Terrestrial sedimentation in the southwestern Neogene Bland Basin, an alluviated palaeovalley in the Lachlan River Catchment, Eastern Australia  

Authors / CoAuthors

Gibson, D.L. | Tan, K.P.

Abstract

The Bland Basin is the broad alluviated palaeovalley of Bland Creek, a tributary of the Lachlan River in the central part of New South Wales, Australia, within the drainage basin of the Murray-Darling River System. It covers about 4000 km2 and contains up to 120 m of terrestrial sediments, interpreted as being deposited by alluvial, colluvial, lacustrine/paludal, and aeolian processes. It is undated, but is likely to be coeval with the downstream contiguous fill of the Lachlan River palaeovalley, dated elsewhere by palynology as Miocene to Recent. The southwestern part of the basin has been studied in detail using airborne geophysics (electromagnetics, magnetics, and gamma ray spectrometry) and drilling. The small erosional catchment area of the modern Basin surface has resulted in a paucity of sediment available for deposition in the Basin, but drainage base level has been driven by the rate of sedimentation of the Lachlan palaeovalley downstream of the Basin. Therefore, most of the sediment derived from the catchment has been trapped in the Basin rather than being transported downstream and into the Lachlan palaeovalley, and at times large lakes and/or swamps have formed in the central part of the Basin. The sediments in the southwest of the Basin are dominated by clay and silt, with local sand and gravel, mostly in basal gravelly sand and a sandier interval in the middle part of the sequence. Quartz silt derived from aeolian dust is a major component of the upper part of the sedimentary sequence. Geophysical responses of the sediment include high conductivity due to saline groundwater, low gamma response dominated by thorium decay emissions due to the leached nature of the sediment, and short wavelength-low amplitude magnetic anomalies resulting from local concentrations of detrital maghemite-rich gravel formed during weathering in the catchment area. Other broad valleys draining to the Lachlan River may contain similar mud-dominated Neogene basins.

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nonGeographicDataset

eCat Id

68497

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• sedimentary basins

( Theme )

• sedimentology

• AU-NSW

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2009-01-01T00:00:00

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Australian Government Security ClassificationSystem    

Classification - unclassified

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Creative Commons Attribution 4.0 International Licence    

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unknown

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geoscientificInformation

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Unknown

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Extents

[-35.0, -34.0, 147.0, 148.5]

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