Late Silurian and Early Devonian biostratigraphy in the Hill End Trough and the Limekilns area, New South Wales

Abstract

The first recorded graptolites from the Chesleigh Formation of the Limekilns district are Monograptus prognatus, ?M. transgrediens, Pristiograptus sp. cf. P. shearsbyi and Linograptus posthumus, which unequivocally indicate a Prídolí (Late Silurian) age for the formation. The Silurian-Devonian boundary appears best placed at approximately the boundary between the Chesleigh Formation and the overlying Cookman Formation, despite the presence of the early Lochkovian graptolite Monograptus uniformis uniformis much higher stratigraphically in the Limekilns Formation.

In the Hill End Trough succession, the Turondale Formation has yielded conodonts including Amydrotaxis praejohnsoni, which indicates the delta to pesavis conodont Zones of late Lochkovian (Early Devonian) age. Conodonts from the upper part of the Cunningham Formation, at a locality in the Trough west of Mudgee, include Polygnathus nothoperbonus / P. inversus, indicating the perbonus zone of middle Emsian age. The base of the Cunningham Formation is diachronous, being late Lochkovian (delta Zone) — the same age as the Turondale Formation — on the west flank of the Trough as previously reported, and late Pragian in the east. The youngest faunas found in the unit are late Emsian.

Key words:

• Silurian
• Prídolí
• Lochkovian
• Devonian
• graptolites
• conodonts
• biostratigraphy
• Hill End Trough
• New South Wales