Application of laser ablation-ICP-MS to determine high-resolution elemental profiles across the Cretaceous/Paleogene boundary at Agost (Spain)

A high-resolution analysis of the distribution of major and trace elements across a Cretaceous/Paleogene boundary (KPgB) was done using Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometry (LA-ICP-MS) and was compared with traditional distinct sampling and analysis. At the Agost site (SE Spain) a 22-cm-long core containing the KPgB was recovered using a Rolatec RL-48L drill. Within this interval, the lowermost 5 cm correspond to the Maastrichtian and the uppermost 17 cm to the Danian. The core section was resin-embedded under O2-free conditions, cut and polished for LA-ICP-MS continuous measurements with 10 μm increments and a laser-beam of 80 μm. Elemental concentrations in discrete samples taken prior to embedding from the same core interval were determined by Inductivity Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The LA-ICP-MS analyses in continuous mode considerably improve the resolution of geochemical profiles, allowing the compositional variability at a micrometer scale within the ejecta layer to be detected. In this study, we obtained profiles with 255 data points for the ejecta layer interval compared to 3 data points obtained by traditional manual sampling and ICP-OES analyses. Yet our recovered core section showed a rather limited preservation of the ejecta layer. This paper focuses on the presentation of LA-ICP-MS analysis as a particularly useful tool to investigate paleoenvironmental changes associated with bio-events. Additionally, the high-resolution of major and trace elemental distribution made it possible to study remobilization across thin but distinct boundaries such as the KPgB.