mid-Cretaceous transgressive succession at the northeastern margin of the Holy Cross Mountains, central Poland. They form a distinctive condensed interval of considerable stratigraphical, palaeontological, and economic value. Here, we correlate the classical section at Annopol with a recently investigated section at Chałupki. We propose a new stratigraphic interpretation of the phosphorite interval, based on lithological correlations, Rare Earth Elements and Yttrium (REE+Y) signatures of phosphorites, age-diagnostic macrofossils, and sequence stratigraphic patterns. This interval has long been considered as exclusively Albian in age. However, new macrofossil data allow us to assign the higher phosphorite levels at Annopol and Chałupki, which were the primary target for the phosphate mining, to the lower Cenomanian. In terms of sequence stratigraphy, the phosphorite interval encompasses the depositional sequence DS Al 8 and the Lowstand System Tract of the successive DS Al/Ce 1 sequence. The proposed correlation suggests that lowstand reworking during the Albian–Cenomanian boundary interval played an important role in concentrating the phosphatic clasts and nodules to exploitable stratiform accumulations. Our conclusions are pertinent to regional studies, assessments of natural resources (in view of the recent interest in REE content of the phosphorites), and dating of the fossil assemblages preserved in the phosphorite interval. On a broader scale, they add to our understanding of the formation of stratiform phosphorite deposits.

Vegetation and climate change at the southern margin of the Neo-Tethys during the Cenomanian (Late Cretaceous): Evidence from Egypt.

Changes in terrestrial vegetation during the mid-Cretaceous and their link to climate and environmental change are poorly understood. In this study, we use plant macrofossils and analysis of fossil pollen and spores from the Western Desert, Egypt, to assess temporal changes in plant communities during the Cenomanian. The investigated strata have relatively diverse sporomorph assemblages, which reflect the nature of parent vegetation. Specifically, the palynofloras represent ferns, conifers, monosulcate pollen producers, Gnetales, and a diverse group of angiosperms. Comparisons of both, dispersed palynoflora and plant macrofossils reveal different characteristics of the palaeoflora owing to a plethora of taphonomical and ecological biases including the depositional environment, production levels, and discrepancies between different plant organs. A combination of detailed records of sporomorphs, leaves, and charcoal from the studied successions provide new understandings of the palaeoclimate and palaeogeography during the Cenomanian and Albian-Cenomanian transition in Egypt. The mixed composition of the palynofloral assemblages reflects the presence of different depositional situations with a weak marine influence, as evidenced by a minor dinoflagellate cysts component. The local vegetation comprised various categories including herbaceous groups including ferns and eudicots, fluvial, open environments, and xeric arboreal communities dominated by Cheirolepidiaceae and perhaps including drought- and/or salt-tolerating ferns (Anemiaceae) and other gymnosperms (Araucariaceae, Ginkgoales, Cycadales, and Gnetales) as well as angiosperms. The presence of riparian and freshwater wetland communities favouring aquatic and/or hygrophilous ferns (of Salviniaceae and Marsileaceae), is noted. The wide variation of depositional settings derived from the palynological data may be attributed to a prevalent occurrence of producers in local vegetation during the early Cenomanian of Egypt. For the purpose of this work on the studied Bahariya Formation and its equivalent rock units, where iconic dinosaurs and other fossil fauna roamed, we attempt to improve the understanding of Egypt's Cenomanian climate, which is reconstructed as generally warm and humid punctuated by phases of considerably drier conditions of varying duration.

The Albian-Cenomanian transition in a shelf-basin transect: Biostratigraphy, sedimentology and paleontology of Jebel Mghila, Central Tunisia

Twenty-two ammonite species are identified in the upper Albian Mortoniceras (Subschloenbachia) rostratum, Mortoniceras (Subschloenbachia) perinflatum and Stoliczkaia (Shumarinaia) africana Zones, and in the lower Cenomanian Mantelliceras mantelli Zone. The species Placenticeras Saadensis Thomas and (Thomas and Peron, 1890, 1890 is revised, including Engonoceras Thomasi Pervinquière, 1907, and is placed within the genus Hypengonoceras Spath, 1922. This accurate biostratigraphic framework allowed to evidence, at the Albian-Cenomanian transition (S. (S.) africana Zone), a significant sea level drop, responsible for emergence and erosion to the SE, and for deposition of a Lowstand wedge to the NW, fed by erosional channels on the shelf slope. Plesiosaur remains found in the upper Albian series (base of M. (S.) rostratum Zone) represent one of the few elasmosaurids known worldwide in the Albian, and the first plesiosaurian reported from Tunisia.

Late Aptian to early Cenomanian dinoflagellate cysts from Agadir Basin, southwestern Morocco: Biostratigraphy and palaeoenvironment

The Agadir Basin (Moroccan Atlantic margin) is characterized by its fossil richness, including organic-walled microfossils. The palynological analysis of the middle Cretaceous succession from the Tamzargout section and EGA.1 well reveals the presence of well-preserved and diverse assemblage, rich in dinoflagellate cysts. The assemblages contain stratigraphic marker taxa and show significant chronostratigraphic events. Based on these bioevents and on the comparison with different palaeogeographic domains, a determination of age was proposed. The biogeographic characteristics of most cosmopolitan taxa in this study confirm the establishment of new oceanic communication related to the opening of the equatorial Atlantic. The Albian-Cenomanian transition has been recognized only in EGA.1 well, whereas the Aptian-Albian transition, the early-mid Albian and the mid-late Albian have been defined in both the section and the well. The recorded associations are comparable to those of neighboring deposits and those of the Tethyian and Atlantic domains. The vertical distribution of the organic matter in the sediments of the Agadir Basin and the compilation of all palaeoenvironmental proxies allowed identifying an Albian transgression with specific palaeoenvironments in each interval. Neritic marine environments alternated with short phases of continental and oceanic influence is deduced for the late Aptian-early Cenomanian in this basin. The late Aptian-early to mid Albian recorded an outer neritic palaeoenvironment under oceanic influence; the mid to late Albian showed littoral conditions during a regressive phase fluctuating to middle to outer neritic environment; finally the late Albian-early Cenomanian transition was characterized by a middle neritic palaeoenvironment under coastal influence.

Tectonic and climate control on allochthonous bauxite deposition. Example from the mid-Cretaceous Villeveyrac basin, southern France

Karst bauxite deposits represent 11% of the global quantity of bauxite (Bardossy and Aleva, 1990). Karst Bauxite is defined as bauxite deposits overlying carbonate rocks above a more or less karstified surface. Allochtonous karst bauxites result from two successive processes: (1) intense weathering and formation of a lateritic profile, involving the development of bauxitic and duricrust horizons; and (2) erosion of the lateritic profile and deposition above a carbonate unit located downstream. In the Villeveyrac basin (southern France), Lower to Mid-Albian allochtonous karstic bauxites are deposited on a Jurassic karstified bedrock, and are overlain by a Late Albian marine siliciclastic cover. A drillcore, sampling the substratum, the bauxites and their cover, is analyzed and offers the opportunity to investigate the depositional conditions and interactions of climate and tectonic during the mid- to late Cretaceous, through the analysis of mechanical and chemical weathering evidence. Sedimentological study allowed the definition of four bauxite facies and three siliciclastic cover facies, overprinted by four different pedofacies. Mineralogical and geochemical analyses allowed the distinction of four mineralogical units controlled by climate-related weathering processes. The bauxite deposits emplaced by mud-flow/debris-flow gravity currents are composed by boehmite-hematite and goethite. The top of the bauxite presents a progressive upward decrease in Al2O3 and TiO2 associated with the occurrence of kaolinite. The base of the cover that overlies the bauxite interval corresponds to a paralic environment, dominated by kaolinite, with a sub-ferricrete paleosol. The following paralic sequence presents a clay-rich suite dominated by smectite, associated with mica/illite and quartz, which suggests aridification of climate around the latest Albian. We interpret this sedimentary succession as the result of erosion of an autochthonous laterite cover, induced by major tectonic uplift in the upstream drainage area, which led to a significant increase in slope gradient, under a wet tropical climate. Mechanical erosion of autochthonous laterite bauxite in the upstream drainage led to a reverse stacking of the reworked autochthonous lateritic profile in the depositional basin. A continuous transgressive trend was responsible for trapping of the allochtonous karst bauxite. This was followed by stacking of siliciclastic paralic sequences, which record progressive erosion of the bedrock in the upstream drainage area, under dry tropical conditions. Our results thus suggest that dismantling of the autochthonous laterite cover was initiated by Albian uplift and this ended with a change towards drier and more seasonal climate at the Albian-Cenomanian transition.

Palaeoclimatic reconstruction for a Cenomanian‐aged angiosperm flora near Schefferville, Labrador

AbstractAn understanding of local and regional climate trends is essential to investigate the remarkable angiosperm radiation that happened during the Albian–Cenomanian transition. However, many of the inland depositional environments pioneered by the first modern angiosperms are poorly represented in the fossil record. Eastern Canada, in particular, has a very poor Mesozoic record. In this paper, we present the first multivariate palaeoclimate analysis (CLAMP) for the environment of a geologically isolated woody dicot dominated flora found in the Redmond no.1 mine, Labrador, near Schefferville, with an estimated Cenomanian age. It reveals that the Redmond flora would have experienced a mean annual temperature of 15.1 ± 2.1°C, one of the coolest recorded for North America at this time. These results confer the Redmond no.1 site a warm temperate and fully humid climate with a hot summer, in accordance with previous qualitative palaeoclimate estimates. This flora fits smoothly into palaeolatitudinal MAT gradients that use other Cenomanian‐estimated North American floras. Despite an inland setting, the climate analysis does not recover a significantly higher degree of seasonality than the sites to which it is compared, which agrees with established climate equability models for the Cretaceous and Palaeogene. This study also introduces 15 new morphotypes discovered in recent fieldwork. The eventual description of the species they represent may refine our dating estimates for the Redmond Formation. A greater understanding of the depositional environment and of the natural history of these angiosperms is required to improve this community's characterization, along with estimates from other proxies.

Biostratigraphy, carbon isotopes and cyclostratigraphy of the Albian-Cenomanian transition and Oceanic Anoxic Event 1d in southern Tibet

During the Albian and Cenomanian, the Earth underwent profound climatic and oceanographic changes that were recorded in sedimentary successions on a global scale. Carbon isotope records spanning this time interval have been established in the western Tethys, eastern Pacific and North Atlantic Oceans, but not yet in the eastern Tethys Ocean. In this paper, we present biostratigraphic, chemostratigraphic and cyclostratigraphic characteristics of the uppermost Albian–lowermost Cenomanian in an eastern Tethyan section (Youxia, southern Tibet). Based on calcareous nannofossil biozones and the bulk rock δ13C curve, the Albian-Cenomanian boundary interval (ACBI) was identified and correlated to the western Tethys and Atlantic Oceans. In the Youxia section, δ13C values range from approximately 0‰ to +1.3‰ (−0.03‰ to +1.31‰). Four subevents (a, b, c and d) were distinguished in the ACBI carbon isotope curve via correlation with other sections. Based on a spectral analysis of the carbonate content, we recognized Milankovitch short eccentricity (~100 kyr) and precession (22.2 kyr) cycles, suggesting that orbital variations modulated depositional processes. The duration of the ACBI was estimated at ~311 kyr, while OAE 1d lasted for ~233 kyr in the eastern Tethys Ocean, consistent with the duration calculated from Atlantic Ocean records.

Palynofloral evolution on the northern margin of the Indian Plate, southern Xizang, China during the Cretaceous Period and its phytogeographic significance

During the Cretaceous Period, the Indian Plate separated from Gondwana and drifted northwards, eventually colliding with Eurasia at the end of the period or in the early Cenozoic. This led to major changes in the composition of the flora and fauna of the region. Palynomorph assemblages from Cretaceous deposits in Gamba County, southern Xizang (Tibet), China, are analyzed herein in an attempt to determine how the vegetation of the northern margin of the Indian Plate changed. The Gamba assemblages were initially similar in composition to those from Australia but by the Santonian Stage they were more similar to those of North Africa. Differences from the former are increasingly apparent through the Albian–Cenomanian transition. The rate of evolution of the Gamba flora was about the same as that of the Australian flora prior to the Albian, somewhat slower during this stage, but faster from the Cenomanian onwards, implying that this was, to a large extent, a result of the separation of the Indian Plate from Gondwana and its northward drift during the Cretaceous Period. During the Albian, the Australian block drifted eastwards whereas the Indian Plate remained relatively static. This resulted in few changes in the Gamba palynoflora but many in palynofloras from Australia. However, the northward movement of the Indian Plate in the Late Cretaceous led to pronounced changes, with numerous inceptions of genera and species in the Gamba succession. Of these, many have an African or equatorial distribution and none has connections with Australia, indicating that the climate at this time was similar to that of North Africa and that separation from Australia was complete. The arrival of the Indian Plate in equatorial regions allowed floral exchange between its northern part and North Africa during the Santonian.

The Albian–Cenomanian transition and Oceanic Anoxic Event 1d – an example from the Boreal Realm

AbstractThe upper Albian to lower Cenomanian interval in the Hanover area (Germany) is characterized by a well‐developed lithological transition from upper Albian monotonous (marly) claystones of several hundred metres thickness, which become enriched in biosilica in the topmost Albian, to increasingly CaCO3‐rich marls and limestones in the lower and middle Cenomanian. This study presents a new 165 m thick composite record spanning the latest Albian to mid‐early Cenomanian (ca 103·0 to 97·5 Ma) based on two core drillings at Anderten in the central Lower Saxony Basin (east of Hanover), which is a sub‐basin of the North German Basin. Due to the lack or delayed occurrences of Tethyan biostratigraphic markers for the late Albian and early Cenomanian in the Boreal Realm, the definition of the Albian–Cenomanian boundary, as based on the lowest occurrence of Thalmanninella globotruncanoides, is not applicable. In order to overcome this issue, an integrated biostratigraphic–chemostratigraphic approach has been employed. In addition to biostratigraphy (calcareous nannofossils, ostracods, planktonic foraminifera and inoceramids), the Anderten succession has been studied using sedimentary geochemistry (CaCO3, total organic carbon, δ13C and δ18O), γ‐ray logging and X‐ray fluorescence core scanning. This approach enabled successful correlation of the composite Anderten record to European reference sections in England, south‐east France and Italy, as well as to further low‐resolution records from the Lower Saxony Basin (Wunstorf and Konrad 101 core). This work has made it possible to identify the δ13Ccarb expression of: (i) the Oceanic Anoxic Event 1d; (ii) the Albian–Cenomanian boundary interval; and (iii) potentially the Lower Cenomanian Event(s). Chemostratigraphic age assignments are supported by biostratigraphic results. Calcareous nannofossils indicate an extended Upper Cretaceous 0 (UC0) zone (upper Albian) up to Upper Cretaceous 2 (UC2; upper lower Cenomanian), and the occurrence of the ostracod Physocythere steghausi supports an early Cenomanian age for most of the upper part of the composite record. Notably, influxes of the planktonic foraminifer Thalmanninella aff. reicheli have previously been described from this area and the first appearance of this taxon is usually used to define the base of the middle Cenomanian Substage. However, findings from the Anderten cores and elsewhere suggest that this taxon has an apparently earlier first appearance, questioning previous age assignments from the Boreal Realm solely based on planktonic foraminifera. Due to both moderately well‐preserved microfossils and high sedimentation rates, the drilled succession of Anderten is considered as a potential Boreal reference section for the Albian–Cenomanian transition.

A mid-Cretaceous angiosperm-dominated macroflora from the Cedar Mountain Formation of Utah, USA

AbstractAngiosperms first appeared in the fossil record as pollen during the Valanginian–Hauterivian; they spread out of the tropics in the Aptian and Albian, and radiated in the Late Cretaceous. Despite these general patterns, details of the taxonomic, geographic, and ecological evolution of Cretaceous angiosperms are relatively poorly known because only a handful of Early and mid-Cretaceous macrofloras have been reported. This is the first detailed report of a fossil leaf flora from the Cedar Mountain Formation from the mid-Cretaceous of the Western Interior. We describe a flora that is overwhelmingly dominated by angiosperms (152 of 153 identified specimens are angiosperms) from the Albian–Cenomanian transition that is preserved in a clay- and carbonate-rich, lacustrine mudstone from the uppermost Cedar Mountain Formation of Emery County, Utah. We recognize 18 leaf morphotypes, all of which are dicotyledonous angiosperms. The majority of the Cedar Mountain morphotypes have taxonomic affinities with forms of similar age described from the Atlantic and Gulf coastal plains and other localities from the Western Interior. From this, we infer that a relatively diverse angiosperm flora grew along the margins of a small pond on the coastal plain. Palynological preparations of the fossil matrix were barren; however, previous studies of other facies within the formation showed that both conifers and ferns were important components of the regional vegetation during Cedar Mountain time. The effective absence of conifers and ferns in this macroflora and low leaf mass per area values among the angiosperms measured suggests that even at the Early–Late Cretaceous transition, angiosperms had come to dominate some sites, particularly those that were disturbed or seasonally ephemeral, where fast-growth or seasonal deciduousness would have been favored.

Recent contributions to the standard Albian/Cenomanian boundary chronology from Hokkaido, Japan: A review for data reintegration and numerical age recalibration

The numerical age of the Albian/Cenomanian (A/C) boundary (=Early/Late Cretaceous Epoch boundary) has recently been updated using new radiometric dates from Hokkaido, Japan. Yet, an element of uncertainty still remains in the age scaling due to inaccurate chronostratigraphic contexts surrounding the tuff beds that have been geochronologically studied in the Oyubari and Soeushinai areas. To ensure stability in the Cretaceous time scale, this paper rigorously reevaluates the current status of Hokkaido A/C chronology, clarifying the limitations and making refinements via proper reintegration of published chronostratigraphic data. In the case of the Oyubari area, its A/C biostratigraphic scheme is limited by near-absence of ammonites and planktonic foraminifera at the Albian–Cenomanian transition, resulting in a large discrepancy in the proposed boundary levels based on these macro- and microfossil taxa. These problems can be solved by solid data integration aided by event- and δ13C-sratigraphy from the adjacent Ashibetsu area, wherein the A/C boundary is well documented by the superior planktonic foraminiferal record. Based on the resultant A/C boundary redefinition for the Oyubari area in conjunction with a simple linear interpolation from two published UPb ages, the A/C boundary age can be independently calibrated to be 100.8 Ma [with ±1.4 Myr uncertainty (=analytical precision)], which is consistent with that currently in use in the Geologic Time Scale 2012 (100.5 ± 0.4 Ma). In the case of the Soeushinai area, its chronostratigraphic framework is limited by rather complex geological structure and vertically/laterally variable lithologies. Moreover, the accuracy of geochronological data from this area is undermined by the fact that the dated tuff levels do not bracket the inferred A/C boundary.

Chemical Characterization and Botanical Origin of French Ambers.

The molecular composition of 10 Cretaceous and one Eocene ambers from France was analyzed by infrared spectroscopy, solid-state (13)C nuclear magnetic resonance spectroscopy, and thermochemolysis gas chromatography-mass spectrometry. The terpenoids identified in the samples were used as biomarkers for the botanical origin of the resins. The Cretaceous samples, comprising the so-called Alpine, Anjou, Charentese, Provence, Pyrenean, and Vendean ambers, ranged from the Albian-Cenomanian transition to the early Santonian (100 to 85 Ma) and correspond to class Ib resins typical of conifers. The extinct conifer family Cheirolepidiaceae was proposed as the plant source of Pyrenean and brown Charentese ambers. Araucariaceae or Cheirolepidiaceae were the plant sources of the Cenomanian Alpine, Anjou, and yellow Charentese ambers. The Santonian ambers of Provence and Vendée were found to derive from the Cupressaceae. The Eocene Oise amber (ca. 53 Ma) is a class Ic resin typical of angiosperms and was produced by a Fabaceae. The evolution of resin sources from the early Cretaceous to the Eocene periods is discussed. Finally, a possible fingerprint hitherto unveiled is proposed for cheirolepidiaceous resins, defined by the simultaneous presence of phenolic diterpenoids, labdanoic acids, callitrisate structures, and their respective derivatives.

The uppermost Albian–lower Cenomanian Bielba Formation of the type-area (Cantabria, northern Spain): facies, biostratigraphy, and benthic Foraminifera

The lithofacies, microfacies, depositional sequences, and benthic Foraminifera of the uppermost Albian–lower Cenomanian Bielba Formation in its type-area in northern Cantabria, Spain, consisting of a lower siliciclastic member and an upper Cobreces Member, have been investigated. The investigated section constitutes a hypostratotype for the Bielba Formation, and the lower siliciclastic member is here formally defined as the Somocuevas Member. The obtained data are framed in the major global paleoenvironmental and paleoceanographic changes that occurred during the Albian–Cenomanian transition. Eleven lithofacies types have been identified from facies analysis and vertical log characterization. These lithofacies accumulated in various depositional settings such as storm, wave, and tidal influenced delta front and shoreface, shallow-water carbonate ramp, and offshore marine environments. Within an overall transgressive trend, the succession of the Bielba Formation comprises two depositional transgressive–regressive sequences corresponding to the Somocuevas and Cobreces Members, bounded by a major relative sea-level fall at the end of the Albian. The sea-level fall was followed by a rapid marine transgression and shifting from siliciclastic-dominated deposition of the Somocuevas Member to carbonate-dominated deposition of the Cobreces Member. The microfauna of the Cobreces Member is characterized by omnipresent orbitolinids, trocholinids, and a variety of other mostly small-sized foraminifera that so far have not attracted much attention. Among them, taxa with biostratigraphic importance and taxonomic–phylogenetic importance can yet be found. The benthic Foraminifera are associated with calcareous green algae (dasycladaleans, udoteaceans) and occur in calcarenites of poorly diversified microfacies containing variable amounts of siliciclastics. The microfauna closely compares to that of the overlying late early to middle Cenomanian Altamira Formation.

Cenomanian transgression in the Basque-Cantabrian Basin (northern Spain) and associated faunal replacement

The available data concerning the environmental changes and faunal replacements that occurred during the Cenomanian marine transgression in the North of Iberia are integrated and discussed on the basis of new evidence from the invertebrate and vertebrate fossil record. New stratigraphical data and the reassessment of known stratigraphic sections support the correlation of the Cenomanian carbonate-ramp successions from the Iberian margin to the centre of the Basque-Cantabrian Basin during a major transgressive episode. This new stratigraphical framework is the key to understand the changing oceanographic conditions in the area that resulted from a progressive inundation of the Iberian continental platform. This transgression seems to have triggered major faunal replacements in this particular geographic area, starting out around the Albian-Cenomanian transition. Ammonite faunal replacement led to a new radiation of this group that spread out rapidly until their new decline around the Cenomanian-Turonian boundary. A new record of Calycoceras (Newboldiceras) asiaticum spinosum and the first record of a Pachyrhizodontidae indet. (Actinopterygii, Teleostei, Crossognathiformes) from the Iberian Peninsula are reported here from the Cenomanian basal units of the major Late Cretaceous transgressive episode. The two new specimens come from the same level in an outer marine ramp succession near Amurrio, Basque Country, northern Spain, and are representatives of the Cenomanian faunal turnover. The new record of a pachyrhizodontoid fish from the Cretaceous of Iberia is an indication of the ichthyofaunal replacement in this part of the world. The relict fish faunas from the Early Cretaceous of the former island of Iberia were mostly formed by basal neopterygian taxa closely related to those of the marine Jurassic of other parts of Europe. During the Early-Late Cretaceous transition they were replaced by the teleostean-based new stock that constitutes the basis of the Late Cretaceous, Cenozoic, and Recent faunas.

Paleoclimatic reconstruction for the Albian–Cenomanian transition based on a dominantly angiosperm flora from the Cedar Mountain Formation, Utah, USA

The Soap Wash flora from the Cedar Mountain Formation of Emery County, Utah (Albian–Cenomanian boundary) consists almost entirely of angiosperms and is positioned stratigraphically near the first appearance of flowering plants in this region. We applied both univariate (leaf margin analysis—LMA, and leaf area analysis—LAA) and multivariate (Climate Leaf Analysis Multivariate Program—CLAMP) methods to the 17 morphotypes recognized in the flora to reconstruct palaeoclimate. LMA produced a mean annual temperature (MAT) estimate ranging from 19 °C to 26 °C. CLAMP yielded 16 °C–18 °C. LAA produced a mean annual precipitation (MAP) of 81 cm, while CLAMP generated a mean growing season precipitation of 134–187 cm, within the range of standard error for the LAA estimation. CLAMP also estimated a nine to ten month growing season with some temperature seasonality and substantial seasonality in precipitation. This reconstruction is broadly consistent with sedimentological data that suggested a semiarid to monsoonal precipitation regime for the region and with climate models that predict warm summers and strong winter seasonality in precipitation. Leaf physiognomic parameters of the Soap Wash flora fall within the range of variation circumscribed by the calibration sets of all three methods, so the differences in reconstructed MAT values cannot be explained exclusively by this kind of systematic error. We propose two alternative hypotheses: First, modern leaf form-climate relationships may not yet have evolved. This seems unlikely because CLAMP has been successfully applied to older material elsewhere. Second, the Soap Wash flora may be out of equilibrium with its prevailing climate due to contemporaneous rapid climate flux. If correct, this pattern may suggest a link between mid-Cretaceous environmental perturbations and the rapid diversification and geographic spread of flowering plants.

Palynological studies of the boundary marls unit (Albian-Cenomanian) from northeastern Spain. Paleophytogeographical implications

ABSTRACT Detailed records of spore-pollen assemblages from four sites located in the Aliaga and Oliete Sub-basins provide new insights into the palaeoclimatic and palaeogeographic settings during the Albian-Cenomanian transition in the Maestrazgo Basin (northeastern Spain). Palynological taxa such as Afropollis jardinus Doyle, Jardine & Doerenkamp, 1982, Elaterosporites klaszii (Jardine & Magloire) Jardine, 1967, Equisetosporites ambiguus (Hedlund 1966) Singh, 1983, Gabonisporis pseudoreticulatus Boltenhagen, 1967, Senectotetradites varireticulatus Dettmann, 1973, Stellatopollis barghoornii Doyle, 1975, and the dinoflagellate cyst Cyclonephelium chabaca Below, 1981 indicate a latest Albian age for this unit. Abundance of Gondwanan elements such as Afropollis Doyle, Jardine & Doerenkamp, 1982, Elaterosporites Jardine, 1967 and Stellatopollis Doyle, 1975 indicates a northward extension of the paleogeographic distributions of those taxa during this time. Comparison between the studied microflora of the Iberi...