This work presents a taxonomic, palaeoecological and palaeobiogeographical study of the ostracod fauna around the Cretaceous–Palaeogene boundary from the El Matuasto section, Neuquén Basin, ...Argentina. The analysis of 64 samples resulted in the recovery of 82 marine ostracod species, of which four are new: Hemiparacytheridea condilomata, Paramunseyella stictus, Hysterocythereis acuminata and Aleisocythereis? picnus. In addition, the genera Sapucariella, Monoceratina, Aracajuia, Microceratina and Pelecocythere are reported for the first time from the Neuquén Basin. Palaeoecological inferences indicate fluctuations in abundance and diversity, occurring alongside environmental change from an inner to medium shelf during the Maastrichtian and to an outer shelf in the Danian. The Maastrichtian fauna was less abundant than that in the Danian, which shows a rapid recovery after the Cretaceous–Palaeogene boundary. During the Danian, a small interval also shows a sudden decrease in abundance and diversity that could potentially be related to the Dan‐C2 event. In addition, the described genera and species in this study suggest a strong palaeobiogeographical affinity with the Paraíba Basin, northeastern Brazil.
Though primarily a recent genus, Conchoecia Dana 1853 has had a number of Cretaceous forms dubiously attributed to it since the description of Conchoecia cretaceaPokorný, 1964. Recently, most of ...these species were reassigned to the genus NeorichterinaTóth and Cséfán, 2018, considered a Cretaceous representative of Family Entomozoidae. However, there are still taxonomic uncertainties regarding this assignment, and much is still unknown about the paleoecology, paleobiogeography, and biostratigraphic significance of these taxa. This paper provides a revision of the taxon based on available literature on Neorichterina and the Cretaceous forms attributed to “Conchoecia”. Considering several problems with the taxonomic description of Neorichterina, we propose the removal of the genus from Family Entomozoidae, and identify two potential new species, which are left in open nomenclature. The earliest occurrence of the genus is the late Hauterivian–early Barremian of the Haha Basin, Morocco. After that, Neorichterina spread to the South Atlantic and Tethys oceans during the late Aptian–late Albian, and became extinct in the lower Cenomanian. Neorichterina was likely a planktonic genus with a preference for warm neritic environments, and was able to tolerate fluctuating oxygenation levels. It frequently occurred in association with blooms of Favusellid foraminifera, and was particularly abundant in the South Atlantic Ocean. Although Neorichterina has a broad stratigraphic range, it occurred only for a small time interval during the late Aptian of the Santos Basin, Brazil, suggesting that it could be a useful regional biostratigraphic marker in the southeastern Brazilian margin.
•Revision of the Conchoecia?/Neorichterina genus and its removal from family Entomozoidae.•Illustration of all Neorichterina species described in the literature so far.•Attribution of a late Aptian-early Cenomanian age range for the genus.•Discussion of the paleobiogeography of Neorichterina between Aptian–Cenomanian.•Attribution of planktonic, neritic marine with warm waters environment for the genus.
Carbon cycle perturbations dramatically affected the ocean-climate system during the Aptian–Albian transition. However, the chronology of this interval is still intensively debated. Here we present a ...comprehensive astronomical calibration of planktonic foraminiferal and calcareous nannofossil bioevents along a complete marine sedimentary succession, comprising the latest Aptian to middle Albian interval at drilling Core SER-03, located in the Sergipe-Alagoas Basin. The SER-03 astrochronology is based on the tuning of a high-resolution gamma ray (GR) record to the long eccentricity (405 kyr) metronome, and is integrated with high-resolution paleomagnetic records. Our results span the interval between ~114.7 and 109.5 Ma, within magnetochron C34n, and our age estimates for biostratigraphic markers agree within one long eccentricity cycle with previous estimates. We also present geochemical records, such as stable carbon isotopes (δ13C), organic carbon and carbonate contents, as well as redox-sensitive elemental ratios, measured on bulk sediments at Core SER-03. Most of these proxy records depict marked changes across the Aptian–Albian boundary, likely characterizing the local expression of Oceanic Anoxic Event 1b (OAE 1b), filling the gap for low-latitude records of this event.
•The Sergipe-Alagoas Basin recorded the latest Aptian to middle Albian interval at low latitude in the South Atlantic.•Astronomical calibration of planktic foraminifera and calcareous nannofossils international markers (GTS).•Low oxygenation conditions at late Aptian and early Albian interval suggest the presence of the OEA1b onset.
Early Danian environmental perturbations related to carbon isotope negative excursions (CIEs) were recognized at Deep Sea Drilling Project (DSDP) Hole 516F, Rio Grande Rise. Within the first ~160 kyr ...of the Danian, environmental stability is evidenced by well‑oxygenated bottom waters, good carbonate preservation, and relatively high primary production. The preservation of carbonates and the oxygenation of the deep water decreased progressively, leading to the formation of red layers in the sediments between 65.86 Ma and 65.71 Ma. The onset of carbonate dissolution and the reduction in dissolved oxygen concentrations occurred approximately 50 kyr before the onset of the Dan-C2 event, and was probably related to the third volcanic event of the Deccan Traps (DT). Our results support the link between enhanced emissions of volcanic gasses and deep ocean carbonate dissolution and deoxygenation during the Early Danian. The CIEs at the Rio Grande Rise are positioned within the planktonic foraminiferal biozone P1b, suggesting that the first appearance of Subbotina triloculinoides within Chron C29r (at 65.89 Ma) is a diachronous datum.
•Drops in carbonate content and deep water oxygenation precede in ~50 kyr the CIEs (Dan-C2 interval).•Dan-C2 event is likely correlated to the third event of the Deccan Trap (Albenali Formation).•Subbotina triloculinoides is probably a diachronous biostratigraphic marker.
This paper presents new taxonomic reports and biostratigraphic inferences based on ostracods in the basal section of the cored well UFRJ-2-LRJ-01-SE, perforated in the Votorantim quarry, ...Sergipe-Alagoas Basin, Brazil. The studied material comprised 44 samples in the range 438.65 to 315.30 m, identifying 52 species of ostracods distributed in 31 genera and 16 families. Five new species are proposed: Aracajuia separatta sp. nov.; Cytheropteron laranjeirensis sp. nov.; Microxestoleberis riachuelensis sp. nov.; Parahemingwayela fauthi sp. nov. and Quasihermanites? punctata sp. nov. The age of the studied interval was established by the occurrence of Aracajuia antiqua (MSA–1) between 434.00 and 347.25 m indicating the upper Albian. The first occurrence of Bythoceratina tamarae marks the upper Albian–lower Cenomanian boundary at 315.30 m. The biozones proposed with ostracodes coincides with the biozones of calcareous nannofossils made found at cored well.
•Ostracod faunas (late Albian/early Cenomanian) of Riachuelo Fm/Brazil were studied.•Five new species of marine ostracods are described.•The upper Albian–lower Cenomanian boundary demarked by Bythoceratina tamarae.•Otracods biozone was correlated with the calcareous nannofossil biozones.
The Cretaceous/Paleogene boundary (K/Pg) event, associated with a meteorite impact at Chicxulub, Mexico, is globally recognized as one of the largest mass extinctions in natural history, marking the ...end of the Mesozoic Era. However, most of the outcrops with records and geochemical evidence of this boundary are distributed in the Northern Hemisphere and at mid-latitudes. Here, aiming to contribute to the knowledge of this event at high southern latitudes, we characterize a single iridium anomaly correlated with the K/Pg boundary, present within a carbonaceous mudstone level in a continental depositional environment in the Río de las Chinas Valley, Chilean Patagonia. High-resolution geochemical and palynofacies analyses were performed on a stratigraphic section from the top of the Dorotea Formation. Results showed that the iridium enrichment coincides with an anomaly of other platinum group elements. In addition, the palynofacies analysis showed a disturbance in the depositional environment, marked by an abrupt change from non-degraded phytoclasts (e.g., cuticles) to pseudoamorphous and degraded cuticles, and by an increase in the abundance of spores at the same level. The Río de las Chinas Valley locality provides new evidence for the comprehensive study of the end-Cretaceous event, from the poorly represented continental environments of high southern latitudes.
•The site with the southernmost K/Pg boundary in the Americas is analyzed.•Ir and other platinoid elements anomalies confirm the K/Pg boundary at high latitudes.•A spore spike and palynological alteration are coeval with the Ir-enrichment level.•The abrupt palynological change shows a disturbance of the depositional environment.
Abstract
Predator–prey dynamics involving ostracod prey across the Cretaceous–Palaeogene (K–Pg) extinction event have not been evaluated rigorously. We studied 3146 Maastrichtian and Danian ostracod ...specimens from a section in eastern Brazil across the K–Pg boundary. The Maastrichtian assemblage level predation intensity (2.7%) is lower than in the Danian (4.7%). However, the drilling intensity in assemblages immediately above the K–Pg boundary is 0%, perhaps due to abrupt palaeoecological and palaeoenvironmental changes resulting from the K–Pg event. For the Maastrichtian, the dorsal and posterior regions are preferentially drilled, whereas the dorsal and median regions are primarily drilled during the Danian. Variation in Maastrichtian and Danian predation intensities between species (0.0–50.0%) and null model analyses suggest significant prey preference and avoidance, particularly in the Danian, unrelated to prey abundance. Drilling intensities for smooth specimens are significantly greater than for ornamented specimens for the Maastrichtian and the Danian. Finally, Danian drill-hole diameters and predator–prey size ratios are statistically larger than in the Maastrichtian, suggesting predatory gastropods were larger after the boundary, also relative to their prey. We conclude that predator–prey dynamics were affected by the K–Pg extinction event.
Abstract
Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of ...urgency. Sedimentary ancient DNA (
sed
aDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and
sed
aDNA damage analysis) metagenomic marine eukaryote
sed
aDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote
sed
aDNA record of ~1 Mio. years and diatom and chlorophyte
sed
aDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU,
psbO
). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that
sed
aDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.
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