contentsMapping Anticlines From The Air
Heli Wopfner
Introduction
In 1957 I was working on a mapping project in the Cordillo Downs area being undertaken by Geosurveys of Australia Ltd for Santos Ltd. The area was part of Santos' oil exploration tenements, spanning 860 000 km2 of northeastern South Australia and southwestern Queensland (Figure 1).
While I was back in at our office in Adelaide, Bruce Wilson, one of the other senior geologists at Geosurveys, confronted me with half a dozen aerial photographs, showing ridgetype structures north of Cordillo Downs Station. "Heli, I think you overlooked some basement outcrops on your Cordillo trip", he said. I recognised that these features were the moderately dipping Cretaceous/Tertiary crests near Haddon Downs and I told him so. He didn't accept my explanation, arguing that "nowhere in the Great Artesian Basin have Tertiary deposits deformed to such steep structures". We left it at that, but on 22 June I received a phone call from Rudi Brunnschweiler, chief stratigrapher at Geosurveys. Wilson had shown him the photographs of the structures and Brunnschweiler suggested that these exposures might be Devonian sandstones, like those of Mootwingee Ranges in New South Wales, forming a structural high penetrating the Cretaceous sedimentary cover. I repeated what I had told Wilson, but he wasn't convinced either. It was decided that Brunnschweiler and
I should fly to Cordillo Downs in the Sokol, the small aircraft owned by Santos, and inspect the structures in the field.
On 3 July we flew from Parafield Airport to Leigh Creek, then proceeded via Marree to Cordillo Downs. The prime target of the next day's reconnaissance flight was the outcrop of moderately inclined strata near Haddon Downs (Figure 2).
We took several low passes across the exposures to show Brunnschweiler the outcrop pattern typical of the Tertiary silcrete and then we viewed the silcrete capped escarpment to demonstrate that here the same rocks were exposed as at the site of the deformed beds. After that we followed the structure north towards Haddon Corner, where we crossed the Nappamilkie Anticline to Birdsville, returning to Cordillo Downs via the southern flank of the dome.
At the end of that flight I had Brunnschweiler convinced, not only that the ridge near Haddon Downs was indeed formed by Cretaceous and Tertiary rocks, but also of the existence of the other structures. We drove to the outcrops the next day and now that Brunnschweiler was convinced that the deformed strata demonstrated a period of rock deformation in mid Tertiary times, he wanted to see more of the region. We devoted the next two days to reconnaissance flights into Queensland as far as Morney and Durham Downs stations.
On the evening before Brunnschweiler's return flight to Adelaide he asked me what I thought of an aerial inspection of the entire Santos licence areas. I thought it was a great idea. By now we had definite proof that the silcrete (siliceous duricrust) and the Cretaceous strata below had been deformed by tectonic forces. Thus the silcrete covering the Tertiary Eyre and the Cretaceous Winton formations could be used as a phantom horizon, reflecting the actual fold structures, and by utilising the readings of the plane's altimeter we could quantify the relative amplitude of the anticline.
Flying on spit and charm
Back in Adelaide, Brunnschweiler quickly convinced Santos chairman John Bonython and Geosurveys' founder Reg Sprigg of the benefits of the proposed air reconnaissance. Brunnschweiler arrived back at Cordillo Downs in the Sokol on 22 July.
The Sokol, meaning 'falcon' in Slavic languages, was a single engine, low-wing monoplane with a wing span of 10 m. It was built in Czechoslovakia after World War II under the official type-designation Mráz M1C. It was more or less an enlarged version of the German war time Bueker 181, fitted with a retractable undercarriage adapted from the German executive aircraft 'Messerschmitt 108'. The Bueker 181 seated two people and was used extensively by the German Air Force for pilot training; I myself obtained basic flight training in one of them. The Sokol was a wooden lattice construction, covered with plywood and fabric, the whole thing being held together by special, two-component glue on a casein base. It had a fixed, wooden propeller which was powered by a 125 hp, 4-cylinder in-line, air-cooled engine, giving it a travelling speed of about 165-180 km/h. For his flight from Europe to Australia Brunnschweiler had the rear seat in the plane replaced by an 80 L fuel tank, giving the aircraft an endurance of five hours. Maximal operational range was about 1600 km. Instrumentation was absolutely basic and there was no wireless. But it was a good looking, slightly gull-winged aircraft and it was a joy to fly (Figure 3).
For any emergency we carried half a dozen tins of corned beef, a box of Sao biscuits and 16 L of water. Aviation fuel was available for purchase at all stations which were on the circuit of the Channel Air Service. Not having a wireless on the p lane, we had to inform air control of our flight plan by telegram via the Royal Flying Doctor Service each morning.
As shown in Figure 4, we flew wing-tip level with the silcrete covered mesas or escarpments at or near the crest of an anticline and noted the elevation indicated on the aircraft's altimeter. Then we descended into the syncline and, flying as low as possible above the ground, we read the altimeter again. Repeating the procedure several times on each individual anticline we obtained fairly accurate values for the construction of a structure contour plan of the area.
The two of us were an ideal team. We were both geologists with an alpine background and we were accustomed to recognise and identify geological features from the air. Although I didn't hold a valid pilot's licence any more I could still handle a plane competently and I had ample experience in visual navigation and low level flying. And, most important of all, we were both on the same wavelength. One of us would fly the aircraft while the other did the navigation and plotted the observations onto a 16 miles to 1 inch scale (roughly 1:1,000 000) aeronautical map. Every 30 minutes we would switch duties, thus assuring that both of us maintained a high degree of concentration. Depending on the nature of the terrain and distance from base we would fly between three and a half to six hours a day.
We divided the total licence area into various segments which we could cover from a central point within it. The first was the south-central portion of the Great Artesian Basin, roughly circumscribed by the latitude of Marree, theeastern edge of Lake Eyre, the latitude of Goyder Lagoon and the western margin of the Strzelecki Desert. None of the stations in that area were served by the Channel Air Service, but when we inquired about the availability of aviation gasoline, we received a confirmative answer from Etadunna Station, combined with a generous invitation from the owners, the Oldfield family, to stay at the homestead as long as we liked.
Before departing for Etadunna we undertook a few flights in the Cordillo-Betoota area to fill in some gaps left on previous flights. On the morning of 25 July we flew from Cordillo to Etadunna. The homestead, situated on the Birdsville Track ~120 km north of Marree, had been built by Jim Oldfield and was one of the finest on the 'Track'. It was a large stone building with a well kept garden and several outhouses. The spacious living room exuded an air of gracious living and housed a grand piano. Brunnschweiler, who was an excellent pianist, entertained the whole house with a one-man performance of a popular musical.
From our base at Etadunna we covered the area between Goyder Lagoon and the southern edge of the Great Artesian Basin. In over 14 hours of flying in four days we identified several smaller structures between the Flinders Ranges and Cooper Creek, and one huge structure between Mungeranie Homestead and Warburton Creek which we called Gason Dome.
After Etadunna we flew across Lake Eyre to Oodnadatta and visited Santos' Oodnadatta-1 wellsite and associated seismic survey being conducted by the Bureau of Mineral Resources. At the wellsite we viewed various drillcore including a fossiliferous sandstone which had yielded traces of yellow oil and on test produced highly saline water and traces of oil (now known as the Early Cretaceous Coorikiana Sandstone).
Next we flew north-northeast to investigate the Dalhousie structure and then across the desert to Poeppel Corner. We were in for a nasty and rather scary surprise. The weather had been warming up and as we flew across the desert willy-willies were raising frequently, sending slender funnels of dust almost to our flight level, about 300 m above ground. Every
time it happened the left engine cowling lifted up a few centimetres accompanied by a draft of air being felt in the cabin. These were tense and alarming moments – should the cowling come loose altogether and flip up, the plane would become very difficult to handle. We were relieved to finally reach Birdsville. My negligence had been the cause of the problem. I had checked the oil before take-off at Oodnadatta and when I closed the cowling I overlooked that the spring-loaded locking pin had not fully snapped into the locking position and hence could unlock during the flight. Fortunately, the second pin had held. After making sure that this time all the pins were locked properly, we carried on to Cordillo Downs.
The survey of the Innamincka Dome took up the following day. Flying along the escarpment formed by the limbs of the anticline we could observe the unconformable contact between the Winton and the Eyre formations in a number of places (Figure 5). An additional day was spent investigating the structures along the Wilson River in Queensland.
One of the ignition magnetos giving us trouble and gibbers catapulted into the air on touchdown of the wheels and punctured the fabric of the fuselage and of the elevators at several places. We had 'repaired' the holes with medical adhesive tape, but by the time we had patched up more than half a dozen holes, some of them the size of a fist, it dawned on us that we better return to Adelaide and seek a more permanent solution.
We left Cordillo Downs for Adelaide on 2 August flying via Birdsville to pick up a parcel of urgent letters from Dr Brian Daily of the South Australian Museum who, together with American colleagues, was investigating marsupial fossil
occurrences southwest of Birdsville. We landed at Birdsville, picked up the letters and took off again. Brunnschweiler thought we had enough fuel to get us to Adelaide; there was no need to waste time topping up the tanks. But by the
time we reached a position around Gawler all our tanks were empty and we had to switch to the emergency tank which gave us about 15 minutes more flying time. With that we landed safely at Parafield Airport and taxied towards the tarmac in front of the airfield control shack. We had barely reached the tarmac when the engine conked out. Including the leg from Cordillo to Birdsville we had been airborne for five hours and 40 minutes; we had stretched the Sokol to its absolute limit of endurance.
The technicians at Parafield Airport assured us that the plane would be ready on 7 August. Meanwhile, Bonython had asked us to report directly to him on 6 August about the progress of our survey and he quizzed us intensely on our opinion about the hydrocarbon potential of the structures. He told us that Dr AI Levorsen (world-renowned American petroleum geologist) had contacted a few American oil companies who had shown interest to join Santos in its search in the Great Artesian Basin. We assured him that we had located more than half a dozen anticlines so far. Each one of them had to be regarded as a potential oil structure and we were confident to locate additional structures in the course of the remaining survey.
We recommenced the survey on 7 August, this time focusing on the Santos licence area in Queensland. We began in its southern part, between Cooper Creek and the southern margin of the Great Artesian Basin near Tibooburra (NSW), including the Stokes Range, the Naryilco and Orientos anticlines and the Durham Downs structure. After that we took a day off flying to put our observations onto the map. As we progressed, the map started to reveal an exciting pattern of anticlinal and synclinal structures. What remained now were the eastern and northern portions of Santos' Queensland licence.
Using Cordillo Downs as a base, we investigated the southern Grey Range and the region between Wilson River, Nockatunga Homestead, Plevna Downs and Mount Howitt. One day we had been delayed by refuelling at Windorah and some additional traverses across the Coleman Range and it was almost dusk when we flew the last survey line in the Grey Range. Recalling a previous invitation from the people at Mount Howitt Station to call on them whenever we needed to do so, we headed for their air strip and landed in the very last light of the day. We were heartily welcomed and, as in so many similar experiences like at Etadunna, Orientos, Plevna Downs and Cordillo Downs, the natural unreservedness with which the most generous hospitality was extended to us was absolutely astounding. Two days later we received a
telegram from the Department of Civil Aviation, severely reprimanding us for taking the risk of such a late landing.
After finishing the survey of the area around the central and northern Grey Range we focused our attention to the remaining, 'uncharted' area, roughly between Windorah, Davenport and Warbreccan. On 16 August we flew our last survey between Cuddapan, Davenport, Curralle and a last sortie across Morney Dome. It was the last time Brunnschweiler and I should fly together. Since our return from Adelaide we had spent 42 hours and 25 minutes in the air. The total flying time which had gone into the preparation of the map was 136 hours, an achievement we were proud of (Figure 6). Before Brunnschweiler left we added the results of our last observations, thus Brunnschweiler had a finished draft version of the structure contour map to take with him to Adelaide. He added an appropriate legend and had the map drawn up under the Geosurveys drawing number SAN 167 (Figure 7). On 17 August Brunnschweiler left for Adelaide and I returned to our base at Haddon Downs.
Conclusion
The structure contour map was one of the most important documents to interest American oil companies to join Santos in its exploration venture in the Great Artesian Basin. In 1958 a checkerboard-style agreement for Santos's Great Artesian Basin exploration tenements was established between Santos and American company Delhi-Taylor Oil Corp. The map provided the best argument against the widely held, preconceived idea that the basin was lacking anticlinal structures. The map has stood up well to the test of time – the general configuration of the structures has been verified by seismic surveys and many of the structures contain productive oil and gas fields (Sprigg 1993).
Unfortunately, it was also the cause for Brunnschweiler to resign from Geosurveys. I didn't learn of his resignation until I returned to Adelaide in the middle of October 1957. Brunnschweiler had already left town, but he had posted a letter to my Adelaide home in which he told me of his resignation and that he was negotiating for the position of exploration manager with Timor Oil Company. He said Sprigg had refused permission to publish our structural contour map in an Australian journal under our joint authorship. So, when Sprigg (1993) wrote that "Brunnschweiler refused to join with me in writing an article describing our new finds", it was only half the truth.
Subsequently Sprigg (1958) published the map as Figure 8 in an article entitled Petroleum prospects of the western parts of the Great Australian Artesian Basin.
Apparently the map was not submitted to the South Australian Department of Mines. The original and possibly only remaining copy of the map was in my possession in Germany until 2009 when I brought it back to Adelaide to be
lodged in the archives of the State Library of South Australia (O'Neil 2010).
After the survey the Sokol was due for its 5000 hour inspection. A month or so after the aircraft had gone in for service I met one of the mechanics. "You guys", he said, "have been flying on spit and charm. At least 15% of the glue points in wing and fuselage have come unstuck".
References
O'Neil B 2010. An important map returns – 1957 structure contour map of the western Great Australian Artesian Basin. MESA Journal 58:30. Department of Primary Industries and Resources South Australia, Adelaide.
Sprigg RC 1958. Petroleum prospects of western parts of Great Australian Artesian Basin. AAPG Bulletin 42(10):2465-2491.
Sprigg RC 1993. A geologist strikes out, recollections, 1954–1993. Arkaroola Pty Ltd, South Australia.
Wopfner H 2011. Aerial mapping of Santos's licence areas in South Australia and Queensland, 1957, Report Book 2011/00011. Department of Primary Industries and Resources South Australia, Adelaide.
See Wopfner (2011) for a mpre detailed account of this article.
