Mark Butler, the environment minister, has deferred a decision on whether to allow dredging at the Abbot Point coalport, near the Great Barrier Reef, citing new reports that could influence whether the project is approved.

Butler was due to decide by Friday whether to allow the dredging of 3m cubic metres of seabed to allow the Abbot Point port, near the Queensland town of Bowen, to double its capacity of exported coal.

But the minister, who previously delayed the decision shortly after being appointed in Kevin Rudd's ministerial reshuffle, has pushed the deadline back again to 8 November, well beyond the election.

Butler said a number of scientific reports, which he had only just received, required that he "stop the clock" on the decision. He has released the reports for public consumption.

One of them, funded by the government and handled by the Great Barrier Reef Marine Park Authority, found that modelling on the impact of dredging "indicates that dredge material placed at sea has the potential to migrate on a much greater scale than previously thought".

The dredging application, by North Queensland Bulk Ports, said the dredged waste would be dumped within the Great Barrier Reef marine park, a plan that has horrified environmentalists concerned about the impact on coral, dolphins, dugongs and other species.

Butler said: "For these matters to be fully considered I have stopped the clock on my department's assessment of the Abbot Point capital dredging proposal for a period of three months.

"This does not prevent a decision being made earlier if I believe I have enough information to make an informed decision.

"In addition I will be calling for public comment on the report of the independent review of the port of Gladstone."

The decision is likely to appease UNESCO's World Heritage Centre, which expressed surprise the government had not informed it of the plans to turn Abbot Point into one of the largest coalports in the world.

Earlier on Friday the Queensland government approved the mining magnate Clive Palmer's $6.4bn coalmine and rail project, which would link to the Abbot Point terminal.

The Alpha project, in the Galilee basin area of Queensland, will involve the clearing of thousands of hectares of vegetation that is the habitat of the endangered black-throated finch and more than 220 different types of plants.

Palmer said the project, which still needs federal government approval, would create 6,000 jobs during construction and nearly 2,500 during its operation.

The Greens senator Larissa Waters said Butler needed to reject, rather than defer, dredging at Abbot Point.

"No amount of extra information will change the fact that this plan would see 3m cubic metres of dredge spoil dumped in a World Heritage area," she said.

"We don't need to dredge and dump in the Great Barrier Reef to expand a coalport which will turn the reef into a shipping super highway, at the end of the fossil fuel era – we have renewable alternatives."

Jeff Seeney, the Queensland deputy premier, said the Abbot Point expansion was "crucial" to the future of the state and criticised the delay in Butler's approval for it.

"Kevin Rudd and his ministers simply cannot make the rational decisions that are needed to build the Australian economy and benefit the nation," he said.

"They have now stalled by another three months a decision on whether or not they will approve the important expansion plans for Abbot Point.

"A decision was due in early July. It was put off until today. Today it is avoided again.

"Rudd and his shambolic ministry are an unmitigated failure. Today they have abrogated any claim to deserve re-election."