MIDDLE TRIASSIC FOSSIL PLANT IMPRESSIONS FROM FREMOUW PEAK, ANTARCTICA

Permineralized plants of Antarctica are so exquisitely preserved and rich in anatomical detail that their fossil plants have been named independently from impression floras. This nomenclatural isolation obscures biostratigraphic correlation of permineralized floras with other floras of the Gondwana supercontinent. The best known Triassic plants from Antarctica are from the Fremouw Formation: a permineralized peat 600 m above the base of the formation on Fremouw Peak, and a fossil forest 318 m above its base in the Gordon Valley, both in the central Transantarctic Mountains. Fossil vertebrates of the Cynognathus zone near the Gordon Valley fossil forest are 368 m above the base of the Fremouw Formation, and indicate a late Spathian to Anisian age. Here we report a new flora of plant impressions from 427 m in the Fremouw Formation on the northern ridge of Fremouw Peak (S84.33105° E164.46877°). Preliminary identifications of plants from lacustrine shales include equisetalean stems (Zonulamites nymboidensis), and corystosperm leaves (Dicroidium elongatum) and fructifications (Pteruchus simmondsii, Umkomasia sp. indet.). A thin peaty paleosol (Aquent) has mainly lycopsid stems and cones (Cyclostrobus ornatus). A weakly developed paleosol (Fluvent) has a diverse flora of osmundalean leaves (Cladophlebis retallackii), corystosperm leaves (Dicroidium dubium, D. coriaceum, D. odontopteroides) and fructifications (Pteruchus africanus, Umkomasia sp. indet.), peltasperm leaves (Lepidopteris africanus) and fructifications (Antevsia sp. indet., Peltaspermum sp, indet.), and enigmatic gymnosperms (Kanaskoppia vincularis, Rochipteris sp. indet.). Our Fluvent flora is similar to that of the permineralized peat, and is most like middle Triassic (Ladinian) floras of the Nymboida Coal Measures of New South Wales, Australia. Less similar are Middle Triassic floras of coastal deposits of New Zealand and of lower paleolatitude basins of Argentina.