Seismic sequence stratigraphy and facies architecture of the Scropes Range Formation in the Blantyre Sub-basin, Darling Basin, NSW

Abstract

In this paper, we propose and present a seismic stratigraphic interpretation, based on two-dimensional seismic data, of units attributed to the Upper Cambrian to Middle Ordovician Scropes Range Formation within the northwestern portion of the Blantyre Sub-basin in the central part of the Palaeozoic Darling Basin, western New South Wales. Data from only two shallow wells of the 831 km² study area dealt with in this paper were available to support the seismic investigations. Six seismic reflection horizons are defined and used to separate five seismic sequences named Units A, B, C, D and E. These features are identified in three seismic lines and demonstrate the continuity of the Scropes Range Formation throughout the northwestern part of Blantyre Sub-basin. All seismic sequence boundaries are based on good continuous markers, with strong amplitudes throughout the study area. The acoustic basement beneath the Scropes Range Formation, was almost certainly metamorphosed in the Delamerian Orogeny (around 500 Ma) within the study area. In addition, acoustic facies recognized in the three seismic lines can be correlated with sedimentary facies observed in outcrop in the Scropes Range, 130 km west of the study area, and are compared with acoustic facies in modern non-marine (fluvial) sandstone units associated with local braided delta depositional systems. The seismic facies identified from the seismic data show features such as low-angle and high-angle clinoforms, parallel and sub-parallel reflections and a few hummocky/wavy reflections indicating shallow channel-fills and small-scale fluvial channels. A combination of horizon mapping, seismic facies analysis and seismic attribute mapping defines the sequences. Complex geological features suggest many potential structural and stratigraphic hydrocarbon traps. A high-resolution seismic survey could lead to the definition of new exploration plays in this underexplored region.