The well-preserved sedimentary structures of the Goli d'Aget Member
(Early Permian) allow to distinguish four successive environments
of deposition: 1) An alluvial plain with important channeling and
evidence of volcanic activity; 2) A shallow lacustrine environment
with a low water level, deposition of massive carbonates and an increasing
contribution of volcanic materials; 3) A fluviatile plain with the
deposition of volcanic tuffs; 4) A deltaic to lacustrine environment
occasionally covered by pyroclastic flows. An ignimbritic rhyolite
from the upper part of the Goli d'Aget Member has an age of 267-282
Ma (U-Pb on zircon). Major and trace elements, as well as zircon
typology point to a calc-alkaline and volcanic-arc affinity for that
high-silica rhyolite. The Goli d'Aget Member may be the best-preserved
unit among the Permian units from the Swiss Penninic Western Alps.
This series provides an important point of comparison with other
local Permian units (Dent de Nendaz and Cleuson Members) and with
similar series in the Western Alps including the Melogno porphyroids
in the Ligurian Alps and the Rochachille Series near Briançon (France).