Climatic and tectonic controls on shallow marine and freshwater diatomite deposition through the Palaeogene

Abstract. Diatoms play a major role in the carbon and silicon cycles, and thus diatom-bearing sediments represent an archive of past climatic and environmental settings. In shallow marine and freshwater environments, the accumulation of diatom frustules forms a sedimentary rock called diatomite. However, most global scale studies of diatom-bearing sediments focus on deep-sea sites, whereas shallow marine and freshwater diatomites are studied mainly at a regional level. To address this problem, we present a global scale compilation of diatomite occurrences spanning the Palaeogene (~66 to ~23 Ma). This period was characterized by initial extreme warmth followed by a prolonged cooling, disrupted by short-term climatic events called hyperthermals, and by a number of palaeoceanographic and palaeogeographic changes. The aim of this compilation is to determine the response of diatom production to Palaeogene environmental fluctuations, by examining the influence of climate, tectonic activity and ocean circulation on diatomite deposition. Although climatic factors appear to have had an indirect impact, our study suggests that palaeogeographic and palaeoceanographic changes were key drivers of diatomite deposition during the Palaeogene, particularly from the Early Eocene Climatic Optimum (~53 to ~49 Ma) onwards. In fact, our compilation suggests the absence of diatomite deposition in epicontinental seas between ~46 and ~43 Ma, while diatomites do not begin to accumulate in open ocean environments until ~43.5 Ma. Moreover, we observe that regional climate and volcano–tectonic activity have had an impact on the deposition of freshwater diatomites.