Sedimentry environments
- 1. Sedimentary Environment BY ABDUL BASIT UNIVERSITY OF THE PUNJAB
- 2. Sedimentary Environment A depositional environment is a specific type of place in which sediments are deposited, such as a stream channel, a lake, or the bottom of the deep ocean. They are sometimes called sedimentary environments The layers of sediment that accumulate in each type of depositional environment have distinctive characteristics that provide important information regarding the geologic history of an area
- 3. The characteristics that can be observed and measured in a sedimentary rock to deduce its depositional environment include its lithology (which is essentially its rock type), its sedimentary structures, and any fossils it may contain
- 4. WHY ARE DEPOSITIONAL ENVIRONMENTS IMPORTANT? Knowledge of depositional environments is important for reconstructing earth history, understanding earth processes, and helping humans survive and prosper on earth Reconstructing earth history By analyzing a sedimentary rock, a geologist can deduce what was happening on earth at the place and time the sediment was originally being deposited
- 5. Types of depositional environments Four types of Sedimentry Environments 1. Continental 2. Transitional 3. Marine 4. Others
- 6. Continental sedimentry environment It has further four types a) Alluvium b) Aeolian c) Fluvial d) Lacustrine
- 7. Alluvium Alluvium is drived from Latin, alluvius, which means"to wash against“ Alluvium is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit
- 8. Aeolian Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets) Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts
- 9. Fluvial Fluvial is a term used in and geology to refer to the processes associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used Fluvial processes include the motion of sediment and erosion or deposition on the river bed
- 10. Lake A lake is an area of variable size filled with water, localized in a basin, that is surrounded by land, apart from any river or other outlet that serves to feed or drain the lake Lakes lie on land and are not part of the ocean (except for sea lochs in Scotland and Ireland), and therefore are distinct from lagoons, and are also larger and deeper than ponds, though there are no official or scientific definitions Lakes can be contrasted with rivers or streams, which are usually flowing. However most lakes are fed and drained by rivers and streams Natural lakes are generally found in mountainous areas, rift zones, and areas with ongoing glaciation Other lakes are found in endorheic basins or along the courses of mature rivers
- 11. Lake In some parts of the world there are many lakes because of chaotic drainage patterns left over from the last Ice Age All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them
- 12. Marine Sedimentary Environments Marginal Marine Environments Marine Environments
- 13. Marginal Marine Sedimentry Environment Marginal marine environments lies along the boundary between continetal and marine depositional environments A wide varity of sediments including Conglomerates, Sand stones, Shales Carbonates and evaporites can accumulate in these various marginal marine environments
- 14. Beach & Barrier Islands These are shoreline deposits exposed to wave energy and dominated by sand with marine fauna Barrier islands are separated from margined from the mainland by a Lagoon The are commonly associated with tidal flat deposits
- 15. Lagoon Environment Lagoons are coastal bodies of water that have very limited connection to the open ocean Lagoons generally develop along the coasts where there is a wave formed barrier and are largely protected from the power of open ocean waves A lagoonal succession is typically mudstone, often organic rich with thin wave rippled sand beds
- 16. Estuarine Environments An estuary is the margined influenced portion of a drowned valley A drowned valley is the seaward portion of a river valley that becomes flooded with seawater when there is a relative rise in sea level They are regions of mixing of fresh water and seawater Sediment supply to the estuary is from both river and marine sources, and the processes that transport and deposit sediments are a combination of river and wave or tidal processes
- 17. Tidal Flats Tidal flats are formed when mud is deposited by tides or rivers Tidal flats are the border of lagoons and estuarine environments Tidal flats are areas of low relief, cut by meandering tidal channels Laminated or rippled clay silt and fine sand may be deposited by a tidal flat
- 18. Marine Environments Marine environments are in the seas or oceans Marine environments include reefs, the continental shelf, slope, rise and abyssal plain
- 19. Continental Shelf The continental shelf is flooded edge of the continent It is relatively flat with a slope of less than 0.1*, shallow less than 200m and may be up to hundreds of kilometers wide Continental shelves are exposed to waves tides and currents and are covered by sand silt mud and gravel
- 20. Reef Deposits Reefs are wave resistant, mound like structures made of calcareous skeletons of organisms such as corals and certain types of algae Most modern reefs are in warm, clear, shallow, tropical seas between latitudes of 30o N and 30o S of equator
- 21. Continental Slope Deposits The continental slope are located seaward of the continental shelf The continental slope is the steep (5-25o) drop off at the edge of the continent The continental slope passes seaward into the continental rise which has a more gradual slope
- 22. Continental Rise Continental rise located between the continental slope and the abyssal plain The continental rise is the site of deposition of thick accumulations of sediments much of which is in submarine fans Deposited by turbidity currents at the base of continental rise Turbidity current deposits are called turbidities are characterized by graded bedding
- 23. Abyssal Plain Abyssal plain is the deep ocean floor It is basically flat, and is covered by very fine grained sediments consisting primarily of microscopic organisms e.g. radiolarians and diatoms Abyssal plain sediments may include chalk diatomite and shale deposited over basaltic oceanic crust