Chapter notes on ch. 16.

Cenozoic

The Cenozoic has been divided into two periods,

Tertiary (66-1.6 million years ago)

Quaternary (1.6 million-present)

Of course they are further divided into epoch

Cenozoic plate tectonism (overwiev)

Late Triassic fragmentation of the supercontinent continued till all the oceans and continents reached their present day location.

-Mid Atlantic ridge and east Pacific rise were established, and along them new oceanic crust were continuously forming.

- India moved northward further, and finally collided with southern Asia

-India along with the northward moving Africa caused the closure of the Tethys ocean

-Australia separated from and moved north to its present position during early Tertiary.

-Continental rifting started in the Late tertiary in east Africa, and still going on.

            1. Gulf of Aden (Miocene, oceanic crust)

            2. Red sea (Late Pliocene, oceanic crust)

            3. East African rift basins (slow thinning, still no oceanic crust)

Active subduction continued along the Cordilleran mobil belt

Cenozoic orogenic belts

Two major mobile belts is known:

1. Alpine-Himalayan mobile belt

2. Circum Pacific

Alpine Himalayan orogenic belt:

Alps:

The deformation is caused by the northward movement of the African and Arabian plates against Eurasia, and some micro plate collision also happened.

This orogenic belt is characterized by  mountain regions of the Mediterranean from the Atlantic ocean to Greece and Turkey.

            Pyrennes

            Alps

            Dinarides

            Apennines

            Hellenides

            Charpatians

            Balkans

            Pontides

            Taurides

And in northern Africa

            Rif

            Tellian

            Atlas

Active volcanoes in Italy (Vesuvio,Etna) and frequent earthquakes indicate that this activity has not been finished. (Iran, 1990; Turkey, 1992)

Major deformation took place during  Eocene to Late Miocene

Himalayas

Along the south facing edge of Asia a subduction started during the Cretaceous.

This subduction continued, and at the same time India moved to the north very fast (15-20cm/year).

Between 40-50 million years this movement abruptly slowed down (5 cm/year). Probably this event is the sign of the beginning collision between India and Asia.

As the Himalayas were uplifted they were also eroded, but at a rate insufficient to match the uplift. Sediment blanket from this source covers much of the Arabian sea and the Bay of Bengal.

Since its collision has started India has been shortened by about 2000 km, beneath Asia, and it still going on with about 5 cm/year

Circum Pacific orogenic belt

The Pacific plate has been consuming at subduction zones all along the Pacific ocean.

-Western and northern margins orogens are arc orogens, characterized by subduction of the oceanic lithosphere, deformation and igneous activity.

            Japan

                        Sea of Japan is a back arc marginal basin

- Spreading at the east pacific rise is carrying the Cocos and Nazca plates eastward, where they are being subducted beneath Central and South America. The active volcanoes and earthquakes lately show, that this zone is still active today.

            1985 earthquake Mexico City

            Volcanic mudflow in Columbia (1985)

            Andes is the result of this convergent plate boundary

                        crustal thickening by folding and granite plutons

-The land connection between north and south America is the result of subduction at the Middle American trench, together with arc magmatism. This connection made an important role in the animal evolution.

The Gulf coastal region

Following the final withdrawal of the Cretaceous Intercontinental seaway (Zuni), in the Cenozoic there was an other brief period of epiric sea in the Gulf Coastal region (Tejas). This sea however was nothing compare to the big Paleozoic epiric seas, it was largely restricted to the Gulf coastal Plain and Mississippi valley, and its max. level (Early Tertiary) it extended up north to southern Illinois.

During the Later Tertiary as this sea was regressing, on the long term regression, there were smaller transgression events, of which eighth is recorded in the Gulf coastal sedimentary rocks.

Detrital sediments came from the Cordilleran region and from the Appalachians.

Sediments here are sand silt shale and some carbonate.

These sediments are studied in big detail, since most of the sandstone stores hydrocarbon.

The oil storages, which are trapped by sedimentary facies change are called

Stratigraphic traps. The environment itself is similar to that of the Mississippi delta today.

Structural traps is the other kind, where the oil is trapped by tectonics movement such as folding, faulting. In the Gulf of Mexico area some of the oil is trapped by salt tectonics.

Salt is a low density  sedimentary rock, and when buried underneath more dense rocks, it tends to rise toward the surface in form of pillars called salt domes. As the salt rises, it penetrates and deform the overlying strata, creating structures, that may trap oil and gas. (They could also be  possible sites for nuclear vaste?!!!)

Florida during this time experienced huge amount of carbonate deposition. The carbonate deposition continues even today!!!! But the major deposition moved southward a little bit, because above Miami two rivers bring silicate sediments, which kills the carbonate production.

Carbonates are almost completely organic in origin, and most of these organisms hate living in dirty water.  In northern Florida there is a famous mammalian fauna found from early Miocene rocks. The fossils are mostly consist of horses and camels.

South east of Florida, about 80 km away (Florida Straight) lies the Great Bahamas BANK. Thick shallow carbonates accumulated there since the Cretaceous.

Eastern North America

This area is a passive continental margin since the Early Jurassic, after the early rifting phase of the Atlantic ocean. Even it is a passive margin, some reactivation can happen along old fault zones, such as the earthquake in 1985 Charleston, killing 60 people.

The present distinctive topography of the Appalachian is the product of Cenozoic uplift and erosion.

Remember, that by the end of the Cretaceous the whole mountain was eroded to a plain.

Cenozoic uplift rejuvenated the streams , which responded by a new downcutting. As they were downcutting they formed large canyons across the strata. For example the distinctive topography of the Valley and Ridge province is the result of preexisting geology and erosion. The resistant rocks would form the ridges, and shale, and other rocks would form the valleys.

Atlantic coastal plain

The coastal plain consists of sediment derived from the Appalachian. The sediment were brought by rivers to the east and deposited in nearshore and shelf environments.  These deposits contain lots of fossil assemblages, vertebrates seacows, whales, sharks, fishes, birds, and reptiles. The sediment here form a so called seaward vedge that dips gently seaward. They are up to 14 km high.

Cenozoic climate

The climate was equally warm during the Eocene. Eocene rocks above the Arctic circle show plant fossils such as palm trees and cycads which would have never lived under a cold climate such as it is there today. Alligators and tortoises were living as high latitude as 77N.

At this time the most climate sensitive living things are the leaves. Under warm climate, leaves are large, thick and they have smooth-edge.

Leaves of cool climate are thinner and smaller, with jagged edges, and are shed every winter.

During the Eocene, there was no good oceanic circulation which also indicate equally warm climate. Sea level was high, which helps. Very active mid oceanic ridge activity could have produce enough CO2 to make this greenhouse effect.

After the Late Eocene a dramatic change happened in the climate. In as little as 15 million years, the average temperature dropped more than 10C. By the end of this episode the earth turned from a warm greenhouse to an icehouse world. Polar glaciers started to form, and big temperature difference formed between the equator and the poles.

By the Middle Oligocene Antarctica built up big icecap, causing a large drop in sea level.

Mineral resources

Oil shale (with kerogen) (10 gallon of oil/ton of rock)

Wyoming, Utah, Colorado

Evaporites

Trona same place for sodium

Phosphate

Florida

Miocene bone valley

Bony fauna, Mastodon

Coal

Lignite

Montana, Wyoming

Reservoir rocks

Persian Gulf. Gulf of Mexico, Arab countries