The ACEX siliceous microfossils: Middle Eocene biogenic silica production and preservation in the central Arctic

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Stickley, Catherine۱; Koc, Nalan۱; Kemp, Alan E.S.۲; Pearce, Richard۲
Holding Date 11 October 2008

In 2004, Integrated Ocean Drilling Program Expedition 302, "The Arctic Coring Expedition" (ACEX) acquired the first long cores from the central Arctic. Over 420 m of Upper Cretaceous to Quaternary sediments were recovered from the Lomonosov Ridge, close to the North Pole. Biogenic silica is preserved between 202 and 313 mcd representing the most significant find of Paleogene siliceous microfossils in nearly 2 decades. These relatively expanded lower middle Eocene (50-45 Ma) sediments are finely laminated and rich in endemic marine to brackish (diatoms, ebridians, silicoflagellates) and in situ freshwater (chrysophyte cysts) siliceous microfossils. They also contain abundant palynomorphs (dinoflagellate cysts, spores, pollen) and other organic material but no calcareous microfossils.
Upper Cretaceous and middle Eocene biosiliceous sediments have been known from the central Arctic for some time, but until now information was scarce and stratigraphically incomplete, i.e., Alpha Ridge piston cores. ACEX drilling helped complete most of the stratigraphic gaps and in doing highlighted the first 5 myr of the middle Eocene as being unique in central Arctic Cenozoic history— the only phase of biogenic silica production and preservation during the last 65 myr for this region. We investigate the reasons for this by exploring the paleoenvironment and tectonic setting under which these sediments were deposited, the climatic changes which affected nutrient supply, salinity and temperature, and the effects of central Arctic middle Eocene ice initiation. We also report on initial investigation into the composition of some of the laminations, which give further clues about the formation of this rich sediment archive.
Our data offer insight into central Arctic history from a siliceous microfossil perspective during a significant phase in Cenozoic climate evolution—the start of the transition from greenhouse to icehouse world. We provide important climatic and oceanographic information for the Arctic region and therefore make a valuable contribution towards achieving an overall understanding of the mechanisms of climate change through this critical transition.