Nannoconus (similar to 5-20 mu m) was a major planktonic producer in the Early Cretaceous seas (similar to 150-120 Ma). The heavy calcitic skeletons (micaliths; similar to 200-1400 picogram) of this extinct nannoplankton genus have contributed to massive carbonate accumulations for over similar to 30 million years. The micalith microstructure is characterized by an interlocking arrangement of calcitic lamellae spanned around a central canal. The biomineralization process involved in producing the sophisticated micalith is investigated for the first time. Ptychography X-ray computed tomography (PXCT) with synchrotron radiation is applied to an isolated micalith, to obtain a 3D set of tomographic images with similar to 40 nm spatial resolution. This 3D set was processed to virtually segment the individual calcitic lamella and reconstruct the full micalith through constraining different lengths and angles. The lamellae are repetitively stacked in two distinct inclinations, one following the other, and producing segments combined to form the entire micalith. Individual lamellae were calcified in a "template" of organic layer containing amino acid(s)/biomolecule(s), responsible for creating the interlocking arrangement. Our study of Nannoconus provides a simple yet potent approach to the analysis of biomineralized microstructures characterized by the repetitive arrangement of calcitic units as commonly seen in the calcareous nannoplankton.

The calcareous nannoplankton comprises haptophyte eukaryotes known as coccolithophores, capable of calcifying elaborate external skeletons (coccoliths s.l.) which differ morphologically depending on the phase of the life cycle considered, and the locus (intra- or extracellular) of mineralization. No study is currently available that analyzes the impact of these differences on coccolith morphology. An analysis of the assembly of their crystals is conducted here in search of the following: (1) identical traits across life cycles; (2) fossil records diagnostic of extracellular calcification; and (3) influence of the geometry of biomineralization during the diploid phase on the long-term evolution of a clade. This study shows patterns such as correlation of characters and structural imprint that unify the haploid and diploid phases, indicating a strong cellular integrity and offering potent means to determine life cycles in living and fossil communities. It also shows that differences in diversity patterns and longevity among families and orders depend on coccolith geometry, concentric geometry being more favorable to stability, and superposition geometry facilitating morphological diversification. Extinction occurs when the potential for diversification is attained. Finally, I propose that the evolution of biomineralization in the calcareous nannoplankton may have been more complex than initially thought, with intra- and extracellular calcification evolving independently.

Calcareous nannofossils, a well-calibrated group of marine microfossils, are widely used to date and correlate Mesozoic and Cenozoic deposits. Despite their importance, relatively few studies have focused on these fossils in onshore deposits of South America. To address this gap, we analyzed calcareous nannofossils from several basins in the Caribbean, Pacific, and inter-Andean regions of Colombia, aiming to develop a regional framework for dating and correlating marine deposits. Our findings indicate that diagenesis significantly affects preservation of microfossils, and that nannofossil abundance is notably lower in coastal and deltaic deposits. Even so, we identified fourteen well-preserved assemblages that serve as key biostratigraphic markers, indicating ages from the Aptian (Cretaceous) to the Calabrian-Chibanian (Quaternary). By integrating these results with existing biostratigraphic data from foraminifera, palynomorphs, diatoms, and ammonites, we constructed a chronostratigraphic framework that compiles and summarizes biostratigraphic, sedimentary, and lithostratigraphic information. This regional perspective on the tropical basins of Colombia is critical for understanding the geological evolution of the Caribbean Sea and the eastern Pacific Ocean.

A French translation of the North American Stratigraphic Code was published in 1986. It concerned the Code of 1983, which was extensively revised into the Code of 2005, itself subsequently formally updated over the years and republished in 2021*. We present here a new French version of the Code. It also includes formally revised Articles 7 and 20 published in two official Reports in 2023 and 2024, respectively. At the request of the North American Commission on Stratigraphic Nomenclature (NACSN) we have provided a new translation of the North American Stratigraphic Code for the benefit of French speaking geologists around the world. We present here this work. The North American Stratigraphic Code of 1983 was translated into French by the << Minist & egrave;re de l'& Eacute;nergie et des Ressources du Qu & eacute;bec >> and published in 1986. While this translation remains available, it does not reflect the conceptual changes that guided the subsequent rewriting of the Code nor the expansion of its content, both of which led to a new publication in 2005. Several articles of the 2005 Code have since been formally amended to reflect advances in stratigraphic thinking over the years. These amendments, published in Stratigraphy, the official journal of the NACSN, were integrated in a recent, slightly revised version of the Code (2021). Nearly forty years have thus elapsed between the current Code and the 1986 French translation, well justifying the need for an updated French version of the Code. Our translation follows as closely as possible the English text, in agreement with the wish of the NACSN. However, it was not always possible to honour this request and simultaneously meet the demands of the French syntax and grammar. We were careful in conciliating the two texts and in respecting the English meaning. We have departed from the English text in two important instances. We have translated << sequence >>, used throughout the English text, into << successions >> because the term << sequence >> has acquired a specific meaning that is not easily dissociated from << sequence stratigraphy >> whereas << succession >> remains a generic term. Perhaps more importantly, we have translated << rock unit >> and << body of rock >>, idioms that describe the basic unit of stratigraphic nomenclature in the English Code, by << ensemble de terrains >> which, we think, carries more soundly and efficiently the meaning of << rock unit >> and << body of rock >> than translations such as << unit & eacute; de roche >>, << unit & eacute; rocheuse >> and << corps rocheux >> would have. In the last two years, several articles in the 2021 Code have been formally amended and their revision officially published as Reports 15 and 16 in Stratigraphy (2023 and 2024, respectively). Our translations of the amended texts of Articles 2, 61 and 62, designed to formalize chemostratigraphic units and published in Report 15, are incorporated in the present work. Report 16, which addresses in Articles 7 and 20 the empathetic matter of respect of the cultural traditions of people living in geologically significant regions, was published together with French and Spanish translations. The French version of Report 16 uses the 1986 French translation of Articles 7 and 20 while the amendments of these articles were translated by the << Bureau de la traduction, Services publics et Approvisionnement Canada >>. By the time Report 16 was submitted for publication we had already translated Articles 7 and 20, and we retain our texts here for stylistic uniformity. For the same reason, we have modified the amended texts.

A controversy has developed in recent years regarding the timing of the closure of the Central American Seaway. This tectonic event significantly impacted oceanic circulation between the tropical Pacific and Atlantic oceans and resulted in the formation of a land bridge connecting the South and North American continents. The long-held view of a Pliocene age (ca. 3 Ma) for the closure of the Central American Seaway has been challenged by the proposal that the Panamá Arc collided with South America during the Middle Miocene (15−13 Ma) as a deep oceanic gap between them closed along the Uramita suture zone. However, direct geologic evidence from this suture zone to support either interpretation has been lacking. Here, we report on a comprehensive study of three stratigraphic transects across the Uramita suture zone, using a host of methodologies including sedimentological, ichnological, micropaleontological, U-Pb detrital geochronological, and provenance analyses. Our data reveal that lower offshore to slope conditions prevailed in the Central American Seaway along the suture zone during the latest Early to earliest Middle Miocene (16.4−15.1 Ma) and that oceanic conditions there ceased to exist between the Middle and Late Miocene. These results agree with the Middle Miocene age proposed for the Central American Seaway closure along the tectonic boundary. However, other deeper portions of the Central American Seaway persisted in western Colombia, which challenges the notion of a Central American Seaway confined to the suture zone between the Panamá Arc and South American Plate during the Middle Miocene.

The International Chronostratigraphic Chart (ICC), as the basis of the International Geological Time Scale, is the primary product of the International Commission on Stratigraphy (ICS), itself the principal commission of the International Union of Geological Sciences (IUGS). The ICC represents a sustained and concerted effort by Earth scientists worldwide to produce a temporal correlation framework that is both informative and practical. As with the International Stratigraphic Guide (Hedberg 1976, Salvador 1994, Murphy et al. 2021) published by the ICS Subcommission on Stratigraphic Nomenclature (ISSC), the ICC is designed to serve the broad scientific community effectively and efficiently. Inspired by the model provided by the Committee on the Silurian-Devonian Boundary (McLaren et al. 1977), the ICS established rules to ensure a consistent and objective approach to scientific procedures in implementing a common chronostratigraphic language (Cowie et al. 1986, Remane et al. 1996). While these rules have encouraged discussion, openness, and objectivity, tensions remain in some areas where compromises have not yet been achieved. We review here one such case concerning the subdivisions of the Cenozoic Era into subseries/subepochs, in which strong opinions have hindered the integration of Cenozoic chronostratigraphy into the accepted standard. In light of long historical precedent, logical consistency with units in the Neogene and Quaternary Cenozoic systems/ periods, broad applicability across marine, terrestrial and transitional strata, and wide acceptance and use by the Cenozoic Earth Sciences community, it is clear that Paleogene subseries/subepochs should be included in the ICC.

Alkenones are long-chain ketones produced by phytoplankton of the order Isochrysidales. They are widely used in reconstructing past sea surface temperatures, benefiting from their ubiquitous occurrence in the Cenozoic ocean. Carbon isotope fractionation (epsilon p) between alkenones and dissolved inorganic carbon may also be used as a proxy for past atmospheric pCO2 and has provided continuous pCO2 estimates back to ca. 45 Ma. Here, an extended occurrence of alkenones from ca. 130 Ma is reported. We characterize the molecular structure and distribution of these Mesozoic alkenones and evaluate their potential phylogenetic relationship with Cenozoic alkenones. Using delta 13C values of the C37 methyl alkenone (C37:2Me), the first alkenone-based pCO2 estimates for the Mesozoic are derived. These estimates suggest elevated pCO2 with a range of 548-4090 ppm (908 ppm median) during the super-greenhouse climate of the Early Cretaceous, in agreement with phytane-based pCO2 reconstructions. Finally, insights into the identity of the Cretaceous coccolithophores that possibly synthesized alkenones are also offered.

The first size reduction (FSR) in the Reticulofenestra-Gephyrocapsa-Emiliania ( RGE ) lineage (order Isochrysidales), which occurred in the early Oligocene (~32 Ma), is of great significance for understanding the Lilliput effect that has affected coccolithophore communities from the late Eocene to this day. We conducted a morphologic analysis on the coccoliths of Reticulofenestra species that lived during the late middle Eocene to early Oligocene (~40–31 Ma), using marine sediments from the South Atlantic Ocean. Our data show increasing size and decreasing abundance of the large species during the late Eocene, leading to their disappearance at the FSR, and a concurrent decrease in the size variability of the small- to medium-sized coccoliths whose central opening diameter had become very reduced. Although the cosmopolitan late Paleogene through Neogene size decrease in coccolithophores has been linked to the concomitant long-term decline in global p CO 2 , we suggest here that the FSR was the result of environmental destabilization caused by the expansion of eutrophic environments following the late Eocene establishment of overturning circulation associated with ice buildup on Antarctica. This study also leads us to propose a hypothetical model that links coccolith morphology of species of the RGE lineage and trophic resources in the upper ocean: the small- to medium-sized, r-selected coccolithophores with smaller coccolith central openings live in nutrient-rich waters where they rely mostly on photosynthesis and little on mixotrophy, whereas the larger, K-selected species with larger coccolith central openings live in oligotrophic waters where they are more dependent on mixotrophy.

The Standard Auxiliary Boundary Stratotype (SABS) has been approved by the International Commission on Stra-tigraphy (ICS) as a formal replacement for the Auxiliary Stratotype Point to support a Global boundary Stratotype Section and Point (GSSP). The SABS provides a detailed complementary expression of the boundary interval with-out designating a specific point. More than one SABS may support a single GSSP and each will be subordinate to the GSSP. SABSs extend the correlative potential of a GSSP between continents, biogeographic provinces, climatic zones, depositional facies and preservational states. Require-ments for SABSs broadly follow ICS guidelines for GSSPs, and will require approval by their respective ICS subcom-mission. Following such approval, each SABS will be listed on the ICS website as well as that of the respective sub-commission, and future SABSs will be accompanied by an announcement published in the International Union of Geological Sciences journal Episodes.

The Sinú-San Jacinto Belt (SSJB) is a set of folded and faulted onshore deposits in the Caribbean region of Colombia near the tectonic boundary of the Caribbean and South American plates. Previous studies relied on biostratigraphic data from mollusks, benthic and subsequently planktonic foraminifera to establish a tectonostratigraphic framework from the Late Cretaceous to Pleistocene for these deposits. In this study, we collected over 10 years of new biostratigraphic information from calcareous nannofossils, an oceanic micropaleontological group with well-calibrated biostratigraphy, providing us the opportunity to evaluate the prior age determinations and to refine the tectonostratigraphic framework of these deposits. We found that the recovery of calcareous nannofossils varied, observing that large barren intervals affected chronostratigraphic constrains on southwestern deposits accumulated in nearshore environments. However, despite this limitation, the occurrences of biostratigraphic markers allowed us to establish that lower Eocene, upper Eocene, Oligocene, Lower Miocene and Upper Miocene deposits occur in different localities of the belt, whereas Upper Cretaceous and upper Paleocene are scarcer. Our results support the previous chronostratigraphic framework, but also indicate that the duration and origin of the hiatuses can vary with location in the belt, complicating regional correlations of the tectonostratigraphic boundaries. We suggest that integrated biostratigraphic and sedimentologic studies from additional cored sections and outcrops would help to understand the polygenetic origin of unconformities that affect the stratigraphic record in the Caribbean region of Colombia.

Auxiliary boundary stratotypes have unquestionable value in extending the knowledge of a Global boundary Stratotype Section and Point (GSSP) between continents, biogeographic provinces, climatic zones, depositional facies and preservational states.Two kinds of such stratotypes are in use, the Auxiliary Stratotype Point and the Auxiliary Stratotype Section, although only the Auxiliary Stratotype Point is recognised by the International Commission on Stratigraphy (ICS).The Standard Auxiliary Boundary Stratotype, which is based on the Auxiliary Stratotype Section, is proposed here as a formal replacement for the Auxiliary Stratotype Point.As such, it would provide a detailed complementary expression of the boundary interval without the designation of a specific point -no such points can replicate the precise level defined by a GSSP either conceptually or in practice.We recommend that requirements for future Standard Auxiliary Boundary Stratotypes broadly follow ICS guidelines for GSSPs but be applied with greater flexibility.Past practice reveals inconsistency in the protocols used for approving such auxiliary boundary stratotypes.We propose that in future they require approval by the respective ICS subcommission.More than one Standard Auxiliary Boundary Stratotype may support a single GSSP but restraint should be exercised in approving them, and each will always be subordinate to the GSSP itself.

Calcareous nannofossils were analyzed in 73 samples collected from the ANH-San Jacinto-1 cored-stratigraphic section drilled in the Sinu-San Jacinto Belt (SSJB) along the tectonic boundary of the South American and Caribbean plates in Colombia. Our quantitative results show that calcareous nannofossils were commonly abundant and moderately preserved. A total of 75 morphotypes, representing 13 genera and 55 species, were quantified. Calcareous nannofossil assemblages were dominated by Reticulofenestra spp., Sphenolithus spp., Coccolithus spp. and Helicosphaera spp. We recognized the standard biostratigraphic events highest occurrence (HO) of Reticulofenestra reticulata, HO of Discoaster saipanensis, lowest common occurrence (LCO) of Clausicoccus subdistichus, HO of Coccolithus formosus, HO of Reticulofenestra umbilicus, lowest occurrence (LO) of Sphenolithus distentus, LO of Sphenolithus ciperoensis, and LO of Discoaster druggii. This indicates that the studied deposits cover a stratigraphic range from zones NP19-20 (CNE19) to NN2 (CNM1) and encompass the 35.2 Ma to 22.5 Ma, interval from late Eocene (Priabonian) to Early Miocene (Aquitanian). The distribution patterns and age model show that the Eocene-Oligocene transition can be traced in the core and overlapping of bioevents as well as reworking of taxa suggest deep-sea stratigraphic unconformities formed during the late Eocene, early Oligocene and the Oligocene/Miocene. According to the duration of the hiatuses,-0.8 Myr,-2.2 Myr and-4.4 Myr, respectively, and the sedimentary context of the studied deposits, we suggest that these stratigraphic gaps represent downslope mass erosional episodes triggered by tectonic events and/or mud diapirism.

Marie-Pierre Aubry, Kenneth G. Miller, Elena Turco, José Abel Flores, Andrey Gladenkov, Patrick Grunert, Frits Hilgen, Hiroshi Nishi, Ann Holbourn, Wout Krijgsman, Fabrizio Lirer, Werner E. Piller, Frédéric Quillévéré, Isabella Raffi, Marci Robinson, Lorenzo Rook, Jun Tian, Maria Triantaphyllou, Felipe Vallejo. Episodes 2022;45:445-53. https://doi.org/10.18814/epiiugs/2022/022008

The IUGS Executive Committee has voted unanimously to ratify the proposal for formal adoption of the chronostratigraphical/geochronological unit divisions subseries/subepoch within the International Stratigraphic Guide as approved by the International Commission on Stratigraphy and forwarded to the IUGS EC on 24 March 2021**. The subseries/subepochs are now incorporated in a six-tiered chronostratigraphic hierarchy of units that are formally defined by a designated GSSP (Global Stage Stratotype and Point) at the base of designated type stages. Henceforth, subseries/subepochs of the Cenozoic are to be denominated by capitalised positional adjectives -Lower/Early, Middle, and Upper/Late ??? added to the names of the relevant series/epochs.

Calcareous nannofossils are micrometric calcite platelets secreted by coccolithophores and incertae sedis photosynthetic algae. Calcareous nannoplankton inhabit the photic zone from coast to open-ocean and have left an abundant fossil record since the Triassic. Therefore, they constitute an interesting material for geochemical studies although it has been overlooked in comparison to foraminifera. We have analyzed manganese distribution and valence in six calcareous nannofossil species representing different ages (Recent to Jurassic) and geological settings (land sections and deep ocean core-tops) and with different ultrastructures to assess the potential of Mn as paleobiological or paleoenvironmental proxy. Nano X-Ray Fluorescence (XRF) maps were established at the ESRF ID22NI and ID21 beamlines and Mn K-edge X-Ray Absorption Near Edge Structure (XANES) at ID21. Mn is more abundant in nannofossils from the pre-Quaternary rock samples than from core-top samples. In nannofossil rock samples, Mn nanoXRF maps show distributions correlated with primary crystalline organization whereas in nannofossil core-top samples, Mn is either absent or doesn’t follow the crystal organization. XANES analyses show that Mn is in the form of MnCO3. All these observations argue for Mn incorporation within calcareous nannofossils controlled by diagenesis through overgrowth of secondary calcite (Ca, Mn)CO3. Crusts grew along the original crystal growth directions. The incorporation of Mn in some core-top samples highlights potential early diagenesis input when the nannofossil lies on the seafloor or is still in the water column. Mn should therefore be considered a critical tool to identify diagenetic overgrowth rather than primary environmental conditions.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.