Discovery of Late Triassic fossils in the Chonos Metamorphic Complex, Southern Chile

The late Triassic bivalve Monotis (Pacimonotis) aff, subcircularis Gabb ind icative of a Norian (probably early late Norian) age has been collected fro m the southeastern end of Patranca island (45 degrees 25'S-74 degrees 09'W) in the Chonos Archipelago, Southern Chile. Another fossil bivalve, Limidae gen, et sp. indet. has been collected from a small unnamed island (45 degr ees 25'S-74 degrees 10'W) 4 km to the north, and indicates a maximum Early Carboniferous, probably Mesozoic age. The fossil bearing unit is the Potran ca Formation (or Potranca Unit) which forms part of the Chonos Metamorphic Complex, interpreted as a subduction complex developed on the southwestern margin of Gondwanaland. As these rocks have been previously considered to b e of Paleozoic age (Late Silurian-Early Devonian), the geologic history of this part of the continental margin must be reinterpreted. These fossils pr ovide clear evidence that marine depositional processes persisted within th e Chonos Metamorphic Complex during Late Triassic time.