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Munnecke A.,GeoZentrum Nordbayern | Zhang Y.,CAS Nanjing Institute of Geology and Palaeontology | Liu X.,CAS Nanjing Institute of Geology and Palaeontology | Cheng J.,CAS Nanjing Institute of Geology and Palaeontology
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

About 500 samples from 11 Ordovician sections in South China have been analysed for their δ13Ccarb composition. Four sections are located in the Yangtze platform region, the remaining seven sections in the Jiangnan slope region. The sections span more or less the entire Ordovician, but the sample resolution in its lower part (Tremadocian to Dapingian) is lower than in its upper part (Darriwilian to Hirnantian). Overall, the data show a good correlation with the published global isotope curve. At the Cambrian-Ordovician boundary positive values are observed. In the succeeding Tremadocian the values decrease and remain negative into the early Floian. In the late Floian, the values increase to slightly positive. The correlation of Dapingian rocks between the Yangtze and the Jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the Yangtze section. In the Darriwilian a small positive excursion is observed in the Yangtze platform area, however, it is missing in the Jiangnan slope area. This excursion probably correlates with the mid-Darriwilian excursion (MDICE) reported from Baltoscandia. Both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the Shihtzupu Formation and the Pagoda Formation, i.e. most of the Sandbian is probably not represented in the Upper Yangtze region. The earliest Katian is characterised by a pronounced positive excursion correlating with the well-known global Guttenberg excursion (GICE). In the late Katian at least one additional positive excursion was determined. The precise biostratigraphy, however, is not clear, and therefore it is not known which of the known four to five remaining Katian δ13C excursions identified in Baltica correlate(s) with the one(s) observed in the present study, and further biostratigraphic study is required. The lower part of the Hirnantian excursion (HICE) is probably not preserved, with only small remnants of the HICE observed near the base of the Kuanyinchiao Bed. © 2011 Elsevier B.V. Source


Teichert S.,GeoZentrum Nordbayern | Freiwald A.,Senckenberg Institute
Biogeosciences | Year: 2014

In this study we present a comparative quantification of CaCO3 production rates by rhodolith-forming coralline red algal communities situated in high polar latitudes and assess which environmental parameters control these production rates. The present rhodoliths act as ecosystem engineers, and their carbonate skeletons provide an important ecological niche to a variety of benthic organisms. The settings are distributed along the coasts of the Svalbard archipelago, being Floskjeret (78° 18' N) in Isfjorden, Krossfjorden (79°08' N) at the eastern coast of Haakon VII Land, Mosselbukta (79 °53' N) at the eastern coast of Mosselhalvøya, and Nordkappbukta (80 °31' N) at the northern coast of Nordaustlandet. All sites feature Arctic climate and strong seasonality. The algal CaCO3 production rates were calculated from fuchsine-stained, presumably annual growth increments exhibited by the rhodoliths and range from 100.9 g (CaCO3) m-2 yr-1 at Nordkappbukta to 200.3 g (CaCO3) m-2 yr-1 at Floskjeret. The rates correlate to various environmental parameters with geographical latitude being the most significant (negative correlation, Combining double low line 0.95, Combining double low line 0.0070), followed by the duration of the polar night (negative correlation, Combining double low line 0.93, Combining double low line 0.0220), the duration of the sea ice cover (negative correlation, Combining double low line 0.87, Combining double low line 0.0657), and the annual mean temperature (positive correlation, Combining double low line 0.48, Combining double low line 0.0301). This points out sufficient light incidence to be the main control of the growth of the examined coralline red algal rhodolith communities, while temperature is less important. Thus, the ongoing global change with its rising temperatures will most likely result in impaired conditions for the algae, because the concomitant increased global runoff will decrease water transparency and hence light incidence at the four offshore sites. Regarding the aforementioned role of the rhodoliths as ecosystem engineers, the impact on the associated organisms will presumably also be negative. © Author(s) 2014. CC Attribution 3.0 License. Source


Krienitz M.-S.,University of Kiel | Garbe-schonberg C.-D.,University of Kiel | Romer R.L.,Helmholtz Center Potsdam | Meixner A.,Helmholtz Center Potsdam | And 4 more authors.
Journal of Petrology | Year: 2012

Lithium elemental and isotopic compositions of 33 glass and whole-rock samples from nine oceanic island regions were determined to characterize the Li inventory of the deep mantle. The Li contents of the investigated lavas range from 1·5 to 13·3 μg g. -1, whereas δ. 7Li ranges from 2·4 to 4·8‰. There are weak co-variations between the Li/Y, δ 7Li, and Sr-Nd-Pb isotope compositions of the lavas, indicating that the Li elemental and isotopic characteristics of ocean island basalt to some extent reflect mantle source heterogeneity. In detail, HIMU-type lavas are characterized by δ 7Li values (up to 4·8‰) slightly heavier than those for average normal mid-ocean ridge basalt (3·4 ± 1·4‰) and by comparatively low Li contents; EM1-type lavas are characterized by isotopically light Li (average 3·2‰) and relative Li enrichment, whereas EM2-type lavas tend to heavier δ 7Li values (up to 4·4‰) with high Li concentrations. The Li contents and isotope characteristics of HIMU-type lavas are consistent with recycling of altered and dehydrated oceanic crust, whereas those of the EM1-type lavas can be attributed to sediment recycling. The Li characteristics of EM2-type lavas may reflect reworking of mantle wedge material that has been infiltrated by fluids derived from the subducting plate. © The Author 2012. Published by Oxford University Press. All rights reserved. Source


Westphal H.,University of Bremen | Hilgen F.,Institute of Paleoenvironments and Paleoclimate Utrecht | Munnecke A.,GeoZentrum Nordbayern
Earth-Science Reviews | Year: 2010

A manual is presented to assist in assessing the suitability of individual calcareous rhythmites for high-resolution stratigraphic applications and orbital dating. While the astrochronological approach offers an unprecedented high temporal resolution for stratigraphy, caution is required to carefully choose suitable rhythmites for the analysis. Diagenesis is known to distort or mimic primary signals in particular in carbonate rhythmites. To keep orbital dating a reliable method, the choice of sedimentary successions has to be undertaken with utmost scrutiny. Here, we review and evaluate the methods that have been used for assessing the record of primary signals in calcareous rhythmites. The goal is to provide the orbital stratigrapher with tools for a straightforward and systematic assessment of such successions. © 2010 Elsevier B.V. Source


Teichert S.,GeoZentrum Nordbayern
Scientific Reports | Year: 2014

Rhodoliths are coralline red algal assemblages that commonly occur in marine habitats from the tropics to polar latitudes. They form rigid structures of high-magnesium calcite and have a good fossil record. Here I show that rhodoliths are ecosystem engineers in a high Arctic environment that increase local biodiversity by providing habitat. Gouged by boring mussels, originally solid rhodoliths become hollow ecospheres intensely colonised by benthic organisms. In the examined shelf areas, biodiversity in rhodolith-bearing habitats is significantly greater than in habitats without rhodoliths and hollow rhodoliths yield a greater biodiversity than solid ones. This biodiversity, however, is threatened because hollow rhodoliths take a long time to form and are susceptible to global change and anthropogenic impacts such as trawl net fisheries that can destroy hollow rhodoliths. Rhodoliths and other forms of coralline red algae play a key role in a plurality of environments and need improved management and protection plans. © 2014 Macmillan Publishers Limited. Source

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