Tamar report land Capability Survey of Tasmania k e noble 1992 Tamar Report

31

Figure 5: 

Wind rose information for Low Head and Launceston.

(Source: Langford, J., 1965, Weather and Climate, in Atlas of Tasmania.  Lands and Surveys

Department, Hobart.)

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9.3

Land Use

The major land uses within the Tamar map area are grazing, dairying, cropping and forestry.

Sheep grazing predominates over beef cattle, with grazing occurring on improved pastures,

native pastures, partially cleared areas, steeper country and stony land.

Dairying is concentrated in the higher rainfall areas in the south west corner of the map,

around Parkham, Moltema and Dunorlan.  Other areas of dairying occur in the West Tamar

area around Frankford, Glengarry, Winkleigh and Flowery Gully.  Supplementary irrigation is

used during summer months to boost pasture production for dairying.

Three major areas of intensive cropping occur on the map: Thirlstane - East Sassafras area,

Moltema - High Plains area, and Selbourne - Westwood area.  These areas are generally

confined to the red basaltic soils (krasnozems), although because of the complex soil pattern,

other areas of poorer grey sandy soils are often utilised.  The risk of out of season frosts and

shorter growing seasons in the southern areas of the map, reduce the range and yields of crops

compared with the northern area around Thirlstane.

The major crops grown are peas, potatoes, onions, beans, poppies and cereals, in particular

barley.  Forage and green fodder crops are also grown for stock feed (oats, turnips, etc).

Vineyards are situated along the Tamar Valley at Rowella, Kayena, Sidmouth, Deviot and at

Glengarry.  Apple orchards and berry fruit farms are situated at Hillwood, Sidmouth,

Glengarry and Elizabeth Town.

Floriculture is a developing industry in the Elizabeth Town, Port Sorell and Glengarry areas.

In recent years there has been a proposal for an irrigation scheme which would include the

south west and south east areas of the Tamar map.  The availability of irrigation water would

boost the production of crops in the area, although care would have to be taken on the more

fragile soils to ensure that soil structural decline, salinity and drainage problems were not

exacerbated.  This would apply particularly to the Parkham and Selbourne - Quamby Bend

areas.

Forestry is also a major land use, with private and commercial forests providing wood for

both pulp and sawlogs.  Forestry occurs mainly on the dolerite, sandstones, slate and quartzite

country, with the majority occurring in unmapped exclusion areas of State Forests.

For further information on land use statistics in Tasmania, refer to `Australian Bureau of

Statistics, 1992.  Agricultural Statistics Tasmania, 1990-91.  Catalogue No. 7114.6.'

9.4

Geology

A wide range of rock types and soil parent materials occur across the Tamar map area.  They

include Quaternary age alluvium and windblown sand; Tertiary age sand, clay, gravel and

basalt; Jurassic age dolerite; Triassic and Permian age sandstone, siltstone and mudstone;

Lower Palaeozoic and Ordovician age sandstone, limestone and quartzite; and Cambrian and

Precambrian slate, sandstone, siltstone and quartzite.

The geology and geological history of the area has a major influence on the present day

topography and landforms.  For example, dolerite generally forms rugged, steep and stony

landforms because it is highly resistant to erosion, whereas mudstones and sandstones are less

resistant, forming lower subdued landforms. Rock type strongly influences the erosion types,

drainage characteristics and soil types, and is a major factor influencing land capability.

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The Tamar map covers part of two physiographic regions of Tasmania: the Tamar Graben

and the North East Coastal Platforms (refer to Figure 6).

Figure 6:

Physiographic regions of Tasmania.

(Source: Australian Bureau of Statistics, 1988, Tasmanian Year Book.  Page 32.)

The Tamar Graben was formed by major faulting with a north westerly trend.  The north

eastern side of the Graben has been dissected by the present Tamar River which drains into

the Tamar Estuary.  This estuary, and Port Sorell in the north west, are former river valleys

drowned by post glacial sea level rise.  Many of the fault depressions which occur in the

Graben, have been infilled by Tertiary deposits of clays, sands and gravels.

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The southern half of the Graben (which is to the south east of the Tamar map) incorporates the

Launceston Tertiary Basin.  The terrace country around Selbourne and Rosevale is the north

western most expression of the Launceston Tertiary Basin.

The Tamar Graben is further dissected by the Asbestos and Dazzler Ranges (quartzite and

slate), and large areas of dolerite intrusion which form high points in the landscape.

Where resistant rocks such as dolerite and quartzite outcrop along the coastline, they form

steep prominent headlands, often with vertical cliffs (e.g. Point Sorell, Badger Head, West

Head).

Along the northern coastline, extensive areas of sand plains and windblown sand dunes occur.

These areas are part of the North East Coastal Platforms, which consist mainly of undulating

low sand plains, with parallel dune ridges and blow-out dunes.  These coastal platforms have

been formed by seaward extensions of emerged platforms, by processes of coastal accretion

and have subsequently been covered by windblown sands.  Coastal sand plains occur east of

George Town, with smaller areas around Greens Beach, Badger Beach, Bakers Beach and Port

Sorell.

The oldest rocks on the Tamar map are the quartzites, slates and greywackes of Precambrian

and Cambrian age.  The major occurrence of these rocks is in the exclusion areas of the

Dazzler Range and Mt Careless.  Other localities where these rock types have been mapped

are Franklin Rivulet, Cabbage Tree Hill, Salisbury Hill and Peaked Hill.

Associated with these older rocks, and formed by tectonic activity and igneous intrusion is an

area of serpentinite, pyroxenite and gabbro, known as the Andersons Creek Ultramafic

Complex.  These rocks occur in a small area around Andersons Creek, west of Beaconsfield.

The Mathinna Beds, of Lower Palaeozoic age, are a sequence of sandstones and siltstones

which have undergone severe deformation such as folding, induration and metamorphism.

These occur in the Lefroy area, with smaller outcrops north towards Beechford and George

Town, which have been subsequently covered in part, by younger sediments such as

windblown sands.

Limestone of Ordovician age occurs in the Flowery Gully area, and this is presently being

mined for commercial fertilisers and industrial use.

Sandstone of Triassic age occurs in the Notley Hills - Bridgenorth area, on the eastern side of

Tippogoree Hills, around Exeter, and east of Parkham.  The sandstone, together with other

sediments principally of Permian age, have been intruded by dolerite which now forms a

protective cap.  Where these sediments have been protected from erosion by the dolerite, they

form steep slopes.  However where there is no protective capping, landscapes are more

subdued and have lower relief (Refer to Photo 2).

Permian age mudstones, sandstones and siltstones occur around the northern and eastern

slopes of Mt George and Tippogoree Hills, in the Beaconsfield area, and in the West

Frankford - Birralee, Holwell - Glengarry - Bridgenorth, and Paramatta Creek - Parkham

localities.

Extensive areas of dolerite occur throughout the map area, mostly in forested exclusion areas.

The dolerite is Jurassic in age, and has intruded into the older basement rocks (Permian and

Triassic).  It occurs as very thick sheets with feeder dykes, and is highly resistant to erosion. It

has been uplifted by faulting and many of the higher points in the landscape are capped by

dolerite, with the exception of Asbestos Range, Dazzler Range and  Mt Careless  (e.g.

Stephens Hill,  Christmas  Hill,  Black  Sugarloaf, Tippogoree  Hills).

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