The age of unconformity-related uranium mineralization in the Athabasca Basin, northern Saskatchewan

Age data are presented for major Athabasca Basin uranium deposits at Cigar Lake, Cluff Lake, Collins Bay, Dawn Lake, Eagle Point, McArthur River, Midwest, and Rabbit Lake, as well as for several minor or undeveloped deposits, including Hughes Lake and Nisto. The best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 Ma. This range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data. The one major exception is the recently discovered NiAs-free deposit at McArthur River, for which a well-determined age of 1514 ± 18 Ma (2σ) has been obtained. Even this deposit yields an age in the1330–1380 Ma range for some material. Periods of reworking–redeposition occurred at ~1280, ~1000, ~575, and ~225 Ma. These may be basin-wide, affecting to some degree all the deposits that we have studied. Other times of redeposition are less well determined, but may be present as well. No ages that approach the ~1700 Ma age of the Athabasca Group have been found to date for unconformity-related deposits, and the Athabasca Basin mineralization is unrelated to the ~1750 Ma pitchblende vein deposits in the Beaverlodge Lake area.

Growth, fecundity, and reproductive biology in the pedunculate cirripede Pollicipes polymerus at San Juan Island, Washington

Four populations of Pollicipes polymerus were sampled monthly for 26 months at two localities and two intertidal levels at San Juan Island, Washington, to determine the breeding season near the northern limit of the distribution of the species and for the comparison of growth, breeding cycles, and fecundity between the four populations.Pollicipes polymerus may reach a rostral–carinal length of 17 mm and sexual maturity during its 1st year after settlement. Subsequently, growth rate is reduced to about 2 mm in rostral–carinal length per year. The mean adult size increases from high intertidal level, Edward's Reef to low intertidal level, Edward's Reef to high intertidal level, Eagle Point to low intertidal level, Eagle Point. Juvenile growth rates, the percentage of breeding adults in an average month, and the mean monthly egg production also followed the above trend. Pollicipes polymerus breeds from late April through early October with a peak in July. The breeding season of the population at Eagle Point is longer than that of Edward's Reef. Obvious environmental factors that may have some effects on fecundity, growth rate, and the breeding season include temperature, wave action, food supply, and salinity. Preferred conditions include heavy surf and oceanic salinity.

Mortalities of fauna of rocky substrates in south-west ireland associated with the occurrence of Gyrodinium aureolum blooms during autumn 1979

Dinoflagellate blooms, chiefly of Gyrodiniwn aureolum Hulburt, occurred along the south and south-west coasts of Ireland in August and September 1978 and mortalities of shore animals and of rainbow trout Salmo gairdneri held in sea cages were described from Dunmanus Bay (Parker, 1980). Since May 1978 four rocky shore sites in Bantry Bay and one in Dunmanus Bay have been monitored monthly (Myers, Cross & Southgate, 1978, 1979). At each site a permanently marked transect is monitored, limpet shell lengths are measured in marked quadrats at M.H.W.N., M.T.L. and M.L.W.N. and settlement, growth and mortality of barnacle species are studied on vertical rock faces. Discoloration of the water was observed at all five monitoring sites in August 1978 but no effects on the littoral or sub-littoral fauna and flora were detected (Cross & Southgate, 1980).In 1979 a reddish-brown discoloration of the water in Bantry and Dunmanus Bays was first observed in early September. Surface water samples taken at the regular sampling sites between 5 and 10 September revealed very high densities of Gyrodinium aureolum. Slight discoloration of the water persisted at Eagle Point until October and at Glengariff Castle until early November. During this period mortalities of shore fauna were observed at four of the regular sampling sites. Highest mortalities were observed at Pointabulloge in Dunmanus Bay. When visited on 8 September many Patella spp. on the transect were either dead or, if alive, could easily be removed. An estimated 75% of Gibbula umbilicalis were lying inverted in rock crevices with partially opened opercula which they could close only slowly.