Geology and Geophysics of the  Offshore Maryborough,  Capricorn and Northern Tasman Basins: Results of AGSO Survey 91

The Australian Geological Survey Organisation (AGSO) completed a major marine multichannel seismic (MCS) reflection survey off southeast Queensland in December 1989 using RV Rig Seismic. The research cruise (AGSO Survey 91) was designed to investigate the structure, stratigraphy and evolution of offshore basins along this sector of the Australian continental margin. About half of the 2900 km of seismic data collected was recorded over the offshore Maryborough Basin; the remainder was collected over the Capricorn Basin and margins of the northern Tasman Basin. The survey included seismic ties to the only deep offshore wells in the region, Aquarius 1 and Capricorn 1A located in the northern Capricorn Basin. It was the first MCS survey shot in the region since 1974.
Sonobuoy refraction, gravity, magnetic and bathymetric data were also collected.

The Maryborough Basin developed in the earliest Triassic - mid Jurassic as an epicratonic downwarp, probably a foreland depression. Neocomian volcanism and rifting, perhaps generated by transtensional movements, led to a second phase of deposition that produced thick elastic shallow marine and deltaic sequences. Subsequent basin inversion in the mid Cretaceous produced major folding along northwest/NNW axes as well as normal and reverse faulting. Peneplanation following uplift has eroded up to several kilometres of section from the basin, leaving it as a remanent basin. The main causes of the uplift are believed to be (i) the mid Cretaceous deformation episode, (ii) rift flank uplift as the adjacent northern Tasman Sea opened (-63 Ma ago), and (iii) rise of the Eastern Highlands in the Late Cretaceous - Cainozoic due to crustal underplating associated with detachment
faulting and transit over mantle plumes.

Up to 5 km of the Early Cretaceous Maryborough Formation (shallow marine elastics) and Burrum Coal Measures are preserved in a NNW-trending syncline beneath the western side of Hervey Bay, just off the coast northeast of Bundaberg. Depth to basement may be as much as 9-10 km. No major anticlines in the Early Cretaceous units are present beneath Hervey Bay. However, small culminations may exist in the more flat-lying strata of the basin deep northeast of Bundaberg.

Reinterpretation of onshore seismic data in the Maryborough Basin has provided new insight into the structural configuration of this part of the basin. 

Survey 91 established that the Maryborough Basin does extend beneath the continental shelf southeast of Fraser Island. The section is folded and faulted, with broad anticlinal structures present. Seismic data quality in the Cretaceous and older section is poor in this area, perhaps a consequence low acoustic impedance contrast (?tight formations). Much of the shelf is underlain by about 2.0 s twt (-4 km) of Maryborough Basin section. A major syncline in Wide Bay contains up to 5 km of Early Cretaceous sediments. Basement here may lie at 8-9 km depth.

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Tags: Earth Sciences, GA Publication, Record, geology, geophysics, marine, marine survey
Organization: Geoscience Australia