A REVIEW OF GEOPHYSICAL EXPLORATION IN THE POLDA BASIN, SOUTH AUSTRALIA

1986 ◽  
Vol 26 (1) ◽  
pp. 319
Author(s):  
R.G. Nelson ◽  
T.N. Crabb ◽  
R.A. Gerdes
Keyword(s):  
Magnetic Material ◽  
South Australia ◽  
Magnetic Data ◽  
History Of ◽  
Magnetic Basement ◽  
Central Australia ◽  
Intracratonic Basin ◽  
Seismic Sections ◽  
Great Australian Bight ◽  
Block Faulting

The Polda Basin is an intracratonic basin, at least 5000 m in depth, extending from the edge of the Great Australian Bight nearly 400 km east to the centre of Eyre Peninsula in southern South Australia, it can now be recognised as a structural feature of some antiquity, originating possibly as a crustal downwarp in Proterozoic time during the same orogenic regime that gave rise to the Officer and Amadeus basins of central Australia, with which it has strong affinities. Its internal structure indicates that it has been subject to the same orogenic episodes that have affected southern and central Australia, culminating in rotational block faulting associated with the final pull-apart of Gondwanaland. Extensive salt mobilisation observed on seismic sections, confirmed by the drilling of the Mercury 1 and Columbia 1 wells, supports the concept of the basin's Cambrian or Precam-brian origins.The exploration history of the basin is a useful example of the application of a number of geophysical disciplines to arrive at a satisfactory interpretation. A reappraisal of geophysical data was undertaken after Outback Oil N.L. drillhole Gemini 1 penetrated 'uneconomic' basement at 856 m, far short of the anticipated sedimentary section of 1830-2440 m. Interpretation of shipborne magnetic data, not previously considered, indicated that a seismic horizon close to where Gemini 1 penetrated igneous rock was related to a thin layer of magnetic material which did not correspond to deep magnetic basement. Further detailed aeromagnetic and seismic studies confirmed this interpretation, which was tested by the drilling of two exploration wells. Mercury 1 and Columbia 1. Although unsuccessful as hydrocarbon discovery wells, these two wells confirmed the overall validity of the interpretation. Stratigraphic information derived from these wells and from further geophysical studies and drilling onshore have led to a new assessment of the basin and its potential.

NEW IDEAS ON THE RIFTING HISTORY AND STRUCTURAL ARCHITECTURE OF THE WESTERN OTWAY BASIN: EVIDENCE FROM THE INTEGRATION OF AEROMAGNETIC, GRAVITY AND SEISMIC DATA

1994 ◽  
Vol 34 (1) ◽  
pp. 529 ◽  
Author(s):  
G.W. O'Brien ◽  
C.V. Reeves ◽  
P.R. Milligan ◽  
M.P. Morse ◽  
E.M. Alexander ◽  
...  
Keyword(s):  
Seismic Data ◽  
Normal Fault ◽  
Magnetic Data ◽  
Data Sets ◽  
Stress Regime ◽  
Petroleum Potential ◽  
History Of ◽  
New Ideas ◽  
Structural Architecture ◽  
Great Australian Bight

The integration of high resolution, image-processed aeromagnetic data with regional geological, magnetic, gravity and seismic data-sets has provided new insights into the structural architecture, rifting history, and petroleum potential of the western onshore and offshore Otway Basin, south-eastern Australia.Three principal structural directions are evident from the magnetic data: NS, NE-ENE and NW-WNW. The structural fabric and regional geological data suggest that the rifting history of the basin may have taken place in two distinct stages, rather than within a simple rift-to-drift framework. The initial stage, from 150 to ~120 Ma, took place within a stress regime dominated by NW-SE extensional transport, similar to that of the basins within the Great Australian Bight to the west. ENE-striking extensional rift segments, such as the Crayfish Platform-Robe Trough and the Torquay Sub-Basin, developed during this period, contemporaneous with the deposition of thick sediments of the Early Cretaceous (Tithonian-Hauterivian) Crayfish Subgroup. In other parts of the basin, NW-striking rift segments, such as the Penola, and perhaps Ardonachie, Troughs onshore, developed within a strongly trans-tensional (left-lateral strike-slip) environment. At ~120 Ma, the regional stress field changed, and the Crayfish Subgroup-aged rift segments were reactivated, with uplift and block faulting extending through to perhaps 117 Ma. Rifting then recommenced at about 117 Ma (contemporaneous with the deposition of the Barremian-Albian Eumeralla Formation), though the extensional transport direction was now oriented NNE-SSW, almost perpendicular to that of the earlier Crayfish Subgroup rift stage. This later rift episode ultimately led to continental breakup at ~96 Ma and produced the 'traditional' normal fault orientations (NW-SE to WNW-ESE) throughout the Otway Basin.

STRUCTURE AND STRATIGRAPHY OF THE CEDUNA TERRACE REGION, GREAT AUSTRALIAN BIGHT BASIN

1979 ◽  
Vol 19 (1) ◽  
pp. 53 ◽  
Author(s):  
A. R. Fraser ◽  
L. A. Tilbury
Keyword(s):  
Upper Cretaceous ◽  
Single Channel ◽  
South Australia ◽  
Magnetic Data ◽  
The West ◽  
Petroleum Potential ◽  
Northern Margin ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data ◽  
Great Australian Bight

The Ceduna Terrace is a bathymetric feature covering some 70,000 sq km, in the continental slope of South Australia. Its most gently sloping part lies between the 500 and 2500m isobaths, and is underlain by the main depocentre of the Great Australian Bight Basin.A systematic interpretation of the region has been made, based on 17,000 km of multi-channel seismic data from Shell surveys, 8000 km of single-channel seismic, gravity and magnetic data from the BMR Continental Margins Survey, and 6000 km of gravity and magnetic data from surveys by Lamont-Doherty Geological Observatory. Seismic ties were made to the wells Potoroo-1 and Platypus-1.Mapping of the key seismic horizons confirms the picture of the basin as a sedimentary wedge, more than 10 km thick, extending from the edge of the shelf to the continental rise. Three important unconformities can be mapped over a wide area and tied to Potoroo-1 well-a basement reflector separating Lower Proterozoic crystalline rocks of the Gawler Craton from an overlying, block-faulted sequence of mainly Lower to mid-Cretaceaus sediments; an unconformity at the base of an Upper Cretaceous sequence which includes a major prograded unit in the west; and a break-up unconformity at the base of a Tertiary marine transgressive sequence, that, in turn, is overlain by marine carbonate deposits. Widespread shallow marine sediments are believed to exist in the west of the basin, in both the Lower and Upper Cretaceous sequences.Structure is dominated by normal, west to NW trending, down-to-the-south faults, many of which are synsedimentary. Fault displacements are greatest beneath the shelf-break, where basement has been downthrown 5 to 6 km. Farther south, synsedimentary faulting has resulted in a marked thickening of both Upper and Lower Cretaceous sequences.The basin has been barely explored for hydrocarbons. Regional seismic coverage is good, but drilling in the main part of the basin is limited to one well on the northern margin. The petroleum potential of the western half of the basin is rated as good, in view of the interpreted existence of abundant marine source beds and the recognition of situations favourable for generation, migration and entrapment of hydrocarbons.

Mission Tracks in the Bush

2019 ◽  
Vol 3 (1-2) ◽  
pp. 103-124
Author(s):  
Gemma Tulud Cruz
Keyword(s):  
Nineteenth Century ◽  
Western Australia ◽  
South Australia ◽  
Nation Building ◽  
Cultural Encounters ◽  
History Of

Christian missionaries played an important role in the Australian nation building that started in the nineteenth century. This essay explores the multifaceted and complex cultural encounters in the context of two aboriginal missions in Australia in the nineteenth century. More specifically, the essay explores the New Norcia mission in Western Australia in 1846-1900 and the Lutheran mission in South Australia in 1838-1853. The essay begins with an overview of the history of the two missions followed by a discussion of the key faces of the cultural encounters that occurred in the course of the missions. This is followed by theological reflections on the encounters in dialogue with contemporary theology, particularly the works of Robert Schreiter.

The Status of the School Shark Fishery in South-Eastern Australian Waters

1959 ◽  
Vol 10 (2) ◽  
pp. 150 ◽  
Author(s):  
AM Olsen
Keyword(s):  
Maximum Yield ◽  
Reproductive Potential ◽  
South Australia ◽  
Slow Growth Rate ◽  
South Eastern ◽  
Pregnant Females ◽  
The Status ◽  
History Of ◽  
Annual Total ◽  
The Mean

The maximum yield of the school shark fishery in south-eastern Australian waters was 4.09 million lb in 1949. The catch has fluctuated since then about a declining trend to 3.18 million lb in 1956. In 1944, 7.3 hooks were required to catch a shark of mean weight 14.7 lb. In 1956 the number of hooks required was almost doubled: 13.6 hooks were needed to catch sharks of mean weight 13.7 lb; the catch per hook dropped from 2.01 to 0.99 lb. Whereas the catch per boat-month remained relatively stable at 4765 lb for 1944 and 4643 for 1956, the number of hooks used per boat-month increased from 2366 to 4668 hooks in 12 years. Throughout this period the mean weight of sharks in eastern Bass Strait remained fairly steady (11-13 lb) whereas there was a drop of 3 lb from a mean weight of 17-20 lb in the predominantly mature portion of the stock in western Bass Strait. Fishermen in South Australia have reported a comparable drop in the mean weight of sharks in their catches. During the period 1941-46 there was unrestricted inshore fishing of juveniles and pregnant females with a consequent severe drop in the inshore population. The subsequent decline in the annual total catch is believed to be due not only to a too intensive offshore fishery but also to the resultant reduced recruitment and depressed reproductive potential caused by the earlier destruction of juveniles and pregnant females. In the data presented in this paper there is evidence that the school shark fishery, which is operating on a single stock of sharks with a slow growth rate, a late sexual maturity, and a low fecundity, shows trends which are suggestive of depletion. Because similar trends in the soupfin shark fishery of California and in the dogfish fishery of British Columbia were followed by depletion, it has been inferred that regulations to protect the vulnerable phases of the life history of the school shark of Australia may be required. Measures for conservation are discussed.

ESTIMATION OF SOURCE PARAMETERS IN IBADAN, SOUTH – WESTERN NIGERIA USING DIGITIZED AEROMAGNETIC DATA

2018 ◽  
Vol 14 (2) ◽  
pp. 15-28
Author(s):  
A A ALABI ◽  
O OLOWOFELA
Keyword(s):  
Magnetic Susceptibility ◽  
Source Parameters ◽  
Granite Gneiss ◽  
Geological Structure ◽  
Magnetic Data ◽  
Susceptibility Map ◽  
Rock Types ◽  
Upward Continuation ◽  
Magnetic Basement ◽  
Local Wavenumber

Airborne magnetic data covering geographical latitudes of 7000‟N to 7030‟N and longitudes of 3 30′E to 4 00′E within Ibadan area were obtained from Nigeria Geology Survey Agency. The data were ana-lyzed to map the sub surface structure and the source parameters were deduced from the quantitative and qualitative interpretation of magnetic data. The upward continuation technique was used to de-emphasize short – wavelength anomaly while the depth to magnetic sources in the area was deter-mined using local wavenumber technique, the analytic signal was also employed to obtain the depths of the magnetic basement. Analysis involving the local wavenumber, upward continuation and appar-ent magnetic susceptibility techniques significantly improves the interpretation of magnetic data in terms of delineating the geological structure, source parameter and magnetic susceptibility within Iba-dan area.. These depth ranges from 0.607km to 2.48km. The apparent susceptibility map at the cut-off wavelength of 50 m ranges from -0.00012 to 0.00079 which agree with the susceptibility value of some rock types; granite gneiss, migmatite biotite gneiss, biotite muscovite granite, hornblende granite, quartz and schists. The result of the local wavenumber suggests variation along the profiles in the surface of magnetic basement across the study area.

Sustainable governance for small desert settlements: learning from the multi-settlement regionalism of Anmatjere Community Government Council

2008 ◽  
Vol 30 (1) ◽  
pp. 137 ◽  
Author(s):  
Will Sanders ◽  
Sarah Holcombe
Keyword(s):  
Local Government ◽  
Northern Territory ◽  
Governance Structures ◽  
History Of ◽  
Basic Desert ◽  
Central Australia ◽  
The Many ◽  
Governance Arrangements

In light of some basic desert demography, this paper examines governance patterns for small desert settlements. It traces policy histories which led to the emergence of highly localised, single settlement governance arrangements during the 1970s and ’80s. It also identifies the many pushes since within the Northern Territory local government system for more regional, multi-settlement governance structures. The paper goes on to examine the history of one such regional, multi-settlement arrangement in central Australia, the Anmatjere Community Government Council established in 1993. The paper details our work with this Council over the last 4 years on ‘issues of importance or concern’ to them. The paper aims to learn from the ACGC experience in order to inform the more radical restructuring of Northern Territory local government currently underway towards larger multi-settlement regionalism. It concludes with four specific lessons, the most important of which is that regionalism must build on single settlement localism.

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