20-EPN2-053: Noble gas (3He) analyses of iridium poor marine sediments to understand the astronomic process responsible for the late Eocene meteor shower
Visit by Jörg Fritz, ZERIN (Germany), to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 06 – 15 April 2022
Report Summary: The project aims to understand the astronomical processes leading to the late Eocene shower of extraterrestrial (ET) material onto Earth. The 3He-carrier phases responsible for the ~ 2 million years enduring 3He anomaly will be characterised geochemically by producing a combined 3He and Ir dataset.
Here, 23 samples of marine micro-fossil ooze form the ODP 689B core, Maud Rise, Southern Ocean were measured at the CRPG Nancy noble gas laboratory. These samples cover the Eocene Oligocene transition (38 to 33 Ma) and these new data document the amplitude and duration of the 3HeET anomaly and confirms that the late Eocene 3He anomaly reported from the Massignano outcrop (Italy) is a global phenomenon. The here-investigated 689B micro-fossil ooze is exceptional because its low terrigenous mineral content and low iridium concentration of 5-15 ppt Ir. These Ir values are close to the expected ET contribution of 12 ppt Ir, as calculated using the current global/annual ET flux and the sedimentation rate and dry density of the 689B deposits.
The 3He data set acquired during the TA visit combined with literature data on Ir concentrations show that the flux of 3He rich ET particles increase by 4 times whereas the Ir concentrations in 689B remain at background values. New Ir data with low detection limits will further constrain the relation between ET 3He and total Ir during the late Eocene shower. ET 3He does not correlate with Ir indicating that the late Eocene 3He anomaly was caused by 3He-rich and Ir poor dust particles. The study illuminates the potential of marine micro-fossil ooze for planetary science.