| Sumari: | <p>Mesozoic Oceanic Anoxic Events (OAEs) are characterised by the widespread burial of organic-rich sediments and the spread of low-oxygen marine environments. These intervals represent some of most extreme perturbations to global climate, environment, and ocean chemistry in Earth’s history. Understanding the complex interplay of processes that caused and sustained these unusual environmental conditions requires proxies that allow quantification of global changes in ocean chemistry. This study explores the use of Zn- and Cd-isotopes as new palaeo-ocean chemistry proxies by using the Late Cretaceous Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE 2, ˜ 94 Ma) as a case study. Previous studies on the cycling of these elements in the modern ocean have suggested Cd and Zn may preserve valuable information on past redox and/or nutrient conditions if such signals are preserved in the sedimentary record. The data presented in this thesis suggest a strong control of local redox conditions on the Cd- and Zn-isotope composition of ancient organic-rich marine sediments. When these local effects are accounted for, δ<sup>66</sup>Zn and δ<sup>114</sup>Cd stratigraphic profiles offer insight into past change in redox environments at a global scale. Specifically, heavy δ<sup>66</sup>Zn and δ<sup>114</sup>Cd values observed during the main phase of the OAE 2 interval can be associated with an increase in organic-rich sediment burial globally, whereas lower values during the Plenus Cold Event interval can be linked to global oxygenation. The data presented in this study highlight the potential of δ<sup>114</sup>Cd and δ<sup>66</sup>Zn as new proxies for global changes in ocean redox chemistry. With improved understanding of the cycling of these elements in the modern ocean, these proxies may ultimately be used to quantify the global extent of ocean anoxia for past oceans.</p>
|
|---|