Late Jurassic to Early Cretaceous stable isotope and geochemical records from the northern high latitudes: implications for palaeoclimate
Merged with duplicate record 10026.1/861 on 07.03.2017 by CS (TIS) The Jurassic and Cretaceous periods are widely accepted as being dominated by greenhouse conditions with elevated CO2 levels and warm polar regions. Although much compelling evidence to support this idea of global warmth exists, some...
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| Format: | Thesis |
| Language: | English |
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University of Plymouth
2007
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| Online Access: | http://hdl.handle.net/10026.1/1760 https://doi.org/10.24382/3859 |
| Summary: | Merged with duplicate record 10026.1/861 on 07.03.2017 by CS (TIS) The Jurassic and Cretaceous periods are widely accepted as being dominated by greenhouse conditions with elevated CO2 levels and warm polar regions. Although much compelling evidence to support this idea of global warmth exists, some recent studies propose that the greenhouse climate may at times have been punctuated by sub-freezing polar conditions and the presence of limited polar ice. The evidence, however, is somewhat equivocal and is both spatially and temporally limited with much of this research until now being concentrated in mid- to low latitudes, despite it being generally accepted that global climate is defined to a significant degree by prevailing conditions at the poles. Existing data are also often plagued by poor sampling resolutions and dubious diagenetic histories. This research presents the first extensive stable isotope and geochemical investigation of well-preserved belemnite rostra from the Callovian-Hauterivian Boreal Realm. Belemnites of the genera Cylindroteuthis, Pachyteuthis, Acroteuthis, Lagonibelus and occasionally Belemnopsis were investigated. Preservation was assessed using Backscattered Scanning Electron Microscopy, Cathodoluminescence, carbonate staining and trace element techniques. Organic carbon isotope analysis of fossilised wood was also undertaken where possible. Material from Staffin Bay, Isle of Skye, and Helmsdale, Sutherland, Scotland; the Izhma River, Timan-Pechora Basin, Russia; the Boyarka River, Yenisei-IChatanga Basin, Siberia; and Festningen and Janusfjellet, Svalbard was analysed. The carbon isotope data record relatively positive values in the Oxfordian, followed by a gradual shift towards more negative values through the Kimmeridgian and into the Volgian/Tithonian. A distinct Late Valanginian positive carbon isotope excursion is identified in both the marine carbonate and terrestrial organic carbon records from the Izhma and Boyarka rivers. The excursion occurs at a time of relatively low sea ... |
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