Geology

Biogenic (Organic) Sedimentary Rocks Biogenic or organic sedimentary rocks are formed from the accumulation and lithification of plant and animal remains, primarily in marine or swampy environments. These rocks contain significant amounts of organic material or biologically produced minerals. 1. Coal Composition: Carbon-rich plant material. Formation Process: 1. Dead plant material accumulates in swampy environments. 2. Burial and compression reduce water content. 3. Heat and pressure convert organic matter into coal over time. Depositional Environment: Swamps, peat bogs, and deltas. Types of Coal (Based on Carbon Content & Maturity): Peat – Loose, partially decomposed plant material. Lignite – Low-rank, brown coal with high moisture content. Bituminous Coal – Medium-rank, black, and commonly used for fuel. Anthracite – High-rank, hard, shiny, and has the highest carbon content. 2. Chalk Composition: Microscopic marine organisms (coccolithophores) made of calcium carbonate (CaCO₃)....

Types of Chemical (Non-Clastic) Sedimentary Rocks Chemical or non-clastic sedimentary rocks form from the precipitation of minerals from solution due to evaporation, chemical reactions, or biological activity. They are classified based on their mineral composition and formation process. 1. Limestone Composition: Calcium carbonate (CaCO₃), mainly in the form of calcite or aragonite. Formation Process: Precipitation of calcite from seawater or accumulation of marine organism shells. Depositional Environment: Shallow marine, coral reefs, caves, and lakes. Varieties: Fossiliferous Limestone – Contains visible fossils. Chalk – Made of microscopic marine organisms (coccolithophores). Travertine – Forms in caves and hot springs. 2. Dolostone (Dolomite Rock) Composition: Dolomite (CaMg(CO₃)₂). Formation Process: Forms when magnesium-rich water alters limestone. Depositional Environment: Shallow marine and lagoonal settings. Key Feature: Harder and less reactive to acid than limesto...

Types of Clastic (Detrital) Sedimentary Rocks Clastic sedimentary rocks are formed from the accumulation, compaction, and cementation of fragments of pre-existing rocks and minerals. They are classified based on grain size, composition, and depositional environment. --- 1. Conglomerate Grain Size: Coarse-grained (> 2 mm) Composition: Rounded pebbles, cobbles, and boulders cemented together by sand, silt, or clay. Depositional Environment: High-energy environments such as fast-flowing rivers, alluvial fans, and beaches. Key Feature: Rounded clasts indicate prolonged transport and erosion. 2. Breccia Grain Size: Coarse-grained (> 2 mm) Composition: Angular fragments of rock cemented together. Depositional Environment: Found in landslide deposits, fault zones, and debris flows. Key Feature: Angular clasts suggest minimal transport before lithification. 3. Sandstone Grain Size: Medium-grained (0.0625 – 2 mm) Composition: Mostly quartz, feldspar, and rock fragments. Depositional Envir...

Rivers pass through different stages of development—Infant, youthful, mature, and old age—each characterized by distinct types of work (erosion, transportation, or deposition) and the formation of specific landforms.  Rivers cause erosion through four main types of processes: 1.  Hydraulic Action The force of moving water hits the riverbanks and bed, causing material to break off. Water enters cracks and compresses air, leading to the weakening of rocks. Most effective in fast-flowing rivers, especially during floods. 2.  Abrasion (Corrasion) Sediments carried by the river (like sand, pebbles, and rocks) scrape against the riverbed and banks, wearing them away. This is the most powerful type of river erosion. It deepens the river channel and widens valleys. 3.  Attrition Rocks and sediments in the river collide with each other and break into smaller, smoother pieces. Over time, this creates rounded pebbles and fine sediments. 4.  Solution (Corrosion) River water...