Geology and Geomorphology

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The oldest outcropping rocks in the Rutherglen area are of Ordovician age. These are marine deposits (sandstone, siltstones, shales, mudstones) that were laid down in a deep ocean basin between approximately 440 - 500 million years ago. During this time, Australia was part of a much larger continent (Gondwana) and did not lie in its present position. It is estimated that during the Ordovician period, for instance, Victoria was located within 20 degrees of the equator. Marine sedimentation finished before the end of the Ordovician period and these sediments were subjected to significant faulting and folding.

During the early Devonian period (approximately 400 - 420 million years ago) large masses (plutons) of granite and granodiorite were intruded through some of the Ordovician sediments. As a result of millions of years of erosion a number of these granite intrusions are exposed today. These form the highest areas in the region such as Mt. Barambogie and Mt. Pilot. Some of the sediments around the edges of the intruded granite have been metamorphosed (changed) into harder rock which is relatively resistant to erosion e.g. mudstones or shales can be metamorphosed into slates, schists or gneiss depending on the intensity of metamorphism. These metamorphosed sediments now form crescent-shaped ridges e.g. the Skeleton Hills, which have been left behind as the softer surrounding rock has eroded away.

During the relatively recent Quaternary period (from approximately 1.6 million years ago), areas of older marine sediments have been covered by mainly alluvial deposits (clays, silts, sands and gravels) called the Shepparton Formation. Lacustrine (lake) and aeolian (wind) deposits also occurred in some areas. The Shepparton Formation deposits can be more than 50 metres deep in some areas. Most of these deposits originated from prior streams. A range of soils have developed on and near these prior stream channels. Some soils have developed as a result of over-bank flooding e.g. lighter sandy loam soils on relic levee areas, grading to heavier clay soils on the more distant lower level plains. Coarse grained sands and gravels were also deposited in prior stream channels.

References

Land Conservation Council (1974). Report on the North Eastern Study Area (District 3,4&5).

Cochrane GW., Quick GW., and Spencer-Jones D. (Ed.) (1991). Introducing Victorian Geology, Geological Society of Australia (Victorian Division).

Poutsma, T.J., and Skene, J.K.M. (1961). The Soils of the Rutherglen Research Station, Victoria. Technical Bulletin 12. Department of Agriculture, Victoria.