Pg Mass Extinction Research Articles

Sharks (Neoselachii) and palynomorphs from Mendoza (Argentina): new evidence of the Late Cretaceous Atlantic marine transgression

Prámparo, M.B., Cione, A.L. & Gonzalez Riga, B., 2013. Sharks (Neoselachii) and palynomorphs from Mendoza (Argentina): new evidence of the Late Cretaceous Atlantic marine transgression. Alcheringa 38, 000–000. ISSN 0311–5518.Neoselachian (modern shark) teeth and palynomorphs have been recovered from the Late Cretaceous Jagüel Formation in the Province of Mendoza, Argentina. The fossiliferous beds were deposited during the Atlantic transgression that covered northern Patagonia and other parts of South America from the Maastrichtian to the Danian. Teeth of several lamniform sharks are attributed to the anacoracid Squalicorax pristodontus and cf. Serratolamna serrata of indeterminate familial affinity. These taxa became extinct at the end of the Cretaceous and confirm the late Maastrichtian age previously assigned to the Jagüel Formation in this northwestern part of the Neuquén Basin. For the first time, the selachian faunas are described together with algae and dispersed organic matter assemblages (palynofacies), revealing new elements of the neritic biota leading up to the Cretaceous–Paleogene (K–Pg) mass extinction in South America. The palynoflora consists exclusively of the prasinophyte algae Tasmanites, Cymatiosphaera and Pterospermella, indicative of stratified saline waters. Dispersed organic components in the profile (mainly opaque equidimensional phytoclasts and prasinophytes) are consistent with an inner neritic environment, with evidence (a great variety of particle sizes, lath-shaped phytoclasts increasing slightly in number and decreasing number of marine components) of slightly more nearshore conditions towards the upper part of the profile. These marine biotas confirm the presence of an epeiric sea over northern Patagonia, which extended westwards to the volcanic arc on the western flank of the Andean Cordillera in Mendoza.Mercedes B. Prámparo [mprampar@mendoza-conicet.gov.ar], IANIGLA-CONICET, CCT-Mendoza. Avda. R. Leal s/n, Parque Gral. San Martín, (5500) Mendoza, Argentina; Alberto Luis Cione [acione@museo.fcnym.unlp.edu.ar], División Paleontología de Vertebrados. Museo de La Plata. 1900 La Plata, Argentina; Bernardo González Riga [bgonriga@mendoza-conicet.gov.ar] IANIGLA-CONICET, CCT, Mendoza. Avda. R. Leal s/n, Parque Gral. San Martín, (5500) and ICB, Universidad Nacional de Cuyo, Argentina. Received 28.5.2013, revised 17.9.2013, accepted 24.9.2013.

Platinum-group element (PGE) geochemistry of Deccan orangeites, Bastar craton, central India: Implication for a non-terrestrial origin for iridium enrichment at the K–Pg boundary

We report platinum group element (PGE) concentrations of twelve bulk-rock samples from the Behradih and Kodomali orangeite intrusions in the Mainpur field, Bastar craton, central India, which are emplaced synchronously with the Deccan flood basalts. Their palladium-group PGE (PPGE) (1.8–5.2ppb Pt, 1.2–6.4ppb Pd) contents are distinctly higher compared to their iridium-group PGE (IPGE) concentrations (0.8–2ppb Os, 0.8–1.2ppb Ir, 3.2–4.2ppb Ru, and 0.2–0.8ppb Rh). Their PGE contents as well as Pd/Ir ratios are either similar or even lower than those from the Mesoproterozoic and Cretaceous kimberlites and orangeites from the Kaapvaal craton (southern Africa), Cretaceous kimberlites from the Sao Fransisco craton (Brazil), Ordovician kimberlites from the North China craton and the Mesoproterozoic southern Indian kimberlites from the Eastern Dharwar craton. Anomalously elevated iridium (and other PGE) contents in sediments at the Cretaceous–Paleogene (K–Pg) boundary are commonly attributed either to a large bolide impact triggering the K–Pg mass extinction or to terrestrial causes such as volcanic eruptions (Deccan flood basalts) or even to mantle-plume derived lithospheric gaseous explosions (Verneshots). Lack of unusually high abundances of PGE in the Mainpur orangeties as well as in the co-eval Deccan flood basalts and associated alkaline rocks implies that the anomalous iridium enrichment reported at the K–Pg boundary sections was not sourced from the mantle and likely originated from an extraterrestrial source.

Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary

The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous-Tertiary, K-T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K-Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K-Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis-like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.

Environmental and vegetational changes recorded in sedimentary leaf wax n-alkanes across the Cretaceous–Paleogene boundary at Loma Capiro, Central Cuba

The stable carbon isotopic compositions ( δ 13C) and chain-length distribution [ACL and n-C 31/( n-C 29 + n-C 31)] of sedimentary leaf wax n-alkanes were investigated across the Cretaceous–Paleogene (K–Pg) boundary at Loma Capiro, Central Cuba, to reconstruct paleoenvironmental changes that are recorded in terrestrial higher plants. The stratigraphic profiles of the n-alkane δ 13C values show a negative excursion in the lowermost Paleocene, although its magnitude is much smaller (∼ 0.3‰) than the global signals (1.5 to 2.0‰) in the surface ocean-atmospheric carbon reservoir. Relations between the n-alkane δ 13C values and the C 31/(C 29 + C 31) ratios exhibit two different trends, suggesting that our δ 13C records are likely affected by two types of paleoenvironmental factors in addition to the δ 13C variations in the exogenous carbon reservoir. Rare occurrence of terrigenous organic matter that is usually transported by rivers suggests that the n-alkanes at Loma Capiro are likely to have been transported by trade winds, which recorded paleoenvironmental conditions of the northwestern part of the African continent. The n-alkane δ 13C values show a parallel decrease with the ACL and C 31/(C 29 + C 31) values in the first 37,000 yr following the K–Pg boundary. Such decreases are consistent with plant physiological responses to reduced net evaporation, suggesting a possible influence of the impact-induced warm-humid condition in the early Paleocene. In contrast, the n-alkane δ 13C values are negatively correlated with the C 31/(C 29 + C 31) ratios from 40,000 to 67,000 yr after the K–Pg boundary. This time period matches well with that required for the recovery of terrestrial floras from the K–Pg mass extinction to those with diversity equivalent to the late Cretaceous, suggesting that the n-alkane signals are also likely affected by the plant diversification process after the mass extinction.