Types

There are several basic types of cross-cutting relationships:

• Structural relationships may be faults or fractures cutting through an older rock.

• Intrusional relationships occur when an igneous pluton or dike is intruded into pre-existing rocks.

• Stratigraphic relationships may be an erosional surface (or unconformity) cuts across older rock layers, geological structures, or other geological features.

• Sedimentological relationships occur where currents have eroded or scoured older sediment in a local area to produce, for example, a channel filled with sand.

• Paleontological relationships occur where the animal activity or plant growth produces truncation. This happens, for example, when animal burrows penetrate into pre-existing sedimentary deposits.

• Geomorphological relationships may occur where a surficial feature, such as a river, flows through a gap in a ridge of rock. In a similar example, an impact crater excavates into a subsurface layer of rock.

Cross-cutting relationships may be compound in nature. For example, if a fault were truncated by an unconformity, and that unconformity cut by a dike. Based upon such compound cross-cutting relationships it can be seen that the fault is older than the unconformity which in turn is older than the dike. Using such rationale, the sequence of geological events can be better understood.

Scale

Cross-cutting relationships may be seen cartographically, megascopically, and microscopically. In other words, these relationships have various scales. A cartographic crosscutting relationship might look like, for example, a large fault dissecting the landscape on a large map. Megascopic cross-cutting relationships are features like igneous dikes, as mentioned above, which would be seen on an outcrop or in a limited geographic area. Microscopic cross-cutting relationships are those that require study by magnification or other close scrutiny. For example, penetration of a fossil shell by the drilling action of a boring organism is an example of such a relationship.

Other use

Cross-cutting relationships can also be used in conjunction with radiometric age dating to effect an age bracket for geological materials that cannot be directly dated by radiometric techniques. For example, if a layer of sediment containing a fossil of interest is bounded on the top and bottom by unconformities, where the lower unconformity truncates dike A and the upper unconformity truncates dike B (which penetrates the layer in question), this method can be used. A radiometric age date from crystals in dike A will give the maximum age date for the layer in question and likewise, crystals from dike B will give us the minimum age date. This provides an age bracket, or range of possible ages, for the layer in question.

While some regional terms are still in use,[3] the table of geologic time presented in this article conforms to the nomenclature, ages, and color codes set forth by the ICS as this is the standard, reference global geologic time scale – the International Geological Time Scale.[1][4]

Principles

See also: Age of Earth, History of Earth, and Geological history of Earth

The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years).[5] It chronologically organizes strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the Cretaceous–Paleogene extinction event, marks the lower boundary of the Paleogene System/Period and thus the boundary between the Cretaceous and Paleogene Systems/Periods. For divisions prior to the Cryogenian, arbitrary numeric boundary definitions (Global Standard Stratigraphic Ages, GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record.[6][3]

Historically, regional geologic time scales were used[3] due to the litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardizing globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The ICC represents this ongoing effort.

The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of:

• Superposition – Newer rock beds will lie on top of older rock beds unless the succession has been overturned.

• Horizontality – All rock layers were originally deposited horizontally.[note 1]

• Lateral continuity – Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.

• Biologic succession (where applicable) – This states that each stratum in a succession contains a distinctive set of fossils. This allows for correlation of stratum even when the horizon between them is not continuous.

• Cross-cutting relationships – A rock feature that cuts across another feature must be younger than the rock it cuts.

• Inclusion – Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming.

• Relationships of unconformities – Geologic features representing periods of erosion or non-deposition, indicating non-continuous sediment deposition.

While some regional terms are still in use,[3] the table of geologic time presented in this article conforms to the nomenclature, ages, and color codes set forth by the ICS as this is the standard, reference global geologic time scale – the International Geological Time Scale.[1][4]

Principles

See also: Age of Earth, History of Earth, and Geological history of Earth

The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years).[5] It chronologically organizes strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the Cretaceous–Paleogene extinction event, marks the lower boundary of the Paleogene System/Period and thus the boundary between the Cretaceous and Paleogene Systems/Periods. For divisions prior to the Cryogenian, arbitrary numeric boundary definitions (Global Standard Stratigraphic Ages, GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record.[6][3]

Historically, regional geologic time scales were used[3] due to the litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardizing globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The ICC represents this ongoing effort.

The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of:

• Superposition – Newer rock beds will lie on top of older rock beds unless the succession has been overturned.

• Horizontality – All rock layers were originally deposited horizontally.[note 1]

• Lateral continuity – Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.

• Biologic succession (where applicable) – This states that each stratum in a succession contains a distinctive set of fossils. This allows for correlation of stratum even when the horizon between them is not continuous.

• Cross-cutting relationships – A rock feature that cuts across another feature must be younger than the rock it cuts.

• Inclusion – Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming.

• Relationships of unconformities – Geologic features representing periods of erosion or non-deposition, indicating non-continuous sediment deposition.

The name Rotliegend has in the past not only been used to address the rock strata themselves, but also the time span in which they were formed (in which case the Rotliegend was considered a series or subsystem of the Permian). This time span corresponds roughly with the length of the Cisuralian epoch.

Facies and formation

In large parts of Pangaea, the last phases of the Hercynian orogeny were still ongoing during the start of the Permian. At the same time local crustal extension formed intramontane basins such as the large Permian Basin which covered parts of present-day Germany, Poland, Denmark, the North Sea, the Baltic Sea and the Netherlands. The early development of the basin went hand in hand with volcanism. Apart from these volcanic deposits the basin was filled by the erosional products of the Hercynian mountains to the south: mostly sands and gravels deposited under an arid and warm climate.[1]

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Stratigraphy

In the north of Germany and in the Netherlands, the Rotliegend is usually subdivided into two groups: a Lower Rotliegend Group (mostly volcanic rocks: tuffs and basaltic lavas) and an Upper Rotliegend Group (sandstones and siltstones). During the formation of the lower group the basin was still small and the deposition was restricted to the centre of the basin in the southeastern North Sea and northern Germany, this group is very limited in thickness in the Dutch subsurface. The upper group has a larger arial distribution since the basin had grown wider.

In Dutch lithostratigraphy, the Rotliegend lies on top of the late Carboniferous Limburg Group and below the Zechstein Group. The Upper Rotliegend Group is divided in the Silverpit Formation and Slochteren Formation, the last is an important reservoir for hydrocarbons. The German Bentheim Sandstone, which crops out in the Münsterland, is part of the Slochteren Formation.

The Rotliegend of northern Germany is continuous with that of the Netherlands. In other parts of Germany contemporaneous basins exist, such as the Saar-Nahe Basin, the Wetterau or the Saale Basin. The Rotliegend of these different intramontane basins is not easy to correlate and the lithostratigraphy of each basin has its own divisions (groups and formations).

A significant mass extinction event occurred at the end of this stage, which was associated with anoxia and acidification in the oceans and possibly caused by the volcanic eruptions that produced the Emeishan Traps.[5] This extinction event may be related to the much larger Permian–Triassic extinction event that followed about 10 million years later.

Stratigraphy

The Capitanian Stage was introduced into scientific literature by George Burr Richardson in 1904. The name comes from the Capitan Reef in the Guadalupe Mountains (Texas, United States). The Capitanian was first used as a stratigraphic subdivision of the Guadalupian in 1961,[6] when both names were still only used regionally in the southern US. The stage was added to the internationally used ICS timescale in 2001.[7]

Definitions

The base of the Capitanian Stage is defined as the place in the stratigraphic record where fossils of conodont species Jinogondolella postserrata first appear. The global reference profile for this stratigraphic boundary is located at Nipple Hill in the southern Guadalupe Mountains of Texas.

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The top of the Capitanian (the base of the Wuchiapingian and Lopingian series) is defined as the place in the stratigraphic record where the conodont species Clarkina postbitteri postbitteri first appears.

The Capitanian Stage was part of the time in which the Zechstein was deposited in Europe.[4] It is coeval with the old European regional Saxonian Stage. In the eastern Tethys domain, the Capitanian overlaps the regional Murgabian Stage, the Midian Stage and the lower part of the Laibinian Stage. In Russia the Capitanian equals the lower part of the regional Severodvinian Stage.