Drilling the Central Arctic: from a Palaeogene ‘Pond’ to a Neogene Ocean

Francesca Sangiorgi², Appy Sluijs², Stefan Schouten³, Timme Donders¹, Judith Barke², Eveline Speelman⁴, Gert-Jan Reichart⁴, Jaap Sinninghe Damste³, and Henk Brinkhuis^2
1Geoenergy and Geoinformation, Geological Survey of the Netherlands, Utrecht, Netherlands.
²Laboratory of Palaeobotany and Palynology, Utrecht University, Utrecht, Netherlands.
³Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research, Den Burg, Texel, Netherlands.
⁴Department of Earth Sciences, Utrecht University, Utrecht, Netherlands.

In September 2004, the first-ever drilling of the Lomonosov Ridge (Arctic Coring Expedition, ACEX, or IODP Expedition 302) recovered unprecedented sedimentary records of the central Arctic Ocean spanning the past ~56 Ma. Age-assessment, largely based on dinoflagellates, includes the recognition of some ~200m each of upper Neogene, and middle Palaeogene deposits, with a conspicuous ~26 Ma hiatus separating these units. The Neogene record has relatively low sedimentation rates and perennial glacial conditions starting from 14 Ma. In contrast, the Palaeogene is a story of waxing and waning of freshwater influence, warm conditions, and relatively high accumulation rates of organic-rich sediments.

Palynological analyses have revealed the successful recovery of the Paleocene - Eocene transition, with the occurrence of an Apectodinium augustum acme at the Paleocene Eocene Thermal Maximum (PETM) some 55.5 Ma ago. This finding contrasts predictions, which had placed the base of the sediment column, above Cretaceous basement, at 50 Ma. During the PETM our dinocyst and TEX86 palaeothermometer records show combined increased runoff and sea level rise and a subtropical Arctic Ocean, with temperatures of ~23 deg C.

Other Palaeogene highlights also include the recovery of the Eocene Thermal Maximum 2 (aka ELMO ~53.5 Ma). Dinocyst assemblages show a freshening of Arctic Ocean surface waters, while TEX86-derived paleotemperatures rise from ~18 - ~22 deg C and palm vegetation suggests frost-free winters. At the early - middle Eocene transition (~49 Ma) stunning concentrations of remains of the fresh water fern Azolla and freshwater tolerant dinocysts suggest that, at least episodically, completely fresh surface water settings characterized the Arctic Basin. During the middle Eocene, shifts in salinity and in ice-rafted debris follow a strong orbitally driven cyclical pattern. Moreover, dinocyst stratigraphy was instrumental in recognizing and assessing the ~26 Ma hiatus, which marks the transition from the greenhouse world to the icehouse world. Sediment erosion and/or non-deposition that generated the hiatus were likely due to a progressive shoaling of the Lomonosov Ridge. Above the hiatus, a new Miocene dinocyst genus Arcticacysta and higher than expected sea surface temperatures (15-19 deg C) mark the recovery of sedimentation on the Lomonosov Ridge near the Miocene Climatic Optimum.

AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia