ALBERT

Beschreibung: Non-intrusive track-based physical properties measurements of sediment cores recovered during ocean drilling are often biased by imperfect recovery within sediment core liners, particularly in heterogeneous and/or partially lithified sediments. These biases result in misrepresentation in measurements of true sediment physical properties, and can complicate integration of the composite site records assembled from recovered cores with borehole logs of the stratigraphic section. Here we develop a strategy utilizing gamma ray attenuation (GRA) density to generate mass-specific magnetic susceptibility (MS) and natural gamma radiation (NGR) data. Shipboard GRA density is collected in all cores that comprise a site at equivalent or higher resolution than the corresponding MS and NGR data. All instruments are calibrated assuming a volume of sediment in their detector windows equivalent to that present in a perfectly full core liner; changes in sediment bulk density related to compaction, and/or imperfect sediment recovery resulting in a partially filled core liner thus influence all three measurements proportional to their detector sensitivities. In principle it may be possible to correct MS or NGR data for variable sediment volume by normalizing them to GRA measured at equivalent depth on a sensing track, assuming that the volumetric bias is comparable in all three datasets. Because GRA is measured in much greater detail, it must be smoothed by the known measurement windows of the other parameters for the assumption of comparable analytical sediment volume to be true. Normalizing MS or NGR by the equivalently smoothed GRA in down-hole records should thus remove the bias associated with variable sediment volume in the detector windows, allowing for robust mass-specific determination of these volume-based sediment physical properties.

Beschreibung: Despite numerous discoveries that have considerably enriched the African-Arabian Tertiary fossil record over the last decades, our knowledge of the evolutionary history of many continental African vertebrate groups during the Paleogene period remains inadequate, particularly when it is compared with the fossil records of Europe or North America. The Eocene Epoch in Africa is especially poorly documented, being restricted to few fossiliferous localities. Our understanding of the early Tertiary emergence, diversification, and paleobiogeographic history of African-Arabian mammals has been further hindered by the lack of a precise temporal framework for these sites. We conducted magnetostratigraphic analyses, associated with biostratigraphic studies, in the fossiliferous sequences exposed in the northwestern Hammadas of the Saharan Platform in the Glib Zegdou area and in the Saharan Atlas at the El Kohol locality (Algeria) to further define the age of these Eocene continental deposits. Based on biostratigraphic constraints, the six polarity zones identified in the El Kohol section can be correlated with chrons C24n to C22r, providing the first direct age estimates for the El Kohol fossiliferous strata between 52 and 51 Ma. Correlation to the geomagnetic polarity time scale, using previously published biostratigraphic data for the Glib Zegdou fauna, suggests an age ranging between 49 and 45 Ma for this section. The high-resolution magnetostratigraphic study of the poorly known continental Eocene Epoch of Algeria provides new insights into the early Tertiary stratigraphy of northwest Africa. The placement of the Algerian localities into a consistent chronological framework constitutes considerable advancement to achieve biostratigraphic correlation of the Paleogene African-Arabian mammal localities.

Beschreibung: We present SuperFly ( http://superfly.crg.eu ), a relational database for quantified spatio-temporal expression data of segmentation genes during early development in different species of dipteran insects (flies, midges and mosquitoes). SuperFly has a special focus on emerging non-drosophilid model systems. The database currently includes data of high spatio-temporal resolution for three species: the vinegar fly Drosophila melanogaster , the scuttle fly Megaselia abdita and the moth midge Clogmia albipunctata . At this point, SuperFly covers up to 9 genes and 16 time points per species, with a total of 1823 individual embryos. It provides an intuitive web interface, enabling the user to query and access original embryo images, quantified expression profiles, extracted positions of expression boundaries and integrated datasets, plus metadata and intermediate processing steps. SuperFly is a valuable new resource for the quantitative comparative study of gene expression patterns across dipteran species. Moreover, it provides an interesting test set for systems biologists interested in fitting mathematical gene network models to data. Both of these aspects are essential ingredients for progress toward a more quantitative and mechanistic understanding of developmental evolution.

Beschreibung: Developmental gene networks implement the dynamic regulatory mechanisms that pattern and shape the organism. Over evolutionary time, the wiring of these networks changes, yet the patterning outcome is often preserved, a phenomenon known as "system drift." System drift is illustrated by the gap gene network—involved in segmental patterning—in dipteran insects. In the classic model organism Drosophila melanogaster and the nonmodel scuttle fly Megaselia abdita , early activation and placement of gap gene expression domains show significant quantitative differences, yet the final patterning output of the system is essentially identical in both species. In this detailed modeling analysis of system drift, we use gene circuits which are fit to quantitative gap gene expression data in M. abdita and compare them with an equivalent set of models from D. melanogaster. The results of this comparative analysis show precisely how compensatory regulatory mechanisms achieve equivalent final patterns in both species. We discuss the larger implications of the work in terms of "genotype networks" and the ways in which the structure of regulatory networks can influence patterns of evolutionary change (evolvability).

Beschreibung: The middle Miocene is a crucial period for the evolution of apes, and it corresponds to their appearance in Europe. The dispersion of apes was made possible by tectonic changes and the expansion of their habitat, (sub-) tropical forest, in Europe. The context in which the middle Miocene climatic optimum occurred still lacks constraints in terms of atmospheric pCO2 and ice-sheet volume and extent. Using a coupled atmosphere-ocean general circulation model (GCM) and dynamic vegetation model, we investigated the sensitivity of Miocene climate and vegetation to pCO2 levels and Antarctic ice-sheet configurations. Our results indicate that higher than present pCO2 is necessary to simulate subtropical forest in Western and Central Europe during the middle Miocene, but that a threshold at high pCO2 makes subtropical forest partly collapse. Moreover, removing ice over Antarctica modifies oceanic circulation and induces warmer and slightly wetter conditions in Europe, which are consistent with the expansion of subtropical forest. These results suggest that a small East Antarctic Ice Sheet (25% of present-day ice volume) together with higher than present pCO2 values are in better agreement with available European middle Miocene data.

Beschreibung: Ice dynamics, tectonic setting, and sediment supply are the key parameters controlling the architecture of high-latitude margins and the formation of trough mouth fans (TMFs). Current understanding of these archives of paleo–ice streams is based on studies of ice sheets adjacent to stable, passive margins, while the behavior of active, convergent glacier-influenced margins remains relatively unconstrained. We integrate high-resolution seismic data and chronology from Integrated Ocean Drilling Program Expedition 341 cores in southeast Alaska across the actively converging Yakutat terrane margin to examine the late Quaternary evolution of the Bering Glacier, the largest outlet glacier of the poorly understood Cordilleran Ice Sheet (CIS). We interpret at least eight glacial advances to the shelf break since the end of the mid-Pleistocene transition, showing a more dynamic CIS than hitherto realized. During the past ~130 k.y., the temperate, meltwater-charged Bering Glacier delivered ~925 km 3 of sediment to the shelf and slope, providing one of the highest rates of sustained sediment accumulation (5–10 m/k.y.) ever reported globally. Rapid formation of a TMF, reaching ~600 m thick in ~130 k.y., emphasizes the extreme sediment flux that can be produced by wet-based glacial systems, and its critical role in the development of high-latitude margin stratigraphy. TMF formation despite initially steep, tectonically controlled slopes in this active setting reflects an autogenic shift in the evolution of the Bering Trough, suggesting that major transitions between sedimentary regimes need not reflect some externally driven change in climate variability.

Beschreibung: Strain resulting from the collision of India with Asia has caused fundamental changes to Asian drainage patterns, but the timing and nature of these changes are poorly understood. One frequently proposed hypothesis involves the connection of the palaeo Tsangpo drainage to a precursor to the Irrawaddy River of central Myanmar in the Palaeogene. To test this hypothesis, we studied the provenance of Palaeogene fluvio-clastic sedimentary rocks that crop out in central Myanmar, namely the Late Middle Eocene–Early Oligocene Pondaung and Yaw Formations. Isotopic analysis on bulk-rock and petrographic data indicate a primary magmatic arc source, and a secondary source composed of recycled, metamorphosed basement material. Although the exact location of both sources is hardly distinguishable because Burmese and Tibetan provinces share common lithological features, the presence of low-grade metamorphic fragments, the heterogeneity in Sr–Nd isotopic values of bulk sediments and westward-directed palaeoflow orientations indicate a proximal source area located on the eastern Asian margin. Central Myanmar was the locus of westward-prograding deltas opening into the Indian Ocean, supplied by the unroofing of an Andean-type cordillera that extended along the Burmese margin. We found no evidence to support a palaeo Tsangpo–Irrawaddy River, at least during the Late Eocene. Supplementary material: Data locations, and isotopic and petrographic results are available at www.geolsoc.org.uk/SUP18655 .