The Late Miocene-Early Pliocene Biogenic Bloom: Duration, Causes and Paleoceanographic Implications

• Main Authors: Gastaldello, María Elena, Agnini, Claudia, Alegret Badiola, María Laia
• Format: Master Thesis
• Language: English
• Published: Universidad de Zaragoza, Prensas de la Universidad 2024
• Subjects: paleontología; paleoclimatología; Planktonic foraminifera
• Online Access: http://zaguan.unizar.es/record/135886

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0 3.5 Ma) is a paleoceanographic phenomenon marked by increased marine biological productivity documented in numerous locations, from the Atlantic, to the Pacific and Indian oceans. In deep-sea sediments, the Biogenic Bloom is characterised by a marked increase in biogenic CaCO3 (mainly from calcareous nannofossils and planktonic foraminifera) and SiO2 accumulation rates (mainly from radiolarians and diatoms). Supporting evidence includes the presence of diatom assemblages indicative of elevated productivity, the abundance of suboxic and dysoxic benthic foraminifera, and changes in sediment geochemistry (e.g. reduced Mn/Sc ratio), which point to low dissolved oxygen levels at intermediate water depths. This phenomenon has remained a mystery in the geological record, as the several-million-years high productivity conditions documented for the Biogenic Bloom necessitate a profound alteration in the global nutrient cycling of the oceans to be explained. Despite its widespread occurrence, fundamental questions regarding the temporal and spatial extent, as well as the driving mechanisms behind this phenomenon remain unanswered. In this context, this Ph.D. thesis aims to comprehensively document the Biogenic Bloom through an integrated quantitative approach. We produced comparable datasets from diverse areas worldwide, from the Pacific (IODP Site U1506 and U1488) to the Atlantic (ODP Site 1085) oceans. The first fundamental step of the project consists of developing a highly resolved calcareous nannofossil biostratigraphic classification for all study sites, aiming to establish reliable chronological frameworks. The age models were employed to calculate the linear sedimentation and derive the carbonate mass accumulation rates, a proxy used to identify the Biogenic Bloom on a global scale. The second phase of the project involves an in-depth benthic foraminiferal investigation. Taxonomic and quantitative studies of the benthic foraminiferal assemblages, as well as ...