Provenance of Cenozoic glaciomarine sediments of East Greenland: constraints to the cryosphere evolution and continental margin erosion

Understanding the evolution and dynamics of polar ice sheets is of the utmost importance for reconstructing the climatic development in the past and estimating the future global climate changes. The Cenozoic climatic evolution has been characterized by repeated fluctuations between somewhat warmer and colder conditions. While the first appearance of continental-scale polar ice sheets on Antarctica is widely inferred and well constrained (Eocene‐Oligocene Transition, EOT; Miller et al., 2009; Cramer et al., 2012), the onset of the glaciation in the Northern Hemisphere remains much more enigmatic and controversial. It is commonly accepted that small ice sheets have been present on Greenland since late Miocene (Larsen et al., 1994) with an intensification of the glaciation and development of extensive polar ice sheets in the late Pliocene (Bailey et al., 2013). Although glacier ice was likely to be present on Greenland at the EOT (Moran et al., 2006; Tripati et al., 2005, 2008) it is still debated if it derived from scattered coastal outlet glaciers or from an actual ice sheet.

In this work we present detrital apatite fission-tracks analysis (AFT) on offshore deposits in order to reconstruct the sediment provenance. In detrital samples, grain-age distributions can be decomposed by statistical means into different main grain-age components or peaks (e.g. Galbraith and Green 1990) thus discerning the provenance of the sediments eroded at the time. Age peaks trends throughout the section also provide information about the exhumation rate and tectonic evolution of the source rock.

We collected detrital apatites from some sites of ODP Leg 152 and ODP Leg 162, conveniently located near the East Greenland coast (southern and central East Greenland, respectively), in order to obtain a continuous record from Eocene to middle Oligocene and from middle Miocene to present. The age peaks inferred for the offshore samples have been compared with the thermochronological data available onshore to find the potential sources. Our results point out a common provenance (at least since late Miocene) for both central and southern East Greenland offshore sediments, despite the distance of >1200 km between the two locations. Moreover, both samples display a mutually consistent trend of increasingly older AFT ages moving up the section, indicative of provenance changes. Such trend seems compatible with ice-rafting from icebergs calved from the Scoresby Sound outlet glaciers and drifting along the East Greenland Current that, should this be the case, would be active with the same modalities as now since the late Miocene. We tentatively argue that the “older ages upwards” trend is determined by climate variations, specifically by the expansion/thickening of the ice sheet. Any change due to tectonic events, if present, cannot be resolved. Conversely, the Eocene to middle Oligocene record displays a younging upwards trend with decreasing lagtime typical of an eroding continental margin.