Valanginian–Hauterivian vegetation inferred from palynological successions from the southern Perth Basin, Western Australia

Abstract

The stepwise fragmentation of Gondwana had a lasting impact on Southern Hemisphere ecosystems, but its consequences remain difficult to ascertain without detailed knowledge of the biota colonizing the supercontinent before and during breakup. This palynological study characterizes the Early Cretaceous vegetation of the southern Perth Basin, a key location during the separation of Greater India from Western Australia. The well-preserved palynological assemblages recorded here include marine and putative freshwater dinoflagellate cysts and diverse spore and pollen associations. The palynomorphs indicate lacustrine, fluvial and estuarine depositional settings in the southern Perth Basin between the Berriasian and Hauterivian. The estuarine assemblages are characterized by rare to common marine dinoflagellate cysts, which indicate the early stages of marine deposition, conditions that later prevailed across most of the basin. The Early Cretaceous vegetation of the study area, as inferred from spores and pollen, is interpreted to consist mainly of conifer forests dominated by Araucariaceae, Podocarpaceae and Cheirolepidiaceae with an understory of ferns (Osmundaceae, Schizaeaceae) and other spore-producers (clubmosses, mosses, liverworts and hornworts). Two vegetation-types are hypothesized for the region with their distribution related to substrate characteristics and water availability: a more mesic, structurally complex, riverine forest within paleovalleys and topographic lows, and a more open forest accross the hinterland.