No abstract

U-Pb detrital zircon (DZ) ages (n = 807) from Lower Cretaceous and lowermost Upper Cretaceous synorogenic conglomerate and interbedded sandstone deposited in and near the foredeep of the Cordilleran foreland basin in central Utah indicate stratigraphic compositional variation among the deposits. Eight DZ age populations, ranging from Archean through Mesozoic, are present in the synorogenic foredeep deposits in varying proportions and permit defi nition of three compositional suites, termed here chronofacies. Chronofacies A, present in uppermost Neocomian-lowermost Aptian foredeep deposits, contains Archean through early Paleozoic DZ grains derived from Jurassic-Pennsylvanian strata of the thrust belt. Chronofacies B, in Aptian-Albian foredeep deposits, contains Archean and Paleoproterozoic grains with an age peak near 1850 Ma, a population distribution similar to that of lower Paleozoic quartzites of the thrust belt. Chronofacies C, in Albian-lower Cenomanian foredeep deposits, contains a trimodal population distribution of Paleoproterozoic and Mesoproterozoic grains similar to that of Cambrian-Neoproterozoic quartzite strata of the thrust belt. The chronofacies of the foredeep deposits thus record systematic erosional unroofi ng of the thrust belt during Early Cretaceous time.

The authors discuss the remobilisation of Sellafield produced radioisotopes from the sediment of the Irish Sea. They include plutonium, americium and caesium/.

Current values for the gut absorption factor of polonium-210 (210Po) are based on very few human data, yet the dose due to 210Po is an important component of the dose to man through food as a result of natural sources of radiation. In this study, three male and three female adult volunteers ate supplies of brown crab meat containing natural concentrations of 210Po, which were analysed from sub-samples. Daily urine and faecal samples, taken for 3 days before and up to 3 weeks after ingestion, were also analysed. Values of apparent absorption were derived from the faecal measurements; estimates of the true absorption were derived taking account of endogenous faecal excretion on the basis of existing data for intravenous administration. The results appear to suggest that the gut absorption factor in current use for 210Po (in connection with ingestion in food) should be increased from 0.1-0.3 to about 0.8. The implications for estimates of dose due to this exposure pathway are noted.

This paper presents the results of a 4 year study to investigate the human alimentary tract transfer factor (f(A) value) and body retention of 210 Po in shellfish. In the first 3 years, mussels (Mytilus edulis L.), cockles (Cerastoderma edule L.) and brown meat from crab (Cancer pagurus L.) were successively studied. In each year five volunteers (from a pool of seven) ate a suitable portion of the shellfish and provided 24 h samples of excreta usually for 3 days before and for at least 7 days during and after eating. Subsamples of shellfish were analysed to determine the intakes of 210 Po. Faeces were analysed and the data used to assess apparent fA values. Urine samples were analysed in the mussel and crab studies to provide urinary excretion parameters. Pb-210 was also analysed during the mussel study; the levels were low, leading to large uncertainties, but confirming the negligible effect of radioactive decay to its granddaughter 210 Po in the main study. In the fourth year, larger samples of brown crab meat were eaten by five volunteers and faecal samples were taken at suitable times over periods of up to 43 days to study body retention of 210 Po. The first approximately 7 days provided additional data on fA values. Pooled results for the apparent fA for the whole study lay in the range 0.15-0.65 with a mean of 0.46; corrections for endogenous excretion suggest a true fA value of approximately 0.51, supporting the value of 0.5 currently used by the International Commission on Radiological Protection (ICRP). The retention data suggest a biological half-time of about 40 days, in broad consistency with the 50 days currently used by the ICRP. Thus there is no strong evidence from this study suggesting a change in dose coefficient for 210 Po. Full experimental data are provided to allow independent further interpretation.