INTRODUCTION

GEOSCIENCE: FIELD OF STUDY

Geology

Physical geography

Geophysics

Soil science

Oceanography and hydrology

Glaciology

Atmospheric sciences

GEOLOGY

Comprise study of solid Earth, the rock of which it is composed & the processes

by which it evolves

History of the Earth, provides primary evidence for plate

tectonics, evolutionary history life and past climates

Mineral & hydrocarbon exploration, evaluate water resources; predicting &

understanding of natural hazards, remediation of environmental problems

PHYSICAL GEOGRAPHY

branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, biosphere and geosphere, as opposed to the cultural or built environment, the domain of human geography

GEOPHYSICS

physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods.

sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation.

SOIL SCIENCE

study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils

OCEANOGRAPHY & HYDROLOGY

is the branch of Earth science that studies the ocean. It covers a wide range of topics, including marine

organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries.

Hydrology is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability.

GLACIOLOGY

study of glaciers, or more generally ice and natural phenomena that involve ice.

ATMOSPHERIC SCIENCES

umbrella term for the study of the atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems

GEOSCIENCE FOR PETROLEUM

EXPLORATION & DEVELOPMENT

unlocking the worlds remaining hydrocarbon resources

from new venture, assessing regional data to

focus in on the most prospective countries and basins, to the ultimate test, drilling the wells.

acquiring the best possible data to image the

subsurface, either seismic data (imaging the rock units 2-4 km below the ground), or undertaking geochemical, gravity or magnetic surveys.

interpreted the data using the latest software to produce 3D subsurface models for optimum locations to drill a well.

To locate hydrocarbons in the subsurface requires integrated teams that model the distribution of reservoirs, source rocks and traps.

Geology the study of the Earth, the materials of which it is

made, the structure of those materials, and the processes acting upon them.

includes the study of organisms that have inhabited our planet.

important part is the study of how Earths materials, structures, processes and organisms have changed over time.

ESSENTIAL BASIC GEOLOGY

study earth processes processes such as landslides, earthquakes,

floods and volcanic eruptions can be hazardous to people

STUDY OF GEOLOGY

understand these processes well enough to avoid building important structures where they might be damaged

Example: can prepare maps of areas that have flooded in the

past, they can prepare maps of areas that might be flooded in the future. These maps can be used to guide the development of communities and determine where flood protection or flood insurance is needed.

study earth materials use earth materials every day. They use oil

that is produced from wells, metals that are produced from mines, and water that has been drawn from streams or from underground.

conduct studies that locate rocks that contain important metals, plan the mines that produce them and the methods used to remove the metals from the rocks. Also to locate and produce oil, natural gas and ground water.

study earth history Today, concerned about climate change.

Working to learn about the past climates of earth and how they have changed across time.

This historical geology news information is valuable to understand how our current climate is changing and what the results might be.

NATURE & COMPOSITION OF EARTH

EARTHQUAKE

Seismic waves

- waves of energy that travel through the earth, for eg. as a result of an earth quake, explosion, or some other process that imparts low-frequency acoustic energy.

EARTHQUAKE WAVES IN THE EARTH

P wave

S wave

P waves Particle motion vibrate in horizontally

Travel the fastest

S waves Vibrate from side to side vertically

Arrive after primary waves

travel through solids, not through liquids or gasses.

Surface waves Move by spherical propagation

Slowest of the three waves types

Surface wave

SIGNIFICANCE OF EARTHQUAKE WAVES

Discriminate between earth layer and establish what is known about their composition

Therefore travel times of seismic waves and their ability or lack ability to be transmitted through various substances are important.

MINERALS & ROCKS MINERALS

Fundamental building blocks of rock materials in the earth

Naturally occurring inorganic substances with a definite chemical composition and specific crystal structure.

Crystal structure is controlled by composition that directly determines which atoms of which elements will be distributed in which arrangement.

PHYSICAL PROPERTIES OF MINERALS Guidelines for field identification of specimens

that may occur combined with other minerals or in very small amounts in particular sample

Hand lens is used for this identification

Permit identification of hand specimens without involving time consuming & difficult laboratory procedures

Minerals grow into consistent crystal shape, which are controlled by chemical composition of mineral

Six crystal system that include all minerals

Some mineral compounds can form more than one mineral with entirely different crystal structures polymorphs which are quite different in appearance

Study of mineral crystal forms is called crystallography

SHAPE

How mineral resists scratching hardness

Only fresh mineral surfaces should be tested

Weathered mineral surfaces will result in hardness measurements that can be quite different from fresh unweathered mineral

Mohs hardness scale scale from softest to hardest by which mineral hardnesses are determined

HARDNESS

Mineral impurities can make mineral nearly any color

Not usually sufficient by itself to identify mineral; however in combination with other physical properties it can assist in mineral identification

COLOR

Specific gravity of mineral its weight relative to the weight of an equal volume of water

Obtained by dividing the weight of mineral in air by difference between its weight in air & its weight in water.

Most mineral specimens are difficult to measure because associated with other minerals

Very heavy and very light minerals easily recognized by specific gravity

WEIGHTS

How mineral reflects light determine its type of luster

Most minerals are considered to have metallic or nonmetallic luster, with few having sub metallic luster.

LUSTER

How mineral parts along weaknesses in its crystal lattice

tendency of crystalline materials to split along definite crystallographic structural planes

result of the regular locations of atoms and ions in the crystal

create smooth repeating surfaces that are visible both in the microscope and to the naked eye

Quartz tightly bonded & produce no cleavage Mica have one direction of cleavage and calcite

has three directions

CLEAVAGE

Green fluorite with prominent cleavage

Random breakage of mineral along no particular orientation

FRACTURE

Some minerals have very distinctive taste qualities that facilitate their immediate identification

Rock salt (halite) & salvite are two minerals with distinctive tastes.

TASTE

Limestone responds to hydrochloric acid

Dolomite responds weakly to hot hydrochloric acid but reacts more vigorously when it is powdered

RESPOND TO CHEMICAL REAGENTS

Radioactive minerals emit particles that activate various types of detectors

Important in identification radioactive minerals & in exploration for them

RADIOACTIVE

CYCLE OF ROCK

Sedimentary rock

- source & reservoir bed

- products of breakdown, transportation,

deposition all three types & developed in many

different environment

- generate & accumulate petroleum

ROCK CYCLE & PETROLEUM

Igneous & metamorphic rocks

- do not generate petroleum but under proper

circumstances can provide seals & reservoir for

petroleum accumulations

Rock cycle forms, changes & destroy rocks as continuum

Petroleum experience similar kinetic history during which time it is being formed, & changed & destroy with its host rock

At any instant oil is being generated in some rocks , changing in others, migrating in still others & being eliminated by geologic processes

Represented by the presence of rock intervals in the geologic column or by the absence of equivalent rocks in correlative columns in adjacent or distant locales

Elapsed geologic time encompasses all of the events that affect the earth

Petroleum forms, migrates and accumulates as direct results of those events represented by the clues to be interpreted as significant exploration data

GEOLOGIC TIME

RELATIVE TIME

Required the development of a sequence of events that could be established on the basis of obvious consecutive criteria

Required events within the sequence be sufficiently identifiable & be widespread enough to have real significance

SUPERPOSITION

Fundamental to the study of layered rocks and means that in any normal sequence the oldest rocks, deposited first, on bottom, and youngest rocks deposited last on top.

As erosion attacks terrain underlain by normal rock sequence, successively older rocks will be exposed as younger rocks are removed

The gap between the oldest rocks exposed by the erosional surface & the rocks laid down by subsequent deposition is represented by the period of erosion.

Examination of sequence of rocks contain gap indicate that the section had undergone deposition, erosion & subsequent deposition

If amount of geologic time represented by the missing portion of the section had been established in adjacent areas, the history of geologic section can be pieced together.

Cretaceous Mancos Shale near Woodside, Utah

Atlantic coast of Tierra del Fuego

SUCCESSION OF FAUNA

Stratigraphic units being deposited, fossils of plants & animals being included with sediments

Deposition continue, evolution of plants & animals changes some of the forms, eliminate others & gives identity to the ages of rocks being laid down

Fossils successions & occurences allow correlations, or comparisons to be made between rock sections

INCLUSION

Igneous rocks that intrude surrounding rocks are invariably younger than the rocks they intrude because they form later

CROSSCUTTING RELATIONS

Pre-existing rocks can be intruded by younger rocks or can be affected by later faulting and/or folding

Scales of crosscutting features are variable, from regional in extent to those on microscopic scale

ABSOLUTE TIME

Until mid-twentieth century, all dating involved relative parameters that permitted estimates for absolute ages, which were subject to considerable error

The development of absolute age dating techniques, however eliminated much of the error & now routinely confine geologic events to narrow time ranges

Determined by measurements involving the half-lives of certain radioactive elements

Half life measure of radioactive decay & is the time required for half of certain element to be eliminated by the loss of its radioactive particles

If the half life of an element is known & compared to the amount of that element remaining in the deposit , time elapsed since mineral was originally crystallized can be calculated

Eg: isotope of uranium (U) is U235, its daughter product is lead (Pb207)

It has been determined that it takes 704 m.y. for

half of an original amount of U235 isotope to convert to Pb207

Thus, rock contains equal amounts of U235 and

Pb207, the rock must formed 704 Ma Amount of time necessary for radioactive isotope

to lose half of its radioactivity is termed the half-lifeof the isotope

Dating for sedimentary rocks is difficult since they often consist of fragments derived from several sources

Ages of individual constituent grains can be determined, but do not date time of deposition of entire rock

Igneous & metamorphic rocks that are closely associated with sedimentary rocks will accurately establish ages of the sediment

RADIOMETRIC TIME SCALE

GEOLOGIC TIME SCALE

RELATIVE TIME

ABSOLUTE TIME

GEOLOGIC TIME SCALE

Eventually conventional nomenclature was required to integrate information from many places in order to standardize the geologic column & make it useful to subsequent workers

A system of descriptive terminology was applied to the various intervals throughout the years & evolved into stratigraphy of today

Systems represented time rock units or the actual rocks that were deposited during a specific time interval, which was called a period.

Groups of periods were called eras, while periods were divided into epochs & ultimately into ages

PLATE TECTONICS

RELATION BETWEEN OCEANIC & CONTINENTAL CRUST

CAUSES OF CONTINENTAL MOTION

Although mantle sufficiently viscous to behave as solid, it may respond to continuous stress applied by heat and develop convection currents.

Convection cells in mantle provide mechanism for separation of continental masses

Movements in the crust, produced by convection, would not exceed a few centimeters per year

Another possible mechanism for continental movements might involve the body forces produced in the earth by rotation on its axis

Rotational forces affect the flow of the hydrosphere & atmosphere & important in the distribution of ocean currents & air masses, respectively

Gravitational effects of the sun, moon, & the planets in the solar system create tides within the earths crust Known as earth tides & possible contribute to the

motions of crustal plates on the earth

CONTINENTAL MARGIN

Continental margins evolve in response to the nature of various motions

Assume 3 different modes according to the types of motions & related deformation that affect them

Divergent continental margins

Convergent continental margins

Transform continental margins

DIVERGENT CONTINENTAL MARGINS

Occur where plates broken apart along spreading centre & moved away from each other

Example: The coasts of north & south America moved away

from the western coasts of Africa & western Europe

Originally joined in the vicinity of Mid-Atlantic Ridge, common spreading centre for both sides of north & south Atlantic oceans

Characterized by : Block faulting with deformation limited to tilting

Red beds deposited as basal sediments in fault-block basins

Salt deposited over the red beds

Marine sandstone & shale as water depths increase

Reef & bedded carbonates

Possible petroleum occurrences in or associated with above sediments & structures

Sediments produce petroleum in the North Sea, the Gulf of Mexico, the coasts of west Africa & Eastern South America & northeastern Canada

CONVERGENT CONTINENTAL MARGINS

Developed where 2 continental plates / 1 continental & 1 oceanic plate collide

In order to accommodate encroachment of 1 plate by another, a zone of plate consumption is developed whereby 1 plate overrides the other along subduction zone

Lighter continental material rides over the denser oceanic material

Subduction zones only develop where there is density difference between crustal materials that are colliding

Where 2 continental plates come together, subduction continues as long as there is oceanic crust in the space between the continental masses

When 2 continental masses meet, subduction zone ceases to exist because

Mass is capable being subducted & a suture or

Resulting mountain range

Separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories. The term is borrowed from surgery where it describes the sewing together of two pieces of tissue.

Characteristic of convergent zone Zone of compression within the subduction zone &

possible extension along the axis of the island arc

Reverse & normal faulting

Volcanic sediments near the volcanic island arc. Sediments become cleaner & better sorted at distance from volcanic sources

Block faulting in marine basin behind the volcanic island arc

Possible petroleum occurences in clean marine sediments on high fault blocks in basin behind island arc

Oil & gas field in Sumatra & fault blocks on Malaysian side

Andes mountains in Columbia, Equador & Peru

Zagros zone of southwestern Iran

TRANSFORM CONTINENTAL MARGINS

Occur where 2 plates move past each other without converging or diverging

Characterization Strike-slip movement along a major shear zone as

2 continental plates move by each other

Fault block structures

Sediment deposition concurrent with deformation along the transform fault system

Development of multiple reservoir & source beds

No volcanic activity

Oil field along San Andreas fault of southern California

Caribbean & south American produces petroleum from related structures in southern Trinidad & northern Venezuela

Schematic illustrations of the Wilson cycle, the fundamental geological processes controlling the evolution of the continents a-b) A continent rifts, such that the crust stretches, faults and subsides. c) Seafloor spreading begins, forming a new ocean basin. d) The ocean widens and is flanked by sedimented passive margins. e) Subduction of oceanic lithosphere begins on one of the passive margins, closing the ocean basin (f) and starting contiinental mountain building. g) The ocean basin is destroyed by a continental collision, which completes the mountain buliding process. At some later time continental rifting begins again.

A basic theory for the formation of sedimentary basins is that thinning of the lithosphere occurs due to extensions caused by plate tectonics and associated convection in the mantle.

This leads to the creation of a surface depression

which is then infilled by sediments eroded off the adjacent uplifted continents.

As the sediments are deposited, they are generally

deformed by continuing extension leading to breakage of the crust, were a break is called a fault. Resulting in a series of fault-defined blocks.

FORMATION SEDIMENTARY BASIN

the study of modern sediments such as sand, mud (silt), and clay, and the processes that result in their deposition which accumulates as sediment in continental and marine environments and eventually forms sedimentary rocks

Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures

SEDIMENTOLOGY

Sedimentary rock types

Clastic Carbonate

Chemical sedimentary rocks

Sedimentary rocks record the history of changing environments on Earth.

Based on the recognition of the signature of changing environments over time, as preserved in the rock record.

Environmental interpretation of rocks

+

Age of rocks

= Earth History

the study of rocks to determine the order and timing of events in Earth history

Study origin & character of layered sedimentary rocks

Study classification layered rocks, depositional succession & geographic distribution

Sedimentary geology = sedimentology +

stratigraphy

STRATIGRAPHY

Large Scale Cross Bedding in Eolian Sandstone at Red Rock National

Park, Las Vegas

Sedimentology focuses primarily on facies and depositional environments (how were sediments /sedimentary rocks formed?)

Stratigraphy focuses on the larger scale strata and Earth history (when and where were sediments/sedimentary rocks formed?)

The law of superposition (or the principle of superposition) is a key based on observations of natural history that is a foundational principle of sedimentary stratigraphy :

Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.

The law was formulated in the 17th century by the Danish scientist Nicolas Steno.

buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous

In general, older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record

UNCONFORMITY

Types of unconformities Disconformity

unconformity between parallel layers of

sedimentary rocks which represents a period of

erosion or non-deposition. Disconformities are marked

by features of subaerial erosion

DISCONFORMITY

Nonconformity

exists between sedimentary rocks and metamorphic or

igneous rocks when the sedimentary rock lies above

and was deposited on the pre-existing and eroded metamorphic or igneous rock. Namely, if the rock

below the break is igneous or has lost its bedding by metamorphism, the plane

of juncture is a nonconformity.

NONCONFORMITY, GRAND CANYON ARIZONA

NONCONFORMITY

Angular unconformity

unconformity where horizontally parallel strata of

sedimentary rock are deposited on tilted and eroded layers, producing an angular

discordance with the overlying horizontal layers.

The whole sequence may later be deformed and tilted by further orogenic activity

ANGULAR UNCONFORMITY

ANGULAR UNCONFORMITIES, GRAND CANYON

TYPES OF UNCONFORMITIES, GRAND CANYON

TUTORIAL Explain three main role of geologist in exploration

of oil and gas industry

Differentiate between P, S and surface wave Differentiate igneous, metamorphic and

sedimentary rock types in terms of origin, how it form and relation between the rocks and petroleum. State 2 example of rocks for each of rock types

Describe the effect of plate tectonics on formation

of basin

Differentiate between relative and absolute time of the rocks for dating technique

Explain in brief your understanding on convergent plate boundary, divergent plate boundary and transform plate boundary

By giving one example, explain the formation process of sedimentary rock types clastic, carbonate, evaporites and chemical sedimentary rocks.

Explain three main role of geologist in exploration of oil and gas industry unlocking the worlds remaining hydrocarbon

resources by knowing the geology of the potential area, the petroleum system and location of hydrocarbon can be identified.

to locate or detect the presence of subsurface structures or bodies and determine their size, shape, depth, and physical properties (i.e density, velocity, porosity), and also fluid content

from new venture, assessing regional data to focus in on the most prospective countries and basins, to the ultimate test, drilling the wells.

interpreted the data using the latest software to produce 3D subsurface models for optimum locations to drill a well.

Differentiate between P, S and surface wave The first kind of body wave or primary wave. This

is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the 'direction of wave propagation'.

The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid. S waves move rock particles up and down, or side-to-side--perpindicular to the direction that the wave is traveling in (the direction of wave propagation)

It's the fastest surface wave and moves the ground from side-to-side. Confined to the surface of the crust, Love waves produce entirely horizontal motion.

A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.

Differentiate igneous, metamorphic and sedimentary rock types in terms of origin, how it form and relation between the rocks and petroleum. State 2 example of rocks for each of rock types

Igneous Sedimentary Metamorphic

Origin Form from volcanic magma when volcano erupts & also referred as volcanic rocks

Result from the accumulation of small pieces broken off from pre-existing rocks

From sedimentary & igneous rocks which were subjected to more intense pressure or heat & as a result underwent a complete change

Igneous Sedimentary Metamorphic

How it form

-Under the surface of the earth, magma kept liquid by high T & P. -As volcano erupts, hot magma reaches the surface, cool down & solidifies

Sedimentary rocks become cemented together by minerals & chemicals present when they are formed & others are held together by electrical attraction

-Transforms the rock into other rocks which are denser & more compact -New minerals are created either by the rearrangement of a minerals components or by reaction with fluids that enter the rocks

Rock & Petroleum

Do not generate petroleum but under proper condition provide seal/& reservoir

Generate & accumulate petroleum

Do not generate petroleum but under proper condition provide seal/& reservoir

Example Granite (intrusive) & basalt (extrusive)

Gypsum & sandstone

Gneiss & Slate

Describe the effect of plate tectonics on formation of basin

A basic theory for the formation of sedimentary basins is that thinning of the lithosphere occurs due to extensions caused by plate tectonics and associated convection in the mantle.

This leads to the creation of a surface depression which is then infilled by sediments eroded off the adjacent uplifted continents.

As the sediments are deposited, they are generally deformed by continuing extension leading to breakage of the crust, were a break is called a fault. Resulting in a series of fault-defined blocks.

Differentiate between relative and absolute time of the rocks for dating technique

Relative Time Required the development of a sequence of events

that could be established on the basis of obvious consecutive criteria

Required events within the sequence be sufficiently identifiable & be widespread enough to have real significance

Superposition, succession of fauna, inclusion & crosscutting

Absolute Time Determined by measurements involving the half-

lives of certain radioactive elements

Half life measure of radioactive decay & is the time required for half of certain element to be eliminated by the loss of its radioactive particles

If the half life of an element is known & compared to the amount of that element remaining in the deposit , time elapsed since mineral was originally crystallized can be calculated

Explain in brief your understanding on convergent plate boundary, divergent plate boundary and transform plate boundary

Convergent plate boundary A tectonic boundary where two plates are moving

toward each other. If the two plates are of equal density, they usually push up against each other, forming a mountain chain. If they are of unequal density, one plate usually sinks beneath the other in a subduction zone. The western coast of South America and the Himalayan Mountains are convergent plate boundaries. Also called active margin, collision zone.

Divergent Plate boundary A tectonic boundary where two plates are moving

away from each other and new crust is forming from magma that rises to the Earth's surface between the two plates. The middle of the Red Sea and the mid-ocean ridge (running the length of the Atlantic Ocean) are divergent plate boundaries. Also called passive margin, spreading zone.

Transform Boundaries Places where plates slide past each other are called transform boundaries. Since the plates on either side of a transform boundary are merely sliding past each other and not tearing or crunching each other, transform boundaries lack the spectacular features found at convergent and divergent boundaries. Instead, transform boundaries are marked in some places by linear valleys along the boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by features like stream beds that have been split in half and the two halves have moved in opposite directions.

San Andreas fault

By giving one example, explain the formation process of sedimentary rock types clastic, carbonate, evaporites and chemical sedimentary rocks.

Clastic sedimentary rocks are made up of little pieces of other rocks called sediment. Mineral crystals called cement hold different types of sedimentary rocks form in different environments. For instance, sandstone, a sedimentary rock made of sand grains, may form in a beach or desert sand dunes. Shale, a sedimentary rock made of mud and clay, may form in a swamp, the bottom of a lake, or some other muddy environment. Conglomerate, a sedimentary rock make of gravel and sand, may form from the sediments at the bottom of a stream.

Evaporites are layered crystalline sedimentary rocks that form from brines generated in areas where the amount of water lost by evaporation exceeds the total amount of water from rainfall and influx via rivers and streams. The mineralogy of evaporite rocks is complex, with almost 100 varieties possible, but less than a dozen species are volumetrically important. Minerals in evaporite rocks include carbonates (especially calcite, dolomite, magnesite, and aragonite), sulfates (anhydrite and gypsum), and chlorides (particularly halite, sylvite, and carnallite), as well as various borates, silicates, nitrates, and sulfocarbonates. Evaporite deposits occur in both marine and nonmarine sedimentary successions.

rock salt, gypsum, or anhydrite,

Limestone is a sedimentary rock composed mainly of calcium carbonate (CaCO3), usually calcite, sometimes aragonite. As well it may contain considerable amounts of magnesium carbonate (dolomite). Most limestones have a granular texture, but limestone can also be massive, crystalline or clastic.

Most limestones are formed by the deposition and consolidation of the skeletons of marine invertebrates, but also limnic limestone exists. Limestone can also be formed by chemical precipitation from solution. Dolostone usually is formed by dolomitisation of limestone during diagenetical processes prior to lithification.

Carbonate sedimentary rocks are sedimentary rocks formed at (or near) the Earth's surface by precipitation from solution at surface temperatures or by accumulation and lithification of fragments of preexisting rocks or remains of organisms. For the formation of sedimentary rocks a longer deposition time is needed , as the sediment has to be compacted and cemented into hard beds or strata.

Chemical rocks are deposited from aqueous solutions and precipitation may be caused by chemical or biochemical processes. The formation of chemical rocks is not dependent on currents or energy, and particle size is not as important in classification as in clastic rocks. Instead, these rocks are classified on the chemistry of the dominant minerals. The three common groups of chemical rocks are Carbonates, Evaporites and Chert.

Chert is a form of the mineral quartz which forms under the temperature and pressure conditions seen at the Earth's surface (quartz also forms under metamorphic and igneous conditions). Chert is a cryptocrystalline form of quartz with the same general properties, but with a different mineralogic structure.

Chert is often formed by biochemical processes. Certain types of algae, called diatoms, are capable of extracting silica from water (both freshwater and marine) and using it to form an exoskeleton. When the algaes die, these skeletons can accumulate into a siliceous ooze layer, which when lithified forms a chert layer, or a chert nodule (a nodule is a lump).

CHERT

ASSIGNMENT

Describe the application of geosciences in petroleum exploration and development.

List two (2) tools for exploration that have been used by the geologist to characterize the reservoir

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