SEDIMENTOLOGY AND ICHNOLOGY OF PERMO-TRIASSIC STRATA AT LAMPING PEAK, CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA: PALEOPOLAR FORESTS, LAKES AND BRAIDED RIVERS IN A GREENHOUSE WORLD

Permian through Triassic (P-T) sediments of the Central Transantarctic Mountains (CTM) were deposited in an evolving foreland basin along the Panthalassan margin of Antarctica at paleopolar latitudes (75–80° S latitude). A 211 m succession of P-T strata at Lamping Peak in the CTM records a marked transition from Permian braidplains with organic-rich floodplains and a high water table to Triassic braidplains with less organic floodplains and a lower water table.

Upper Permian strata preserve sandy braided rivers encased in organic-rich floodplain deposits. Permian floodplains contained abundant shallow lakes and lake-margin forests. More than 80 trees from 40+ horizons were identified, typically preserved in lake-margin paleosols developed on shallow lake sediments as either upright permineralized tree stumps or carbonaceous to manganiferous “rings” with associated root systems. Paleosols are weakly developed and gleyed and may contain abundant logs, some with morphologies suggesting fire damage. Permian trace fossils found in lakes, rivers, and paleosols include Kouphichnium, Undichna, Planolites, Palaeophycus, Cochlichnus, anabranching < 1-mm-diameter burrow networks, and shallow rhizoliths.

In contrast, Lower Triassic strata record deposition in sandy braided rivers with relatively little inorganic floodplain preserved. Evidence for in-situ forests are absent in early Triassic sediments at Lamping Peak; however, rhizoliths on braid bars and floodplain muds are common. Triassic trace fossils found primarily on river barforms, in abandoned channels, and on proximal floodplain deposits include Fuersichnus, Kouphichnium, Planolites, Palaeophycus, Aulichnites, Cochlichnus, Cylindrichum, Diplichnites, Macanopsis, rhizoliths, rhizohaloes, rhizotubules, and vertebrate tracks.

Strata at Lamping Peak preserve a previously unrecognized P-T boundary crossing succession and fortuitously preserve a diverse Antarctic paleopolar ecosystem. Combined sedimentological and ichnological observations indicate an overall decrease in accommodation and a lowering of the water table. Facies and architectural changes across the P-T boundary suggest that these sediments were deposited in a dynamic foreland basin that may have been transitioning from an underfilled to overfilled state.