Citation

Davies, P.J., 1979. Marine geology of the continental shelf off southeast Australia. Scale 1:1000000. Bulletin  195. Bureau of Mineral Resources, Geology and Geophysics, Canberra.

Abstract

The continental shelf of southeast Australia between Sugarloaf Point and Gabo Island, New South Wales, varies in width from 72 km east of Newcastle to 17 km east of Montague Island. Over much of this area an inner shelf zone (less than about 60 m water depth), a middle shelf zone (60-130 m), and an outer shelf zone (more than 130 m) can be distinguished by morphology and sediment type. Three groups of terraces are present, shallower than 60 m, between 70 and 110 m, and between 110 and 140 m. The shelf break lies between 130 and 170 m. There is a correlation between the depth of the shelf break and the depth of basement. It is likely that the morphology of the outer shelf is related to morphological variations in basement surface, which is the little-modified Atlantic-type rift scar produced during sea-floor spreading in the Cretaceous. The declivity of the upper continental slope is usually less than 2° to the north of Jervis Bay, but to the south it progressively increases so that slopes steeper than 10° are common. Ten submarine canyons or canyon-like features dissect the slope to the south of Jervis Bay. A sequence of sediments above acoustic basement (S2), thickening eastwards from the midshelf position, is shown in seismic profiles. This sediment wedge is divided into two parts by an unconformity (SI); the lower part is transgressive on S2, and the upper is progradative on SI, and is best seen offshore from the Sydney Basin. Twice as much sediment occurs on the narrow shelf south of Jervis Bay as on the wider shelf to the north. Basement highs crossing the shelf have been identified southeast of Sugarloaf Point and northeast of Jervis Bay; basement lows occur off Newcastle and off Disaster Bay. The probable axis of eastward tilt of the continental shelf in the mid-shelf position has been identified as a basement ridge or step. Tilting and the development of a sediment wedge have probably continued since the Late Cretaceous. Surface sediments are dominantly terrigenous in water depths shallower than 60 m; eastwards, carbonate components become increasingly dominant with increasing depth. Kaolinitic and chloritic muds occur as discrete zones in the mid-shelf area. Nearly all the shelf sediments are sands, with minor quartz or calcareous gravel occupying the inner and outer shelf areas. Fine to very fine-grained sands have a distribution similar to that of the muds. An unstable amphibole-pyroxene-epidote heavymineral suite occurs on the outer shelf, and a stable tourmaline-rutile-zircon suite predominates in water depths less than 60 m. The north-to-south variation in heavy minerals is similar to that in onshore localities, where ilmenite decreases and rutile/zircon increase from south to north. All sediments on the shelf are considered to be relict, with the possible exception of the muds which may be accumulating at present. Sediments between 15 and 60 m were probably deposited during the Holocene transgression; the mid-shelf sands and muds possibly represent a mixed barrier facies, and the outer shelf carbonates probably date back to the end-Wisconsin sea-level low. Sedimentation on the continental shelf at the present day is therefore limited to the zone 0-15 m, and possibly to the muds of the middle shelf. The principal controls on geochemical differentiation in the shelf sediments are depositional environment, provenance, and effluent input. Nickel, iron, cobalt, and cadmium occur predominantly in the middle and outer shelf sediments; carbonate, phosphate, strontium, and arsenic increase with depth; and copper, lead, and zinc occur principally in the mid-shelf muddy sands. Manganese is unusually deficient in east Australian shelf sediments. Zinc, arsenic, cobalt, and cadmium occur in concentrations considered high when compared with standard rocks and sediments from other continental shelves. This is a result of high input together with minimum
Google map showing geographic bounding box with values North bound -31.5 East bound 153.5 West bound 149.0 South bound -38.0
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Product Type/Sub Type

dataset - GA Publication - Bulletin

Constraints

license
Creative Commons Attribution 3.0 Australia Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

1979

Product Type

dataset

Topic Category

geoscientificInformation

Keywords

GA Publication
Bulletin
geology
marine survey
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-31.5
East bound
153.5
West bound
149.0
South bound
-38.0

Lineage

Unknown

Digital Transfer Options

onLine

DISTRIBUTION Format

pdf

Distributor

Role
distributor
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Metadata File Identifier

a05f7892-7f9e-7506-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

Metadata Date Stamp

1996-10-29

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

Role
pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Downloads
For information on acquiring this product,
please contact the Geoscience Australia Sales Centre via:

fax:
+61 2 6249 9960; or
phone:
1800 800 173 (within Australia);
 
+61 2 6249 9966 (outside Australia).

Please note that support hours are 9 am to 5 pm weekdays