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Home , Geology of Namibia

Earth's climate is predicted to change rapidly with serious consequences for humanity. However, during its more In some cases, however, rocks are created by geological processes regardless of climatic than four billion years of existence, the climate on our conditions. For example, igneous intrusions, shown here in red, are formed by the uprising planet has been changing continously, accompanied Climate Through Time of molten material from the Earth's interior, while metamorphic rocks (e.g. gneisses and by more or less severe extinction events (for instance related rock types here referred to as "Ancient Mountains") originate during episodes of at the end of the , some 250 million years ago, Our rocks reveal the story of change tectonic activity or mountain building. Conversely large amounts of ash from volcanic eruptions, N V more than 85% of all lliving organisms on land and in V may accumulate in the atmosphere to such a degree as to effectively block out sunlight, and the sea became extinct, due to a disastrous global Q thus influence the climate. M warming caused among other factors by enormous V volcanic eruptions). What is new today is, that while N Rundu before the appearance of h o m o s a p i e n s these climate V Opuwo changes had natural causes, and took place over N long periods of time, in the present day human activity M

contributes considerably to the ill effects on our environ- K N Ne N ment (including climate), as well as brings about change K more quickly. N N N Temperature and sea levels Position of the Fossil evidence and Rocks record the climate and conditions under which they originated Geological periods V M through time continents through time palaeoenvironments and thus are a window to the geological past of Planet Earth. As N N N M N environments are directly influenced by the prevailing climate, so are the N N sediments and rocks formed in them. On this poster each environment is N M M Archaic Homo sapiens, Q 30º represented by a particular colour to indicate the climatic changes that Q Africa 0 º EQ Quaternary (Q) N UA M TO have led to the geology of , as we know it today. For example R 2 million years N a c K ri e J m A orange areas on the map show the location of modern and ancient deserts, h t Neogene (Ne) u M o S M 3 0 º while grey indicates the remnants of the various glaciations (ice ages), to 23 million years a li ta 6 s Arriesdrift in 0 º u N A the Miocene which the region was subjected. Colours used on the map correspond to the N Antarctica Palaeogene ¡ geological timetable on the right as well as the insets below, showing the climatic ¤ (G) ¡ Present development of Namibia and the southern African subcontinent, and examples of N ¡ ¤ these palaeoenvironments and their products, respectively. K 65 million years K Tropical sea of ¡ ¡ 30º N the

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r a Cretaceous N b 0 a i º c Africa a E ri Q U e A T m O (K) R K A ¡ th N u N o S Q N In Deserts d ia 3 ¡ 0 Evidence: dunes are preserved as º ¡ Ne 145 million years cross-bedded with a Antarctica N a i Nama rocks near Maltahöhe N l a Massospondylus, ¡ t reddish colour. Mud cracks, salt and N s Warm Seas u gypsum deposits also indicate a dry A Jurassic Etjo Desert climate. Examples are the young Environment: Warm shallow to (J) deep seas, where sand, mud and deposits of the Kalahari and N N calcareous oozes are deposited, M 115 m.y. ago - Deserts, as well as the Twyfelfontein ¡ N Gobabis Breakup of and reefs build up. N sandstone (Cretaceous). ¡ Windhoek 200 million years Kannemeyeria, M N Waterberg Plateau Environment: hot, arid to semi- arid, with few seasonal rivers Evidence: sandstone, mudstone Walvis Bay Q and lakes, wind-shaped sand and limestone containing abund- dunes, and salt pans formed ant plants and animals. Examples N N through evaporation. are the sedimentary rocks of the , Namib Desert N N (¤) , which contain some M of the oldest known fossils on M Q 251 million years Earth. Nama fossil , M Permian Ecca swamp M (P) Ne N Subtropical swamps, 299 million years North Europe N J rivers and seas 0º E Q U A TO Environment: Tropical to subtropical R Stereospondylus, a swamps, rivers and sshallow seas. Ice Ages ic 3 r 0º Lake Gai-As e R H E I C O C E A N Carboniferous m Sand and mud accumulate in A Environment: very cold periods h Q rt N o (C) layers, sometimes rich in fossils N with extensive ice sheets and 6 0º Cypress swamp G glaciers, alternating with more A O r a b N i temperate interglacial intervals a Africa a c ri D Evidence: bedded sandstone e m W A A Glacier th and mudstone, containing the u o N S remains of alternating marine A 359 million years Chuos diamictite and freshwater organisms. Austalia Molluscs of the Evidence: grooved rock surfaces ¡ Dwyka glaciation Examples are the sedimentary caused by moving ice; ill sorted rocks of the Karoo Sequence, rocks (tillites), with larger pebbles 350 m.y. ago - in the Huab and main Karoo Southern continents are Time Gap Petrified Forest near Khorixas in a fine-grained groundmass. P basins. combined in Gondwana Examples are the Dwyka tillite M Ordovician (Carboniferous) and the Chuos to Devonian Formation (). P-C

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J-K M 488 million years P-C Cold to Luderitz Keetmanshoop Fjord landscape C FI CI PA Siberia - N TO Nama sea, temperate seas RO North ¡ P M Europe Environment: Coastal waters and Brandberg Intrusive Complex Igneous Intrusions southern Namibia deep seas in cold to temperate ¡ Process: intrusion of molten rock ¡ ( ) latitudes. Sand and mud accumu- M N (magma) into the Earth's crust P G late on the sea bed in layers O N North D W from below, crystallizing slowly America South A Q America N A 6 at depth. May produce geyers 0º Africa Kuiseb Canyon S and hot springs at the surface. 542 million years N 3 Evidence: bedded sandstone 0º S Q 0 º

and mudstone, alternating with P-C E Q U A T O thick sequences of carbonate N M R Australia Neoproterozoic rock. Most of the rocks of the Evidence: coarse-grained ¡ The blue curve* shows the average sea level compared to today for the whole Stromatolites, (N) Otavi Mountainland Neoproterozoic Damara and gabbros are evidence that N Q Planet Earth through geological time. This global sea-level is affected, among other factors, by the volume of water in the oceans and the shape of the ocean 550 m.y. ago - Sequence and Gariep Belt magma crystsallized slowly under Formation of Gondwana formed in this environment. the Earth's surface. Namibia has basins. Note that relative sea-level changes affecting the Southern African sub- M 635 million years plenty intrusive rocks of varied P-C N continent may have differed markedly from this 'global' curve (for example due to localised vertical changes of the land surface caused by the interaction of the 60º composition and age which can N P plates making up the Earth’s crust, or the formation and melting of ice-sheets. be found all over the country. Kobos , Gamsberg area We cannot measure sea level changes in the ancient past directly, and a variety 720 million years P of techniques are used to estimate it, such as erosion by the sea, and fossil reefs 30º Q Q approximating to sea level. R Time gap Oranjemund O M * Sea-level curve simplified after Collins (2008), "The carbonate analogs through D Q 1000 million years I EQUATOR N 0º time (CATT) hypothesis and the global atlas of carbonate fields. A systematic and I Kalahari predictive look at Phanerozoic carbonate systems" Craton A Namaqua gneiss, Ai-Ais (M) Ancient Mountains The red curve† shows the average global temperature back to the Cambrian Time gap period. We cannot directly measure past temperatures, instead we use evidence 30º Process: ancient rocks of 1600 million years varied origin, deformed and Flood , Etendeka Plateau preserved in the rocks. One such method uses the proportion of the oxygen-18 Volcanic Rocks isotope found in fossil shells - a high oxygen-18 content is associated with cold Palaeoproterozoic baked under high pressures 60º Process: molten rock pours sea temperatures and times of glaciation. During ice ages (marked by white bars) (V) and temperatures, forming ice caps covered the Earth's polar regions. out onto the Earth's surface 750 m.y. ago - Time gap the roots of mountains ranges. as lava. Stickier, silica- † Temperature curve after N.J. Saviv and J. Veizer (2003) "Celestial driver of 0 50 100 200 300 400 Rodinia Supercontinent 2500 million years rich rhyolite lava erupts explo- Phanerozoic climate?" Archaean (A) Evidence: schist and gneiss are -bearing paragneiss sively. Kilometers 4600 million years Earth forms formed by the metamorphism of 1:2,000,000 existing rocks, which often involves the growth of new minerals, such Continental drift Colours in the geological time Phases of: Palaeoenvironments found as garnet. Examples are the Evidence: basaltic to rhyolitic through the ages table only indicate the predomi- in Namibia; drawings by Volcanic Namaqua and Epupa Metamorphic lava and ash. Fine-grained rocks nant environment or processes; C. Marais N A M I B I A eruptions Complexes, and other indicate rapid cooling. Examples not drawn to scale G

3 Igneous E complexes throughout Namibia 0

include the flood basalts of the O 9

1 intrusions L - (Meso- to Palaeoproterozoic). O Etendeka Plateau (Cretaceous), Y

G E Mountain I V planetearth and the rhyolites of the Sinclair C A R Earth Science for Society building L U Sequence (Mesoproterozoic). Lava flow S

Adepted for Namibia after "Climate through Time - Our Rocks reveal the story of change" by British Geological Survey and Geological Survey of Northern Ireland, 2009