Unveiling a new oceanic anoxic event at the Norian/Rhaetian boundary (Late Triassic)

The latest Triassic was characterised by protracted biotic extinctions concluding in the End-Triassic Extinction (~ 200 Ma) and a global carbon cycle perturbation. The onset of declining diversity is closely related to reducing conditions that spread globally from upper Sevatian (uppermost Norian) to across the Norian-Rhaetian boundary, likely triggered by unusually high volcanic activity. We correlate significant organic carbon cycle perturbations to an increase of CO2 in the ocean-atmosphere system, likely outgassed by the Angayucham igneous province, the onset of which is indicated by the initiation of a rapid decline in 87Sr/86Sr and 188Os/187Os seawater values. A possible causal mechanism involves elevated CO2 levels causing global warming and accelerating chemical weathering, which increased nutrient discharge to the oceans and greatly increased biological productivity. Higher export production and oxidation of organic matter led to a global O2 decrease in marine water across the Norian/Rhaetian boundary (NRB). Biotic consequences of dysoxia/anoxia include worldwide extinctions in some fossil groups, such as bivalves, ammonoids, conodonts, radiolarians.

Genetic diversity of Salmonella enterica recovered from chickens farms and its potential transmission to human

BACKGROUND

Salmonella is a zoonotic bacterium transmitted through the food chain and is an important cause of disease in humans. The current study is aimed to characterize Salmonella isolates from broiler breeder chickens farms using, polymerase chain reaction (PCR) and sequencing analysis of representative isolates.

METHODS

S. Kentucky (n=11), S. Enteritidis (n=4), S. Typhimurium (n=3), S. Breanderp (n=1), and Sand S. Newport (n=1), were identified from chicken farms. Antimicrobial sensitivity test among the strains were investigated using 13 antibacterial discs. The amplified fragments of fliC and sefA genes were used to characterize S. Kentucky, S. Enteritidis and S. Typhimurium strains. Sequence analysis of the amplified PCR products for Salmonella Kentucky, Enteritidis and Typhimurium were carried out.

RESULTS

Antimicrobial sensitivity testing revealed that 95% of the isolates were resistant to penicillin, 85% to norfloxacin and colistin sulfate (each), 75% to gentamicin, 70% to nalidixic acid and 60% to flumequine. The obtained sequences revealed the close identity of the isolated strains with other Salmonella reference strains in different countries.

CONCLUSION

Analysis of the selected salmonellae confirm the report of Salmonella Enteritidis, Salmonella Typhimurium and Salmonella Kentucky circulation among broiler breeder flocks and the need to determine antibacterial susceptibility pattern regularly to detect multidrug-resistant salmonellae. The present study reports the circulation of Salmonella Kentucky, Enteritidis and Typhimurium among broiler breeder farms in Egypt. Emergency control of salmonellae is a global public health concern.

Africa’s petroleum systems: four tectonic ‘Aces’ in the past 600 million years

We relate the depositional and structural histories of the sedimentary rocks containing Africa’s primary petroleum systems to four tectonic intervals, which in the light of their widespread and beneficial consequences we designate as ‘Aces’. The Ace of Clubs was the assembly of Gondwana by continental collision and the collapse and erosion of the mountains constructed during that assembly, which generated accommodation space through thermal subsidence over a vast area. Africa’s oldest great reservoir rocks accumulated in that space during Cambro-Ordovician times (520-440 Ma). After a short-lived glacial interval, Silurian and Devonian source rocks formed parts of a thick section that was deposited as long-term subsidence continued. The Ace of Diamonds consists of the collision of Baltica with Laurentia at c. 380 Ma and the collision between Gondwana and Laurussia at c. 310 Ma. It also includes the intracontinental deformation and orogenic collapse associated with the latter event, during the course of which regionally important structures and rifts now containing hydrocarbon-bearing fill were generated. Productive petroleum systems involving older Palaeozoic source rocks are concentrated in the rifts and sedimentary rocks of this phase.

The two other aces relate to the plume-dominated break-up of Pangaea. The Aces of Hearts and Spades were the eruption of the Karroo Plume at 183 Ma and the eruption of the Afar Plume at 31 Ma. These plumes, because they both generated huge volumes of basalt during brief intervals, are considered to have come from the deep mantle where, for more than 200 million years there has been a discrete large volume of hot rock over which Africa has been slowly rotating. Perhaps as many as six other deep-seated plumes have risen from that deep hot volume. The importance of the Karroo and Afar Plumes comes from the fact that they arrested the motion of the African Plate and, on each occasion, fostered the establishment of a new shallow-mantle convective circulation pattern. Intracontinental rifts, basins and swells developed above the new convection pattern after both arrests. Organic-rich sedimentary rocks deposited in rifts and at continental margins that formed in response to the Karroo-Plume-induced plate-pinning episode (K-pippe, 183-133 Ma) are being buried today under piles of sedimentary rock eroded from swells that have been rising since the later Afar-Plume-induced plate-pinning episode (A-pippe) began at 31 Ma. The Afar Plume eruption is designated ‘Ace of Spades’ because oil and gas generated following source-rock burial by sediments eroded from Africa’s active swells during the past 31 Ma together make up three-quarters of Africa’s hydrocarbon resource. In addition, half of that petroleum lies in reservoirs deposited during this phase.

Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary

The Triassic/Jurassic boundary, 208 million years ago, is associated with widespread extinctions in both the marine and terrestrial biota. The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province. This volcanic event is thought to have released significant amounts of CO2 into the atmosphere, which could have led to catastrophic greenhouse warming, but the evidence for CO2-induced extinction remains equivocal. Here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations, spanning a 20-Myr period across the Triassic/Jurassic boundary. Using a standard diffusion model, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000-4,000 p.p.m. increase. The relative stability of atmospheric CO2 across this boundary suggests that environmental degradation and extinctions during the Early Jurassic were not caused by volcanic outgassing of CO2. Other volcanic effects-such as the release of atmospheric aerosols or tectonically driven sea-level change-may have been responsible for this event.