SEISMIC STRATIGRAPHIC ANALYSIS AND STRUCTURAL DEVELOPMENT OF AN INTERPRETED UPPER CAMBRIAN TO MIDDLE ORDOVICIAN SEQUENCE IN THE NW BLANTYRE SUB-BASIN, DARLING BASIN (WESTERN NEW SOUTH WALES, AUSTRALIA)

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Abstract

In this paper, a new interpretation is presented of the seismic stratigraphy of units equivalent to the upper Cambrian to middle Ordovician Scropes Range Formation in the NW Blantyre Sub-basin in the central part of the Palaeozoic Darling Basin, western New South Wales. This succession was previously unrecognised, attributed to the lower part of the overlying Winduck Interval, or regarded as basement. The structural development of the study area is described, and may contribute to a better understanding of the regional stratigraphic evolution of the Lower Palaeozoic section in this part of the Darling Basin

This study presents interpretations of a regional two-dimensional seismic survey which investigated the upper Cambrian to middle Ordovician Scropes Range Formation in the NW Blantyre Sub-basin. A shallow marine Cambro-Ordovician succession is well established in the Bancannia Trough in the western Darling Basin but this interval appears to have been ignored in the central Darling Basin where a deeper-marine environment and suitable kitchen conditions may have provided greater petroleum potential. Data from two shallow wells in the 831 km2 study area were available to support the seismic investigations. Seismic sequences were defined by a combination of horizon mapping, the configuration of internal reflections, termination patterns and thicknesses. Six seismic reflection horizons were defined and used to identify five seismic sequences named Units A, B, C, D and E. These features were identified in three seismic lines and demonstrate the continuity of the Scropes Range Formation throughout the NW Blantyre Sub-basin. All seismic sequence boundaries are based on fair to good continuous markers, with strong amplitudes throughout the study area. The acoustic basement beneath the Scropes Range Formation was metamorphosed in the Delamerian Orogeny (around 500 Ma). Acoustic facies recognized in the three seismic lines can be correlated with sedimentary facies observed in outcrops in the Scropes Range, 130 km west of the study area, and are comparable to acoustic facies in modern fluvial sandstones associated with local braided delta deposits. Complex geological features suggest potential structural and stratigraphic hydrocarbon traps.

This study emphasizes the reservoir potential of the Scropes Range Formation in the central Darling Basin where extensive exploration efforts are currently occurring. The detailed interpretation of the seismic stratigraphy may lead to the definition of new exploration plays in this under-explored region.

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