Llandovery‐Ludlow graptolites from central Victoria: New correlation perspectives of the major formations

Abstract

The Darraweit Guim Province of the Melbourne Trough contains a sequence of Uandovery ‐ early Ludlow clastic rocks. New biostratigraphic data permit revised correlations and reinterpretation of published and unpublished descriptions of the sequence. The sequence is divided into the Keilor Group, of Llandovery age, comprising the Deep Creek Siltstone, Springfield Sandstone and Chintin Formation; and the Dargile Group, of Wenlock ‐ early Ludlow age, comprising the Anderson Creek Formation, Wapentake Formation, Bylands Siltstone (new), Costerfield Siltstone, Yan Yean Formation and Melbourne Formation. Graptolite faunas from the sequence represent a greater number of bio‐zones than hitherto recognised, and trilobite faunas indicate a number of stratigraphically discrete shelly assemblages. A synthetic approach to biostratigraphic and lithostratigraphic data is adopted to alleviate reliance on lithostratigraphy in what is a lithologically monotonous, poorly exposed sequence; the approach facilitates the extensive revision of sequence boundaries in accord with the biostratigraphic data. New graptolite taxa described are: Monograptus ludensis yarraensis, Monograptus uncinatus praeprognatus, Bohemograptus (Egregiograptus) tsegelnuki, Saetograptus colonus heathcotensis and Pristiograptus jolimontensis. The distribution of graptolitic and benthic faunas accords with a history of deposition dominated by eustatic events.