Rare earth elements as provenance indicators in North Australian estuarine and coastal marine sediments

Rare earth elements (REE) in three grain size fractions of clay-dominated estuarine and coastal sediments from the North Australian coastline have been investigated for use as potential provenance indicators. Comparisons of data based on instrumental neutron activation analysis and inductively coupled plasma mass spectrometry revealed that HF digestions of zircon-bearing samples resulted in unsatisfactory recovery of REE. Instead, a relatively simple, fast and safe partial digestion using HClO4+HNO3 was used to extract REE mainly from clay minerals while excluding extraction of REE from zircons. A comparison with published data for primary rock units within river catchments showed that the main REE systematics has been preserved in downstream clay-rich sediments. Analysis of variance of La/Gd(PAAS), La/Yb(PAAS) and Eu/Eu*(PAAS) ratios in five areas showed that the <63 lm fraction possessed the greatest discriminating power. All five areas could be distinguished from each other at highly significant levels based on one or more of these ratios.