Triassic paleoecology of the Lashly Formation, Transantarctic Mts., Antarctica

Abstract

The Lashly Formation, an alluvial plain sequence of Triassic age in South Victoria Land, contains a variety of fossil plant material and other features such as trace fossils and paleosols. This study examines the paleoecological record, and uses it to provide a scenario of geography and climate of the period. Twenty varieties of megaflora are described. A further two specimens are identified to genus level, and seven are recorded as unidentified foliage, seeds, sporophytes or cones. Samples of silicified wood provided growth ring data for 'sensitivity' and 'complacency' statistical analysis. Five fresh water and terrestrial trace fossils are also described. They include Cylindricum, Skolithos, Scoyenia and Heimdallia. Root casts and impressions are found associated with paleosols and mudstone horizons. They are described in four categories: horizontal, taproot, adventitious and rhizomatous root systems. Seven types of developed paleosols were recognised. They are classified according to their morphological and sedimentological similarities with modern soil types. Paleoflora, paleosol and sedimentological records at specific sites are used to provide models for floral succession, and the effect of flood events on the floodplain vegetation. Interpretation of paleoenvironment and paleofloral characteristics provides the basis for a model of paleolatitude of the field area through the Trassic. There is a close correlation between the apparent polar wander curve of Irving & Irving 1981) and the field evidence of this study. The model developed shows the field area at approximately 75°S in early Triassic, moving to beyond the Antarctic Circle to approximately 61°S by late Triassic.