Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

During 1950-51 pendulum gravity observations were made at 59 stations throughout Australia using invar pendulums on loan from the Department of Geodesy at Cambridge University. A national gravity base station was established at Melbourne. Subsequent comparisons with gravity meter ties suggest that the pendulum value is about 2 mgal. low. The standard errors of the gravity differences from Melbourne to the other stations have been estimated from internal consistency of the pendulum observations and from comparison with gravity meter measurements; the mean standard error is about 0.6 mgal. A small systematic difference from gravity meter values is assumed to be caused by the effect of the earth's magnetic field on the pendulums; after correction for this, the results agree fairly well with the American calibration system. Free air, Bouguer and isostatic anomalies have been calculated for all stations. The isostatic anomalies are for both Airy-Heiskanen and Pratt-Hayford hypotheses, and for four different assumed crustal thicknesses in each case. The isostatic and Bouguer anomalies are predominantly negative. A degree of isostatic compensation is present, but some large anomalous areas are uncompensated. The pendulum survey forms a basic network to which past and future gravity surveys can be referred.

Mollusca from the Nanutarra Formation, a recently defined strata! unit cropping out along the north-eastern edge of the Carnarvon Basin of Western Australia, are described and the age of the' formation is discussed. The fossils occur largely as moulds of the original shells, so that their study has been based mainly on artificially prepared casts. Of about 48 forms recorded in the paper, only one (Pseudavicula anomala) has been definitely referred to a previously described species, four (Maccoyella aff. corbiensis. M. aff. barklyi, M. aff. moorei, and Modiolus aff. ensi/ormis) have been assigned qualified identifications with known species, and 18 are described as new; the remainder have been given only generic identifications, owing to the limitations of the material. The new species are as follows:-Nuculana hoelscheri, Glycymeris mckellari, Pacitrigonia? nanutarraensis, Pterotrigonia australiensis, "[socyprina" fairbridgei, "Corbicellopsis," nanutarraensis, Lucina macroporum, Mutiella? teicherti, Protocardia wapeti, Astarte (Nicaniella) mcwhaei, Eriphyla playjordi, Pleuromya ashburtonensis, Panopea glaessneri. CQrbula nanutarraensis, Muricotrochus? australiensis, Purpurina? yanreyensis, Procerithium (Rhabdocolpus) brunnschweileri, and" Acteonina" australiensis. Apart from the species of Pseudavicula, Maccoyella, and Modiolus, which have been identified, mostly with qualification, with Australian Lower Cretaceous species, the fossils bearing particularly on the age of the formation are those belonging to the genera Pterotrigonia (hitherto solely Cretaceous apart from one record from the Tithonian), Eriphyla (hitherto mainly Cretaceous, but known from the Upper Jurassic), Glycymeris (known from the Cretaceous but not from the Jurassic), and large Panopea (resembling several Cretaceous species and unlike any from the Jurassic). No species belongs to an exclusively Jurassic group. It is concluded that, notwithstanding palaeobotanical evidence of a Jurassic age, the Nanutarra Formation should be most probably referred to the Lower Cretaceous. It has yielded no ammonites or brachiopods.

A number of selected specimens from the Tennant Creek mining field were submitted for examination by N.J. McMillan. The object was to investigate the possibility that the talc in the area was derived by the metamorphism of ultrabasic rocks.

The Betoota No. 1 well was drilled by Delhi Australian Petroleum Ltd, Frome-Broken Hill Company Pty Ltd, and Santos Limited, in far southwest Queensland to a total depth of 9,824 feet. Drilling was commenced on 22nd December 1959 and the well was completed on 18th April 1960 as a dry hole. The rig used was a National 130 owned by Delta Drilling Company. Delhi Australian Petroleum Ltd, as the operating company, supplied the supervisory, engineering, and geological personnel. A comprehensive programme to obtain all data relative to the hydrocarbon potential of the strata penetrated by the drill bit and stratigraphic information concerning the geological history of the area was diligently carried out. The operation also provided for a complete programme of electric and mud logging, testing and coring, carried out by the operating company and their contracted service companies. The Betoota No. 1 well established the presence of 5,757 feet of Mesozoic strata overlying 4,067 feet of sediments of probable Palaeozoic age at the site of the bore hole. Several showings of hydrocarbons were detected in sediments between 4,400 feet and 5,757 feet. Mter testing and examination of all evidence, they were considered to be noncommercial. From 3,450 feet to 5,757 feet some zones exhibiting very good porosity were encountered, but all were found to be water-bearing. Shales of both marine and brackishwater origin, regarded as suitable source rocks, occurred in the well between 1,350 feet and 3,245 feet and between 5,000 feet and 5,757 feet. The rest of the section penetrated was composed of sediments whose origin did not suggest conditions of accumulation likely to foster the generation of fluid hydrocarbons.

Thangoo No. lA well was drilled as a result of mechanical difficulties encountered at the drilled depth of 3 ,475 feet in Thangoo No. 1 well which were insurmountable and prevented further operations on this well. Total loss of circulation at 3,475 feet in Thangoo No. 1 well resulted in unexpected total collapse of the hole below the 10 3/4" casing in a section of friable sandstone and conglomerate (Grant Formation). In Thangoo No. lA well these formations were cased off. A lost circulation zone was tested for potential hydrocarbon production and found to contain water only. The well was drilled to 5,429 feet into basement rocks (programmed depth 4,500 feet). Excellent hole control was maintained to total depth by drilling below the 16" conductor shoe with high pH, low shear and waterloss, freshwater mud. The 1,366 feet of Mesozoic and 1,377 feet of Permian section in Thangoo No. lA closely resemble that of Thangoo No. 1. The Ordovician section is 2,318 feet thick, consisting of 695 feet of Goldwyer Formation (new name) and 1,623 feet of Thangoo Limestone (amended name). Basement, consisting of Precambrian phyllite , was encountered at 5,100 feet in Thangoo No. lA. Traces of oil were observed throughout the Ordovician section. Oil shows are confined predominantly to vuggy veins of coarse crystalline dolomite. A minor show was also observed in the sandstone of the basal unit of the Thangoo Limestone. A porous zone within the Thangoo Limestone, causing some lost circulation, appeared at about 3,670 feet in Thangoo No. lA. A formation test of this zone recovered only brackish water (11,999 ppm. total salts) with no signs of oil or gas. It is possible that the small shows of oil in the Thangoo Limestone are retained by the impervious Goldwyer Formation, as no shows were present in the Roebuck Bay and Dampier Downs wells, where porous Permian rocks directly overlie the Thangoo Limestone. The correlation of the sections of the Thangoo Limestone in all the exploratory wells on the Broome Platform indicates that the Thangoo No. lA well occupies a low structural position. Consequently the objectives of testing the structure in the Ordovician and Permian Grant Formation were not achieved. The chances of finding commercial oil accumulations in the Ordovician section of the South Canning Basin in the vicinity of Thangoo Nos. 1 and lA are very small at this time, because of the low source rock potential and flushing by meteoric waters of the Thangoo Limestone, the lack of porosity in the Goldwyer Formation, and the difficulties experienced in resolVing the structure of the Ordovician with present seismic methods.

The Barlee No. 1 Well was drilled with WAPET's National 100 rig to the total depth of 8101 feet. Below a thin cover of the surface sand, 1562 feet of Mesozoic sediments were encountered, and drilled to the depth of 1594 feet. These sediments are represented by the Broome Sandstone (Lower Cretaceous) and Jurassic rocks, consisting of Jarlemai Siltstone, Alexander Formation, and Wallal Sandstone. The Jarlemai Siltstone interval which is 850 feet thick, is the thickest section of this formation which has been drilled in the Canning Basin. Unconformably below Mesozoic sediments, a uniform section of Carboniferous rocks was encountered and drilled to the total depth. All 6507 feet of the Carboniferous section are included in the Anderson Formation, to which an Upper Carboniferous age is tentatively assigned. In the lower part of the formation (7825 - 7856 feet) an intrusive body of dolerite was encountered. Some induration was observed in rocks adjacent to the intrusion. The well was abandoned in moderately porous sandstone beds of the Anderson Formation. Average dips of 20 degrees were observed in cores and recorded by the dipmeter survey in the Carboniferous section. The dipmeter survey shows that the well was located on the northern flank of the Barlee Anticline. Some very slight shows of gas were present in the sandstone beds of the Anderson Formation. Below 5600 feet some sandstone beds contained impregnations of black, rubbery bituminous material - very probably oil residue. No signs of live oil were observed in the well. The drilling results indicate that the Barlee No. 1 Well (like Fraser River No. 1) is located in the deep Fitzroy Trough on a structure originated by an igneous intrusion. The prospective beds of Ordovician, Devonian, and Lower Carboniferous rocks are buried under the thick cover of the unprospective Upper Carboniferous sediments and probably are intruded by igneous rocks. It seems likely that the sediments of the Fitzroy Trough in the Barlee area extend south as far as the Darnpier Fault; thus the Dampier Fault in the western part of the Canning Basin may replace the Fenton Fault, which dies out before reaching the Dampier Land area. The concept of the Jurgurra Terrace still remains valid, but only for the eastern part as shown on Plate .No. 1.

This report refers to seismic work carried out in the Puri area of Papua by Seismograph Service Ltd. for Australasian Petroleum Co. Pty. Ltd. during the period 6th May - 15th December, 1959. The objective ofthe survey was to determine the structural pattern of the Tertiary limestones in order to define any closed structures that may have economic oil accumulations. Altogether some 75 miles of continuous reflection traverses were observed and also a single refraction in-line profile of two spreads. An anticlinal feature was observed along one line but as there was no evidence of any significant pitch reversal along the strike line it seems there is no structure worth drilling in the area south of the Puri and Kereru Anticlines. The overall quality of the reflection data was poor but was considered adequate to disprove the presence of any major closed structures.