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The Cretaceous was a time of significant global change, particularly around the Cenomanian-Turonian Boundary (CTB) (93.5 Ma). The mid-Cretaceous is considered to mark a period of intense global warming related to widespread tectonic activity, leading to periods of high sea level and no polar ice. This had great effects on the ocean's structure, chemistry and circulation, and led to both extinction and diversification of biota. At the time of the CTB a number of events occurred. Particularly well researched is the oceanic anoxic event (OAE 2) and the organic-rich black shales deposited during this interval. Associated with these organic-rich sediments is a positive carbon isotope anomaly. This excursion has a distinct profile and has hence been used for global correlation. There was also a significant extinction event, 26% of all genera disappeared making it one on the five largest extinction events to have occurred in the last 100 my. This study looks at a number of sites (ODP Sites 762, & 766 (Exmouth Plateau), Aksudere (in the Crimea), Flaine (French Alps) and Rio Mondego (Portugal)), at a range of palaeodepths from epicontinental seas to abyssal plains. These sites were chosen from both the northern and southern hemispheres, giving a range of sites spanning all faunal realms. Each site was analysed at a high resolution for foraminiferal and isotopic analysis, along with TOC, trace element and Rock Eval analysis where necessary, in order to understand the events surrounding the CTB, their effects, and the timings of them at each location to ultimately produce a global palaeodepth model of the CTB. It is clear that a record of OAE 2 is seen in all locations examined, both with or without organic rich sediments being recorded. At all locations a characteristic increase in 5'3C values is seen at the CTB, from -2 to 4%o. The start of the 813C excursion is in the upper part of the Cenomanian R. cushmani Zone. This is particularly well seen in the Crimea, a site on the northeastern Tethys margin at a palaeodepth of -500m. Data from ODP Sites 762 and 766 also show similar carbon isotope trends in both bulk and foraminiferal samples. These data do, however, also indicate a degree of diagenetic alteration. Trace elements and SEM analysis of the foraminifera enable a better understanding of the diagenesis at these sites and demonstrate the importance of understanding diagenetic effects when looking at these materials. Taking this into account, all sites studied show more negative values of 5180 over the CTB, possibly indicating warming over this period. Foraminiferal analysis of the localities has enabled correlation and timing of the isotopic and depositional events globally, as well as giving further insight into the extinction and diversification events seen. Increased productivity is evidenced at all sites and explains the deposition of both the organic-rich sediments and the associated sediments. A stepwise extinction and diversification of species is recorded as well as a progression from oligotrophic competitive species opportunistic eutrophic species as the marine environments changed and the oxygen minimum zone expanded. This is observed in regions of organic rich sediment deposition and also settings where no organic matter was deposited, such as Flaine and Portugal, indicating the global effect of changes in the ocean structure, chemistry and circulation in all marine environments.

Late Cretaceous laminated diatomaceous sediments from the Marca Shale (California) and CESAR 6 core (Arctic Ocean) have been analysed using scanning electron microscopy techniques and found to contain marine varves. The varve interpretation is based on the pervasive occurrence of laminae types that can be related to different seasons and placed into robust annual flux cycles. In the Marca Shale this consists of intermittent near-monospecific laminae of Azpeitiopsis morenoensis deposited in the late summer, succeeded by a ‘fall dump’ mixed assemblage laminae, dominated by fragmented Hemiaulus polymorphus, Stephanopyxis spp. and Stellarima spp. Intermittent near-monospecific Chaetoceros-type resting spore laminae, deposited in spring follow and are in turn overlain by terrigenous laminae, reflecting enhanced fluvial runoff during the summer. A mixed floral diatomaceous and terrigenous laminae couplet constitute the annual flux cycle in the majority of varves. Summer terrigenous flux may indicate that the ~43°N palaeolatitude estimate is incorrect, and deposition actually occurred at lower latitudes or alternatively, that the Marca basin was influenced by intense monsoonal summer storms. The CESAR 6 annual flux cycle consists of alternating diatom resting spore and vegetative cell laminae (often dominated by Hemiaulus), interpreted to represent spring bloom flux and ‘fall dump’/intermittent summer blooms flux, respectively. Near-monospecific Rhizosolenia laminae frequently occur above vegetative laminae, relating to subsequent ‘fall dump’ flux. Common silicoflagellate/setae-rich laminae, often containing diatom hash, occur beneath resting spore laminae, interpreted as the early spring flux of silicoflagellate blooms and grazed diatoms. Seasonally occurring detrital ‘blebs’ and rare detrital laminae are also observed, which may represent ice rafted debris, consistent with Campanian model simulations. Diatom taxa adapted to exploit stratified conditions, sedimented over the summer or in a ‘fall dump’, are important components of both sequences. Spring bloom flux was important in the CESAR 6, but was only a subsidiary component in the Marca Shale. The abundance of Hemiaulus spp. at both localities may be evidence for diatom blooms powered by N2-fixing cyanobacteria. Diatom biostratigraphy indicates a late Late Campanian age for the CESAR 6, although an earliest Maastrichtian age cannot be discounted. Time-series analysis of laminae thickness data from both sequences and bioturbation index data from the Marca Shale, reveal both sites contain strong quasi-biennial signals (mean periodicities of 27.4 and 30.4 months, respectively), inferred to relate to the Quasi-Biennial Oscillation (QBO). The CESAR 6 contains strong sub-decadal/quasi-decadal peaks interpreted to relate to Northern Hemisphere Annular Mode (NAM) variability. Together with the QBO signals, this suggests NAM variability was robust during the Late Cretaceous. Similar frequency peaks occur in the Marca Shale which, supported by several sedimentological lines of evidence, indicates the presence of an El Niño Southern Oscillation (ENSO)-like oscillation. Theory dictates that a weakening of the ‘Bjerknes’ feedback loop in the equatorial Pacific will lead to a reduction or shutdown of ENSO variability, resulting in a permanent El Niño climate. The Late Cretaceous was witness to a severe weakening of the ‘Bjerknes’ feedback, yet the results of this study demonstrate that there was robust ENSO variability during this greenhouse period, adding to the evidence against permanent ‘El Niño’ climate states. A 10.66 year harmonic peak in the CESAR 6 is taken as evidence for modulation of the NAM by solar variability. Peaks at 10.0, 10.3 and 10.8 years in the Marca Shale are interpreted to relate to the solar modulation of strong ENSO events. Both sites also contain multi-decadal peaks, the frequency of which may also have been modulated by solar variability. Quasi-bidecadal peaks are inferred to relate to the NAM or an oscillation analogous to the Pacific Decadal Oscillation (PDO), possibly influenced by the Hale cycle. A 44 year peak in the Marca Shale is also inferred to relate to the PDO. The CESAR 6 contains a harmonic peak at 78.74 years, interpreted to relate to modulation of the NAM over the Gleissberg solar cycle or alternatively, to modulation of the PDO.

By integrated stratigraphy of the Zumaia and Sopelana sections in northern Spain, a detailed astronomical time scale is obtained for the Maastrichtian. The cyclic alternations of hemipelagic limestones and marls at Sopelana and Zumaia display the range of periodicities of eccentricity-modulated precession. The rhythmic bedding pattern is primarily caused by variations in siliciclastic supply and to a lesser extent to variations in biological productivity, both of which controlled by eccentricity modulated precession through its influence on the hydrological cycle. Together, the Zumaia and Sopelana sections span almost the entire Maastrichtian, and encompass thirteen 405-kyr cycles, spanning a total duration of 5.3 Myr. Consecutive 405-kyr minima in the lithological and geophysical data records are tuned to successive 405-kyr minima in the new La2011 eccentricity solution. Assuming a K/Pg boundary age of 65.97 Ma, orbitally tuned ages of biostratigraphic and magnetostratigraphic events are obtained. The bases of Chrons C29r and C30n have been reliably established at Zumaia and their astronomically tuned ages are in good agreement with previous studies. Data from Sopelana provide a refinement of the age of the base of Chron C31r. Planktonic foraminifera and calcareous nannoplankton data from Zumaia, and new calcareous nannoplankton data from Sopelana allow for worldwide correlation of the cyclostratigraphy of the Basque country. Additionally, the orbitally tuned bulk carbonate carbon isotope curve displays a remarkable amplitude of variation. Strong oscillations in δ13C seem regularly paced by the 405-kyr periodicity of eccentricity modulated precession. Sharp negative shifts associated with falls in sea-level occur at regular intervals of ~1.2 Myr. A new global correlation of carbon isotope stratigraphies is presented, with an astronomically tuned age model based on the cyclostratigraphy of Zumaia and Sopelana and site 762C (Exmouth Plateau). The Late Campanian/Maastrichtian carbon isotope correlation scheme displays a series of trends and excursions that can be observed across the different depositional settings. These results suggest that the 405-kyr cycle of eccentricity, and potentially longer periodicities, paced the latest Cretaceous climate and carbon cycle.