Some quantitative studies of coarse‐bedded conglomerates of late silurian‐early Devonian age in the Tallarook and Seymour east Synclines, Victoria

Abstract

Some quantitative properties of the cobbles and pebbles from the bedded Siluro‐Devonian conglomerates in the Tallarook and Seymour East synclines have been studied, with a view to determining the origin of the sediments. The pebble traits of petrological composition, bedding, and shape have been plotted areally. Strong trends of contoured values and modal frequencies are shown from the south and south‐west along the Tallarook Syncline, with SSE trends paralleling the Seymour East Syncline. Concentrations of pebble tràits suggest at least two separate sources, one from south‐west of the Tallarook Syncline, the other to the north and east from the Trawool Anticline. Land plant debris in the core of the Seymour East Syncline associated with southerly directional phenomena from the south suggests that parts of the Trawool “High” were above sea‐level. Agreement of current bedding and flute cast data with the contour patterns and modal trends of pebble traits indicates that the conglomerates were emplaced by turbidity currents, the directions of slumping being indicated by the trends. The turbidite pattern is concordant with an hypothesis of highs rising slowly from the south as well as along the line of the Trawool Anticline in Upper Silurian times.