AR-40-AR-39 AGE OF SIBERIAN BASALTIC VOLCANISM

Five of six samples representing the entire stratigraphic sequence (si milar to 3700 m thick) of basaltic flows in the Noril'sk section in th e northwestern part of Siberian flood basalt province, Russia yield Ar -40 - Ar-39 plateau ages between 248.3 +/- 1.7 Ma and 246.9 +/- 2.5 Ma relative to an age of 520.4 Ma for the hornblende standard, MMhb-1. T hese results clarify some discrepancies in existing data and confirm t hat eruption of the bulk of Siberian basalts was close to 248 Ma and p ossibly lasted less than 2 Ma, Although the violence of this volcanism may have caused the massive extinctions at the Permo-Triassic boundar y, the onset of changes across this boundary seems to have been distin ctly earlier.