The Latrobe Group in the Gippsland Basin consists of well-developed, stacked shoreface and coastal plain deposits, cut by large, incised channel systems up to 500 m deep. These large channels are conspicuous on seismic intersections and have previously been interpreted as the result of fluvial incision associated with basin inversion/compressional tectonics. Here we have used 3D seismic, well log, and core to re-evaluate the origin of these channel systems. We interpret three major phases of channel incision-infilling; Tuna Channel 1, Tuna Channel 2 and the Marlin Channel. Biostratigraphic data shows that the channels range in age from the Palaeocene-Eocene transition to the Late Eocene. These ages indicate channel formation occurred prior to the onset of compressional tectonics in the Gippsland Basin, which began at the Eocene-Oligocene transition.
Correlation of these channels with coeval palaeoshoreface systems reveals that the channels are located seaward of, and in close proximity to these shorelines. Well data indicates that the channel fill sediments are of marine origin, consisting of glauconite, dinoflagellates, foraminifera, and marine macro fossils. We do not observe evidence for a regional unconformity which would correlate with over 500 m of subaerial channel incision. These channels are therefore interpreted as submarine canyons, rather than channels of fluvial origin. They are interpreted as shelf-incising, with canyon heads located close to coeval palaeoshorelines where they received sediment via longshore/littoral processes. The erroneous identification of submarine canyons as incised valleys in sedimentary basins has significant implications for tectonic and eustatic histories globally.
