DETERMINATION OF TRACE METAL VARIABILITY IN OOID LAMINAE USING LA-ICPMS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was employed in the determination of trace metal ratios and concentrations in the laminae of hypersaline and normal marine water aragonitic ooids from the Bahamas, Mexico and Great Salt Lake. Three ooid samples, from Joulter’s Cay, Bahamas; Lake Texcoco, Mexico, and Great Salt Lake, Utah, were analyzed for B, Mg, Mn, Sr, Ba, La, Ce, Sm, Eu, Gd, Yb, Pb, and U using a Merchantek UP-213 Laser Ablation System (20 mm spot size) and a Finnigan MAT Element2 ICP-MS. Elemental concentrations were determined using calibration curves determined from NIST-611, NIST-612, and NIST-614 glass standards. Mg/Ca and Sr/Ca ratios were determined on 6 ooids per sample. While Sr/Ca ratios appear consistent between ooids within a sample as well as between samples, Mg/Ca ratios show tremendous variability between the individual ooids as well as between the marine and hypersaline specimens. LA-ICPMS has the capability to acquire detailed chemical analysis, in parts per trillion, between successive ooid laminae; thus the potential exists for understanding the nature of the aqueous conditions from which the ooids precipitated, regardless of the depositional environment.