Jurassic and Cretaceous Periods: Geology, Climate, and Life

JURASSIC

Tethys opened to the west and separated Laurasia to the north from Gondwana to the south. The Cimmerian orogenic phase took place.

Jurassic climate

Criteria are based on biological types (reefs and plants). The climate was tropical and subtropical in the area of the Tethys, and temperate in the Boreal zone. In general, temperatures were high and more humid than in the Triassic.

Jurassic lithofacies

Liassic transgression (rifting phase)

1. Development of carbonate platforms of the Bahamas type, with reefs in the Tethys. Liassic platform limestones and corals were deposited.
2. Calcareous pelagic facies, rhythmic and ammonitico rosso.

Oxfordian transgression

An expansion phase marked by the opening of the North Atlantic. Evaporites formed in the new basins, carbonates formed on shallow platforms, and siliceous deposits formed in deeper waters. Radiolarites are competent layers with more than 50% non-detrital quartz derived from radiolarians.

Final Jurassic regression

Shallow carbonate facies, sometimes evaporitic and detrital, with development of Purbeck facies.

Jurassic biosphere

Dominant groups: ammonites, foraminifera, coccoliths, radiolarians, and diatoms; reptiles; gymnosperms.

New groups: mammals, birds, and angiosperms.

CRETACEOUS

Features: opening of the Atlantic, a transgressive phase. Source rocks of petroleum are abundant. The dating of the end of the period is relatively precise, marked by an iridium-rich layer. The creation and expansion of the Atlantic Ocean occurred, leading to the destruction of lithosphere. Sea level rose by more than 200 m.

Atlantic opening

1. Rising sea level: detrital deposits, shallow carbonates, and evaporites in new basins; basin facies.
2. Alpine mountain ranges: circum-Pacific orogen (North American Cordillera and the Andes); the Alpine-Himalayan chain.

North American Cordillera: an orogenic margin formed by the destruction of oceanic lithosphere as the continent advances westward.

Andes: a unique situation; an orogenic margin formed by the destruction of oceanic lithosphere as the continent advances westward, producing thermal orogeny without compression.

Iberian Peninsula: with the opening of the North Atlantic, a triple junction formed that allowed the Iberian Peninsula to shift and rotate.

Cretaceous facies

• Weald (continental deposits)
• Urgonian (shallow platform deposits)
• Chalk (white limestone/marl with calcareous nannoplankton)

Black shale: an event of phytoplankton explosion that led to the development of anoxic conditions.

Cretaceous biosphere

Dominant groups: ammonites, foraminifera, coccoliths, and reptiles. Angiosperms predominated in the Late Cretaceous, leading to the radiation of insects. Birds diversified.

Cretaceous-Tertiary mass extinction

Causes:

1. Intense volcanic activity
2. Change in the Earth's magnetic field
3. Meteorite impact

Possible global consequences of the impact:

1. Effects on the atmosphere, eliminating the ozone layer
2. Blocking sunlight by darkening the Earth's surface
3. Acidification of the upper part of ocean waters