AbstractBy 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 theage 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.
|Date of Award||Jan 2013|
|Supervisor||Andy Gale (Supervisor) & David Loydell (Supervisor)|