Chicxulub impact spherules in the North Atlantic and Caribbean: age constraints and Cretaceous-Tertiary boundary hiatus

The Chicxulub impact is commonly believed to have caused the Cretaceous-Tertiary boundary mass extinction and a thin impact spherule layer in the North Atlantic and Caribbean is frequently cited as proof. We evaluated this claim in the seven best North Atlantic and Caribbean Cretaceous-Tertiary boundary sequences based on high-resolution biostratigraphy, quantitative faunal analyses and stable isotopes. Results reveal a major Cretaceous-Tertiary boundary unconformity spanning most of Danian subzone P1a(1) and Maastrichtian zones CF1-CF2 (~400 ka) in the NW Atlantic Bass River core, ODP Sites 1049A, 1049C and 1050C. In the Caribbean ODP Sites 999B and 1001B the unconformity spans from the early Danian zone P1a(1) through to zones CF1-CF4 (~3 Ma). Only in the Demerara Rise ODP Site 1259B is erosion relatively minor and restricted to the earliest Danian zone P0 and most of subzone P1a(1) (~150 ka). In all sites examined, Chicxulub impact spherules are reworked into the early Danian subzone P1a(1) about 150-200 ka after the mass extinction. A similar pattern of erosion and redeposition of impact spherules in Danian sediments has previously been documented from Cuba, Haiti, Belize, Guatemala, south and central Mexico. This pattern can be explained by intensified Gulf stream circulation at times of climate cooling and sea level changes. The age of the Chicxulub impact cannot be determined from these reworked impact spherule layers, but can be evaluated based on the stratigraphically oldest spherule layer in NE Mexico and Texas, which indicates that this impact predates the Cretaceous-Tertiary boundary by about 130-150 k

Mercury enrichments of the Pyrenean foreland basins sediments support enhanced volcanism during the Paleocene-Eocene thermal maximum (PETM)

The Paleogene records the most prominent global climate change of the Cenozoic Era with a shift from a greenhouse to an icehouse world. Several transient hyperthermal events punctuated this long-term evolution. The most pronounced and the best known of these is the Paleocene-Eocene Thermal Maximum (PETM-56 Ma). This event is associated with global warming, a worldwide perturbation of the carbon cycle, and significant biotic changes. The PETM is primarily recorded by a sharp negative carbon isotope excursion (NCIE) in both carbonates and organic matter of sedimentary successions. The source of the 13C-depleted carbon for the NCIE and whether it was released in one or numerous events is still debated. Several carbon sources have been proposed to explain the PETM-NCIE and the mechanisms that triggered this abrupt climate upheaval. These include, among others, the magmatic and thermogenic release of carbon associated with the emplacement of Large Igneous Provinces (LIP). One proxy for tracking past volcanic emissions in the geological record and testing hypothetical links between volcanism and hyperthermals is the use of mercury (Hg) anomalies found in marine and continental sedimentary successions. Here, we present new high-resolution mercury and stable isotopic records from a continental-marine transect in Pyrenean peripheral basins during the PETM. Compared to deeper marine settings, the significant sedimentation rate that characterizes these high-accommodation and high sediment-supply environments allows the preservation of expanded successions, providing reliable information about the fluctuations of Hg concentration in deposits across the PETM. Our data reveal two large negative carbon excursions across the studied successions. Based on biostratigraphy and the similarity of shape and amplitude of the isotopic excursions with global records, we interpret the largest NCIE as the PETM. This main excursion is preceded by another that we interpret as the Pre-Onset Excursion (POE), found in other profiles worldwide. We find that the POE and the PETM are, in our studied sections, systematically associated with significant Hg anomalies regardless of the depositional environment. These results suggest that large pulses of volcanism, possibly related to the North Atlantic Igneous Province's emplacement, contributed to the onset and possibly also to the long duration of the PETM. Furthermore, the record of higher Hg anomalies in nearshore than offshore settings suggests a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant Hg loading in shallow marine ecosystems. If this is correct, these findings confirm the primary role of the solid Earth in determining past terrestrial climates

Deccan Volcanism: a main trigger of environmental changes leading to the K/Pg mass extinction?

Recent studies indicate that the bulk (80%) of Deccan trap eruptions occurred over a relatively short time interval in magnetic polarity C29r, whereas multi-proxy studies from central and southeastern India place the Cretaceous-Paleogene (K/Pg) mass extinction near the end of this main phase of Deccan volcanism suggesting a cause-and-effect relationship. Beyond India multi-proxy studies also place the main Deccan phase in the uppermost Maastrichtian C29r below the K/Pg (planktic foraminiferal zones CF2-CF1), as indicated by a rapid shift in ¹⁸⁷Os/¹⁸⁸Os ratios in deep-sea sections from the Atlantic, Pacific and Indian Oceans, coincident with rapid climate warming, coeval increase in weathering, a significant decrease in bulk carbonate indicative of acidification due to volcanic SO2, and major biotic stress conditions expressed in species dwarfing and decreased abundance in calcareous microfossils (planktic foraminifera and nannofossils)

Sedimentary geochemistry of Chaudon-Norante section, France

Data from Chaudon-Norante section near Digne in France. The section is dated from the upper Aalenian to the lower Bajocian (Middle Jurassic). Samples are labelled CN. Phosphorus content quantification was based on the ascorbic acid method (Mort et al., 2007) using a Perkin UV/Vis spectrophotometer Lambda 25. The concentration of PO4 was determined by calibration of BD47 and NU81 standards. TOC was measured after decarbonatization using an elementary analyzer Thermo-Finnigan Flash EA 1112. d13C organic carbon was measured using a Thermo Fischer Scientific Delta V isotope ratio mass spectrometer. d13C-d18O carbonate was measured using a Multiprep auto-sampler coupled to a GV Isoprime mass spectrometer calibrated based on NIST NBS19. CaCO3 content was measured using a Dietrich-Frühling calcimeter based on measuring the CO2 evolved after acidification of a sample

Reconstructing lower Bajocian carbon cycle perturbations using phosphorus content, carbon isotopes and sediments accumulation rates

International audienceThe lower Bajocian (Middle Jurassic) deposits record two successive carbon isotopes excursions (CIE) with a negative ~0.5‰ CIE near the Aalenian-Bajocian boundary followed by a more protracted positive ~1.5‰ CIE ending at the base of upper Bajocian deposits. Both events are observed in both northern and southern Tethys and have been attributed to a global carbon cycle perturbation. In order to constrain the possible cause of the lower Bajocian CIEs, we present new geochemical and sedimentological data from Chaudon-Norante (France) and Murtinheira (Portugal) sections. We have measured δ13Corg values and phosphorus content and calculated CaCO3, siliciclastics, organic matter and phosphorus accumulation rates using published astronomical age models. In the sections studied, there is no carbonate crisis as opposed to south Tethyan localities, pointing to a strong geographical control of calcium carbonate accumulation in the western Tethys during the Bajocian. Both sites record an increase in siliciclastics and phosphorus AR but relatively constant organic matter AR. The δ13Cbulk carbonate vs δ13Corg stratigraphic variations suggest that both negative and positive CIEs were likely caused by an increase in phosphorus and weathered carbon riverine input. Together, our new results suggest that this event was triggered by an increase in productivity and organic carbon burial. However, there are no recurrent black shales nor organic-rich deposits identified for this time interval in western Tethys. In summary, the lower Bajocian carbon cycle perturbation bears many similarities with the Valanginian event and direct comparison between both events may help to refine current hypotheses about the causes of Mesozoic positive CIEs

Sedimentary geochemistry of Murtinheira section at Cabo Mondego, Portugal

Data from Murtinheira section at Cabo Mondego in Portugal. The section is dated from the upper Aalenian to the lower Bajocian (Middle Jurassic). Samples are labelled CN. Phosphorus content quantification was based on the ascorbic acid method (Mort et al., 2007) using a Perkin UV/Vis spectrophotometer Lambda 25. The concentration of PO4 was determined by calibration of BD47 and NU81 standards. TOC was measured after decarbonatization using an elementary analyzer Thermo-Finnigan Flash EA 1112. d13C organic carbon was measured using a Thermo Fischer Scientific Delta V isotope ratio mass spectrometer. d13C-d18O carbonate was measured using a Multiprep auto-sampler coupled to a GV Isoprime mass spectrometer calibrated based on NIST NBS19. CaCO3 content was measured using a Dietrich-Frühling calcimeter based on measuring the CO2 evolved after acidification of a sample

Reconstructing lower Bajocian carbon cycle perturbations using phosphorus content, carbon isotopes and sediments accumulation rates

International audienceThe lower Bajocian (Middle Jurassic) deposits record two successive carbon isotopes excursions (CIE) with a negative ~0.5‰ CIE near the Aalenian-Bajocian boundary followed by a more protracted positive ~1.5‰ CIE ending at the base of upper Bajocian deposits. Both events are observed in both northern and southern Tethys and have been attributed to a global carbon cycle perturbation. In order to constrain the possible cause of the lower Bajocian CIEs, we present new geochemical and sedimentological data from Chaudon-Norante (France) and Murtinheira (Portugal) sections. We have measured δ13Corg values and phosphorus content and calculated CaCO3, siliciclastics, organic matter and phosphorus accumulation rates using published astronomical age models. In the sections studied, there is no carbonate crisis as opposed to south Tethyan localities, pointing to a strong geographical control of calcium carbonate accumulation in the western Tethys during the Bajocian. Both sites record an increase in siliciclastics and phosphorus AR but relatively constant organic matter AR. The δ13Cbulk carbonate vs δ13Corg stratigraphic variations suggest that both negative and positive CIEs were likely caused by an increase in phosphorus and weathered carbon riverine input. Together, our new results suggest that this event was triggered by an increase in productivity and organic carbon burial. However, there are no recurrent black shales nor organic-rich deposits identified for this time interval in western Tethys. In summary, the lower Bajocian carbon cycle perturbation bears many similarities with the Valanginian event and direct comparison between both events may help to refine current hypotheses about the causes of Mesozoic positive CIEs