Sedimentary Rock PDF

# Sedimentary Rock - Secondary rocks formed near the earth surface under low pressure and temperature. - It appears as layers. ## Process to Form Sedimentary Rock 1. Weathering 2. Erosion 3. Transportation 4. Sedimentary Basin 5. Diagenesis 6. Uplifting ## 1. Weathering - Break down or disinte...

# Sedimentary Rock - Secondary rocks formed near the earth surface under low pressure and temperature. - It appears as layers. ## Process to Form Sedimentary Rock 1. Weathering 2. Erosion 3. Transportation 4. Sedimentary Basin 5. Diagenesis 6. Uplifting ## 1. Weathering - Break down or disintegration of rock by physical or chemical processes. ### Types of Weathering 1. Mechanical Weathering 2. Chemical Weathering ### 1.1 Mechanical Weathering - Break rock into smaller pieces without change in chemical composition. - Nothing is created or destroyed. - Mineral composition is the same. - Occurs faster in cold climates. #### Types of Mechanical Weathering 1. **Thermal Expansion** - At morning, hot temperature causes expansion. - At night, cold temperature causes contraction. - Heating and cooling due to fractures or cracks in the rock. 2. **Frost Wedging** - The freezing and thawing of water in the cracks. ### 1.2 Mechanical Weathering Features 1. **Exfoliation**: - It is the process by which rock feels off or peels away. - Occurs as a result of: - Warming and cooling. - Pressure change (unloading). 2. **Salt Weathering**: - Saline water enters in pores or cracks in stones then evaporation occurs and salt crystallizes in the cracks. 3. **Biomechanical Weathering**: - By living organisms - By humans: - Tunnel pits - Road construction - Explosions ### 2. Chemical Weathering - Change chemical composition and change in internal structure by addition or removal of elements. - Occurs faster in warm climates. #### Types of Chemical Weathering 1. **Solution**: - First process in chemical weathering. - Minerals in the rock are dissolved by acidic water and form holes. 2. **Hydrolysis**: - Rock mineral transforms to other rock minerals. - Example: Feldspar + water → Kaolinite + Quartz + Ions. This breaks down the chemical bond. #### Differentiate Between Solution and Hydrolysis 1. Solution: Original rock completely dissolved leaving no solid behind. 2. Hydrolysis: Original rock transforms into new rock. 3. **Oxidation**: - Addition of oxygen. - External color change into: - Black - Reddish-brown - Example: Pyrite → Hematite (brown). 4. **Carbonation/Carbonization**: - Rainwater reacts with carbon dioxide and forms carbonic acid. - Chemical reaction: - H₂O + CO₂ → H₂CO₃ - H₂CO₃ + CaCO₃ → Ca(HCO₃)₂ (unstable) - Lime stone (calcium carbonate) dissolves the rock, forming caves. 5. **Hydration**: - Union of water with minerals. - Example: CaSO₄ + 2H₂O → CaSO₄ · 2H₂O - Anhydrite → Gypsum ### 2.1 Chemical Weathering Features 1. **HoneyComb Weathering/Alveolar**: - Forms from: - Chemical weathering due to salt water dissolving rock. - Mechanical weathering due to salt weathering. 2. **Tofoni**: - Similar to honeycomb in forming method, but they are large and have a different shapes. - Arch-shaped entrance, concave inner walls, and smooth floor. ## 3. Erosion - Removal of weathering products from their original location (the site of weathering) to a lower height. ## 4. Transportation - Movement of corroded particles. ### Agents of Transportation - **Wind**: Fine grains. - **Water**: Ions, sediments. - **Gravity**: Slope. - **Glaciers**: Large amounts of sediments with different sizes. - **Torrents**: Large amounts of sediments with different sizes. ## 5. Sedimentary Basin - The area where sediments are deposited. - *Marine* (sea-ocean) - Loose unconsolidated. - *Continental* (lakes-fluvial) - Loose unconsolidated. - *Terrestrial* (desert) - Loose unconsolidated. - *Transitional* (beach lagoons, deltas) - Loose unconsolidated. ## 6. Diagenesis (Post Depositional Change) - Chemical and mechanical processes affecting sediments after their deposition. ### Stages of Diagenesis 1. **Compaction**: - Close packing of grains by elimination of pore space and expulsion of water. - Occurs in small-grained sediment rock such as clay rock. 2. **Cementation**: - Individual grains of cemented sedimentary rock are held together by chemical precipitation of secondary minerals. - Cementing materials: - Silica (clear) - Calcium carbonate (calcareous, white) - Ferruginous (reddish-brown) ## 7. Uplifting - Uplifting of rocks by the effect of tectonic movement. - It leads to exposing of the rock. ## Sedimentary Cycle - Part of the major rock cycle. - Occurs near the surface. - Explains how sedimentary rock is formed. ## Rock Cycle - Describes the process through the three main rock types (Igneous, sedimentary, metamorphic). - One rock type transforms into another. ## Classification of Sedimentary Rocks - Divided into three types based on grain size: - **Coarse-grained** - **Medium-grained** - **Fine-grained** ### 1. Coarse-grained Rocks - Rocks that have a grain size greater than 2 mm. - Examples: conglomerates and breccia. - **Conglomerates**: Rock fragments with rounded or subrounded grains and a long transportation distance. - **Breccia**: Rock fragments with angular grains and a short transportation distance. ### 2. Medium-grained Rocks - Rocks that have a grain size between 2 mm and 1/16 mm. - Examples: sandstone. - **Sandstone**: - If it contains more than 90% quartz, called arenite. - If it contains 25% feldspar, called arkose. - If it contains more than 25% matrix, called a graywacke (unsorted). ### 3. Fine-grained Rocks - Rocks that have a grain size less than 1/16 mm. - Examples: siltstone, claystone, mud. - **Siltstone**: Grain size between 1/16 mm and 1/256 mm. - **Claystone**: Grain size less than 1/256 mm, have more than 80% water. - **Mud**: Mixture of silt and clay, blocky material. - Clay loses water due to pressure, which turns it into shale rock. - Shale rock has a laminated structure, the reason behind that is the layers of clay being compact. ## Chemical Rocks - Formed by: - Transfer of ions dissolved in water to the sea or ocean. Sea water evaporates and salts remain (Halite). - Direct precipitation of NaCl (Halite). ### Types of Chemical Rocks 1. **Calcareous Rocks**: - White rock that consists of CaCO₃ (calcium carbonate). - Examples: Limestone, Oolithic limestone. - **Limestone**: Formed from small and spherical grains (ooids) that are less than 2 mm in diameter. Ooids have a nucleus surrounded by layers of calcite. 2. **Siliceous Rocks**: - Consists of SiO₂ (silica) and forms crystalline or non-crystalline silica. - Examples: Flint, Chert. - **Flint**: Crystalline and non-crystalline silica. - **Chert**: Crystalline silicate; can also be red (jasper). 3. **Evaporite Rocks**: - Formed by the evaporation of water. - Examples: Halite, Gypsum. - **Halite**: Sodium chloride (NaCl). - **Gypsum**: CaSO₄·2H₂O. ## Organic Rocks - Formed from the remains of living organisms. - Examples: Coquina, Chalk, Coal. - **Coquina**: Type of limestone formed from the accumulation of shells and has high porosity. - **Chalk**: White coloured, fine-grained remains of foraminifera. - **Coal**: Formed from the accumulation and decomposition of plants.