Geochronology/Mesozoic

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany. Credit: Gerhard Boeggemann.

Geochronology/Mesozoic is the science of applying dates in the past to rocks of the Mesozoic.

Notations

Let

1. ALMA represent the Asian Land Mammal Age,
2. b2k represent before AD 2000,
3. BP represent before present, as the chart is for 2008, this may require an added -8 for b2k,
4. ELMMZ represent the European Land Mammal Mega Zone,
5. FAD represent first appearance datum,
6. FO represent first occurrence,
7. Ga represent Gegaannum, billion years ago, or -10⁹ b2k,
8. GICC05 represent Greenland Ice Core Chronology 2005,
9. GRIP represent Greenland Ice Core Project,
10. GSSP represent Global Stratotype Section and Point,
11. HO represent highest occurrence,
12. ICS represent the International Commission on Stratigraphy,
13. IUGS represent the International Union of Geological Sciences,
14. LAD represent last appearance datum,
15. LO represent lowest occurrence,
16. Ma represent Megaannum, million years ago, or -10⁶ b2k,
17. NALMA represent the North American Land Mammal Age,
18. NGRIP represent North Greenland Ice Core Project, and
19. SALMA represent South American Land Mammal Age.

"The term b2 k [b2k] refers to the ice-core zero age of AD 2000; note that this is 50 years different from the zero yr for radiocarbon, which is AD 1950 [...]."^[1]

Mesozoic time frames

Cretaceous

The quarry pit in Mantua Township in central New Jersey has been owned by the Inversand Company for nearly a century. Credit: Rowan University.

This is a Catapleura repanda fossil from the Rowan quarry. Credit: Eric Tomenga.

"Paleogeographically, the sub-alpine terrain of southeastern France [...] was located on the proximal part of the South-European Tethys margin. It includes the Vocontian Basin, which experienced relatively high rates of subsidence during Jurassic and Early Cretaceous times, bordered by carbonate platforms limited by a net of extensional or strike–slip faults (Graciansky et al., 1999)."^[6]

This phraseology connects "Early Cretaceous" with "times".

The aerial image on the right shows the quarry pit in Mantua Township in central New Jersey has been owned by the Inversand Company for nearly a century.^[7]

"When an asteroid hit the Earth around 66 million years ago, it wiped out almost 75 percent of the plants and animals on the planet. All dinosaurs, except those that would eventually give rise to modern birds, were killed following the impact. Yet despite such a vast die-off, no bone bed containing a concentration of fossils as a result of this event has been found."^[7]

“We don’t know yet [if it dates from the mass extinction], but we are testing this hypothesis by examining the fossils, the sediments and the chemistry.”^[8]

"At the end of the Cretaceous, when the dinosaurs met their maker, the region was a shallow tropical sea full of fish, sea turtles, crocodiles, and even mosasaurs. But at some point around 66 million years ago, whether it was due to the asteroid impact or some other cause, many of the inhabitants of the sea died and were preserved in a large bone bed."^[7]

On the left is a specimen of Catapleura repanda from the Rowan quarry found in the Cretaceous marl.

Late Jurassic

Paleontologists appear to prefer "Late Jurassic", "Middle Jurassic", and "Early Jurassic".^[9]

Time frame references such as "We applied the method of frequency ratios (Huang et al., 1992; Mayer and Appel, 1999) to compare the observed spectral frequencies with orbital frequencies estimated for Late Jurassic time (Berger and Loutre, 1994) (Tables 1A and B)."^[6] use "Late Jurassic" as a time frame, but "Upper Jurassic" as a stratigraphic frame.

Upper Jurassic

The International Commission on Stratigraphy (ICS) uses only "Upper Jurassic", "Middle Jurassic", and "Lower Jurassic" in its Global Boundary Stratotype Section and Point (GSSP) Table for all periods.^[10]

Aalenian

This chart shows the magnetic polarity and ammonite zones for the Aalenian. Credit: S. Cresta, A. Goy, S. Ureta, C. Arias, E. Barrón, J. Bernad, M. L. Canales, F. García-Joral, E. García-Romero, P. R. Gialanella, J. J. Gómez, J. A. González, C. Herrero, G. Martínez, M. L. Osete, N. Perilli and J. J. Villalaín.

The image and overlain labels display the type strata for the Jurassic stage Aalenian. Credit: S. Cresta, et al.

Leioceras opalinum, Graphoceratidae; has a diameter: 4.5 cm; Lower Aalenian, Middle Jurassic; between Ohmenhausen and Reutlingen, Germany. Credit: H. Zell.

"The Global Boundary Stratotype Section and Point (GSSP) for the Aalenian Stage, formally defined at the base of bed FZ107 in the Fuentelsaz section, Castilian Branch of the Iberian Range (Spain), has been ratified by the IUGS."^[11]

"The position of the boundary coincides with the first occurrence of the ammonite assemblage characterized by Leioceras opalinum and Leioceras lineatum and corresponds with a normal polarity interval correlated with the up-to-date Jurassic magnetic polarity time scale (Gradstein and others, 1994; Ogg, 1995)."^[11]

The "first occurrence of the species of the genus Leioceras, evolved from Pleydellia, has been widely accepted as being the biochronological event which best enables the recognition of the basal boundary of the Aalenian Stage."^[11]

On the right is a chart which indicates the ammonite zones that serve as geochrons for the Aalenian.

The second image down on the right displays the type strata for the Aalenian.

An example of Leioceras opalinum is shown on the left.

Hettangian

Psiloceras spelae tirolicum has its first occurrence at the Triassic-Jurassic boundary as geochron for the base of the Jurassic. Credit: Axel von Hillebrandt et al.

Fossil shell of Psiloceras planorbis from Germany, on display at Galerie de paléontologie et d'anatomie comparée in Paris. Credit: Hectonichus.

In this image of the Kuhjoch East section, the "Golden Spike" is at the Triassic-Jurassic boundary. Credit: Axel von Hillebrandt et al.

"Since the 1960’s, the LO (lowest occurrence) of the ammonite Psiloceras (usually the species P. planorbis [first image on the right]) has provided the working definition of the TJB (e.g., Lloyd, 1964; Maubeuge, 1964; Cope et al., 1980; Warrington et al., 1994; Gradstein et al., 2004)."^[12]

"The Global Stratotype Section and Point (GSSP) defining the base of the Jurassic System Lower Jurassic Epoch and Hettangian Stage is situated at the Kuhjoch pass, Karwendel Mountains, Northern Calcareous Alps, Austria (47°29'02"N/11°31'50"E). The Triassic-Jurassic (T-J) boundary is exposed at Kuhjoch West and at Kuhjoch East [in the second image on the right], and corresponds to the first occurrence (FO) of the ammonite Psiloceras spelae tirolicum [at the top of this section]."^[13]

Another FO is that of "the aragonitic foraminifer Praegubkinella turgescens"^[13]

Triassic

This is an example of Psiloceras tilmanni from the Jurassic. Credit: Günter Knittel.

"What must underlie discussion of the definition of the TJB is the well accepted concept that global correlateability should be the main emphasis in the selection of a GSSP (e.g., Cowie et al., 1986; Remane et al., 1996; Gradstein et al., 2004; Walsh et al., 2004). As Remane et al. (1996: 79) expressed it, “the boundary definition will normally start from the identification of a level which can be characterised by a marker event of optimal correlation potential.” Thus, our goal here is to evaluate the possible marker events that could be used to define the TJB and to argue that an ammonite-based marker event has optimal correlation potential. This marker event is the LO of Psiloceras tilmanni in the New York Canyon section of Nevada."^[12]

Upper Triassic

The chart in the Norian section describes the chronology of Upper Triassic time frames.

Rhaetian

The "extinction of Conodonta has long been seen as a terminal Triassic event, and the presence/absence of conodonts thus is routinely used to distinguish Triassic from Jurassic strata. Rhaetian conodont assemblages are of low diversity and abundance, and conodonts can be easily reworked. Therefore, the HO of Conodonta is not a reliable criterion for TJB definition. However, it is very useful to know that the presence of autochthonous Conodonta is a pre-Jurassic indicator, and this micropaleontological criterion has been widely used and accepted."^[12]

Norian

The Norian chart shows the chronological positions of Upper Triassic Stages and Substages. Credit: Heinz W. Kozur & Gerhard H. Bachmann.

The chart above shows the chronological positions of Upper Triassic Stages and Substages, including the Norian.

Sevatian

The chart in the Norian section describes the chronology of Upper Triassic time frames, including the Sevatian.

Alaunian

The chart in the Norian section describes the chronology of Upper Triassic time frames, including the Alaunian.

Lacian

The chart in the Norian section describes the chronology of Upper Triassic time frames, including the Lacian or Early Norian.

Carnian

The chart in the Anisian section places the Carnian in the Late, or Upper, Triassic.

Tuvalian

The chart in the Norian section describes the chronology of Upper Triassic time frames, including the Tuvalian.

Julian

The chart in the Anisian section places the Julian in the Carnian.

Cordevolian

The chart in the Anisian section places the Cordevolian in the Carnian.

Middle Triassic

The chart in the Anisian section places the Middle Triassic below the Late Triassic.

Ladinian

The chart in the Anisian section places the Ladinian above the Asinian.

Longobardian

The chart in the Anisian section places the Longobardian above the Fassanian.

Fassanian

The chart in the Anisian section places the Fassanian at the base of the Ladinian.

Anisian

The chart indicates the time frames at and above the Anisian. Credit: Heinz W. Kozur & Gerhard H. Bachmann.

The chart above indicates the time frames at and above the Anisian.

Illyrian

The chart in the Anisian section places the Illyrian at the top of the Anisian.

Pelsonian

The chart in the Anisian section places the Pelsonian below the Illyrian.

Bithynian

The chart in the Anisian section places the Bithynian below the Pelsonian.

Aegean

This chart shows the stratigraphic position of the Aegean in the Middle Triassic. Credit: Heinz W. Kozur & Gerhard H. Bachmann.

The chart above shows the Aegean as the lowest time frame of the Anisian.

The magnetostratigraphy in the farthest right column of the above chart has black as normal polarity, white as reversed polarity, and gray for no reliable data.

Lower Triassic

The chart in the Aegean section shows the Scythian to be equivalent to the Lower Triassic.

Scythian

The chart in the Aegean section shows the Scythian to be equivalent to the Lower Triassic.

Olenekian

The chart in the Aegean section indicates that the Scythian is divided into the Olenekian above and Induan below.

Spathian

The Spathian is sometimes referred to as the Late Olenekian.^[14]

Smithian

This diagram is a time-rock north-northwest to south-southeast cross section of the Lower Triassic of Idaho, Wyoming and Utah. Credit: Spencer G. Lucas, Thomas H. Goodspeed and John W. Estep.

As indicated in the above stratigraphy, the Sinbad Formation is entirely within the Smithian, or Early Olenekian.

The Smithian is sometimes referred to as the Early Olenekian.^[14]

Brahmanian

The chart in the Aegean section indicates that the Brahmanian is equivalent to the Induan.

Induan

The diagram shows the Permian-Triassic boundary at the base of the Induan. Credit: Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao.

Hindeodus parvus is now recognized as the index fossil, occurring in the Zone above the P-T boundary. Credit: Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao.

In the diagram on the right, the Permian-Triassic boundary is at the base of the Induan limestone that occurs within the Yinkeng Formation.

"The Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary [...] is defined at the base of Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan section D, Changxing County, Zhejiang Province, South China."^[15]

"Hindeodus parvus is now recognized as the index fossil" occurring in the Zone above the P-T boundary.^[15]

Dienerian

The chart in the Aegean section indicates that the Dienerian is equivalent to the Gandarian.

Gandarian

The chart in the Aegean section indicates that the Gandarian is in the Brahmanian.

Gangetian

The chart in the Aegean section indicates that the Gangetian is in the Brahmanian.

Locations on Earth

Paleontologists excavate part of the bone bed that contains thousands of fossils from close to the mass dinosaur extinction. Credit: Rowan University.

At the Inversand quarry, "Located in South Jersey, the cradle of dinosaur paleontology, the quarry in Mantua Township, N.J., contains thousands of fossils dating back 65 million years."^[16]

Research

Hypothesis:

1. Each time frame or span of time in geochronology has at least one dating technique.
2. Late Jurassic and Upper Jurassic are different time frames.

Control groups

This is an image of a Lewis rat. Credit: Charles River Laboratories.

The findings demonstrate a statistically systematic change from the status quo or the control group.

“In the design of experiments, treatments [or special properties or characteristics] are applied to [or observed in] experimental units in the treatment group(s).^[17] In comparative experiments, members of the complementary group, the control group, receive either no treatment or a standard treatment.^[18]"^[19]

Proof of concept

Def. a “short and/or incomplete realization of a certain method or idea to demonstrate its feasibility"^[20] is called a proof of concept.

Def. evidence that demonstrates that a concept is possible is called proof of concept.

The proof-of-concept structure consists of

1. background,
2. procedures,
3. findings, and
4. interpretation.^[21]

See also

References

External links

• The Denisens of Cretaceous Mantua
• Global Boundary Stratotype Section and Point (GSSP) of the International Commission on Stratigraphy

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