U-Pb Geochronology and Cyclostratigraphy of the Middle Ediacaran Upper Jibalah Group, Eastern Arabian Shield

The Ediacaran Period (ca. 635–539 Ma) represents a major transition in Earth history, beginning with the end of the Cryogenian snowball Earth glaciation and ending with the appearance and early diversification of bilaterian animals. Whereas a steady flow of new radioisotopic ages from key stratigraphic successions has resulted in much improved age constraints for the earliest and latter Ediacaran, few ages exist for the middle Ediacaran Period. The Jibalah Group, in the eastern part of the Arabian Shield, comprises minimally deformed volcano-sedimentary successions deposited in discrete basins, previously constrained to date between ca. 620 Ma and 560 Ma. The Antaq basin is one of the largest and best exposed of the Jibalah basins and contains the Muraykhah Formation (upper Jibalah Group), which is of particular interest because it contains putative Ediacaran fossils, textured organic surfaces, multiple tuff horizons, and spectacular 1–10 m-scale siltstone-sandstone cycles. Here we report new high-precision U-Pb zircon ages from the Muraykhah Formation anchoring an astrochronological analysis of these cycles. The radioisotopic ages confirm that two strong peaks identified in the stratigraphic height domain reflect accumulation paced by the long (405 kyr) and short (131–91 kyr) eccentricity cycles, the latter of which corresponds to the m-scale cyclicity that is visually apparent in the stratigraphy. The combination of radioisotopic ages and astrochronology allows us to develop a continuous, tuned record spanning from 599.1 ± 0.4 to 590.4 ± 0.6 Ma. This record complements other astrochronological analyses from slightly younger Ediacaran strata spanning the global Shuram negative carbon isotope excursion. The integrated radioisotopic and astronomical time scale ages also provides new constraints on the Ediacaran tectonic evolution of the eastern Arabian Shield

Chromosomal characterization of cultured populations of Chilean coho salmon (Oncorhynchus kistuch)

Chromosomal characterization of coho salmon samples from three fish farms in southern Chile (Polcura, Castro and Coyhaique) was carried out in order to compare their chromosome constitutions. All populations had a 2n = 60; however, Polcura and Coyhaique had a different chromosome arm number (NF = 110; 40m + 10sm + 10st/t) than Castro (NF = 108; 40m + 8sm + 12st/t). Variation in NF was due to chromosome pair 25, which was submetacentric in Coyhaique and Polcura, but subtelocentric in Castro. In all karyotypes, a large submetacentric chromosome pair exhibited an interstitial secondary constriction in the short arm. The observed variability in chromosome arm number agrees with previous reports for O. kisutch, and in this particular case it seemed to be caused by a pericentric inversion of pair 25. Cultured populations of Chilean coho salmon are, therefore, likely to be cytogenetically variable.<br>A caracterização cromossômica de amostras de salmon tipo coho de três criações de peixes do sul do Chile (Polcura, Castro e Coyhaique) foi feita com a intenção de comparar suas constituições cromossômicas. Todas as populações apresentaram 2n = 60; contudo, Polcura e Coyhaique tiveram um número de braços cromossômicos (NF = 110; 40m + 10sm + 10st/t) diferente de Castro (NF = 108; 40m + 8sm + 12st/t). A variação no NF deveu-se ao par cromossômico 25, que era submetacêntrico em Coyhaique e Polcura e subtelocêntrico em Castro. Em todos os cariótipos, um grande par cromossômico submetacêntrico exibiu uma constrição secundária intersticial no braço curto. A variabilidade observada no número de braços cromossômicos concorda com relatos prévios para O. kisutch e, neste caso particular, parece ter sido causada por uma inversão pericêntrica no par 25. Portanto, populações cultivadas de salmão chileno do tipo coho provavelmente são citogeneticamente variáveis

Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

U-Pb geochronology by isotope dilution−thermal ionization mass spectrometry (ID-TIMS) has the potential to be the most precise and accurate of the deep time chronometers, especially when applied to high-U minerals such as zircon. Continued analytical improvements have made this technique capable of regularly achieving better than 0.1% precision and accuracy of dates from commonly occurring high-U minerals across a wide range of geological ages and settings. To help maximize the long-term utility of published results, we present and discuss some recommendations for reporting ID-TIMS U-Pb geochronological data and associated metadata in accordance with accepted principles of data management. Further, given that the accuracy of reported ages typically depends on the interpretation applied to a set of individual dates, we discuss strategies for data interpretation. We anticipate that this paper will serve as an instructive guide for geologists who are publishing ID-TIMS U-Pb data, for laboratories generating the data, the wider geoscience community who use such data, and also editors of journals who wish to be informed about community standards. Combined, our recommendations should increase the utility, veracity, versatility, and “half-life” of ID-TIMS U-Pb geochronological data.</p

Genomic analysis of diversity, population structure, virulence, and antimicrobial resistance in Klebsiella pneumoniae, an urgent threat to public health

Klebsiella pneumoniae is nowrecognized as an urgent threat to human health because of the emergence of multidrug-resistant strains associated with hospital outbreaks and hypervirulent strains associated with severe community-acquired infections. K. pneumoniae is ubiquitous in the environment and can colonize and infect both plants and animals. However, little is known about the population structure of K. pneumoniae, so it is difficult to recognize or understand the emergence of clinically important clones within this highly genetically diverse species. Here we present a detailed genomic framework for K. pneumoniae based on whole-genome sequencing of more than 300 human and animal isolates spanning four continents. Our data provide genomewide support for the splitting of K. pneumoniae into three distinct species, KpI (K. pneumoniae), KpII (K. quasipneumoniae), and KpIII (K. variicola). Further, for K. pneumoniae (KpI), the entity most frequently associated with human infection, we show the existence of >150 deeply branching lineages including numerousmultidrug-resistant or hypervirulent clones.We show K. pneumoniae has a large accessory genome approaching 30,000 protein-coding genes, including a number of virulence functions that are significantly associated with invasive community-acquired disease in humans. In our dataset, antimicrobial resistance genes were common among human carriage isolates and hospital-acquired infections, which generally lacked the genes associated with invasive disease. The convergence of virulence and resistance genes potentially could lead to the emergence of untreatable invasive K. pneumoniae infections; our data provide the whole-genome framework against which to track the emergence of such threats