The use of quantitative relationships and palaeoecology in stratigraphic palynology of the Murray Basin in New South Wales

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Abstract
Near the eastern margin of the Murray Basin in western New South Wales, thick sections of up to 170 m may be placed in the Proteacidites tuberculatus Zone, of Oligocene to Early Miocene age. In this region, this zone cannot be subdivided using conventional stratigraphic palynology, yet some stratigraphic control within the zone is necessary for groundwater exploration. Some pollen types are occasionally present in unusually high frequencies and their use for stratigraphic purposes has been investigated. In order to give precision to the meaning of ‘high frequencies’, ratios have been constructed and a cut-off point chosen empirically to define the high ratios. Those selected are: (1) Phyllocladidites mawsonii, as a ratio of total gymnosperms; (2) Nothofagus (= Nothofagidites) flemingii, as a ratio of total Nothofagus and (3) total Myrtaceae as a ratio of total Nothofagus. In all three cases, the high ratios are useful stratigraphically, giving some of the required control within the P. tuberculatus Zone. The overall control of these quantitative events through the P. tuberculatus Zone is mainly climatic and hydrologic. Their precise expression at any one stratigraphic level, however, may be modified by other factors. The ecological tolerances of the three selected taxa form a series, with P. mawsonii in the wettest habitat, N. flemingii intermediate and Myrtaceae in the driest habitat. The high P. mawsonii ratios are associated with dark grey carbonaceous clays and high Myrtaceae with light grey clays. N. flemingii appears to be associated with channelling of the river systems which would probably produce better drainage in an otherwise swampy environment. Thus at any one stratigraphic level, the quantitative events are modified if the habitat requirement of the selected taxon is not met. In the Murrumbidgee area, the quantitative events correspond to the sedimentary cycles of the southern Australian margin. Presumably, drainage has been controlled by sea levels. The quantitative events in the Lachlan area do not correspond to the sedimentary cycles for here slight tectonic uplift has put this region beyond the direct influence of changing sea levels. This technique may give stratigraphic control within thick sections of a zone, but it cannot be extrapolated to other regions without due consideration of the controlling factors, even when the same quantitative events are identified in the second area.