Modelo Estadístico Tendencial

In geological terms the survey area falls very largely within the Pilbara Craton with granite-greenstone terrane in its northern third and volcano-sedimentary successions (Hamersley Basin) in the remainder (Trendal 1990). Small southern and eastern parts of the survey area fall within the Bangemall, Bresnahan and Savory Proterozoic sedimentary basins. Minor parts of the area fall within the Carnarvon and Canning Phanerozic sedimentary basins.

Jutson (1950) considered that the physiography of the area resulted from the incomplete dissection of an ancient peneplain, part of the ‘Great Plateaux of Western Australia’. North of the Fortescue River Jutson named this old land surface the ‘Nullagine Plateau’ but it is now commonly referred to as the ‘Hamersley Surface’ and is preserved as extensive plateaux and dissected plateaux with prominent erosion scarps.

Physiographically most of the survey area falls within the Pilbara Province of Jennings and Mabbutt (1986). Smaller areas in the north-east and south-east fall within the Sandland

Province and a very small area in the far west falls within the Western Coastlands Province (Figure 1). Within the Pilbara Province the survey area occupies all or parts of the following component sections of the Province - the De Grey Lowlands, Fortescue Valley, Nullagine Hills, Chichester Range, Hamersley Plateau and very small parts of the Augustus Ranges and Rudall Tablelands. These sections and those sections occupied by the survey area in the Sandland and Western Coastlands Provinces are described in Table 1.

A major drainage divide (the Chichester Ranges) traverses the southern part of the survey area in a generally west north- west direction. South of the divide the Fortescue River passes through almost the full width of the survey area in a westerly direction to the Indian Ocean. The present valley of the Fortescue River contains the most prominent alluvial valley fill deposits in the State (Hocking and Cobain 1990) and constitutes the Fortescue Valley physiographic section. North of the drainage divide a number of substantial, more or less parallel rivers such as the Sherlock, Yule, Turner, Shaw and De Grey flow generally north north-westerly to the Indian Ocean (Figure 2). All rivers in the survey area are seasonally intermittent.

The regional geology of the northern half of the survey area is characterised by the best exposed and oldest granite- greenstone terrane in Australia (Griffin 1990), occurring in broad expanses of granitoid rocks interspersed with arcuate and linear belts of greenstone formations. Granitoid rocks constitute about 60% of the total and generally occupy anticlinal culminations and domes, up to 100 km across and separated by greenstones in synclinal structures. The granite- greenstone terrane formed between 3,500 and 2,800 million years ago as a result of probably four major phases of complex deformation and associated metamorphism (Griffin 1990).

The regional geology of southern parts of the survey area is characterised by sequences of volcano-sedimentary rocks of the Mt Bruce Supergroup which go to make up the

Table 1. Brief description of the physiographic regions in the survey area (Jennings and Mabbutt 1986)

Province Sections

Pilbara De Grey Lowlands – flood plains and deltaic plains; granitic and limestone lowlands; scattered ranges of metamorphic rocks in the north.

Nullagine Hills – dissected flat topped hills of granites and metamorphic rocks with partial lateritic cappings; narrow estuarine plain and islands.

Chichester Range – narrow range of dipping quartzite and sandstone. Fortescue Valley – mainly alluvial lowlands, possibly a graben.

Hamersley Plateau – dissected bold plateaux and ranges of flat lying or moderately folded sandstone and quartzite. *Augustus Ranges – parallel ranges and dissected plateaux with intervening sandy lowlands.

*Rudall Tablelands – dissected low sandstone tablelands. Sandland Eighty Mile Plain – coastal dunes and estuarine plains.

Anketell Hills – low mesas, buttes and stony rises of lateritized sandstone and shale among E-W longitudinal dunes and sandy plains.

Great Sandy Desert Dunefield – E-W longitudinal dunes and minor salt lakes.

Stanley Hills and Dunes – isolated sandstone ridges among E-W longitudinal dunes and sandplains. Western Carnarvon Dunefield – S-N longitudinal dunes.

Coastlands Onslow Plain – alluvial, deltaic and littoral plains; minor islands. * Only very small parts of these sections fall within the survey area.

Figure 1. Physiographic regions of the Pilbara (after Jennings and Mabbutt 1986)

Hamersley Basin (Trendall 1990). This supergroup is the younger (2,760 to 1,700 million years old) of the two components of the Pilbara Craton and forms a relatively undisturbed cover over the older granite-greenstone terrane. Along the northern boundary of its main outcrop area the supergroup rests unconformably on granite-greenstone terrane while the southern boundary is a complex arcuate zone of tectonic disturbance. The Mt Bruce Supergroup consists mainly of mafic volcanic and volcaniclastic rocks plus subordinate acid volcanics, sandstone, greenstone, siltstone and carbonate. In parts it contains economically important banded iron formations.

Land surface types (groups of land systems)

Fourteen land surface types were defined within the survey area and grouped primarily on whether they represent erosional or depositional surfaces and secondly on genesis and soil and drainage features (Table 2). Colloquialisms are used to maintain brevity in description.

More than a third of the Pilbara consists of rugged ranges, hills and plateaux which are source zones for run-off to lower surfaces. Some of the most prominent are the ridges and plateaux of the Newman land system of the Ophthalmia and Hamersley Ranges. These are based on jaspilite, chert and shale, and relief above the surrounding plains is up to 450 m.

Table 2. Land surface types of the Pilbara survey area

Land surface type Relief Land system Predominant Characteristic Distribution surface geology landform(s)

Predominantly erosional surfaces

(i) Hills and ridges Low to very high Augustus Sedimentary rocks Strike ridges, hills South and west, rare (30-450 m) Black Dolerite Ridges many Central, common

kilometres long

Boolaloo Granite Tor fields, domes Northern half, common Capricorn Sandstone, Strike ridges Wide, common

greywacke

Charley Dolerite, basalt Hills, ridges South-east, common Granitic Granite, gneiss Hills Central and east,

common

Houndstooth Shale Low hills West, common

Marandoo Basalt Hills South-central,

common McKay Sedimentary rocks Hills Wide, common Newman Jaspilite Ridges, plateaux Southern half, very

common Robertson Sedimentary rock Hills, ridges, South-east, very

plateaux common

Rocklea Basalt Hills, plateaux Wide, very common Ruth Volcanics, Low hills, ridges North-west,

sedimentary rocks uncommon

Talga Greenstone Ridges, hills North-central, common (ii) Plateaux and Very low to low Callawa Sandstone Low dissected hills, North-east, common

breakaways (9-90 m) mesas

Coongimah Silcrete, Plateaux, hills East, common sedimentary rocks

Kumina Jaspilite, laterite Low plateaux, Mainly west,

uplands uncommon

Laterite Laterite Low mesas, South-east, common gravelly plains

Nanutarra Conglomerate, Mesas West, common sandstone

Oakover Calcrete, limestone Mesas, low plateaux Mainly east, common Robe Limonite Mesas, mesa chains Wide, common Table Calcrete Mesas, low plateaux South-central,

Table 2. continued...

Land surface type Relief Land system Predominant Characteristic Distribution surface geology landform(s)

Predominantly erosional surfaces (continued)

(iii) Dissected plains Very low Billygoat Colluvium Incised plains East, common (9-30 m)

Egerton Colluvium Incised hardpan Mainly south, common plains

Platform Colluvium Incised slopes Central, south & west, common

(iv) Stony plains Low Adrian Silcrete Stony rises, South-east,

and hills (30-90 m) rounded hills uncommon

Bonney Basalt Undulating stony Mainly central, plains, hills common Collier Sedimentary rocks Uplands, hills, ridges South-east,

uncommon

Mosquito Schist Stony plains, ridges Central east, common Nirran Basalt, metabasalt Undulating plains South, uncommon Prairie Granite Hills, gritty surfaced South-east, common

plains

Tanpool Sandstone Stony plains, Far west, uncommon low ridges

(v) Stony plains and Very low Ford Shale, colluvium Gently undulating South-east, rare

gritty surfaced (9-30 m) plains

plains

Lochinvar Granophyre, felsic Level stony plains North-east, & intermediate lava with sand dunes uncommon Macroy Granite, colluvium Gently undulating Central north, very

gritty surfaced plains common

Stuart Schist, gneiss Gently undulating Far west, common colluvium, alluvium quartzy plains

Sylvania Granite, colluvium Gently undulating South-east, common gritty surfaced

Taylor Shale, sedimentary Stony plains Central north,

rocks uncommon

Wona Basalt, eluvium Stony gilgai uplands Central and west, common

Predominantly depositional surfaces

(vi) Stony plains Very low Boolgeeda Colluvium Gently sloping plains Wide, very common (9-30 m)

Dollar Colluvium, alluvium Level plains West, rare

Elimunna Alluvium, eluvium, Gently undulating Central east & south,

basalt plains common

Paraburdoo Colluvium, alluvium Stony gilgai plains South-west and west, common

Paterson Sand, alluvium, Sandy plains, East, common colluvium, sandstone low hills

Peedamulla Gravel, alluvium Level gravelly plains, Far west, common low rises

Pyramid Alluvium, eluvium Stony gilgai plains North-west, uncommon

Satirist Alluvium, colluvium Level plains with North & central west, some gilgais, uncommon

low rises

White Springs Eluvium, colluvium Level stony gilgai Central, uncommon plains

Table 2. continued...

Land surface type Relief Land system Predominant Characteristic Distribution surface geology landform(s)

Predominantly depositional surfaces (continued)

(vii) Hardpan wash

plains Extremely low Cadgie Alluvium, sand Hardpan plains with South-east, common

to very low sandy banks

(<9-30 m) Fan Alluvium Hardpan plains Central south, common Jamindie Alluvium Stony hardpan East, common

plains, low rises

Jurrawarrina Alluvium Hardpan plains, Mainly central west, gilgai plains common

Nooingnin Alluvium Hardpan plains, Mainly south-east, large groves common

Pindering Alluvium Stony or gravelly Central south, hardpan plains common

Spearhole Alluvium Gently undulating South and south-east, gravelly hardpan common

plains

Three Rivers Alluvium Hardpan plains Far south, rare Wannamunna Alluvium Hardpan plains, Central south,

internal drainage flats common

Washplain Alluvium Hardpan plains with South-east, common drainage tracts

Zebra Alluvium Hardpan plains, South-east, common gravelly banks

(viii) Sandy surfaced Extremely low Uaroo Alluvium, colluvium, Sandy surfaced North and far west,

plains on old (<9 m) sand plains very common

alluvium

(ix) Plains on Extremely low Balfour Alluvium, gravel, Level plains South-east, common

non-saline (<9 m) shale (some saline)

(occasionally Brockman Alluvium Gilgaied alluvial Central west and east,

saline) alluvium plains common

Christmas Alluvium Stony alluvial plains Central, rare Cowra Alluvium, gravel Gravelly alluvial Central, common

plains

Cundelbar Alluvium Alluvial plains South-east, rare (saline)

Hooley Alluvium Gilgai clay plains Central west, common Horseflat Alluvium Gilgai clay plains North and west,

common Kanjenjie Alluvium Gilgai clay plains Central west,

uncommon Marillana Alluvium Alluvial plains, Central, uncommon

unincised drainage tracts

Narbung Alluvium, sand Alluvial plains, Central south, internal drainage foci uncommon

Pullgarah Alluvium Gilgai clay plains North-east, common Sherlock Alluvium Stony alluvial plains West, uncommon Talawana Alluvium, sand Alluvial plains Far east, rare

(some saline), pans, swampy depressions

Turee Alluvium Stony gilgai clay Central, common plains

Table 2. continued...

Land surface type Relief Land system Predominant Characteristic Distribution surface geology landform(s)

Predominantly depositional surfaces (continued)

(x) River flood plains Extremely low Cane Alluvium Flood plains, West, uncommon

(<9 m) river channels

Coolibah Alluvium, calcrete Flood plains Central, uncommon Fortescue Alluvium Flood plains, Mainly south-east,

river channels uncommon

Jigalong Alluvium, gravel Flood plains South-east, common Mallina Alluvium Flood plains, Mainly north, common

alluvial plains

Paradise Alluvium Flood plains, North, common alluvial plains

River Alluvium River channels, Wide, common banks, alluvial plains

Urandy Alluvium Alluvial fans, Mainly west, common flood plains

Yamerina Alluvium Flood plains, deltas Coastal, common (xi) Calcreted Extremely low Calcrete Calcrete, alluvium Calcrete platforms Wide, common

drainage plains (<9 m) Lime Calcrete, alluvium, Calcrete plains, North coastal, rare sand alluvial plains

Warri Calcrete, alluvium Calcrete platforms Mainly south, common (xii) Salt lakes Extremely low Marsh Alluvium, gypsum Lake beds, saline South central,

and marshes (<9 m) flood plains common

Weelarrana Alluvium, sand Lake beds, saline South-east, rare alluvial plains, sandy

plains

(xiii) Sandplains, Very low Buckshot Gravel, sand, Gravelly plains, Mainly south-east,

gravelly (9-30 m) laterite Low rises common

sandplains and Divide Sand Sandplain Mainly south-east,

sand dunes common

Giralia Sand, minor Linear dunes, Far west, rare alluvium sandy plains

Gregory Sand Linear dunes North central,

uncommon Little Sandy Sand Linear dunes, Far east, very

sandplains common

Nita Sand Very gently North-east, very

undulating common sandplains

(xiv) Littoral plains Extremely low Anna Estuarine alluvium Littoral plains North-east coast,

and coastal dunes to very low common

(<9-30 m) Cheerawarra Sand, alluvium Sandy plains, saline Coastal, common clay plains

Dune Sand Linear and reticulate Far west coast, dunes, sandplains uncommon Eighty Mile Sand Coastal dunes, North east coast,

beach foredunes common

Littoral Estuarine alluvium Bare mud flats, Coastal, common saline littoral plains

Mannerie Alluvium Alluvial plains North-east coastal, (some saline) uncommon Onslow Sand, alluvium Gently undulating Far west coast,

sandplains, common littoral plains

Roebuck Estuarine alluvium Saline littoral plains, North-east coast, rare bare mud flats

In document PROSPECTIVA DEL SECTOR ELECTRICO (página 67-70)