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K1 Bulla - Kaolinized Granodiorite

This information has been developed from the publications:

  • Sites of Geological and Geomorphological Significance in the Western Region of Melbourne (1986) by Neville Rosengren
  • Sites of Geological and Geomorphological Significance on the Coast of Port Phillip Bay (1988) by Neville Rosengren.
  • Sites of Geological and Geomorphological Significance in the Shire of Otway (1984) by Neville Rosengren.
Geological heritage sites, including sites of geomorphological interest and volcanic heritage sites, are under regular revision by the Geological Society of Australia, especially in the assessment of significance and values. Reference should be made to the most recent reports. See the Earth Science Heritage section of the Geological Society of Australia website (external link) for details of geological heritage reports, and a bibliography.

LocationKeilor - 061327. Shire of Bulla. Eastern side of Deep Creek upstream of the Sunbury Road bridge.

K1 - Newer Volcanics lava flows overlying weathered granite, Bulla.
AccessTrack along river from Felspar Street.
OwnershipSome Crown land, some private land

Site Description

Abandoned quarries into the steep hillslope east of Deep Creek expose Bulla Granodiorite beneath Newer Volcanics lava flows. The granite is generally deeply weathered and the felspars have decomposed to kaolinite - a grey-white aluminium rich clay which has a number of industrial uses. In places there are concentrations of remnant quartz in the kaolin. At the lower levels in the quarry, along the track above Deep Creek, less weathered strongly jointed granodiorite is intruded by a number of aplite dykes up to 25 cm wide. In the quarry at the end of the track, there is a clear section exposing the base of the lava flows overlying the kaolinite.

State. The site is an outstanding example of deep weathering of granodiorite to produce an
in situ deposit of kaolinite. It shows clearly the uneven nature of subsurface weathering as fresh sections of granodiorite lie adjacent to deeply weathered ones. It is therefore an important site to demonstrate stages in the origin of boulders (tors). It also clearly displays the unconformity between the lava flows and the weathered granodiorite. It is readily accessible and is used extensively by schools and tertiary institutions as a teaching site.

Class 2. The unused quarry sections should be retained as teaching sites. No reclamation or filling should be permitted and they should not be used as refuse pits. In the longer term, access to the site could be improved by providing a parking bay or widening the intersection near the bridge to increase the safety for vehicles entering or leaving the site.
James, A.V.C. (1920). The Physiography and Geology of the Bulla/Sydenham Area.
Proc. R. Soc. Vict. 32:323-349.
Gaskin, A.J. (1944). Kaolinized Granodiorite in the Bulla/Broadmeadows area. Proc. R. Soc. Vict. 56:1-18.

Map:  K1K1

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