New biochronological scales of planktic foraminifera for the early danian based on high-resolution biostratigraphy

After the Cretaceous/Paleogene boundary (KPB) catastrophic mass extinction event, an explosive evolutionary radiation of planktic foraminifera took place in consequence of the prompt occupation of empty niches. The rapid evolution of new species makes it possible to establish high-resolution biozonations in the lower Danian. We propose two biostratigraphic scales for low-to-middle latitudes spanning the first two million years of the Danian. The first is based on qualitative data and includes four biozones: the Guembelitria cretacea Zone (Dan1), the Parvularugoglobigerina longiapertura Zone (Dan2), the Parvularugoglobigerina eugubina Zone (Dan3), and the Parasubbotina pseudobulloides Zone (Dan4). The latter two are divided into several sub-biozones: the Parvularu-goglobigerina sabina Subzone (Dan3a) and the Eoglobigerina simplicissima Subzone (Dan3b) for the Pv. eugubina Zone, and the Praemurica taurica Subzone (Dan4a), the Subbotina triloculinoides Subzone (Dan4b), and the Globanomalina compressa Subzone (Dan4c) for the P. pseudobulloides Zone. The second scale is based on quantitative data and includes three acme-zones (abundance zones): the Guembelitria Acme-zone (DanAZ1), the Parvularugoglobigerina-Palaeoglobigerina Acme-zone (DanAZ2), and the Woodringina-Chiloguembelina Acme-zone (DanAZ3). Both biozonations are based on high-resolution samplings of the most continuous sections of the lower Danian worldwide and have been calibrated with recent magnetochronological and astrochronological dating

Revalidation of the genus Chiloguembelitria Hofker: Implications for the evolution of early Danian planktonic foraminifera

Guembelitria is the only planktonic foraminiferal genus whose survival from the mass extinction event of the Cretaceous/Paleogene (K/Pg) boundary has been clearly proven. The evolution of Guembelitria after the K/Pg boundary led to the appearance of two guembelitriid lineages in the early Danian: one biserial, represented by Woodringina and culminating in Chiloguembelina, and the other trochospiral, represented by Trochoguembelitria and culminating in Globoconusa. We have re-examined the genus Chiloguembelitria, another guembelitriid descended from Guembelitria and whose taxonomic validity had been questioned, it being considered a junior synonym of the latter. Nevertheless, Chiloguembelitria differs from Guembelitria mainly in the wall texture (pustulate to rugose vs. pore-mounded) and the position of the aperture (umbilical-extraumbilical to extraumbilical vs. umbilical). Chiloguembelitria shares its wall texture with Trochoguembelitria and some of the earliest specimens of Woodringina, suggesting that it played an important role in the evolution of early Danian guembelitriids, as it seems to be the most immediate ancestor of both trochospiral and biserial lineages. Morphological and morphostatistical analyses of Chiloguembelitria discriminate at least five species: Chg. danica, Chg. irregularis, and three new species: Chg. hofkeri, Chg. trilobata and Chg. biseriata

Smooth and rugose wall textures in earliest Danian trochospiral planktic foraminifera from Tunisia

New scanning electron microscopy (SEM) photographs of planktic foraminiferal specimens from Tunisian sections (El Kef, Aïn Settara, Elles) have revealed the occurrence of two lineages of primitive trochospiral species in the lowermost Danian. The first lineage to appear, which evolves at the P0-Pa transition, exhibits a smooth and/or granular wall texture (with pore-murals), and its species were attributed to the parvularugoglobigerinids (Parvularugoglobigerina and Palaeoglobigerina). The second to appear at the Pa-P1 transition has a rugose wall texture (with rugosities and isolated irregular pore-mounds) and is herein assigned to the new genus Trochoguembelitria. Both lineages co-occur in the upper part of Pa (middle-upper part of Eoglobigerina simplicissima Subzone), containing quasi-homeomorph species - pseudocryptic under stereomicroscopy - only differentiated under SEM by their wall texture (e.g., Palaeoglobigerina alticonusa vs Trochoguembelitria alabamensis). The data at our disposal suggest Trochoguembelitria derived from triserial Guembelitria and its species evolved in parallel with the parvularugoglobigerinids in the earliest Danian.Fil: Arenillas, Ignacio. Universidad de Zaragoza; EspañaFil: Arz, José A.. Universidad de Zaragoza; EspañaFil: Nañez, Carolina Adela. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Did Late Cretaceous cooling trigger the Campanian–Maastrichtian Boundary Event?

The Campanian-Maastrichtian (83-66 Ma) was a period of global climate cooling, featuring significant negative carbon-isotope (delta C-13) anomalies, such as the Late Campanian Event (LCE) and the Campanian-Maastrichtian Boundary Event (CMBE). A variety of factors, including changes in temperature, oceanic circulation and gateway opening, have been invoked to explain these delta C-13 perturbations, but no precise mechanism has yet been well constrained. In order to improve our understanding of these events, we measured stable carbon and oxygen isotopes of hemipelagic sediments from the Shuqualak-Evans cored borehole (Mississippi, USA) and compared the data with previously published sea-surface temperature (SST) estimates from the same core. We found that the CMBE can be recognised, unambiguously, in the Shuqualak-Evans core, and that it is associated with an interval of cooler SSTs suggesting a possible mechanistic link between palaeotemperat ure change and this event. Determining the precise position of the LCE in the Shuqualak-Evans core is more problematic, but it may also be associated with cooler SSTs. Our combined records of carbon cycling and SSTs compare well with other studies and provide evidence that cooling during the CMBE (and possibly LCE) was global in nature and affected surface waters, in addition to the deep-ocean. We suggest that short-term cooling drove intensification of high-latitude deep-water formation, which in turn led to changes in the ratio of carbonate to organic carbon burial that led to a negative delta C-13 excursion. Critically, the absence of warming during these intervals implies that the Late Cretaceous events must not have been associated with an appreciable increase in atmospheric pCO(2), and was likely associated with decreased pCO(2)

Morphostatistical analysis of Maastrichtian populations of Guembelitria from El Kef, Tunisia

Three species of Guembelitria with regular triserial arrangement are recognized in the late Maastrichtian, based on biometric measures of specimens from El Kef (Tunisia) and morphostatistical analysis. They are mainly recognized based on their test height and rate of increase in size of the chambers. Guembelitria blowi, nov. sp. is proposed for the short-spired morphotypes that were previously ascribed to Guembelitria trifolia. Guembelitria cretacea Cushman, 1933, is restricted to medium-spired morphotypes, and Guembelitria dammula Voloshina, 1961, to high-spired morphotypes. The three morphospecies have a papillate test surface, usually with pore-mounds, but some specimens exhibit imperforate papillae. The origin of this variability in the guembelitrid test surface might be linked to ecophenotypy or ontogeny, but the presence of cryptic species cannot be ruled out.Fil: Arz, José A.. Universidad de Zaragoza; EspañaFil: Arenillas, Ignacio. Universidad de Zaragoza; EspañaFil: Nañez, Carolina Adela. Secretaria de Industria y Mineria. Servicio Geológico Minero Argentino. Subsecretaria de Mineria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Dinoflagellate biostratigraphy at the Campanian-Maastrichtian boundary in Zumaia, northern Spain

Dinoflagellate cyst assemblages from a well-exposed uppermost Cretaceous section at Zumaia (northern Spain) provide a basis for comparison with previous biostratigraphic and magnetostratigraphic studies on the problematic location of the Campanian-Maastrichtian boundary in the section. The position of the last occurrence of Corradinisphaeridium horridum and first common occurrence of Alterbidinium acutulum, correspond well with the bioevents defining the Campanian-Maastrichtian boundary in the Global boundary Stratotype Section and Point of Tercis les Bains (130 km to the North). Together with other age-diagnostic dinoflagellate cyst bioevents, we suggest that the boundary should be placed between 239.75 and 224.75 m below the Cretaceous-Palaeogene boundary, about 46 m lower than an interpretation based on the first occurrence of the planktonic foraminifer Pseudoguembelina palpebra and the last occurrence of the nannofossil Broinsonia parca subsp. constricta. A conspicuous acme of the dinoflagellate cyst Thalassiphora cf. delicata is encountered around the lower-upper Maastrichtian boundary (calibrated by foraminiferal, calcareous nannoplankton and magnetic polarity data), which may prove to be a useful correlatable event

Maastrichtian-basal Paleocene charophyte biozonation and its calibration to the Global Polarity Time Scale in the southern Pyrenees (Catalonia, Spain)

A new charophyte biozonation for the non-marine Maastrichtian−lowermost Paleocene deposits in the South-Eastern Pyrenean Vallcebre Basin is proposed and calibrated to the Global Polarity Time Scale (GPTS) using magnetostratigraphic data. Planktonic foraminifera associated with charophyte assemblages provide maximum ages for correlation between non-marine and marine biostratigraphic zonations. The new charophyte biozonation is intended to be useful for terrigenous floodplain facies (red beds) with poorly developed lacustrine intervals and strong palaeoecological constraints for the development of charophytes. The taxonomy of charophytes was revisited and two new species were defined, Microchara nana Vicente and Martín-Closas and Peckichara serrata Vicente and Martín-Closas. Sedimentological analyses carried out in parallel with taphonomic observations allow us to infer the palaeoecological constraints of charophyte species. The new biozonation encompasses three biozones for the late Campanian−early Paleocene interval. The partial range biozone of Peckichara cancellata starts in chron C32r (∼73.91 Ma) according to previous studies, and extends its upper limit to chron C31r, with an age of ∼69.90 Ma in the Vallcebre Basin. The new Microchara punctata local biozone includes biozones of Septorella ultima (upper part), Microchara cristata and Peckichara sp. 1 (lower part) previously defined by Feist in Riveline et al. (1996). Some of these biozones were poorly characterized or were based on species with strong palaeoecological constraints. The lower Danian is characterized by the biozone of Peckichara toscarensis, replacing the previous biozone of Peckichara llobregatensis. The latter species was found to occur in the Maastrichtian

Multiproxy analysis of paleoenvironmental, paleoclimatic and paleoceanographic changes during the early Danian in the Caravaca section (Spain)

After the Chicxulub impact and mass extinction at the Cretaceous-Paleogene boundary (K-PgB), ecosystems haltingly recovered under unstable conditions. An early Danian (65.9 Ma) perturbation of the carbon cycle known as Dan-C2, which includes two carbon isotopic excursions (CIEs), has been ascribed to inputs of greenhouse gases through large-scale volcanism of the Deccan Traps. However, the relationship between Dan-C2, volcanism and environmental and climatic changes during the early Danian remains ambiguous. Based on stable isotopes, calcium carbonate content, magnetic susceptibility and planktic foraminifera, we present a paleoenvironmental, paleoclimatic and paleoceanographic reconstruction of the early Danian from the Caravaca section, Spain, one of the most complete and continuous K-PgB sections worldwide. The paleobiological response of planktic foraminifera suggests very volatile environmental conditions during the first 230 kyr of the Danian, as reflected in the rapid succession of opportunistic/generalist blooms and episodic high occurrences of aberrant specimens. According to our age model, the Dan-C2 has been identified at the Caravaca section from 65.92 to 65.74 Ma. No evidence of strong carbonate dissolution through ocean acidification was observed in the Dan-C2 interval or the rest of the studied section, excluding the K-PgB clay bed. We find that blooms of highly eutrophic Chiloguembelitria and increases in aberrant planktic foraminifera coincided with a major early Danian eruptive episode of Deccan Traps (Ambelani Formation), occurring before the Dan-C2. Conversely, during both Dan-C2 CIEs, less opportunistic taxa thrived, indicating changes in the upper part of the water column. This study demonstrates that the relationship between marine biota and climate change was very complex and rapidly changing during the early Danian. In addition, we propose that the Deccan volcanism had adverse effects on marine plankton, mostly through strong eutrophication, while an increased water column stratification during the Dan-C2 event resulted in a transient boost in the recovery of ecosystems. © 2021 Elsevier B.V