RIPPLE MARK.pptx

RIPPLE MARK.pptx

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  Presented by: Kuki Monjori Boruah ASSAMUNIVERSITY, SILCHAR DEPARTMENT OF EARTH SCIENCE Submitted to: Dr. Nagendra Pandey Professor Department of Earth Science Assam University, Silchar
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   INTRODUCTION  ANATOMYOF RIPPLE MARK  CLASSICATION  STRUCTURE RELATED TO RIPPLE MARKS  SIGNIFICANCE  CONCLUSION  REFERENCES
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   A seriesof small ridges produced especially on sand by the action of wind, a current of water, or waves.  Found in modern sedimentary environments and in the ancient.  Usually form in conditions with flowing water in the lower part of the flow regime.  Ripple marks are caused by water flowing over loose sediment which creates bed forms by moving sediment with the flow. Bed forms are linked to flow velocity and sediment size, whereas ripples are characteristic of shallow water deposition and can also be caused by wind blowing over the surface.
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   Ripple marksin cross section Symmetrical ripple marks o Also known as oscillation or vortex ripple. o Created by two way current. o Ripples have symmetrical limbs. o Commonly found in sandstone from shallow marine environment.
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   Asymmetrical ripplemarks oCreated by one way or unidirectional current. oLimbs of the ripple are not equal with one side is more shallow and one is steeper. oThis type of ripple can tell the direction of current.
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   Another differenttypes of criteria used for classification of ripple marks are shape (crestline) and magnitude (wavelength and height).  Ripple marks based on crestline- Generate cross laminae that all dip in the same direction and these type of ripple constructed by unidirectional flow of current STRAIGHT Generate curvy cross laminae and formed by unidirectional flow of current SINUOUS Generate curvy cross laminae with unidirectional swoop CATERNARY Liguoid ripples have lee slope surfaces curved an lunate ripples have stoss surface curved LINGUOID/ LUNATE
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   Ripples basedon magnitude-  Magnitude wise ripples have been classified into ripples, megaripples, dunes and sandwaves  The main controlling parameter is the velocity of current.
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   When thedepositional system contains mud as well as sand, intermittent breaks in the current flow may lead to preservation of streaks of mud within the ripple troughs and the resultant structure is flasher beddings.  With increasing proportion of mud, wavy beddings are produced.  When the proportion of mud is very high compared to that of sand then isolated lenticles of sand may be preserved within thick layer of mud and the structure is termed as lenticular bedding.
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   The firstand most obvious information we can get from the presence of ripples in sedimentary rocks is that a current must have been present- either a water current or a blowing wind. Their crests are always oriented perpendicular to the current that formed them, telling us what the direction of currents in past environments was.  Ripple marks, both wave-formed and current-formed, are of value in determining the environments under which sediments are deposited.  Recognizing wave ripples can tell us whether an ancient sandstone deposited on a shoreline rather than on a river bank or a dune field.  Ripples are very useful in structural geology because, as they mark the surface of deposition, they are useful indicators of the stratigraphic top in a sedimentary sequence.
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   Ripples arecommon sedimentary structures occur in both siliciclastic and carbonate sediments.  They can form by both water and wind transport.  Ripples that develop in response to unidirectional flow are asymmetrical in shape.  Ripples that form by wave action under oscillatory flow are called oscillation ripples or symmetrical ripple.  On the basis of shape of crestline ripple marks can be straight, sinuous, caternary, linguoid or lunate.  Ripple marks have many significance in determining paleocurrent direction, stratigarphic sequence etc.
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   Sengupta, S.M.:Introduction to Sedimentology; second edition.  Boggs, Sam Jr. : Principles of Sedimentology and Stratigraphy; 5th Edition.  https://blogs.egu.eu/divisions/ts/2019/10/11/features- from-the-field-ripple-marks/  https://www.geologypage.com/2017/11/ripple- marks.html  https://en.wikipedia.org/wiki/Ripple_marks