LA-ICPMS elemental imaging of complex discontinuous carbonates: An example using large benthic foraminifera

Abstract

Trace element concentrations in biogenic and inorganic carbonates are a valuable source of palaeoenvironmental information. Because laser-ablation spot or 1D track analyses do not fully capture the complex (bio)mineralisation processes, 2D maps are required to arrive at a better understanding of the controls on minor/trace element incorporation. Foraminifera (marine protists) have a complex internal geometry and yield discontinuous sections characterised by calcite–resin–calcite transitions over distances as small as 10 μm. Order of magnitude differences in the total ion beam intensity over such transitions enables effective data exclusion. Inline signal smoothing devices, despite slightly increasing washout time and thus reducing spatial resolution, prevent excessive artificial noise in analyses, of particular concern when utilising small laser spot sizes (<30 μm) in order to maximise spatial resolution. We find surface Al/Ca and Zn/Ca ratios elevated by two and 5–10 times respectively, highlighting the need for pre-acquisition ablation cleaning. Through these analytical considerations we show how the quality of images acquired from discontinuous samples can be maximised, enabling – in this case – seasonality reconstruction in the fossil record from large benthic foraminifera.