Iridium and trace element measurements from the Cretaceous-Tertiary boundary, Site 752, Broken Ridge, Indian Ocean

Abstract

Fourteen samples spanning a 2.5 m interval from Hole 7542B were studied in order to search for anomalous enrichments of iridium (Ir) and shock-metamorphosed quartz grains. No allogenic quartz grains >10 μm were observed, hence the presence of quartz containing diagnostic evidence of shock-metamorphism could not be confirmed. Two Ir anomalies of 2.2±0.6 and 2.0±0.4 parts per billion (ppb) were measured in samples of dark green ash-bearing chalk at depths of 357.93 and 358.80m below seafloor (mbsf), respectively. (Samples 121-752B-11R-3, 13-14 cm, and 121-752B-11R-3, 100-101 cm) using conventional Instrumental Neutron Activation Analysis (INAA). These samples containing anomalous enrichments of Ir were taken from approximately 82 cm above and 5 cm below the extinction level of Globotruncanids. -from Authors