Cenozoic Marine Environments in the North Atlantic and Norwegian-Greenland Sea

Abstract

A warm ocean, with an abundant and diverse flora and fauna invaded the newly forming branches of the North Atlantic, first the Labrador Sea (Late Cretaceous), then, beginning with the Eocene, the northeastern North Atlantic. Land and marine biotas at high latitudes indicate equable climates and low Paleogene latitudinal thermal gradients. The Greenland-Scotland Ridge, forming along with the opening ocean may have acted as an oceanic barrier, but not as an impenetrable hindrance to surface exchange of flora and fauna. Rising rates of biogenic silica deposition during the Eocene suggest high fertility, and thus, upwelling. The global Eocene/Oligocene cooling impoverished North Atlantic planktonic floras and faunas, while the deep water environment was drastically changed, both qualitatively and dynamically. Extinctions, speciations and fundamental depth and abundance readjustments of deep water benthic faunas bear witness to the physicochemical and structural changes of the deep hydrosphere; unconformities and a change in the sedimentation regime suggest a marked intensification of deep currents. It is uncertain whether these events are related to the onset of North Atlantic bottom water formation. Calcareous oozes on Voring Plateau indicate that substantial influx of North Atlantic surface water into the Norwegian Sea occurred during the middle and late Oligocene, following the opening of a seaway to the Arctic. An early Miocene warming trend was interrupted at the beginning of middle Miocene, expressed In the establishment of cool and temperate microfaunas and floras, as well as in oxygen isotope ratios. A dramatic drop in North Atlantic biological productivity, a change in the style of sedimentation (drift deposits), and the appearance of carbon-isotopically young water coincides with an inferred subsidence of the Iceland-Faeroe Ridge In the middle Miocene. Initiation of cold water reflux across the ridge was probably the last principal event towards the establishment of the modern global deep water circulation; the benthic microfaunas assumed their present day aspects through a major taxonomic turnover during the middle Miocene.