Classnotes on Ch. 14. Mesozoic

Mesozoic (245-66 million years ago)

It is divided into three periods

Triassic 37 million years (Mountains in Germany)

Jurassic 64 (Jura mountains in Switzerland)

Cretaceous 78 million years (Paris basin France)

During Mesozoic the major event was the break up of the supercontinent Pangea.

This of course very much influenced the climate, and the ocean currents, of course  the evolution of life was also influenced. Populations became separated or were brought into contact giving rise to lots of evolutionaly possibilites.

Mesozoic most commonly is called the age of “Dynosaurs” or Reptiles, it was also the time for the evolution of birds, mammals and angiosperms (flowering plants).

Break up of Pangea

As part of the new Wilson cycle the supercontinent started to breake up almost as soon as it got together.

The break up has four general stages.

1. first stage

rifting between Laurasia and Gondwana during the Late Triassic.

By the end of the Triassic the expanding Atlantic Ocean had separated North America from Africa.  This was followed by the rifting of North America from South America during Late triassic, Early Jurassic.

Mixing of Tethys and Pacific, and Pacific ocean waters flowed into the new forming Gulf of Mexico. (low latitude, arid climate lots of evaporite!!!)

2. Second stage

Rifting and movement of the various Gondwana continents during Late Triassic, Early Jurassic periods. As early as the Late Triassic, Antarctica and Australia separated from South America and Africa, while India split away from all Gondwana continents and began to move northward.

3. Third stage

Late Jurassic South America and Africa began to separate.

Narrow basins have been formed and thick evaporates developed.

During this stage the Tethys seaway began to close as a result of clockwise rotation of Laurasia and the northward movement of Africa, ---- Mediterranean sea. By the end of Late Cretaceous Australia and Antarctica had separated, India riched the equator, South America and Africa were widely separated, and Greenland started to separate from Europe.

Global sealevel rise happened in the Cretaceous. Uniqe conditions again.  

4. Final stage

This happened during Cenozoic, Australia moved northward and Greenland completely separated from Europe and rifted from north America to form a separate land mass.

Effects of the breakup on the climate

Climate of the Pangea!!!!! Megamonsoon

Dry continental landmasses. Temperate climate only at high latitude. Triassic is ice-free, therefore the temperature gradient is small.

The break up caused larger temperature gradient, cooling toward the Jurassic. However, the general climate remained warm, bec. there were no continents at the pole.

The Mesozoic history of the North American craton

          The Triassic  essentially is the same as the Permian. Red beds are wide spreaded on the caton and in the Appalachian, Greenland region.

The continental area remained very large, sea level was still low, and rivers carried sandstone to the bordering seaways.

          Along the eastern and southern margin as the biginning of the break up of Pangea, normal faulting and igneous activity had started. The faulting started during the Late Triassic, and continued into the Jurassic.

          Marine deposition was continuous over much of the Cordilleran region, however the island arc continued to collide with the craton during the Triassic. This activity is called Sonoma orogeny. During the Jurassic the whole Cordilleran region has experienced a serious of mountain forming episodes that resulted in the formation of the Sierra Nevada and the Rocky Mountains. The entire mountain building event is called Cordilleran orogeny.

Continental interior

During the Mesozoic most of the craton was well above the sea level and did not experience epiric sea indunation. However the Triassic and early Jurassic period still belong to the Absaroka sequence. The next cratonic sequence is called Zuni and we will incorporated its sediments into the three continental margin regions.

Eastern coastal region

During the Early and Middle Triassic coarse detrital sediments derived from the erosion of the newly rised Appalachian filled the different intramountain basins. The erosion of the Appalachian almost completely finished, by the end of the mesozoic.

During the Late Triassic the first stage of the Pangean breakup resulted in the formation fault block basins from Nova Scotia to North Carolina.

Along the chain of rift basin block faulted mountains gave source for the huge amount sediment in this basin. 6000 m of immature, coarse grained detrital sediment accumulated here preserve the best climate induced cyclicity in the whole earth history.

The name of the whole rift basin sedimentation is Newark Supergroup. The basins are clearly freshwater basins, and they contain lots of evaporite, lots of important fossils, Dinosaur footsteps.

Interlayered with the sediment wide basalt lava flows blanketed the basin floors. Formation of basalt sills and dykes also important. The most famous basalt sill is the so called Palisades sill (200 million years old) along the Hudson river in New York-New Yersey area.

As the Atlantic ocean started to grew the rifting ceased along the eastern marging which finally became a passive margin. The block faulted mountains formed during the rifting continued to be the source of detrital sediment filling up the ocean basin of the newly forming Atlantic ocean.

During the Cretaceous the Appalachian mountain reelevated again and shed sediment onto the continental shelf, forming a gently dipping seaward thickening wedge  of rocks up to 300m thick. These rocks today exposed in a belt expending from Long Island toNewYork, to Georgia.



Gulf coastal region

This area was above the sea level until the Late Triassic, when the Gulf of Mexico began to form as the result of breaking up of North America and South America. Some oceanic water flew into this narrow, restricted basin and with arid continental climate it produced huge amount of evaporite. More than 1000 m of evaporite has formed. (These evaporites made it possible to study the great salt dome tectonism during Tertiary, which associeted with great oil formation).

During the late Jurassic the basin was not that much restricted, and evaporite deposition ended. Normal marine condition has returned and cyclic deposition of sandstone, shale and limestone started.

During the early Cretaceous the area was experienced transgression and deep marine wter covered this region during the rest of the Cretaceous.

Reef forming became characteristing for this area during the Cretaceous.

The reefs during the Cretaceous were different from the Jurassic ones. During the Cretaceous the major reef builders are Bivalves called Rudists. These reef are also excellent oil reservoirs, because of their high porosity. (Texas)

Western region

During the Early Triassic the island arc collided with the continent forming an oceanic continent convergent boundary. The tectonic event is called Sonoma orogeny. The subduction here was steep and fast in response of the westward moving craton as the Atlantic ocean was opening up. During these tectonic event the sedimentationof this region consisted of shallow marine sandstone, shale and limestone. During the Late Triassic the regression of the sea brought even lower sea level, so the exposed areas of the former seafloor experienced erosion. During this time over this region red sandstone which are as spectacular as the ones from Permian in the Painted desert in Western North America.

One of the most famous Triassic Formation of the western margin Triassic is the Late Triassic Chinle Formation widely exposed over the Colorado Plateau spectacularly exposed in Petrified Forest National Park, Arizona. (Conifers (Gymnosperms). Fossilization resulted here from the silification of plant tissues. The Chinle Formation also famous about the Labirinthoid amphibians, phytosaurus, and small dynosaurus.

Jurassic, Cretaceous Cordilleran tectonism

It is very complex. Its name is Cordilleran orogeny. The tectonic activity started during the Jurassic and continued into the Cenozoic. Most of this activity related to the westward movic North American continent. The orogeny has three phases.

1. Nevadan orogeny

It began during the Late Jurassic and continued into the Cretaceous.

During this phase the major event is the generation of large amount grenite-granodiorite magma (huge batoliths of Sierran Nevada, Idaho, Southern California, Coast Range.

2.Sevier orogeny

This happened mostly in the Cretaceous. The major event of this phase was the formation of low angle thrust faults as a result of the subduction of the pacific plate beneath the North American plate. This thrusting produced north to south trending mountain ranges consisting blocks of the paleozoic shelf and slope strata.Southern California-Utah and from Montana to Western Canada.

3.Laramide orogeny

Late Cretaceous, early Cenozoic, east of the Sevier orogenic belt in the present day Rocky Mountain areas of New Mexico, Colorado and Wyoming.

During this phase there were some thrust faulting, but more commonly folding has occured. As a result anticlines, domes and basins formed in the Middle and southern Rockies.


The sediment in the Western region of North America during the Early Jurassic was clean, crossbedded sandstone, indicative of windblown deposits.

The thickest and most prominent of this is the Navajo Sandstone (Zion National Park, Utah). The most fantasting pattern of this sandstone is the large scale cross beds, some of which are more than 25 m high. The upper part of the sandstone has smaller cross beds and contain Dynosaur and Crocodilian fossils. Based on its features it is most probably represent a coastal dune environment.

During the Middle Jurassic a transgression happened Sundance seaway

resulting sediments accumulating from the closeby highlands.

After the regression of Sundance sea, the area was covered by multicolored sandstone called Morrison Formation. Morrison Formation represent continental lake environment, which cyclically dried out having just a few stream. The Morrison Formation is world famous, because it contains a very rich dynosaur fauna. Minimum of 50 individuals have been found in a small flood plain area along stream beds. The amount of skeletons indicate, that they were brought together during floods (Dynosaur National Monument Vernal, Utah).

During the Late Cretaceous a big marine transgression  happened Cretaceous Interior seaway, that occupied the area east of the Sevier orogenic belt. This seaway is more than 1500 km wide and it effectively divided North America into two large land masses until just before the end of the Cretaceous.

Eastern margin did not have more than 100 m thickdeposit, indicating, that sucduction was very low. On the west however, lots of sediment formed from the erosion of the newly uplifted mountains; congl. sandstone, siltst. shale, depending on the small scale sealevel changes.

Microplate tectonism

Mountain building, and continental accretion not only possible by partial melting along subduction zones. Geologists discovered, that parts of mountains formed by accretion of small lithospheric blocks, that are clearly foregin in origin.

Geologic evidence indicates that at least 25% of the entire  Pacific coast from Alaska to Baja California consists of accreted microplates.

They are composed of island arc, oceanic plates, and small fragments of continents. The growth by microplates are faster along active margin, than passive ones.

Mesozoic mineral resources

Coal: lignite and bituminous coal, with some local antracite

Rocky Mountains

Australia, russia, China, Hungary


Gulf of Mexico

Source: mesozoic microorganisms


in Triassic, Jurassic sandstone




Kimberlite, Cretaceous

Porphyry copper

in the batholites