Site Selection Process and Definitions

Sites of Geological and Geomorphological Significance in the Shire of Otway (1984) by Neville Rosengren. Environmental Studies Series: No. 399. Dept. of Conservation, Forests and Lands, Victoria.  

Geology is a diverse science which deals with the physical and chemical properties of rock materials, their internal texture and structure, external geometric form and dimensions, and their mutual relationships in time and space. Geological investigations range in scale from the sub-atomic e.g. the internal structure of minerals and crystals to the continental and global e.g. the division of the earth into tectonic plates and analysis of the evolution and mobility of these global units. The emphasis is on the delineation of localities, which may be recognised in the field although detailed analysis of some features may only be undertaken in the laboratory. Much geological data is obtained by recovery of materials by drilling the sub-surface or by remote sensing their properties e.g. analysis of seismic wave motion generated by earthquakes or by artificially introduced shocks from explosion or percussion. This report does not include an assessment of localities where this type of remote survey is important, as they are barely affected by changes in surface form or land use.

Geomorphology is that branch of geological science traditionally concerned with the origin and configuration of landforms. More recent work has tended to emphasise the importance of measurement of processes operative in landscape development rather than the mere description and classification of surface configuration. This involves a rigorous approach to the measurement of the movements of liquids and gases in the atmosphere, on the surface and subsurface of soil, sediment and rock. The geomorphological sites have therefore been selected on the basis of both approaches to the study of landforms as well as sites which have potential for detailed process studies. Although soils are a component of many landforms, it is considered that an assessment of soil variation as a criterion for site selection is beyond the scope of this report. Hence, no sites have been determined solely on the basis of soil characteristics.

All landforms to some degree reflect the nature of geological materials, especially those related to broad scale structures or those developed on hard rocks with distinctive lithology, bedding, folding or fracture systems. Therefore the report is not separated into distinct geological and geomorphological sections, as such a division would to a degree be arbitrary. The emphasis of this report is on the selection, assignment of significance and management of the site, rather than on site description. I have also not attempted to provide a full geological and geomorphological analysis of each site but rather a summary and emphasise on aspects which are of greatest significance.

The sites are represented in the text on extracts from a 1:25 000 map series of the shire. Each site has a map number which identifies the sheet in the above series, followed by a site number on that sheet, e.g. 14.1 refers to sheet 14, site 1. This site number does not refer to the significance or priority rating of the site. The site description includes a six-figure grid coordinate reference, which locates the site exactly or defines the approximate central point of a larger area site. Some of the larger sites have several grid references to delineate their boundaries. The grid coordinates are identical with those on the National Topographic Map Series 1:100 000 sheets. A composite sheet reduced to 1:50 00 scale showing the distribution of all sites is included as Appendix I.

Sites have been selected on the basis that they display one or more of the following characteristics:

Geological:

a. An outcrop or other exposure which has been used as the type locality of a geological material e.g. the coastal cliffs northwest of the mouth of the Gellibrand River which are the type section for the Gellibrand Marl.

b. A site which displays a contact between formations, e.g. the angular unconformity between the Mesozoic and Tertiary sediments that is visible in the coastal cliffs east of Point Margaret.

c. An area with extensive outcrop that is used to determine the lithological and structural characteristics of a rock formation or group, e.g. the sedimentary beds exposed between Moonlight Head and Castle Cove.

d. An exposure of a geological structure, e.g. the small plunging folds at the western end of Milanesia Beach, or the scarp of the Colac Fault north west of Carlisle River.

e. Beds that contain fossil material, e.g. the outcrops at the Chapple Creek ford on Morris Track which contain fossil plant materials.

f. Sites which display a rare mineral e.g. the bentonite at Gellibrand, or sites of historical interest as a record of past mining or quarrying activity, e.g. the Gellibrand shale pits.

Geomorphological:

a. Sites which show the influence of lithology (rock type) in landform development, e.g. the distinctive hill east of Gellibrand corresponding to the outcrop of Older Volcanic basalt.

b. Landforms that display the control exercised by geological structures, e.g. the ramparts on the shore platforms near Wye River or the parallel drainage patterns in the northwest of the Shire near Simpson.

c. Sites which display the action of a geomorphological process e.g. weathering at Rotten Point, stream potholing above Cumberland Falls, and the landslip that blocks the Barwon River to form Lake Elizabeth.

d. Landforms or materials that clearly reflect the action of a geomorphological process that is not operative at the present time or does not operate with the same intensity, e.g. the coastal terraces at Marengo which indicate higher Pleistocene sea levels and the abandoned boulder beach at Boggaley Creek.

e. Sites which are representative of the major landform units of the Otway Ranges and the adjacent plains and piedmont downs e.g. the section of the Gellibrand River south of Carlisle River where the valley is constricted and the floodplain has well developed levee banks.

Site Descriptions:
For each site, a statement has been prepared detailing:

Locality
Grid reference, position in relation to a prominent feature on the mapsheet, e.g. town, highway, mountain.

Access
Name of the closest road, vehicular track, walking route, or if a boat is needed.

Ownership
Distinguished as Crown Land or private land.

Geology
Name and description of major rock types, structures, or fossils.

Geomorphology
Name and description of main landforms and geomorphic processes.

Significance
All sites have been assigned a significance rating of either International, National, State, Regional, Local, or Unknown significance. The latter category is used where there is insufficient information about the site to allow a significance assessment to be made. In some cases this is due to the site not being located during field work and the assessment is based on aerial photograph interpretation only. Supplementary information could be made available about these or other new sites at a later stage.

Factors considered in determining the significance rating were:

a. The contribution the site makes to understanding in the earth sciences, in relation to geology and/or geomorphology on a local, regional, state, national, or international basis.

b. Frequency of replication, i.e. if the site is a unique, rare or unusual example of a geological formation and/or surface morphology.

c. Degree of disturbance and/or quality of display of outcrop structure, or landform.

d. Value as a reference and research site, displaying classic characteristics of a geological formation and/or a relict or active geomorphological process.

e. Need for further investigation - where there is doubt as to the nature or origin of the feature, or where little detailed investigation has been undertaken.

f. Where landforms and/or outcrops provide spectacular landscape.

The actual rating assigned to a site is determined by evaluating the degree to which the six criteria outlined above are fulfilled.

International Significance: These are landforms, structures, rock formations or fossils which are rare in the world and/or by the nature of their scale, state of preservation or display are comparable with examples known internationally. They include some of the fossil sites and the coastal slopes near Lion Headland. They would be included in an international register of sites of scientific significance.

National Significance: A site of National Significance is either unusual or unique in Australia and has been minimally disturbed or modified so that the essential properties of the site are clearly displayed. The site represents a major contribution to the research and teaching of the earth sciences in Australia and has the potential for further research, often in several fields. This applies to some of the fossil plant sites where species are recorded that are uncommon or unknown in other Mesozoic rocks in the continent.

State Significance: These sites include features which are important in the context of developing an understanding of the geological and geomorphological development of Victoria. They include several stratigraphic sites, e.g. the type sections of Tertiary rocks in the Aire, Johanna and Princetown districts, and the river gorge and rapids of the Aire River.

Regional Significance: These sites include landforms or rock types representative of the Otway region, for example the meander patterns of the Gellibrand River, or some of the common structural features of the Otway Group rocks, e.g. the dip and jointing of the arkose in the shore platforms near Skenes Creek.

Local Significance: These are typically clear examples of very common landforms, e.g. the constricted lower valley of the Barham River near Paradise or the back-swamps of Chapple Creek at Chapple Vale.

Unknown Significance: Some sites are awarded this rating if there is insufficient data to allow a more complete assessment to be made or if the site could not be located in the field during this survey.

The concept of significance is difficult to quantify satisfactorily as significance can be assigned various meanings (Joyce and King, 1980). The earth's surface is a mosaic of interacting components. From the geological and particularly the geomorphological point of view, the entire land surface is significant, in that the form and evolution of one part may contribute to understanding the nature of all the others.

The purpose of selecting sites of significance is to represent the array of land form and land forming processes that comprise the present landscape. Many sites display features that are relict, in that they represent geological processes (either climatically or tectonically controlled) that are no longer active. However in some cases, the sites are of interest for their dynamics where the landforms are subject to change over time, at a rate that can be measured and analysed.

Management
Each site has been assessed to determine the extent to which the features of significance are being or could be degraded by current land use, or be effected by a change in land utilisation at or adjacent to the site. This sensitivity of site characteristics is summarised by classifying the site in one of three broad classes as explained below.

Class 1. These are sites most sensitive to change either because the feature is small and hence easily obscured, removed or detached, or is of 'delicate' structure and so liable to be broken, displaced, mobilised or damaged in a direct physical sense. The interference may be direct or primary, e.g. burial or quarrying of a rock outcrop or the regrading of a slope. It may however be indirect, e.g. vegetation clearing adjacent to a lake alters run-off and groundwater movement and may cause the lake to rapidly infill or dry out and desiccate and allow deflation of an important pollen bearing peat horizon.

Class 2. These are sites of moderate sensitivity which may tolerate some degree of accelerated change and still retain the essential features of significance. This may be due to the site being large or consisting of numerous similar forms which are independent or self-contained in the properties they display.

Class 3. These typically are large sites displaying a macro variation in relief or geology which is unlikely to be obscured or removed. The site may demonstrate a major terrain pattern e.g. a recurrence of ridges and valleys, where intensive or point disturbance will not alter this essential broad geometrical characteristic.

The allocation to a sensitivity class is independent of the significance rating assigned to a site.

A short statement is provided which indicates the degree to which disturbance to the site will alter its geological or geomorphological value. This statement must be taken as a broad guideline only and it is emphasised that specific land use proposals, must be evaluated in terms of the degree of alteration they would cause to a particular site. The value of some geological sites may be enhanced by controlled excavation. Hence, road widening, new cuttings or limited quarrying may, by exposing new and fresh sections, be compatible with the maintenance of the site as one of geological significance. However, the total impact of such operations needs to be taken into account as the removal of strata that contain restricted fossil deposits for example, or the production of rock debris that obscures an existing outcrop, may seriously degrade the value of a site.

In areas of limited outcrop, quarries and road-cuttings often provide the major exposures upon which stratigraphic, lithological and palaeontological studies are based. Quarry management, particularly in such areas, should endeavour to preserve those sections which are instructive in terms of understanding the geology of the area. McKenzie (1980) has listed a set of guidelines for quarry management. The guidelines numbered 1 to 3 have particular relevance to sites of significance. However, it is suggested that guideline 3 - "all quarries should be reclaimed after production ceases" - be modified to allow for the retention and maintenance of any quarry faces which display important geological features.

The management statement presented with the sites has not attempted to specify all possible sources of disturbance and it is stressed that land use proposals must be assessed in view of their particular impact on the quality of these sites.

Some sites, by their dynamic or unstable nature, present a real or potential hazard to property and this risk has been indicated for a number of sites. Proposals for land use changes at such localities must take this factor into account.

References:

Joyce, E. B. & King, R. L., eds, 1980. Geological Features of the National Estate in Victoria. Geological Society of Australia, Melbourne, i - x, 208.

McKenzie, D.A. 1980. Scoria and tuff quarrying in Victoria. Geological Survey of Victoria. Report 1977/9. Reference ID: 37872.