A basal cretaceous dinoflagellate suite from northeastern Australia

Abstract

A palynological sequence is described from the Neocomian of the Carpentaria Basin in Northern Queensland. Emphasis is given to the dinoflagellate biostratigraphy in the oldest marine Cretaceous sequence known from eastern Australia. The phytoplankton documentation includes 72 species (and 2 lower categories) assigned to 38 genera. Three informal intervals are described in chronological succession as zones DK1, DK2, and DK3, and their lower limits are marked by the oldest stratigraphic appearances of certain widely known dinoflagellate species; namely Chlamydo‐phorella nyei, Dingodinium cerviculum, Muderongia tetracantha, M. staurota, Odontochitina operculata, and Canningia colliveri.

Restricted stratigraphic occurrences of certain dinoflagellate species in Australia, Europe, and North America are taken as evidence for tentatively dating zone DK1 as latest Jurassic‐Berria‐sian, zone DK2 as Valanginian, and zone DK3 as Hauterivian. Contemporaneous spore and pollen subzones of the Murospora florida Zone in Queensland are dated by direct association with the dinoflagellate record.

Geological age and paleoenvironments of the associated Gilbert River Formation, Helby Beds, and basal part of the Rolling Downs Group are briefly summarized. Palynology indicates that the base of the Rolling Downs Group becomes progressively younger to the south, reflecting diachronous facies boundaries as a Neocomian sea gradually transgressed in that direction.