L032 Haddon Downs experimental seismic survey, SA, 1957

An experimental seismic survey was conducted at Haddon Downs, South Australia, during Octobor and November.1957. The area lies within the Eromanga Sub-basin of the Great Artesian Basin, and at least 5,500 feet of Mesozoic section are known to exist there, part of which is of a marine facies. Preliminary reconnaissance work by geologists of Santos Ltd. which holds an Oil Prospecting Licence over thearea, revealed some large anticlines on the surface. The Company has already completed a limited amountof gravity work which gives promise of supplying useful information on both regional and detailed subsurface structure.Two important refractors were recorded which may be useful for semi-regional mapping. A refractor of velocity 10,250 ft/sec. was recorded from a depth of about 2,700 feet, and this may represent the top of the marine Cretaceous section. The second refractor of velocity 17,000 ft/sec. and aidoroximate depth 7,250 feet may be just below the base of the Mesozoic section.Large multiple geophone arrays and pattern shots were needed to obtain good quality reflections over most of the area, except when shooting on the alluvial plains of the larger creeks. The sedimentary section was shown to be at least 8,000 feet and possibly 16,000 feet thick, The base of the Mesozoic section is interpreted as being 7,250 feet deep on the refraction traverse and 8,600 feet at the south-east end of the reflecta.on traverse. The rest of the section probably consists of Palaeozoic sediments. If so, the high velocity (17,000 ft/sec.) suggests that a dense elastic or crystalline limestone is probably present near the top of them. The structure of the Mesozoic section is subhorizontal, but there may be minor structures with dips less than 1 degree which correlate with the surface structures.

1957年10月至11月期间，在澳大利亚南部的哈登唐斯（Haddon Downs）开展了实验性地震勘探（seismic survey）。该区域位于大自流盆地（Great Artesian Basin）的伊罗曼加次盆地（Eromanga Sub-basin）内，已知存在至少5500英尺厚的中生代地层（Mesozoic section），其中部分为海相（marine facies）。持有该区域石油勘探许可证（Oil Prospecting Licence）的Santos有限公司地质学家进行的初步勘察工作显示，地表存在若干大型背斜（anticlines）。该公司已完成有限的重力勘探工作（gravity work），有望为区域及详细地下构造（subsurface structure）提供有用信息。

记录到两个重要的折射层（refractors），可能对开展半区域制图（semi-regional mapping）具有价值。其中一个折射层速度为10250英尺/秒，深度约2700英尺，或代表白垩纪海相地层（marine Cretaceous section）的顶部；另一个折射层速度为17000英尺/秒，深度约7250英尺，或恰位于中生代地层底部之下。

除在较大溪流的冲积平原（alluvial plains）区域开展勘探外，大部分区域需采用大型多检波器组合（geophone arrays）与组合激发（pattern shots）以获取高质量反射波（reflections）。沉积地层（sedimentary section）厚度被证实至少为8000英尺，或可达16000英尺。中生代地层底部在折射测线（refraction traverse）上的解释深度为7250英尺，在反射测线（reflection traverse）东南端则为8600英尺。该地层其余部分可能由古生代沉积物（Palaeozoic sediments）组成；若然，其顶部附近或存在致密弹性或结晶石灰岩（dense elastic or crystalline limestone），这可由17000英尺/秒的高速特征佐证。中生代地层构造呈近水平（subhorizontal）状态，但可能存在倾角（dips）小于1度的小型构造（minor structures），且与地表构造（surface structures）具有相关性。