QA_Vol 24_No 1_July 2007 - Australasian Quaternary Association

Figure 4. Ostracod, mollusc and stable isotope profiles of Section 1at the Slippery Dip locality, Brachina Gorge, central Flinders Ranges.Dotted line marks position of palaeosol.Carbon and oxygen isotopic signaturesThe results of the stable isotopic analysis of ostracodvalves and mollusc shells recovered from Section 1 atthe Slippery Dip locality are presented in Table 3and plotted in Figures 4 and 5.The two microfossil populations have broadly similarcarbon and oxygen isotopic signatures (Figure 5), whichin turn are typical of freshwater limestones (Hudson,1977). In samples from which multiple specimens ofostracods and/or molluscs were analysed, each phylumfor the most part is both isotopically uniform andindistinguishable from the other. This phenomenon ofisotopic congruence is best illustrated by the elevensub-samples from 207–197 cm height in the section(Table 3). The mean values for their two populations areas follows: ostracod δ 13 C = –8.5 ± 1.2‰, δ 18 O = –2.6 ±0.6‰ (n = 5); and mollusc δ 13 C = –8.1 ± 0.6‰, δ 18 O =–2.8 ± 0.8‰ (n = 6). There is one notable instance wherethis isotopic uniformity does not prevail. The ostracodsub-sample from 417–409 cm comprises solely juvenileCandonocypris novaezelandiae, which are markedlyheavier (δ 13 C = –4.8‰, δ 18 O = –1.6‰) than the shellfragments in the mollusc sub-samples (n = 3) from thesame interval (δ 13 C = –8.4 ± 1.1‰, δ 18 O = –3.3 ± 0.8‰).Accordingly, data on the aforementioned ostracodsample were omitted when calculating the averageisotopic values of this sample interval.25 | Quaternary AUSTRALASIA 24 (2)(a)(b)Figure 5. Plot of δ 18 O against δ 13 C for calcareous microfossils(a: ostracods; b: molluscs) from Section 1 at the SlipperyDip locality, Brachina Gorge, central Flinders Ranges. Field foraverage freshwater limestones is taken from Hudson (1975).