Discoveries of lumps of bitumen, weighing as much as several kilograms, have been recorded on beaches from Fremantle to Tasmania since the beginning of European settlement.

A large proportion of the specimens found over the past 200 or so years were washed up near Beachport in the southeast of South Australia and on Kangaroo Island.

This concentration of discoveries was a big factor in the location of Australia's first oil exploration well in the Coorong district in 1866.

Previous studies, notably a PhD by Geoscience Australia's Di Edwards, had shown a remarkably uniform composition across the many samples of bitumen, more commonly known as asphaltite.

This suggested a single source of origin.

Edwards' colleague, Chris Boreham, also narrowed down the source to a Cretaceous rock that is distinctive of restricted marine environments, probably related to an oceanic anoxic event.

Academics and oil explorers have not been able to have more confidence in the location of the source.

An answer, however, is finally becoming clear thanks to a PhD by University of Adelaide's Tony Hall.

Hall has developed a method for solving the mystery by studying the weathering characteristics of the samples and combining this with information about ocean currents on the southern margin.

His conclusion is that the source is probably the underexplored Morum sub-basin of the Otway Basin, located under the edge of the narrow continental shelf running along western Victoria and southeast SA.

"There is a very strong likelihood in data produced so far that the Morum is certainly host to a source of these asphaltites," Hall said.

"There is a reasonable likelihood of other source pods - maybe another one in the southern area of the Ceduna sub-basin - but we also know the likely source rocks are not exposed in that location."

Hall's work is one chapter in a much larger PhD on the biogeochemistry of wide areas of SA, with a particular focus on Cambrian shales.

The PhD was encouraged by Hall's supervisor, David McKirdy, who began studying asphaltites in the 1970s.

McKirdy in turn followed Reg Sprigg, who was one of the world's great biogeologists and instrumental in the foundation of Santos and Beach Energy.

Hall's study was based on a small sample of only 11 asphaltites but four of these were from new locations - the Eyre Peninsula and Invercargill in New Zealand - and had not been studied previously.

His PhD could have immense value for petroleum explorers in the western Otway Basin, where bidding closed last month on an area (S12-4) released in May by the federal government.

The value of study lies not just in the identification of the likely source but also in an understanding of how the asphaltites most likely formed.

Hall told Energy News the fine laminations and flow structures in the asphaltites suggested they were viscous in the subsurface environment, before being extruded on the seafloor.

"We are now seeing asphaltites with these structures in the Gulf of Mexico - where it is very unusual for any to be washed ashore - but a number have been recovered in recent years by remotely operated vehicles," he said.

Hall said there were two possible mechanisms for the formation of the asphaltites.

One possibility was precipitation out of an oil reservoir that was subjected to an in-flood of gas.

The more favoured explanation was a subsea outcrop of a tar mat.

Tar mats are a sticky trail of residue left behind by oil as it migrates, particularly along flat-lying pathways.

For oil explorers, a tar mat is evidence of substantial oil charge and also points to where potential reservoirs might be found.

Hall said seismic surveys over the deep canyons on the edge of the continental shelf off southeastern SA had shown these probably incised the Cretaceous rocks considered to be the source of the asphaltites.

"It's very unusual to have a tar mat outcropping on the seafloor but of course there's no reason for it not to happen," he said.

"We also have a number of factors that explain why they are washing up along the coast after a number of decades rather than staying in deep water.

"Similarly to the specimens in the Gulf of Mexico, our asphaltites have almost the same density as water.

"However, unlike the benign deepwater conditions of GoM, the southeastern region is an area of earthquakes which help to dislodge the specimens and there is also a strong upwelling current along those canyons that brings them up onto the shelf."

The asphaltites are highly unusual in a global sense, with similar occurrences only in the GoM and the Dead Sea.

Hall is continuing to investigate what local explorers might be able to learn from any analogies between the Dead Sea and the asphaltites of Australia's southern margin.

In the meantime, his PhD has paved the way for a much larger study on oil seepages and asphaltites in the Great Australian Bight.

The study will begin with a three-year baseline survey of all occurrences on beaches throughout the Bight.

The study is being funded by CSIRO and BP and will be managed by the University of Adelaide's Sprigg Geobiology Centre.

That centre was officially opened by its director Martin Kennedy last month.

David McKirdy has been enticed out of retirement to supervise the study by a PhD student.

Hall said funding for the PhD had recently become available and the Sprigg Geobiology Centre was looking for applicants to take on what will be a major and very exciting study.

Anyone interested in the opportunity should contact David McKirdy through the university.

BP is spending hundreds of millions of dollars on exploration in the Bight in the hunt for giant oil deposits.

It will be vitally interested in the outcome, along with unlisted Bight Petroleum and other explorers which have been pushing the government to release acreage in the region.