Radiometric dating of a tuff bed in the middle Albian Hulcross Formation at Hudson's Hope, British Columbia

Abstract

U-Pb, Rb-Sr, and K-Ar methods were employed to estimate the age of a thin crystal tuff bed in the middle Albian Hulcross Formation at Hudson's Hope, northeastern British Columbia. The biotite-plagioclase isochron yields an age of 102.4±1.0 (2σ × MSWD0.5) Ma and an initial ratio of 0.71311 ± 0.00030. Different size fractions of clear prismatic zircons define a U-Pb discordia line that intersects the concordia at 102.5+2.4 -2.8 (2σ) Ma. The four heaviest gravity fractions of biotite give a K-Ar age of 106.0 ± 1.8(2σ) Ma. The most probable age of deposition of the tuff bed is estimated to be very close to or a little more than 102 Ma, but does not exceed 106 Ma. -from Authors Show more