An early Arenig age for the Pinbain sequence of the Ballantrae Complex

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Abstract
Synopsis: The Pinbain volcano-sedimentary sector of the structurally involved ophiolitic Ballantrae Complex (early Ordovician) has yielded Bendigonian (early Arenig), graptolites including Tetragraptus cf. decipiens T. S. Hall and Acrograptus cf. filiformis (Tullberg). These graptolites contradict previous assumptions that the Pinbain sequence was one of the younger sectors of the Ballantrae Complex which has elsewhere yielded graptolites indicative of an age-range from lowest Arenig (Lancefieldian 3) to upper Arenig (Castlemainian-Yapeenian). Adjacent to the southern margin of the Pinbain sequence, but structurally separate from it, the well-known mélange section has provided only fragmentary fossils undiagnostic of age. The only evidence for the age of the mélange is, therefore, the presumed correlation of contained clasts with radiometrically-dated early Ordovician lithologies exposed elsewhere in the Ballantrae Complex.