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
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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)
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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
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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
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• 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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