Sites of Geological and Geomorphological Significance in Merri Creek

Photo of Barry Road Gorge unconformity at Galada Tamboore, Cambellfield.

This part of MCMC's website is heavily based on a report prepared for MCMC by Neville Rosengren, Latrobe University Bendigo in 1993.

A full copy of the report can be purchased from MCMC.

Prepared for: Merri Creek Management Committee Incorporated.

All views expressed are those of the author and are not to be taken as the official position of the Merri Creek Management Committee.

A Google Earth virtual tour of the Merri Creek Catchment's geological and geomorphological sites is available here. You need Google Earth version 4 or above for the tours to work.

 

TABLE OF CONTENTS

 
 

2.1 Geology

2.2 Geomorphology

2.3 Modifications to the Merri Creek Valley and Channel.

CHAPTER 3 - SITE LISTINGS

3.1 Alphabetical List of Site Names

3.2 Significance Rating List

3.3 Municipality Site, List

REFERENCES

INDEX

 

ACKNOWLEDGMENTS

I am grateful to Sigrid Kraemers and Rod McLellan (the previous and current Managers of the Merri Creek Management Committee Incorporated) for establishing and supporting this project. This study was funded through the Federal Governments National Estate Grants Program - Project No 747

SUMMARY

This study identifies sites of geological and geomorphological significance in a corridor of variable width along the Merri Creek valley in the Municipalities of Whittlesea, Broadmeadows, Preston, Coburg, Northcote, Brunswick and Collingwood. Edgars Creek and Central Creek were also studied. The corridor includes Public Land and some private land. Although much of the area studied has been greatly modified by the impact of European settlement, a variety of authentic geological features are displayed. As many of these are safely accessible to the public, there are opportunities for geological education and interpretation. A total of 38 sites is identified as significant. Four sites are significant at the State level, 16 at the Regional level and 18 at the Local level.

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Map of Merri Creek and its catchment

Figure 1. Study area location.

 

 

 

Chapter I

SELECTION OF SIGNIFICANT SITES

1.1 STUDY AREA LOCATION

This study of part of the Merri Creek catchment is in response to a brief from the Merri Creek Management Committee Inc. The brief required the consultant to document sites of geological and/or geomorphological significance in the Merri Creek valley and to provide guidelines for management of sites with particular regard to "...site sensitivity, potential threats ...and potential utilisation of the site."

The study has examined a corridor of variable width along, the Merri Creek valley south of the boundary of the Shire of Kilmore at Wallan East Road to the confluence of the Merri Creek and the Yarra River. Edgars Creek south of Cooper Street and Central Creek were also studied (Figure 1). The corridor includes Public Land adjacent to the creek in the metropolitan area and private land in the adjoining rural areas. This is an area of flat to gently undulating terrain developed on flows of basaltic lava from Mount Ridley, Bald Hill, Mount Fraser and Hayes Hill. Stream valleys cut into this lava surface comprise the main elements of relief and terrain variation and provide exposure of the basalt and in places older sedimentary rocks. Despite a long history of disturbance in the catchment by agriculture, extractive industry, flood protection and landfill, there is much to interest the earth scientist in this landscape. Natural outcrop in the bed and valley slopes is supplemented by exposures of rock in road cuttings and abandoned quarries and these can provide the basis for a natural history interpretation of the region. It is important that the planning of access, recreational facilities and general landscaping works takes these geological features into account.

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. This report describes localities in which geological features are evident in the field although detailed analysis of some features may only be completed or undertaken in the laboratory. Much geological data is obtained by recovery of materials from sub-surface (by drilling) or by remote sensing of their properties, e.g. by seismic exploration. Much sub-surface data exists for the volcanic plains adjacent to the Merri Creek, due mainly to an extensive programme of drilling to determine the nature and extent of stone, clay and underground water resources. This report does not include an assessment of localities where this type of remote survey is important as these are very little affected by changes in surface form or land use.

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1.2 METHODOLOGY OF SIGNIFICANCE ASSESSMENT

Geomorphology is that branch of geological science traditionally concerned with the origin and configuration of landforms. 'More recent work emphasises 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 in soil, sediment and rock. Geomorphological sites are therefore selected on the basis of both approaches to the study of landforms, and sites which have potential for detailed process studies have been included. Soil is a significant landscape variable along the Merri Creek and several sites have been nominated on the basis of soil properties.

All landforms to some degree reflect the influence of geological materials, especially those related to broad scale structures or developed on hard rocks with distinctive lithology, bedding, fold, or fracture systems. Therefore the report is not separated into distinct geological or geomorphological sections as such a division would be arbitrary. Site descriptions include comments about both aspects where such data is available. The emphasis of this report is on the selection, assignment of significance and management of the site and I have not attempted to provide a full geological and geomorphological analysis of each site. Site descriptions summarise and emphasise those aspects which are of greatest known significance.

The purpose of selecting sites of significance is to identify and argue for the preservation of localities and features that illustrate the geological and geomorphological character and diversity of landscape. They may be used as the basis for understanding the origin of land and observing the processes by which it is modified. Many sites display features that are relict, in that they represent geological processes (either climatically or tectonically controlled) that are no longer active. In some cases, the sites are of interest for their dynamics in that the landforms are subject to change over time, at a rate that can be measured and analysed.

The concept of significance is difficultto quantify satisfactorily as significance can he assigned various meanings (Joyce and King, 1980). The earth's surface is a mosaic of interacting components and 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 the understanding of the nature of all others. In practice, it is possible and necessary to define discrete segments of the landscape which do display particular scientific values. These sites may not coincide with those contained in traditional conservation systems e.g. National Parks which in part are chosen for their scenic and biological values and recreational opportunities and are afforded special status and protection by legislation. This present study has therefore applied criteria for the recognition of specific scientific values of landscape elements as distinct from scenic or aesthetic qualities.

1.2.1 Site selection

This study has identified 38 sites as significant. The criteria used to select sites is that established by Rosengren (1986) and includes the following attributes:

Geological Significance:

A. Type locality for a geological formation or other stratigraphic subdivision;

B. Outcrop or artificial exposure of mineral, rock, sediment or soil. This may be an outstanding example of a geological material, may display unique, rare or unusual attributes, or may simply be a good and accessible example of the major characteristics of a geological type.

C. Contact between geological formations.

D. Fossil locations;

E. Geological structure such as a fold or fault.

F. Rare mineral or unusual rock type.

Geomorphological Significance

A. Showing the relationship between rock type and landform.

B. Showing the relationship between a geological structure and landform.

C. Showing the present or past action of geomorphological processes.

D. Sites which are representative of the major landforms of the region.

1.2.2 SIGNIFICANCE RATING

Factors considered in determining the significance rating are modified from Rosengren (1986).

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. 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 at the site.

D. The value as a reference and teaching site displaying classic characteristics of a geological formation and/or a relict or active geomorphological process.

D. Past, present or potential use as a research site.

E. Where there is doubt as to the nature or origin of the feature.

The actual rating assigned to a site is determined by the extent to which the 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 may form global type examples and are widely known as reference sites by the international geological community. This site would be included in an international register of sites of scientific significance and would rate listing on the Register of the National Estate by the Australian Heritage Commission.

National Significance

These are landforms, structures, rock formations or fossils which are rare in Australia and/or by the nature of their scale, state of preservation or display are comparable with examples known nationally. They may form national type examples and are widely known as reference sites by the Australian geological community. This site would be included in a national register of sites of scientific significance and would be considered for listing on the Register of the National Estate by the Australian Heritage Commission.

State Significance

These sites are important in defining the geology and geomorphology of Victoria and may be reference sites or type localities of geological formations. They are an excellent display of geological or landform units and have substantial value for geological education and research.

Regional Significance These sites include landforms or geologies representative of the "Melbourne region" (defined as an arc extending around Port Phillip Bay from Kilmore in the north, the Dandenongs in the east to Geelongin the west). It is dominated by low hills and ridges of Palaeozoic sedimentary and granitic rock and with extensive plains of Tertiary basalt lava.

Local Significance: These are features representative of the Merri Creek catchment.

Unknown Significance: Sites are assigned this rating if there is insufficient data to allow a more complete assessment to be made.

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1.3 MANAGEMENT OF SITES OF SIGNIFICANCE

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 would be affected by a change in land use at or adjacent to the site. This sensitivity is summarised by referring the site to one of three broad classes as explained below.

Class 1 These are sites most sensitive to change either because the feature is either small and/or fragile and hence easily damaged, obscured, removed or detached. The interference may be direct and deliberate, e.g. burial or quarrying of a rock outcrop or the reshaping or stabilising of a slope, or it may be indirect or inadvertent. These sites require planning of activities and use to maintain their special qualities.

Class 2. These are sites of moderate sensitivity which may tolerate some degree of introduced change and still retain the essential features of significance.

Class 3. These are either large or robust features that can tolerate a substantial degree of interaction or change and still retain the essential features of significance.

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. 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 or previously inaccessible 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 fossil deposits or the production of rock debris that obscures an area of existing outcrop, may seriously degrade the value of a site.

The removal of any material (soil, rock, mineral or fossil) by individuals and excursion groups should be controlled by the management authorities and limited to authentic users and researchers. Uncontrolled sampling by excursion groups should be prohibited.

The management statement presented with the sites has not attempted to specify all possible sources of disturbance and 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.

This survey should not be regarded as definitive,. New localities will be identified over time as further geological research takes place and as other geologists study the area. It is recommended that the Merri Creek Management Committee maintain a system to allow the incorporation of such sites into their evaluation and planning procedures.

1.4 AN EVALUATION OF THE SIGNIFICANCE OF SITES IN THE STUDY AREA

The study area includes diverse geology and terrain and being close to Melbourne provides a number of opportunities for geological study and research. The region includes many features not only of Local and Regional significance and some localities rated as significant at the State level.

Excellent and accessible exposures of the Silurian bedrock that underlies the Melbourne region occur at Studley Park (opposite the Merri Creek confluence with the Yarra River), in a former quarry at Preston and in the gorge south of Barry Road. Although the volcanic features are older than those of Western Victoria, the region includes excellent examples of basaltic lava flows and the distinctive eruption points of Bald Hill, Mount Fraser and Hayes Hill. The entire Merri Creek drainage system is an excellent example of a stream developed on, and disrupted by, the lava flows. At several sites along the Merri Creek between Coburg and Fairfield and particularly in the narrow gorge at Northcote near Rushall Station, there are outstanding examples of the different cooling regimes and joint patterns developed in massive lava flows. These are very clear and many are safely accessible. They form an excellent basis for developing an interpretive trail along this part of the creek.

Many of the significant geological features described in early geological reports have now been destroyed by industrial and residential development or by extractive industries - especially in the Brunswick, Coburg, Preston and Campbellfield areas. Drainage of wetlands, reclamation of meanders, masonry and cement lining of creek channels and regrading and resurfacing of the floodplain has covered over significant exposures and obliterated the initial landforms of much of the Merri, Edgars and Central Creeks. The open space areas along Merri Creek north of Mahoneys Road thus provide the best opportunity for displaying the natural variation of the terrain. Land use changes in these areas should take the nature, significance and sensitivity of the sites described into account. Expansion of suburban, industrial and small farm development in the shires of Whittlesea and Kilmore poses the real risk that a depressing artificial uniformity will be imposed on the landscape to the north of Melbourne similar to that developing to the west. This impact is exemplified by the spread of subdivisions into the volcanic hills between Gisborne and Sunbury. Such close residential development should not be permitted on the volcanic hills and ridges of the Merri Creek catchment. Insensitive planning and distribution of buildings will mask the subtle terrain variation of the volcanic plains and spoil the outline of the volcanic hills. It may ultimately disguise the volcanic origins of the area.

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Information on this site is based on the 1993 report The Merri Creek Sites of Geological & Geomorphological Significance by Neville Rosengren La Trobe University, Bendigo.

 
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