Geochronology/Mesozoic

Mesozoic geochronology 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 [...]."

Cretaceous
The Cretaceous/Cenozoic boundary occurs at 65.0 ± 0.1 Ma (million years ago).

Late Cretaceous
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.

"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."

“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.”

"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."

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

"Three Antarctic Ocean K/T boundary sequences from ODP Site 738C on the Kerguelen Plateau, ODP Site, 752B on Broken Ridge and ODP Site 690C on Maud Rise, Weddell Sea, have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies. Results show that Site 738C, which has a laminated clay layer spanning the K/T boundary, is biostratigraphically complete with the earliest Tertiary Zones P0 and P1a present, but with short intrazonal hiatuses. Site 752B may be biostratigraphically complete and Site 690C has a hiatus at the K/T boundary with Zones P0 and P1a missing."

"The cosmopolitan nature of the dominant fauna began during the last 200,000 to 300,000 years of the Cretaceous and continued at least 300,000 years into the Tertiary. This indicates a long-term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature, oxygen, salinity and nutrient conditions. A few thousand years before the K/T boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress. There is no evidence of a sudden mass killing of the Cretaceous fauna associated with a bolide impact at the K/T boundary. Instead, the already declining Cretaceous taxa gradually disappear in the early Danian and the opportunistic survivor taxa (Ch. waiparaensis and Guembelitria cretacea) increase in relative abundance coincident with the evolution of the first new Tertiary species."

"The Chicxulub impact is commonly believed to have crashed into Yucatan precisely at the KT boundary and caused the mass extinction. However, the stratigraphically oldest impact glass spherule ejecta documented from NE Mexico and Texas predate the mass extinction by 100-150 ky. Elsewhere in the North Atlantic, Caribbean, Belize, Guatemala and southern Mexico, there is a consistent pattern of impact spherules reworked in early Danian sediments and overlying a major KTB unconformity. This indicates that the Chicxulub impact predates the KT boundary and did not cause the mass extinction (Keller et al., 2009, 2013)."

In the top center is a 2.7 cm section of a polished shell with 6 sutures. It is from the extinct cephalopod Baculites compressus; Cretaceous, 100 million years old, Bearpaw Formation, Montana, USA.

The middle center photo is of Baculites ovatus, at the Naturalis Museum, Leiden.

The lower center is a fossil cast of a Baculites grandis shell taken at the North American Museum of Ancient Life.

On the right is an example of Plesiacanthoceras wyomingense from the late Cretaceous in Wyoming, USA. It is exhibited in Smithsonian National Museum of Natural History: Hall of Fossils.

Upper Cretaceous
Discoscaphites iris on the right is an ammonite from the Owl Creek Formation (Upper Cretaceous), Owl Creek, Ripley, Mississippi USA.

Maastrichtian
The Maastrichtian, in the International Commission on Stratigraphy geologic timescale, the latest age (uppermost stratigraphy stage) of the Late Cretaceous epoch or Upper Cretaceous stratigraphy series, of the Cretaceous period or system, and of the Mesozoic era or erathem, spanned the interval from 72.1 to 66 million years ago, preceded by the Campanian and succeeded by the Danian (part of the Paleogene and Paleocene).

At the end of this period, there was a mass extinction known as the Cretaceous–Paleogene extinction event, (formerly known as the Cretaceous–Tertiary extinction event).

At this extinction event, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups, died out linked to an Chicxulub impactor (asteroid) about 10 to 15 km wide colliding with Earth at the end of the Cretaceous.

The base of the Maastrichtian stage is at the first appearance of ammonite species Pachydiscus neubergicus, at the original type locality near Maastricht, a reference profile for the base was then appointed in a section along the Ardour river called Grande Carrière, close to the village of Tercis-les-Bains in southwestern France.

The Quiriquina Formation, a unit of the Arauco Group of the Late Maastrichtian, is in Chile, where it overlies granitic rocks and underlies the Lebu Group.

The glauconitic sandstones and conglomerates of the formation were deposited in a marine environment.

The Viñita Formation is in Coquimbo, Chile, whose strata date back to the Santonian to Maastrichtian.

Campanian
The Campanian, in the International Commission on Stratigraphy geologic timescale, the fifth of six ages of the Late Cretaceous epoch (or, the fifth of six stratigraphy stages in the Upper Cretaceous series, spans the time from 83.6 ± 0.7 Ma to 72.1 ± 0.6 Ma and is preceded by the Santonian and followed by the Maastrichtian.

The Bearpaw Formation or Bearpaw Shale is a geologic formation of the Late Cretaceous (Campanian) age that outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear Paw Mountains in Montana. It includes a wide range of marine fossils, the remains of a few dinosaurs and is known for its fossil ammonites.

The formation was deposited in the Bearpaw Sea, which was part of the Western Interior Seaway that advanced and then retreated across the region during Campanian time. It is composed primarily of dark grey shales, claystones, silty claystones and siltstones, with subordinate silty sandstones, including bedded and nodular concretions (both calcareous and ironstone concretions) and thin beds of bentonite, then as the seaway retreated toward the southwest, the marine sediments of the Bearpaw became covered by the deltaic and coastal plain sediments of the overlying formations.

Coal beds (black bands) are common in the Horseshoe Canyon Formation and were formed in coastal swamps.

The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta, that takes its name from Horseshoe Canyon, an area of badlands near Drumheller.

The Horseshoe Canyon Formation crops out extensively in the area around Drumheller, as well as farther north along the Red Deer River near Trochu, Alberta and along the North Saskatchewan River in Edmonton. It is overlain by the Battle, Whitemud, and Scollard formations. The Drumheller Coal Zone, located in the lower part of the Horseshoe Canyon Formation, was mined for sub-bituminous coal in the Drumheller area from 1911 to 1979.

The Judith River Formation is a fossil-bearing geologic formation in Montana, part of the Judith River Group, dating to the Late Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age, laid down during the same time period as portions of the Two Medicine Formation of Montana and the Oldman Formation of Alberta.

The Judith River Formation conformably overlies the Claggett Formation and Pakowki Formation, overlain by the Bearpaw Formation, equivalent to the Belly River Formation in the southern Canadian Rockies foothills, the Lea Park Formation in central Albert and the Wapiti Formation in the northwestern plains.

Santonian
The Santonian, an age in the geologic timescale or a stratigraphy stage, a subdivision of the Late Cretaceous epoch or Upper Cretaceous stratigraphy series, spans the time between 86.3 ± 0.7 mya and 83.6 ± 0.7 mya, and is preceded by the Coniacian and followed by the Campanian.

The base of the Santonian stage is defined by the appearance of the Inoceramidae bivalve Cladoceramus undulatoplicatus and its top (the base of the Campanian stage) is marked by the extinction of the crinoid Marsupites testudinarius.

Coniacian
The Coniacian, an age or stage in the geologic timescale, a subdivision of the Late Cretaceous epoch or Upper Cretaceous stratigraphy series spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma and is preceded by the Turonian and followed by the Santonian.

Beginning in the Middle Coniacian, an anoxic event (OAE-3) occurred in the Atlantic Ocean, causing large scale deposition of black shales in the Atlantic domain, which lasted till the Middle Santonian (from 87.3 to 84.6 Ma) and is the longest and last such event during the Cretaceous period.

Turonian
The base of the Turonian stage is defined as the place where the ammonite species Wutinoceras devonense first appears in the stratigraphic column, the GSSP for the base of the Turonian located in the Rock Canyon anticline near Pueblo, Colorado (United States, coordinates: 38° 16' 56" N, 104° 43' 39" W).

Cenomanian
The Cenomanian per the International Commission on Stratigraphy is the oldest or earliest age of the Late Cretaceous or the lowest stratigraphic stage of the Upper Cretaceous.

As a unit of geologic time measure, the Cenomanian age spans the time between 100.5 ± 0.9 Ma and 93.9 ± 0.8 Ma, preceded by the Albian and is followed by the Turonian, where the Upper Cenomanian starts approximately at 95 Ma.

The base of the Cenomanian is placed at the first appearance of foram species Rotalipora globotruncanoides in the stratigraphic record, located in an outcrop at the western flank of Mont Risou, near the village of Rosans in the French Alps (département Hautes-Alpes, coordinates: 44°23'33"N, 5°30'43"E), in the reference profile, located 36 meters below the top of the Marnes Bleues Formation.

Early Cretaceous
"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)."

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

Angiosperms (flowering plants) appeared for the first time during the Early Cretaceous. This time also saw the evolution of the first members of the Neornithes (modern birds).

The Jurassic/Cretaceous boundary occurs at 144.2±2.6 Ma (million years ago).

Albian
The Albian, the youngest or uppermost subdivision of the Early/Lower Cretaceous, approximate time range of 113.0 ± 1.0 Ma to 100.5 ± 0.9 Ma is preceded by the Aptian and followed by the Cenomanian.

A reference profile for the base of the Albian stage (GSSP) had not yet been established.

The top of the Albian stage (the base of the Cenomanian stage and Upper Cretaceous series) is defined as the place where the foram species Rotalipora globotruncanoides first appears in the stratigraphic column.

The following representatives of the Albian stage are worthy of notice: the phosphorite beds of the Forest of Argonne and Pays de Bray areas in France; the Flammenmergel of northern Germany; the lignites of Utrillas in Spain; the Upper sandstones of Nubia, and the Fredericksburg beds of North America.

Aptian
The Aptian, a subdivision of the Early or Lower Cretaceous, encompasses the time from 125.0 ± 1.0 Ma to 113.0 ± 1.0 Ma, succeeds the Barremian and precedes the Albian.

The Selli Event, also known as OAE1a, was one of two oceanic Anoxic events, which occurred around 120 Ma and lasted approximately 1 to 1.3 million years.

The Aptian extinction was a minor one hypothesized to have occurred around 116 to 117 Ma.

Barremian
The Barremian, between 129.4 ± 1.5 Ma and 125.0 ± 1.0 Ma is a subdivision of the Early Cretaceous or the Lower Cretaceous preceded by the Hauterivian and followed by the Aptian stage.

Hauterivian
The Hauterivian in the Early Cretaceous or in the Lower Cretaceous between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma is preceded by the Valanginian and succeeded by the Barremian.

Valanginian
The Valanginian stage succeeds the Berriasian stage of the Lower Cretaceous and precedes the Hauterivian stage of the Lower Cretaceous.

Berriasian
The Berriasian, the oldest, or lowest, subdivision in the entire Cretaceous, spanned the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago), succeeds the Tithonian (part of the Jurassic) and precedes the Valanginian.

Jurassic
The Jurassic/Cretaceous boundary occurs at 144.2±2.6 Ma (million years ago).

The Jurassic period is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago (Mya) to the beginning of the Cretaceous Period 145 Mya. A 140 Mya age for the Jurassic-Cretaceous instead of the usually accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. One of the authors of the study proposing the 140 Ma boundary age, sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences.

"Si logramos publicar esos nuevos resultados, sería el primer paso para cambiar formalmente la edad del Jurásico-Cretácico. A partir de ahí, la Unión Internacional de la Ciencias Geológicas y la Comisión Internacional de Estratigrafía certificaría o no, depende de los resultados, ese cambio."

The start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, and the Tithonian event at the end; neither event ranks among the "Big Five" mass extinctions, however.

The separation of the term Jurassic into three sections originated with Leopold von Buch. The faunal stages from youngest to oldest are:

Late Jurassic
Paleontologists appear to prefer "Late Jurassic", "Middle Jurassic", and "Early Jurassic".

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)." use "Late Jurassic" as a time frame, but "Upper Jurassic" as a stratigraphic frame.

On the right is an example of Kosmoceras cromptoni from the Late Jurassic, Chippenham, England.

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.

Kimmeridgian
Lithacosphinctes achilles is from the Kimmeridgian.

Callovian
On the right is an image of Peltoceras solidum, an ammonite from the Matmor Formation (Jurassic, Callovian), Makhtesh Gadol, Israel.

On the left is an example of Kosmoceras medea.

Another species of Kosmoceras is on the lower right, specifically Kosmoceras proniae.

Aalenian
"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."

"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)."

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."

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.

Lower Jurassic
Uptonia jamesoni from the lower Jurassic is in the family Polymorphitidae, superfamily Eoderocerataceae, order Ammonitida, subclass Ammonoidea, class Cephalopoda.

Toarcian
The Toarcian, in the International Commission on Stratigraphy (ICS) geologic timescale, an age and stage in the Early or Lower Jurassic, spans the time between 182.7 Ma and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.

The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus Eodactylites first appears, a GSSP for the base is located at Peniche, Portugal. The top of the stage is at the first appearance of ammonite genus Leioceras.

Pliensbachian
Pleuroceras spinatum (Bruguière 1789) is of the family Amaltheidae. The Pliensbachian, an age of the geologic timescale and stage in the stratigraphic column, is part of the Early or Lower Jurassic epoch or series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma. The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.

The base of the Pliensbachian is at the first appearances of the ammonite species Bifericeras donovani and genera Apoderoceras and Gleviceras, with The Wine Haven profile near Robin Hood's Bay (Yorkshire, England) has been appointed as global reference profile for the base (GSSP).

It is a pyritic specimen. The biozone index is to the end of Pliensbachian.

Sinemurian
The Sinemurian is an age in the Early or Lower Jurassic that spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago).

The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian.

Hettangian
"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)."

"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]."

Another FO is that of "the aragonitic foraminifer Praegubkinella turgescens"

The Triassic/Jurassic boundary occurs at 205.7±4.0 Ma (million years ago).

Triassic
"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."

Late Triassic
"During the Late Triassic, the Newark rift basin of Eastern North America was in the interior of tropical (2.5–9.5° N) Pangaea. Strikingly cyclical lacustrine rocks comprise most of the 6770 m of continuous core recovered from this basin by the Newark Basin Coring Project."

"A consistent hierarchy in frequencies of the lake level cycles is present throughout the Late Triassic (and earliest Jurassic) portions of the cores, an interval of about 22 m.y.. Calibration of the sediment accumulation rate by a variety of methods shows that these thickness periodicities are consistent with an origin in changes in precipitation governed by celestial mechanics. The full range of precession-related periods of lake level change are present, including the two peaks of the ∼20,000 year cycle of climatic precession, the two peaks of the ∼100,000 year eccentricity cycle, the single peak of the 412,900 year eccentricity cycle, and the ∼2,000,000 year eccentricity cycle."

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."

Norian
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 above indicates the time frames at and above the Anisian.

An example of Ussuriphyllites amurensis (Kiparisova) is on the right. It is from the Lower-most Anisian, Atlasov Cape area.

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
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.

Early Triassic
"Global warming is widely regarded to have played a contributing role in numerous past biotic crises. Here, we show that the end-Permian mass extinction coincided with a rapid temperature rise to exceptionally high values in the Early Triassic that were inimical to life in equatorial latitudes and suppressed ecosystem recovery."

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.

Smithian
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.

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

Induan
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."

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

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.

The Permian/Triassic boundary occurs at 248.2 ± 4.8 Ma (million years ago).

Inversand quarry
At the Inversand quarry, imaged on the right, "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."

But asteroid impacts, though rare, occur once in a while, over very large areas, at aperiodic intervals such as the Chicxulub crater, diagrammed on the left. Most scientists agree that this impact is the cause of the Cretatious-Tertiary Extinction, 65 million years ago (Ma), that marked the sudden extinction of the dinosaurs and the majority of life then on Earth. This shaded relief image of Mexico's Yucatan Peninsula shows a subtle, but unmistakable, indication of the Chicxulub impact crater.

Hypotheses

 * 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.