Geology Uluru

uluru rock formations



panorama top of uluru, showing typical gully



close-up view of uluru s surface, composed of arkose

uluru inselberg, literally island mountain . inselberg prominent isolated residual knob or hill rises abruptly , surrounded extensive , relatively flat erosion lowlands in hot, dry region. uluru referred monolith, although ambiguous term avoided geologists. remarkable feature of uluru homogeneity , lack of jointing , parting @ bedding surfaces, leading lack of development of scree slopes , soil. these characteristics led survival, while surrounding rocks eroded. purpose of mapping , describing geological history of area, geologists refer rock strata making uluru mutitjulu arkose, , 1 of many sedimentary formations filling amadeus basin.

composition

uluru dominantly composed of coarse-grained arkose (a type of sandstone characterized abundance of feldspar) , conglomerate. average composition 50% feldspar, 25–35% quartz , 25% rock fragments; feldspar k-feldspar minor plagioclase subrounded grains , highly altered inclusions within k-feldspar. grains typically 2–4 millimetres (0.079–0.157 in) in diameter, , angular subangular; finer sandstone sorted, sorting decreasing increasing grain size. rock fragments include subrounded basalt, invariably replaced various degrees chlorite , epidote. minerals present suggest derivation predominantly granite source, similar musgrave block exposed south. when relatively fresh, rock has grey colour, weathering of iron-bearing minerals process of oxidation gives outer surface layer of rock red-brown rusty colour. features related deposition of sediment include cross-bedding , ripples, analysis of indicated deposition broad shallow high energy fluvial channels , sheet flooding, typical of alluvial fans.

age , origin

rain water flows off uluru along channels marked dark algae, forming small ponds @ base

the mutitjulu arkose believed of same age conglomerate @ kata tjuta, , have similar origin despite rock type being different, younger rocks exposed east @ mount conner, , unrelated them. strata @ uluru vertical, dipping south west @ 85°, , have exposed thickness of @ least 2,400 m (7,900 ft). strata dip below surrounding plain , no doubt extend beyond uluru in subsurface, extent not known.

the rock sand, deposited part of extensive alluvial fan extended out ancestors of musgrave, mann , petermann ranges south , west, separate nearby fan deposited sand, pebbles , cobbles make kata tjuta.

the similar mineral composition of mutitjulu arkose , granite ranges south explained. ancestors of ranges south once larger eroded remnants see today. thrust during mountain building episode referred petermann orogeny took place in late neoproterozoic cambrian times (550–530 ma), , mutitjulu arkose believed have been deposited @ same time.

the arkose sandstone makes formation composed of grains show little sorting based on grain size, exhibit little rounding , feldspars in rock relatively fresh in appearance. lack of sorting , grain rounding typical of arkosic sandstones , indicative of relatively rapid erosion granites of growing mountains south. layers of sand horizontal when deposited, tilted near vertical position during later episode of mountain building, possibly alice springs orogeny of palaeozoic age (400–300 ma).