on 05-11-201704:39 AM - edited on 11-09-202104:14 AM by usermigration2
1) GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany, 2) Department of Earth Sciences, Institute of Geological Sciences, Freie Universität Berlin, Germany, 3) MARUM – Center for Marine Environmental Sciences, Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany Earth and Planetary Science Letters (2015), V428, pp293–303, doi: 10.1016/j.epsl.2015.07.018 The silicon isotope record of early silica diagenesis Michael Tatzel 1,2), Friedhelm von Blanckenburg (1,2), Marcus Oelze (1), Jan A. Schuessler (1), Gerhard Bohrmann (3) The heavy isotopes of silicon are strongly enriched in some of the youngest, early diagenetically formed porcellanite layers from the Southwest Indian Ridge (Pleistocene) and the Maud Rise (Pliocene). These porcellanite layers are composed of opal-CT and were formed by the conversion of amorphous silica (opal-A) from siliceous sediment via dissolution–reprecipitation. Their bulk δSi30 values range between 1.7 and 2.3‰. Detritus-poor siliceous sediment surrounding these layers is significantly lower at −0.3 to 1.5‰. Sequential chemical extractions of bulk siliceous sediment show (i) preferential dissolution of diatoms featuring higher δSi30 than radiolaria and Al–Si components. The detailed investigation of porcellanite layers by micro-scale Si isotope and Al/Si analyses using UV femtosecond laser ablation ICP mass spectrometry show that (ii) precipitation of authigenic aluminum silicates enriched in light Si isotopes drives pore waters to even higher δSi30.