Introduction to the Mesozoic Era
The Triassic World
The Jurassic World
The Cretaceous World
Introduction to the Cenozoic
Tertiary - Neogene
Upper Paleozoic World Permian
Middle Paleozoic World Devonian
Lower Paleozoic World Ordovician
Introduction to the Paleozoic Era
eon era period
Mesozoic Triassic 251 51
Permian 299 48
Carboniferous 359 60
Devonian 416 57
Silurian 444 28
Ordovician 488 44
Cambrian 542 54
• The Cambrian climate was probably moderate at first, becoming warmer over the
course of the period, as the second-greatest sustained sea level rise in the Phanerozoic
got under way. However, as if to offset this trend, Gondwana moved south with
considerable speed, so that, in Ordovician time, Most of West Gondwana (Africa and
South America) lay directly over the South Pole. The Early Paleozoic climate was also
strongly zonal, with the result that the "climate", in an abstract sense became warmer,
but the living space of most organisms of the time -- the continental shelf marine
environment -- became steadily colder. However, Baltica (Northern Europe and Russia)
and Laurentia (eastern North America and Greenland) remained in the tropical zone,
while China and Australia lay in waters which were at least temperate. The Early
Paleozoic ended, rather abruptly, with the short, but apparently severe, Late Ordovician
Ice Age. This cold spell caused the second-greatest mass extinction of Phanerozoic
• The Middle Paleozoic was a time of considerable stability. Sea levels had dropped
coincident with the Ice Age, but slowly recovered over the course of the Silurian and
Devonian. The slow merger of Baltica and Laurentia, and the northward movement of
bits and pieces of Gondwana created numerous new regions of relatively warm, shallow
sea floor. As plants took hold on the continental margins, oxygen levels increased and
carbon dioxide dropped, although much less dramatically. The north-south temperature
gradient also seems to have moderated, or metazoan life simply became hardier, or
both. At any event, the far southern continental margins of Antarctica and West
Gondwana became increasingly less barren. The Devonian ended with a series of
turnover pulses which killed off much of Middle Paleozoic vertebrate life, without
noticeably reducing species diversity overall.
• The Late Paleozoic was a time which has left us a good many unanswered
questions. The Mississippian Epoch began with a spike in atmospheric oxygen, while
carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to
one, and perhaps two, ice ages during the Carboniferous. These were far more severe
than the brief Late Ordovician Ice; but, this time, the effects on world biota were
inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to
more normal levels. On the other hand, the assembly of Pangea created huge arid
inland areas subject to temperature extremes. The Lopingian is associated with falling
sea levels, increased carbon dioxide and general climatic deterioration, culminating in
the devastation of the end-Permian extinction.
• Geologic Time! (mya = million years ago)
Navigating Our Geology Wing Precambrian (4,500 to 543 mya)
• Hadean (4500 to 3800 mya)
Archaean (3800 to 2500 mya)
Proterozoic (2500 to 543 mya) Vendian (650 to 543 mya)
• Phanerozoic (543 mya to today)
• Paleozoic Era (543 to 248 mya)
• Cambrian (543 to 490 mya)
Tommotian (530 to 527 mya)
• Ordovician (490 to 443 mya)
Silurian (443 to 417 mya)
Devonian (417 to 354 mya)
Carboniferous (354 to 290 mya)
• Mississippian (354 to 323 mya)
Pennsylvanian (323 to 290 mya)
• Permian (290 to 248 mya)
Mesozoic Era (248 to 65 mya)
• Triassic (248 to 206 mya)
Jurassic (206 to 144 mya)
Cretaceous (144 to 65 mya)
Cenozoic Era (65 mya to today)
• Tertiary (65 to 1.8 mya)
Paleocene (65 to 54.8 mya)
Eocene 54.8 to 33.7 mya)
Oligocene (33.7 to 23.8 mya)
Miocene (23.8 to 5.3 mya)
Pliocene (5.3 to 1.8 mya)
Quaternary (1.8 mya to today)
Pleistocene (1.8 mya to 10,000 years ago)
Holocene (10,000 years ago to today)
The Paleozoic systems may be defined in terms of Some
distinctive form of life:
Permian = primitive reptiles.
U. Paleozoic Pennsylvanian = Lycopod plants(scale trees) and
Mississipian = Brachiopods and Bryzoa.
Devonian = Tetracorals and Fishes.
Silurian = Tabulate Corals.
L. Paleozoic Ordovician = Graptozon & Cystoids.
Cambrian = Trilobites.
The Paleozoic is divided into two:-
Upper Paleozoic = Age of Ferns and Vertebrates.
Lower Paleozoic = Age of Algae and invertebrates.
The Cambrian Period
543 to 490 Million Years Ago
• The Cambrian Period marks an important point in the history of life on earth; it is
the time when most of the major groups of animals first appear in the fossil record.
This event is sometimes called the "Cambrian Explosion", because of the
relatively short time over which this diversity of forms appears. It was once thought
that the Cambrian rocks contained the first and oldest fossil animals, but these are
now to be found in the earlier Vendian strata.
The Cambrian Period (from a Latin form of the Welsh name for Wales)
begins the Paleozoic Era about 544 mya, and comes to a close about
490 mya. it was during the Cambrian that life "exploded," developing
almost all of the major groups in a relatively short time.
Originally, the bottom of the Cambrian was defined as the point where
fossils began. Subsequently, older fossils have been found, and this
definition is no longer valid. Now, it is roughly determined to be the
point at which there is the first appearance of numerous fossil shells
Duration: 54 millions years
Maximum thickness : 40,000 feet.
Cambrian ( SEDGWICK 1835) from Cambria = Wales.
The Pre-Cambrian ended with the Huronian orogeny which raised the land
into dominant mountains, after this formation , these Huronian mountains were subjected to
prolonged period of intensive erosion lowered them into a peniplain ., over this , the lower
Paleozoic (Cambrian) are gradually transgressed.
The Cambrian exposures are well represented in the basin
ranged of Utah and Nivada.
The Lower Cambrian deposits consists chiefly of Quartzite.
Some zones are shally, other are calcareous, but the sandy
sediments are remarkable. These sands derived from the
crystalline Pre-cambrian rocks.Most of these deposits are
marine due to the presence of Trilobites and other annelid
The Middle Cambrian formations are mainly L.s
The Upper Cambrian series is largely dolomitic L.S. with
• The Cambrian Explosion
• There is currently some debate concerning the rapidity of life form
developments during the Cambrian Period but, regardless, it was
during this time that almost all of the major life form types appeared
• Mass Extinction
• The Cambrian ended with a mass extinction of about 75% of the
trilobite families, half the sponge families, and many brachiopods
and snails. The cause of the extinction is not known
Subdivisions of the
-The chart at left shows the major subdivisions of the Cambrian Period for
North America (Laurentia during the Cambrian).
-International ages (subdivisions) have not been established.
-The size of the bars does not correlate with the length of time for each age. The
oldest unnamed age is 543 to 520 million years ago, while the remaining six ages
are from 520 to 490 million years ago, each approximately 5-6 million years long.
This chart is mapped to allow you to travel back to the Vendian, or forward to
You may also click to see our close-up look at the Tommotian.
The Cambrian Period is part of the Paleozoic Era.
The Paleontological classification of the system is based upon the vertical distribution of
-Three stages have been distinguishes in two geographic provinces:-
Stages Atlantic Provinces Pacific Provinces
• Upper Cambrian= Potsdamian Olenus Dikellocephalus
• Middle Cambrian = Acadian Paradoxides Ptychuparia
• Lower Cambrian = Georgian Olenellus Olenellus
1. A lot can happen in 40 million years, the approximate length of the
Cambrian period. Animals showed dramatic diversification during this
period of Earth's history. This has been called the "Cambrian
Explosion". When the fossil record is scrutinized closely, it turns out
that the fastest growth in the number of major new animal groups took
place during the Tommotian and At dabanian stages of the Early
Cambrian, a period of time which may have been as short as five million
years! In that time,
2. the first undoubdted fossil annelids, arthropods,
brachiopods, echinoderms, molluscs,
onychophorans, poriferans, and priapulids show up in
rocks all over the world. Perhaps we should call this bit of time the
• The dominant creatured of the Cambrian seas were Trilobites (60% of
the fauna). Next to the Trilobites in importance , came Brachiopods(30% ).
• More than 1.5oo species of the invertebrates are known in the Cambrian, all
marine, of which 60% are trilobites, and 30% brachiopods. Calcareous Sponges were
also reef building organisms. Vertebrates and land plants were not represented. Blue –
green algae were abundant, they form limy reefs.
• Life was entirely marine during the Cambrian Period. It includes representatives of all groups of the animal kingdom
except vertebrates and thus the Cambrian does not mark the down of life on the Earth.
• The most characteristic animals of the Cambrian period
were the trilobites, a primitive form of arthropod
remarkable for it's highly developed eyes (unusual
• Archiocyathids: They are reef building organisms , characteristic
• of the upper part of Cambrian( Archaeocyatha The Archaeocyatha or
archaeocyathids were sessile, reef-building marine organisms of warm tropical
and subtropical waters that lived during the early Cambrian period
• Calcareous Algae: were widely spread reef builders,e.g. Creptozoon
• Calcareous Sponges: were also reef building organisms characteristics of the upper part
of the Lower Cambrian.
• Brachiopods: abundant inarticulate Brachiopods such as Lingula and Obelus in sandy
litteral facies indicating old beaches.
• Trilobites: they are the most important fossils in Cambrian rocks,e.g. Paradoxides,
• Gastropods: recorded since the lower Cambrian becoming important by the end of the period
Paleogeography of the Cambrian
• The Cambrian rocks are separated from the older ones by on of the
most remarkable unconformities.
• The Paleogeographic picture for the beginning of the lower
Paleozoic is as follows:
• A number of continental masses corresponding to the various
shields which were folded in the Huronian movement were lowered
down after prolonged period of erosion. Over these folded Pre-
Cambrian rocks, the sea of the Paleozoic advanced.
• The Cambrian sea expanded continously and flooded the low-land.
It is the first system to contain fossils that allow correlation
between distant regions.
• The Cambrian ocean was covering what are now Pacific Ocean,
central and northern Australia, eastern and central Asia and nearly all
Europe :but the northern part of the Atlantic ocean being
communicated with pacific ocean across panama.
• A southern continent Gondwana Land was existing comprising what
are now south America, Africa, Arabia, the western half of India and
west Australia, all having in connection.
• Cambrian: Localities
• Rocks of Cambrian age are distributed in the Great Basin of the western United States, parts of the northeastern
United States, Wales, Scandinavia and the Baltic region, Siberia, and China, among other places. These localities
were not where they are now: the position of the continents was very different. It may seem strange to imagine
California on the equator, or Venezuela near the South Pole, but that's how things were! Check out this map to
• Cambrian localities on this server: (see map above)
• Aldan River - Lower Cambrian fauna from this site in Yakutia, Siberia, trace the early evolution of animals with
• Burgess Shale - One of the greatest fossil finds ever made is the Burgess fauna of British Columbia. Thousands of
soft-bodied animal fossils paint us a picture of early marine life.
• House Range, Utah - A varied array of Cambrian critters has been found in the Wheeler Shale and the Marjum
Formation, both of which are exposed in the House Range.
• Marble Mountains - In the hottest part of the Mojave Desert of California is the rich Latham Shale where
Olenellid trilobites are numerous.
• White-Inyo Mountains - You can visit ancient reefs in the mountains of eastern California.
• Information about Cambrian localities from other websites: Paleontology Portal: the Cambrian - Learn more
about the Cambrian paleontology and geology of North America.
• Burgess Shale fossils - This Middle Cambrian site in present-day British Columbia is known for its excellent
preservation of soft-bodied invertebrates. The website is maintained by the University of Calgary.
• Strange Creatures - A Burgess Shale Fossil Sampler - Another website about these unusual critters, this one from
The Cambrian rocks are known as
a-Continental facies b-Geosynclinal facies
They are found in the following areas:-
• The border zone of the in Baltic shield
• The border zone of the in Hebrides
• In N. Europe in the geosynclinal zone.
• N. America around the Canadian shield
• In Mediterranean geosynclinal zone (Moracoo, Sardinia,..)
• In Atlantic area
• In Pacific area
• In Egypt
• Um Bogma-Abu Durba----Sinai
• Western Desert (Northern part)[ Gib Afia, Ghazalat;
• Betty, Bhariya Wells} the most important fauna is
Cambrian: Tectonics and Paleoclimate
• The Cambrian follows the Vendian period, during which time the continents had been joined in a
single supercontinent called Rodinia (from the Russian word for "homeland", rodina). As the
Cambrian began, Rodinia began to fragment into smaller continents, which did not always
correspond to the ones we see today. The reconstruction below shows the rifting of Rodinia
during the Tommotian. Green represents land above water at this time, red indicates mountains,
light blue indicates shallow seas of the continental shelves, and dark blue denotes the deep ocean
basins. (For clarity, the outlines of present-day continents have been superimposed on the map.)
• Zones of climate were poorly defined. The temperature of the seas were mild, temperate or warm i.e
higher and much ore uniform over great distances north and south of the equator than it is now.
This reconstruction shows the rifting of Rodinia. Green represents land above water at this
time, red indicates mountains, light blue indicates shallow continental shelf seas, and dark
blue denotes the deep ocean basins. (For clarity, the outlines of present-day continents have
been superimposed on this map.)
• As you can see, the Cambrian world was concentrated in the southern hemisphere. The largest landmass (lower right)
was Gondwana (a collection of today's southern continents). The second largest continent, Laurentia is just left of
center in the map below, and includes most of North America (the southeastern US can be seen wedged between
Africa and South America as part of Gondwana). Between Gondwana and Laurentia lie Siberia (just south of the
equator) and Baltica (Scandinavia, eastern Europe, and European Russia). The rest of Europe and much of what is today
Asia lay in fragments along the north coast of Gondwana.
• These landmasses were scattered as a result of the fragmentation of the supercontinent Rodinia that had existed in the
Late Proterozoic. Laurentia stradled the equator, while Baltica and Siberia were southeast of that continent. Tectonism
affected regions of Gondwana is what are presently Australia, Antarctica, and Argentina the most. This is evident
because of the presence of volcanic island arcs, which show that seafloor spreading and crustal subduction occurred.
The continental plate movement and collisions during this period generated pressure and heat between continents.
this resulted in the folding, faulting, and crumpling of rock which formed large mountain ranges.
• The Cambrian world was bracketed between two ice ages, one during the late Late Proterozoic and the other during
the Ordovician. During these ice ages, the decrease in global temperature led to mass extinctions. Cooler conditions
eliminated many warm water species, and glaciation lowered global sea level. However, during the Cambrian there was
no significant ice formation. None of the continents were located at the poles, and so land temperatures remained
mild. In fact, global climate was probably warmer and more unifrom than it is today. With the beginning of the
Cambrian at the retreat of Proterozoic ice, the sea level rose significantly. Lowland areas such as Baltica were flooded
and much of the world was covered by epeiric seas. This event opened up new habitats where marine invertebrates,
such as the trilobites, radiated and flourished.
• Plants had not yet evolved, and the terrestrial world was therefore devoid of vegetation and inhospitable to life as we
know it. Photosynthesis and primary production were the monopoly of bacteria and algal protists that populated the
world's shallow seas.
• Also during the Cambrian, oxygen first mixed into the world's oceans in significant quantity. Although there was
plentiful atmospheric oxygen by the opening of the Cambrian, only in the Cambrian did the numbers of oxygen-
depleting bacteria reduce in numbers sufficiently to permit the high levels we know today. This made dissolved oxygen
available to the diversity of animals, and may have triggered the "Cambrian Explosion". This was when most of the
major groups of animals, especially those with hard shells, first appear in the fossil record
The Tommotian Age
530 Million Years Ago
• The Tommotian Age, which began about 530 million years ago, is a
subdivision of the early Cambrian. Named for rock exposures in Siberia, the
Tommotian saw the first major radiation of the animals, or metazoans,
including the first appearance of a great many mineralized taxa such as
brachiopods, trilobites, archaeocyathids, molluscs, echinoderms, and more
problematic forms. Soft-bodied members of many other phyla were also
appearing and diversifying at this time.
A few million years before the Tommotian, in the Vendian, the
continents had been joined in a single supercontinent called Rodin
(from the Russian word for "homeland", rodina.) As the Cambrian
began, Rodinia began to fragment into smaller continents which did
not always correspond to the ones we see today. Much later, in the
Permian, the continents came back together to form a new
supercontinent, called Pangaea.
• Extinction strikes in both the land and the sea.
• On the land, while animals suffer repeatedly, plants tend to be highly resistant to mass
• Preferential disappearance of tropical forms of life during mass extinctions.
• Tendency of certain groups of animals to experience them repeatedly (for example,
trilobites and ammonoids).
• Alleged equal spacing, or periodicity in geological time (occurring about every 26 million
• These similarities between distinct extinction occurrences aid paleontologists in determining
the agents the agents that perpetuated the disappearances of species in each extinction event.
Such agents are currently divided into two types:
• Catastrophic Agents- such as meteorite impacts and comet showers,
• Earth Agents- such as volcanism, glaciation, variations in sea level, global climatic changes,
and changes in ocean levels of oxygen or salinity
• Although these agents can explain mass extinction, the causes of mass extinction events
remains relatively unknown.
The Precambrian and Vendian Mass
• - Precambrian period
• (4.500 million to 523 million years ago)
- Vendian period (4.500 to 543 million years ago) .
- Both Precambrian and Vendian periods host to at least one mass extinction each
-Speculated Causes of the Precambrian and Vendian Extinctions
• The first extinction of the Precambrian, which largely affected stromatolites and
acritarchs, has been correlated with a large glaciation event that occurred about 600 million
years ago. This event was of such severity that almost all micro-organisms were completely
• The Vendian extinction, occurring near the close of the Vendian period, is currently under
debate as to whether an extinction event occurred or not. Many paleontologists believe that
the Vendian fauna were the progenitors of the Cambrian fauna. However, others believe
that the Vendian fauna have no living representatives. Under this latter hypothesis, the
Vendian fauna is believed to have an undergone an extinction, after which the Cambrian
fauna evolved. Until more information can be collected, details on the Vendian extinction
event will remain open to debate
• The Cambrian Mass Extinction
-The Cambrian period ranges from 543-488 million years ago
- The most important animal group of the Cambrian were the trilobites
-Three mass extinctions occurred during the course of the Cambrian
The Cambrian Mass Extinction
• Fast Facts
• The Cambrian period ranges from 543-488 million
• The most important animal group of the Cambrian
were the trilobites
• Three mass extinctions occurred during the course
of the Cambrian
Speculated Causes For the Cambrian
• The two most accepted
current hypotheses for the
Cambrian extinction are:
1-Glaciation in the early
2-Cooling and depletion of
oxygen in marine waters
1-Glacial Cooling Hypothesis
• The advancement of the theory of glaciation as the predetermining agent for the
Cambrian extinctions has been developed by James F.Miller of Southwest Missouri
State University. Through research undertaken by Miller, evidence of early Ordovician
sediment of glacial origin has been uncovered in South America.
• Miller suggests in his hypothesis that this evidence of continental glaciation at the
Cambrian-Ordovician boundary is responsible for a decrease in global climatic
conditions. Such a decline in temperature is implied by Miller to destroy Cambrian fauna
which are intolerant of cooler conditions, producing a mass extinction of mostly warm
• He also suggests that a significant continental glaciation would bring large amounts of
ocean water onto the land in the form of frozen glacial ice. This trapping of ocean
water inevitably results in the decrease of sea-level and the withdrawal of shallow
seas. Miller implicates that this reduction in sea-level would produce reduced habitat
for marine species as continental shelves are obliterated. Ecological competition would
consequently ensue, perhaps acting as a driving agent for extinction.
• 2-Oxygen Depletion Hypothesis
• The development of a hypothesis invoking the cooling and depletion
of water in marine waters as a causative agent for the Cambrian
extinctions has been advanced by several geologists, primarily
Allison Palmer and Michael Taylor of the U.S. Geological Survey and
James Stilt of the University of Missouri.
• The cooling and oxygen depletion would occur when cool waters
from deep zones of the ocean spread up onto the continent,
eliminating all organisms not able to tolerate cool conditions. The
cooling would also result in stratification of the water column.
• Thus, species would ultimately perish due to their inability to
tolerate dramatic shifts in such limiting factors as temperature and
oxygen availibility. Further research is required to more fully test
the validity of the above outlined Cambrian extinction hypotheses
• Duration: 44 million years
• Maximum thicknes: 60,000 feet
• The Ordovician Period (from the name of an ancient British tribe, the
Ordovices) extended from 488 mya until 444 mya.
• The Ordovician rocks cover wider areas than Cambrian, on which they commonly lie
• At the end of the Cambrian, sea levels fell, causing extinctions.
• The continents were moving together during this period, and mountain-building was taking
place in the northeastern North American continent. The rest of the continent was
• Ordovician periods, thick accumulation of shallow water sands and deep
water black muds were deposited in a gradually sinking floor of some seas,while
carbonates were chemically or organically deposited in warm seas
Deposits are mainly marine, conglomerates, grits,
sandstones, shales, slates mudstones and radiolarian chets.
Zoned by means of graptolite faunas. Four different
facies representing different areas are well exhibited:-
• Shelly facies : sandy and calcareous indicating
shallow water deposits, very fossilliferous, containing
Trilobites, brachiopods, corals, cystoids, and
• Dolomitic facies: being formed chemically or
organically in warm and closer seas, giving rise to thick
limestone and dolomite.
• Graptolitic( shaly ) facies: thinner and finer
sediments laid down far from the shore, containing
common graptolites and abundant trilobites.
• Volcanic facies: chiefly lava flows, may be
interstratified with deposits of other facies, often
deposited upon the ocean floor.
Ordovician: Significant Events
• First Vertebrates
• It was in the Ordovician that the first animals with backbones arose. The Agnatha, the
jawless fishes, were the first animals with true bony skeletons.
• Mass Extinction
• The Ordovician Period ended with a mass extinction. About 25% of all families did
not make it into the Silurian.
The Ordovician period began approximately 490 million years
ago, with the end of the Cambrian, and ended around 444
million years ago, with the beginning of the Silurian. At this
time, the area north of the tropics was almost entirely ocean,
and most of the world's land was collected into the southern
super-continent Gondwana. Throughout the Ordovician,
Gondwana shifted towards the South Pole and much of it
was submerged underwater.
490 mya to 444 mya Million Years Ago
• The Ordovician is best known for the presence of
its diverse marine invertebrates, including
graptolites, trilobites, brachiopods, and the
conodonts (early vertebrates). A typical marine community
consisted of these animals, plus red and green algae,
primitive fish, cephalopods, corals, crinoids, and
gastropods. More recently, there has been found evidence
of tetrahedral spores that are similar to those of primitive
land plants, suggesting that plants invaded the land
at this time.
• From the Early to Middle Ordovician, the earth experienced
a milder climate in which the weather was warm and the
atmosphere contained a lot of moisture. However, when
Gondwana finally settled on the South Pole during the Late
Ordovician, massive glaciers formed causing shallow seas to
drain and sea levels to drop. This likely caused the mass
extinctions that characterize the end of the Ordovician, in
which 60% of all marine invertebrate genera and 25% of all
families went extinct.
• The Ordovician was named by the British geologist
Charles Lapworth in 1879.
• He took the name from an ancient Celtic tribe, the
Ordovices, renowned for its resistance to Roman
domination. The epochs and series of the
Ordovician each have a type location in Britain,
where their characteristic faunas may be found.
• The age of the Ordovician boundaries were
determined using potassium-argon and uranimum
• Graptolites, extinct planktonic organisms, are
most often used to correlate Ordovician
• The boundary between the Cambrian
and the Ordovician is marked by the
appearance of planktic dictyonemid
• The boundary between the
Ordovician and the Silurian has been
designated as the base of the
graptolite zone by international
agreement. Dobs Linn, near Moffat, in
southern Scotland is the type locality for
that boundary. There, black graptolite-
bearing shales are exposed
The general classification of the Ordovician rocks both in Europe and North America is as
Upper Ordovician= Clincinatian = Cardocian
Middle Ordovician=Champlanian =Llandelian
Lower Ordovician= Canadian = Arenigian
Life of the Ordovician
Nearly all the important groups of the marine animals are represented.
The most important members of the Ordovician fauna are the Trilobites, graptolites, and
The fauna of the Ordovician time are much richer in species and individuals than that of the Cambrian of these the most
Trilobites :forming the most important Ordovician fauna attaining their climax of
development in number and species e.g. Agnostus, Trinucleus, Asaphus
Graptolites: widely distributed, reached their climax of development, used for
zoning of Ordovician few species sediments e.g. Diplograptus, Phyllograptus,
Didymograptus, Diplograptus, Tetragraptus.
Brachiopods : much more abundant than the Cambrian ones, e.g. Lingula,
Strophomena. Orthis. Some genera are used in subdividing the system.
Corals: first appeared , both Rugose and Tabulates few species widely
distributed in Late Ordovician.
Mollusca: gastropods are of little stratigraphical value. Cephalopods are abundant
and better represented by loosell coiled shells.
Echinoderms: represented by a variety of cystoides and by numerous
crinoides and the earliest known blastoides.
• Rather hot and dry nearly uniform temperature condition
prevailed over large portions of the globe.
• No glacial formations are known
• Towards the close of the Ordovician , a great Taconic mountains
building revolution in N. A merica . In Western Europe, the
Caledonian movement which is to continue in the Silurian and
Devonian makes its debut as mountain builders.
. Main vlocanic activity begins in wales. Extensive submarine and
subaerial volcanic activity in the British area.
Ordovician localities on this server: (see map above)
Canning Basin, Australia - A great diversity of fossil gastropods has been uncovered in the
Lake Winnipeg, Manitoba, Canada - The limestones of this region have preserved many
spectactular fossils of macroalgae.
In Egypt: Ordovician deposits occur :
-Um Bogma-Abu Durba---Central Sinai
-Western Desert (Northern part)[ Gib Afia, Ghazalat;
-Betty, Bhariya Wells} the most important fauna is
Paleogeography of the
• Towards the close of the Cambrian period, the seas began to retreat. The Ordovician began
with a new spreading of the sea and thus the two system are separated in as in North
America, there was nearly a continent sedimentation.
• The distribution of Ordovician deposits clearly show that during these times, there was four
continents: North Atlantic continents, Arctic Continent, Asiatic
(Angara) Continent, Equatorial (Gondwana) continent.
• The geography of Cambrian and Ordovician systems seems to proof the existence of what is
• N. Alantic continent ----this was the land extending from N. America to N. Europe.
• Asiatic continent was that part forming North and Central Asia.
• Africa was possibly a continent.
• An Arctic continent is supposed to be existed in Nort of Greenland
• Brazile, Central africa , Madgascar, India and W. Australia were in
connection forming an equatorial continent of great extent ; that is Gondwana-land
The Ordovician Mass Extinction
• Fast Facts
• -Ordovician period (488- 444 million years ago).
- Ordovician extinction (444 million years ago).
- Ordovician extinction was second most devastating in earth history.
• Geological Setting
• The Ordovician period was an era of extensive diversification and expansion of numerous
marine clades. Although organisms also present in the Cambrian were numerous in the
Ordovician, a variety of new types including cephalopods, corals (including rugose and
tabulate forms), bryozoans, crinoids, graptolites, gastropods, and bivalves flourished.
Ordovican communities typically displayed a higher ecological complexity than Cambrian
communities due to the greater diversity of organisms. However, as in the Cambrian, life in
the Ordovician continued to be restricted to the seas
Speculated Causes of the Ordovician
Glaciation and Sea-Level Lowering
• The Ordovician mass extinction has been theorized by paleontologists to be the
result of a single event; the glaciation of the continent Gondwana at the end of the
period. Evidence for this glaciation event is provided by glacial deposits discovered
by geologists in the Saharan Desert. By integrating rock magnetism evidence and
the glacial deposit data, paleontologists have proposed a cause for this glaciation.
When Gondwana passed over the north pole in the Ordovician, global climatic
cooling occured to such a degree that there was global large-scale continental
resulting in widespread glaciation. This glaciation event also caused a lowering of
sea level worldwide as large amounts of water became tied up in ice sheets. A
combination of this lowering of sea-level, reducing ecospace on
continental shelves, in conjunction with the cooling caused by the
glaciation itself are likely driving agents for the Ordovician mass extinction