The Cenozoic history of the Lomonosov Ridge; palynology a go go!

In September 2004, the first-ever drilling of the Lomonosov Ridge (Arctic Coring Expedition, ACEX, aka IODP Expedition 302) recovered unprecedented climate records of the Arctic Ocean spanning the past ~56 Ma. Initial, mainly dinoflagellate based age-assessments include the recognition of some ~200m each of upper Neogene, and middle Paleogene deposits, with a conspicuous ~25 Ma hiatus separating these units. The Neogene record appears one of slow sedimentation rates and frequent glacial conditions – contrasting the Paleogene, which is a story of waxing and waning of freshwater influence, warm conditions, and relatively high accumulation rates of organic-rich sediments. Paleogene highlights include the early–middle Eocene transition (~50 Ma) yielding stunning concentrations of remains of the freshwater fern Azolla suggesting that at least episodically, completely fresh surface water settings characterized the Arctic Basin. Moreover, although predictions had placed the base of the sediment column at 50 Ma, palynology revealed the successful recovery of the Paleocene–Eocene transition. During this time of super-greenhouse conditions, ~55.5 Ma ago, our records show the Arctic to be subtropical. ACEX also penetrated into some 30m of 'basement', the underlying tectinized sedimentary bedrock. Palynology confirmed the hypothesis that the top of the Lomonosov Ridge 'basement' is of shallow-water origin, and has a Campanian age.