Cretaceous-Tertiary Boundary Research Articles

Cretaceous-Paleogene Boundary in the Shapsug Section (Southern Slope of the Northwest Caucasus)

A silicite horizon corresponding to the global catastrophic event of the Cretaceous-Paleogene boundary was found in the flysch sequence of the Shapsug section on the southern slope of the Northwest Caucasus for the first time. Complexes of radiolarians and planktonic foraminifers, which substantiate the age of the sediments, were identified. Mineralogical and analytical studies testify to the presence of tectites, impact minerals, increased iridium content in the boundary layer of the studied section.

Deccan volcanism's influence on Chicxulub impact signatures at the continental Cretaceous-Paleogene boundary in the Sichuan Basin, China

The Cretaceous-Paleogene (K-Pg) extinction is linked to two primary causes: the Chicxulub asteroid impact in Mexico and the Deccan Traps eruptions in India. While substantial geological evidence supporting both events has been found worldwide, to understand their potential interactions, it is crucial to study sites that preserve records of both events simultaneously. The terrestrial K-Pg boundary located in the Sichuan Basin, China (∼15,500 km from the Chicxulub Crater and ∼5,600 km from the Deccan Traps correspond to 66 Ma), preserves evidence of both the Chicxulub impact and the Deccan Traps eruptions, along with the effects of subsequent events on the earlier ones. It offers a new perspective on the K-Pg boundary. Detailed petrological examination and geochemical analyses, including platinum-group element (PGE) and black carbon concentrations, were conducted across a 2 m K-Pg boundary section. The K-Pg boundary layer (∼2.5 cm thick) is composed of very fine-grained, brick-red sandstone and exhibits significant enrichments in Ir (9.050 ppb) and Os (10.72 ppb), along with elevated black carbon (1.10 ‰), strongly indicating contributions from the impact. Intriguingly, another PGE anomaly was detected approximately 50 cm below the K-Pg boundary. The strata surrounding the K-Pg boundary display evidence of alteration by acidic and HSˉ-rich fluids. These fluids likely caused the observed downward migration of PGE within the boundary, resulting in two distinct PGE anomalies - one at the K-Pg boundary itself and another approximately 50 cm below. These fluids resulted in the overlying sandstones exhibiting minimal matrix content and bleached the underlying brick-red sandstones. Volcanic gas emissions from the Deccan Traps after the impact are a potential source for these fluids. Our findings support the hypothesis that the most voluminous Deccan eruptions had occurred close to, but not necessarily immediately after, the Chicxulub impact, potentially lasting 100–131 ka. The hiatus after the impact weakens the possibility of a direct causal link between the Deccan eruptions and the impact.

Ruthenium isotopes show the Chicxulub impactor was a carbonaceous-type asteroid.

An impact at Chicxulub, Mexico, occurred 66 million years ago, producing a global stratigraphic layer that marks the boundary between the Cretaceous and Paleogene eras. That layer contains elevated concentrations of platinum-group elements, including ruthenium. We measured ruthenium isotopes in samples taken from three Cretaceous-Paleogene boundary sites, five other impacts that occurred between 36 million to 470 million years ago, and ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers. Our data indicate that the Chicxulub impactor was a carbonaceous-type asteroid, which had formed beyond the orbit of Jupiter. The five other impact structures have isotopic signatures that are more consistent with siliceous-type asteroids, which formed closer to the Sun. The ancient spherule layer samples are consistent with impacts of carbonaceous-type asteroids during Earth's final stages of accretion.

Late Cretaceous ammonoids show that drivers of diversification are regionally heterogeneous

Palaeontologists have long sought to explain the diversification of individual clades to whole biotas at global scales. Advances in our understanding of the spatial distribution of the fossil record through geological time, however, has demonstrated that global trends in biodiversity were a mosaic of regionally heterogeneous diversification processes. Drivers of diversification must presumably have also displayed regional variation to produce the spatial disparities observed in past taxonomic richness. Here, we analyse the fossil record of ammonoids, pelagic shelled cephalopods, through the Late Cretaceous, characterised by some palaeontologists as an interval of biotic decline prior to their total extinction at the Cretaceous-Paleogene boundary. We regionally subdivide this record to eliminate the impacts of spatial sampling biases and infer regional origination and extinction rates corrected for temporal sampling biases using Bayesian methods. We then model these rates using biotic and abiotic drivers commonly inferred to influence diversification. Ammonoid diversification dynamics and responses to this common set of diversity drivers were regionally heterogeneous, do not support ecological decline, and demonstrate that their global diversification signal is influenced by spatial disparities in sampling effort. These results call into question the feasibility of seeking drivers of diversity at global scales in the fossil record.

End of the Cretaceous

Abstract The Cretaceous ended when the Chicxulub asteroid struck the Yucatán platform, and all deposits and landforms generated are earliest Paleocene in age. Drill core from the Cretaceous–Paleogene (K–Pg) boundary sequence deposited on top of the Chicxulub impact structure's peak ring paired with geophysical data within the crater and other well-preserved marine and terrestrial K–Pg boundary sites provide insight into impact processes and effects on Earth's ecosystems, in terms of extinction and recovery. Key findings as reviewed here are: (1) the confirmation of acoustic fluidization as a physical principle to explain impact structure formation; (2) the importance of the target rock properties and marine setting for impactite depositional processes and drivers of climate change; (3) the state of understanding of extinction mechanisms and ecological recovery; and (4) implications for impact-generated hydrothermal habitat creation. Areas highlighted for the next stages of discovery include: (1) physics and chemistry of impact vapour plumes and ejecta processes; (2) sampling of the K–Pg boundary deposit and impact melt sheet within the central basin of the impact structure; (3) examination of ecosystem recovery in an ‘Early Ocean’ scenario at a range of K–Pg boundary sites; and (4) experiments and observations of impact hydrothermal systems as habitats on Earth and other worlds.

Imbalanced speciation pulses sustain the radiation of mammals.

The evolutionary histories of major clades, including mammals, often comprise changes in their diversification dynamics, but how these changes occur remains debated. We combined comprehensive phylogenetic and fossil information in a new "birth-death diffusion" model that provides a detailed characterization of variation in diversification rates in mammals. We found an early rising and sustained diversification scenario, wherein speciation rates increased before and during the Cretaceous-Paleogene (K-Pg) boundary. The K-Pg mass extinction event filtered out more slowly speciating lineages and was followed by a subsequent slowing in speciation rates rather than rebounds. These dynamics arose from an imbalanced speciation process, with separate lineages giving rise to many, less speciation-prone descendants. Diversity seems to have been brought about by these isolated, fast-speciating lineages, rather than by a few punctuated innovations.

Carbonate mounds formed by mud volcanism at the Cretaceous-Paleogene boundary, Saudi Arabia

More than 1000 mound structures have been mapped in shallow marine sediments at the Cretaceous-Paleogene boundary in the Rub’ Al-Khali of Saudi Arabia. Mapping used 3D reflection seismic data in a 37,000 km2 study area. No wells penetrate the mounds themselves. The mounds are at a present-day subsurface depth of approximately 1 km, and they are convex-up with diameters of 200–400 m and elevation of 10–15 m. The mounds display spatial self-organization with a mean separation of approximately 3.75 km. Comparison with mound populations in other study areas with known spatial distribution statistics and modes of origin indicates that the mound population in this study has the characteristics of fluid escape structures, and they are interpreted here as mud volcanoes. The observation that the mounds occur at the Cretaceous-Paleogene boundary demands a singular trigger at that moment in time. We develop a model of seismic energy-related mud volcanism mechanism including the Chicxulub asteroid impact as the energy source that accounts for the timing of the mound structures and a drainage cell model based on producing water wells that provides a mechanism for spatial self-organization into a regular pattern.

Terrestrial records of two hyperthermal events in the Cretaceous-Paleogene boundary suggest different control mechanisms

Two hyperthermal events with different carbon cycle perturbations occurred across the Cretaceous-Palaeogene boundary, i.e., the late Maastrichtian Warming Event and the Early Danian Dan-C2 event. However, the roles played by Deccan volcanism and orbital forcing in these two hyperthermal events are still debated. Here we obtain a terrestrial δ13Ccarb record in the Nanxiong Basin (southeastern China) and compare it with marine records. The results show that both hyperthermal events can be well distinguished and that the Dan-C2 event is characterized by a typical hyperthermal event. In addition, the δ13C excursion during the late Maastrichtian Warming Event was more muted and prolonged than that during the Dan-C2 event, and the short-eccentricity cycle disappeared in the marine record during the late Maastrichtian Warming Event, indicating that Deccan volcanism perturbed the carbon cycle during the late Maastrichtian Warming Event, while the Dan-C2 event was less influenced by volcanic perturbation.

Last 150 kyr volcanic activity on Mauritius island (Indian ocean) revealed by new Cassignol-Gillot unspiked K–Ar ages

We present new K–Ar ages extending the volcanic history of Mauritius Island towards the Holocene. Mauritius volcanism is associated with the activity of the Réunion hotspot, the magmatism of which produced the Deccan Traps across the Cretaceous-Tertiary (KT) boundary and continues up to present on Réunion Island. After shield building from before 8.9 Ma to 4.7 Ma, Mauritius Island underwent an unusual volcanic evolution involving two rejuvenation stages (3.5–1.9 Ma and <0.7 Ma) separated by a 1.2 Myr hiatus. The lower bound of the second rejuvenation stage being poorly constrained, it is not clear whether volcanism in this island has come to a rest. Given the occurrence of uneroded, and yet undated strombolian cones in Mauritius, it is important to better constrain the latest activity of this island in order to assess its volcanic hazard. The importance of dating the end of this stage is also enhanced by the fact that most of the surface of Mauritius is covered by the lavas of the rejuvenation stages, hence indicating a recent volcanic activity that needs to be better characterized for risk assessment.We focus here on the last 150 ka interval which lacked precise age controls with only a few whole-rock and groundmass 40Ar/39Ar plateau ages available (Moore et al., 2011), ranging from 138 ± 29 to 40 ± 48 ka (uncertainties are 1 σ). Our six new Cassignol-Gillot unspiked K–Ar ages obtained on plagioclase or groundmass range from 113 ± 7 to 14 ± 3 ka, with much lower uncertainties than previous ages available. Our major and trace element analyses of the dated samples highlight the compositional homogeneity of the lavas erupted in the last rejuvenation stage, showing no geochemical evolution.Our results, with ages as young as 14 ± 3 ka, demonstrate that near-Holocene volcanism is present in Mauritius Island, with no evidence of fading magmatism in the last 150 ka. Our second youngest age at 44 ± 5 ka implies that the latest activity occurred after a ∼30 kyr repose interval, with the consequence that Mauritius volcanism may resume at any time.

A giant bowfin from a Paleocene hothouse ecosystem in North America

Abstract Aquatic biodiversity changed dramatically at the start of the Paleogene. Although comparatively little is known about global freshwater ecosystems that appeared just after the Cretaceous–Paleogene mass extinction, available data suggest that they were buffered from the worst effects of the extinction event. Here, we describe a nearly complete skeleton of a large-bodied ray-finned fish from a wetland ecosystem that existed fewer than 10 Myr after the end-Cretaceous extinction in western North America. With a maximum length likely exceeding 2 m, †Amia basiloides sp. nov. is one of the largest species in Holostei, a once species-rich clade of ray-finned fishes now survived by the nine living species of gars and bowfins. High-resolution computed tomography scans illuminate the anatomy of †A. basiloides and suggest it was an analogue of living large-bodied, piscivorous freshwater fishes found in the Southern Hemisphere and southern North America. When considered in a phylogenetic context, †A. basiloides shows that close relatives of living bowfins rapidly achieved gigantism in the Early Paleogene of North America after the largest members of an ancient clade closely related to bowfins went extinct. Although the Cretaceous–Paleogene boundary likely induced turnover of freshwater vertebrate predatory guilds, holostean faunas remained ecologically comparable across the extinction due to exceptionally fast episodes of convergence.

Response of the calcareous nannofossils to the Cretaceous-Paleogene boundary event: A case study from Sinai, Egypt

A detailed study of calcareous nannofossils was conducted on a well-exposed succession encompassing the Cretaceous-Paleogene (K-Pg) boundary interval at Wadi Nukhul, Sinai, Egypt, as a part of the southern Tethyan margin. The nannofossil biostratigraphic data show that the Nukhul succession sustains a complete K-Pg boundary interval. The nannofossil assemblage indicates a shift from cool/oligo-mesotrophic conditions in the late Maastrichtian Micula murus Zone to warm/oligotrophic in the latest Maastrichtian M. prinsii Zone prior to the K-Pg boundary. At the K-Pg boundary, diversity, and total abundance of the calcareous nannofossils remarkably decreased signifying unstable marine conditions. The post-impact assemblage (lowermost part of NP1 Zone) was marked by acme of Cervisiella operculata indicating oligotrophic conditions in the photic zone related to the diminished of the marine primary producers in the lowermost Danian. At the upper portion of the NP1 Zone, the assemblage is still dominated by C. operculata, besides the successive occurrence of the small-sized incoming Paleocene taxa Biantholithus sparsus and Neobiscutum romeinii. This pattern was accompanied by increased frequencies of Zeugrhabdotus sigmoides indicating stressful cool/meso-eutrophic surface water conditions signify the initial recovery interval. Upward in the early Danian NP2-NP3 zones, the nannofossil species diversity and total abundance progressively increased. Also, the nannofossil assemblage characterized by the existence of the new Paleocene oligotrophic indicators like Cruciplacolithus primus, Coccolithus pelagicus, and Ericsonia subpertusa. This probably indicates a tendency toward rebuilding of the biological pump efficiency and, therefore, a full recovery phase was resumed.

Paleoenvironmental shifts across Cretaceous–Paleogene boundary: insights from multi-proxy chemo stratigraphy of the Mahadeo–Cherrapunji section, Meghalaya, India

Paleoenvironmental shifts across Cretaceous–Paleogene boundary: insights from multi-proxy chemo stratigraphy of the Mahadeo–Cherrapunji section, Meghalaya, India

The Cretaceous–Paleogene Boundary in the Shapsug Section (Southern Slope of the Northwestern Caucasus)

The Cretaceous–Paleogene Boundary in the Shapsug Section (Southern Slope of the Northwestern Caucasus)

Long-term variations in terrestrial carbon cycles and atmospheric CO2 levels: Exploring impacts on global ecosystem and climate in the aftermath of end-Cretaceous mass extinction

The short-term climate and environmental consequences (<∼1.0–10 Kyr) immediately following the end-Cretaceous extinction have been attributed to transient effects originating from Deccan volcanism and the Chicxulub impact. These two events have received significant attention for their role in precipitating extreme climate conditions. In contrast, the long-term (> ∼100 Kyr) climate and environmental changes of the post-extinction have been extensively studied in the marine systems, yet their ramifications within terrestrial ecosystems are less well-characterized and require further elucidation. This study presents a carbon isotope analysis of pedogenic carbonates from matured calcisols in the Nanxiong Basin, South China, to reconstruct carbon cycles and atmospheric CO2 concentrations (pCO2) spanning from 76.0 Ma to 62.0 Ma, aiming to decipher the long-term terrestrial environmental and climatic conditions. Results show that δ13C values range from −12.4‰ to −5.0‰ (mean − 9.0‰) and pCO2 varies between ∼250 ppmV and ∼ 2200 ppmV (mean 920 ppmV). When combined with δ13C data from Songliao Basin, NE China, the carbon cycle variation exhibits a 13C collapse and smooth towards subsequent rebound, indicating a process of ∼600 Kyr deterioration, ∼600 Kyr stabilization and ∼ 400 Kyr recovery in the terrestrial ecosystem. The fluctuation of estimated pCO2 aligns with the change pattern of sea surface temperatures, attesting to the strong perturbation of climate and environment at the same pace as the carbon cycle variations. It is proposed that ecosystems and environments in both terrestrial and surface ocean experienced a more unstable, difficult and erratic recovery process and were much more sensitive to climatic changes than in deep ocean for ∼1.5 million years in the aftermath of the end-Cretaceous mass extinction. In addition, the divergence of proxy variations from expected effects implies the Deccan eruption and Chicxulub impact could not have played a long-term role in governing the climatic and environmental perturbations following the Cretaceous-Paleogene Boundary.

Combined cadmium and chromium isotopes record a collapse of bioproductivity across the Cretaceous—Paleogene boundary in the Danish basin

Cadmium (Cd) isotope signatures (δ114Cd) deduced from modern and ancient marine deposits are often used as a proxy for bioproductivity and for micronutrient cycling, whereas chromium (Cr) isotope signatures (δ53Cr) are used as a potential proxy for oxygenation. The Cretaceous—Paleogene (K/Pg) boundary records one of Earth's five big mass extinctions, which contains geochemical fingerprints of the Chixculub asteroid impact and is coeval with the Deccan Trap volcanism. Here we present for the first time a combined record of Cd and Cr isotopes from the Danish Basin to interrogate the effects on bioproductivity across the K/Pg boundary. The δ114Cd values range between −0.28‰ and 0.27‰ defining an average of 0.05‰ ± 0.24 (2σ, n = 87). Authigenic δ53Cr values range between 0.06‰ and 1.06‰ and define an average of 0.59‰ ± 0.51 (2σ, n = 81). An abrupt jump, across the K/Pg boundary layer, from consistently positively fractionated Cd and Cr isotope signatures recorded in Late Maastrichtian white chalks towards less positively fractionated δ114Cd values and heterogeneous δ53Cr values in the Early Danian carbonates, likely indicates a decrease in surface water bioproductivity. This decrease is accompanied by redox fluctuations in the water column as a consequence of environmental changes either related to the Chixculub impact event and/or to the Deccan volcanic eruptions coeval with this boundary. Assuming an efficient removal of Cd and Cr through consumption and/or adsorption by primary producers, or by incorporation into the skeleton/shells of calcifiers, and using the fractionation factor of Cd into carbonates, we reconstruct surface water conditions during the Late Masstrichtian—Early Danian that are compatible with those of modern oceans, with δ114Cd varying from 0.17 to 0.72‰. Overall, the combined Cr-Cd isotope fluctuations over the K/Pg boundary are consistent with a scenario characterized by climate-induced changes of nutrient availability and concomitant responses of primary production levels, ultimately related to the asteroid impact and to the proceeding volcanic activities that influenced the ocean's chemistry. We anticipate our results to point for further studies of other stratigraphic sections worldwide to reveal an extensive Cd-Cr record for the Cretaceous—Paleogene boundary and its corresponding collapse of bioproductivity and decreasing ocean oxygenation.

Genomes, fossils, and the concurrent rise of modern birds and flowering plants in the Late Cretaceous

The phylogeny and divergence timing of the Neoavian radiation remain controversial despite recent progress. We analyzed the genomes of 124 species across all Neoavian orders, using data from 25,460 loci spanning four DNA classes, including 5,756 coding sequences, 12,449 conserved nonexonic elements, 4,871 introns, and 2,384 intergenic segments. We conducted a comprehensive sensitivity analysis to account for the heterogeneity across different DNA classes, leading to an optimal tree of Neoaves with high resolution. This phylogeny features a novel Neoavian dichotomy comprising two monophyletic clades: a previously recognized Telluraves (land birds) and a newly circumscribed Aquaterraves (waterbirds and relatives). Molecular dating analyses with 20 fossil calibrations indicate that the diversification of modern birds began in the Late Cretaceous and underwent a constant and steady radiation across the KPg boundary, concurrent with the rise of angiosperms as well as other major Cenozoic animal groups including placental and multituberculate mammals. The KPg catastrophe had a limited impact on avian evolution compared to the Paleocene-Eocene Thermal Maximum, which triggered a rapid diversification of seabirds. Our findings suggest that the evolution of modern birds followed a slow process of gradualism rather than a rapid process of punctuated equilibrium, with limited interruption by the KPg catastrophe. This study places bird evolution into a new context within vertebrates, with ramifications for the evolution of the Earth's biota.

Elasmobranch assemblages from a bathyal environment spanning the Cretaceous-Paleogene boundary in Austria

Abstract Extensive bulk-sampling of the continuous Cretaceous-Paleogene boundary section at Gams (Styria, Austria) allows for the first time the description of the elasmobranch communities inhabiting the bathyal environment of this well-known section. The sampled succession comprises six horizons from the uppermost Maastrichtian (upper part of Nephrolites frequens Zone CC26) and five horizons from the lowermost Danian (Zone NP1), which yielded a total of 1852 elasmobranch teeth. Although the majority of the teeth are not well preserved, this study enabled the description of at least 16 taxa of the orders Hexanchiformes, Squaliformes, Orectolobiformes, Lamniformes and Carcharhiniformes, providing a rare snapshot of elasmobranch diversity of this specific environmental setting. Beside minor diversity fluctuations between the assemblages, the extensive bulk-sampling of this section did not reveal a marked diversity decline related to the end-Cretaceous mass extinction event. However, a noteworthy correlation between the deepening upward trend of the section with the appearance of frilled and goblin sharks points to changes in palaeobathymetry, which is also reflected in the increase of the total proportion of squaliform teeth in the uppermost sampled horizon. Furthermore, teeth of the extinct triakid Palaeogaleus were recovered exclusively from the Danian deeper deposits, expanding the palaeoecological range of the genus down to fairly deep marine environments. In addition, this study provides the first record of the lamniform Cretolamna ex gr. borealis from the Danian of the Tethyan Realm expanding the palaeogeographic distribution of this group.

Mechanistic phylodynamic models do not provide conclusive evidence that non-avian dinosaurs were in decline before their final extinction

Abstract Phylodynamic models can be used to estimate diversification trajectories from time-calibrated phylogenies. Here we apply two such models to phylogenies of non-avian dinosaurs, a clade whose evolutionary history has been widely debated. Although some authors have suggested that the clade experienced a decline in diversity, potentially starting millions of years before the end-Cretaceous mass extinction, others have suggested that the group remained highly diverse right up until the Cretaceous-Paleogene (K-Pg) boundary. Our results show that model assumptions, likely with respect to incomplete sampling, have a large impact on whether dinosaurs appear to have experienced a long-term decline or not. The results are also highly sensitive to the topology and branch lengths of the phylogeny used. Developing comprehensive models of sampling bias, and building larger and more accurate phylogenies, are likely to be necessary steps for us to determine whether dinosaur diversity was or was not in decline before the end-Cretaceous mass extinction.

The Cretaceous carbonate platforms of the Americas and their rudist bivalves

Abstract Following the break-up of Pangaea, many rifted margins of the Americas became carbonate platforms. During the Cretaceous, these platforms, as well as those associated with volcanic arcs, were populated by rudist bivalves that underwent a major radiation from the Early to Late Cretaceous. Carbonate platform development was episodic with major platforms represented by the Hauterivian to early Aptian, the early to late Albian and the Campanian to Maastrichtian. Different rudist bivalves characterized different phases of platform development. The Hauterivian to Aptian saw the rise of the Rethinae and Caprinidae, and was terminated by Oceanic Anoxic Event 1a (OAE1a). The Albian saw the rise of the Caprinuloideina and Youngicaprininae together with the first radiolitids. The Cenomanian is poorly understood in term of rudist bivalve development and the effects of the Cenomanian–Turonian boundary event (CTBE or OAE2) are not well documented in the Americas. The Turonian to Maastrichtian saw a major radiation at the genus level of the rudists – hippuritids were initially represented by cosmopolitan genera, but through the late Santonian to early Campanian these were replaced by endemic genera. The radiolitids and antillocaprinids also underwent major radiations at this time, and numerous new endemic taxa characterized the carbonate platforms of the Americas. The Cretaceous–Paleogene boundary event decimated the carbonate platforms of the Americas and wiped out the rudist bivalves. Two new radiolitid genera are described: Vermuntia and Thiadensia .

Mafic adakite-like magmatism at the Cretaceous–Paleogene boundary from the Northwest Rhodopes, Bulgaria

Mafic adakite-like magmatism at the Cretaceous–Paleogene boundary from the Northwest Rhodopes, Bulgaria