TECTONOSTRATIGRAPHIC ANALYSIS OF THE UPPER CAMBRIAN – DEVONIAN SEDIMENTARY SUCCESSION IN THE CENTRAL DARLING BASIN, SE AUSTRALIA: AN INTEGRATED INTERPRETATION OF SEISMIC, GRAVITY AND WELL DATA

M. Kh. Khalifa^a*, K J. Mills^b and Kh. M. Al-Kahtany^c

^a Department of Geology, Faculty of Science, University of Zawia, Zawia, Libya.

^b Lithosearch Geological Consulting, Broken Hill, NSW, Australia.

^c Department of Geology and Geophysics, College of Science, King Saud University, Riyadh, Saudi Arabia.

^* Corresponding author, email: mohamed20au@yahoo.com

Key words: Seismic stratigraphy, Darling Basin, Lachlan Fold Belt, Australia, Blantyre sub-basin, Pondie Range sub-basin, Cambrian, Silurian, Devonian, seismic megasequences, basement architecture, Gondwana.

This paper presents a tectonostratigraphic interpretation based on seismic, gravity and well data of the Upper Cambrian through Devonian sedimentary succession in the central part of the Darling Basin, New South Wales (SE Australia). A composite roughly north-south trending 2D seismic section through this area, tied to two exploration wells, defines four unconformity-bound second-order seismic megasequences. The megasequences are: A, Upper Cambrian – Middle Ordovician (Llanvirnian?); B, uppermost Silurian – Lower Devonian (Emsian); C, upper Lower Devonian – lower Middle Devonian (Givetian); and D, upper Middle Devonian – Upper Devonian (Famennian). The megasequences are bounded by prominent seismic marker horizons which represent phases of regional-scale orogenic activity.

The composite 2D section studied is about 150 km long and traverses from north to south the Pondie Range sub-basin, the inverted Wilcannia High and the Blantyre sub-basin. Along the section, the Upper Cambrian to Devonian succession is deformed into a series of large-scale, fault-associated anticlines and synclines including the Avon High, an asymmetric anticlinal fold associated with several high-angle reverse faults. Major faults extend into, and flatten within, the basement. The top-basement surface is characterized by broad highs and lows which are represented on a gravity map of the study area. The map shows that the Wilcannia High defines the northern margin of the Blantyre sub-basin and the southern margin of the Pondie Range sub-basin. These sub-basins are in general defined by gravity lows.

The development of the Blantyre and Pondie Range sub-basins can be divided into five tectonostratigraphic phases during which there were distinct patterns of fault activity and regional subsidence. These phases are investigated using a restoration model which involves the successive removal of each seismic megasequence in turn, assuming simple vertical shear. The model provides new constraints on the distribution of structural and stratigraphic features which are relevant for future hydrocarbon exploration.

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