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Abstract: Sequence Stratigraphy and Coastal Sedimentary Evolution of the Late Quaternary Brisbane River Delta, Southeast Queensland, Australia

HERDY, TRINETTA J.

The Brisbane River is a large subtropical estuary in southern Moreton Bay, southeast Queensland, Australia. Influx of fluvial sediment has formed an extensive Late Pleistocene to Holocene delta covering an area of approximately 300 km{2}.

The study aims to develop a sequence stratigraphic model for a delta of mixed fluvial/tidal influence, useful for petroleum exploration in similar settings. Additionally, the work provides a valuable and timely baseline environmental study of an area soon to be subjected to extensive Port development.

Vibrocoring and seismic profiling have been undertaken to determine the stratigraphic evolution of the delta system during the post-glacial period. A closely spaced seismic grid, covering an area of 1.5 km{2} at approximately 100 m spacing, was recorded over the subtidal part of a major distributary mouth bar complex. A substantial geotechnical drillhole database was utilized to aid interpretation.

The seismic profiles show several unconformity-bounded sequences. The youngest sequence comprises a well-developed incised valley fill succession of early transgression fluvial gravel and sand, topped by late transgressive estuarine mud and silt (18,000 - 6,500 years BP). The upper half of the sequence contains progradational deltaic sand and silt formed by the late Holocene stillstand (6,500 years BP to present).

The depositional model involves an incised valley complex (less than 30 m deep and 1 km wide) with an adjacent interfluve cut by smaller tributaries (less than 15 m deep and 1 km wide). The channel facies would have possible reservoir potential, are sealed by estuarine mud, and topped by. deltaic sand and silt with intermediate to good reservoir potential.  

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid