Sedimentology and Sedimentary Processes

1. Sedimentology and Sedimentary Processes Virginia T. McLemore

2. Sedimentology • "The scientific study of sedimentary rocks and of the processes by which they were formed; the description, classification, origin and interpretation of sediments" (Glossary of Geology, AGI, 1974) • Study of modern sediments such as sand, mud (silt),and clay • Understanding the processes that deposit them • Studies of ancient sedimentary rocks

3. http://www.geo.umass.edu/faculty/cooke/geo101/GeologicTime.htmhttp://www.geo.umass.edu/faculty/cooke/geo101/GeologicTime.htm

4. http://www.bbc.co.uk/schools/gcsebitesize/chemistry/changestoearthandatmosphere/0rocksrev5.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/chemistry/changestoearthandatmosphere/0rocksrev5.shtml

5. http://csmres.jmu.edu/geollab/fichter/SedRx/SimpModl.html

6. Sedimentary rock types • Clastic rocks • particles derived from the weathering and erosion of precursor rocks and consist primarily of fragmental material • classified by grain size and composition • Carbonates • precipitated by a variety of organic and inorganic processes • Evaporites • evaporation of water at the Earth's surface • Chemical sedimentary rocks (chert, jasperiod)

7. Principles • Uniformitarianism, which states that the sediments within ancient sedimentary rocks were deposited in the same way as sediments which are being deposited at the Earth's surface today • Principle of superpositionSedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top. • Principle of original horizontality sediments are deposited at their angle of repose which, for most types of sediment, is essentially horizontal

8. Principles • Principle of lateral continuity states that layers of sediment initially extend laterally in all directions unless obstructed by a physical object or topography • Principle of cross-cutting relationships states that whatever cuts across or intrudes into the layers of strata is younger than the layers of strata

10. http://en.wikipedia.org/wiki/Image:Taum_Sauk_precambrian-cambrian_unconformity.jpghttp://en.wikipedia.org/wiki/Image:Taum_Sauk_precambrian-cambrian_unconformity.jpg

11. http://en.wikipedia.org/wiki/Image:Vallisvale.jpg

12. Methodology • Measuring and describing the outcrop and distribution of the rock unit • Descriptions of rock core • Sequence stratigraphy (Describes the progression of rock units within a basin ) • Describing the lithology of the rock • Analysing the geochemistry of the rock

13. Sediment characteristics • Porosity is the volume of voids within a rock which can contain liquids. • Permeability is the ability of water or other liquids (e.g. oil) to pass freely through a rock. • Roundness refers to the roughness of the surface of the sedimentary grain. • Sorting refers to the range of particle sizes in a sediment or sedimentary rock. • Matrix is the fine-grained material (usually clays or silt) that is deposited originally with the coarser-grained material

14. http://www.eos.ubc.ca/courses/eosc221/sed/sili/silpet.html

15. Classification by GRAIN SIZE • Gravel > 2mm • Sand >1/16 mm < 2 mm • Mud <1/16 mm • Decide what the relative proportions of each size

16. http://www.eos.ubc.ca/courses/eosc221/sed/sili/siligsize.html#sizehttp://www.eos.ubc.ca/courses/eosc221/sed/sili/siligsize.html#size

17. Grain Size Distribution

18. Folk (1980)

19. COMPOSITION • Gravel • Sand • Mud

21. TEXTURE • Grain shape (attributes which refer to the external morphology of particles) • surface texture, • roundness • form. is determined by: • Grain shape (Bustin, 1995) • internal structure • mineral cleavage • characteristics of source rock such as jointing and bedding • lithology • hardness • fracture • transport

24. COLOR • Munsell color chart

25. Any other features? • Is there anything outstanding about this rock? • Does it have any important minerals or clasts? • Anything worth making note of? • Any important clasts? • Are there any fossils? • Any visible sedimentary structures (ie cross bedding)?

26. Give the rock a NAME • [colour][texture][cement][important minerals or clasts] ROOT NAME [with...]

27. http://www.eos.ubc.ca/resources/slidesets/clastic/clastic.htmlhttp://www.eos.ubc.ca/resources/slidesets/clastic/clastic.html

28. http://darkwing.uoregon.edu/~millerm/depenvsmap.html

29. Sediment transported by • Suspension load is when sediments are carried in suspension (usually fine-grained sediments that can be carried along easily by the flow) • Bed load is when the forward force of the moving current acts more directly on the larger particles at the bottom as it pushes, rolls, and slides them along • Saltation is more complex and usually affects sand-sized particles. Here, the particles are sucked up by eddies into the flow, travel with the flow for a while, and then fall back to the bottom

30. Sediment structures • Asymmetrical ripples are ripples that have a gentle slope upstream and a steep slope downstream. • Cross-bedding is inclined bedding and commonly forms in alluvial environments. • Potholes are rounded depressions caused by swirling currents and eddies. • Mud cracks are formed by evaporation on mudflats or in shallow lakes.

31. Sedimentary environments

33. Alluvial Fans • Alluvial fans are sedimentary deposits that typically form at the margins of a dry basin. • They typically contain coarse boulders and gravels and are poorly sorted. • Fine-grained sand and silt may be deposited near the margin of the fan in the valley, commonly in shallow lakes. • These lakes may periodically dry, and evaporite deposits may result.

34. http://www.uoregon.edu/~millerm/fan.html

35. Eolian • Wind is an effective sorting agent and will selectively transport sand. • Gravel is left behind and dust-sized particles are lifted high into the atmosphere and transported great distances. • Windblown sand forms dunes that are characterized by well-sorted grains showing large-scale crossbedding.

36. http://www.uoregon.edu/~millerm/sanddunes.html

37. Glacial • Glaciers do not effectively sort the materials that they transport. • Common type of resulting deposit is an unstratified accumulation of boulders, gravel, sand, and fine silt for which the term "till" is usually applied.

38. Rivers • Fluvial environments include braided and meandering river and stream systems. • River channels, bars, levees, and floodplains are parts (or subenvironments) of the fluvial environment. • Channel deposits consist of coarse, rounded gravel, and sand. • Bars are made of sand or gravel. • Levees are made of fine sand or silt. • Floodplains are covered by silt and clay.

39. Flood Plains • Rivers commonly meander across a flat flood plain before reaching the sea and depositing a considerable amount of sediment. • Rocks formed in a flood plain environment are commonly lenses of "fluvial" sandstone deposited in the meander channel enclosed in a shale deposited on the flood plain.

40. http://www.uoregon.edu/~millerm/braided.html

41. Lakes • Lacustrine environments (or lakes) are diverse; they may be large or small, shallow or deep, and filled with terrigenous, carbonate, or evaporitic sediments. • Fine sediment and organic matter settling in some lakes produced laminated oil shales.

42. http://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htmhttp://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htm

43. Delta • Deltas are large accumulations of sediment that are deposited where a river empties into a standing body of water. • They are one of the most significant environments of sedimentation and include a number of subenvironments such as stream channels, flood plain beaches, bars, and tidal flats. • The deposit as a whole consists of a thick accumulation of sand, silt, and mud. • Because of the abundance of vegetation in geologically young deltaic environments, coals of various ranks commonly are associated with these clastic sediments.

44. http://www.uoregon.edu/~millerm/delta.html

45. Swamps • Swamps (Paludal environments) Standing water with trees. Coal is deposited.

46. http://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htmhttp://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htm

47. http://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htmhttp://www.gpc.edu/~pgore/geology/historical_lab/sedenvirons.htm

48. Shoreline • Beaches, bars, and spits commonly develop along low coasts and partly enclose quiet-water lagoons. • Such sediments are well washed by wave action and is typically clean, well-sorted quartz sand. • Behind the bars and adjacent to the beaches, tidal flats may occur where fine silt and mud are deposited; evaporites may be present locally. • Barrier islands

49. Shoreline • Lagoons are bodies of water on the landward side of barrier islands. They are protected from the pounding of the ocean waves by the barrier islands, and contain finer sediment than the beaches (usually silt and mud). Lagoons are also present behind reefs, or in the center of atolls. • Tidal flats border lagoons. They are periodically flooded and drained by tides (usually twice each day). Tidal flats are areas of low relief, cut by meandering tidal channels. Laminated or rippled clay, silt, and fine sand (either terrigenous or carbonate) may be deposited. Intense burrowing is common. Stromatolites may be present if conditions are appropriate.

50. http://www.uoregon.edu/~millerm/beaches.html