The nature and relationships of the Tertiary Brown coal flora of the Yallourn area in Victoria, Australia

Abstract

To date, sixteen taxa from the brown coal have been identified satisfactorily. Almost all of these had a wider distribution in Australia during the Tertiary period than they do at present, and only about half of them still occur in Victoria. A search for comparable modern floras shows that all sixteen taxa are still represented in New Guinea. with somewhat smaller numbers in New Caledonia. part of the eastern Australian coast and northern New Zealand. The nature of these modern floras and the climatic conditions under which they occur suggest that the brown coal vegetation consisted mainly of Nothofagus rain forests and gymnosperm or mixed gymnosperm-broadleaf forests, possibly with some overlap between these types, and that the rainfall was high and the temperatures were moderate. Pollen analysis has shown that, with the exception of the Lauraceae and Oleaceae (the vertical distribution of which is not known) and the Restionaceae/Centrolepidaceae (which only occurs at the top of the coal). the taxa concerned occurred throughout the period of formation of the coal, but that their relative abundance varied considerably nothofagous pollen dominates the diagram as a whole. with values of up to 95%, and when the few low values for this genus are recorded the values for one or more of Casuarina, Myrtaceae and Gymnosperms are high. Complex changes in the diagram suggest a major change in environmental conditions at about the middle of the coal-forming period, with the possibility that conditions were much less stable during the second half of this period.