OFR 151.pdf - CRC LEME

Rare taxa which first appear in the Late Oligocene-Early Miocene in the central Murray Basin
are Chenopodiaceae-Amarathaceae, Mimosaceae (Acacia) and Rubiaceae (Randia) and a
plethora of taxa that have not been recorded, or are extremely rare in, correlative microfloras
in the Gippsland Basin. Examples are: Pteris (Asseretospora), Podocarpaceae
(Microstrobos), Alangiaceae (Alangium), Palmae (Dicolpopollis), Callitriche
(Retistephanocolpites sp.), Convolvulaceae, Fuchsia (Diporites aspis), Malpighiaceae,
Malvaceae, Mimosaceae (Acacia, Archidendron-type), Onagraceae (cf. Epilobium),
Polygonaceae (Glencopolis ornatus), Portulacaceae, Sapindaceae (Dodonaea triquetra-type)
and numerous Proteaceae including Banksia serrata-type and Isopogon (Proteacidites
isopogiformis). Rhizophoraceae (Zonocostites) pollen are present in very low numbers, but
otherwise it is not clear which plants occupied the salt-marsh or mangrove niche within the
basin, or if tidal regimes within the basin allowed extensive halophytic vegetation types to
develop.
Inferred climate
The high diversities almost certainly reflect the very large area and diversity of plant
communities from which the fossil pollen and spore were sourced. Many of the taxa found in
the Murray Basin, but not in the Gippsland Basin, have modern pan-tropical distributions,
implying mean annual temperatures within the Murray Basin were relatively warm (possible
upper mesotherm range). Rainfall was high to very high (perhumid) but the change from
Nothofagus (Brassospora) spp.-dominated to Casuarinaceae/Myrtaceae-dominated
microfloras via a transitional phase in which Araucariaceae were prominent is reliable
evidence that precipitation became increasingly seasonal during the Oligo-Miocene.
c. Eastern Murray Basin
Harris and Morgan (1976) have described a possible Early Oligocene Upper Nothofagidites
asperus-Proteacidites tuberculatus Zone Equivalent microflora from the Jerilderie district on
the southeastern margin of the Murray Basin. This includes a number of taxa with warm
temperate to tropical NLRs, e.g. Cupanieae, Ilex, Proteaceae (including Embothrium),
Santalum and Sapotaceae but lacks Lophosoria. Otherwise the bulk of the
palynostratigraphic data from boreholes in the eastern Murray Basin is centred on changes in
the relative abundance of five commonly occurring taxa (expressed in ratio form) viz.
Nothofagidites flemingii/total Nothofagidites, total Myrtaceae/total Nothofagidites and,
Araucariacites/total gymnosperms (Martin 1986).
Martin (ibid) suggests that the individual taxa form an ecological continuum, with Nothofagus
occupying the driest and Lagarostrobos the wettest sites. These results are difficult to
compare with other regions. Presentation of the same data in alternative formats (Martin
1993) indicates that the microfloras are dominated by either Nothofagus (Brassospora) spp. or
Myrtaceae, with the latter becoming relatively more abundant during C. bellus Zone
Equivalent time. Lagarostrobos and Phyllocladus were more common and persisted longer in
the eastern Murray Basin than elsewhere, and this also appears to have been the case with
Lophosoria (M.K. Macphail unpubl. results). Lophozonia spp. increases in abundance
relative to other Nothofagus subgenera, especially in sites located close to the Southeastern
Highlands of New South Wales.
Inferred climate
The data confirm that conditions were wet (perhumid) relative to the western Murray Basin
and probably cooler (lower mesotherm range) than the central Murray Basin. Martin (1993)
argues expansion of Myrtaceae and Nothofagus (Lophozonia) spp. indicates that climates
became effectively drier (possibly more seasonal) during the mid Miocene. Whilst drier/more
seasonal climates are supported by the diminishing relative abundance of riparian swamp taxa
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