Depositional processes on the distal Scoresby Trough Mouth Fan (ODP Site 987): Implications for the Pleistocene evolution of the Scoresby Sund Sector of the Greenland Ice Sheet

Abstract

The investigation of trough mouth fans (TMFs), important paleoclimatic archives on mid- and high-latitude continental margins, has so far mainly been based on the integration of various types of acoustic data supplemented with short sediments cores. In consequence, sedimentological and chronological data about parts of TMFs deposited prior to the Last Glacial Maximum remains sparse. Here, we re-evaluate the upper part of ODP Site 987 drilled on the distal part of the Scoresby Sund TMF on the east Greenland continental margin, which records the former dynamics of the Scoresby Sund sector of the Greenland Ice Sheet. Based on a more detailed sedimentological description than previously available we find that lithological unit I, deposited over the last ~ 2.14 Ma, can be divided into two parts, a lower part dominated by glacimarine and marine deposits including some scattered, sandy turbidites and an upper part of debris flow deposits interbedded with sandy turbidites. The transition between these parts occurred at about 0.99 Ma, i.e. at the same time when the mode of ice-sheet variation changed globally, the average ice sheet size increased significantly and the periodicity of ice-volume variation increased from around 41 ka to approximately 100 ka (the “Mid-Pleistocene Transition”). On the distal Scoresby Sund TMF, this change appears to be reflected through a marked increase in the abundance of sandy turbidity flows accompanied by a longer run-out of some of the debris flows due to the delivery of larger sediment volumes during longer-lasting glacial maxima. This suggests that long sediment cores from TMFs have the potential to record the major climatic trends occurring during the Pleistocene.