Depositional environments
- 1. Depositional Environments And their Diagnostic Criteria
- 2. Group Members Zain Ahmed Faizan Sabir Fahad Sultan Haider Sikandar Umer Shahid
- 3. Contents Depositional Environment How to identify them Types of environments Diagnostic criteria or Field recognition
- 4. Depositional Environment Earth material is broken down by processes of weathering and erosion, and is transported by the action of wind, water, or ice, and/or by the force of gravity A sedimentary environment has been defined as a “part of the earth's surface which is physically, chemically and biologically distinct from adjacent areas” Physical characteristics and geographical location determines the type of sediment that will be deposited
- 5. Cont. Layers of sediment have distinctive characteristics that provide important information regarding the geologic history of an area The characteristics that can be observed include its Lithology Sedimentary structures Fossils
- 6. How to Identify The characteristics of a sedimentary rock that are affected by its depositional environment are Sedimentary Lithology (the minerals and texture of the rock) Sedimentary Structures Fossils Sedimentary rocks contain sedimentary structures that were formed as the sediments were being deposited. Many sedimentary rocks also contain fossils, which are our main source of information of the history of life on earth.
- 7. Cont. Sedimentary structures and fossils are best found and examined in outcrops, where whole beds of sedimentary rocks are exposed in their undisturbed geological setting. The structures and fossils in sedimentary rocks reveal what was happening on the earth at the place and time the sediments were being deposited.
- 8. Depositional Environments TerrestrialContinental: Deposited on land or in fresh water FluvialAlluvial Glacial EolianDesert Lacustrine Transitional: Deposited in an environment showing influence of both fresh water or air and marine water. Deltaic Esturine Lagoonal
- 9. Types cont. Marine: Only influenced by sea water. Shallow marine clastic Carbonate shelfReefs Continental slope Deep marine
- 11. Fluvial River: Confined water body moving downhill in channels Fluvial: Processes associated with rivers and streams, deposits and landforms created by them Fluvial processes: Motion of sediments Erosion deposition
- 12. Types StraightBraided Rivers Almost straight, less bends Consists of network of small channels Separated by temporary islands called Bars Occurs in river with high slope and large Sediments load Also typical in environments that dramatically decrease in channel depth and channel velocity
- 13. Cont. Meandering Rivers A sinuous river with bends Forms as moving water erode stream at outer banks(widens the valley) Deposition at the inner part of river Snaking pattern as stream meanders back and forth Oxbow lakes forms as meander gets cut off from main channel
- 14. Stages Young High gradient, High velocity, Erosion, Tributaries, StraightBraided, boulders mostly deposits Mature Low Gradient, Erosion and Deposition, Meanders forms, Velocity decreases Old Very Low Gradient, Deposition, Low Velocity, Distributaries, Meanders
- 15. Depositions Channel Lag: Boulders left at upstream in young age Bars: Sediments deposition in rivers Natural Levees: Elongated naturally occurring ridgeswalls of sediments which regulates water levels Flood Plain: Area of land adjacent to stream or river which experience flooding during high discharge
- 16. Concave convex oxbow lake
- 17. Cont. Crevasse Splay: Formed when river breaks natural levees and deposits sediments on floodplain
- 18. Alluvium Loose, unconsolidated(not cemented) soil or sediments Eroded and reshaped by water in some form Redeposited in a non-marine setting Alluvial fan Fan or cone shaped deposits of sediments built up by streams Stream enters from high-land to low-land Typically found where canyons draining from mountain enters flat area Poorly sorted material Caused by flash floods
- 20. Diagnostic criteria Absence of marine fossils (Typically Unfossiliferous) Presence of plant fossils Red beds (Oxidation) Scoured channels Unidirectional-flow Lamination, Cross-lamination, Ripple marks, Graded beddings Physical Grain size, angularity decrease from source to mouth Sorting, sphericity, roundness increases from source to mouth
- 21. AeolianDesert
- 22. Desert Desert areas cover about 20-25 percent of land surface Within latitudinal belts about 10-30 degrees north and south These areas have dry climate with low air pressure and low rainfall ( <25cm 10 inches ) These dry areas are dominated by wind activity and covered by sand Wind Actions Deflation -- the removal of loose, fine-grained particles by the turbulent action of the wind Abrasion -- the wearing down of surfaces by the grinding action by windborne particles
- 23. Types of Dunes Traverse – these are perpendicular to the prevailing wind, and form a wave like pattern Longitudinal (Seif) dunes – stretch parallel to the prevailing wind with rounded or pointed tops. These can reach 300m in height and range up to 300km in length.
- 24. Cont. Barchans – A curved, arc shaped sand mound with horns facing downwind formed in arid regions. Parabolic – These are U-shaped mounds that form in the reverse direction of a barchans. They consist of sand tails which may hold vegetation Blowout – These are most commonly found on beaches, and are sandy depressions in a sand dune caused by the removal of sediments by wind
- 25. Cont. Star – These dunes are mounds that are subject to different wind directions, forming their star-like pyramidal structure.
- 26. Erosional features Mountains eroded by wind actions
- 27. Depositional features Loess – This is the lightest material carried by the winds which form a so-called blanket covering the existing land. This blanket is easily eroded and rain penetrates through them rapidly Bajada – desert alluvial fan, broad surface area, fine grained
- 28. Diagnostic criteria Sand - Sandstone Well sorted- large scale cross beds terrestrial reptile traces Vertebrates, pollen and spores (fossils) Yellowish – brownish colour sediments Hematite coating of grains
- 29. Lacustrine Lake: Land locked water body having its own drainage system Environment: Still water in lakes permits very fine particles (fine sand, silt, and clay) to settle out and to form lacustrine deposits These deposits get exposed by elevation of old lakebeds Lacustrine deposits are very well sorte Characterized by thin layers that reflect annual deposition of sediments
- 30. Cont. These layers causes different flows in lake Flow are due to difference in density of water and material Overflow – in upper layer, fine particles Interflow – in between layers, medium size particles Underflow – at the bottom, coarse particles As water enters lake, currents are produced which is high energy zone and fine particles remain suspended and move away towards centre As energy gets low fine particles settles in middle of lake
- 31. Types: On basis of Basin: How each basin originates is where the distinction between lacustrine deposit types stem Rift graben - lakes are formed from crustal stretching also known as rifting. Sediment influx is typically dominated by precipitation runoff and discharge through channels migrating towards the depression Oxbow lakes - form lacustrine deposits from seasonal overbank flooding as well as precipitation runoff which refills these isolated basins with fresh water and new sediments.
- 32. Cont. Glacial lakes - form when terminal moraines block water from escaping the newly carved valley from glacial erosion. As the glacier melts, the valley fills with melt water that creates a glacial lake. Crater lakes - can be meteoritic or of the caldera variety. Crater lakes sediments are provided from precipitation runoff descending their steep slopes
- 33. Lake Classification by Mixing Monomictic Lakes – one turnover per year Cold Monomictic Lakes – ice covered most of the year – turnover when lake warms slightly during short ice free period in the summer (Arctic and high altitude lakes) Warm Monomictic Lakes – no ice cover – warm and stratified for most of the year, turnover in winter when surface cools (lower temperate region lakes) Dimictic Lakes – turnovers in spring and fall, ice covered in winter (temperate regions) Amictic Lakes – always ice covered (Antarctica and Arctic regions, very high altitude lakes)
- 34. Types on basis of oxygen Oligotrophic lakes – are characterized by low nutrient values, which limits the lake's ability to support animal life, the water remains clear. Eutrophic lakes – are characterized by high nutrient values, which allows microorganisms and algae to grow in large numbers, which then allows animals that feed on those algae to also be supported
- 35. Diagnostic criteria Lacustrine rocks appears circular to sub- circular in map Fine sediments in middle Turbidites Rhythmic bedding ( showing seasoning ) Natron, Trona ( salts ) Fossils – Gastropods, Bivalves, Ostracods, Green Algae ( charophytes ) Lamination ( organic ) Siderite ( Iron carbonate )
- 36. Glacial Ice is a major transport process. Liquid water and wind can also transport sediment in these environments Wind transport is common when there is little vegetation. Liquid water transport occurs when the ice melts the high viscosity of ice makes all ice transport of sediment laminar. grain sizes are not sorted All of the sediment is transported together, with the ice, and it is deposited when the ice melts
- 37. Features Zone of Accumulation – is the area above the firn line, where snowfall accumulates and exceeds the losses from ablation Zone of Ablation – area of a glacier or ice sheet below firn with a net loss in ice mass due to melting Firn line – separates the accumulation zone from the ablation zone Firn – type of snow that has been left over from past seasons and has been recrystallized into a substance denser than snow. It is ice that is at an intermediate stage between snow and glacial ice Crevasses: cracks in glacier
- 39. Depositional Features Moraines – glacier deposition making land features Lateral: ridge of sediments along sides of glacier Medial: ridges formed in middle of glacier EndTerminal: ridges at the end ( last stop of glacier ) Ground: thin sheet deposits Drumlin – spoon shaped sediment deposits formed due to streams Esker – long sinuous deposition Kettle – small depression and cavity formed in bedrock due to glacier movement
- 41. Erosional Features Cirques – Half Bowled shaped valley formed by glacial erosion Arête – Sharp long narrow ridges at mountain tops formed by glacial erosion Horn – sharpest and elevated point of Arête
- 42. Diagnostic criteria Poorly sorted and unstratified deposits Striations Angular sediments with unspecific origins Oxidising environment with few fossils Stromatolites ( fossils )
- 44. Delta When riverstream enters stillstanding water body, sediments are deposited in triangle shape Major parts: Delta Plain: landward portion Sand size particles, distributaries Delta Front: Slightly grades into ocean, silt ( sand and clay ) Pro-Delta: Submerged into ocean, majority clay(silt and sand also)
- 46. Delta Morphology The shape of a delta is influenced by sediment input, wave energy, and tidal energy River-dominated deltas – occur in micro tidal settings with limited wave energy, river contribution > ocean all three parts of delta developed controlled by the water density difference between the inflowing river water and the standing water on the basin
- 47. cont. Tide-dominated deltas – Deltas which undergo strong tidal interaction ocean contribution > river resembles bird’s feet High tides and flood tides confine sediment on the delta plain and low tides carry sediment seaward. Sediment supply is over powered by strong tidal currents so the delta tends to be very small
- 48. Cont. Wave-dominated deltas – An open ocean basin accepts more water input so potential for greater wave energy, making wave- dominated deltas High wave interference causes conflicted or deflected river mouths. Less influence from fluvial sources Breaking waves cause immediate mixing of fresh and salt water. Typically, the fresh water flow velocity decelerates rapidly.
- 49. Diagnostic Criteria Majority sand size particles – sandstone Cross-beddings, ripple marks, laminations Yellowish-brownish colour Best reservoir Particle size decreases towards ocean Forams, Brachiopods, Pelecopods, leaves, Gastropods (fresh + marine water)
- 50. Estuary An partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea Less saline than lagoon due to fresh water Inflows of sea and fresh water provide nutrients, so it is more productive
- 51. Lagoon A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs little or no fresh water inflow, and little or no tidal flow More saline
- 52. Diagnostic Criteria Mostly Evaporates Thin beds of carbonates Salt pseudo-morphs
- 54. Marine Only influenced by sea water Shallow marine clastic – Regions near the mouths of rivers are usually clastic dominated because the critters that secrete CaCO3 tend to have trouble living in muddy water Carbonate shelf – Regions with clear water shallow enough to be penetrated by sunlight are often dominated by the skeletons of marine organisms
- 55. Cont. Continental slope – Dominated by the deposition of submarine landslides Deep marine – Very thin sediments formed by the slow accumulation of skeletons ( Planktons ) and clasts ( clay ) dropped into the ocean by wind
- 58. Conclusion Help understand Paleo-climates Plate tectonics Find hydrocarbons and minerals
- 59. References: Applied Sedimentology by Richard C. Selley https://commons.wvc.edu/rdawes/g101ocl/basics/BscsTables/depenv.html#contine ntal https://geo.libretexts.org/LibreTexts/UCD_GEL_109%3A_Sediments_and_Strata_(Su mner)/Alluvial_Fans/Glacial_Environments https://www.geol.umd.edu/~jmerck/geol100/lectures/14.html