AIM:The Cape Grim to Cape Jaffa Marine Seismic Survey was undertaken by Haematite Explorations Pty Ltd in its petroleum exploration leases held over the Otway Basin, to provide subsurface seismic reflector data along the narrow continental shelf from Tasmania, through western Victoria to southeastern South Australia, and to provide better quality data in the South Australian part of the Otway Basin. The initial single spread seismic coverage acquired in 1963 during the Flinders Island to Kingston Marine Seismic Survey had provided moderately useful but not good quality data.METHODS: Survey dates: 14/12/64 - 7/4/65. Energy source: Explosives. SP coverage: 300% generally, and 600% on 5 selected lines. Recording mode: 24 channel analogue - Western FA 40 recorder. SP interval: 1500 feet; group interval: 200 feet.RESULTS:52 reflection lines (19 offshore of SA) containing 8069 profiles were recorded by acquisition contractor Western Geophysical Co. of America using the M/Vs F.B. Walker and Miss Freeport as dedicated shooting and recording boats respectively, for a total of 1553.50 miles of 3-fold common depth point coverage, plus 320.625 miles of single-fold coverage concentrated in the area west and southwest of King Island. Playback processing of the field tapes was performed by Western in its Perth, WA office. The use of CDP shooting procedures has clearly provided better quality data over the whole of the Otway Basin sedimentary extent, bearing out the original intent of this survey. The maps presented with this report incorporate data prepared during a regional basin study of the Otway Basin conducted in co-operation with Frome Broken Hill Co. Pty Ltd, Alliance Oil Development NL, Planet Oil Co. NL, Beach Petroleum NL and the SA Department of Mines, who allowed the use of their most recent geophysical and drilling results.The seismic results have been integrated into the geological history of the basin. However, the shape of the offshore area and the broad reconnaissance nature of the survey make it impractical to attempt to carry seismic events as a single map. Accordingly the major mapping units here chosen for contouring are: - the unconformity at the base of the Tertiary, - basement configuration, and - an horizon within the lower Tertiary (not carried over the whole survey area). Several areas of promising petroleum potential within all the tenements of Haematite's offshore Otway Basin acreage were outlined by the combined results of the 1965 and 1963 seismic surveys. A recommendation has been accepted by management to farm out the entire area to a major exploration company, on a similar basis to Haematite's May 1964 farm-out of the Bass and Gippsland Basins. The results of the Cape Grim to Cape Jaffa Marine Seismic Survey have demonstrated that the stratigraphy of the Otway Basin must henceforth be considered broadly in terms of just two units - Mesozoic and Tertiary - each forming a distinct sedimentary basin and being separated by a major hiatus and angular unconformity. There is now little justification for continuing to look upon the basin in terms of two to five embayments.Results from onshore drilling allow some broad divisions of the Mesozoic, the main one being based on lithologic character and the presence of marine fossils assigned to the Upper Cretaceous. Zoning from spores and pollen and from petrographic studies has also been possible. From the recent seismic profiles of the offshore area, however, such subdivisions have not been feasible. Therefore only the generalized divisions most applicable to the offshore conditions have been used. For purposes of reference the term Mesozoic is used where Otway Group and Upper Cretaceous are indistinguishable.The onshore Tertiary strata are well known and have been broken down into two generalized rock units and into several correlatable formations. Some geologists classify as unconformities the variation in thickness and character of sediments associated with formation boundaries: but only the unconformity separating the Tertiary from the Mesozoic is of regional extent and conspicuous because offshore the Tertiary dips south, whereas the Mesozoic dips north. It has now been mapped over the entire basin by means of the seismic records. Within the Tertiary depositional irregularities are conspicuous, especially in the upper beds. The entire Tertiary disappears on the continental slope through progressive foreset bedding. Only two portions of the Otway Basin have been affected by large-scale movements, the Otway Horst - Anglesea area and the southern edge of the basin. The majority of the basin sediments appear little disturbed and what structures are present comprise normal faults, gentle uplifts and fold-like structures. Only those in the offshore area, or southern half of the basin, have been begun to be mapped in detail. The latest survey has outlined 5 areas in which the search for potential drilling locations should be concentrated: (a) an area of Mesozoic folding south of Mount Gambier, covering approximately 25 miles x 6 miles in less than 500 feet water depth; (b) a Mesozoic fault trap and associated tilting of the Tertiary west of Lake Bonney, over an area 30 miles x 6 miles, 85% of which is in less than 500 feet water depth; (c) two Mesozoic pinchout structures west of Beachport and Robe respectively, both covering broadly 40 miles x 5 miles, 80% being in less than 500 feet water depth; (d) a Tertiary nosing feature southwest of Cape Otway, covering 10 miles x 20 miles of which only 10% is in less than 500 feet water depth; and (e) folded pre-Tertiary sediments west of King Island - more study is required to establish the nature of these sediments. Notes: These geological consultant's reports form two sections to the final report of the 1963 marine seismic survey, Cape Grim to Cape Jaffa (PDF pages 32-51).