The use of LA-ICP-MS in a pilot study for determining the concentration of selected trace elements in rudist shells

Abstract

A protocol for the determination of the concentration of selected elements in two rudist shells was developed using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Element analysis in rudists has never been performed beyond including major and some minor elements, and thus this work presents the first results in this field. The concentrations of 35 isotopes were analyzed. Low iron and manganese concentrations reflect the absence of a diagenetical imprint on both shells. There is a negligible amount of crust-associated elements, which reveal little evidence of terrigenous input. Phosphorus amount is also low; however, it is high enough to mask reliable Rare Earth + Yttrium (REY) pattern measurements. Strontium and magnesium concentrations in the inner layers of a shell of Titanosarcolites show relicts of an original aragonitic composition. On the contrary, concentrations of these elements in a shell of Biradiolites rudissimus reveal an original low Mg-calcite mineralogy in its outer layers. The two shells were selected, considering their apparently a priori good preservation, based on the petrological examination of thin sections. No significant concentrations of elements such as chromium, cobalt, nickel, copper, zinc, molybdenum or antimony could be found. The concentrations of vanadium and barium may reflect evidence of biological activity, since they apparently do not correlate significantly with silicon, aluminium or sulphur. The low cost and precision of this method in comparison to others such as the use of electron microprobe, or X-ray fluorescence, makes it an optimum alternative for geochemical analyses of fossils, thus opening a new line of research.