Question

Briefly describe sedimentary processes and lithification. Describe the sources and particle sizes of sedimentary rocks.

Short answer

Sedimentary processes comprise of weathering, erosion, transport, deposition, burial, and diagenesis stages that lead to the formation of sedimentary rocks. Lithification is the process which hardens these sediments into rock through compaction and cementation. Sources of sedimentary rocks include preexisting rocks or pieces of once-living organisms. The particle size can range from smaller than 0.002 mm to several meters in diameter.

Step-by-step solution

Description of Sedimentary Processes

Sedimentary processes involve the creation of sedimentary rocks through a series of stages. These stages include weathering, erosion, transport, deposition, burial, and diagenesis. Weathering is the breakdown of rocks, soil, and minerals through contact with the Earth's atmosphere, biota, and waters. Erosion is the subsequent movement of the weathered materials by wind, water, or ice. Deposition occurs when the eroded materials are dropped in a new location while diagenesis involves the change of sediments or existing sedimentary rocks into a new sedimentary rock during and after rock formation.

Explanation of Lithification

Lithification is the process of hardening of sediments into sedimentary rock through compaction and cementation. Compaction occurs when sediments are deeply buried, placing them under pressure because of the weight of overlying layers. This causes a reduction in pore space and forces out water. Cementation is where dissolved minerals seep into the remaining pore spaces and bond the sediments together, forming rock.

Describing the Sources and Particle Sizes of Sedimentary Rocks

Sedimentary rocks come from a variety of sources. They can originate from preexisting rocks or pieces of once-living organisms. They include rocks like sandstone, shale, or limestone. The particle size within sedimentary rocks can vary greatly, from tiny clay particles which are less than 0.002mm in diameter, to large boulders 10's of meters in diameter. The size of the particles provides clues about the speed and distance of transport of the sediment.

Key concepts

Lithification

Imagine you're baking a cake, where ingredients represent sediments, and the oven's heat represents the natural processes gluing these ingredients together. That's lithification for you – the 'baking' that turns loose sediments into solid sedimentary rock. This process involves two steps: compaction and cementation. During compaction, sediments are squeezed together by the weight of layers above them, much like compressing a sponge under water; the excess 'water' or in this case, pore fluids such as water and air, are expelled. Following this, cementation binds these compacted sediments. Here, minerals like quartz, calcite, or iron oxides, work as natural 'glues' filling the spaces between the compacted particles and solidifying the mass into rock. The type of minerals acting as cement can affect the color, hardness, and durability of the resulting rock.

Sedimentary Rock Formation

The life story of a sedimentary rock is quite epic – it's crafted from the remnants of older rocks or organic materials and molded by Earth's geological forces. The journey starts with weathering - nature's way of breaking down rocks into smaller pieces. Think of this as erosion's prequel, where elements like wind, water, or even plants and animals cause the rock to crumble. Then comes erosion, the actual transport of these fragmented materials by agents such as rivers, glaciers, or the wind to their new home. But the journey doesn't end there. Once settled in an area, called deposition, these particles lie and accumulate layer upon layer. Over time, they're buried deeper by additional layers, and that's where our friend lithification steps in to harden these layers into sedimentary rock.

Birth of a Rock

Once the rock forms, it still remains subject to change; it can be lifted up to form mountains, or it can sink and be buried even deeper. This ongoing story, full of plot twists, exemplifies the dynamic nature of Earth's surface and the fascinating cycle of rock creation.

Particle Sizes in Sedimentary Rocks

The cast of characters in the story of sedimentary rocks has a large and varied cast - the particles that make them up. Similar to different characters adding depth to a story, particles of different sizes contribute to the diversity of sedimentary rocks. Fine clays, those tiny particles less than 0.002 mm across, whisper tales of calm conditions, often found in still waters where only the gentlest of currents can carry them. Silt particles, slightly larger and ranging up to 0.05 mm, suggest a bit more energy in their environment, likely carried by slow-moving water.

Jump to sand-sized grains, between 0.05 to 2 mm, and you've got particles that needed a more vigorous transport, such as a river channel or blustery winds. Finally, the plot thickens with gravel-sized particles (over 2 mm) and large boulders, where powerful forces like glaciers or strong rivers are the transport culprits. Piecing this information together, geologists act like detectives, using clues from these sizes to reconstruct the history of Earth's surface at the time the sediment was laid down.

Clues in the Grain

The size of these particles doesn't just tell us about their journey; they also influence the rock's appearance and properties. For instance, fine-grained rocks like shale can appear smooth and may even split into thin layers, while coarse-grained rocks like conglomerates look rough with visible chunks of rock or mineral.