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Townsville Region evolution and geological history:
Blast From The Past(Townsville Region evolution and geology)
Run to the top of Castle Hill and think about this! (1mm soil erosion annually in 1 million years digs a hole 1km deep, life first climbed out of the sea about 400 million years ago, boy how things must have changed)
The time when life (bacteria?) first evolved into single cells in the sea is indistinct but was somewhere about 3500 to 1800m yr (million years) ago. About 600m yr ago, an ancient PreCambrian continent existed inland of Townsville but closer to the modern coast in the Innisfail/Ingham area. All land visible today eastwards of this has formed since.
Before life left the sea to colonise land, a sequence of volcanoes and erosion extended the continent towards Townsville. Isolated outcrops of this ancient land are visible only on the lower slopes of Hervey Range and Frederick Peak.
Successive cycles of mountain building and the erosion of these into valleys to form sedimentary basins then began to dominate Eastern Australia. This period is called the "Tasman Mountain Building Time Zone". At times the mountains may have rivalled today's European Alps in size.
About the time plants first evolved from the sea to colonise the land (~400m yr. ago) the Hervey Range limestone deposits at Calcium, south of Townsville and another 5 km this side of Keelbottom Creek, were formed from undersea reefs.
Several North Queensland sedimentary basins formed from eroded mountains. The closest is the "Burdekin-Star", formed 350-300m yrs ago, where depths built up to more than 4 kilometres.
Wow, so the landscape as viewed from Castle Hill was all formed after life began to colonise the land.
After a quiet sedimentary period, huge explosive, cataclysmic and overlapping volcanic eruption activity (the Carboniferous Volcanics) became widespread in Eastern North Queensland. A considerable thickness of this rock forms parts of Hervey and Paluma Ranges, Frederick, Margaret and Black peaks. Towards the end of this period, when the earliest conifer and fern plant ancestors were abundant, the Keelbottom Creek granites, with some granite also on Mt Stuart, were laid down by successive intrusions; some are exposed on the Hervey Range escarpment. The Pinnacles outcrops were active volcanic plugs arguably occurring about this time (or much later).
It's hard to believe that many of today's outcrops have been buried under kilometres of rock later eroded.. not just once, but in repeated cycles, in parallel with the evolution of life.
Erosion exposed the earlier granites, then short duration, but very powerful volcanic activity (the Julago Volcanics) occurred in a belt from Biloela to Townsville. This occurred about the time that Araucaria and Podocarpus conifers, Ferns, Cycad, Pandanus, and the earliest angiosperm ancestors were being eaten by dinosaurs. Volcanic debris kilometres deep again accumulated that is now largely eroded away. Many Peak Range may be the remnant of a volcanic plug active about this time. Towards the end of this activity Mt. Stuart grew again in size, and Castle Hill formed. Activity was a composite of several successive overlapping granite intrusions formed deep under the surface of the newer volcanic overlay. Granitic intrusions of Magnetic Island, Cape Cleveland, Mt. Elliott and Mt. Storth formed also.
What finally resulted, after a long subsequent period of erosion interrupted by another volcanic period associated with a Mackay/Proserpine/(East of Townsville?) volcanic arc, was a flat plain approximately level with the Hervey/Paluma Range top, with Mt. Elliott rising above this plain!!!! Due to these volcanics, and possibly a general raising of the earths crust associated with the Gondwana continent breakup, Townsville's location was now hundreds of kilometres inland!!!
A particularly significant event then took place about 60 m yr ago. The part of the continent extending from just beyond the present reef position and out to the east, all sank below the sea. This was millions of years after the first continents split off from the ancient Gondwana continent, but millions of years before Antarctica split from Australia. At this time many of our current plant family ancestors proliferated.
Ever since then, as no doubt occurred before, the sea level has fluctuated greatly. The beach/coast line has not only been many times out at the reef proper, but also right up to the Hervey Range. Indeed the Hervey/Paluma/Mingela Range has been left in it's present position after the coastline was eroded tens of kilometres back from the rift at the present reef position. Mostly the Range erosion occurred during periods of high sea level by coastal wave erosion!!!! Harder formations like Castle Hill, Magnetic Island, and all the other hills on the coastal plain, were more resistant to erosive forces.
The young barrier reef was exposed above the sea level for most of this Range erosion period, only when the sea level rose above the reef would the reef building processes recommence. The various valleys eroded by rivers through the reef during the long periods of low sea level are still evident, many are used for shipping channels.
The evidence of all this erosion and deposition must still be present or our geologists must all have the same very inventive crystal ball. But the continuing process of erosion and deposition from the most recent times is very visible. Freshwater swamps covered large portions of the present coastal plain. River borne sediments carried by coastal currents built up sand dune systems of various age along the entire coast. These dunes also formed land bridges from the mainland connecting Many Peaks Range, Cape Cleveland, and formed Cape Bowling Green. The most notable sediment contributions came from the Burdekin River.
So endeth the fairy tale for now. When and how will it really end?
summarised by Doug Silke from references:
Especially: Rocks and Landscapes of the Townsville District, Trezise D. L; and Stephenson P.J; 1990 (out of print)
world evolution overview | world evolutionary time scale | to Townsville region info main page | top |
Townsville area, a summary of developments
Pleistocene to now Barrier reef development commenced, but only with short periods of growth and long periods of exposure. Formation of swamps, alluvial fans, soils and coastlines/dunes continued to now.
late Cretaceous/early Tertiary >65 Landmass extended much further east than now. Rifts opened, segments sank, and westwards erosion of the escarpment commenced, leaving behind more resistant rocks as remnant mountains and hills. Little erosion has occurred since 2 my.
100-55 Extensive NE Qld. erosion surface formed (possibly segments >144), eg. remaining slightly modified on Harvey Range and Frederick Peak plateaux.
Cretaceous 129 Volcanics all eroded away, with a granite/hornblende small intrusion at Mt Margaret, but exist more commonly out west. Associated with Mackay/Proserpine/(East of Townsville?) volcanic arc.
Early Permian 270-258 Granitic intrusions were widespread: Mount Storth Granite, Muntalunga Range Granite, Magnetic Island Granite, Castle Hill Granite(older?). Others: Cape Cleveland formation, much of Mt Stuart, numerous smaller NW coastal areas. Biotite granite generally except Mt Stuart with several phases. Mt Elliott is a batholith of pale Pink Granite. Metamorphosed "hornfels", and Xenoliths (islands of Julago Volcanics in granite). All commonly cut by basalt, dolerite, (some felsite) dykes. Then a long period of sedimentation followed.
286-270 following erosion exposing Carboniferous granites, short duration/major accumulations volcanic activity (Camboon Volcanic Arc) from Townsville to Biloela. (caused by ocean plates overlapping) Called "Julago Volcanics" Remnants include parts of Mt Stuart, hills to East, south of Bruce Highway, and Mt Saint John, Mount Bohle and Many Peaks Range. Lower sedimentation was followed by thick sequences: andesitic pyroclastics and larva (more common SE of city); rhyodacitic to rhyolitic larvas, tuff and breccia (more common Mt Stuart and to NW).
Carboniferous\much earlier Frederick Peak intrusion, small intrusive plugs and dykes of rhyolite. Possibly late stage magma from buried granites?
Late Carboniferous 320-286 After a long period of sedimentation, huge widespread N.Qld. volcanic explosive/cataclysmic overlapping eruption activity. Rhyolite, dacite and andesite type magma converted to debris - "pyroclastic" (tough and very hard rocks) were welded and compacted: tuffs, agglomerates and ignimbrites. A considerable thickness of these rocks, with interlayered sediments, forms parts of Hervey and Paluma Ranges (rocks little affected by later earth deformations). Percy Ck (Hervey Range) volcanics, and in vicinity of the Frederick, Margaret and Black peaks.
Towards the end of this activity granite magma batholiths, chiefly quartz and feldspar, adjacent volcanics recrystallised to metamorphic "hornfels". Most are out west: the Keelbottom batholith, and several smaller intrusions on Mt. Stuart, also Hervey and Paluma Range, and small localised at Cape Cleveland and Round Mountain Creek.
Palaeozoic era 500-250 Geological developments were dominated by the Eastern Australian "Tasman (mountain building) Zone", a changing belt of sedimentary basins and volcanic regions. The mountains may have rivalled today's European Alps in size.
Rocks remaining comprise: conglomerates, sandstones, shales, limestone (with fossils - Fanning River, or better 30km NW of Charters Towers) Limestone mainly calcite with Mg and Fe, for cement and lime manufacture.
Mountain landscapes subsided, and the sea invaded more.
Marine sedimentation. There are several N.Qld. thick sedimentary basins, the closest is the "Burdekin-Star" formed 350-300, with depths more than 4 km Forming after a major "Tasman Zone" upheaval gave rise to new basins that filled with sea water.
408-360 Marine reef/sedimentation formed the Calcium and Keelbottom Creek limestone deposits (later somewhat metamorphosed)
Cambrian/Ordovician 600-460 The Lolworth-Ravenswood block was a once extensive sedimentary and volcanic sequence formed on the eastern side of the PreCambrian continent. These were crumpled (deformed) and metamorphosed (recrystallised)about 480. Rock was transformed to schist, quartzite, gneiss, and metavolcanic rocks. Mineral layering (schistosity) is not necessarily in the same plane as sedimentation. Isolated outcrops occur on the lower slopes of the Hervey Range and Frederick Peak plateaux, main exposure is around Charters Towers.
PreCambrian an ancient continent existed inland of Townsville, but closer to the modern coast at Ingham/Innisfail.
summarised by Doug Silke from other references
world evolution overview | world evolutionary time scale | to Townsville region info main page | top |
Hopley, D; 1970; Monograph series No. 1; The Geomorphology of the Burdekin Delta, North Queensland
Open Learning Geological series entitled "The Evolution Of life" 1992
Stevens,N.C.; 1972; G19 Geology and Landscape of Queensland, National Science Curriculum Materials Project.
Trezise, D.L;Stephenson,P.J.; 1990; Rocks and Landscapes of the Townsville District
VickersRich,P;HewittRich,T; 1993; Wildlife of Gondwana
White,M.E.; The Greening Of Gondwana
Wyatt,D.H.; 1972; 1:250,000 Geological Series and notes; Townsville