An unusual assemblage of algal cysts from the late cretaceous of the gippsland basin, southeastern Australia

Abstract

Turonian to early Santonian algal cysts from intra‐rift sediments within the offshore Gippsland Basin are the oldest cyst assemblages known from offshore southeastern Australia. The cysts were deposited in either nonmarine or nearshore environments that existed prior to the appearance of open marine conditions in the basin during the Santonian. The cyst assemblages contain a varied group of acritarchs belonging to 13 species, and 5 dinoflag‐ellate species comprising 4 peridiniaceans and Spiniferites sp. New taxa described are the dinoflagellate Luxadiniutn lingulatum sp. nov., the acritarch genera Limbicysta gen. nov. and Rimosicysta gen.nov, and the species Limbicysta pediformis gen. et sp. nov., L. guttularis gen. et sp. nov., Rimosicysta eversa gen. et sp. nov., R. kipperii gen. et sp. nov., R. aspera gen. et sp. nov., R. cucullata gen. et sp. nov., R. concava gen. et sp. nov., R.? ovata gen. et sp. nov., and Tetrachacysta? keenei sp. nov. Limbicysta and Rimosicysta possess some dinoflagellate‐like features, but lack definitive characteristics, including an archeopyle. The only evidence of an aperture on these genera are areas of thinning around the periphery of the cyst where the wall often splits apart parallel to the cyst outline. These unusual openings and the shape of some forms distinguish the genera from any previously described type of algal cyst.

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