The geology of the Carnarvon Basin, Western Australia Part 2: Permian stratigraphy

The report on the Geology of the Carnarvon Basin is issued in three separate and relatively independent Parts. Each Part treats an individual section of the subject and is accompanied by a Summary and an appropriate list of References. Part 1 deals with the Pre-Permian Stratigraphy and also includes a General Summary and other introductory information. Part 2 deals with the Permian Stratigraphy and Part 3 details the Post-Permian Stratigraphy and also contains information on Regional Structure, Palaeogeography, and Economic Geology. These Parts are being published separately, but, as they are parts of a single report, text-figure numbers are continued through the Parts. The regional map of the basin is included in Part 1. The Carnarvon Basin is an epicontinental basin of Proterozoic, Palaeozoic, Mesozoic, and Tertiary sediments. On land it extends from Onslow in the north to near Geraldton in the south and eastwards from the coast for about 130 miles. Proterozoic and Lower Palaeozoic sediments crop out at the south end of the basin. Silurian dolomite has been found in bores; marine Devonian sandstone, limestone, and siltstone crop out at the north-eastern edge of the basin and are found in bores in the central coastal area. Lower Carboniferous marine limestone and greywacke overlie the Devonian in outcrop; the limestone is doubtfully recognized in coastal bores. Permian marine sediments, including marine glacial sediments, rest unconformably on Lower Carboniferous, Devonian, and Precambrian rocks. Jurassic rocks are known in outcrop only on the far northern and southern margins, but form an important part of the subsurface sequence in the northern coastal area. Cretaceous marine sediments rest unconformably on Precambrian, Permian, and Jurassic rocks, mainly in the western part of the basin. Tertiary sandstone rests unconformably on Permian and Cretaceous rocks in a belt running north-south in the centre of the basin; Tertiary limestones cover the Cretaceous rocks near the coast. Maximum known thicknesses are: Proterozoic, about 30,000 feet; Lower Palaeozoic, 10,600 feet plus possibly 10,000 feet; Devonian, 4800 feet; Lower Carboniferous, 2300 feet; Permian, 15,200 feet (Sakmarian 7200 feet, Artinskian 5500 feet, and Kungurian 2500 feet); Jurassic, 11,460 feet; Cretaceous, 2670 feet; and Tertiary, 1500 feet. The Palaeozoic sediments were laid down on a surface of Precambrian rocks with strong relief. Minor basins sagged as sediments were laid down, and increased the original major structural relief. No evidence has been found of tangential stress in the sediments of the basin: all structures from the largest to the smallest are depositional structures affected only by large-scale down-warping. The geological history of the basin is related to intermittent transgression and regression of the sea which may have been caused by large eustatic rises of sea level or by epeirogenic movements of the continent or its margin. The basin is regarded as likely to contain commercial accumulations of petroleum, because of the combination of source beds in Devonian, Permian, Jurassic, and Cretaceous formations, reservoir beds in Devonian, Permian, Jurassic, and Cretaceous formations, and structural relief which has been present since deposition of the sediments.

Tags: AU-WA, Bulletin, Earth Sciences, GA Publication, Published_External, geology, stratigraphy
Organization: Geoscience Australia Data