Triassic Period Notes

The Triassic period is a part of the Phanerozoic Eon, Mesozoic Era.
It falls between the Permian and Jurassic periods, spanning from 252 to 201 million years ago (Ma).
The Triassic is divided into epochs: Early, Middle, and Late.
Key ages within these epochs include:
- Rhaetian
- Norian
- Carnian
- Ladinian
- Anisian
- Olenekian
- Induan

The Triassic time scale is defined by various geological and biological markers.
GSSP (Global Boundary Stratotype Section and Point) markers are used to define the boundaries between stages.
Examples of markers include:
- FAD (First Appearance Datum) of Psiloceras spelae
- FAD of Misikella posthernsteini s.s.
- FAD of Misikella posthernsteinis.l.
- FAD of Metapolygnathus parvus
- FAD of Daxatina canadensis
- FAD of Eoprotrachyceras curionii
- FAD of Chiosella timorensis
- FAD of Novispathodus waageni
- FAD of Hindeodus parvus
Isotopic excursions ($\delta^{13}C$ and $\delta^{18}O$) and sea-level changes are also important markers.
Sea level during the Triassic varied, with coastal onlap indicated on the time scale.

The Triassic period saw the beginning of the breakup of the supercontinent Pangea.
Rifting is a linear zone where the lithosphere is being pulled apart due to extensional tectonics.
Rifting can lead to the breakup of landmasses and the formation of new ocean basins with a mid-ocean ridge (MOR).
Rifts often feature a central valley (graben) with uplifts on one or both sides, frequently filled with lakes when continental.
Rifting between North America and South America/Africa began in the late Permian/Triassic.
The Neotethys Ocean opened during this period.
The continent of Cimmeria was created.
The breakup of Pangea occurred in several phases during the Mesozoic:
- Laurussia separated from Gondwana.
- Splitting between South America/Africa and Antarctica, accompanied by basaltic lava flows.
- South America split from Africa, with the Atlantic rift extending southward, opening the Atlantic Ocean.
- Breakup of Laurussia occurred in the early Cenozoic (~45 Ma).

The rifting of Pangea formed basins between North America and Africa.
The Appalachians started eroding during the Triassic.
These basins trapped continental sediments, forming the Newark Supergroup of terrestrial rocks.
The Newark Supergroup consists of conglomerates, sandstones, and siltstones, and contains dinosaur tracks.
The NY-NJ area has extensive basaltic (gabbro) lava flows from the rifting of Pangea within the Newark Supergroup.
These flows, now called the Palisades of the Hudson River, may be earliest Jurassic in age based on radiometric dating.

Moenkopi Formation: Shales associated with the Absaroka regression.
Shinarump Conglomerate: Derived from erosion of uplifted areas in Colorado, Arizona, and Idaho.
Chinle Formation: Colored shales with outcrops in the Painted Desert of Arizona and Petrified Forest National Park; known for agate petrified trees (permineralization) and oldest known US dinosaur fossils (discovered by Dr. Sterling Nesbitt).
- Part of the Dockum Group in Texas.
- Includes the Monitor Butte, Petrified Forest, and Owl Rock Members.

The Sonoma orogeny had its maximum at the Permian-Triassic (P-T) boundary.
Oceanic rocks were thrusted on top of eroded structures from the Antler orogeny.
During the Triassic and Jurassic, the Gulf of Mexico was a large depositional basin in the rift.
Evaporites formed from the concentration of seawater.
Salt domes formed, producing fold and fault structures and traps for oil and gas.
Triassic sea level was generally low, with a sea-level fall during the regression of the Absaroka sequence, though not as low as during the Permian.

Triassic deposition was characterized by many terrestrial areas with alluvial deposits and red beds.
Mountains were eroding along the eastern seaboard.
Orogenies were occurring along the west coast.
Evaporites were forming in the proto-Gulf of Mexico.
The climate was very warm and dry early in the period, becoming more temperate later.
A pluvial event occurred in the Carnian, representing an abrupt shift from arid to humid climate.

The Carnian Pluvial Episode involved:
- Enormous input of siliciclastic sediments.
- Anoxia.
- A change in the carbonate factory, with a shift from high microbial to low metazoan production or cessation of production.
- Four episodes of increased rainfall.
- Multiple C cycle perturbations (negative excursions).
- Biotic changes on land and in the ocean, including ammonoid and conodont extinction and land fauna and flora turnover.
- Global warming.
Dinosaurs originated in the Early to Middle Triassic but radiated explosively during the Carnian Pluvial Episode.
Scleractinian corals originated in the Middle Triassic but became major components of reefs during the Carnian, replacing microbial reefs.

Approximately 76% of all marine and terrestrial species and about 20% of families went extinct.
Causes are debated but include:
- Climate change.
- Rising sea level.
- Ocean anoxia.
- Volcanism from the rifting of Pangea.
- Possible impact-related events (though the Manicougan crater in Quebec predates the extinction by ~13 million years).
- Slow speciation rates.
The favored cause is linked to large igneous province (LIP) volcanism, specifically the Central Atlantic Magmatic Province (CAMP).
Massive $CO_2$ emissions from CAMP led to global warming and ocean acidification.
Significant impacts of the extinction:
- Ammonite cephalopods, bivalves, conulariids, coral reef collapse, land plant turnover, almost all remaining conodonts, last placodonts and giant ichthyosaurs, amphibians, reptiles, and synapsids were affected.
- Set the stage (along with the Carnian Pluvial Event) for dinosaurs to become dominant land vertebrates in the rest of the Mesozoic.