Editing Uluru (section)

==Geology==
[[File:TreesUpUluru.JPG|thumb|right|Uluru rock formations]]
[[File:Panaorama from on top of Uluru.jpg|thumb|right|Panorama from the top of Uluru, showing a typical gully]]
[[File:Uluru close up.JPG|thumb|Close-up view of Uluru's surface, composed of [[arkose]]]]
Uluru is an [[inselberg]].<ref name="Young_etal_2002">Young, David N.; Duncan, N.; Camacho, A.; Ferenczi, P.A.; Madigan, T.L.A. (2002). ''Ayers Rock, Northern Territory, Map Sheet GS52-8'' (2nd edition) (Map). 1:250&nbsp;000. Northern Territory Geological Survey. Geological Map Series Explanatory Notes.</ref><ref name="Twidale2005b">{{cite book |url=https://books.google.com/books?id=WCbCAgAAQBAJ&pg=PA141 |title=Australian Landforms |publisher=Rosenberg |first1=C. R. |last1=Twidale |author-link=Charles Rowland Twidale |first2=Elizabeth M. |last2=Campbell |page=141 |year=2005 |isbn=1-877058-32-7}}</ref><ref name="Quinn2015">{{cite book |url=https://books.google.com/books?id=ErkxBgAAQBAJ&pg=PA719 |title=Earth's Landscape: An Encyclopedia of the World's Geographic Features |publisher=ABC-CLIO |editor1-first=Joyce Ann |editor1-last=Quinn |editor2-first=Susan L. |editor2-last=Woodward |pages=719–720 |year=2015 |isbn=978-1-61069-446-9}}</ref> An inselberg is a prominent isolated residual knob or hill that rises abruptly from and is surrounded by extensive and relatively flat erosion lowlands in a hot, dry region.<ref name="NeuendorfOthers2005a">{{cite book |title=Glossary of Geology |publisher=American Geological Institute |location=Alexandria, VA |editor1-first=Klaus K.E. |editor1-last=Neuendorf |editor2-first=James P. Jr. |editor2-last=Mehl |editor3-first=Julia A. |editor3-last=Jackson |edition=5th |year=2005 |isbn=0-922152-76-4}}</ref> Uluru is also often referred to as a [[monolith]], although this is an ambiguous term that is generally avoided by geologists.<ref name="Sweet_1992"/>

Uluru's homogeneity and lack of [[Joint (geology)|jointing]] and parting at [[Bed (geology)|bedding]] surfaces inhibits the development of [[scree]] slopes and soil. These characteristics led to its survival, while the surrounding rocks were eroded.<ref name="Sweet_1992">{{cite book |title=Uluru & Kata Tjuta: A Geological History |publisher=Australian Geological Survey Organisation |type=Monograph |first1=I.P. |last1=Sweet |first2=I.H. |last2=Crick |location=Canberra |year=1992 |isbn=0-644-25681-8}}</ref>

For the purpose of mapping and describing the geological history of the area, geologists refer to the rock [[Stratum|strata]] making up Uluru as the Mutitjulu [[Arkose]], and it is one of many [[sedimentary rock|sedimentary formations]] filling the [[Amadeus Basin]].<ref name="Young_etal_2002"/>

===Composition===
Uluru is dominantly composed of coarse-grained [[arkose]] (a type of sandstone characterised by an abundance of [[feldspar]]) and some [[Conglomerate (geology)|conglomerate]].<ref name="Young_etal_2002"/><ref name="engovaugeology">{{cite web |url=http://www.environment.gov.au/parks/uluru/nature-science/geology.html |title=Uluṟu-Kata Tjuṯa National Park – Geology |publisher=Australian Department of the Environment and Water Resources |access-date=3 April 2007 |url-status=dead |archive-url=https://web.archive.org/web/20071028194412/http://www.environment.gov.au/parks/uluru/nature-science/geology.html |archive-date=28 October 2007}}</ref> Average composition is 50% feldspar, 25–35% [[quartz]] and up to 25% rock fragments; most feldspar is [[Feldspar#Alkali feldspars|K-feldspar]] with only minor [[plagioclase]] as [[Roundness (geology)|subrounded]] grains and highly altered inclusions within K-feldspar.<ref name="Young_etal_2002"/> The grains are typically {{cvt|2|–|4|mm}} in diameter, and are angular to subangular; the finer sandstone is [[Sorting (sediment)|well sorted]], with sorting decreasing and with [[grain size]] increasing.<ref name="Young_etal_2002" /> The rock fragments include subrounded [[basalt]], invariably replaced to various degrees by [[Chlorite group|chlorite]] and [[epidote]].<ref name="Young_etal_2002"/> The minerals present suggest derivation from a predominantly [[granite]] source, similar to the [[Musgrave Block]] exposed to the south.<ref name="Sweet_1992"/> When relatively fresh, the rock has a grey colour, but weathering of iron-bearing minerals by the process of [[redox|oxidation]] gives the outer surface layer of rock a red-brown rusty colour.<ref name="Young_etal_2002"/> Features related to deposition of the sediment include [[cross-bedding]] and [[Ripple marks|ripples]], analysis of which indicated deposition from broad shallow high energy [[fluvial]] channels and sheet flooding, typical of [[alluvial fan]]s.<ref name="Young_etal_2002"/><ref name="Sweet_1992"/>

===Age and origin===
[[File:UluruRockWater.jpg|thumb|Rain water flows off Uluru along channels, marked by dark [[algae]], forming small ponds at the base]]
The Mutitjulu Arkose is about the same age as the [[Conglomerate (geology)|conglomerate]] at [[Kata Tjuta]], and has a similar origin, despite the different rock type. It is younger than the rocks exposed to the east at [[Mount Conner]],<ref name="Young_etal_2002"/> and unrelated to them. The strata at Uluru are nearly vertical, [[Strike and dip|dipping]] to the south-west at 85°, and have an exposed thickness of at least {{cvt|2400|m|-2}}. The strata dip below the surrounding plain and no doubt extend well beyond Uluru in the subsurface, but the extent is not known.

The rock was originally sand, deposited as part of an extensive [[alluvial fan]] that extended out from the ancestors of the [[Musgrave Ranges|Musgrave]], Mann and [[Petermann Ranges (Australia)|Petermann Ranges]] to the south and west, but separate from a nearby fan that deposited the sand, pebbles and cobbles that now make up Kata Tjuta.<ref name="Young_etal_2002"/><ref name="Sweet_1992"/>

The similar mineral composition of the Mutitjulu Arkose and the [[granite]] ranges to the south is now explained. The ancestors of the ranges to the south were once much larger than the eroded remnants we see today. They were thrust up during a [[Orogeny|mountain building]] episode referred to as the [[Petermann Orogeny]] that took place in late [[Neoproterozoic]] to early [[Cambrian]] times (550–530 [[Megaannum|Ma]]), and thus the Mutitjulu Arkose is believed to have been deposited at about the same time, hence then in Gondwana (now in Australia).

The arkose [[sandstone]] that makes up the formation is composed of grains that show little sorting based on grain size and exhibit very little rounding; the [[feldspar]]s in the rock are relatively fresh in appearance. This lack of sorting and grain rounding is typical of arkosic sandstones and is indicative of relatively rapid erosion from the granites of the growing mountains to the south. The layers of sand were nearly horizontal when deposited, but were tilted to their near vertical position during a later episode of mountain building, possibly the [[Alice Springs Orogeny]] of [[Paleozoic|Palaeozoic]] age (400–300 [[Annum|Ma]]).<ref name="Young_etal_2002"/>