Palynology of the Middle Jurassic (Bajocian–Bathonian) Wanaea verrucosa dinoflagellate cyst zone of the North West Shelf of Australia

• Published in: Review of palaeobotany and palynology Vol. 180; pp. 41 - 78
• Main Authors: Mantle, Daniel J., Riding, James B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.07.2012
• Subjects: Australia; basins; biostratigraphy; dinoflagellate cysts; Dinophyceae; Jansonia; Middle Jurassic (Bajocian–Bathonian); new species; North West Shelf; palynology; species diversity; spores; Wanaea verrucosa Zone; wells; Australia; Europe; Wanaea verrucosa Zone; North West Shelf; dinoflagellate cysts; biostratigraphy; Australia; Middle Jurassic (Bajocian–Bathonian)
• ISSN: 0034-6667; 1879-0615
• DOI: 10.1016/j.revpalbo.2012.03.005

Marine and terrestrial palynomorphs from the Middle Jurassic Wanaea verrucosa dinoflagellate cyst zone are documented from subsurface sections of the North West Shelf of Australia. Selected intervals in the Perseus-3A, Sunrise-2 and Sunset West-1 wells were studied in detail and record evidence of brackish to shallow marine successions in the Northern Carnarvon and Bonaparte basins. The palynological data derived from these three wells constitute the basis for the formal definition of this important dinoflagellate cyst biozone and its three constituent subzones. The base of the Lower W. verrucosa Subzone is defined by the first appearance of the index species and is a relatively sparse, low diversity microphytoplankton assemblage; species richness increases up-section. The base of the succeeding Middle W. verrucosa Subzone is defined by the range base of Valvaeodinium spinosum, and the Upper W. verrucosa Subzone is defined by the incoming of the large and distinctive species Endoscrinium kempiae. Two new species, Meiourogonyaulax straussii sp. nov. and Valvaeodinium cookii sp. nov. are described and Jansonia scarffei is reattributed as Fostericysta scarffei (Tykoezinski et al. 2001) comb. nov. Taxa with epicystal and multiplate precingular archaeopyles are prominent, particularly in the Lower W. verrucosa Subzone; this represents the coeval evolutionary explosion of the gonyaulacacean dinoflagellate cysts observed in the latest Early to Late Bajocian of Europe. Further cosmopolitan dinoflagellate cyst occurrences are compared with European ranges to assign a Late Bajocian to Early Bathonian age to the W. verrucosa Zone. The associated spore–pollen assemblages are transitional from the upper Dictyotosporites complex to the lower Contignisporites cooksoniae zones. The latter zone is defined by the first appearance of the index species, but considerable care is required to separate this species from the many intermediate forms of Striatella–Contignisporites that occur through this interval. The palynofloras are dominated by araucariacean monosaccates (particularly Callialasporites spp.), corystosperm bisaccates (mostly Alisporites spp.) and moderately diverse bryophyte–lycophyte–pteridophyte spore assemblages. ► Taxonomic review of L. Bajocian–E. Bathonian dinocysts of the NW Shelf of Australia. ► Formal definition of the Wanaea verrucosa dinoflagellate cyst zone. ► Dinocyst range chart illustrating the subzonal division of the W. verrucosa Zone. ► Comparison of the W. verrucosa Zone palynofloras to those in Europe. ► Discussion on the age of the W. verrucosa Zone and ties to the geological timescale.