Geological Landforms

Ormiston Gorge
Heavitree Quartzite, exposed in the spectacular vertical cliff on the western side of Ormiston Gorge and upstream of the waterhole, has an exaggerated thickness. There, the upper part of the cliff is a that lying upper limb of the Ormiston fold containing horizontally bedded Heavitree Quartzite. Below the horizontal Ormiston Thrust separates the upper limb from the near vertical or overturned Heavitree Quartzite underneath.
Ormiston Pound, about 1 km upstream of the waterhole, is surrounded by both Heavitree Quartzite and Chewings Range Quartzite which have been thrust aside by the intrusion of the Ormiston Pound granite. This granite has weathered and eroded away much more quickly than the quartzites, and it now forms the sunken floor of the Pound. On the ridge north of the visitor Centre and below the main quartzite hills an anticline in tightly folded beds of the Bitter Springs Formation is well exposed (Plate 8c).
Mount Sonder is also part of the Ormiston Thrust system. The top is formed of a pale coloured slab of Heavitree Quartzite. Below this and clearly separated by a thrust plain on the southeast face are the Arunta metamorphic rocks.
Source: A Guide to the geology and landforms of Central Australia by R B Thompson
Simpsons Gap
The narrow gorge cut by Roe Creek through the Rungutjirba ridge of Heavitree Quartzite, probably follows a pre-existing joint trend and some dramatic scenery has resulted. The northward clip of the bedding in the quartzite has been locally folded to an overturned position which can be matched with the outcrop in Ellery Creek Big Hole. The northward clipping quartzite at Simpsons Gap and the southward clipping Heavitree Quartzite on Mount Gillen, are remnants of a huge arch (anticline) of quartzite which once extended over the Larapinta Valley. Weathering and erosion during the last 300 million years have now removed all but the remnant abutments. The rocks exposed in Rocky Gap, 5 km northwest of the Ranger's station are quite different. Fresh water-worn granite, cut by narrow zones of foliation and mylonitization are intersected by thin dolerite dykes. All are features of the Proterozoic basement.
Source: A Guide to the geology and landforms of Central Australia by R B Thompson

Standley Chasm
This is a narrow gorge with very steep sides of quartzite in which erosion has been strongly influenced by major joints. The walls of the gorge are formed along two parallel vertical joint planes, and all the rock between those two planes has been removed during erosion by the creek. There are a number of long vertical dolorite dykes in the area, which are parallel to and about the same width as the gorge, and the joints probably formed at the same time as the dolerite was intruded. The gorge itself, however, does not seem to have been eroded along one of the dykes.
Source: Laymans Guide to Geology

MacDonnell Ranges
Many of the localities described are within the MacDonnell Ranges, but the Ranges are also interesting as a whole. They consist of a long east-belt of low mountains in which there are two basic rock types - a northern zone of ancient metamorphic rock, and a southern zone of folded sedimentary rocks. This is, in fact, the root zone of the ancestral MacDonnell Ranges, formed during the deveniar earth movement period, and gradually exposed by erosion.
The sedimentary rocks are perhaps more interesting scenically than the metamorphic rocks. They occur in long sharp ridges in gently sweeping curves which are exceptionally striking from the air. Most of the more popular places in the MacDonnell Ranges occur in these rocks. The colour which is such a feature of the ranges is due to varying amounts of iron oxides both in and on the rocks. The old Telegraph Station is located within two metamorphic rocks of the MacDonnell Range. The spring is in fact a permanent water hole in the sandy ridge of the Todd River. Source: Laymans Guide to Geology

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