Geology

Most of the coastline of the shire lies on the Cattamarra Coal Measure, formed during the Jurassic period from volcanic and sedimentary rocks and consisting of siltstone, shale, claystone, coal and sandstone. The Greenough area lies on the Yarragadee formation, formed during the Jurassic period from volcanic and sedimentary rock and consisting of fine to coarse grained sandstone interbedded with shale. Between the Cattamarra Coal Measure and the Yarragadee formation is the Cadda formation, formed during Jurassic period from volcanic and sedimentary rocks and consisting of grey shale, siltstone and sandstone.

The geology of the Moresby Ranges is made up of a combination of the above formations and quartzofeldspathic gneiss associated with the Northampton Complex. The area between Mullewa and Geraldton lies on the the Nangetty formation and Tumblagooda Sandstone, formed during the Carboniferous-Permian and Ordovician periods respectively, from sedimentary and volcanic rock. The Nangetty formation consists of diamictite, shale and sandstone and Tumblagooda Sandstone consists of fine to coarse grained red-bed sandstone and minor siltstone. The area to the south lies on Holmwood Shale, formed during the Permian era from sedimentary and volcanic rock and consisting of grey shale and clayey siltstone interbedded with limestone. Mullewa town site and the eastern portion of the shire lie on the gneiss and granitic rocks of the Yilgarn Craton.

Coastal soils of the shire are deep, calcareous and sandy, associated with alluvial plains and a complex dune system. Inland soils are loamy and earthy and the terrain is gently undulating. Deep siliceous sandy soils are often associated with lateritic breakaways and the eastern portion of the shire is characterised by red shallow loams and red-brown hardpan soils.

Environment

The shire is located within the Geraldton Hills (GES01), Tallering (YAL02) and Merredin (AVW01) IBRA sub-regions and is characterised by low open woodlands, sandy Banksia heath and proteaceous scrub. Patches of Subtropical and Temperate Coastal Saltmarsh can be found in the shire. This is a nationally protected Threatened Ecological Community listed as vulnerable under Australia’s national environment law. The plant, animal and micro-organism community is found in the intertidal zone, often associated with estuaries. Plants are salt-tolerant (halophytes) and include grasses, herbs, reeds, sedges and shrubs. Several Priority Ecological Communities occur in the shire, including the vegetation complexes of Tallering Peak Banded Ironstone Formation, the plant assemblages of the Moresby Range System and the mallee eucalypt and Acacia rostellifera Coastal Sands south of Tarcoola Beach. The shire is home to Houtman Abrolhos Islands Nature Reserve, one of the largest and most diverse temperate limestone reef systems in Australia and one of the world’s 18 coral reef biodiversity hotspots. The Abrolhos Islands are home to endemic species such as the Abrolhos Painted Button Quail Turnix varius scintillans and Abrolhos Bearded Dragon Pogona minor minima. They are also extremely important breeding grounds for sea birds including Endangered Lesser Noddy Anous tenuirostri and Vulnerable Fairy Tern Sternula nereis.