Famennian-Tournaisian conodonts and Devonian-Early Carboniferous transgressions and regressions in northeastern Australia

Conodont data are presented from stratigraphic sections and spot samples from the Keelbottom Group (Famennian-Tournaisian) of the Burdekin Basin and the Venetia Formation (early Tournaisian) of the Clarke River Basin of the Townsville hinterland of northeastern Australia. Though much of the Devonian-Early Carboniferous sedimentary sequences of this region is nonmarine, the marine intervals document at least eight transgression-regression (T-R) cycles in the Burdekin Basin and adjacent areas of onlap during the late Emsian-Tournaisian. Three (?four) of these are suggested to be reflections of global transgressions rather than regional tectonically driven events: in the Early marginifera and expansa zones (Famennian), in the sandbergi-Early crenulata interval, and seemingly also early in the sulcata Zone (Tournaisian, but perhaps commencing late in the Late praesulcata Zone). The eighth transgression event, in the upper Hardwick Formation, is not chronologically constrained; it too may have been eustatically driven. The sandbergi-Early crenulata transgressive interval is clearly expressed in the Venetia Formation of the Clarke River Basin. The major marine event expressed as the Teddy Mountain Formation in the Broken River Province is assumed to align with transgression events 7 and 8, but available data are not compelling. T-R events additional to the above may be deciphered from the pre-Emsian stratigraphy of the Broken River Province: an early Lochkovian regression event (following the upper limestone "member" of the Jack Formation), plus two more T-R cycles inferred from an unnamed post-Jack unit with allochthonous carbonates and from the three members of the Shield Creek Formation (late Lochkovian-early Pragian). These pre-Emsian events do not coincide with Euramerican T-R events; they are accordingly assumed to have been tectonically driven. A major early Frasnian regression, inferred to have been tectonically driven (?Tabberabberan Orogeny), is reflected in the Mytton Formation-Bulgeri Formation unconformity and associated dramatic change from shallow marine to fluvial environments in the Broken River Province. This event is presumed to have been contemporaneous with the change from marine Cultivation Gully Formation to nonmarine conditions low in the Vanneck Formation of the Burdekin Basin. The Early marginifera Zone conodont faunas of the Myrtlevale Formation, dominated by species of Polygnathus associated with minor palmatolepids, seemingly represented the deepest Late Devonian-Tournaisian environments of the region, perhaps "outer shelf" environments. Carbonates from the suggested shallowest marine environments for the late Famennian-Tournaisian interval, exemplified by the Teddy Mountain Formation of the Broken River Province, have produced only bispathodid conodonts. More diverse late Famennian (expansa Zone) and Tournaisian faunas include Polygnathus and/or siphonodellid conodonts; these are inferred to have been deeper water than contemporaneous faunas (specifically Tournaisian) from the Broken River Province. None of the conodont-bearing Late Devonian-Tournaisian units of the Townsville hinterland had relatively pure palmatolepid or siphonodellid faunas that one might associate with truly pelagic contexts. The conodont faunas of the Keelbottom Group (Famennian-Tournaisian) and the Venetia Formation (early Tournaisian) are documented. As a consequence of the Famennian correlations having been tied preferentially to palmatolepids, extensions of ranges are suggested for Ancyrognathus and for several species of icriodontids and Polygnathus. Four new species are proposed, one icriodontid and three polygnathids: Icriodus scalariformis, Polygnathus costulifera, P. hieroglyphica, and P. wyatti.