Environmental and diagenetic controls on the morphology and calcification of the Ediacaran metazoan Cloudina

Abstract Cloudina is a globally distributed Ediacaran metazoan, with a tubular, funnel-in-funnel form built of thin laminae (ca. 1–10 μm). To what degree local environmental controlled morphology, and whether early diagenesis controlled the degree of calcification of Cloudina, is debated. Here we test these hypotheses by considering assemblages from four, coeval localities from the Upper Omkyk Member, Nama Group, Namibia, from inner ramp to mid-ramp reef across the Zaris Subbasin. We show that sinuosity of the Cloudina tube is variable between sites, as is the relative thickness of the tube wall, suggesting these features were environmentally controlled. Walls are thickest in high-energy reef settings, and thinnest in the low-energy, inner ramp. While local diagenesis controls preservation, all diagenetic expressions are consistent with the presence of weakly calcified, organic-rich laminae, and lamina thicknesses are broadly constant. Finally, internal ‘cements’ within Cloudina are found in all sites, and pre-date skeletal breakage, transport, as well as syn-sedimentary botryoidal cement precipitation. Best preservation shows these to be formed by fine, pseudomorphed aragonitic acicular crystals. Sr concentrations and Mg/Ca show no statistically significant differences between internal Cloudina cements and botryoidal cements, but we infer all internal cements to have precipitated when Cloudina was still in-situ and added considerable mechanical strength, but may have formed post-mortem or in abandoned parts of the skeleton

Análisis paleontológicos a través límite Ediacárico-Cámbrico, Grupo Alto Corumbá, Brasil

This work presents the results of a palaeontological analysis focused on twenty-six species sampled in five sections of the Tamengo and Guaicurus formations, Corumbá and Ladário regions: Corcal and Laginha quarries, Porto Sobramil, Porto Figueiras and Ecoparque Cacimba. Besides, palaeoecological and palaeoenvironmental inferences are presented based on the occurrence of this fossil assemblage. Cloudina carinata Cortijo et al., 2010, previously documented in Spain and Siberia, presents an unprecedented occurrence in the American continent, in siltstones of the Tamengo Formation at Porto Figueiras section, Municipality of Corumbá, Mato Grosso do Sul State, Brazil. The biota of the Tamengo Formation is updated and composed of three biomineralizing metazoans, including poriferan spicules, putative sponge gemmule, and a sessile epibiontic prokaryotic colony. The present work also deals with the taxonomy and stratigraphic distribution of four ichnospecies and three vendotaenid species that integrate the updated benthic fauna for the upper portion of Corumbá Group. The species diversity of the Tamengo Formation was complemented by the occurrence of sixteen microfossil species that possibly represent a marine planktic assemblage. A dramatic change was identified in the palaeoenvironmental conditions of the Tamengo to Guaicurus formations, followed by a mass extinction event, possibly linked to the global Ediacaran- Cambrian mass extinction. In addition, organic-walled microfossils were prepared and analyzed from sections of three countries: nine species from the Nomtsas Formation, Namibia; four species from the Tagatiya Guazu Formation, Paraguay; and six species from the Dengying Formation, China. An international biostratigraphic essay consisting of six biozones is proposed for the uppermost Ediacaran and one biozone for the earliest Cambrian.Se presenta en este trabajo el análisis paleontológico de 26 especies fósiles muestradas en cinco cortes de las Formaciones de Tamengo y Guaicurus en las regines de Corumbá y Ladário: canteras de Corcal y Laginha, Porto Sobramil, Porto Figueiras y Ecoparque Cacimba. Además, se añaden varias interpretaciones paleoecológicas y ambientales, basadas en el registro fósil. Cloudina carinata Cortijo et al., 2010, previamente citada en España y Siberia, aparece por primera vez en el continente Americano, concretamente en limolitas de la Formación Tamengo en el corte de Porto Figueiras, Corumbá, Estado de Mato Grosso do Sul, Brasil. La biota de la Formación Tamengo incluye tres metazoos mineralizados, que incluyen espículas de poríferos, posibles gémulas de esponjas y una colonia sésil de procaiotas epibentónicos. Este trabajo se centra en la taxonomía y distribución estratigráfica de cuatro icnoespecies y tres especies de vendoténidos que forman la fauna bentónica de la parte superior del Grupo de Corumbá. La biodiversidad de la Formación Tamengo ha sido completada con el registro de 16 especies microfósiles que representan posiblemente una asociación plantónica marina. Se ha identificado un cambio drástico en las condiciones ambientales de las Formaciones Tamengo y Guaicurus, que culminan en un evento de extincinón masiva posiblemente relacionado con la extincición en masa que marca el tránsito global Ediácarico- Cámbrico. Por otro lado, se han extraído microfósiles de pared orgánica de varios afloramientos: nueve especies de la Formación de Nomtsas (Namibia), cuatro de la Formación Tagatiya Guazu (Paraguay) y seis de la Formación Dengying (China). Se propone un marco bioestratigráfico para el Ediacárico terminal que incluye seis biozonas y una biozona para el Cámbrico basal

Approaching disorder-free transport in high-mobility conjugated polymers.

Conjugated polymers enable the production of flexible semiconductor devices that can be processed from solution at low temperatures. Over the past 25 years, device performance has improved greatly as a wide variety of molecular structures have been studied. However, one major limitation has not been overcome; transport properties in polymer films are still limited by pervasive conformational and energetic disorder. This not only limits the rational design of materials with higher performance, but also prevents the study of physical phenomena associated with an extended π-electron delocalization along the polymer backbone. Here we report a comparative transport study of several high-mobility conjugated polymers by field-effect-modulated Seebeck, transistor and sub-bandgap optical absorption measurements. We show that in several of these polymers, most notably in a recently reported, indacenodithiophene-based donor-acceptor copolymer with a near-amorphous microstructure, the charge transport properties approach intrinsic disorder-free limits at which all molecular sites are thermally accessible. Molecular dynamics simulations identify the origin of this long sought-after regime as a planar, torsion-free backbone conformation that is surprisingly resilient to side-chain disorder. Our results provide molecular-design guidelines for 'disorder-free' conjugated polymers.We gratefully acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) through a programme grant (EP/G060738/1) and the Technology Strategy Board (TSB) (PORSCHED project). D. Venkateshvaran acknowledges financial support from the Cambridge Commonwealth Trust through a Cambridge International Scholarship. K. Broch acknowledges post-doctoral fellowship support from the German Research Foundation (DFG). Mateusz Zelazny acknowledges funding from the NanoDTC in Cambridge. The work in Mons was supported by the European Commission / Région Wallonne (FEDER – Smartfilm RF project), the Interuniversity Attraction Pole program of the Belgian Federal Science Policy Office (PAI 7/05), Programme d’Excellence de la Région Wallonne (OPTI2MAT project) and FNRS-FRFC. D.B. and J.C. are FNRS Research Fellows.This is the accepted manuscript. The final version's available from Nature at http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13854.html

Low-oxygen waters limited habitable space for early animals

The oceans at the start of the Neoproterozoic Era (1,000–541 million years ago, Ma) were dominantly anoxic, but may have become progressively oxygenated, coincident with the rise of animal life. However, the control that oxygen exerted on the development of early animal ecosystems remains unclear, as previous research has focussed on the identification of fully anoxic or oxic conditions, rather than intermediate redox levels. Here we report anomalous cerium enrichments preserved in carbonate rocks across bathymetric basin transects from nine localities of the Nama Group, Namibia (~550–541 Ma). In combination with Fe-based redox proxies, these data suggest that low-oxygen conditions occurred in a narrow zone between well-oxygenated surface waters and fully anoxic deep waters. Although abundant in well-oxygenated environments, early skeletal animals did not occupy oxygen impoverished regions of the shelf, demonstrating that oxygen availability (probably >10 μM) was a key requirement for the development of early animal-based ecosystems