Abstract
Abstract. Marine smaller foraminifera from a 350 m thick, non-carbonate borehole succession are described from the upper Lower Triassic to lowermost Middle Triassic (Spathian–Lower Anisian) of offshore Western Australia. This is only the second foraminiferal fauna of this age described from the Southern Hemisphere and it differs from a coeval fauna previously described from the same area (Heath & Apthorpe, 1986). The new fauna contains some ‘Tethyan’ genera previously recorded from South China and the Alps, including Duostomina, Krikoumbilica, Gsollbergella, Trocholina, Endothyra and Endothyranella. Other genera and species appear to persist from the Permian. Three species are described as new: Dentalina septacosta, Krikoumbilica compressa and Trocholina planoconvexa. The age of the fauna is based on palynological evidence, correlated with conodont dating.
Highlights
Marine microfaunas of Early and Middle Triassic age are poorly known in Australia, as marine sedimentation during the Triassic was largely confined to offshore areas on the northwestern margin of the continent
From 2180–2185 m and 2220–2225 m, are similar to the Rhaetian species Quinqueloculina nucleiformis Kristan-Tollmann, 1964, but have chambers that are slightly less produced at the aperture
Krikoumbilica pileiformis He: 16, edge view showing gently concave umbilical surface; 17, spiral; and 20, umbilical views, all of WAM 02.391 (W69-9), Hampton-1, 2125–2130 m, all 150; 18, spiral; and 19, umbilical views of WAM 02.392 (W75-9), Hampton-1, 2290–2295 m, 150; the umbilical area is partly obscured by rock matrix; scale bar for 11–12, 15–20 is 100 μm; 21, transmitted light view from the spiral side of WAM 02.393 (W163-11), Hampton-1, 2290–2295 m, 170; this view shows the short, moderately oblique sutures on the spiral side and the large proloculus, which is equal in size to the four chambers in the whorl
Summary
Marine microfaunas of Early and Middle Triassic age are poorly known in Australia, as marine sedimentation during the Triassic was largely confined to offshore areas on the northwestern margin of the continent. Hemigordius volutus Palmieri, WAM 02.337 (M87-11), Hampton-1, 2170–2175 m: 18, oblique edge view, showing apertural region at centre of edge; 19, side view; both 112; scale bar 100 μm for figs 18, 19.
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