MAASTRICHTIAN BIVALVIA (EXCLUDING INOCERAMlDAE) FROM THE MIRIA FORMATION, CARNARVON BASIN, NORTH WESTERN AUSTRALIA

WA Museum Records and Supplements | Updated 9 years ago

Abstract: Thirty species of Bivalvia (excluding lnoceramidae) from the Late Maastrichtian Miria Formation of the Carnarvon Basin are examined. Preservation is selective, favouring pteriomorph groups of primary-calcitic mineralogy; aragonitic groups, in particular the Heterodonta, may be under-represented.

Sixteen species are considered to be endemic representatives of long-ranging or cosmopolitan genera of the Late Cretaceous; five species appear to have been widely distributed at that time; five species may represent up to four endemic genera. One new genus - Giraliapecten gen. nov. is erected and seven species - Grammatodon (Nanonavis) subdiscors sp. nov., Pseudolimea flabellulina sp. nov., Giraliapecten oboloides sp. nov., Chlamys (Microchlamys) propesalebrosa sp. nov., Chlamys (s.l.) cracenticostata sp. nov., Spondylus schekkermanae sp. nov. and Panopea stenopleura sp. nov. - are newly described and named.

The Miria bivalve assemblage shows no particular affinity with any other known from Australia or from the lndo-Southwest Pacific region, reflecting the geographic isolation of Australia from other land masses, except Antarctica, during the Late Cretaceous. Generic endemism of up to 20% is consistent with the existence of a biogeographic subprovince in northwestern Australia at that time. The environment of deposition was that of the middle shelf, moderately energised. The climatic regime was temperate.