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DASAR LAUTAN

Bathymetric Chart of the Sea Floor

Physiographic Map of the Sea Floor 3-D Computer Generated Image of the East Pacific Rise

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Relief of Sea Floor (Bentuk Dasar Laut)

Major relief ocean bottom : * Continental margin

* Ocean basin floor

* Mid ocean ridge

Continental margin: * Continental Shelf

* Continental Slope

* Continental Rise

Ocean basin floor: * Oceanic rise

* Abyssal floor

* Seamount dan Guyot

* Trenches (palung)

Mid ocean ridge (punggung ditengah samudera):

- Mid Atlantic Ridge

- Mid Indian Ridge

- Pacific-Atlantic Ridge

- East Pacific Rise

Basins are depressions of the sea floor more or less equi-

dimensional in form and of variable extent.

Canyon are relatively narrow, deep depressions with steep

slopes, the bottoms of which grade continuously downward.

Continental (or island) shelves are zones adjacent to a continent

(or around an island) and extending from the low-water line to

the depth at which there is usually a marked increase of slope

to greater depth.

Continental (or island) slopes are the declivities seaward from

the shelf edge into greater depth.

Plains are flat, gently sloping or nearly level regions of the sea

floor, e.g. an abyssal plain.

Ridges are long, narrow elevations of the sea floor with steep

sides and irregular topography.

Seamounts are isolated or comparatively isolated elevations

rising 1000 m or more from the sea floor and of limited extent

across the summit.

Sills are the low parts of the ridges separating ocean basins from

one another or from the adjacent sea floor.

Trenches are long, narrow, and deep depressions of the sea floor,

with relatively steep sides.

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Asal –usul Ocean Basin (Dasar Lautan)

(1) Continental Drift

Pergerakan daratan gunung-gunung dalam skala yang lebih luas

pergerakan benua (movement of continent) continental

drift Pergerakan massa benua pada permukaan bumi

(2) Sea Floor spreading

Mengapa benua bergerak relatif terhadap yang benua lainnya

berkembang teori ‘sea floor spreading’

Kerak (crust) dasar benua yang baru dan materi kulit (mantle)

bagian atas yang kaku bertambah sepanjang rangkaian deretan

gunung-gunung pada dasar lautan dan bergerak tegak lurus

menjauhi punggung (ridges) gunung-gunung tersebut.

(3) Mencakup proses secara menyeluruh : Plate Tectonic

Ada sejumlah lempengan (plate) utama kedalam mana batuan

atau lithosphere dapat di pisah-pisahkan.

Interaksi antara lempengan ini saat mereka bergerak

menghasilkan bentuk-bentuk struktur kerak bumi yang

dapat diamati.

Tectonic (Junani) pembentukan Struktur Kerak bumi.

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Precambrian 4.6 B - 570 Ma solidification

Cambrian 514 Ma Gondwana, hard shell anim.

Ordovician 458 Ma separation, coldest

Silurian 425 Ma Laurentia collides with Baltica

Devonian 390 Ma pre-Pangea, equatorial forests

Early Carboniferous 356 Ma

Late Carboniferous 306 Ma western Pangea is complete

Permian 255 Ma deserts, reptiles, major ext.

Triassic 237 Ma Life begins to rediversify,Pangea

Jurassic 195 Ma Dinosaurs, Pangea starts to break

Late Jurassic 152 Ma Pangea rifts apart, Atlantic

Cretaceous 94 Ma New oceans, India

K/T extinction 66 Ma end of dinosaurs

Eocene 50.2 Ma India collides with Asia

Miocene 14 Ma Modern look

Modern

Future World +50 Ma N. Atlantic widens, Med. vanish

Future +100 Ma new subduction

Future +250 Ma new Pangea

Geological Periods Precambrian break-up of the supercontinent, Rodinia,

which formed 1100 million years ago. The Late Precambrian was an

"Ice House" World, much like the present-day.

Cambrian Animals with hard-shells appeared in great

numbers for the first time during the Cambrian. The continents were flooded

by shallow seas. The supercontinent of Gondwana had just

formed and was located near the South Pole.

Ordovician During the Ordovician ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and

Gondwana. The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana.

Silurian Laurentia collides with

Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent. Coral reefs expand and land plants begin to colonize the barren

continents.

Devonian By the Devonian the early Paleozoic oceans were closing, forming a "pre-Pangea". Freshwater fish

were able to migrate from the southern hemisphere continents to North America and Europe. Forests grew for the first time in the equatorial regions of Artic

Canada. Early Carboniferous During the Early

Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains. An ice cap grew

at the South Pole as four-legged vertebrates evolved in the coal swamps near the Equator.

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Late Carboniferous By the Late Carboniferous the

continents that make up modern North America and Europe had collided

with the southern continents of Gondwana to form the western half

of Pangea. Ice covered much of the southern hemisphere and vast coal

swamps formed along the equator.

Permian Vast deserts covered

western Pangea during the Permian as reptiles spread across the face of

the supercontinent. 99% of all life perished during the extinction event that

marked the end of the Paleozoic Era.

Triassic The supercontinent of Pangea, mostly

assembled by the Triassic, allowed land animals to migrate from

the South Pole to the North Pole. Life began to rediversify after the great

Permo-Triassic extinction and warm-water faunas spread across Tethys.

Jurassic

By the Early Jurassic, south-central Asia had assembled. A wide

Tethys ocean separated the northern continents from Gondwana. Though

Pangea was intact, the first rumblings of continental break up

could be heard.

Subduction zone Rocky Mountains

Formation of the Rocky Mountains http://wrgis.wr.usgs.gov/docs/parks/province/rockymtn.html

Late Jurassic The supercontinent of Pangea began to break apart in the Middle Jurassic. In the Late Jurassic the Central Atlantic

Ocean was a narrow ocean separating Africa from eastern North America. Eastern Gondwana had begun to separate form Western Gondwana

Cretaceous During the Cretaceous the South Atlantic Ocean

opened. India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that

Australia was still joined to Antarctica.

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K/T extinction The bull's eye marks the location of the Chicxulub

impact site. The impact of a 10 mile wide comet caused global climate

changes that killed the dinosaurs and many other forms of life. By

the Late Cretaceous the oceans had widened, and India approached the

southern margin of Asia.

Eocene 50 - 55 million years ago

India began to collide with Asia forming the Tibetan plateau and

Himalayas. Australia, which was attached to Antarctica, began to

move rapidly northward.

Collision of continental crust

• Whereas oceanic ridges indicate tension,

continental mountains indicate compressional forces are squeezing the land together.

3-2 Sea-Floor Spreading

Sedimentary Rocks Squeezed by Compression

Miocene

20 million years ago, Antarctica was coverd by ice and the northern continents were cooling rapidly. The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea.

Last Ice Age

When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago.

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Modern World

We are entering a new phase of

continental collision

that will ultimately result in the

formation of a new

Pangea supercontinent in

the future. Global climate is warming because we are

leaving an Ice Age

and because we are adding greenhouse

gases to the

atmosphere.

Modern World

If we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closingthe Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska.

Future +100

Future +250

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Bukti-bukti bahwa benua pernah bersatu:

(1) Umur Batuan: * fossil * Umur radioaktif batuan

(2) Kehidupan purbakala dan Cuaca:

rekaman fossil lingkungan masa lalu

(3) Orientasi magnet benua:

* perubahan posisi kutub (polar wandering)

* Pembalikan arah magnet (magnetic reversal)

(4) Sea Floor Spreading

* Umur batuan makin semakin jauh dari MOR

* Orientasi magnit batuan

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Figure 1-8a Tectonic Plates

Evidence for Continental Drift: Puzzle

According to Wegner, the continents are sections of a past super

continent called Pangea, which broke apart and drifted to their

present locations.

Now-Extinct Life Forms Preserved in the Geologic Record tell a story

Source: J. C. Carton/Carto/Bruce Coleman, Inc. New York

Evidence for Continental Drift: Fossils

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Source: William E. Ferguson

Evidence for Continental Drift: Rock Record Pangaea 200 to 300 Millions of Years Before the Present

• Axis of the oceanic ridge is offset by transform

(strike-slip) faults which produce lateral displacement. Ridges and rifts indicate movement.

3-2 Sea-Floor Spreading:

Movement at ridges

Segmented Ocean Ridge

Earth’s geomagnetic field is recorded as new crust cools.

3-3 Global Plate Tectonics

Driving Mechanisms for Plate Motions

New crust. Parallel bands of crust with the same magnetism form along the ridge.

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Geomagnetic Polarity Reversals

When new crust materials crystallizes,

some minerals align themselves with

Earth’s magnetic field, as it exists at that

time, imparting a permanent magnetic

field, called paleomagnetism, to the rock.

Periodically Earth’s magnetic field

polarity (direction) reverses poles.

Magnetic Anomalies

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Modern humans

Extinction of dinosaurs

Flowering plants and grasses

First mammals

Earliest dinosaurs

Early reptiles

Primitive fish

Geologic Time

• Rocks forming at the ridge crest record the magnetism existing at the time they solidify.

• Sea floor increases in age and is more deeply buried by sediment away from the ridge

because sediments have had a longer time to collect.

• Rates of sea-floor spreading vary from 1 to 10 cm per year for each side of the ridge and can be determined by dating magnetic anomaly stripes of the sea floor and measuring their distance from the ridge crest.

• Continents are moved by the expanding sea floor.

3-2 Sea-Floor Spreading

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Because Earth’s size has not changed, expansion of the crust in one area requires destruction of the crust elsewhere.

•Currently, the Pacific Ocean basin is shrinking as other ocean basins expand.

•Seismicity is the frequency, magnitude and distribution of earthquakes. Earthquakes are concentrated along oceanic ridges, transform faults, trenches and island arcs.

•Tectonism refers to the deformation of Earth’s crust.


•Destruction of sea floor occurs in subduction zones.

•Subduction is the process at a trench whereby one part of the sea floor plunges below another and down into the asthenosphere.


• Benioff Zone is an area of increasingly deeper seismic activity, inclined from the trench

downward in the direction of the island arc.


South Figi Basin and Cross Section Showing Benioff Zone

Earth’s surface is composed of a series of lithospheric plates. Plate edges extend through the lithosphere and are defined by seismicity.

•Plate edges are trenches, oceanic ridges and transform faults.

•Seismicity and volcanism are concentrated along plate boundaries.


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Movement of plates is caused by thermal convection of the “plastic” rocks of the asthenosphere which drag along the overlying lithospheric plates.


Driving Mechanisms for Plate Motions

Plate Rifting (cont'd): Earths Internal Heat Engine

Figure 1-10 Mid-Ocean Ridge

•Mantle plumes originate deep within the asthenosphere as molten rock which rises and melts through the lithospheric plate forming a large volcanic mass at a “hot spot”.


Mantle Plume

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Wilson Cycle refers to the sequence of events leading to the formation, expansion, contracting and eventual elimination of ocean basins.

• Stages in basin history are:

– Embryonic - rift valley forms as continent begins to split.

– Juvenile - sea floor basalts begin forming as continental fragments diverge.

– Mature - broad ocean basin widens, trenches eventually develop and subduction begins.

– Declining - subduction eliminates much of sea floor and oceanic ridge.

– Terminal - last of the sea floor is eliminated and continents collide forming a continental mountain chain.

3-3 Global Plate Tectonics The Wilson Cycle

3-4 Transform Faults

• If these plate motions continue, Baja will splinter off California.

The San Andreas fault in southern California is a transform fault that connects the sea-floor spreading ridge of the Gulf of California with the spreading ridge off Oregon and Washington.

Because the San Andreas fault has an irregular trace, strike-slip motion can cause local compression or tension.

3-4 Transform Faults

Fault Geometry

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•The Red Sea is a juvenile ocean basin that is forming as the African plate diverges from the Arabian plate.

•New basaltic ocean crust is just beginning to form in the center of the Red Sea.

3-4 Juvenile Ocean Basin

Hot, salty groundwater is dissolving metals from the rocks and depositing them as metal sulfides in dense brine pools like the Atlantis II Deep.

3-4 Juvenile Ocean Basin

Atlantis II Deep

Quiz 1

•Apa beda plate teori plate tektonik dan continental drift

•Apa yg di maksud dgn siklus wilson

•Apa yang dimaksud dengan

–Ridge

– sill

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