Structural-Stratigraphic Development of the Gidgealpa-Merrimelia-Innamincka Trend With Implications for Petroleum Trap Styles, Cooper Basin, Australia

Abstract

A successful approach to basin analysis requires the broad-scale reconstruction of the three dimensional depositional systems in relation to concurrent structural development of the basin. The Gidgealpa-Merrimelia-lnnamincka (GMI) Trend is a prominent, asymmetric, mildly compressional anticlinal trend located in the Late Carboniferous to Triassic Cooper Basin. Its northwest flank is controlled by high angle thrust faults which were reactivated repeatedly throughout geological time. The present study addresses both the structural style and depositional character of the GMI Trend, focusing on selected areas. It is an integrated approach utilising wire-line logs, seismic interpretation, isopach and structural maps and detailed palynology. This approach has produced a detailed chronostratigraphic subdivision of the Permo-Triassic sequence, particularly the Patchawarra Formation, which points to evidence of synsedimentary tectonics. Evidence from crestal unconformities suggests that the GMI Trend was uplifted during at least four distinct structural episodes. These phases of uplift result from the rejuvenation of pre-Permian faults. Regional investigation of chronostratigraphic units incorporating palynological information, clearly demonstrates the palaeogeography and the presence of internal unconformities within the Patchawarra Formation. Subsurface distribution of hydrocarbon pools and improved definition of areas of prospectivity relate to the episodic uplifts. Although known hydrocarbon reserves have largely accumulated in structural traps, additional potential exploration targets in the Permian sequence exist in stratigraphic, combination, pinchout and downflank fault traps as well as onlap plays along the mid flank areas of the GMI Trend.

Paleo stress contribution to fault and natural fracture distribution in the Cooper Basin

“…2), and are called by Apak et al (1993Apak et al ( , 1995Apak et al ( , 1997 initial and second Sakmarian uplifts. Another significant hiatus is recorded palynologically separating the Early Permian from the Late Permian sequences called Daralingie Unconformity (Paten, 1969).…”

“…2). The depositional environment was controlled by highly sinuous fluvial system flowing northward over a floodplain with peat swamps, lakes and gentle uplands (Apak et al, 1993(Apak et al, , 1995(Apak et al, and 1997. The remaining Cooper Basin sediments were deposited during a period of tectonic quiescence, within an open basin environment with restricted access to the sea from the east followed by a meandering fluvial system (Stuart, 1976;Thornton, 1979).…”

Tectonic fingerprints in siderite cement, Tirrawarra Sandstone, southern Cooper Basin, Australia

“…Compressive forces reactivated basement thrusts resulting in an angular contact between the Toolachee Formation and various underlying formations (Wopfner, 1966;Kapel, 1972;Pyecroft, 1973;Thornton, 1979). The erosion is particularly apparent over the GMI trend (Apak, Stuart & Lemon, 1993) and is strong enough to be present in the study area in the middle of the Patchawarra Trough (Hill & Gravestock, 1995) but may be less prominent in the deeper Nappamerri Trough to the east of the GMI ridge. A hiatus in sedimentation of about 12 Ma at the end of early Permian time is recorded by palynological studies (Thornton, 1979).…”

“…Compression again reactivated the main basement faults (Apak, Stuart & Lemon, 1993) but the main effect of this event was to tilt the basin to the Stratigraphic column for the southern Cooper Basin with the main tectonic events. The fluvio-deltaic Tirrawarra Sandstone was deposited during the early subsidence history of the Cooper Basin when Australia was at high latitudes (modified from Apak, Stuart &Lemon, 1993 andSeggie et al 1994). Figure 3.…”

“…Some of the tectonic events are minor, such as the one which occurred during the Tirrawarra Sandstone deposition (T0a), and some of them are major tectonic events (T1 to T3). Apak, Stuart & Lemon (1993) documented another weak tectonic event within the Patchawarra Formation (here referred to as T0b). This event is seen as local truncation of section over the GMI Trend but fades towards the depocentres, including the study area.…”