The Absaroka sequence was a

cratonic sequence A cratonic sequence (also known as megasequence, Sloss sequence or supersequence) in geology is a very large-scale lithostratigraphy, lithostratigraphic sequence in the rock record that represents a complete cycle of marine transgression and Mari ...

that extended from the end of the Mississippian through the

Permian 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 ...

periods. There is an

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

between the Absaroka and the lower Kaskaskia sequence. This unconformity divides the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

into the Mississippian and Pennsylvanian periods in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. Like the Kaskaskia sequence, Absaroka sedimentary deposits were dominated by

detrital Detritus (; adj. ''detrital'' ) is particles of rock derived from pre-existing rock through weathering and erosion.Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7 A fragment of detritus is called a clast.Essentials of Geology, 3rd Ed, Stephen ...

or siliclastic rocks. These are mostly

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

siltstones Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed ...

and shales. The first sediments were deposited near the

continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...

al margins, particularly near the Ouachita and Appalachian highlands. Characteristic of the strata from this time are cyclothems: alternating marine and non-marine strata indicative of changes in sea-level, probably due to cyclic glaciation in the Southern Hemisphere. In North America, the waters of the Absaroka sequence regressed (thinned) westward as the highlands to the east steadily eroded. Restricted oceanic circulation in the west led to extensive

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

formation. By the end of the period, the regression was complete, and the marine strata were superseded by extensive red bed deposition.

Transgressive–regressive units

These cycles of

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

change have been divided into at least six magnitudes of order.Busch, R. M., and Rollins, H. B. (1984). Correlation of Carboniferous strata using a hierarchy of transgressive-regressive units. ''Geology'', v. 12, p. 471-474. Each order is a span of years that become smaller. The smallest unit is described as a punctuated aggradational cycle (PAC) and represents between 225,000 and 100,000 years of sediment accumulation.Anderson, E.J., and Goodwin, P.W., (1980). Application of the PAC hypothesis to limestones of the Helderberg Group. Society of Economic Paleontologists and Mineralogists, Eastern Section Guidebook, p. 32. In the field, these units are usually one to five meters thick and contain several different rock units. These units show quick changes in sea level that were controlled by climate change due to glaciers. The fifth order is often called a

cyclothem In geology, cyclothems are alternating stratigraphy, stratigraphic sequences of marine and non-marine Sedimentary structures, sediments, sometimes interbedded with coal seams. The cyclothems consist of repeated sequences, each typically several m ...

and may contain several PAC sequences and generally represent about 500,000 years. Again, glaciation seems to be the cause of the cyclic nature of the strata.

References

*Monroe, James S., and Reed Wicander. ''The Changing Earth: Exploring Geology and Evolution'', 2nd ed. Belmont: West Publishing Company, 1997. {{ISBN, 0-314-09577-2(pp. 544-9) Geology of the United States Historical geology Carboniferous System of North America Permian System of North America