Ripple marks in Moenkopi Formation rock off of Capitol Reef Scenic Drive

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, ripple marks are

sedimentary structures Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different parti ...

(i.e., bedforms of the lower

flow regime A bedform is a geological feature that develops at the interface of fluid and a moveable Bed (geology), bed, the result of bed material being moved by fluid flow. Examples include Current ripples, ripples and dunes on the Stream bed, bed of a riv ...

) and indicate agitation by

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

( current or

waves United States Naval Reserve (Women's Reserve), better known as the WAVES (for Women Accepted for Volunteer Emergency Service), was the women's branch of the United States Naval Reserve during World War II. It was established on July 21, 1942, ...

) or directly by

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

Defining ripple cross-laminae and asymmetric ripples

* ''Current ripple marks'', ''unidirectional ripples'', or ''asymmetrical ripple marks'' are asymmetrical in profile, with a gentle up-current slope and a steeper down-current slope. The down-current slope is the

angle of repose The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or Strike and dip, dip relative to the horizontal plane on which the material can be piled without slumping. At this angle, the material ...

, which depends on the shape of the sediment. These commonly form in

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

and aeolian

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

s, and are a signifier of the lower part of the Lower

Flow Regime A bedform is a geological feature that develops at the interface of fluid and a moveable Bed (geology), bed, the result of bed material being moved by fluid flow. Examples include Current ripples, ripples and dunes on the Stream bed, bed of a riv ...

. * Ripple cross-laminae forms when deposition takes place during migration of current or wave ripples. A series of cross-laminae are produced by superimposing migrating ripples. The ripples form lateral to one another, such that the crests of vertically succeeding laminae are out of phase and appear to be advancing upslope. This process results in cross-bedded units that have the general appearance of waves in outcrop sections cut normal to the wave ''crests''. In sections with other orientations, the laminae may appear horizontal or ''trough''-shaped, depending upon the orientation and the shape of the ripples. Ripple cross-laminae will always have a steeper dip downstream, and will always be perpendicular to paleoflow meaning the orientation of the ripples will be in a direction that is ninety degrees to the direction that current if flowing.Boggs Jr., Sam. (2006) Principles of Sedimentology and Stratigraphy, 4th ed. Scientists suggest current drag, or the slowing of current velocity, during deposition is responsible for ripple cross-laminae.Potter, Pettijohn. (1977) Paleocurrents and Basin Analysis

Ripple marks in different environments

Wave-formed ripples

* Also called bidirectional ripples, or symmetrical ripple marks have a

symmetric Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is invariant under some transformations ...

al, almost

sinusoidal A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic wave whose waveform (shape) is the trigonometric sine function. In mechanics, as a linear motion over time, this is '' simple harmonic motion''; as rotation, it correspond ...

profile; they indicate an environment with weak currents where water motion is dominated by wave oscillations. * In most present-day streams, ripples will not form in sediment larger than coarse sand. Therefore, the

stream bed A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...

s of sand-bed streams are dominated by current ripples, while gravel-bed streams do not contain bedforms. The internal structure of ripples is a base of fine sand with coarse grains deposited on top since the size distribution of sand grains correlates to the size of the ripples. This occurs because the fine grains continue to move while the coarse grains accumulate and provide a protective barrier.

Ripple marks formed by aeolian processes

;Normal ripples: Also known as impact ripples, these occur in the lower part of the lower

sands with grain sizes between 0.3-2.5 mm and normal ripples form wavelengths of 7-14 cm. Normal ripples have straight or slightly sinuous crests approximately transverse to the direction of the wind. ;Megaripples: These occur in the upper part of the lower flow regime where sand with bimodal particle size distribution forms unusually long wavelength of 1-25 m where the wind is not strong enough to move the larger particles but strong enough to move the smaller grains by saltation. ;Transverse aeolian ridges: There is some thought that transverse aeolian ridges are a form of fossilized ripple, but there is no conclusive evidence so far. ;Fluid drag ripples: Also known as aerodynamic ripples, these are formed with fine, well-sorted grain particles accompanied by high velocity winds which result in long, flat ripples. The flat ripples are formed by long saltation paths taken by grains in suspension and grains on the ground surface.

Definitions

;Crest: The point on a wave with the maximum value or height. It is the location at the peak of the wave cycle as shown in picture to the right. ;Trough: The opposite of a crest, so the minimum value or height in a wave. It is the location at the very lowest point of a wave cycle also shown in picture to right. ;Lee: The lee side has a steeper slope than the stoss. The lee is always on the back side of the ripple, which is also on the opposite side of where the current flow meets the ripple. The current flows down the lee side. ;Stoss: The stoss is the side of a wave or ripple that has a gentle slope versus a steeper slope. Current always flows up the stoss side and down the lee side. This can be used to determine current flow during the time of ripple formation. File:Dakota ripples.jpg, Ripple marks in

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Dakota Formation The Dakota is a sedimentary rock, sedimentary geologic unit name of Formation (stratigraphy), formation and Group (stratigraphy), group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and ...

, east side of

Dinosaur Ridge Dinosaur Ridge is a segment of the Dakota Hogback in the Morrison Fossil Area National Natural Landmark located in Jefferson County, Colorado, near the town of Morrison, Colorado, Morrison and just west of Denver. In 1877 Arthur Lakes, a clerg ...

. Scale bar on notebook is 10 cm. File:Wren's Nest National Nature Reserve - ripple beds.jpg, Ripple beds in the Wren's Nest National Nature Reserve, Dudley, England File:WaveRipple.JPG, Wave/symmetrical ripple, Nomgon, Mongolia File:Climbing ripples.JPG, Cross-section through asymmetric climbing ripples, seen in the Zanskar Gorge,

Ladakh Ladakh () is a region administered by India as a union territory and constitutes an eastern portion of the larger Kashmir region that has been the subject of a Kashmir#Kashmir dispute, dispute between India and Pakistan since 1947 and India an ...

, NW Indian

Himalaya The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than 100 pea ...

. Ripples climb when sediment fluxes in the flow are very high. File:Complex ripples.jpg, Complex ripple marks on

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

tidal flat at Blackberry Hill, Wisconsin.

References

* Easterbrook, Don J. Surface processes and landforms. Upper Saddle River, N.J: Prentice Hall, 1999. Print. pp. 479-480. * Greeley, Ronald, and James D. Iversen. Wind as a Geological Process On Earth, Mars, Venus and Titan (Cambridge Planetary Science Old). New York: Cambridge UP, 1987. pp. 153-154 * Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution, 2nd ed. Belmont: West Publishing Company, 1997. pp. 114-15, 352.

External links

Ripple Marks and Uniformitarianism

Unidirectional flow: Sand ripples and grain distribution 2D model

Unidirectional flow: Sand ripples and topography 2D model

Waves: Sand ripples and grain distribution 2D model

Waves: Sand ripples and topography 2D model
{{Authority control Sedimentary structures Patterned grounds