Sedimentary Environments and Structures
Sedimentary Environments
Sedimentary environments are areas of the Earth’s surface where sediments accumulate. These environments have certain physical, chemical, or biological characteristics. Depending on where sedimentation occurs, the environments can be:
- Continental (glaciers, wind farms)
- Transitional (beaches, lagoons, deltas)
- Marine (from platform edges to slopes and the ocean floor)
Types of Sedimentary Environments:
- Glacier: Ice produced by the accumulation of snow leaves deposits of materials, which are poorly sorted. These deposits accumulate, forming moraines.
- Waterways: Rivers produce sediments that form terraces or, at the mouth of gullies, alluvial fans.
- Lakes: Lakes contain organic sediment produced by the remains of animals and plants, as well as sediment and clastic material that come from rivers.
- Lagoons: Lacustrine plains, separated from the sea by a bar.
- Karstic: Carbonation on land forms mainly carbonates. When conditions are favorable, the carbonates precipitate and form speleothems.
- Reef: Buildings formed by the skeletons of polyps. Deposits of these environments are made of limestone.
- Wind: Wind causes the formation of sand and silt deposits. If the grains are isometric, large mounds called dunes can be formed. Smaller grains can form ripples. Silts can cover large areas, very suitable for cultivation, and form potent deposits called loess.
- Estuaries: Produced at the mouth of rivers in seas with just enough power to drag the river deposits and erode the river mouth.
- Beaches: A band formed by the river sediment that occupies the space between the sea and the continent.
- Platform: Where materials, preferentially calcareous clay, accumulate along with other materials from the continent.
- Slope Edges: Sediments fall by gravity and accumulate on the edge of the slope, where they form large-scale deposits, alternating with calcareous clay and mud.
- Deltas: Formed with materials transported by rivers and deposited at the mouth, where the sea does not have enough energy to drag them away.
- Ocean Floor: With many sources, exclusively marine sediments.
Types of Sedimentary Structures
- Internal Structures
- Parallel Lamination: Particles may have formed in a uniform way.
- Ripples: Water currents and wind produce small ripples in the sand.
- Cross-Bedding: Particles are arranged in sheets tilted at a certain angle to the plane of stratification.
- Graded Bedding: The progressive variation of the grain size of sediments from the base to the top of the stratum.
- Structures on the Surfaces of Stratification: Provide information about the causative agent and also indicate the position of the top of the stratum, so they are used as a criterion of polarity.
- Of Form: Desiccation cracks indicate that the sediment formed was alternately wet and dry.
- Current Marks: Crevices caused by the erosion of a stream or an object dragged by it.
- Scars of Erosion: Erosion produced during a period when sedimentation has not occurred.
- Deformation Structures: Destroy the stratification.
- Load-Bearing Structures: Caused by materials deposited on less dense and softer materials.
- Slumps: Slides produced by strata.
- Organizational Structures
- Stromatolite Reefs: Large buildings formed by the calcareous skeletons of organisms such as corals, or living activity that causes the precipitation of calcium carbonate, such as stromatolites.
- Tracks, Footprints, and Bioturbation: The action originated by organisms that modify or destroy the original structure of unconsolidated sediment.