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Cylindrical borings assigned to ichnospecies Trypanites mobilis Neumann, Wisshak & Bromley, 2008, are common in bulbous echinoid spines (Tylocidaris baltica and Ty. vexilifera) and globular calcareous sponges (Porosphaera globularis) from the Maastrichtian chalk and Danian limestone of eastern Denmark. Trypanites mobilis was originally described as being restricted to these substrates but is here reported also from crinoid fragments and asteroid ossicles. A revised diagnosis of Tr. mobilis is proposed to accommodate the broader spectrum of host bioclasts and the fact that some bioclasts, notably Porosphaera, are fully penetrated. Trypanites mobilis is interpreted as a mobile shelter for sipunculan worms and the first appearance of this trace fossil around the Early/Late Cretaceous transition is inferred to reflect intensified predation pressure, and a general shortage of hard substrates on the muddy chalk sea floor. Trypanites mobilis is very common in the Maastrichtian of Denmark. It then nearly disappears in the lower Danian, re-occurs in the middle Danian, at first with smaller sizes and in low numbers, before becoming numerous and large-sized again around the middle/upper Danian transition. The near absence of Tr. mobilis in the lower Danian and its low abundance in the middle Danian is suggested to reflect that the ‘substrate makers’ were affected by ecological instability following the Cretaceous–Palaeogene mass extinction. Trypanites mobilis disappeared after the mid/late Danian transition, i.e. before extinction of its Danian substrate-maker Ty. vexilifera. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • First study of combined Cd and Cr isotopes as tracer applied to carbonates across the Cretaceous—Paleogene boundary. • Coupling of the double tracer Cd-Cr isotopes to bioproductivity in ambient seawater. • Severe changes in Cd and Cr isotopes across the K/Pg boundary linked to the collapse of bioproductivity. • First study to correlate C and O stable isotopes with the non-traditional isotope systems. [ABSTRACT FROM AUTHOR]

We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions of the Corsicana and Kincaid formations exposed along the Brazos River in Falls County, Texas. An abundant fauna of eight species comprising four genera of ammonites is described from the Corsicana Formation, including Discoscaphites mullinaxorum n. sp. The presence of abundant aptychi (probably lower jaws) of Discoscaphites and Eubaculites, as well as juvenile specimens, indicates a living population that experienced little postmortem drift. The lytoceratid genus Gaudryceras is also reported for the first time from the Brazos River area. Presence of the index taxon Discoscaphites iris (Conrad, 1858) indicates that the fauna belongs to the D. iris Range Zone, the highest ammonite range zone in North America. Correlation with new and existing microfossil data indicates that the fauna represents the uppermost Maastrichtian, and comparison with published records further suggests that this is the most diverse D. iris Zone fauna yet reported from the Gulf and Atlantic Coastal Plains of North America. Three ammonite genera are recorded from the basal units of the K-Pg event deposit at Brazos, which likely represents deposition in the immediate aftermath of the Chicxulub impact event. A single specimen of the nautilid Eutrephoceras is reported from the Danian Kincaid Formation, less than 300 kyr after the K-Pg boundary. These data provide new information on the differing fate of these cephalopod groups during the K-Pg mass extinction and add to the picture of diverse and abundant Maastrichtian ammonite faunas prior to the Chicxulub impact event. [ABSTRACT FROM AUTHOR]

A 460 m long profile of the Cretaceous-Paleogene (K-T) boundary strata at Stevns Klint was measured by the late Professor A. Rosenkrantz probably in 1944. The measured profile was inherited by Finn Surlyk around 1974 together with other original boundary data. This material was dug up in a long-forgotten drawer in connection with detailed field work by the co-authors on the boundary succession in the late spring and summer of 2021. The profile illustrates the stratigraphy, geometry and palaeotopography of the boundary strata in unprecedented detail. The part of the cliff illustrated in the profile is today partly covered by beach ridges composed of flint rubble but is situated below the finest section of the lower Danian bryozoan mounds exposed at Stevns Klint. This coastal section is situated immediately adjacent to a large limestone quarry and was planned to be quarried away around 1937, but was saved by A. Rosenkrantz who demonstrated its great scientific and educational value to the authorities. [ABSTRACT FROM AUTHOR]

Abstract Changes in the size and in the shape of the cross of the early Danian Cruciplacolithus lineage have been studied along with bulk carbon isotope data at two reference Cretaceous–Paleogene boundary sections: Bidart, SW France (Basque Basin) and Elles, central Tunisia (SW Tethys). Our study documents a progressive increase in the size of this lineage in the early Danian and allows for the definition of a new sub-lineage with a narrow central area and a broad axial cross composed of two species: a small, primitive and rare form, Cruciplacolithus praebornemannii n.sp. and a large common form Cruciplacolithus bornemannii n.sp. Successive first occurrences in the lineage of "axial cross" Cruciplacolithus can be correlated between the two sections. This correlation shows that the recovery phase in carbon isotopes following the Cretaceous–Paleogene boundary negative excursion is delayed in the southwestern Tethys compared to the Basque Basin. The delayed recovery in carbon isotopes at the Elles section could be related to the lengthened environmental stress in shelfal settings as compared to the pelagic settings of the Basque-Cantabrian basin. The emergence of Cruciplacolithus , the occurrence of the different lineages in this genus and the change in dominance from small to large forms are likely to be all related to the progressive ecosystem recovery in the early Danian. [ABSTRACT FROM AUTHOR]

Late Cretaceous to Early Paleogene time represents a critical transitional period in Earth history. Global events include short-term instability in climate and ocean circulation, large igneous province emplacement, and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event. The response of the ocean system to Cretaceous-Paleogene (K-Pg) global events has been the subject of much research, yet fundamental questions remain regarding carbon cycling, climate, ocean mixing, and redox conditions. To help elucidate paleoceanographic changes across the K-Pg transition, we revisit the classic Maastrichtian to Danian chalk-limestone succession at Stevns Klint, Denmark with a suite of new geochemical data, including insights from the redox-sensitive chromium isotope system. We use carbon and oxygen isotope trends to form a well-constrained framework for the succession, before presenting strontium isotope, chromium isotope, and rare-earth element data for the units deposited both before and after the K-Pg event. Carbon isotopes show only minor perturbation across the K-Pg boundary and oxygen isotopes record a prominent positive excursion, with both of these trends standing in contrast to many K-Pg boundary sections worldwide. Strontium isotopes record a spike towards more radiogenic values, which is consistent with a globally-observed, short-term weathering pulse. The chromium isotope profile of Maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the Chalk Sea. δ 53 Cr values then recover, before falling steadily across the K-Pg boundary and into the Danian limestone. Chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions—instead, we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability. The local mixing event inferred from our Maastrichtian chromium isotope data could be related to a temporary inflow of Tethyan bottom waters, or the shift from end-Maastrichtian greenhouse warming (associated with Deccan volcanism) to the worldwide cooling phase that immediately preceded the K-Pg boundary. No immediate change in chromium isotopes is recorded across the K-Pg boundary, indicating that the bolide impactor did not substantially perturb the marine chromium cycle, at least at the scale resolvable by our data. Instead, chromium isotope trends continued to be controlled by local oceanographic processes, highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans. [ABSTRACT FROM AUTHOR]

We integrate previous Bayesian and astronomically tuned age calibrations of the calcareous nannofossils events with our large-scale correlations to discuss using the standard calcareous nannofossil zonal schemes in the SW Neo-Tethys platform during a period of significant paleoceanographic, tectonic, and paleoclimatic perturbations (middle Eocene to early Oligocene). Two marine on-land sections extend from NP15 (Nanno-Plankton zone) to lower NP23, equivalent to upper CNE9 (Calcareous Nannofossil of the Eocene) to lower CNO3 (Calcareous Nannofossil of the Oligocene), are studied. Calcareous nannofossils have been investigated at less than 96 kyr resolution between 45.55 Ma and 31.9 Ma. The Souar section covers the Top (T) of the Nannotetrina alata group zone (CNE9, Lutetian) to the Isthmolithus recurvus zone (CNE18, Priabonian) in the Pelagic facies of the Tunisian dorsal. The El Rahma section extends from the Helicosphaera compacta zone (CNE21) to the Reticulofenestra umbilicus (CNO2) zone in the Cap Bon peninsula. The distribution patterns were studied through semi-quantitative counts to test the reliability of the biohorizons used in the standard biozonations schemes (Martini, 1971; Agnini et al., 2014). We discuss 14 biohorizons that span 13.65 Myr to highlight the limitations (absence/scarcity) of the Chiasmolithus group, particularly Ch. grandis, Ch. oamaruensis , and Ch. solitus, as biohorizons in the SW Neo-Tethys. Our study shows that Sphenolithus furcatolithoides , Dictyococcites bisectus, Sphenolithus obtusus, and Reticulofenestra erbae are reliable horizons for large-scale correlations with the northern margins of the Neo-Tethys. Calcareous nannofossils from the SW Neo-Tethys margin were highly affected by the paleo-circulation changes due to the episodic restriction of the westward subtropical Eocene Neo-Tethys (STENT) current (Jovane et al., 2009), followed by the closure of the eastern Neo-Tethys. • Calcareous nannofossil biostratigraphy at time resolution below 96 kyr. • Correlation of calcareous nannofossils events between the SW Neo-Tethys and Northern Neo-Tethys (Italy and Turkey). • Reliability of 14 early Paleogene biohorizons between 45.55 Ma to 31.9 Ma. • Sphenolithus furcatolithoides and Sphenolithus obtusus are reliable horizons for correlations with the northern Neo-Tethys. • C hiasmolithus grandis, Ch. oamaruensis , and Ch. solitus are diachronous and inconsistent in the SW Neo-Tethys. [ABSTRACT FROM AUTHOR]

Criticism of the age-model used by Dameron et al. (in press) is commented hereby. This criticism essentially concerns the age of the first occurrence of calcareous nannofossil Micula prinsii at Shatsky Rise, central Pacific, which should not be considered older than 66.6 Ma, rather than 67.3 Ma as considered by the authors. Although this criticism does not fundamentally change the environmental and paleoceanographic interpretations of Dameron et al. (in press), the age of this bioevent influences quite a lot the time scale used for the latest Maastrichtian and thus the actual age of the termination of their main dissolution interval and the duration of the partial recovery in carbonate preservation. We recommend the authors to modify their age-model and to provide alternative durations and ages for the sequence of events in the end-Maastrichtian interval as such revised ages constitute an important base for comparison with the timescale of Deccan volcanism and other end-Cretaceous perturbations. [ABSTRACT FROM AUTHOR]

• The Upper Cretaceous-Paleogene stratigraphy of the western Tajik Basin sequence. • Dating the western Tajik Basin using Sr-isotope and biostratigraphy. • Emplacement of the OAE2 and PETM within the western Tajik Basin sequence. • Deciphering the major and minor sea level cycles in the western Tajik Basin sequence. The Tajik-Afghan Basin is a large basin in Central Asia, whose sediments document the area's long tectonic and climatic history from the Paleozoic to the present. However, the sedimentary characteristics and stratigraphy of these successions remain poorly understood. The study of this basin is critical for understanding the depositional conditions that prevailed during the transformation of this area from a part of the Western Oceanic Tethys to a more restricted Para-Tethys. In the southwestern corner of the Tajik Depression, a well-exposed sedimentary sequence associated with a large anticlinal limb was sampled. The authors proposed a new age model based on a combination of biostratigraphic data from planktic foraminifera, calcareous nannofossils, and strontium chemostratigraphy (87Sr/86Sr). The lower part of the studied section is of the upper Cenomanian age (95.5 Ma), while the upper part is assigned to the early Oligocene age (34.05 Ma). The carbon isotope profile shows several excursions linked to major paleoenvironmental events including the Oceanic Anoxic Event 2 (OAE2) and the Paleocene-Eocene Thermal Maximum (PETM). The latter is revealed in the study area for the first time. New sedimentological observations and interpretations of the depositional environments and sea-level cycles are provided. The deposition in the Aktash area occurred between upper coastal lagoonal and transitional environments before fully transitioning to continental environments in the Neogene. The stratigraphic record in Aktash is divided into large-scale progradation/ retrogradation cycles that can be tentatively linked to global sea-level signals. [ABSTRACT FROM AUTHOR]

The recovery time of marine productivity following the Cretaceous-Paleogene (KPg) mass extinction varies tremendously with location (hundreds to millions of years), with possible delays in the tropics as compared to higher latitudes. This heterogeneity is based on prevalent oligo- to mesotrophic marine environments. While highly productive eutrophic environments are less prevalent, they play a greater role in the carbon cycle. Here we present data from a eutrophic region within the tropical southern Tethys. Records of both organic matter and calcite production in this locality exhibit stability across the KPg boundary. In addition, our study points to a remarkably rapid recovery (<11 kyr), even possibly continuous high productivity across the KPg boundary, despite the tropical location. Moreover, the characteristic KPg δ13C negative excursion is observed in our locality, but is independent of high productivity, possibly indicating a reduction in the δ13C of the DIC of the ocean due to the input of light carbon from the atmosphere. Thus, this study provides new insight into the functioning of eutrophic ecosystems during environmental stress imposed by the ecological crisis. • A complete stratigraphic section for the Cretaceous-Paleogene (KPg) boundary is described in a eutrophic ecosystem. • Primary and export productivity seems to be continuous or very rapid (<11 ky) recovered following the KPg mass extinction. • δ13C excursion is independent of productivity, suggesting additional light carbon source to the ocean, possibly volcanism. [ABSTRACT FROM AUTHOR]

Deccan volcanism in India and the Chicxulub impact in Mexico are both linked to the end-Cretaceous mass extinction but the relative timing of the impact and volcanic eruptions remains controversial, precluding a full assessment of their respective roles. Recent discovery of mercury (Hg) anomalies, from volcanic emissions and following atmospheric fallout, in stratigraphic records provides a potential tool to directly assess the cause-and-effect relationship between Large Igneous Provinces (LIPs) volcanism and climate change and mass extinctions. We report the first high-resolution Hg record across the Cretaceous-Paleogene boundary (KPB) in the astronomically tuned Elles section in Tunisia (auxiliary Global Stratotype Section and Point), correlated with U-Pb geochronology from the Deccan Traps in Western India. Results support Hg as a robust proxy for Deccan volcanism and reveal a direct link between the environmental changes that led to the end-Cretaceous mass extinction and Deccan volcanic activity: (1) onset of Hg loading near the base of C29r, 340 ky before the KPB, correlative with onset of global warming; (2) peak in Hg loading at the CF1/CF2 zone boundary correlative with a bottom water temperature increase of 3.2 ºC; (3) maximum Hg loading correlative with hyperthermal warming, which rapidly raised bottom water temperatures by 3.5 ºC within ~2 ky, and ocean acidification in the last 25 ky of the Maastrichtian ending with the mass extinction at the KPB. These volcanically-induced environmental changes led to increased stress on marine life evident by reduced species size (Lilliput effect), decreased species populations and a carbonate crisis that ultimately led to the end-Cretaceous mass extinction when threshold life conditions were reached during paroxysmal volcanic eruptions in the last 25 ky before the KPB. The timing of the Chicxulub impact and its environmental effects relative to Deccan volcanism remain enigmatic and still need to be investigated. [ABSTRACT FROM AUTHOR]