Abstract

Devonian rocks outcropping in the Buller and Takaka terranes appear to have had significantly different geological histories and faunal associations.

In the Buller Terrane, the Reefton Group occurs in two adjacent major outliers and comprises 1450 m of mixed limestone, mudstone and sandstone lithologies, representing inner shelf, shoreface and beach environments. Ten formations have been described. Upper and lower contacts are tectonic, and the group is also cut by low angle faults. The sequence is synclinally folded in each outlier. Recent collecting has yielded a varied and abundant molluscan and brachiopod fauna which can be used to demonstrate transgressive and regressive cycles within the limestone/mudstone sequence. Faunas indicate an Emsian age, and contain at least three endemic genera.

In the Takaka Terrane lying further east, the Baton Formation comprises 2600 m of monotonous, thickly bedded, calcareous siltstones and sandstones that are relatively poorly fossiliferous. Well sorted horizons and limestones are rare. The structure is more simple than at Reefton.

The Baton Formation and Reefton Group faunas each show geater affinities with Australia than they do to each other. Faunal studies suggest that the Baton faunas are probably slightly older than those at Reefton. The Reefton faunas also contain two Malvinokaffric elements.