The Gap (Sydney) - Geology, Fauna and Flora

Geology, Fauna and Flora

The Gap is formed from Sydney sandstone making it part of Sydney basin. The cliff was laid as sediment more than 200 million years ago in the Triassic period. During the Jurassic era, 40 million years later, a cataclysmic event resulted in an enormous crack forming within the strata. This fault allowed erosion from wave action to create the cliff line around Sydney. Tessellated basalt rock platforms lie at the base of the cliff because The Gap is bordered to the south and west by an older sequence of largely low-grade metamorphic and granitic rocks of the Lachlan Fold Belt. Northwards these rocks pass into the Hunter Region sequence that is transitional between the Sydney Basin and New England Fold Belt. The Gap itself forms a sequence that continues offshore to the edge of the Sahul Shelf. The total maximum thickness of rock formations within the Sydney Basin are in depth ranges of 5,000 metres (16,000 ft).

The rock is a very porous stone. It is composed of very pure silica grains and a small amount of the iron mineral siderite in varying proportions, bound with a clay matrix. The Gap's warm yellow-brown colour is due to oxidation of the stone.

Skinks and Eastern water dragons can often be seen moving among the rocks. Sea birds, such as the Silver Gull and the Pacific Gull use the cliff for nesting sites. The sandstone cliff has created nutrient-poor soils similar to those found around Sydney. As nutrients are scarce, plants which survive on The Gap cannot afford to lose leaves to herbivores so they defend their foliage with toxins. Vegetation includes the Eucalypts which produces such toxins.

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