Tuesday, June 22, 2010

Sedimentary Rocks in the Field (Geological Field Guide) By Maurice E. Tucker


Sedimentary Rocks in the Field (Geological Field Guide) By Maurice E. Tucker

Sedimentary Rocks in the Field (Geological Field Guide) By Maurice E. TuckerPublisher: Wiley 2003 244 Pages ISBN: 0470851236 PDF 8 MB
This handy pocket-sized guide shows how to achieve successful fieldwork on sedimentary rocks, paying particular detail to the precision and accuracy of recording detail. Various sedimentary rock-types, textures and all the basic field techniques required are clearly described.Thoroughly revised to incorporate up-to-date information, this 3rd edition will be of use to all students and professionals with a geological background.Features include:* New sections on safety in the field, the use of GPS in sedimentary studies, core description, fossils as depth indicators and facies models.* Improved illustrations and a new updated layout.
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Saturday, June 19, 2010

Sedimentology and Stratigraphy, Second Edition

Sedimentology and Stratigraphy, Second Edition
Product Description
This fully revised and updated edition introduces the reader to sedimentology and stratigraphic principles, and provides tools for the interpretation of sediments and sedimentary rocks. The processes of formation, transport and deposition of sediment are considered and then applied to develop conceptual models for the full range of sedimentary environments, from deserts to deep seas and reefs to rivers.
Different approaches to using stratigraphic principles to date and correlate strata are also considered, in order to provide a comprehensive introduction to all aspects of sedimentology and stratigraphy. The text and figures are designed to be accessible to anyone completely new to the subject, and all of the illustrative material is provided in an accompanying CD-ROM. High-resolution versions of these images can also be downloaded from the companion website for this book atwww.wiley.comgonicholssedimentology.
Publisher Wiley-Blackwell
Number Of Pages 432
Publication Date 2009-06-02
ISBN-10 ASIN 1405135921
ISBN-13 EAN 9781405135924

By Gary Nichols, 2009

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Wednesday, June 16, 2010

Bangladesh Tectonic System


Regional Geological Setting

Bangladesh lies between 20o 34′ and 26o 38′ north latitudes and 88o 01′ and 92o 41′ east longitudes and as a consequence falls in the north eastern South Asia. The Indian States of West Bengal, Meghalaya and Tripura border Bangladesh in the west, north, and east and Burma forms the southern part of the eastern frontier. The Bay of Bengal limits the land area in the south. Bangladesh having about 80% of its area as flat fertile alluvial land is rightly considered as an agricultural country. But the presence of abundant coal, hard rock, and limestone within mineable depths, large reserve of gas, peat, white ceramic clay, and glass sand can assist Bangladesh in gaining recognizing as an industrial country. Physically Bangladesh may be classified in to four distinct regions each having distinguished characteristis of its own.

I. The Eastern and Northern Frontier Hilly Regions comprising the extensive eastern hilly regions, hills of Lalmai and north-eastern Sylhet district and a narrow strips of a series of low hill ranges and isolated circular and elongated hillocks separated by recent alluvium along the northern frontier of districts of Sylhet and Mymensingh.

II. The great Table Land is trisect by the river systems of Meghna and Jamuna giving rise to three large blocks of high lands that exhibit smooth rolling topography.

III. Flood plains of the Ganges, the Brahmaputra and the Meghna River systems cover approximately 40% of Bangladesh.

IV. The Delta at present appears to be a combination of three deltas, namely, the Ganges delta, the Old Brahmaputra-Meghna delta, and the Ganges-Jamuna delta.

Structure and Tectonics

The major tectonic elements of Bengal Basin are the Pre-Cambrian Indian Platform and the Bengal Foredeep. The Indian Platform is divided into four parts including Rangpur Saddle, Northern Slope of Rangpur Saddle, Southern Slope of Rangpur Saddle and a Hinge Zone [Bakhtine, 1965].

The Bengal Foredeep filled with thick strata of Neogene is divided into two parts naming the Western Platform Flank and Eastern Folded Flank. The Western Platform Flank represents an area of deep subsidence, having simple structure of platform type, which sharply differs from eastern folded part of the Flank.

The Eastern Folded Flank is characterized by folding of intermediate or transitional type. By structural peculiarities of folds, it can be sub-divided into the following three tectonic zones;

A. The western zone:

The quietest zone of box like structures, which indicates that this folding is not yet accomplish. This zone includes Dakhin Nhila, Inani, Sitakind Maheshkhali, St. Martin’s, Jaldi, and Walataung.

B. The middle zone:

More disturbed, predominantly asymmetrical and includes Matamuhuri, Bandarban, Gilasari, Siatpahar, and Kasalong, etc.

C. The eastern zone:

This zone includes narrow, ridge like elongated and tightly folded structures like Mowdak, Borcal, Uttar Chatra and Shisok etc.

The present study area, Chittagong city lies in the western marginal part Chittagong Hill Tracts within the folded part (Eastern Folded Flank) of the Bengal Foredeep of the Bengal Basin. The development of Bengal Foredeep is directly related to the development of Himalayan Mountains in the north and the Arakan Yoma Hill Range in the east due to the north and northeastern collision of Indian plate with Eurasian Plate and Burmese Plate respectively. Folds of Chittagong and Chittagong Hill Tracts are situated near the eastern edge of the Indian plate. An attempt has been made to interpret the mechanism for the formation of the folded belt of Chittagong and Chittagong Hill Tracts in the light of plate tectonic theory.

Figure 2.4: Major structural elements of the Bengal basin and its adjacent areas (modified after Bakhtine, 1966; Guha, 1978; Alam, 1990; Reimann, 1993 and Gunguly, 1997).

According to Curray and Moore (1974), the present relative plate motion between the Indian and Eurasian plates is apparently in a north-east south-west direction at a rate of convergence 5 to 6 cm per year. This movement is evidenced by the seismic activities in the plate boundaries and is confirmed by the studies of paleomagnetism of rocks and oceanic magnetic anomalies (McKenzie and Sclater, 1971). The Indian plate being subducted and has been underthrusting the Burmese plate in the east and the Tibet plate in the north and finally is being consumed beneath the Benioff zone. The under thrusting of the Indian plate has also been supported by the study of local mechanism solution for some earthquakes in the north eastern India and Burma (Rastogi et al., 1973). The movement of the Arakan subplate (bounded by the Ninety East Ridge and covering the eastern and the southeastern part of Bangladesh) has been suggested to has resulted the formation of folds of the eastern flank of the Bengal Basin (Faruquee, 1975).

The regional setting of South- Eastern Folded Belt has been described in various literature- Bakhtine[1965], Raju [1968], Guha [1978], Hossain (1985) Alam[1989], Khan[1989], Shamsuddin and Abdullah[1997], Sikder [1998], Murphy and stuff of BOGMC[1998] etc.

All works conclude that the Chittagong and Chittagong Hill Tracts, the Geological name of southeastern folded belt is considered to be the youngest structural subdivision of the western flank of the Indo-Burma Ranges. The rocks of these north-south trending hills of this belt are ranging in age from Lower Miocene to Recent. The folded belt is separated from Arakan-Yoma Anticlinorium by the NNW-SSE striking Kaladan Fault [Rajib, 2002].

Folds of Chittagong and Chittagong Hill Tracts are the western extension of the Arakan Yoma geanticlinorium, which are known in Bangladesh as folded flank of Bengal Foredeep of Bengal Basin. The surface relief of the area is represented by north-south stretched hills of sedimentary cover. The axes of folds run along NNW-SSE directions, which are parallel to the trend of the Arakan Yoma geanticlinorium. The structure is disrupted and complicated by the presence of numerous faults. It is generally observed that the intensity of folding increases towards the east. The amplitudes of the anticlines range from several hundred meters to more than 3500m. Most of the anticlines are asymmetrical and plunging in nature. The axial planes are mostly inclined to the east and the plunge of anticlines ranges from 20 to 150.

From the above discussion, it is observed that the relative movement of the Indian and Burmese plate has developed the main east west compression in the region. The Burmese plate being overridden the Indian plate has been serving as the main pushing agent and as a result the magnitude of force is higher in the east than the west. The analysis shows that the intensity of deformation and folding is higher in the east than the west, which is very much conformable with the field evidences. The tectonic forces thus generated from the east caused intensive deformation in the east become progressively weak towards the west to raise the formation of relatively broad and box-shaped folds in the western zone.

The folded region of Chittagong and Chittagong Hill Tracts is characterized by asymmetrical box-shaped folds associated with reversed type of faults. Such structures can not be satisfactorily explained to have formed by horizontal compression alone. Similar structures have been studied extensively by Millar (1971) in the Tripura–Surma valley of India.

From his studies it has been found that such structure is developed due to vertical crustal movement. In the present study it is believed that the differential vertical movement of the curstal rock might have taken place due to the relative movement of the Indian and Burmese plate. When two plates came finally closer to each other, the basinal material may have bounced up to form the present structure. The upward movement of material in the region has also been confirmed by the abnormal gravity anomaly and elevation relationship (Verma & Mushapadhya, 1976). From the field study it has been observed that adjacent to the high angle reverse fault like Sitakund (Hossain & Akhter, 1983), the sedimentary rocks have been on the up thrown block due to gravity. This bending or draping effect can be responsible for the formation of asymmetrical anticlines.

Udden–Wentworth grain-size scale for sediments and the equivalent phi (ϕ) scale


Udden–Wentworth grain-size scale for sediments and the equivalent phi (ϕ) scale

GEOLOGIC TIMELINE

Cenozoic Era (Recent Life). Two periods: Quaternary and Tertiary

Quaternary Period: Holocene and Pleistocene Epochs

Time

Geologic Development

Life Forms

Holocene Epoch
10,000 years ago to the present

· The Holocene Epoch may be an interval between glacial incursions, typical of the Pleistocene Epoch and therefore not a separate epoch in itself.

· However, it is a period marked by the presence and influence of Homo sapiens.

· During this time, the glaciers retreat, sea levels rise, the climate warms, and deserts form in some area

· Human civilization develops.

· Activities of mankind begin to affect world climates.

· The extinction of other species continues.

Pleistocene Epoch
1.6 million-10,000 years ago

· This epoch is best known as the "Great Ice Age."

· ce sheets and other glaciers encroach and retreat during four or five primary glacial periods.

· At its peak, as much as 30% of the Earth's surface is covered by glaciers, and parts of the northern oceans are frozen.

· The movement of the glaciers alters the landscape.

· Lakes, such as the Great Lakes in North America, are formed as ice sheets melt, and retreat.

· Global warming begins after the last glacial maximum, 18,000 years ago.

· The oldest species of HomoHomo habilis—evolves.

· The flora and fauna in the regions not covered by ice are essentially the same as those of the earlier Pliocene Epoch.

· Mammalian evolution includes the development of large forms: woolly mammoth, woolly rhinoceros, musk ox, moose, reindeer, elephant, mastodon, bison, andground sloth.

· In the Americas, large mammals, such as horses,camels, mammoths, mastodons, saber-toothed cats, and ground sloths, are entirely extinct by the end of this epoch.

Tertiary Period: Pliocene, Miocene, Oligocene, Eocene, and Paleocene Epochs

Time

Geologic Development

Life Forms

Pliocene Epoch
5-2 million years ago

· The emergence of the Isthmus of Panama changes ocean circulation patterns and coincides with the formation of an Arctic ice cap.

· Plate tectonic interactions result in the uplift of the Sierra Nevada, formation of the Cascade Range

· Onset of strike-slip faulting on the San Andreas Fault.

· In Europe, the Alps continue to rise.

· The global climates become cooler and drier.

· Camels and horses are abundant throughout North America.

· Ground sloths also evolve

· Primates continue to evolve, and the australopithecines—antecedents to Homo sapiens—develop late in the Pliocene in Africa.

· In North America, rhinoceroses and ordeodonts become extinct.

Miocene Epoch
25-5 million years ago

· Modern ocean currents are essentially established.

· A drop in sea level near the end of the Epoch isolates and dries up the Mediterranean Sea, leaving evaporite deposits on its floor.

· The climate is generally cooler than the Oligocene Epoch.

· A cold transantarctic ocean current isolates the waters around Antarctica, and the continent becomes permanently frozen.

· Mammal forms are essentially modern, and almost half of modern placental mammal families are present

· Almost all the modern groups of whales, birds are present, as well as the early seals and walruses.

· Higher primates undergo substantial evolution; advanced primates, including apes, are present in southern Europe and Asia.

· On land, grasslands replace forests over large areas on several continents.

Oligocene Epoch
38-25 million years ago

· Tectonic plate movement is still very dynamic.

· Africa and Europe nearly collide, closing the Tethys Sea and leaving as a remnant the Mediterranean Sea.

· Volcanism and fragmentation of western North America is associated with the emplacement of major ore deposits.

· The southeren ocean forms

· The climate is generally temperate.

· Glaciation begins in Antarctica.

· Representatives of modern mammals become the dominant vertebrate life form, including horses, pigs, true carnivores, rhinoceroses, elephants, and camels.

· Oreodonts diversify in North America.

· Early primates appear in North America, and early apes appear in Egypt.

· Many archaic mammals become extinct.

· The earliest representatives of modern cetaceans (baleen and "toothed" whales) evolve.

· Grasslands expand, and forest regions diminish.

Eocene Epoch
55-38 million years ago

· Plate tectonics and volcanic activity form the Rockies in western North America.

· Erosion fills basins.

· Continental collisions between India and Asia culminate in the Alpine-Himalayan mountain system.

· Antarctica and Australia continue to separate and drift apart.

· The climate is subtropical and moist throughout North America and Europe.

· Early forms of horse, rhinoceros, camel, and other modern groups such as bats evolve in Europe and North America.

· Creodonts and ruminant ungulates evolve.

· Archaic whales (archeocetes) evolve from terrestrial meat-eating ungulates.

· Sirenians (dugongs and manatees) first evolve in the shallow Tethys Sea.

Paleocene Epoch
65-55 million years ago

· During the Paleocene, the vast inland seas of the Cretaceous Period dry up, exposing large land areas in North America and Eurasia.

· Australia begins to separate from Antarctica, and Greenland splits from North America.

· A remnant Tethys Sea persists in the equatorial region.

· Mammalian life diversifies, spreading into all major environments.

· Placental mammals eventually dominate the land, and many differentiated forms evolve, including early ungulates (hoofed animals), primates, rodents, and carnivores.

Mesozoic Era (Middle Life).
Three periods: Cretaceous, Jurassic, and Triassic.

Time

Geologic Development

Life Forms

Cretaceous Period
144-66 million years ago

· South America and Africa separate.

· The Atlantic ocean widens.

· A circum-equatorial sea, Tethys, forms between the continents of the Northern and Southern Hemisphere.

· The westward movement of North America forms the ancestral Rocky Mountains and the ancestral Sierra Nevada.

· Sea levels rise, submerging about 30% of the Earth's present land surface.

· The global climate is generally warm. The poles are free of ice.

· Dinosaurs and other large reptiles peak as the dominant vertebrate life form on Earth.

· In the shallow seas, invertebrates live in great diversity. Ammonites are a dominant group.

· Gastropods, corals, sea urchins flourish.

· The early flowering plants (angiosperms), modern trees, and many modern types of insects evolve.

· Near the end of the Cretaceous Period, several mass extinctions occur, including the extinction of five major reptilian groups: dinosaurs, pterosaurs, ichthyosaurs, pleisosaurs, and mosasaurs.

· Extinctions also occur among ammonites, corals, and other marine invertebrates.



Jurassic Period
208-144 million years ago

· The supercontinent of Pangea begins to breakup as North America separates from Eurasia and Africa.

· The Atlantic & Indian Ocean begins to form.

· Tectonic plate subduction along western North America causes the Earth's crust to fold and mountains form in the western part of the continent.

· Gulf of Mexico & Tethys Sea opens

· Newark group lava & Caru volcanism

· Reptiles adapt to life in the sea, in the air, and on land. Dinosaurs are the dominant reptile on land.

· Archaeopteryx, the first bird, evolves.

· Early amphibians, extinct by the late Triassic, are succeeded by the first frogs, toads, and salamanders.

· Mammals are small, shrew-like animals.

· Plant forms are dominated by the cycads and cycadeoides.

· Conifers and gingkoes are widespread.

Triassic Period
245-208 million years ago

· Pangaea covers nearly a quarter of the Earth's surface.

· Toward the end of the Triassic Period, continental rifting begins to break apart the supercontinent.

· The general climate is warm, becoming semiarid to arid.

· Life began to diversify after the end-Permian extinction.

· First dinosaurs evolve.

· Amphibians in fresh water, retreating.

· Primitive mammals appear.

· Forests of gymnosperms and ferns.

· First modern coral appear.

Paleozoic Era (Ancient Life).
Six periods: Permian, Carboniferous, Devonian, Silurian, Ordovician, Cambrian

Time

Geologic Development

Life Forms

Permian Period
286-245 million years ago

· A single supercontinent, Pangaea, forms as Earth's landmasses collide and merge.

· Pangaea extends across all climatic zones and nearly from one pole to the other. This supercontinent is surrounded by an immense world ocean.

· Extensive glaciation persists in what is now India, Australia, and Antarctica.

· Hot, dry conditions prevail elsewhere on Pangaea, and salt forming deserts become widespread.

· Index Fossil: Fusulinid foraminifera

· Invertebrate marine life is rich and diverse at the beginning of the Permian period.

· Toward the end of this period, mass extinctions occur among large groups of corals, bryozoans, arthropods, and other invertebrates.

· 99% of all life perishes.

· On land, insects evolve into their modern forms; dragonflies and beetles appear.

· Amphibians decline in number, but reptiles undergo a spectacular evolutionary development of carnivorous and herbivorous, terrestrial and aquatic forms.

· Ferns and conifers persist in the cooler air.

Carboniferous Period
360-286 million years ago

· Two major land masses form: Laurasia to the north of the equator, and Gondwana to the south.

· Collisions between Laurasia and Gondwana form major mountain ranges.

· Coal-forming sediments are laid down in vast swamps.

· Global climate changing from warm and wet to cooler and drier

· Age of amphibians. Sharks abundant

· First reptiles, Variety of insects.

· Great swamps; forests of ferns, gymnosperms (naked seed plants) and horsetails.

· 2nd glaciation in Africa, Antarctic & India between Carboniferous to Permian period.

Devonian Period
408-360 million years ago

· Europe and North America collide, forming the northern part of the ancestral Appalachian mountain range.

· Europe and North America straddle the equator

· Africa and South America are positioned over the South Pole.

· The climate is generally warm and moist.

· Marked by Acadian Orogeny

· Catskill Delta

· This period is called Age of fishes—armored fish, lungfish, and sharks.

· Ammonites evolve from nautiloids and become one of the dominant invertebrate forms.

· As the ozone layer forms, the first air-breathing arthropods—spiders and mites—evolve on land.

· First Amphibians evolve and venture onto land.
First seed producing Plants including lowland forests of giant psilophyta plants develop and spread over the planet.

Silurian Period
438-408 million years ago

· The North American, European, and Asian land masses are situated on or near the equator.

· Laurentia and Baltica collide.

· Mountain building in Europe.

· Gondwana sits in the South Polar Region.

· Shallow flooding of continental areas deposits sediments

· Later withdrawal of ocean water leaves oxidized "red beds" and extensive salt deposits.

· Extensive Shallow sea over The Sahara

· Clinton Iron formation in S. Appalachian

· Shell-forming sea animals abundant.

· Rise of Fishes( placoderms)

· First Shark

· Sea lilies (stalked crinoids), eurypterids, land scorpions.

· Invasion of land by arthropods.

· Earliest vascular plants (psilopsids, lycophytes).

· Modern groups of algae and fungi.

Ordovician Period
505-438 million years ago

· The barren continents of Laurentia, Baltica, Siberia, and Gondwana are separated by large oceans.

· Shallow seas cover much of North America at the beginning of the period.

· As the seas recede, they leave a thick layer of limestone.

· Later in the period, the seas recover North America, depositing quartz, sandstones, and more limestone.

· Beginning of Appalachian mountain.

· The global climate is generally mild.

· Coral reefs developed

· Agnatha (no jaw fishes, first vertebrates).

· First primitive fishes (ostracoderms, vertebrates).

· Invertebrates dominant. Crustaceans, trilobites, graptolites, brachiopods, bryozoa, echinoderms, corals, mollusks, cephalopods.

· First fungi.

· Possible invasions of land by plants.

Cambrian Period
540-505 million years ago

· Sedimentary rocks (sandstone, shale, limestone, conglomerate) form in shallow seas over the continents.

· Rodinia begins to break up into northern and southern portions.

· Extensive Seas in major Synclines

· Much volcanic activity & Long period of marine Sedimentation

· The global climate is generally mild.

· Pan African orogeny occurred

· First Glaciations Cambrian to Ordovician period in Africa.

· Marine metazoans with mineralized skeletons, such as sponges, bryozoans, corals, brachiopods, molluscs, arthropods, and echinoderms, flourish.

· The trilobites are particularly dominant in the shallow-water marine habitats.

· Trilobites & Agnathids made up 60% of Cambrian fossils

· Plant life is limited to marine algae.

· First Shelled marine invertebrates

· Another important Index fossil is The Archeocyathiels.

Precambrian Time. Three Eons: Proterozoic, Archean, and Hadean.

Time

Geologic Development

Life Forms

Proterozoic Eon
2.5 billion years ago-538 million years ago

· The supercontinent Rodinia forms approximately 1.1 billion years ago.

· Plate tectonics slows to approximately the same rate as the present.

· Large mountain chains form as the continents collide.

· Quartz-rich sandstones, shales, and limestones are deposited over the continents.

· Oxygen levels increase as life on Earth develops the ability to obtain energy through photosynthesis.

· The late Proterozoic is an "Ice House" world.

· Eukaryotes (single-celled organisms with a nucleus) evolve

· These are more advanced forms of algae and a wide variety of protozoa.

· Eukaryotes can reproduce sexually, which makes genetic diversity possible, as well as the ability to adapt to and survive environmental changes.

· Multi-celled, soft-bodied marine organisms (metazoans) evolve.

Archean Eon
3.8-2.5 billion years ago

· The Earth's permanent crust is formed.

· Vast amounts of metallic minerals are deposited.

· The oceans and atmosphere result from volcanic out gassing.

· The earliest life forms evolve in the seas.

· They are the prokaryotes—single-celled organisms with no nucleus—cyanobacteria (blue-green algae).

· The earliest bacteria obtain energy through chemosynthesis (ingestion of organic molecules).

Hadean Eon (Azoic)
4.6-3.8 billion years ago

· The Earth forms as a solid planet.

· No evidence of life yet known.