The Hellefjord Schist, a volcaniclastic psammite-pelite formation in the Caledonides of Arctic Norway contains discoidal impressions and apparent tube casts that share morphological and taphonomic similarities to Neoproterozoic stem-holdfast forms. U-Pb zircon geochronology on the host metasediment indicates it was deposited between 437 ± 2 and 439 ± 3 Ma, but also indicates that an inferred ba...

Calcite is a common mineral precipitated within upper crustal fault zones and associated fractures, forming veins, cements coatings. It has the potential to be dated using several radioisotopic systems if parent/daughter isotope abundances are suitable for currently available analytical techniques. U-Pb dating can most readily achieved in-situ laser ablation technique, which led rapid growth ar...

The metamorphic facies of the subsurface Precambrian of Alberta are charted for the first time as a contribution to the new tectonometamorphic map of the Canadian Shield. Inferences about facies are based primarily on petrographically determined mineral assemblages. A few P–T determinations from results of electron-microprobe analyses are available. The chronology of metamorphic events is based...

Mass spectrometry is fundamental to measurements of isotope ratios for applications in isotope geochemistry, geochronology, and cosmochemistry. Magnetic-sector mass spectrometers are most common because these provide the best precision in isotope ratio measurements. Where the highest precision is desired, chemical separation followed by mass spectrometric analysis is carried out with gas (noble...