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Sedimentary Rocks. 1. What is a Sedimentary Rock?. Sediments that have been compacted and cemented to form solid rock bodies. Sed Rx cover 75% of continents Can be composed of: Fragments of other rocks Chemical precipitates Organic materials. 2. Sedimentary Formation.
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1. What is a Sedimentary Rock? • Sediments that have been compacted and cemented to form solid rock bodies. • Sed Rx cover 75% of continents • Can be composed of: • Fragments of other rocks • Chemical precipitates • Organic materials
2. Sedimentary Formation • Formed on the Earth’s surface by the hydrologic system. • Formation involves: • Weathering of preexisting rock • Transportation to a new site • Deposition of eroded material • Lithification (gluing together)
3. Sedimentary Rocks Preserve a Record of: • Ancient landscapes • Climate • Mountain ranges • Erosional history of an area • Fossils
4. Continental Sedimentary Environments: • Alluvial Fans are fan-shaped deposits of gravel, sand, and mud that accumulate in dry basins at the bases of mountain ranges. • Eolian(wind) environments include sand seas of deserts, where sand dunes are built and transported by wind, areas where windblown dust accumulates. • Fluvial(river) environments are river channels, river bars and adjacent floodplains. • Lakes (Lacustrine) are bodies of non marine water, including freshwater lakes on continental lowlands and saline lakes in isolated basins. • Glacialenvironments are the areas where sediment is deposited by glaciers. Most obvious are the margins of ice, where sediment carried by the glacier is dropped as the ice melts. Other sub environments of a glacier lakes and melt water streams.
5. Shoreline Sedimentary Environments • Deltas are deposits of mud, silt, and sand that form at the mouths of rivers, where they empty into the sea or lake. • Beaches are shoreline accumulations of sand. • Barrier islands are linear bodies of sand built offshore by the action ocean waves. • Lagoonsare elongated bodies of seawater located between the mainland and barrier islands of reefs. Low wave energy permits the deposition of mud. • Tidal flats are shoreline areas that are covered with water at high tide and uncovered at low tide. Mud is the major type of sediment deposited.
6. Marine Sedimentary Environments • Shallow-marine environments extend from the shore to the edges of the continental shelves. Lime and mud are the principal types of sediment deposited. • Organic reefs are solid structures built from corals, algae, and the shells of other marine organisms. Reefs grow in warm, shallow water near islands and continents. • Deep-marine environments characterize the deep oceans beyond the continental slopes and include deep-sea fans and abyssal plains.
7. Sedimentary Structures • Crossbedding– layers are inclined at an angle in the strata • Often indicates an ancient sand dune
7. Sedimentary Structures b. Graded Bedding – progressive decrease in rock size through river bed. • Indicative of a river bed. • Rock size may indicate the flow rate of river
7. Sedimentary Structures c. Ripple Marks and Mud Cracks • Ripple marks indicate movement by shallow water or wind • Mud cracks indicate repeated cycle of evaporating water.
8. Transgression Regression Sequences An important aspect of stratification is that the rock layers do not occur randomly, but overlie one another in definite sequences and patterns. One of the simpler and more common patterns in a vertical sequence is the cycle of sandstone, shale and limestone. This pattern is produced by the advance and retreat of shallow seas over the continental platform. The following cross section is a representation of a transgressive-regressive sequence.
b. Shale Formed from layers of mud deposited in lagoons, river deltas and deep quiet water.
c. Limestone Rock composed of grains from remains of shelled organisms. Indicative of deep ocean floor.
9. Transgressive and Regressive Sequence • Sandstone • Shale • Limestone • Shale • Sandstone
