Mineralogical Evidence of Middle Miocene Glacial Ice in the Central Arctic Ocean Sediments

Early glaciations in the surrounding continents of the polar Arctic Ocean have been revealed through the occurrence of ice rafted detritus (IRD) in the marine sediments. The glacigenic origin of the deposited sediment is generally recognised either by the grain size, but also by distinctive grain morphology, grain surface textural features and clay mineral compositions. In this study the mineralogy of the submarine Lomonosov Ridge sediments are analysed using X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. The study combines both the quartz sand grain surface microtextural and clay mineralogical data from drill cores obtained during the IODP Arctic Coring Expedition (ACEX) 302. The studied interval (141–197 m below sea floor) of the coring Site M0002 represents a time slice of 6 million years critical for the onset of glaciation, between ca. 12–18 Ma at the Middle Miocene. The sediments consist mainly of homogenous siliciclastic detritus characterised by low organic carbon concentrations. The specific glacial crushing and transport features – high angularity, conchoidal fractures, steps and subparallel linear fractures – were observed from quartz sand grain surfaces, coinciding with significant drops in the smectite contents. The reduced smectite and corresponding increase in the chlorite and illite contents refer to cooler climate conditions, continental ice generation and increased physical erosion on land.