Cratonic sequence

Abstract: A newly discovered Middle Devonian sequence uplifted and exposed along a major thrust fault truncating the western limb of the Mt Beaufort Anticline of the Drummond Basin, Alpha district, central Queensland is described and named the Sedgeford Formation. Two informal members within the formation consist of a lower unit dominated by non‐marine sandstone which is conformably succeeded by an upper unit of richly fossiliferous marine sandstone with limestone interbeds. Conodonts and marine invertebrates indicate that the marine member is of Eifelian (Middle Devonian) age. A locally developed paludal facies within the lower member contains a diverse fish assemblage. The exposed sequence exceeds 1 km in thickness and is unconformably overlain by Upper Carboniferous Joe Joe Formation to the west. To the east it abuts the Bottle Tree Fault but boulder‐size metamorphic clasts from the Devonian succession suggest that a metamorphic basement lies beneath, and relatively close to, the lowest preserved horizons. The S...

Abstract: Sedimentological analyses of middle Paleozoic epeiric sea successions in North America suggest a hierarchy of discontinuity surfaces and condensed beds of increasing complexity. Simple firmgrounds and hardgrounds, which are comparatively ephemeral features, form the base of the hierarchy. Composite hardgrounds, reworked concretions, authigenic mineral crusts and monomictic intraformational conglomerates indicate more complex histories. Polymictic intraformational conglomerates, ironstones and phosphorites form the most complex discontinuity surfaces and condensed beds. Complexity of discontinuities is closely linked to depositional environments duration of sediment starvation and degree of reworking which in turn show a relationship to stratigraphic cyclicity. A model of cratonic sequence stratigraphy is generated by combining data on the complexity and lateral distribution of discontinuities in the context of facies successions. Lowstand, early transgressive and late transgressive systems tracts are representative of sea-level rise. Early and late transgressive systems tracts are separated by the maximum starvation surface (typically a polymictic intraformational conglomerate or condensed phosphorite), deposited during the peak rate of sea-level rise. Conversely the maximum flooding surface, representing the highest stand of sea level, is marked by little to no break in sedimentation. The highstand and falling stage systems tracts are deposited during relative sea-level fall. They are separated by the forced-regression surface, a thin discontinuity surface or condensed bed developed during the most rapid rate of sea-level fall. The lowest stand of sea level is marked by the sequence boundary. In subaerially exposed areas it is occasionally modified as a rockground or composite hardground. RESUME