Geologic Time Scale and Pakistan

GEOLOGIC TIME SCALE AND PAKISTAN

ASSINGMENT

SUBMITTED TO: MUHAMMAD IBRAHIM SECTION HEAD GEOLOGY & GEOPHYSICS

“OMV ISLAMABAD”

SUBMITTED BY: MUHAMMAD TALHA BUTT STUDENT OF BAHRIA UNIVERSITY ISLAMABAD

SUBMITTING DATE: 28 July, 2009

Chapter 1

INTRODUCTIONThe geologic scale is sub-divided the 4.6 billion year history of the earth into many different units and provides a meaningful time frame within which the events of the geologic past are arranged and is divided into Eon, Era, Period and Epoch.

EON:

It represents the greatest expanses of time. It is divided into 2 parts Phanerozoic and Precambrian. Precambrian eon has 3 types Proterozoic, Archean and Hadean.

ERA:

Each Eon is further divided into another unit called Era. Phanerozoic Eon is divided into 3 Eras Cenozoic, Mesozoic and Paleozoic. All 3 types of Pre-Cambrian Eon is divided into 3 Eras Late, Middle and Early.

PERIOD:

Each Era is further divided into another unit called Period. Cenozoic is divided into 2 periods. Mesozoic is divided into 3 periods. And Paleozoic is divided into 7 periods.

EPOCH:

Each Period is further divide into another unit called Epoch. The Epoch of Quaternary and Tertiary period has specific names while the others are simply divided into Late, Middle and Early. Quaternary is divide into 2 Epoch and Tertiary is divided into 5 Epoch.

PHANEROZOIC EON

CHAPTER 2

CENOZOIC ERA

(65.5 million years ago to the present)

It is also called “Recent Life”. The Cenozoic (also Caenozoic or Cainozoic) Era is the most recent of the three classic geological eras and covers the period from 65.5 million years ago to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic era is ongoing.

SUB-DIVISION:

The Cenozoic Era is divided into two periods, the Quaternary and Tertiary, and they are in turn divided into epochs. The Quaternary consists of Holocene and Pleistocene epochs, and Tertiary consists of the Miocene, Pliocene, Paleocene, Eocene, and Oligocene epochs. And the Holocene is ongoing.

CLIMATE:

The Cenozoic Era has been a period of long-term cooling. After the tectonic creation of Drake Passage, when South America fully detached from Antarctica during the Oligocene, the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface. The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents,

eventually leading to the glaciations of the Pleistocene ice age, the current

interglacial of which is the Holocene period

FOSSILS OF CENOZOIC ERA:

Quaternary Period (1.8 to Present) Fossils:

The Quaternary Period that began less than 2 million years ago marked the origin of the close human ancestors as well as the modern forms of the animals we see today.

Tertiary Period (65 to 1.8 mya) Fossils ( Tertiary Fossils ) : Invertebrates, fish and reptiles were similar to those of modern types, but mammals, birds, protozoa and flowering plants would undergo considerable evolutionary change.

Pliocene - The Pliocene Epoch extends from 5.3 million to 1.8 million years before present. The name comes from the Greek words pleion (more) and ceno (new) and roughly means the continuation of the recent in reference to the fact that mammals were essentially modern in form. The Pliocene climate was also relative cool and dry as in modern times. These modern climates reduced tropical vegetation and shrank tropical forest to a band near the equator. Concurrently, deciduous and coniferous forests, tundra, grasslands, dry savannahs and deserts filled the space.

Both marine and terrestrial life was for the most part modern, though discernibly more primitive. Herbivores grew in size, as did their predators. The first recognizable human ancestors, the australopithecines, appeared in the Pliocene. Mammalian life evolved in continent-dependent ways, and some migration occurred between continents. In North America, rodents, mastodonts, elephant-like gomphotheres, and opossums were notably prolific, while hoofed animals generally declined. Africa’s hoofed animals and primates were notably successful, and the australopithecines (some of the first hominids) appeared late in the Pliocene. The Pliocene seas were thrived with mammals such as seals and sea lions.

Miocene - The Miocene Epoch extends from about 23 to 5 million years ago. The name comes from the Greek words meion (less) and ceno (new) because of the smaller proportion of modern sea invertebrates than the subsequent Pliocene Epoch. The Miocene is thus a very long 18 million years and generally marks the transition from the far prehistoric world to a pseudo-modern world. A major expansion of grasslands occurred as forests declined in the cooler and dryer climate, driving selection and radiation of large herbivores, including the ruminants which are ancestors of modern cattle and deer. Mammals such as wolves, horses and deer as well as birds also generally evolved to closely resemble forms extant today.

Oligocene - The Oligocene Epoch extends from about 34 million to 23 million years ago. The name Oligocene comes from the Greek oligos (meaning few) and ceno (meaning new) and is in reference to the paucity of new mammalian animals after their radiation during the preceding Eocene Epic. The Oligocene is often considered as an important window of environmental transition from the tropical Eocene and the cooler Miocene. The start of the

Oligocene is marked by a major extinction event that might have been caused by a meteor impact in Siberia or near the Chesapeake Bay. Angiosperms continued their expansion throughout the world, as did grasses. Among the animals, mammals diversified markedly, and marine fauna evolved to forms closely resembling those extant today. Ancestors of modern elephants and rhinoceros grew to large size in Africa, where the first ape’s primate belonging to suborder Anthropoidea that includes monkeys, apes, and humans, also appeared.

Eocene - The first grasses appeared in the Eocene Epoch (from about 54 to 37 million years ago) with growth near the root as opposed to the tip, providing a vastly expanded and renewable food resource for the herbivores; this allowed adaptation to life on the savanna and prairie and the evolution of running animals such as the Equiidae (the horse family). The grazing mammals evolved the teeth enabling a diet of harsh grass. The Eocene Epoch was a period when flowering plants continued a massive radiation that began in the Paleocene Epoch. Plants thrived, and with that many animals as new environmental niches were filled. The first grasses also provided a refuge for many animals. Many new species of shrubs, trees and small plants appeared. A variety of trees thrived in a warm Eocene climate, including beech, elm, chestnut, magnolia, redwood, birch, and cedar, and more. The evolution of plants was providing a powerful selective pressure across the entire animal Kingdom, and many new symbiotic systems appeared.

Paleocene - The Paleocene Epoch began after the extinction of the dinosaurs. Mainly nocturnal mammals that had cowered in the shadows of dinosaurs for millions of years eventually evolved into a vast number of different forms to fill the newly vacant environmental niches. At the beginning of the Paleocene, most mammals were tiny and rodent-like. With passage of time, mammals grew in size, number, and diversity. Many early mammal designs of this time would soon become extinct, but others would survive and then evolve into other forms. The diversity of birds, other animals, and plants increased, and species became more specialized. Although dinosaurs were gone, their reptile cousins lived on in the form of turtles, crocodiles, lizards, and snakes.

LIFE:

The Cenozoic Era is the age of new life. During the Cenozoic, mammals diverged from a few small, simple and generalized forms into a diverse collection of terrestrial, marine, and flying animals giving this period its other name, the Age of Mammals, despite the fact that birds still outnumbered mammals two to one. The Cenozoic is just as much the age of savannas, the age of co-dependent flowering plants and insects, or the age of birds. Grass also played a very important role in this epoch, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well was the snakes. Evolving in the Cenozic, the snakes evolved into a huge amount of forms, especially colubrids, following the evolution of their current prey source, the rodents

In the earlier part of the Cenozoic, the world was dominated by the gastornid birds, terrestrial crocodiles like Pristichampsus and a handful of primitive large mammal groups like uintatheres, mesonychids, and pantodonts. But as the forests began to recede and the climate began to cool, other mammals took over. The cenozoic is full of mammals both strange and familiar, including chalicotheres, oreodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceross like Indricotherium, and brontotheres.

Chapter 3

MESOZOIC

(251.0 mya to 65.5 mya)

The Mesozoic Era is one of three geologic eras of the Phanerozoic eon. It is Lying between the Paleozoic and the Cenozoic, "Mesozoic" means "middle animals", deriving from Greek word “meso” means "between" and “zoon” meaning "animal" or "living being". It is often called the "Age of the Reptiles", after the dominant fauna of the era. The Mesozoic was a time of tectonic, climatic and evolutionary activity. The continents gradually shifted from a state of connectedness into their present configuration; the drifting provided for speciation and other important evolutionary developments.

SUB-DIVISION:

Following the Paleozoic, the Mesozoic extended roughly 180 million years: from 251 million years ago (Ma) to when the Cenozoic era began 65 Ma. This time frame is separated into three geologic periods. From oldest to youngest.

Cretaceous (145.5 Ma to 65.5 Ma)

Jurassic (199.6 Ma to 145.5 Ma)

Triassic (251.0 Ma to 199.6 Ma)

The lower (Triassic) boundary is set by the Permian-Triassic extinction event, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became extinct. It is also known as the "Great Dying" because it is considered the largest mass extinction in the Earth's history. The upper (Cretaceous) boundary is set at the Cretaceous-Tertiary (KT) extinction event (now more accurately called the Cretaceous–Paleocene (or K–Pg) extinction event), which may have been caused by the impact that created Chicxulub Crater on the Yucatán Peninsula. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs.

Climate:

The climate of the Cretaceous is less certain and more widely disputed. Higher levels of carbon dioxide in the atmosphere are thought to have caused the world temperature gradient from north to south to become almost flat: temperatures were about the same across the planet. Average temperatures were also higher than today by about 10°C. The circulation of oxygen to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter that was unable to decompose accumulated, eventually being deposited as "black shale".

Sea levels began to rise during the Jurassic, which was probably caused by an increase in seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m more than today, which flooded coastal areas. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the Tethys Sea .

The Triassic was generally dry, a trend that began in the late Carboniferous, and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high specific heat capacity, water acts as a temperature-stabilizing heat reservoir, and land areas near large bodies of water-especially the oceans-experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of desert. Abundant evidence of red beds and evaporates such as salt support these conclusions.

FOSSILS OF MESOZOIC ERA:

Cretaceous Period (146 to 65 mya) - ( Cretaceous Fossils ):

During the Cretaceous, the rays, modern sharks and teleosts, or the ray-finned fish became widespread and diverse. The marine

reptiles persisted, including the ichthyosaurs in the in the Lower and Middle of the Cretaceous, the plesiosaurs throughout the Cretaceous, and the mosasaurs that dominated the Upper Cretaceous. Baculites, a straight-shelled ammonite flourished in the seas. The Cretaceous also saw the first radiation of marine diatoms in the oceans.

The arch saurian reptiles, particularly the dinosaurs, continue to dominate the land. Climate changes due to the breakup of Pangaea allowed flowers and grasses to appear for the first time. The most well known dinosaurs, Tyrannosaurus rex, Triceratops, Velociraptor and Spinosaurus all lived in the Cretaceous. Pterosaurs remain common until the Upper Cretaceous when competition occurs from evolving birds. Insects became even more diverse as the first ants, termites and butterflies appeared along with aphids, grasshoppers, and gall wasps. Another important Hymenopteran insect, the eusocial bee appeared, which was integral to and symbiotic with the appearance of flowering plants.

The Cretaceous ended at the so-called KT boundary, or the Cretaceous-Tertiary (K-T or KT) extinction event, that occurred some 65.5 million years ago. While the duration of this extinction remains unknown, half of all life’s genera disappeared; most famous was the extinction of the non-avian dinosaurs.

Jurassic Period (208 to 146 mya) - dinosaurs rule the land ( Jurassic Fossils ):

While the dinosaurs appeared in the Triassic, it was during the Jurassic that they prodigiously radiated and ascended to be the rulers of the land. Dinosaurs are a clade of reptiles defined by somewhat ambiguous criteria. Compared with other reptiles, the dinosaur hind limbs are beneath

the body. In recent years dinosaurs have been viewed as transitional between ordinary reptiles (especially crocodiles) and the birds. The fossil record supports the appearance of the large theropod’s dinosaurs within 10,000 years after the Triassic-Jurassic boundary.

The immense plant-eating dinosaurs (the sauropods) were ubiquitous and were the prey of the large theropods, including Ceratosaurs, Megalosaurs, and Allosaurs. Among plantae, Gymnosperms (especially conifers, Bennettitales and cycads) and ferns are common providing abundant food for the sauropods. Birds evolved during the late Jurassic. The pterosaurs, the flying reptiles, were common in the Jurassic. Fish and

reptiles dominated marine environs. The ichthyosaurs, plesiosaurs, and marine crocodiles flourished, as did bivalves, belemnites, brachiopods, echinoids, starfish, sponges and ammonites among the invertebrates. As a general rule, the mammals remained diminutive and backstage during the Jurassic.

Triassic Period (245 to 208 mya) Fossils ( Triassic Fossils ):

The Permian-Triassic (P/T) Extinction Event marked the end of the Permian Period of the Paleozoic Era, and the start of the Triassic Period of the Mesozoic Era. The P/T extinction decimated the brachiopods, corals, echinoderms, mollusks, and other invertebrates. The last surviving trilobite Order, the Proetids, also did not survive.

Among the enchinodermata, the inadunate crinoids which had barely survived the end-Permian extinction with one family finally disappeared. While crinoids were the most abundant group of echinoderms from the early Ordovician to the late Paleozoic, they nearly went extinct during the Permian-Triassic extinction. All the post-Paleozoic crinoids, namely the Articulata, are presumed to be a monophyletic clad that originated from the inadunate Order Cladida.

Other invertebrates, notably the bivalves, ammonoids and brachiopods recovered to dominate the marine environment, and the squid-like Belemnites appeared and became abundant. New groups of echinoderms appeared as well. Marine reptiles were highly diverse, including the Sauropterygia, nothosaurs, pachypleurosaurs, placodonts, and the first plesiosaurs. The ichthyosaurs appeared in the early Triassic, and radiated into huge, marine-dominating

species. Seed plants dominated the land, especially conifers to the north and the Glossopteris, or seed ferns, to the south. The first flowering plants (the Angiosperms) probably evolved during the Triassic.

LIFE:

The extinction of nearly all animal species at the end of the Permian period allowed for the radiation of many new life forms. In particular, the extinction of the large herbivorous and carnivorous dinocephalia left those ecological niches empty. Some were filled by the surviving cynodonts and dicynodonts, the latter of which subsequently became extinct. Animal life during the Mesozoic was dominated, however, by large arch saurian reptiles that appeared a few million years after the Permian extinction: dinosaurs,

pterosaurs, and aquatic reptiles such as ichthyosaurs, plesiosaurs, and

mosasaurs.

The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first birds and placental mammals also appeared. Angiosperms radiated sometime in the early Cretaceous, first in the tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that biomass was still dominated by cycad and ferns until after the KT extinction.

As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including lizards, snakes, and perhaps the ancestor mammals to primates, evolved. The KT extinction exacerbated this trend. The large archosaur became extinct, while birds and mammals thrived, as they do today.

CHAPTER 4

PALEOZOIC ERA

(543 mya to 248 mya)

The Paleozoic (meaning "time of ancient life)" Era lasted from 544 to 245 million years ago, and is divided into six periods. These 300 million years of the Paleozoic era realized many critical events in evolution, including the development of most invertebrate groups, life's conquest of land, the evolution of fish, reptiles, insects, and vascular plants, the formation of the supercontinent of Pangea. Fish and fish-like vertebrates arose in the early Paleozoic and comprise more than half of the diversity of vertebrates that inhabit the world today. Also importantly, there were also no less than two ice ages in the Paleozoic. The Paleozoic was ended by the greatest mass extinction event in geologic history, the Permian/Triassic extinction, when some 95% of all marine species met extinction.

The Paleozoic took up over half of the Phanerozoic, approximately 300 million years.

CLIMATE:

The Early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. 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 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 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. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life.

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.

FOSSILS IN PALEOZOIC ERA:

Permian Period (286 to 245 mya) :

The Permian Period extends from about 286 to 245 million years ago, and is the last geological period of the Palaeozoic Era. The Permian was named in the 1840s by Sir Roderick Murchison, a British geologist, from the extensive Permian exposures near Perm in Russia. The Permian ended with the most extensive extinction event recorded in paleontology: the Permian-Triassic

extinction event, where some 90% to 95% of marine organisms and 70% of all terrestrial organisms became extinct.

Life on land included a diversity of plants, arthropods, amphibians and reptiles. The reptiles were mainly synapsids (Pelycosaurs and Therapsids) that appeared in the Upper Carboniferous, and were bulky, cold-blooded animals with small brains Towards the very end of the Permian the first archosaur appear, the ancestors of the soon to follow Triassic dinosaurs. Permian marine environments were abundant in mollusks, echinoderms, and brachiopods.

Carboniferous Period (360 to 286 mya) "The Age of Plants" - Reptiles and the amniotic egg appear ( Carboniferous Fossils ):

The Carboniferous Period derives its name from the massive deposits of coal found in U.K. and Western Europe. In North America, the

Carboniferous is divided into the Mississippian Period and the Pennsylvanian Period. During the Carboniferous, the continents below the equator still formed the super-continent Gondwana.

Life flourished in the seas in the wake of the late Devonian Extinction. Ammonoids re-diversified very quickly. Crinoids, blastoids, brachiopods

and bryozoans and single-celled Eukaryotes fusulinids known as fusulinids became abundant. The ray finned fishes radiate enormously. However, the age of the trilobite was drawing to a close. After radiations Ordovician, Silurian, and Devonian periods, the nine trilobite orders had shrunk to one remaining in the Carboniferous, the Order Proetids, that too would go extinct at the end of the Permian.

Despite the appearance of seeds, most Carboniferous plants continued to use spores from reproduction. The moist and swampy environments of the Carboniferous enabled the Lycophytes (i.e., scale trees and club mosses) that evolved during the late Silurian to early Devonian to continue to diversify and flourish throughout the Carboniferous. However, the dependency on a moist environment caused the extinction of most taxa during arid conditions that prevailed near the end of the Paleozoic. Similarly, Calamites and ferns were other spore-bearing plants that appeared during the Devonian and thrived during the following Carboniferous period.

Devonian Period (410 to 360 mya) "The Age of Fishes" - Colonization of the land ( Devonian Fossils ):

The Devonian was a time of great change across the Tree of Life. Reef eco-systems saw new and more varied forms, including the ammonoids and

fish. A time of great transition, two major clades of animal moved ashore and rapidly radiated. Both the first tetrapods, or four legged land-living vertebrates, and the first arthropods colonized the land, including wingless insects and the earliest arachnids. In the sea, ammonoids and fish evolve and quickly diversify. Primitive plants that gained a foothold in the Silurian went on to form forests.

Arthropods and ultimately tetrapods were plodding the lands. The first insects, spiders, and tetrapods evolve.

In the Lower Devonian, plants were very tiny and primitive, generally lacking the leaf, root and vascular systems that would soon appear. By the late Devonian earth had forests of tall rooted trees covered with leaves. The lycophytes (Phylum Lycopodiophyta) are the oldest extant lineage of vascular plants e.g., club moss and gave rise to all descending vascular plants in a major phylogenetic split. The Lycopods that reproduced by way of spores went on to form vast swamp forests during the

Carboniferous period with the Lepidodendrales (e.g., Lepidodendron) reaching heights more than 100 feet. Sigillaria is another example of a lycopod tree. The seed-bearing Gymnosperms appeared near the end of the Devonian, an adaptation ultimately leading to propagation to dryer habitats.

Silurian Period (440 to 410 mya) - Life gains a foothold on land ( Silurian Fossils ):

The Silurian, so named after a Celtic tribe called the Silures, realized additional marked changes for Earth that affected life significantly. Sea levels rose as the climate stabilized, at least compared to the prior millions of years. Coral reefs made their first appearance and expanded. Land plants evolved in the moist regions near the Equator. The Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly

significant appearances of both the first known freshwater fish as well as the first fish with jaws, which resulted from an adaptation of an anterior gill arch. The Silurian strata have fossils that are substantive evidence of life on land, particularly the arthropod groups. The fossils of the earliest of vascular plants are also prevalent. In the oceans, there was a widespread radiation of crinoids and a continuation of the expansion of the brachiopods.

Ordovician Period (505 to 440 mya) - Massive marine life diversification ( Ordovician Fossils ):

The Ordovician is named after a Celtic tribe called the Ordovices, and was a time that life diversified and specialized. Owing to continental separation, trilobites drifted apart genetically taking on new, location-dependent forms, some quite exotic. The first plank-tonic graptolites evolved and other graptolite species became extinct. Most profound perhaps was the colonization of land. Terrestrial arthropod fossils occur in Ordovician strata, as do microfossils of the cells, cuticle, and spores of the early land-based plants.

Ordovician strata are characterized by numerous and diverse trilobites and conodonts (phosphatic fossils with a tooth-like appearance) found in sequences of shale, limestone, dolostone, and sandstone. In addition, blastoids, bryozoans, corals, crinoids, as well as many kinds of brachiopods, snails, clams, and cephalopods appeared for the first time in the geologic record in

tropical Ordovician environments. Remains of Ostracoderms (jawless, armored fish) from Ordovician rocks comprise some of the oldest vertebrate fossils.

The Ordovician ended with a major extinction event that caused the demise of some 60% of marine genera. A Late Ordovician glaciation contributed to profound ecological disruption and mass extinctions. Reef-building fauna were broadly decimated. Nearly all conodonts disappeared in the North Atlantic Realm while only certain lineages became extinct in the Mid-continental Realm. Trilobites were greatly affected with the Agnostids and the vast majority of Asaphid trilobites meeting extinction, and many groups of echinoderms, brachiopods, bryozoans, graptolites, and chitinozoans also disappearing. The Atlantic Ocean closed as Europe moved towards North America.

Cambrian Period (544 to 505 mya) - Most major animal groups appear ( Cambrian Fossils ):

The name Cambrian derives from Cambria, the Roman name for Wales, where rocks of this age were first studied. Hard-shelled animals appeared in great numbers for the first time during the Cambrian, significantly because shallow seas flooded the continents. Gondwana formed near the South Pole.

The Cambrian truly is an astonishing period in evolution of life on earth. Most major groups of animals first appear in the fossil record, an event popularly and scientifically called the "Cambrian Explosion".

Many marine metazoans having mineralized exo-skeletons flourish in the Cambrian, including

sponges, corals, molluscs, echinoderms, bryozoans, brachiopods and arthropods. The first shelled metazoans that are characteristic of the Cambrian occur well after the earliest complex trace fossils. This suggests that hard parts evolved later. Hence, trilobites, archaeocyaths, and small shelly animals did not evolve before the middle part of the Early Cambrian. The evolution of shelled metazoans is reflected by the appearance of successively more advanced shelly fossils.

Trilobites dominate the Cambrian fossil record, and these arthropods actually attained their peak number of families near the end of the Cambrian. It is believed there were some 15,000 species that evolved during the Paleozoic. Hence, the Paleozoic is sometimes called the “age of trilobites”. Modern times are sometimes called the age of insects (that are also arthropods), and it is believed there may be some 10,000,000 species of insects on Earth today (with beetles predominating).

The first detailed record of vertebrates appears during the Cambrian as fossils of jawless fish. These bottom-dwellers some of which had skeletons made of cartilage rather than bone first appeared 500 million years ago. Many were covered in plate-like armour.

LIFE:

The Paleozoic covers the time from the first appearance of abundant, soft-shelled fossils to the time when the continents were beginning to be dominated by large, relatively sophisticated reptiles and modern plants. The lower (oldest) boundary was classically set at the first appearance of creatures known as trilobites and archeocyathids. The upper (youngest) boundary is set at a major extinction event 300 million years later, known as the Permian extinction . Modern practice sets the older boundary at the first appearance of a distinctive trace fossil called Trichophycus-pedum.

At the start of the era, all life was confined to bacteria, algae, sponges and a variety of somewhat enigmatic forms known collectively as the Ediacaran fauna. A large number of body plans appeared nearly simultaneously at the start of the era -- a phenomenon known as the Cambrian Explosion. There is some evidence that simple life may already have invaded the land at the start of the Paleozoic, but substantial plants and animals did not take to the land until the Silurian and did not thrive until the Devonian. Although primitive vertebrates are known near the start of the Paleozoic, animal forms were dominated by invertebrates until the mid-Paleozoic. Fish populations exploded in the Devonian. During the late Paleozoic, great forests of primitive plants thrived on land forming the great coal beds of Europe and eastern North America. By the end of the era, the first large, sophisticated reptiles and the first modern plants

(conifers) had developed.

PRE-CAMBRIAN EON

(550 mya to 3,800 mya?)

Chapter 5

The earliest part of Earth’s history has been divided into the Priscoan, Archean and the Proterozoic Eons. A very little is known about the Priscoan Eon which covers the first 600 m.y. of Earth’s History. Therefore, we begin review of sequence of Crustal rocks formed during the Archean and Proterozoic Eon collectively known as Pre-Cambrian.

The Archean Eon ranges from 4,000 Ma to 2,500 Ma. In the shield areas of the world such as North America, Eastern Europe, Central China, South Africa and India, the Archean rocks largely occur as Cratons within Proterozoic belts. In general the Archean sequences are comprised of crystalline rocks which are unconformably overlain by little deformed Shelf-type Proterozoic rocks. This unconformity varies slightly in time from continent to continent. For-Example, it is dated 2,500 Ma in North America and 2,600 Ma in Russia and China (Windley 1984).

DIVISION OF PAKISTAN ON GEOLOGIC TIME SCALE BASES

PHANEROZOIC EON

Chapter 6

CENOZOIC ERA

(65.5 million years ago to the present)

In Pakistan exceptionally thick and well-exposed Cenozoic sedimentary sequences are observed along the north-western margin of Indian plate. A wide spread hiatus marks a period of emergence in part of Pakistan at the close of Mesozoic Era causing variable boundary at Mesozoic-Cenozoic contact from place to place(Kazmi & Rana 1982). In the Baluchistan ophiolite thrust belt, and middle and upper Indus Basin, hiatus is usually marked by unconformity. In the sulaiman province, Salt Range and Kohat-Potwar province, the Paleocene clastic sequence lays unconformity over progressively older formation of Mesozoic and Permian age. In parts of lower Indus basin, the contact between the Cretaceous and Paleocene formations is reported to be transitional (HSC 1960). Many of the Paleocene fossils such as echinoids show strong Cretaceous affinity. However, the appearance of nummulites and operculines in these areas is sudden and abrupt (Pascoe 1963).

Tertiary Period:

Paleocene Epoch:

The Paleocene rocks are well exposed in most parts of sedimentary basins of Pakistan, including Chagai-Makran and Baluchistan ophiolite thrust belt. In the lower Indus Basin Paleocene rocks are known as the Ranikot Group (Landenian) containing flows of Deccan Trap in the lower part. The Traps occur above the Cardita-beaumonti beds of Upper Danian age. The lower Paleocene fauna is characterized by the abundance of Miscellanea miscella (d’ Archaic and Haime) in association with Lokhartia hainei (Davies), Operculina sub-salsa (Davies and Pinfold) and

Lockhartia conditi (Nuttal). Whereas, the addition of Ranikothalia sindensis (Davies), Ranikothalia nuttalli (Davies), Actinosiphon tibetica (Douville), Discocyclina ranikotansis (Davies and Pinfold), Operculina patalensis (Davies and Pinfold), Lockhartia tipper (Davies) and Assilina subspinosa (Davies and Pinfold) distinguish an upper Paleocene age (Akhtar and Butt 2000).

Paleocene rocks constitute major part of the Paleogene succession in Kohat, Potwar, Salt and Trans Indus range, Kalachitta and Hazara area, and are exposed over a wide area. The Paleocene succession in the Himalayan fold-and-thrust belt (Upper Indus Basin) is comprised of the Hangu Formation at the base overlain by the Lockhart Limestone and Patala Formation at the top.

Eocene Epoch:

In Potwar area and particularly in Kohat basin to the west, partial separation from open sea caused the development of restricted marine evaporation trough resulting in basal infill of gypsiferous clay stone followed by rock salt and gypsum. In the Salt and Trans Indus Ranges, Kalachitta and Hazara area, open marine platform conditions prevailed during most of early and middle Eocene time depositing thick carbonate sequence. Most part of Sulaiman fold belt and adjoining areas were inundated by the mixed assemblage of sediments deposited as coastal swamps, paralic sands and shallow shelf limestone. Farther south in Kirthar fold belt, carbonate sedimentation continued during the greater part of Early Eocene. Widespread sea level rise during the Middle Eocene resulted in deposition of thick carbonate deposits in almost all parts of sedimentary basins of Pakistan. Marine condition gradually shifted to the South during late Eocene and shallow marine sedimentation continued in Sulaiman and Kirthar basins. The region presently covered by Kohat-Potwar, Kalachitta, Hazara and Salt and Trans Indus Ranges become part of a Peneplain. Clastic input from north and west started pouring into these parts of basin during Middle-Late Eocene time. In North-western Baluchistan, Kalachitta and Kohat some of the Eocene sequences have provide a rich vertebrate fauna, including many species of land mammals and cetaceans.

The Paleocene-Eocene boundary in north Pakistan is characterized by the absence of Lokhartia haimei (Davies), Miscellanea miscella (D’ Archiac and Haime) and the appearance of Nummulites mamillatus

(Fichtel and Moll), Assilina granulosa and Discocyclina dispansa (Akhtar and Butt 1999).

Oligocene Epoch:

Most of the Oligocene, particularly its earlier part, was a period of non-depositional in the Himalayan foreland belt of Potwar and Kohat basins, and in northern part of Sulaiman sub-basin. The Detritus shed by the rising of Himalayas was mostly deposited in Hazara and Kashmir areas where thick Molasse sediments of the Kuldana and Murree Formation were deposited during Middle Eocene-Early Oligocene time. The drainage system during Oligocene time was not large enough to cover the entire Potwar and Kohat Basin.

Farther south in Kirthar and Sulaiman sub-basins, marine sedimentation not only continued during Late Eocene and Oligocene time when mixed carbonate-clastic sediments of the Nari formation (including the Nar member) were deposited. During the Oligocene shallow marine and deltaic sands of the Nari formation prograded across the shelf area from north and north-west but were restricted against Kirthar carbonate shelf edge.

In Chagai-Makran area, clastics supplied from the central Afghan block formed a series of red-brown fluvial and grey-green gypsiferous estuarine clastics of the “Amalaf formation”. In the Kakar-Khorasan (also known as Katawaz Basin) turbidite sequence of Khojak Formation was deposited as part of a major deltaic system.

Quaternary Period:

Quaternary stratigraphic sequence in Pakistan represents a wide range of depositional environment including the marine coastal deposits, shore and offshore deposits, the volcanic deposits of Koh-i-Sultan, Aeolian deposits of Thar and other deserts, evaporates of the salt lakes in Sindh, playa and lacustrine deposits in intermountain basins, deeply-weathered residual soil, glacial and fluvioglacial deposits in the vast piedmont zone, flood plain and delta of the Indus River (Kazmi and Jan 1997).

Chapter 7

MESOZOIC ERA

(251.0 mya to 65.5 mya)

Mesozoic sedimentary rocks crop out extensively in Kirthar-Sulaiman Ranges and Kohat-Potwar-Salt Range region. They form a thick, buried cover sequence over basement rock in greater part of the Indus Platform zone. In Lower Indus Basin (Kirthar-Sulaiman region), the Mesozoic rocks are largely Marine, Calcareous and Argillaceous and several thousand meter thick. Northward, in the Upper Indus Basin (Kohat-Potwar-Salt Range), they describe in thickness to about one thousand meter and include a substantial amount of terrestrial deposits. In the Chagai area of Baluchistan as well as in Kohistan Island Arc Complex, Mesozoic sedimentary sequence consists largely of Cretaceous Volcanic and sedimentary rocks.

Cretaceous Period:

Cretaceous sedimentary rocks are exposed in Himalayan Fold-and thrust belt, Kohistan magmatic arc, Karakoram block and in Chagai magmatic arc. These rocks extensively cover the Indus platform and the fore deep region and have been encountered in several oil-wells. At many localities the Cretaceous sequence contains volcanic rocks, obducted masses of mélanges and igneous intrusion.

In Kirthar-Sulaiman region of the Lower Indus Basin, except for local disconformities there is a complete sequence of the Cretaceous ranging from Late Tithonian through Neocomian to Maestrichtian. This sequence comprises 2,000 m of fossiliferous marine Shale, Carbonate and Calcite sediments (Sembar and Goru Formation, Parh Limestone, Mughal Kot, Fort Munor, Bibai and Moro formation and Pab Sandstone).

In Kohat-Potwar region of Upper Indus Basin, the Lower part of the Cretaceous sequence consists of marine sandstone and Shale (Chichali and Lumshiwal formation) whereas the Upper part is comprised of Limestone (Kawagarh Formation). In this sequence there are unconformities and strata of Cenomanian, Turonian and Meastrichtian age are missing.

Jurassic Period:

The Jurassic sedimentary constitute a thick (820m-3,000m) sequence of marine, pericratonic shelf deposits consisting of Limestone, Shale and Sandstone with subordinate Dolomite and Ferruginous beds. They form a part of platform cover in the entire Indus Basin. In Kirthar-Sulaiman region, Jurassic outcrop are largely restricted to anticlinal cores whereas in Baluchistan Ophiolite-and-thrust belt and the Himalayan fold-and-thrust belt, they form extensive thrust blocks and sheets. In the Karakorams, Jurassic metasediments occur in antiformal thrust staks or thin thrust slices.

Triassic Period:

The Triassic sedimentary sequence in Pakistan is rather restricted in its thickness and extent. Triassic rocks assigned to the Wulgai Formation are present as tectonised blocks in Zhob ophiolite-and-thrust belt in Baluchistan and Himalayan thrust-and-fold belt in the north. Triassic rocks belonging to the Mianwali Formation, Tredian Formation, Chak Jabbi Limestone and Kingriali Formation are exposed in the Kohat-Potwar-Salt Range region of Upper Indus Basin. The Himalayan thrust belt in Swat-Mardan region contains outcrop of Kashala and Nikanai Ghar formations, which are the Triassic component of the Alpurai Group. East of this region, in Hazara area, the Triassic sequence is missing and Jurassic rocks unconformably overlie the Paleozoic rocks. In the Karakorams, Triassic Zait Limestone is exposed in Mastuj Valley of Chitral.

In Upper Hunza Valley, the Triassic sequence comprises Borom and Aghil formation and farther eastward, in Shaksgam-Baltoro region of the Karakoram, Triassic Urdok conglomerate, Chikchi-ri Shale and Aghil limestone are exposed.

Chapter 8

PALEOZOIC ERA

(543 mya to 248 mya)

Paleozoic sedimentary rocks occur at several localities in Pakistan but a complete Paleozoic sequence is lacking. Paleozoic rocks have been reported from the northeast Baluchistan, Khisor Range, Peshawar Basin, Hazara-Kashmir syntaxial region, Sawat, Besham, Hazara, Kaghan, Nanga Parbat-Haramosh Range and the Karakoram. However, they are best developed in the Peshawar Basin.

Permian-Carboniferous Period:

The Carboniferous Period was the time when the extensive Coal beds were formed round the world, including the Indo-Pak Sub-continent. In the Peninsular region, this Period heralded the beginning of deposition of a great thickness of Terrigenous, Coal bearing fluvial sediments spanning a vast time interval more than 160 million years, extending from Late Carboniferous to Early Cretaceous.

This non-marine, fossiliferous sedimentary sequence often referred as the Gondwana system and the time span represented by them is known as Gondwana Era (Pascoe 1959). The Gondwana sequence doesn’t occur in Pakistan, though a limited fresh-water sequence occurs in the Central Salt Range and the presence of Gondwana rocks in the Indus Platform zone cannot be ruled out. Marine sedimentary sequence, counterparts of the Gondwana crop out in the Himalayas and the Karakoram. Despite Paleo-enviromental and Paleo-ecological contrast between these two distinct facies, marine and non-marine, they have a Basal Glacial bed in common (Pascoe 1959).

In Pakistan Carboniferous to Permian sedimentary sequence are confined to the Khyber-Hazara metamorphic belt and zone of crystalline nappes, Hazara-Kashmir Syntaxes, Karakoram Block, Salt Range and its westerly extension.

Devonian Period:

Devonian sedimentary rocks are confined to outcrops of relatively small extent in Khyber Pass and Nowshera-swabi area of the Khyber-Hazara metamorphic belt, in the Yarkhun Valley of Chitral and in the western part of Karakorams. These rocks are largely fossiliferous.

Silurian-Ordovician Period:

Ordovician and Silurian sedimentary sequences are poorly developed in Pakistan. In the northern areas they crop out mainly as thin faulted blocks or thrust sheets, and unconformably overlie the Cambrian or Proterozoic sequences. They are largely confined to Attock-Cherat Ranges, Swabi area west of Tarbela (Khyber-Hazara Metamorphic Belt) and Upper Yarkhun valley (Chitral) in the western Karakorams.

Cambrian Period:

In Khisor Range the Upper Part of Cambrian consists of White Gypsum and Crystalline Dolomite. Its total thickness is almost 450 to 500 meters. This sequence is comprised of four main Litho-stratigraphic units.

The Cambrian sequence is the thickest and best developed in Eastern Salt Range and sharply thins and wedges out towards the west. Test drilling by Pakistan Shell Oil co. at Karampur, south of Salt Range, has revealed that this sequence continues southward and overlies the Pre-Cambrian rocks of Indus Platform zone. The Cambrian rocks of Khisor and Salt Range apparently conformably overlain the Late Proterozoic Salt Range formation and are unconformably overlain by Permian strata. In Eastern Salt Range, at places the Paleogene sequence directly overlies the Cambrian.

The Cambrian sequence of Salt Range has yielded several fossils. These have been referred to as Redlichia fauna. A number of species and genera discovered in this sequence were new. Many observers have placed the Redlichia fauna at the top of Lower Cambrian, whereas King (1937) considered it Lower Middle Cambrian (Pascoe 1959).

In Potwar, Salt Range and Trans-Indus Ranges, the Cambrian sequence is collectively known as Jhelum Group and is comprised of the Khewra Sandstone, Khussak formation, Jutana formation and Khisor formation.

PRE-CAMBRIAN EON

(550 mya to 3,800 mya?)

Chapter 9

The earliest part of Earth’s history has been divided into the Priscoan, Archean and the Proterozoic Eons. A very little is known about the Priscoan Eon which covers the first 600 m.y. of Earth’s History. Therefore, we begin review of sequence of Crustal rocks formed during the Archean and Proterozoic Eon collectively known as Pre-Cambrian.

Proterozoic Sequence in Pakistan:

Proterozoic rocks crop out as small scattered inliers on the Indus Platform in Nagar-Parkar area of Sindh and the Sargodha-Shahpur region of Punjab. Subsurface data shows that these rocks form the basement and are a continuation of the Proterozoic sequence in Dehli-Arravalli belt and the Rajasthan Platform of India. North of Indus platform, Late Proterozoic (Eocambrian) sedimentary rocks are exposed in the Salt Range. Meta-sedimentary sequence occurs in the Sufaid Koh-Cherat-Lower Hazara Ranges and Kaghan, and Early to Late Proterozoic formation are exposed in the deeply incised Indus gorge near Besham. Early to Late Proterozoic gneisses form the core of the Nanga Parbat-Haramosh Massif.

Archean Terrains In Indo-Pakistan Sub-continent:

In the Indo-Pakistan sub-continent the Archean rocks crop out only in the Indian part and are largely confined to the Indian Peninsular Shield. Pre-Cambrian sequence does occur in the Himalayas, but these mostly comprise Proterozoic meta-sedimentary rocks and thrust sheets of crystalline rocks (schist and gneisses). However, at places, the high Himalayan gneisses and granites (Manaslu granite) have yielded Nd model ages of 1.7 to 3.8 Ga (Vidal et al. 1982; Deniel et al. 1985) and some of these may represent ripped up thrust slices from Archean basement of the Indian shield.

References http://geomaps.wr.usgs.gov/socal/geology/geologic_history/images/

geologic_time_scale.jpg

http://en.wikipedia.org/wiki/Cenozoic

http://www.ucmp.berkeley.edu/cenozoic/cenozoic.html

http://www.fossilmuseum.net/Paleobiology/ Cenozoic_Paleobiology.htm#QuaternaryPeriod

http://en.wikipedia.org/wiki/Mesozoic

http://www.fossilmuseum.net/Paleobiology/Mesozoic_Paleobiology.htm

http://www.cambridge.org/uk/catalogue/catalogue.asp? isbn=0521781426.

Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6

Chemical & Engineering News, Vol. 86 No. 35, 1 Sept. 2008, "O2 Requirement for Burning Rises", p. 12

http://www.fossilmuseum.net/Paleobiology/Paleozoic_paleobiology.htm

http://en.wikipedia.org/wiki/Paleozoic

http://www.ucmp.berkeley.edu/paleozoic/paleozoic.html

The Earth: An Introduction to Physical Geology by Edward J. Turbuck.

http://images.google.com.pk/imgres?imgurl=http:// wpcontent.answers.com/wikipedia/commons/c/ca/Cenozoic_cosmo_1894_beard_1913.gif&imgrefurl=http://www.answers.com/topic/cenozoic&usg=__SfzNdliwUYxiUwiQPklHsSk_tPA=&h=462&w=558&sz=175&hl=en&start=63&um=1&tbnid=fRt2zTdPsuaPfM:&tbnh=110&tbnw=133&prev=/images%3Fq%3Dclimate%2Bof%2Bcenozoic%2Bera%26ndsp%3D20%26hl%3Den%26rlz%3D1R2RNTN_enPK332%26sa%3DN%26start%3D60%26um%3D1

http://images.google.com.pk/imgres?imgurl=http://venusaracne.com/ Documents/cretac.gif&imgrefurl=http://venusaracne.com/Documents/Cretaceous.html&usg=__NnLLLQ7bLiPXNs_umxGQw3i35vY=&h=480&w=640&sz=192&hl=en&start=17&um=1&tbnid=wmoy8P45dHh72M:&tbnh=103&tbnw=137&prev=/images%3Fq%3Dlife%2Bof%2Bmesozoic%2Bera%26ndsp%3D20%26hl%3Den%26rlz%3D1R2RNTN_enPK332%26um%3D1

http://images.google.com.pk/imgres?imgurl=http:// www.palaeos.com/Mesozoic/Images/diplodocus.jpg&imgrefurl=http://www.palaeos.com/Mesozoic/Mesozoic.htm&usg=__g8jMkfPSClD4pUAFPasrsbUlDR4=&h=281&w=419&sz=39&hl=en&start=2&um=1&tbnid=yJXurHSLdlMl4M:&tbnh=84&tbnw=125&prev=/images%3Fq%3Dclimate%2Bof%2Bmesozoic%2Bera%26ndsp%3D20%26hl%3Den%26rlz%3D1R2RNTN_enPK332%26um%3D1

Stratigraphy & Historical Geology of Pakistan BY KAZMI & ABBASI.