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13. Evidence for major climatic change at the Smithian-Spathian boundary from low palaeolatitudinal records Hermann Elke*, Hochuli Peter A.*,**, Bucher Hugo*,**, Brühwiler Thomas*, Goudemand Nicolas* & Ghazala Roohi*** *Paläontologisches Institut und Museum, Karl Schmid-Strasse 4, CH-8006 Zürich (ehermann@pim.uzh.ch) **Geologisches Institut, Universitätsstrasse 16,CH-8050 Zürich ***Pakistan Museum of Natural History, Garden Avenue, PK-44000 Islamabad The delayed recovery of marine and terrestrial ecosystems after the end-Permian extinction event is still up for debate. Focusing on the Smithian-Spathian boundary, palaeoecological changes are reflected by a significant global faunal turnover as indicated by ammonoids (Brayard et al. 2006) and conodonts (Orchard 2007) as well as a change in the palynological associations of the Boreal realm. There, the Smithian-Spathian transition is marked by a conspicuous change from spore dominated assemblages in the Smithian to gymnosperm dominated assemblages in the Spathian (Galfetti et al. 2007a). Here, we present the composition of the Early Triassic microfloras of Nammal, Salt Range, Pakistan. Ammonoids and conodonts provide the high resolution age control of the studied section (Brühwiler et al. 2007). The late Smithian palynological assemblages are characterized by a general dominance of hygrophytic elements. Slightly below the Smithian-Spathian boundary, between the Anasibirites beds and the Glyptophiceras beds, the composition changes dramatically with a drastically increasing proportion of xerophytic elements. This event coincides with the onset of a positive shift in the δ 13 C record marking the Smithian-Spathian boundary (Galfetti et al. 2007b). Preliminary results from southern Tibet also indicate a similar trend from hygrophyte-dominated to xerophyte-dominated assemblages across the boundary. Thus, there is evidence for the Smithian-Spathian boundary climatic event from high as well as from low palaeolatitudes, demonstrating its global significance. REFERENCES Brayard, A., Bucher, H., Escarguel, G., Fluteau, F., Bourquin, S., Galfetti, T. 2006: The Early Triassic ammonoid recovery: Paleoclimatic significance of diversity gradients, Palaeogeography, Palaeoclimatology, Palaeoecology, 239, 374-395. Brühwiler, T., Bucher, H., Goudemand, N., Brayard, A. 2007: Smithian (Early Triassic) Ammonoid successions of the Tethys: New preliminiary results from Tibet, India, Pakistan and Oman, New Mexico Museum of Natural History and Science Bulletin, 41, 25-26. Galfetti, T., Hochuli, P. A., Brayard, A., Bucher, H., Weissert, H., Virgan, J. O., 2007a: Smithian/Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis, Geology, 35, 291-294. Galfetti, T., Bucher, H., Ovtcharova, M., Schaltegger, U., Brayard, A., Brühwiler, T., Goudemand, N., Weissert, H., Hochuli, P. A., Cordey, F., Goudun, K. 2007b: Timing of the Early Triassic carbon cycle perturbations inferred from new U-Pb ages and ammonoid biochronozones, Earth and Planetary Science Letters, 258, 593-604. Orchard, M.J. 2007: Conodont diversity and evolution through the latest Permian and Early Triassic upheavals, Palaeogeography, Palaeoclimatology, Palaeoecology, 252, 93-117. 13.10 Reduced oxygen concentrations in the abyssal North Pacific during the last glacial period – implications for oceanic carbon storage Jaccard Samuel*, Galbraith Eric**, Haug Gerald*, Sigman Daniel** *D-ERDW, ETHZ, Universitätstr. 16, CH-8092 Zurich (samuel.jaccard@erdw.ethz.ch). **Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. The deep North Pacific represents an end-member of the modern circulation regime. It is far from sites of deep-water renewal, and so is enriched in CO 2 and dissolved nutrients due to the accumulation of the products of remineralised organic matter along the path of global deep-water circulation. For the same reasons, deep North Pacific waters show a depletion in dissolved oxygen. 33 Symposium 13: Global change – lessons from the geological past
336 Symposium 13: Global change – lessons from the geological past Reconstructions of δ 13 C distribution for the glacial Pacific Ocean show that deep water below 2000 - 2500 m was depleted in δ 13 C when compared with mid-depth and upper ocean waters. Below 2000 m, the deep waters were enriched in nutrients and metabolic CO 2 , while nutrient concentrations in the intermediate depth Pacific were apparently lower. Partition of CO 2 in favor of the deep ocean would have contributed to decrease atmospheric ρCO 2 during cold periods. This hypothesis has been tested by studying the sedimentary distribution of redox-sesitive trace metals (Mo & U) in two sediment cores spanning the abyssal subarctic Pacific. The fundamental control on sediment redox state is the balance between the flux of organic matter to the seafloor and the flux of oxidants to the sediment from overlying seawater. Thus, variations in sedimentary redox state are linked to changes in the magnitude of biological export and the role of ocean circulation. Comparison of redox-sensitive trace metals abundance with reconstruction of biogenic flux to the sediment will yield inferences about relative changes of oxygen concentrations at the water-sediment interface. Sediments deposited during the last ice age are enriched in authigenic U when compared to the Holocene Here, the export production proxies Ba/Al and biogenic opal indicate that the local flux of biogenic detritus to the seafloor was generally reduced during the last glacial period. Given this evidence, the enhanced U accumulation must have been a response to substantially lower bottom water O 2 and, by inference, the glacial North Pacific contained a higher concentration of respired carbon than today. Although the absence of Mo enrichments argues that anoxia did not develop in the vicinity of our core sites, oxygen concentrations may have dropped far below their current concentrations during the last ice age. If this elevated respired carbon burden is representative of the deep glacial Indo-Pacific Ocean, it could represent the primary reservoir of glacial CO 2 sequestration. It results, that a significant fraction of CO 2 has been sequestered into the deep ocean during glacial periods leading to a large reduction of atmospheric ρCO 2 , that is widely documented in Antarctic ice cores. 13.11 Cretaceous carbon cycle and climate: The Barremian-Early Aptian C-cycle perturbation Keller Christina E.*, Giorgioni Martino*, Garcia Therese I.*, Bernasconi Stefano M.*, Hochuli Peter**, Weissert Helmut* *Geological Institute, ETH Zürich, Universitätsstr. 16, CH-8092 Zürich (Christina.Keller@erdw.ethz.ch) **Palaeontological Institute, University of Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich Late Early Cretaceous marine sediments feature a fascinating succession of repeated greenhouse pulses interrupted by episodes of cool climate, which is indicated by the several important positive carbon isotope anomalies documented in the sedimentary record. The Ontong-Java volcanism is thought to be the trigger of the major positive carbon isotope excursion in the Aptian (Larson & Erba 1999). However, this volcanic activity predates the isotope excursion considerably (Tejada et al. 2002). This led to the hypothesis that the “Aptian greenhouse pulse” already began in the Barremian (Weissert & Erba 2004; Coccioni et al. 2004) with a first CO 2 pulse initiating climate warming and a first perturbation of the global carbon cycle. This is evidenced by deposition of black shales and a positive carbon isotope excursion during the mid-Barremian (mid-Barremian event of Coccioni et al. 2004). Accelerated organic carbon burial caused a decrease of the atmospheric CO 2 levels and induced a cooling event, which is thought to have resulted in a renewed carbonate-dominated sedimentation in the Late Barremian/Early Aptian oceans. In this study, a composite Late Hauterivian-Early Aptian Tethyan record is presented combining carbonate carbon isotope values with magnetostratigraphic and biostratigraphic data. From the Late Hauterivian to the early Early Aptian, the carbonate carbon isotope values fluctuate essentially between 1.6‰ and 2.4‰. The most positive values are reached during the early Aptian pre-OAE 1a excursion with carbonate carbon isotope values of up to 3‰. The different sections feature extremely variable thicknesses, which seems to be due to frequent sedimentary hiati, a pattern that is well-known from Barremian-Aptian successions and is interpreted to result from increased current intensities. The distribution pattern of black shales combined with the carbon isotopes allows to assign the black shales to the known over-regional events such as the Faraoni Event in the Late Hauterivian or the OAE 1a in the Early Aptian. The studied sections highlight the variability and complexity of sedimentary deposits at various positions in the different basins at the southern margin of the Tethyan Ocean and allow a varied insight into the ocean-atmospheric evolution of the Early Cretaceous.
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