Fig. 37 Continental, shoreline and marine sedimentary environments



Classification and chemical differential of sedimentary rocks

Sediments are described on the basis of their grain size, chemical and mineralogical composition and modes of accumulation. Classification by grain size is most readily applied to clastic sediments because particle size is related to the origin of the rock.Among the clastic rocks, we recognize four main grain-size groups:

1. conglomerates containing particles greater than 2 millimeters in diameter;

2. sandstones with grains of 1/16 to 2 millimeters size range;

3. siltstones contain grains between 1/256 to 1/16 millimeter in diameter;

4. claystones carry particles finer than 1/256 millimeter in diameter. Where planar fractures or parts along bedding surfaces are developed, claystones and fine-grained siltstones collectively are termed shale. If fractures parallel to bedding layering are not present in a deposit containing both clay and silt, the massive rock is termed as mudstone.

Limestones produced principally through the accumulation of calcareous fossil materials include coquina, chalk and reef limestones. The low-temperature process where source rock is converted to secondary accumulations of contrasting compositions is termed sedimentary differentiation.Weathering of preexisting rocks at or near the Earth’s surface results in the solution of readily dissolved constituents and in the hydration and oxidation of others. Materials transported as clastic grains are separated


on the basis of mechanical properties; relatively soft minerals possessing good cleavages are more rapidly and more finely abraded than fragments lacking fractures and perfect cleavage. Therefore, grain size and mineralogical composition are related in sediment.

The average compositions of igneous source rock of the continental crust and of typical sedimentary lithologies, sandstone, shale and limestone are markedly different. The average bulk composition of continental sedimentary rock is approximately 60 to 80% shale, 15 to 20% sandstone and conglomerate and approximately 10 to 15% carbonate. (Barret E , Hunt A. And Milner B.” Earth and Atmosphere”, 1993, Longman)

Read the following text and fill in the missing words.

The volume of _____________  ________  (1) is about 10%. However,

sedimentary units have an economic importance and include mineral ores

such as coal, ________  (2), and natural gas. Sedimentary rocks are the

___________  (3) of detritus or _______  (4) sediments. The formation of

sedimentary rocks includes the following processes: _______    (5),

transportation, ________  (6) and lithification. Lithification is a combination

of ______  (7) and _______  (8). The nature of sediment depends on several

factors: _______  (9), attendant weathering, ________________  (10) and

___________  (11) of transportation. Rapid accumulation of ill-sorted

clastics results in ________  (12) sands, while slow build-up of fine-grained

matter produces ______  (13) sediments. There are two basic types of

sediments: ______  (14) and ___________  (15). ___________  (16) is the

reaction among original chemically dissimilar fragments that produces new minerals.

Terrestrial fine-bedded sedimentary rocks coarse marine deposition source weathering diagenesis compaction length petroleum mode chemical cementation accumulation

3.3.9. Complete the following sentences.

1. Sediments are described according to……………………………………...

2. Clastic sediments are based on …………………………………………….

3. There are four main grain-size groups……………………………………...

4. Limestones are produced…………………………………………………...

5. Sedimentary differentiation is …………………………………………

6. Materials transported as clastic grains…………………………………

7. The average bulk composition………………………………………… .


3.3.10 Fill in the chart and make a short report on the topic-Sedimentary rocks as the bulk composition of the Earth’s crust.

Definition Formation Factors Nature of sediments Types Classification Examples
             

LISTENING COMPREHENSION

You will hear a short lecture about rock formation. At the end you will be asked several questions. Each question will be spoken only once. For this reason, you must listen very carefully to understand what the speaker says. After you hear a question, read the three selections and choose the one that is the best answer to the question the speaker asked. Before you listen to the lecture, you have 45 seconds to look at the questions. (PAUSE 45 seconds)

1. Where do coals get carbon?

A. swamp flora

B. forest vegetation

C. mountain vegetation

2. What happens when plants die in wet acid conditions?

A. rot completely

B. turn into peat

C. become limestone

3. How is soft brown coal called?

A. bituminous coal

B. lignite

C. anthracite

4. Why do seawater animals need calcium carbonate?

A. to form shells

B. to make up limestones

C. to protect shells

5. How is a cemented mass of shelly debris called?

A. chalk

B. sandstone

C. coquina


4.2 You will hear a lecture. You will hear it twice. For questions 6-10
choose the best answer A, B or C.

A. extracted from calcium carbonate

B. contains calcium carbonate

6. Oolites are tiny balls

C. formed from calcium carbonate

A. dolomite

7. Dolomite limestone is mainly

B. limestone

formed of

C. both equally

A. seashore salt lakes

8. Chemical deposits accumulate in

B. seashore areas

desert lakes and

C. undersaturated sea waters

A.calcium carbonate,   gypsum, sodium chloride

B. gypsum, sodium chloride, calcium

9. Three main minerals settle in the

carbonate following sequence

C.sodium  chloride,  calcium carbonate, gypsum

A. rock gypsum

B. chalk rock

10. Another term for halite is

C. rock salt

4.3 You will hear short conversations between two people. At the end of
each conversation, a third person will ask a question about what the two
people said. Each conversation and each question will be spoken only one
time. For this reason, you must listen very carefully to understand what
each speaker says. After you hear the conversation and the question, read
the three selections and choose the one that is the best answer to what the
speaker asked.

1. Listen to these two people. They are:

A. two students

B. a parent and a child

C. a teacher and a student

2. Listen to two students. They are discussing:

A. formation of sedimentary rocks

B. destruction of sedimentary rocks

C. consolidation of sedimentary rocks


3. Listen to the dialogue. Sediments are cemented by:

A. water

B. pressure

C. minerals

You will hear short conversations between two people. At the end of each conversation, a third person will ask a question about what the two people said. Each conversation and each question will be spoken only one time. For this reason, you must listen very carefully to understand what each speaker says. After you hear the conversation and the question, read the three selections and choose the one that is the best answer to what the speaker asked.

1. How are the main ingredients of sedimentary rocks called?

A. clasts

B. clay minerals

C. grains

2. What is the size of grains forming shales?

A. large

B. medium

C. fine

3. What substance refers to orthoquartzite?

A. shale

B. siltstone

C. arenite

5. DISCUSSION: Classification of sedimentary rocks (R.P – 6.1, 6.2) 5.1. Situational games: use the following key words and communicative formulas

 

KEY WORDS COMMUNICATIVE FORMULAS
sediment I image that
chemicals we tend to think
dissolve it is (was) a common view that
oolites I wish I could agree with you that
evaporates I partially agree with you that
gypsum unfortunately
offshore (waters, basin) could you comment on

weathering the words
diagenesis it may have disappointing results
bedding plane a great advantage is
swampy vegetation  
acid conditions  
extract  
include  

A. Discuss the following statements, discussing them with your group
mates (agree / disagree / doubt)

• When parent rock breaks up its minerals behave in similar ways

• Coal types vary according to the processes involved

• Three main minerals tend to settle in a sequence­- gypsum

 

- sodium chloride

- calcium carbonate

B. You are going to take your exam in geology. There is one difficult
question that you don’t understand – HOW THICK EVAPORATE
LAYERS WERE FORMED.

C. Image that you are sediment. Your group mates are minerals. Act out
the processes of converting sediments into a rock.

5.2 You have to give a lecture on sedimentary rocks. Use the following diagram.



Sedimentary Rocks


mechanical sediments


chemical sediments


organic sediments


 



destructive chemical action of water


consolidated (firmly cemented particles)

rock salt, gypsum


destructive mechanical action of water, wind, etc.

unconsolidated

(uncemented

particles)


action of the decay of the remains of organisms

coal, peat,



Group discussion

STAGE 1: Group work responding to a text discussion. During this stage, each group will discuss its own topic.


GROUP A

GROUP B

GROUP C

GROUP D


1. Classification of sedimentary rocks according to grain-size

2. Classification of sedimentary rocks according to components.

3. What are conglomerates?

4. What are breccias?


STAGE 2: Sharing ideas of response to the text. Divide the students into 2 new groups, so that each group has a member with different information

Now the members of each new group will share their ideas.

Then, each group will prepare a summary, which is presented to the whole

class.

II. Jig-saw plan (1-2 minute) short one-point talk.

III. Multi-point conversation. (5 minutes)


GENERAL FORMULAS FOR O

Let me think

By the way

First of all

To come back to

To my mind

If you ask me

I don’t quite follow you

I mean to say

Do you mean to say

I am inclined to think

It’s not to the point

You’ve got it all wrong

Keep to the point

Suppose

As far as I know

As a matter of fact

The matter (thing/fact/point) is that

On the whole

In short

Oh, well, just simply

You see (you know)

So to say


AL COMMUNICATION

Дайте сообразить

Между прочим

Прежде всего

Возвращаясь к …

По-моему

Если Вы хотите знать мое мнение

Я не совсем Вас понимаю

Я имею ввиду

Вы хотите сказать, что …

Я склонен думать

Это не по существу

Вы совершенно неправильно это

поняли

Говорите по существу

Предположим

Насколько мне известно

По сути дела

Дело в том, что…

Подводя итоги

Короче говоря

Просто

Видите ли

Так сказать



6. WORDLIST


6.1 PRONUNCIATION


 

6.2 TERMS  
abrasion абразия, истирание
accumulation накопление, аккумуляция
bedding plane плоскость напластования
cement цементировать, скреплять
cementation цементация
compaction уплотнение
cross bedding косая слоистость
deposition осаждение
digenesis диагенез
graded bedding градационная слоистость
sedimentary rock(s) осадочная порода
sedimentation отложение осадка, осадконакопление
transportation перенос, транспортировка
weathering выветривание

WORDS AND PHRASES

bar

basin

bed

borax

boulder

chert

coalmine

coarse-grained

cobble

dune

fibrous

fine-grained

flint

grain

offshore

particle

peat

pebble

ripple

scrap

skin

slope

to abrade

to behave

to bulk

to carry

to consolidate

to cover

to deposit

to drift

to erode

to pile up

to precipitate

to rain down

to round

to squeeze

to tap


бар, береговой вал

бассейн

пласт, слой

бура

валун

кремень, кремнистый сланец

шахта

крупнозернистый, грубозернистый

булыжник, крупная галька

дюна

волокнистый

мелкозернистый

кремень, кремневая галька

песчинка, зерно

прибрежно-морской

частица

торф

галька

рябь, зыбь

остатки, обломки

кожа, оболочка

склон, откос

стирать, изнашивать трением

вести себя

принимать преувеличенные размеры

переносить, транспортировать

объединять, затвердевать

покрывать

отлагать(ся)

относить течением, дрейфовать

эродировать

нагромождаться, скапливаться

осаждать(ся) (о хим. осадке)

выпадать дождем

делать(ся) круглым

выжимать, отжимать

откупоривать


 


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