Provenance of Ordovician and Devonian sandstones from southern Peru and northern Bolivia - U-Pb and Lu-Hf isotope evidence of detrital zircons and its implications for the geodynamic evolution of the Western Gondwana margin (14° - 17° S)

In an attempt to trace the provenance of sedimentary detritus and to gain information on the crustal evolution of the Early Paleozoic western Gondwana margin (14°-17°S) we applied a combined in situ U-Pb and Lu-Hf LA-ICP-MS isotope analysis on detrital zircon from 12 Ordovician and Devonian sandstones in southern Peru and northern Bolivia. The sandstones are exposed in the Eastern Cordillera, the Altiplano and the Coastal Cordillera. The sedimentary basins are part of the Peru-Bolivia trough. Few intrusive and extrusive Early Paleozoic rocks indicate that the Ordovician basins developed in a back-arc position, with the arc on the Arequipa Massif in the west and the Amazonian craton in the east. This plate-tectonic setting appears to have changed into a passive margin in the Early Devonian. The U-Pb zircon age distribution of the Ordovician sandstones from the Eastern Cordillera has the most distinctive peak between 0.7 and 0.5 Ga (Brazilian interval). Contrastingly, the most prominent U-Pb zircon age peak of the Ordovician sandstones from the Altiplano is at 1.2-0.9 Ga (Grenvillian interval) with a smaller peak at 1.85-1.7 Ga. The Devonian sandstones from the same locality on the Altiplano contain zircons with a major age peak at 0.5-0.4 Ga (Famatinian interval). Smaller U-Pb age peaks can be connected to the Brazilian, Grenvillian and Transamazonian (2.2-1.8 Ga) intervals. Zircons of the Devonian sandstones from the Coastal Cordillera have a similar age distribution but the Grenvillian ages, in one case also the Transamazonian ages are significantly more pronounced than the Brazilian ages. Zircons formed during the Brazilian interval could have been derived from various eastern sources on the Amazonian craton, those with Grenvillian ages were derived either from the Sunsas belt to the east or from the Arequipa Massif to the west of the sedimentary basin. Zircons related to the Famatinan event most probably originated in the Arequipa Massif, the closest place where respective magmatic arc rocks were available. Thus, the Ordovician sandstones of the Eastern Cordillera and the Altiplano had an eastern source, while the Altiplano locality was fed from a very limited source area, probably the Sunsas belt. The Devonian siliciclastic strata instead were mainly influenced by the Arequipa Massif. Minor influences of eastern sources are documented by the presence of Brazilian zircon ages. The in situ Lu-Hf isotope signature provides information about crustal recycling. Together with the U-Pb zircon ages, crustal evolution paths can be reconstructed. εHf(t) values of the analysed zircons spread between –20 and +12. Zircons with a very juvenile signatures (less than 5 εHf-units below the respective depleted mantle composition) we detected only in the interval between 1.5 and 0.9 Ga. Hence, of the Brazilian and Famatinian events we only find zircons derived from an evolved crust. A striking feature is the common Hf model ages (c.1.5-1.2 Ga) of zircons formed during the Grenvillian, Brazilian and Famatinian orogenies. This indicates that Famatinian-aged crystalline rocks of the Arequipa Massif and the Brazilianaged crystalline rocks of the Amazonian craton have a similar crustal origin

Hochwasser und andere Katastrophen - was haben wir gelernt?

Der Beitrag versucht, eine erste Bilanz zu ziehen im Hinblick auf Schlussfolgerungen und Konsequenzen aus der 500-Jahres-Flut, die im Herbst 2002 das Gebiet von Elbe und Mulde heimgesucht hat. Dabei werden "Lernprozesse" im Einzelnen und in all ihren Widersprüchlichkeiten skizziert sowie in den Kontext des bereits im Gang befindlichen Klimawandels gestellt. Im Ergebnis werden Perspektiven für eine vorsorgende Raumplanung aufgezeigt und es wird verdeutlicht, dass und in welchem Maße Vorsorge möglich ist.The article attempts to take initial stock of the conclusions and consequences arising from the 500-year flood, which struck the area surrounding the river Elbe and river Mulde in autumn 2002. "Learning processes" are outlined individually, detailing all their inconsistencies, and are placed in the context of the climate change, which is already underway. Finally, the prospects for precautionary regional development planning are explained, and the article demonstrates that precautionary measures can be taken and reveals the extent to which they are possible

B cell–intrinsic TLR signals amplify but are not required for humoral immunity

Although innate signals driven by Toll-like receptors (TLRs) play a crucial role in T-dependent immune responses and serological memory, the precise cellular and time-dependent requirements for such signals remain poorly defined. To directly address the role for B cell–intrinsic TLR signals in these events, we compared the TLR response profile of germinal center (GC) versus naive mature B cell subsets. TLR responsiveness was markedly up-regulated during the GC reaction, and this change correlated with altered expression of the key adaptors MyD88, Mal, and IRAK-M. To assess the role for B cell–intrinsic signals in vivo, we transferred MyD88 wild-type or knockout B cells into B cell–deficient μMT mice and immunized recipient animals with 4-hydroxy-3-nitrophenylacetyl (NP) chicken gamma globulin. All recipients exhibited similar increases in NP-specific antibody titers during primary, secondary, and long-term memory responses. The addition of lipopolysaccharide to the immunogen enhanced B cell-intrinsic, MyD88-dependent NP-specific immunoglobulin (Ig)M production, whereas NP-specific IgG increased independently of TLR signaling in B cells. Our data demonstrate that B cell–intrinsic TLR responses are up-regulated during the GC reaction, and that this change significantly promotes antigen-specific IgM production in association with TLR ligands. However, B cell–intrinsic TLR signals are not required for antibody production or maintenance

The missing link of Rodinia break up in western South America: A petrographical, geochemical, and zircon Pb-Hf isotope study of the volcanosedimentary Chilla beds (Altiplano, Bolivia)

The assembly of Rodinia involved the collision of eastern Laurentia with southwestern Amazonia at ca. 1 Ga. The tectonostratigraphic record of the central Andes records a gap of ∼300 m.y. between 1000 Ma and 700 Ma, i.e., from the beginning of the Neoproterozoic Era to the youngest part of the Cryogenian Period. This gap encompasses the time of final assembly and breakup of the Rodinia supercontinent in this region. We present new petrographic and whole-rock geochemical data and U-Pb ages combined with Hf isotope data of detrital zircons from the volcanosedimentary Chilla beds exposed on the Altiplano southwest of La Paz, Bolivia. The presence of basalt to andesite lavas and tuffs of continental tholeiitic affinity provides evidence of a rift setting for the volcanics and, by implication, the associated sedimentary rocks. U-Pb ages of detrital zircons (n = 124) from immature, quartz-intermediate sandstones have a limited range between 1737 and 925 Ma. A youngest age cluster (n = 3) defines the maximum depositional age of 925 ± 12 Ma. This is considered to coincide with the age of deposition because Cryogenian and younger ages so typical of Phanerozoic units of this region are absent from the data. The zircon age distribution shows maxima between 1300 and 1200 Ma (37% of all ages), the time of the Rondônia–San Ignacio and early Sunsás (Grenville) orogenies in southwestern Amazonia. A provenance mixing model considering the Chilla beds, Paleozoic Andean units, and data from eastern Laurentia Grenville sources shows that >90% of the clastic input was likely derived from Amazonia. This is also borne out by multidimensional scaling (MDS) analysis of the data. We also applied MDS analysis to combinations of U-Pb age and Hf isotope data, namely εHf(t) and 176Hf/177Hf values, and demonstrate again a very close affinity of the Chilla beds detritus to Amazonian sources. We conclude that the Chilla beds represent the first and hitherto only evidence of Rodinia breakup in Tonian time in Andean South America.publishedVersio

Sedimentological analysis of tsunami deposits along the coast of Peru

The Peru-Chile-Trench is one of the most active seismic areas in the world (Kulikov et al., 2005). The subduction of the Nasca Plate under the South American Plate causes earthquakes with magnitudes greater than 8 every 5 to 10 years. Consequently, the risk for destructive tsunami along the coast of Peru is very high. The greatest historical tsunami events in this region are the two Arica tsunami in 1604 and 1868 (Okal et al., 2006) and the Chile tsunami in 1960 (Cisternas et al., 2005). The most recent tsunami are the Chimbote tsunami in 1996 (Bourgeois et al., 1999) and the Camaná tsunami in 2001 (Jaffe et al., 2003). Additionally, in 2007, a magnitude 7.9 earthquake 150 kilometres SSE of Lima generated a tsunami with run up heights of 10 m along the southern Paracas Peninsula (Fritz et al., 2008). Despite a large increase in tsunami studies in the last years, there is still no complete tsunami facies model. Furthermore the hydrodynamical processes leading to deposition of sediment by a tsunami wave are still not well understood. We surveyed various locations along the 2400 km Peruvian coastline to locate deposits of recent and historical tsunami events. Deposits were studied in trenches and boreholes down to depths of 3 m. We separated the foraminifera content for identification and inference of water depths of sediment entrainment by the tsunami. The grain-size distributions of the sampled deposits were optically determined with a PartAn 2001 particle analyser. The grain-size data were used to re-model the flow depths, using the inverse tsunami model of Jaffe & Gelfenbaum (2007)

Sedimentological aspects of recent and historical tsunami events along the coast of Peru

The coast of Peru is greatly endangered by tsunami events. The subduction of the Nasca Plate below the South American Plate triggers strong submarine earthquakes that are capable of causing tsunami. High-energy wave events are major coast shaping processes. In some regions, e.g. the Caribbean, a distinction between storm/hurricane and tsunami deposits is difficult. Therefore, the absence of heavy storms makes the Peruvian coast a good target for tsunami research. Other meteorological phenomena, like El Niño events that occur in Peru are not associated with strong storms or surges. Deposits of El Niño-caused flooding can easily be distinguished from tsunami events, since their sedimentary structures imply transport from the land to the sea, the deposited material derives from the mountain ranges and no indicators (e.g., foraminifera, shells) of marine inundations are present. In our study we re-surveyed locations of the three most recent regional tsunami events in order to learn about the sedimentary structures and their preservation potential. We visited the areas affected by the Chimbote-Tsunami of 21st February 1996 (5 m run up; Bourgeois et al., 1999; Kulikov et al., 2005), by the Camana-Tsunami of the 23rd June 2001 (9 m run up; Jaffe et al., 2003) and by the Pisco-Paracas-Tsunami of 15th August 2007 (10 m run up; Fritz et al., 2007). Secondly, we surveyed the coast of Peru in order to find traces of historical or paleotsunami events. All sediments were sampled for grain size analysis, foraminifera determination and optically stimulated luminescence dating. For historical events, the inverse tsunami model of Jaffe & Gelfenbaum (2007) was applied to calculate onshore tsunami flow depths. Both recent and historical tsunami deposits are present as (1) (graded) layers of coarse sand, some including shell fragments or pieces of rock, (2) (imbricated) shell layers, (3) heavy mineral accumulations and (4) mud caps or mud balls. Imbricated shells can give information on flow directions and hence can help to distinguish between run up and backwash sediments. Unfortunately, the preservation potential of onshore tsunami deposits is very low. Erosion by wind, rivers or heavy rain falls (e.g., during El Niño events) and bioturbation (e.g., by crabs) can modify or destroy the sediments. For recent events, human activity (e.g., the use of beach / tsunami sand for rebuilding) is a limiting preservation factor. This study shows that muddy tsunami sediments and backwash sediments have the highest preservation potential. This is due to the cohesion of mud that makes the deposits less sensitive for erosion during backwash and due to fast hardening of mud layers in the dry Peruvian climate

The impact of salps (Salpa thompsoni) on the Antarctic krill population (Euphausia superba): an individual-based modelling study

Krill (Euphausia superba) and salps (Salpa thompsoni) are key macrozooplankton grazers in the Southern Ocean ecosystem. However, due to differing habitat requirements, both species previously exhibited little spatial overlap. With ongoing climate change-induced seawater temperature increase and regional sea ice loss, salps can now extend their spatial distribution into historically krill-dominated areas and increase rapidly due to asexual reproduction when environmental conditions are favorable. Understanding the potential effects on krill is crucial, since krill is a species of exceptional trophic significance in the Southern Ocean food web. Negative impacts on krill could trigger cascading effects on its predators and prey. To address this question, we combined two individual-based models on salps and krill, which describe the whole life cycle of salp individuals and the dynamic energy budget of individual krill. The resulting new model PEKRIS (PErformance of KRIll vs. Salps) simulates a krill population for 100 years under varying chlorophyll-a concentrations in the presence or absence of salps. All of the investigated krill population properties (abundance, mean length, and yearly egg production) were significantly impacted by the presence of salps. On the other hand, salp density was not impacted if krill were present. The medians of krill population properties deviated during variable maximum chlorophyll-a density per year when salps were introduced by − 99.9% (− 234 individuals per 1000 m3) for krill density, − 100% (− 22,062 eggs per 1000 m3) for krill eggs and − 0.9% (− 0.3 mm) for mean length of krill. If both species compete for the same food resource in a closed space, salps seem to inhibit krill populations. Further simulation studies should investigate whether this effect prevails if different phytoplankton sizes and consumption preferences of krill are implemented. Furthermore, direct predation of the two species or consumption of krill fecal pellets by salps could change the impact size of the food competition

HIV Risk Activity Among Persons With Severe Mental Illness: Preliminary Findings

This paper reports on HIV-related risk activities among 95 people with severe mental illness in psychiatric care in New York City