Diagenetic alteration in low-Mg calcite from macrofossils: a review

This is the final version of the article. Available from the publisher via the DOI in this record.The quality of palaeoenvironmental reconstructions based on macrofossil car bon ate critically de pends on preservation of the shell material because post-depositional pro cesses can modify its structural, chemical and isotopic composition, potentially over printing or completely erasing palaeoenvironmental information. A suite of methods can be employed to evaluate the impact of diagenetic processes on the primary geochemical signatures of samples. Here we review the benefits and short comings of the most commonly employed optical (optical microscopy, cathodoluminescence microscopy, scanning electron microscopy) and chemical (trace element abundances, isotopic ratios) screening techniques used to assess the alteration degree of low-Mg calcite macrofossils and summarize the findings on diagenetic trends observed for elemental and isotopic systems in such materials. For a robust evaluation of the preservation state of biogenic calcite, it is advisable to combine a set of complementary techniques. Absolute limiting values of element and isotope ratios for discarding diagenetically altered materials cannot be universally applied, but should rather be evaluated on a case to case basis. The evaluation can be improved by analyses of diagenetic carbonate and altered fossil materials, which help constraining the diagenetic trajectories in the sampled specimens. Quantification of post-depositional alteration is possible, but in most cases the complexity of diagenetic systems hampers the possibility of retrieving original proxy values for palaeoenvironmental reconstructions from partially altered materials

Clover - A B-mode polarization experiment

Clover is a new instrument being built to detect the B-mode polarization of the CMB. It consists of three telescopes operating at 97, 150, and 220 GHz and will be sited in Chile at the Llano de Chajnantor. Each telescope assembly is scaled to give a constant beam size of 8 arcmin and feeds an array of between 320 and 512 finline-coupled TES bolometers. Here we describe the design, current status and scientific prospects of the instrument.Comment: 11 pages, 6 figures. Proceedings of the Fundamental Physics With CMB workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy Review

Etched graphene quantum dots on hexagonal boron nitride

We report on the fabrication and characterization of etched graphene quantum dots (QDs) on hexagonal boron nitride (hBN) and SiO2 with different island diameters. We perform a statistical analysis of Coulomb peak spacings over a wide energy range. For graphene QDs on hBN, the standard deviation of the normalized peak spacing distribution decreases with increasing QD diameter, whereas for QDs on SiO2 no diameter dependency is observed. In addition, QDs on hBN are more stable under the influence of perpendicular magnetic fields up to 9T. Both results indicate a substantially reduced substrate induced disorder potential in graphene QDs on hBN

Morphological Characterization of the Radiation Sensitive Cell Line, XRS-5

Morphometric analysis was performed on the radiation sensitive Chinese hamster ovary (CHO) xrs-5 cell line, reverting xrs-5 cells and parental K1 cells. Several ultrastructural parameters (increased nuclear envelope membrane separation, cell and nuclear volume, nuclear to cytoplasmic ratio, and the nuclear surface area per unit volume of the cell) were measured and correlated with radiation sensitivity. A trend in increased cell size and radiosensitivity was observed. However, only the substantially increased nuclear envelope membrane separation in sensitive xrs-5 cells significantly correlated with radiation sensitivity. The maximal nuclear envelope membrane separation in sensitive xrs-5 cells was 270.8 nm. The maximal K1 cell nuclear envelope membrane separation was 134.8 nm, although, on average the K1 cell nuclear envelope membrane separation was 36.8 nm. The reverted xrs-5 cells had a smaller nuclear envelope membrane separation (maximal 83.6 nm), but the measured space did not completely revert to that for K1 cells. Therefore, we conclude that the nuclear envelope membrane separation is correlated with radiation sensitivity of xrs-5 cells, but it cannot be considered as the only defect correlatable with the radiation sensitivity

Element/Ca, C and O isotope ratios in modern brachiopods: Species-specific signals of biomineralization

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Fossil brachiopods are of major importance for the reconstruction of palaeoenvironmental conditions, particularly of the Paleozoic. In order to better understand signals of ancient shell materials, modern analogue studies have to be conducted. Here we present C and O isotope data in conjunction with Mg/Ca, Sr/Ca, Mn/Ca and Fe/Ca data for nine modern rhynchonellid and terebratulid brachiopod species from tropical to intermediate latitudes and shallow to very deep marine settings. C and O isotope signals of most species suggest formation of secondary shell layers near or in isotopic equilibrium with ambient seawater. Some species – especially in the suborder Terebratellidina – show partly distinct disequilibrium signals, suggesting some degree of phylogenetic control on the expression of vital effects. Mn/Ca and Fe/Ca ratios measured in the modern species form a baseline to assess fossil preservation, but also yield environmental information. Mg/Ca and Sr/Ca ratios follow previously observed patterns, with all studied brachiopod species comprising low-Mg calcite. Strong covariation of Sr/Ca ratios with Mg/Ca ratios is only observed in rhynchonellids and possibly one terebratulid species, potentially linking the incorporation behaviour of alkaline earth metals to phylogeny. Sr/Ca show a strong negative correlation with δ13C values in terebratellidinid species which exhibit major isotopic disequilibrium and also combined data from three localities for which two species were studied indicate such a negative relation. The observed covariation of Sr/Ca ratios with δ13C values may therefore become a useful tool to detect δ13C disequilibrium and to robustly estimate δ13C values of ambient DIC in deep time.The authors acknowledge comments from two anonymous reviewers and Alberto Pérez-Huerta as well as the editor Michael E. Boettcher which helped to improve the quality and clarity of the manuscript. The authors thank the Museum für Naturkunde Berlin for providing brachiopod specimens of the species F. sanguinolenta (ZMB Bra 1934), M. venosa (ZMB Bra 2028), N. nigricans (ZMB Bra 2441), S. crosnieri (ZMB Bra 2442), C. inconspicua (ZMB Bra 2443), C. racovitzae (ZMB Bra 2444) and L. neozelanica (ZMB Bra 2445) and Andy Gale for providing specimens of T. transversa and Terebratulina sp. The authors are indebted to the crews of RV SONNE during the cruises SO 168 ZEALANDIA and SO 233 WALVIS 2 and their respective shipboard scientific parties. Financial support by the German Ministry of Education and Research (BMBF) within the project SO 168 ZEALANDIA (FKZ: 03G0168) and SO 233 WALVIS 2 (FKZ: 03G0233A) to CL is gratefully acknowledged. CVU acknowledges funding from the Leopoldina – German National Academy of Sciences (grant no. LPDS 2014-08)

Direct determination of the band offset in atomic layer deposited ZnO hydrogenated amorphous silicon heterojunctions from X ray photoelectroscopy valence band spectra

The chemical composition and band alignment at the heterointerface between ALD grown zinc oxide ZnO and hydrogenated amorphous silicon a Si H is investigated using monochromatized X ray photoelectron spectroscopy. A new approach for obtaining the valence band offset DeltaEV is developed, which consists in fitting the valence band VB spectrum obtained for a Si H with a thin ZnO overlayer as the sum of experimentally obtained VB spectra of a bulk a Si H film and a thick ZnO film. This approach allows obtaining DeltaEV 2.71 0.15 eV with a minimum of assumptions, and also yields information on the change in band bending of both substrate and ZnO film. The band offset results are compared to values obtained using the usual approach of comparing valence band edge to core level energy differences, DeltaEB,CL DeltaEB,VB. Furthermore, a theoretical value for the VB offset is calculated from the concept of charge neutrality level line up, using literature data for the CNLs and the experimentally determined ZnO a Si H interface dipole. The thus obtained value of DeltaEVCNL 2.65 0.3 eV agrees well with the experimental DeltaE

Tectonic forcing of Early to Middle Jurassic seawater Sr/Ca

types: ArticleThis is the author formatted version of Ullman et al. (2013) Geology 41(12), 1211-1214. doi:10.1130/G34817.1 http://geology.gsapubs.org/content/41/12/1211.full Uploaded under the terms of Green Open Access in GSA's Open Access PolicyThe Jurassic Period (ca. 201–145 Ma) is marked by fundamental reorganizations of paleogeography, paleoceanography, ecosystems, and the progressive shift from aragonite to calcite as the favored marine biogenic carbonate polymorph. Sr/Ca ratios of well-preserved Jurassic oysters and belemnites from sections in the UK and Poland demonstrate that the Sr/Ca ratio of seawater varied systematically throughout the Early and Middle Jurassic in parallel with already documented seawater 87Sr/86Sr. The Sr flux from increased mid-ocean ridge activity in the Early Jurassic outbalanced the input of riverine Sr, leading to gradually lower seawater 87Sr/86Sr associated with the parallel and strong decrease in seawater Sr/Ca ratios. This downward trend was reversed by enhanced continental input in the Toarcian and Aalenian, but resumed in the Bajocian and continued to the Callovian. Parallel changes of seawater 87Sr/86Sr and Sr/Ca suggest a common cause for these long-term variations and are best explained by changes in the balance of continental weathering and hydrothermal fluxes. These findings underline the strong control of global tectonic processes on the evolution of biomineralization and downplay the role of biomineral evolution in influencing strontium chemistry of seawater in the mid-Mesozoi

Oxygen and carbon isotope and Sr/Ca signatures of high-latitude Permian to Jurassic calcite fossils from New Zealand and New Caledonia

Article available online 12 November 2015This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Calcite fossils from New Zealand and New Caledonia provide insight into the Permian to Jurassic climatic history of Southern High Latitudes (southern HL) and Triassic Southern Intermediate Latitudes (southern IL). These results permit comparison with widely studied, coeval sections in Low Latitudes (LL) and IL. Oxygen isotope ratios of well-preserved shell materials indicate a partially pronounced Sea Surface Temperature (SST) gradient in the Permian, whereas for the Triassic no indication of cold climates in the southern HL is found. The Late Jurassic of New Zealand is characterized by a slight warming in the Oxfordian–Kimmeridgian and a subsequent cooling trend in the Tithonian. Systematic variations in the δ13C values of southern HL samples are in concert with those from LL sections and confirm the global nature of the carbon isotope signature and changes in the long-term carbon cycle reported earlier. Systematic changes of Sr/Ca ratios in Late Triassic brachiopods, falling from 1.19 mmol/mol in the Oretian (early Norian) to 0.67 mmol/mol in the Warepan (late Norian) and subsequently increasing to 1.10 mmol/mol in the Otapirian (~ Rhaetian), are observed. Also Sr/Ca ratios of Late Jurassic belemnite genera Belemnopsis and Hibolithes show synchronous changes in composition that may be attributed to secular variations in the seawater Sr/Ca ratio. For the two belemnite genera an increase from 1.17 mmol/mol in the Middle Heterian (~ Oxfordian) to 1.78 mmol/mol in the Mangaoran (~ late Middle Tithonian) and a subsequent decrease to 1.51 mmol/mol in the Waikatoan (~ Late Tithonian) is documented.This project was funded by the Danish Council for Independent Research– Natural Sciences (project 09-072715), the Carlsberg Foundation (project nr 2011-01-0737) provided for CK, and by the University of Copenhagen (IGN). CVU acknowledges funding from the German National Academy of Sciences – Leopoldina (grant nr LPDS 2014-08