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The rock cycle In the view of EARTH MATERIALS ד"ר חנן גינת ד"ר ירון פינצי The rock cycle in the view of internal and external PROCESSES external Internal The external processes Weathering Transportation Deposition Solidifying Weathering The destructive processes that change the physical and chemical characteristics of rocks at the earth's surface. Physical Weathering – mechanical breakdown of large rocks into smaller rocks is called mechanical weathering Physical weathering does not involve chemical changes to rock. Mechanical weathering results from the disintegrating action of high or low temperature, large changes of temperature, frost, or the impact of windborne sand or water Changes in a rock's composition due to exposure to the atmosphere and water is called chemical weathering. Factors which effect the rate of chemical weathering are: 1. The particle size and the surface area 2. Climate 3. Type of rock Chemical weathering can be solution by water, hydrolysis reactions, oxidation and other chemical processes. Biogenic Weathering – Caused by plants or animals - roots - digging - Involving in chemical processes זיהוי סוגים שונים של בלייה 2 1 4 3 5 -Write the main factors of the Weathering process 7 9 6 8 9 11 10 12 In which areas we can find the maximum physical and/or chemical weathering? Transportation of the weathering products Can be by: 1. Streams and rivers (fluvial) 2. By wind (Aeolian) 3. By ice and glaciers (glacial) 4. By sea currents Water in streams transport: 1. Raking pebbles 2. Floating materials 3. Dissolving materials The amount and characteristic of the loaded materials depend on: 1. Intensity of floods 2. Available loaded materials from the weathering processes 3. The type of the stream/river 4. Characteristic of the catchments area Loaded alluvial sediments during floods The fluvial process valleys Wide river highlands angular rounded Pebbles transport by the stream and change their shape and size (physical weathering). What are the factors that influence the amount of change? Clastic sediments are also characterized by the degree of particle sorting, and by the roundness of their grains, which usually implies something about the distance and mode of transport. Transport of sand grains by winds – the aeolian process Characteristic of transport: 1. Small grains 2. No pebbles 3. Deposit mostly in dunes Different kinds of dunes depends on the wind direction and intensity, the topography and the plants Transport by ice – the glacial process Glaciers are large masses of snow, recrystallized ice and rock debris that accumulate in great quantities and begin to flow outwards and downwards under the pressure of their own weight The Glacial features The glacial materials can be in different sizes – from boulders to clay grains. Signs in the rocks Deposition will be in: -Front moraines -Side moraines -Medial moraines And other remnants will be U shaped valleys and fiords Transport by sea currents Most fine sediments can be transferred long distances Reconstruction of the Geological History from a geological cross section A movie: Flood in the Isaron 18.1.2010 The rock cycle In the view of EARTH MATERIALS Different types of bedding Graded beds form when a rapidly flowing turbid slurry of water and mixed clasts, usually in a river or stream, slows down on entering a larger body of water and the largest clasts settle first. Cross bedding in ripples and dunes is formed by the migration of sand up the shallow, windward face and down the steep, leeward face windward face. Planner bedding Gradded bedding Cross bedding By wind By stream Bedding and stratification are the hallmark of sedimentary rock. The layers, or strata, are built up from the accumulation of particles of various sizes and arrangements. These particles formed during the breakdown and transport of pre-existing rock, or by precipitation from ions in solution. Sediments and sedimentary rocks, like those in the Grand Canyon preserve records of past climatic, environmental, and biological change on the Earth. Sedimentary environments on land are: fluvial (stream), lacustrine (lake), glacial, aeolian. Where the land meets the sea typical environments are: Beach, Estuary, Delta, Lagoon, Tidal Flat. In the ocean some common sedimentary environments are: Reef, carbonate shelf, submarine canyon. In some lakes, sediments are deposited in annual cycles called varves. The light colored silty layers were deposited when rivers flowed into the lake, while the dark clay rich layers formed when the lake was frozen over. Lithification (Solidification) Particle size is the primary basis for classifying clastic sediments and sedimentary rocks, regardless of the mineralogy of the clasts. Clastic rocks Loose sediments are transformed into rock, that is they are lithified, by compaction, recrystallization, and cementation. Together, these changes are commonly referred to as diagenesis. Clastic rocks–made of cemented sediments—are classified by their grain sizes. http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Sedrocks/Sedrocks9.html The story of different kind of bedding Use page 7 to identify the size and )roundness of the grains) What are the main types of sedimentary rocks? Classified into three groups include the types of particles they contain. Clastic rocks built from grains that have been cemented as a rock Biogenic rocks built from remains of plants or animals, mostly from the sea Chemical sedimentary rocks – were formed in an over saturated liquid (as lagoon or salty lakes) Deposition Environment of Clastic and Biogenic Rocks High Lands stream 200m Conglomerate Continental shelf: chalk Limestone Dolomite Clay Volcano Clay Chert lake Marl Clay Limestone Clay Limestone Sandstone Marl Dolomite Chalk Chert ―Black‖ Sea Shallow sea Very Shallow Deep Ocean Reconstruction of the Geological History from a geological cross section A movie: Flood in the Isaron 18.1.2010 Fossils A fossil is any evidence of a plant or animal that has been preserved in the Earth’s rocks The importance of fossils: 1. Giving more details about the Environment of the plant/animals 2. Compare about the Time Scale. 3. Giving data about the development of animals and/or plants through evolution How can we classify the fossils ? 1. By the parts of the animal that were fossilized; - Body fossils (Shells, bones, teeth) - Trace fossil – footstep, burrow 2. By the kind of the Animal or plant: Shell, snail, Dinosaur…. 1. Identify the fossils 2. Classify the fossils to groups. 3. Try to identify to the environments in which the animals were fossilized 3. The age of the animal Young …..some thousands of years or Old…. some millions 4. By the kind of rocks that include the fossils Soft rocks (clay) Or hard rock (limestone) Body fossils and trace fossils are uncovered Creation of Biogenic Rocks 1. The animal or the plant dies 2. The skeleton or the shell lie on the fine sediments on the floor of the sea, lake or swamp. 3.The skeleton or the shell is buried under the surface and becomes hard. 4. Most of the biogenic materials dissolve and are deposited on the bottom of the sea 5. By compression process the soft sediment becomes a hard rock 6. The sea dries out and the rocks on the sea floor are uncovered. The Rock Biogenic materials Environment Limestone Shelf, marine snails, carbonate foraminifera Shallow sea Marl Shallow sea rich with clay Chalk Nano-plankton Open sea Chert Diatomite and Radiolaron Deep Sea Or: Chemical change Carbonate foraminifera Big fossils in limestone Chalk Chert Diatomite Chemical Sedimentary rocks When water washes over and through rocks, some of the minerals from the rocks are dissolved and carried in the water. When the water evaporates or the minerals precipitate out of it the chemical sediment (the previously dissolved minerals) are deposited. These sediments go through the same lithification process as detrital sedimentary rocks Chemical sedimentary rocks form when mineral solutions, such as sea water, evaporate. Examples include the evaporite minerals such as halite and gypsum. The needed conditions to create chemical sedimentary rock: 1. Saturated water 2. Hot climate 3. Evaporation > Precipitation Dolomite (Ca,Mg)C03 Gypsum CaSO4(2H2O) 2/3 of the liquid was evaporated Salt Na Cl 9/10 of the liquid was evaporated Crystallization from saturated liquid The Natural Environments Lagoon A bay inshore from an enclosing reef or island paralleling a coast. Close lake in hot climate Open lake Bardawill Lagoon Close lake The chemical sedimentary rocks have high economic value Sedimentary rocks are economically important in that they can be used as construction material. In addition, Chemical rocks as gypsum and salt are mined in quarrys בדרך להר המלח הדנקילים – מלח ומים חמים עשירים במינרלים חוצבים מלח...או מפעלי ימת המלח... Metamorphic rocks and processes New rock textures and new mineral assemblages develop when rocks are subjected to elevated temperatures and pressures. Changes that take place while the rock is still solid are called metamorphism. Metamorphic changes start at about 150oC (equivalent to a depth within the Earth of 5 km) and cease around 800oC where the rocks start to melt. The Pietà, Michaelangelo's most famous statue, was carved from marble, a metamorphic rock from the Carrara quarries in Italy. What are the three types of metamorphism? The processes that cause changes in texture and in mineral assemblage in metamorphic rocks are mechanical deformation and chemical recrystalization. The origin rocks Granite Limestone Metamorphosed rocks Gneiss Marble Schist Clay Sandstone Quartzite And Some times with new metamorphic minerals Schist Garnet Tourmaline Mica Schist Pore fluids allow dissolved minerals to be transported and reprecipitated elsewhere; they also speed up chemical reactions. FoliationThe schist The composition of metamorphic rock is strongly controlled by the composition of the parent rock, but other factors also apply. The growth of new mineral phases during metamorphism is primarily controlled by temperature. High temperatures, pressures and abundant pore fluids result in metamorphic rocks with large mineral grains The original structure Elongated structure after metamorphism The changes that occur during metamorphism often produce a texture called foliation. This is caused by the preferential orientation of newly-formed micaceous minerals Foliation in low-grade metamorphic rocks is called slaty cleavage. Both foliation and cleavage develop perpendicular to the direction of maximum stress The diagram shows the conditions of pressure and temperature in which diagenesis, metamorphism, and melting occur in the Earth's crust. Metamorphic changes start at about 150oC (equivalent to a depth within the Earth of 5 km) and cease around 800oC where the rocks start to melt How do solid rocks change? As temperature and stress increase on a sedimentary rock, like shale, different mineral assemblages are formed, ultimately resulting in the metamorphic rocks slate, phyllite, schist, and gneiss. What are the metamorphic facies? For a given rock composition, the assemblages of minerals that are formed under a specific temperature and pressure are always the same. This fact allows us to define specific metamorphic facies. Sedimentary rocks that are saturated with water and subjected to elevated temperatures and pressures undergo burial metamorphism. Regional metamorphism occurs under differential stress and elevated temperatures as a result of the collision of tectonic plates. Regionally metamorphosed rocks commonly extend over areas of thousands of square kilometers Subduction Zone Paired metamorphic facies are common in subduction zone tectonic environments. Ocean floor basalts exposed to variable pressures and temperatures form well-foliated greenschists and amphibolites, or weakly-foliated blueschists and eclogites. Reconstruction of the Geological History from a geological cross section The rock cycle In the view of EARTH MATERIALS Summary – the main rocks and their story http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Rocks/Rocks8.html 1. Identify Rocks Environments (page 10) - Limestone - Chert - Granite - Basalt 2. Why are there so many kinds - Dolomite - Gypsum of sedimentary rocks? - Marl - Clay - Schist - Salt - Sandstone Some definitions: Normal Fault – A dip-slip fault marked by a generally steep dip along which the hanging wall has moved downward relative to the footwa Thrust Fault – fault on which the hanging wall appears to have moved up-ward, relative to the footwall Strike slip Fault – A fault which has horizontal movement, or movement parallel to the strike of the fault plane Antycline – A fold in which the limbs dip away from the hinge. After erosion, the oldest rocks are exposed in the central core of the fold Syncline - fold in rocks in which the strata dip inward from both sides (limbs) toward the axis Normal and Thrust Faults Normal and thrust faults and their influence on the topography Strike slip Faults Complex Geological Structures Folds Syncline Anticline -Sort the cards of the Ggeological Structure Puzzle Exercise: Find the geological structures along the Arava Valley and its margins The main geological ideas connecting to sedimentary rocks are: 1. Superposition – The lower layer is the older one 2. Horizontal laying – In a body of standing water the sediments accumulate always horizontal 3. ―The present is the key to understanding the past‖ …and other principles connecting relationships in the field 4. ―Chilled zones‖, xenolithes and magmatic pebbles in sedimentary rocks can help us to know the relative date between magmatic and sedimentary rocks 5. In a field outcrop metamorphic rock will be always older than its neighbors 6. The shaping of the recent landscape will be always the last stage of the Geological History Reconstruction of the Geological Field trip to Canyon Shehoret The Goals 1. Meet the main rock-landscape units of south Israel and Jordan 2. Identify rocks near their origin 3. Reconstruct the main stages of the Geological History of the region Geomorphology of Arid Zones Climate factors Amount of rain Climate Time Geological structures Rocks Geology ―Black box‖ The human impact Some remarks for the trip: 1. Leaving Ketura dinning room at 07.30 after breakfast 2. Bring with you walking shoes, Water (ar least 1.5 litter), hat, pen 3. We will work with field notebooks (4-5 stations). 4. Last task will be navigating in coupls 5. Back in Ketura at 14.00. -Going out side and figure a geological cross section between Ketura Hills and Edom Mountains Dating rocks 1. Relative dating by field relationships 2. Dating with fossils 3. Accurate dating by radiometric measuring The rock cycle In the view of EARTH MATERIALS Summary – the main rocks and their story