Gondwanan floristic and sedimentological trends during the Permian–Triassic transition: new evidence from the Amery Group, northern Prince Charles Mountains, East Antarctica

摘要

The Permian–Triassic boundary within the Amery Group of the Lambert Graben is placed at the contact between the Bainmedart Coal Measures and overlying Flagstone Bench Formation, based on the first regular occurrence of Lunatisporites pellucidus and the first appearance of Aratrisporites and Lepidopteris species. The Permian-Triassic boundary is marked by the extinction of glossopterid and cordaitalean gymnosperms, and by the disappearance or extreme decline of a range of gymnospermous and pteridophytic palynomorph groups. Earliest Triassic macrofloras and palynofloras of the Flagstone Bench Formation are dominated by peltasperms and lycophytes; corystosperms, conifers, and ferns become increasingly common elements of assemblages through the Lower Triassic part of the formation and dominate floras of the Upper Triassic strata. The sedimentary transition across this boundary is conformable but marked by a termination of coal deposits; overlying lowermost Triassic sediments contain only carbonaceous siltstones. Typical red-bed facies are not developed until at least 100 m above the base of the Flagstone Bench Formation, in strata containing ?Middle Triassic palynofloras. Across Gondwana the diachronous disappearance of coal deposits and appearance of red-beds is suggestive of a response to shifting climatic belts, resulting in progressively drier seasonal conditions at successively higher palaeolatitudes during the Late Permian to Middle Triassic. The abrupt and approximately synchronous replacement of plant groups at the Permian–Triassic boundary suggests that factors independent of, or additional to, climate change were responsible for the turnover in terresrtial floras.