A rhythmite consists of layers of

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

which are laid down with an obvious periodicity and regularity. They may be created by annual processes such as seasonally varying deposits reflecting variations in the runoff cycle, by shorter term processes such as tides, or by longer term processes such as periodic floods. Rhythmites serve a significant role in unraveling prehistoric events, providing insights into

sea level change The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...

, glaciation change, and Earth's orbital variations which serve to answer questions about

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

Annually-laminated rhythmites

Annually-laminated deposits (

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. Of the many rhythmites in the geological record ...

s) are rhythmites with annual periodicity: annual layers of

are laid down through seasonal variations that result from precipitation, or from temperature, which influences precipitation rates and debris loads in runoff. Of the many rhythmites found in the geological record, varves are among the most important and illuminating to studies of past climate change. Varves are amongst the finest resolution events easily recognised in

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

Periodically laminated rhythmites

Rhythmites may be deposited with periodicities other than annual. The geologic record captures both more frequent events (e.g., tides) and less frequent events (glacial floods).

Tidal rhythmites

Geologic tidal rhythmites display layered

Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the Permian Period, Ma. It is the fifth and penultimate perio ...

beds which record tidal cyclical events such as semi-diurnal, diurnal or

neap tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables c ...

spring tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

cycle that demonstrate marine influence in sediments that were previously interpreted as purely continental. The geologic record captures layered beds comparable to those found currently in sediments in the

Bay of Fundy The Bay of Fundy () is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its tidal range is the highest in the world. The bay was ...

in Canada and the Bay of

Mont Saint-Michel Mont-Saint-Michel (; Norman: ''Mont Saint Miché''; ) is a tidal island and mainland commune in Normandy, France. The island lies approximately off France's north-western coast, at the mouth of the Couesnon River near Avranches and is i ...

in France. The Storm Mountain area of

Big Cottonwood Canyon Big Cottonwood Canyon is a canyon in the Wasatch Range southeast of Salt Lake City in the U.S. state of Utah. The -long canyon provides hiking, biking, picnicking, rock-climbing, camping, and fishing in the summer. Its two ski resorts, Bright ...

, Utah, has rhythmites which record sea-level sedimentary deposit fluctuations consistent with the cycle of the tides. Tidal rhythmites are also known from other geological periods and times, such as the late

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

Proglacial rhythmites

One common mechanism is the episodic flooding which results from glacial dam bursts. In one such example geologists estimate that the Missoula Floods cycle of flooding and reformation of the lake took an average of 55 years and that the floods occurred approximately 40 times over the 2,000-year period between 15,000 and 13,000 years ago. Distinct rhythmites with an approximately 55-year periodicity have been observed.

Glacial epicycle rhythmites

Sea-level changes which correspond to the glacial periods also show up as extremely long-term rhythmites. As an example, the ice surge in the Quaternary resulted in changes in sea level of 127 meters to 163 meters. The regression and transgression of the sea level from waxing and waning glaciers have been identified in the rhythmites of the

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the International Commission on Stratigraphy, ICS geologic timesc ...

and

Permian period The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

References