Английский язык в сфере профессиональной коммуникации. Геология. Учебное пособие

UNIT 13. ELEMENTS OF STRUCTURAL GEOLOGY: FOLDS

II. Переведите без словаря:

horizontal position, modification, deformation, geologic structure, region, erosion, product of atmospheric agents, combination.

III. Прочитайте и переведите текст:

Beds of sedimentary rock usually are laid down in horizontal position, but departure from this attitude is sometimes noted, especially where deposition takes place on steeply sloping shores and in deltas. Examination of the beds over wide regions of the earth's surface reveals the fact that they often no longer preserve a horizontal attitude, but show all degrees of inclination to the plane of the horizon because of the folding which they have undergone. It is especially seen in mountain regions. The modification of the original attitude of the beds, called deformation of strata, has resulted from earth movements.

Outcrop. Over wide regions of the earth's surface the solid rock, known as bedrock, is covered with a mantle of loose rock, the product of atmospheric agents. Within such regions the bedrock projects in places through the overlying mantle of unconsolidated rock, or in steep erosion slopes along streams and on high steep slopes of mountains. Exposures of bedrock at the surface are known as outcrops, and by a careful field study of them, including dip and strike, the geologic structure of a region is determined. The most likely places to search for exposures of bedrocks are on steep slopes and hilltops, in stream beds and roads, in cliffs along the shore, and in artificial excavations, including railroads.

Dip. By dip is meant the angle of inclination of the beds with a horizontal plane. It is measured in degrees by an instrument known as a clinometers, which consists of a pendulum with a graduated arc. For convenience the clinometers is usually combined with the compass, so that from the former the amount of dip may

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be ascertained, and from the latter the direction. In measuring dip, the direction as well as the amount of inclination is taken. Thus, 25°S, 300E expresses the exact position of the particular bed. The maximum angle of inclination of the bed always is taken as the dip.

Strike. This is the direction of the line of intersection of the dipping bed with a horizontal plane, and necessarily is measured at right angle to the dip. Like dip, the direction of strike is read with a compass from the north point; thus N.60°W. If the direction of the dip remains constant, the strike is a straight line, but with change in direction of dip there also follows change of strike.

VIII. Отвечая на вопросы, кратко изложите содержание текста:

1.Why are beds inclined to the plane of the horizon?

2.Where can folding of beds boo well seen?

3.What is an outcrop?

4.What is a dip and by what instrument is it measured?

5.What is a strike and by what instrument is it read?

6.What is the practical importance of dip and strike observations?

IX. Переведите текст без словаря:

TILTING (опрокидывание) OF STRATA

Dip. When a bed is tilted (опрокинут) so as to be inclined in some direction, the direction of the inclination is called a dip.

The amount of inclination, usually called the angle of dip, is always measured from plane of the horizon.

The direction of the dip is determined with a compass and the amount of dip — with clinometers.

The amount of the dip may vary from 0° to 90°. At 90° beds are said to be vertical.

Strike. The horizontal line along the tilted stratum is called a strike and it is always at right angles to the dip.

Folds. A fold is a bend (изгиб) in a layer or formation.

When rocks are subjected to tremendous pressure and stresses within the earth's crust they are folded in many places.

Folds may be of different shapes according to the force exerted, the character of rocks and the pressure of the overlying rocks.

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Synclines. These are folds produced by the beds being bent in a downward flexure so that they dip from both sides towards the bottom of the trough. They vary in the same manner as anticlines.

A single or isolated fold sometimes occurs, but as a rule the area of disturbed strata will show a group of connecting anticlines and synclines, which are, either broad and open or narrow and compressed. In the latter case the beds are often twisted and contorted in the most complex manner. The Ural mountains form a typical example of this type of structure.

Unconformity. Strata that have been deposited one above another in orderly sequence, so as to form a continuous succession of beds, are said to be conformable, and the structure is known as conformity. In a conformable series the beds are usually parallel to one another.

In many places, however, this orderly succession of beds has been interrupted by cessation in deposition for a period of time, represented by a break in the geological record, and marked by an erosion interval. The formations are discordant and are said to be unconformable, the structure being called unconformity.

Two main groups of unconformities are generally recognized: (1 ) disconformity when the two formations are in parallel position, the erosion line between which may or may not be entirely visible; and (2) non-conformity or angular unconformity when the line of unconformity is plainly visible between the beds of the lower series and the beds of the series above.

Unconformities are of great importance in the interpretation of geological history.

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VI. Ответьте на вопросы:

1.What is the pitch of a fold?

2.How is the plane which bisects the angle between the limbs of a fold called?

3.What are the principal types of folds?

4.What is the difference between an anticline and a syncline?

5.What is conformity of beds and what is unconformity of beds?

6.What is the practical importance of unconformities?

VII. Переведите текст без словаря:

UNCONFORMITIES

When strata are deposited in uninterrupted succession, layer upon layer, they are said to be conformable. Often, however, there is a break or interruption in the succession of strata which is usually indicated by the fact that one set of strata rests upon the eroded surface of another set.

An unconformity is a surface of erosion that separates younger strata from older rocks. The development of an unconformity involves several stages. The first stage is the formation of the older rock. Most commonly this is followed by uplift and erosion. Finally, the younger strata are deposited.

Sedimentary, igneous or metamorphic rooks may be involved in unconformities.

Kinds of unconformities. Unconformities may be divided into two main groups: In the first group the lower formation shows at once its non-conformity with the series of beds above it. It is called an angular unconformity because the stratification planes of the two series are at an angle. In the second group the stratification planes are in a parallel position. Such an unconformity is termed a disconformity.

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4.The lower wall of the fault.

5.An inclined fracture along which the rocks above have moved up with respect to the rocks below.

VI. Перескажите текст, отвечая на вопросы:

1.What is a joint?

2.In what position can joints lie?

3.Why cannot joints exist below the depth of 15 or 20 miles?

4.What are the main causes of joints?

5.What is a fault?

6.What kind of faults do geologists distinguish?

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VII. Прочтите текст без словаря и выполните тесты:

Almost all consolidated rocks at or near the earth's surface are intersected by systems of fractures or cracks which divide the rocks into blocks of various size and shape.

When very little or no displacement of their adjacent walls has taken place, such cracks are called joints.

In many places there are two sets (группа) of joints crossing (пересекать) each other at high angles and dividing the rock into prismatic blocks of approximately uniform shape and size.

In some cases, however, numerous joints traverse (пересекать) rock formations very irregularly.

Joints may vary from a fraction of an inch to many yards.

Some large joints are hundreds and even thousands of feet long and deep as may often be seen in steep canyon walls and great cliffs (скалы).

Joints very often stand in approximately vertical positions, but they may lie in any position when the rocks containing them have been disturbed by folding or tilting.

The causes of most joints are considered to be stresses and strains (натяжения) within the zone of fracture.

VIII. Определите, какой из заголовков соответствует содержанию прочитанного текста?

1.Folding.

2.Joints.

3.Faulting.

IX. Найдите предложения, которые отвечают на вопросы:

a.What fractures are called joints?

b.What are the causes of most joints?

c.In what position may joints lie?

d.What is the size of joints?

X. Переведите текст со словарем:

In the outer shell of the Earth the rocks are traversed in all directions by fractures which vary from microscopic crevices to important breaks on which large displacement has occurred. Such fractures have great geologic value because of the aid they give to various geologic processes. A fracture on which there has been no appreciable displacement parallel with the walls is a joint. If there has been relative displacement of the walls parallel with fracture, so that corresponding points on the two sides are distinctly offset, the fracture is a fault.

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Joints in igneous rocks. A common type of jointing in igneous rocks is caused by the contraction resulting from the cooling of the igneous material during and after solidification from the liquid state, depending on the rate of cooling, the size and shape of igneous body and other factors. Large intrusive masses of granite and similar rocks are cut by joint planes that divide them into large blocks or prisms.

Jointing in metamorphic rocks. As a rule, metamorphic rocks have many joints, due to the extensive deformation to which such rocks have been subjected. The character of the jointing varies considerably with the nature of the rock. Many of the massive gneisses have joint systems like those that are characteristic of granite, whereas rocks that retain original bedding, such as quartzite, have joints similar to those found in sedimentary rocks.

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