Earth Sciences Fieldwork

Along

Jaintapur-Tamabil-Jaflong Section; Sylhet

A Report Submitted In partial fulfillment of the Requirement for the Syllabus of

1st year, B.S. Honors in Disaster Science & Management

A Report Submitted by

Name: Ariful Islam

Exam Roll: 313

Registration no: 2012-212-208

Session: 2012-2013

Department of Disaster Science & Management

Faculty of Earth and Environmental Science

University of Dhaka

May, 20

I

Acknowledgement

I first express my gratitude, devotion, love and respect to Almighty ALLAH for making this

happen. This field work along Jaintiapur-Tamabil-Jaflong section was really very exciting and a

very memorable one. I got chance to become more friendly and free to my friends and my teachers

by this field work in Sylhet.

I express my thanks and deepest sense of gratitude to our Honorable Chairman Sir Prof. Dr. A.S.M.

Maksud Kamal, Chairman of Disaster Science and Management, University of Dhaka for his

spontaneous arrangement and caring guidance.

I also owe a debt of gratitude to our Team Leader Md. Shakhawat Hossain, Lecturer of Disaster

Science and Management, University of Dhaka. He deserves our thanks for his valuable lectures,

good planning for the trip and great affection.

My sincere appreciation and indebtness goes to our respected teacher Dewan Mohammad Enamul

Haque, Lecturer of Disaster Science and Management, University of Dhaka for his technical

suggestion and cordiality and his friendly attitude during field work. His theoretical knowledge

and previous research paper help me much to clarify my concept and complete this report.

My deepest gratitude and appreciation goes to our respected teachers Md. Marufur Rahman,

Lecturer of Disaster Science and Management and Tasnuva Tabassum, Lecturer of Disaster

Science and Management for their technical information, valuable lectures and quotes and much

more their friendly attitudes.

Special thanks to Jaintapur Upazilla Parishad and UNO for accommodation support and in other

purposes. My sincere appreciation also goes to the CITRUS RESEARCH CENTRE, Jaintiapur. I

am quite convinced with the committee of food, transport and other first aid for their great and

quick voluntary service and all to my classmates and to my group members for their sincere co-

operation. My thanks also extend to the personnel of Disaster Science and Management

Department, the cooks and office assistants.

II

Abstract

Our field work was held in Jaintiapur-Tamabil-Jaflong sections which are situated in Sylhet

division and the report is an overview of the earth sciences field work. The study area lies between

25°04’ and 25°11’ North Latitudes and in between 92°00’ and 92°12’ East longitudes.

The main purpose of our field work is to get familiar with different types of geologic structure,

observe the stratigraphic succession of Sylhet Trough, study lithology of the formations and

identify hazards of the investigated area.

The Sylhet trough is a sub-basin of the Bengal basin which has thick layer of sediments. On its

North lies the Shillong plateau which was created by the Dauki Thrust Fault with about 5 Km wide

fault zone. The Dauki fault is evident near Dauki River by fault breccias, anomalous dipping and

massive difference of elevation between the Sylhet trough and Shillong Plateau.

The stratigraphic succession of Sylhet trough (geo syncline part of Bangladesh) shows the

fomations from Pleistocene age to Eocene age. It indicates that in Sylhet trough sediment

deposition started at Eocene age, while the youngest layer is found at Pleistocene Age. As the

outcrops of most of the formations are well viewed in this region, this place was chosen for the

study. The oldest rock exposed in Bangladesh is Tura Sandstone of early Eocene age. But this is

not found in our investigated area. The Sylhet limestone formation is the oldest exposed rock in

our studied area, the middle unit of the Jaintia group of sediments. They are overlain by from older

to younger- Kopili Shale, Barail group (Jenum and Renji), Surma Group (Bhuban and Bokabil),

Tipam group (Tipam Sandstone, Girujan Clay and Dupi Tila) and Dihing (Sonatila Gravel)

sediments. A significant layer is the Laterite bed between Surma and Barail which indicates a

unconformity. Also the fossiliferous Kopili Shale residing on top of Sylhet Limestone points to

sea level regression.

While doing the study it was also found out that the soil of investigated area is acidic which hamper

the natural growth of plants, crops. Institute like Citrus Research Centre is conducting research

works to make the plants adaptive to this kind of soil condition.

The purpose of the study was not only studying the stratigraphic succession of the area but also to

know about the associated natural hazards environmental problems of that area. The study helped

to know the common hazards of this area (landslide, mudslide, flashflood, earthquake etc.), their

causes and effects on the inhabitants and environment, which will be helpful in designing an

adequate and appropriate disaster management system for these areas.

III

Table of Contents

Page No

Abstract I

Acknowledgements II

Table of Contents III

Chapter 1: Introduction 01

1.1 Location Extent and Access 02

1.2 Objective, Purpose and Scope 03

1.3 Methodology 04

1.4 Demography 05

1.5 Climate and Weather of the Study Area 05

1.6 Drainage and Water Supply 06

1.7 Soil and Agricultural Condition of Study Area 07

Chapter 2: Geology of the Studied Area 09

2.1 Tectonic Evolution of Bengal Basin 10

2.2 Tectonic Setup of Sylhet Trough and Surroundings 14

2.3 General Stratigraphy of Sylhet Trough 18

2.4 Lithological Description of the Investigated Formation 21

2.4.1 Sylhet Limestone 21

2.4.2 Kopili Shale 23

2.4.3 Barail 25

2.4.4 Surma 26

2.4.5 Tipam Sandstone 29

2.4.6 Girujan Clay 31

2.4.7 Dupi Tila 32

2.4.8 Dihing 35

2.4.9 Alluvium 36

IV

Chapter 3: Hazards and Environmental Problems in the Studied Area 37

3.1 Introduction 38

3.2 The Common Hazards of Bangladesh 39

3.3 Hazard & Environmental Problem in the Sylhet Trough and

Their Causes and Effects 43

Chapter 4: Conclusion 46

References 49

Appendix I 51

Appendix II 52

1

Chapter-1

Introduction

Chapter Contents-

1.1 Location Extent and Access

1.2 Objective, Purpose and Scope

1.3 Methodology

1.4 Demography

1.5 Climate and Weather of the Study Area

1.6 Drainage and Water Supply

1.7 Soil and Agriculture of the Study Area

2

1.1 Location Extent and Access

The study area was Jaintiapur, Tamabil and Jaflong which are situated in Sylhet Division in the

north-eastern part of Bangladesh. Sylhet is located in between 24°36 and 25°11 North latitudes

and 92°30 and 91°38 East longitudes .Our specific study area (Jaintiapur–Tamabil–Jaflong

section) lies between 25°04 and 25°11 North Latitudes and in between 92°00 and 92°12 East

longitudes. This area lies on the southern foothills of Khassia-Jaintiapur Ranges of Meghalaya and

is mapped between latitude 25°0 North and 25°1230 North and longitude 92°0 East and

92°2730 East (Figure 1.1).

Figure 1.1: Location Map of Jaintiapur, Sylhet.

Jaintiapur upazila(Figure 1.2) covers an area of 280.27 sq km. It is surrounded by Meghalaya State

of India on the North, Kanaighat and Gopalganj Upazillas on the South, Kanaighat Upazilla on the

East, Gowanighat and Sylhet Sadar Upazilla on the West. The Jaflong Hill Range is located on the

Northeast of the Upazilla.

It is situated 43 km to the north of sylhet town, on the Sylhet-Shillong road.The road distance of

Jaintiapur from Dhaka is 303 Km and flight distance from Dhaka is 235 Km.

The investigated area comprises Dupigoan area, Shari river section, Afafifanagar tea state area,

Nayagang area, Jaintiapur–Tamabil road section, Dauki river section. The total studied area covers

about 140 sq km.

3

Figure 1.2: Location Map of Jaintiapur Upazilla.

The communications of Jaintiapur with Dhaka is dependent on roads, railroads and aerial

transportation considering Sylhets’ Osmani International Airport. Jaintiapur Upazilla is connected

with the Sylhet town by the metalloid road. Nayagang section is well communicated very near

from the base camp and easily accessible by footpath.

1.2 Objective, Purpose and Scope

The objective of the field work in the investigated area was to observe the stratigraphic succession

of the Sylhet Trough and the natural hazards associated with the area.

The purpose of the study was to gather practical knowledge of the stratigraphic succession of

Sylhet trough (group: Tipam, Surma, Barail, Jaintia), study lithology of the formations, the hazards

associated with the area (Flood, Flash Flood, Landslide etc) and find out the causes behind the

Natural Hazards, their effects and losses on population, environment and society.

The area had a scope for study, As the study area has been cut by many rivers (like Shari, Piyan,

Ranga Pani Etc.) the outcrops of stratigraphic layers are well exposed. So the area was chosen for

the study. The winter season was selected for the tour because water level is low at that time and

the outcrops could be viewed easily. The scope of the study was to design an adequate and

appropriate disaster management system for these areas to reduce losses and environmental

degradation.

4

1.3 Methodology

The investigation was carried out in the field by adopting two methods: Geological Investigation

Methods and Hazard Identification Tools. Field investigation involves the following procedures:

Geological Investigation Methods: Geological Investigations in these areas include taking

location and bearing, structural investigation, lithologic changes and stratigraphical investigation,

collecting samples, construction of geologic maps, measuring dip-strike (Figure 1.5) and taking

photographs.

Hazard Identification Tools: Hazard identification tools include personal interview (Figure 1.3

& Figure 1.4) that is talking with local people, asking them about hazards in their locality and

FGD-Focus Group Discussion that is discussing with a group of people on a focused topic.

Figure 1.3: Interviewing Local People (a). Figure 1.4: Interviewing Local People (b).

Figure 1.5: Measuring Dip-Strike with Clinometer.

5

1.4 Demography

The total area of Jaintiapur Thana is about 280.27 sq km and according to the 2001 Bangladesh

census, Jaintiapur has a population of 1,21,458. The density of population is 433.36/km2. Males

constitute 52.08% (63,254) of the total population and females constitute 47.92% (58,204) of the

total population.

People of all religion live here but Muslims are dominant in number. 89.84% of the total population

is Muslim. Among rest of the population 9.9% are Hindu, 0.07% are Buddhist, 0.05% are Christian

and 0.14% are of other religion. Religious institutions Mosque 227, temple 7, church 2, tomb 4.

Average literacy of Jaintiapur is 35.11%. Among which 39.51% are male and 30.34% are female.

This upazila has 5 colleges, 16 secondary schools, 53 community schools, 11 community schools,

5 kindergartens and 23 madrasas.

Cultivation is the main source of the livelihood of the people. Almost half of the population

(53.38%) depends on agriculture for their livelihood. Main occupations Agriculture 38.69%,

agricultural laborer 17.77%, wage laborer 12.52%, fishing 2.5%, commerce 7.70%, service 5.69%,

and others 14.99%. Among this 1,21,458 population around 48.95% are land owner and 51.05%

are landless. Land control among the peasants 50.32% are landless, 14% marginal, 29%

intermediate and 6.68% rich. Land use Single crop 58.25%, double crop 38.79% and triple crop

land 2.96%; tea garden 6.

Besides Bangladeshi local people, different indigenous communities of people like Khasia

Saotals, Oriyas and nunayas also live here. Mostly they are employed in the tea gardens. The

khasias are mainly Christians and have a language of their own. They live in group of 10-30

families. They are very hard working and even the women work side by side of the men.

1.5 Climate and Weather of the Study Area

Climate is average condition of weather over a long period of time in a specific area. It covers a

very large area. As our study area is in Sylhet so it mostly follows the climatic condition of Sylhet.

The climate here is humid subtropical with a pre dominantly hot and humid summer and a

relatively cool winter. It is situated in a monsoon climatic zone. The area is very susceptible to

heavy monsoonal rainfall. Nearly 80% of the annual average rainfall of 3,334 mm occurs between

May and September. (Source: wikipedia.org)

6

Table 1.1: Climate Data for Sylhet, Bangladesh

1.6 Drainage and Water Supply

There are a number of streams and streamlets in the area. Numerous streams and streamlets have

been set up a dendritic pattern of drainage network. It suggests that the area was eroded unevenly.

The relatively major streams are fewer in number and are of perennial type, that is they flow even

in the dry season, but during rainy season they flow with their full strength and become able to

carry large boulders to distant places whereas the minor streams are large in number and of

intermitted type, that is they are seasonal in their flow, and water ceases to flow during the dry

spell. The Dauki and Hari (enclosure) are the prominent rivers of the investigated area.

The Dauki River originated from Khasi-Jaintia Hill Ranges (Khan, 1978) and flowing southward

and enters Bangladesh near Dauki Bazar,India. It flows with tremendous current with carried a

large amount of boulders of igneous and metamorphic origin from Shillong massif.

The Shari River originated from Khasi-Jaintia Hills near Jowai, India and Bangchara (Paul, 1988).

It takes a meandering course and joins the Surma near kalaruka. The two main tributaries of the

Hari River, namely the Rangapani and Nayagang are the other two important rivers of the

investigated area which maintains the drainage system of the central portion of the area. Among

these two, the Rangapani flows into Bangladesh near Sripur and flows southeast ward for some

distances and turn towards southwest for flowing down to the marshes. The Nayagang enters

Bangladesh near Puranassampara, flows southwest and finally meet the marshes (Paul, 1988). It

is to note that the Nayagang is a meandering river and the Rangapani is a braided river.

Water supply becomes scarce in the hilly areas where streamlets and the deep wells are the only

source of water. But in the dry season, that is, in the time of March or April the water table becomes

drop. As a result, most of the tube wells become dry. The people of the area face a water crisis in

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

Average high (°C) 23 27 30 31 29 30 31 31 30 28 27 24 29

Average low (°C) 10 13 18 21 22 24 25 24 24 21 17 13 19

Precipitation

(mm)

10 30 104 348 556 810 800 622 513 241 30 8 4067

Source: Weatherbase

7

that time. Few electrical pumps are used to supply water but this is very costly. The water of ponds

is used for household purposes as well as drinking water in the plain land. This scarcity continues

till rain.

Figure 1.6: Drainage Pattern of Investigated Area.

1.7 Soil and Agricultural Condition of Study Area

Soils of the area are grey silty clay loams and clay loam on higher parts that dry out seasonally and

grey clays in the wet basins. The soils have a moderate content of organic matter and soil reaction

is mainly acidic. Fertility level is medium to high. (S.M. Imamul Huq, Jalal Uddin Md. Shoaib;

The Soils of Bangladesh). The pH of the soil of Jaitiapur is less than 7(low) which means the soil

is acidic. It hinders the crop production. The content of nitrogen and boron is low. Probably,

denitrification process leads to the loss of nitrogen in the basin soil.

Rice is the main crop of this area as the floodplain lands are useful for the cultivation of paddy.

The low lying areas are used for Boro cultivation. Tea is also very important cash crop of the area

and a series of tea gardens are situated in hillocks and valleys from Jaflong to Afifanagar (Figure

1.7). Jantiapur and it’s surrounding places have three agricultural season. During monsoon they

cultivate "Aush" rice as the lands get flooded with water and it is proved to be a favourable

condition for cultivating rice crops. In winter they grow various types of seasonal vegetables, fruits

such as pineapple, water melons, oranges, banana, papaw, jackfruit etc. Several fields near river

8

bank are under water melon cultivation as observed during our investigation. But in summer the

lands remain barren because the scarcity of water becomes severe (Figure 1.8). Under this

condition cultivation becomes quite impossible for the inhabitants.

Figure 1.7: Tea Garden at Hill Slope in Afifanagar.

Figure 1.8: Fallow Land for the Scarcity of Water.

9

Chapter-2

Geology of the Studied Area

Chapter Contents-

2.1 Tectonic Evolution of Bengal Basin

2.2 Tectonic Setup of Sylhet Trough and Surroundings

2.3 General Stratigraphy of Sylhet Trough

2.4 Lithological Description of the Investigated Area

10

2.1 Tectonic Evolution of Bengal Basin

The Bengal basin, a complex foreland basin south of the eastern Himalayas, exhibits dramatic

variability in Neogene sediment thickness that reflects a complicated depositional and tectonic

history (Ashraf Uddin, Neil Lundberg). The Bengal Basin is the northeastern part of Indian

subcontinent, between the Indian Shield and Indo-Burman Ranges. The Bengal Basin includes, in

addition to Bangladesh, part of Indian state of West Bengal and Tripura. The Bengal Basin is

bordered to the west by Precambrian Indian Shield, to the north by Shillong Plateau and to the east

by the frontal fold belt of Indoburman Range. It is open to the south by Bay of Bengal (Figure 2.1).

Figure 2.1: Location of Bengal Basin.

The Bengal Basin has evolved from collision of the Indian Plate and the Eurasian Plate (Figure

2.3). According to Plate tectonic theory, the north western part of Bangladesh (Bogra-Rangpur-

Dinajpur area) was initially joined, along with Indian landmass, with Antarctica, Australia and

others forming a vast super continent named Gondwana far in the southern hemisphere (Figure

2.2). Rest of the landmass of Bangladesh i.e. the southeastern part did not exist at that time. This

basin originally formed as a trailing margin SE of the Indian continental crust, complicated by

convergence with Asia to the north and oblique convergence with Burma to the east (Figure 2.4).

N

11

Figure 2.2: Break-up of Paleo-Continent Figure 2.3: Collision of Indian and

(Pangea) to Current Continents Through Eurasian Plate.

the Passage of Time.

Figure 2.4: The Ongoing Collision of India and Asia. A. Converging Plates Generated a

Subduction Zone. B. Position of India in Relation to Eurasian at Various Times. C. Eventually

the Two Landmasses Colided, Deforming and Elevating the Sediments That Had Been

Deposited Along the Continental Margins.

12

Bengal Basin comprises three geo-tectonic provinces:

(1) NW Bengal Basin or the Stable Shelf;

(2) NE Bengal Basin or the Central Deep Basin (extending from the Sylhet Trough in the

northeast towards the Hatia Trough in the south); and

(3) SE Bengal Basin or the Chittagong-Tripura Fold Belt. (Figure 2.5)

Figure 2.5: Stratigraphic Framework of the Bengal Basin. Miocene Sediment Thickness is Much

Lower near the Indian Platform in the Northwestern Part of the Basin. This Shelf Area of the

Basin is Floored by Continental Crust (after Khan and Muminullah, 1980; Uddin and Lundberg,

1999; and Many Other Sources).

13

Figure 2.6: Schematic Cross-Section of the Bengal Basin; (a) N– S, Through the Shillong

Plateau; (b) E–W, Through the Northern Chittagong Hill Region, after Murphy (1988). These

Show Sediment Thickening toward the South and East, Respectively.

Due to location of the basin at the juncture of three interacting plates, viz., the Indian, Burma and

Tibetan (Eurasian) Plates, the basin-fill history of these geo-tectonic provinces varied

considerably. Precambrian meta sediments and Permian–Carboniferous rocks have been

encountered only in drill holes in the stable shelf province. After Precambrian peneplanation of

the Indian Shield, sedimentation in the Bengal Basin started in isolated graben-controlled basins

on the basement.

With the breakup of Gondwanaland in the Jurassic and Cretaceous, and northward movement of

the Indian Plate, the basin started downwarping in the Early Cretaceous and sedimentation started

on the stable shelf and deep basin; and since then sedimentation has been continuous for most of

14

the basin. Subsidence of the basin can be attributed to differential adjustments of the crust, collision

with the various elements of south Asia, and uplift of the eastern Himalayas and the Indo-Burman

Ranges. Movements along several well-established faults were initiated following the breakup of

Gondwanaland and during down warping in the Cretaceous.

2.2 Tectonic Setup of Sylhet Trough and Surroundings

The Sylhet trough, a sub-basin of the Bengal Basin in northeastern Bangladesh, contains a thick

fill (12 to 16 km) of late Mesozoic and Cenozoic strata that record its tectonic evolution.

Stratigraphic, sedimentologic, and petrographic data collected from outcrops, cores, well logs, and

seismic lines are here used to reconstruct the history of this trough.

By Eocene, because of a major marine transgression, the stable shelf came under a carbonate

regime, whereas the deep basinal area was dominated by deep-water sedimentation. A major

switch in sedimentation pattern over the Bengal Basin occurred during the Middle Eocene to Early

Miocene as a result of collision of India with the Burma and Tibetan Blocks. The influx of elastic

sediment into the basin from the Himalayas to the north and the Indo-Burman Ranges to the east

rapidly increased at this time; and this was followed by an increase in the rate of subsidence of the

basin. At this stage, deep marine sedimentation dominated in the deep basinal part, while deep to

shallow marine conditions prevailed in the eastern part of the basin.

By Middle Miocene, with continuing collision events between the plates and uplift in the

Himalayas and Indo-Burman Ranges, a huge influx of elastic sediments came into the basin from

the northeast and east. Throughout the Miocene, the depositional settings continued to vary from

deep marine in the basin to shallow and coastal marine in the marginal parts of the basin.

From Pliocene onwards, large amounts of sediment were filling the Bengal Basin from the west

and northwest; and major delta building processes continued to develop the present-day delta

morphology.

Since the Cretaceous, architecture of them Bengal Basin has been changing due to the collision

pattern and movements of the major plates in the region. However, three notable changes in basin

configuration can be recognized that occurred during Early Eocene, Middle Miocene and Plio-

Pleistocene times, when both the paleogeographic settings and source areas changed. The present

basin configuration with the Ganges - Brahmaputra delta system on the north and the Bengal Deep

Sea Fan on the south was established during the later part of Pliocene and Pleistocene; and delta

progradation since then has been strongly affected by orogeny in the eastern Himalayas.

15

Pleistocene glacial activities in the north accompanied sea level changes in the Bay of Bengal

(Alam, M, Alam MM, Curray JR, Chowdhury ALR, Gani MR).

Figure 2.7: Tectonic Framework of Bangladesh and Adjoining Area (Source: BANGLAPEDIA:

Tectonic Framework).

16

The Sylhet trough occupied a slope/basinal setting on a passive continental margin from late

Mesozoic through Eocene time. Subsidence may have increased slightly in Oligocene time when

the trough was located in the distal part of a foreland basin paired to the Indo-Burman ranges.

Oligocene fluvial-deltaic strata (Barail Formation) were derived from incipient uplifts in the

eastern Himalayas. Subsidence increased markedly in the Miocene epoch in response to western

encroachment of the Indo-Burman ranges. Miocene to earliest Pliocene sediments of the Surma

Group were deposited in a large, mud-rich delta system that may have drained a significant

proportion of the eastern Himalayas.

Subsidence rates in the Sylhet trough increased dramatically (3-8 times) from Miocene to Pliocene-

Pleistocene time when the fluvial Tipam Sandstone and Dupi Tila Formation were deposited. This

dramatic subsidence change is attributed to south-directed overthrusting of the Shillong Plateau on

the Dauki fault for the following reasons:

(1) Pliocene and Pleistocene strata thin markedly away from the Shillong Plateau, consistent

with a crustal load emplaced on the northern basin margin.

(2) The Shillong Plateau is draped by Mesozoic to Miocene rocks, but Pliocene and younger

strata are not represented, suggesting that the massif was an uplifted block at this time.

(3) South-directed overthrusting of the Shillong Plateau is consistent with gravity data and

with recent seismotectonic observations.

Sandstone in the Tipam has a marked increase in sedimentary lithic fragments compared to older

rocks, reflecting uplift and erosion of the sedimentary cover of the Shillong Plateau. If the Dauki

fault has a dip similar to that of other Himalayan overthrusts, then a few tens of kilometers of

horizontal tectonic transport would be required to carry the Shillong Plateau to its present

elevation. Uplift of the Shillong Plateau probably generated a major (∼300 km) westward shift in

the course of the Brahmaputra River.

The Sylhet trough was structurally developed by the simultaneous interaction of two major tectonic

movements- Uplift of the Shillong Plateau to the north and the west progradation of the mobile

Indo-Burma fold belt (Hiller and Elahi, 1984). The trough is bounded by the Assam-Tripura fold

belt of the Indo-Burman range on the East and Southeast, Indian Shield on the West and Shillong

Plateau on the North. The sub-basin is connected with the Fore-deep part the Bengal basin to the

South-Southeast.

The Dauki Fault indicates the border of the Sylhet Trough and the Shillong Plateau. It is about 5

Km wide. It is recognized by the abrupt elevation difference between Sylhet trough and Shillong

Plateau (Figure 2.8). Fault Breccia is also present here. The fault is potential zone for future

earthquakes in Bangladesh. The Dauki Fault separates the plateau from an approximate 17 km

thick Tertiary section of recent sediments in the Bengal Basin to the south.

17

Figure 2.8: Dauki Fault Marks the Border Between Shillong Plateau and Sylhet Trough Through,

Abrupt Elevation Change.

N

Indian

Shield

Himalayan Mountain Range

Shillong Plateau

Mikhir Hills

Chittagong Hill Tracts Burmese Mountain

Range

Figure 2.9: Sylhet Trough and it’s Surroundings.

Sylhet Trough

Dauki Fault

Shillong Plateau

Burmese Mountain Range

Shillong Plateau

Mikhir Hills

Himalayan Mountain Range

Chittagong Hill Tracts

Indian Shield Sylhet Trough

18

2.3 General Stratigraphy of Sylhet Trough

Stratigraphy is the scientific discipline concerned with the description of the rock successions and

their interpretation in terms of a general time scale. It provides a basis for historical geology, and

its principle and methods have found application in such fields as petrology and archeology

.Stratigraphic studies deal primarily with sedimentary rocks but may also encompass layered

igneous rocks or metamorphic rocks.

The Bengal Basin is considered as the deepest basin of the world; however not much works have

been done in the basin. Therefore, the stratigraphic framework of the exposed Eocene to Miocene

sediments in the Jaintiapur and surrounding areas, northeastern Sylhet involves surface

sedimentological studies along with the sequence stratigraphic modeling of the Sylhet trough.

Analyses of the facies and facies-associations have been considered one of the better ways to

understand the depositional environment and it has been chosen in the present study for the

interpretation based on the available sedimentological data. Hence the research work on the

sequence stratigraphy of the exposed Eocene to Miocene sediments of Jaintiapur and surrounding

areas of northeastern Sylhet is undertaken in order to understand the sequence stratigraphic

framework of the area which may include future sub-surface studies in the basin. For the present

study, parasequences, system tracts, bounding surfaces and sequences of the exposed Eocene to

Miocene sedimentary deposits of the study area have been redefined and are recognized in

response to changes in relative sea level, sediment influx and paleo-physiography (Haque, Alam,

Downey; A Sequence Stratigraphic Approach of Sylhet Trough).

The area under investigation is underlain in part by Holocene and flood plain deposits and in part

by deformed Tertiary sediments. Most of the outcrops are covered with thick jungle and soil and

accessible with difficulty. Along the Shari River there is an excellent section which can be

considered on the type section for the Neogene sequence in N-E Bangladesh. From the Dauki river

where Eocene limestone crops out to the plain ,south of Dupitila ,2800ft thick sediments has been

estimated (Haque,1982).This monotonous succession of sediments which have been affected by

the movements associated with the Himalayas orogen. Except for Sylhet limestone, the sequence

represents a clastic section composed mainly of sandstone, siltstone, clay and associated

conglomerate. The rock strata were investigated on the basis of lithologic characteristics and were

subdivided on the basis of lithologic contrasts.

19

The stratigraphy of the area has been differentiated into a number of formations. Sylhet limestone

formation is found as the oldest in the normal sequence. The normal sequence of the studied

formation is given below according to the law of superposition (Figure 2.10).

1. Alluvium

2. Dihing formation

3. Dupitila formation

4. Giruja clay

5. Tipam sandstone

6. Surma group

7. Barail sandstone

8. Kopili shale

9. Sylhet limestone

The names of the formations are established by Evans (1932) for the tertiary successions of Assam.

Although it is difficult to correlate formations separated by hundred of kilometer without the

support of paleontological data and also because of frequent facies changes

Figure 2.10: Satellite Image of Sylhet Trough.

20

Table 2.1: Stratigraphic Succession of NE Bangladesh, Sylhet Trough (sources: Khan,

1980, Reimann 1993, Uddin and Lundberg, 1999).

Age Group Formation Thickness

(meter)

Rock Types

Pleistocene Madhupur Clay

30 Reddish Clay

Plio-Pleistocene

Pliocene

Tipam

Dupi Tila

2500

Unconsolidated

sandstone

Girujan Clay

1000

Mainly Shale

Tipam Sandstone

2500

Predominantly

sandstone with

minor shale

Mio-Pliocene

Miocene

Surma

Bokabil

1500

Alternating shale

and sandstone

with minor

siltstone

Bhuban

3500

Alternating

sandstone and

shale with minor

conglomerate

Oligocene

Barail

Renji

700

Predominantly

sandstone (pink)

with minor shale

Jenum

260

Predominantly

shale with minor

siltstone

Eocene

Jaintia

Kopili Shale

170

Mostly shale

Sylhet Limestone

240

Nummulite

limestone

Tura Sandstone

200+

Mostly sandstone

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

21

2.4 Lithological Description of the Investigated Formation

The oldest rock exposed in Bangladesh is Tura sandstone of Early Eocene age in Takerghat area

in Sunamganj district in Sylhet division. But this is not found in our investigated area. The Sylhet

limestone formation is the oldest exposed rock in our studied area, the middle unit of the Jaintia

group of sediments. They are overlain by from older to younger the Barail group, Surma Group,

Tipam group, Dupitila and Dihing (Sonatila Gravel) sediments.

2.4.1 Sylhet Limestone

The term Sylhet limestone as a rock unit was first used by F.H.Khan (1963). It is the oldest

(Eocene) rock of the investigated area. The hard limestone is highly jointed and fractured .The

brecciated limestone occurs due to large Dauki Fault. The outcrop forms an inlier surrounded by

recent deposits and rock of the Barail group.

The formation is exposed on the east bank of Dauki River near the Bangladesh-Meghalaya border

at N25°9053.5 and E92°15.5 and the area was studied on 15 February, 2014.

It consists of subvertical thick bedded, fossiliferous limestone that is also highly jointed (Figure

2.11), Nummulite limestone (Figure 2.12). Measurements taken showed that the dip direction of

the beds was found to be pointing towards the South-East. The Strike direction was found to be

258° and the amount of dip was found to be 36°. Limestone is formed in warm, shallow, clean and

calm marine environment which indicates that shallow marine environment was present in Sylhet

in the Geologic past (Eocene period).

The Dauki fault was identified in the presence of the following conditions- There are beds missing

and highly jointed beds, Fault Breccia is found, which is the strong evidence of Dauki fault (Figure

2.13), Elevation and abrupt change, and Tura sandstone is missing.

22

Figure 2.11: Jointed Subvertical Beds of Sylhet Limestone.

Figure 2.12: Nummulitic Limestone Found near Dauki River.

23

Figure 2.13: Fault Breccias and Kopili Shale Created by Dauki Fault in Jaflong.

2.4.2 Kopili Shale

The name of Kopili shale was given by P.Evans(1932) to the beds forming the upper stage of the

Jaintia group after the kopili river of Garo hills in India. It gives a minor outcrop on the west bank

of the Rangapani River. It is dark grey to black colored very much fissile, thickly bedded to

laminated, highly jointed shale (Figure 2.14). In field, we found in the east bank of the Dauki River

interbedded with Sylhet Limestone (Figure 2.15) and barail group of sediments. Interbeded

sandstone with argillaceous matrix is present. It is conformably overlain on the Sylhet limestone.

Base of kopili shale is not seen.

The area of study where we found Kopili shale was in between N25°1034.3 to N25°1043.2

and E92°138.9 to E92°344 Longitude on 14 February, 2014. This formation had a good outcrop

near the Dauki River.

It is dark grey to black colored very much fissile, thickly bedded to paper laminated, highly jointed

shale. Interbeded fine to medium grained pinkish sandstone was also present. Composed of dark

24

grey to black fossiliferous shale with few limestone beds, Gypsum mineral is found. Since Shale

is created from the deposition and compaction of fine clay particles on still water surface we can

assume that the type of depositional environment that was present in the Eocene period when

Kopili shale formed was Marine environment. Measurements taken showed that the dip direction

of the beds was found to be pointing towards the North-West. The Strike direction was found to

be 108° and the amount of dip was found 6°.

Figure 2.14: Dark Coloured, Fissile, Laminated Kopili Shale.

Figure 2.15: Jointed Beds of Sylhet Limestone Overlain by Organic Matter Rich Kopili Shale.

Kopili Shale

Sylhet

Limestone

25

2.4.3 Barail

The Barail group represents the only Oligocene outcrop in Bangladesh and consists of 2 formations

Renji and Jenum. The Renji formation is exposed in Sonatila near Sripur as well as along the road

section of Tamabil and along Rangapani River. But the Jenum formation is deeply buried and

outcrops could not be found for study.

Barail was found in between N25°839.3 to N25°1054.9 latitude and E92°159.9 to

E92°747.6 longitude. A good outcrop of Barail was found in Sripur in the location N25°1037

and E92°435.7 on 14 February, 2014.

It’s lithology consists mainly of fine grained pinkish coloured sandstone with ferruginous

cementing materials (Figure 2.16). Smaller amounts of shale and siltstones were also found. Fine

grained highly compacted sandstone beds with joints (Figure 2.17) were also found and cross

lamination and pisolitic structures were also seen in the jointed beds. And a laterite bed was also

seen. The Barail group was deposited under Deltaic environment. Measurements taken showed

that the dip direction of the beds was found to be pointing towards the South-West. The Strike

direction was found to be 280°-353° and the amount of dip was found to be 34°-27°.

Figure 2.16: Pinkish Sandstone with Ferruginous Cementing Materials.

26

Figure 2.17: Jointed Beds of Sandstone in Barail.

2.4.4 Surma

The Surma Group after Surma valley by Evans (1932) has a thickness of about 3500 to 4500 meter

and is composed of monotonous alteration of subequal proportion of sandstone and shale with

siltstone and some conglomerate. The Surma Group is divided into two Formations, both

essentially composed of alternating sandstone and shale. A lower more, more sandy Bhuban

Formation is overlain by an upper more argillaceous (clayey) Bokabil Formation. It’s age ranges

between Mio-Pliocene to Miocene.

Its location lies in between 25°0655N to 25°0824.4N and 92°1055.7E to 92°0717.9E in the

local area named Tetulghat and Nayagang khal and it was studied on 13 February, 2014.

It’s lithology consists of yellowish grey sandstone, bluish grey shale. The shale is bluish grey in

color, well laminated, hard and jointed. There is also trace amount of haematite rich pinkish fine

27

grained sandstone. Shale with trough cross bedding (Figure 2.18) and flaser bedding (Figure 2.19)

was found which indicates that the type of depositional environment was shallow marine to deltaic.

Figure 2.18: Trough Cross Bedding found in Tetulghat.

Figure 2.19: Flaser Bedding found near the Contact of Surma and Tipam Sandstone.

Sand Layer

Mud Layer

28

Drag fold (Figure 2.20) was also found which is a minor geological fold produced in soft or thinly

laminated beds lying between harder or more massive beds in the limbs of a major fold (Figure

2.21). The dip direction of the beds was found to be pointing towards the South-West. The Strike

direction was found to be 296°-254° and the amount of dip was found to be 46°-54°.

Figure 2.20: Drag Fold in Surma Group in Nayagang.

Figure 2.21: Surma Formation Folded Outcrop in Tetulghat.

29

2.4.5 Tipam Sandstone

The Tipam Sandstone Formation, of Pliocene age, is typically consists mainly of gray brown

medium to coarse grained, cross bedded to massive sandstone with minor intervals of clay beds. It

unconformably overlies the Surma Group in marginal part of the basin.

The Tipam Sandstone formation’s outcrop was found and observed between N25°0620.9 to

N25°0633.7 and E92°1039.2 to E92°1042.1 which is in Lalakhal near Kalanji Bazar on 13

February, 2014.

The Tipam sandstone consists predominantly of yellowish brown and greyish brown medium to

fine grained moderately friable sandstone with minor presence of greyish blue shale beds and also

thin layers of conglomerate with pebble sized particles. Parallel laminations, massive trough cross

bedding along with clay galls (Figure 2.22) indicate that the type of depositional environment was

fluvial. Wave ripple, conglomerate bed (Figure 2.23) and minor fault (reverse) along bedside was

also found (Figure 2.24).

Figure 2.22: Clay Galls found near Lala Khal in Tipam Sandstone.

Clay Gall

30

Figure 2.23: Conglomerate Bed in Tipam Sanstone.

Figure 2.24: Fault (reverse) in Tipam Sandstone.

31

Figure 2.25: Lenticular Bedding in the Contact of Surma and Tipam Group.

2.4.6 Girujan Clay

The name has been given after the Girujan clay stage of Tipam series in Assam,India. Top of this

formation is exposed in the Shari river bank having a conformable contact with the overlying

Dupitila formation. The formation develops conformably and gradationally from the underlying

Tipam sandstone formation. It consists of whitish grey to bluish grey, 100% clay and mottled clay

(Figure 2.26).

Girujan Clay was found between N25°554.3 to N25°620.9 latitude and E92°840.4 to

E92°906.8 longitude and was studied on 12 February, 2014.

It consists of grey to bluish grey, massive mottled structured, very fine clay.

Sand Layer

Mud

32

Figure 2.26: Mottled Girujan Clay.

2.4.7 Dupi Tila

Dupi Tila is sand dominated formation with minor presence of claystone. It is the major aquifer of

ground water in Bangladesh. Dupitila sandstone formation conformably overlies the Girujan clay

formation. The sandstone is yellowish brown colored, medium to coarse grained, less compact and

highly porous. It is massive to thick bedded. The sandstone is quartz predominated with significant

amount of mica and dark colored minerals. Significant amount of clay matrix is present in the rock

and ferruginous cementing material gives the rock this yellowish brown color.

Dupi Tila was found between N25°546.4 to N25°554.3 latitude and E92°74 to E92°840.4

longitude on 12 February, 2014. It was first studied on the right bank of the Shari River near

Jaintiapur Sharighat Government Primary School. It was a 30m undulated hilly terrain and

presence of clay gall (Figure 2.28) represents it was deposited in fluvial environment.

It’s yellowish brown, light grey and occasionally pink colored fine to medium grained sandstone

with the alternation of claystones. Presence of organic matter and pebble sized particles observed

and also occasionally characterized by iron incrustation (Figure 2.29). Parallel lamination, cross-

33

bedding are found (Figure: 2.30) and it is also exposed at surface (Figure 2.31). The dip direction

of the beds was found to be pointing towards the South-East. The Strike directions ranged from

261° to 270° and the amount of dip was found to vary between 55° to 70°.

Figure 2.27: Outcrop of Dupi Tila. Figure 2.28: Clay Gall in Dupi Tila Right

Bank Side of Shari River.

Figure 2.29: Iron Incrustation in Dupi Tila.

Clay Gall

34

Figure 2.30: Cross Bedding in Dupi Tila at Right Bank of Shari River.

Figure 2.31: Outcrop of Dupi Tila.

35

2.4.8 Dihing

The Dihing formation of Pleistocene age has unconformable contact with the Surma group and

with Barail group, sonatila Chara. The formation consists of yellow and grey, medium-grained,

occasionally pebbly sandstone and clayey sandstone with interbeds of mottled clay and boulders.

The rocks are in most part poorly consolidated. A time gap between the Pliocene Dupitila

formation and recent alluvium is represented by these gravel beds of Pleistocene age.

This formation was studied in the location N25°85.3 and E92°745.3 near the base camp on 14

February, 2014.

Yellowish brown, light grey cobbles with occasional presence of pebbles. Grains are sub-rounded

to granite, quartz and quartzite, massive structure (Figure: 2.32). Cobbles and pebbles represent

the deposition in fluvial environment.

Figure 2.32: Dihing Formation.

SURMA

DIHING

36

2.4.9 Alluvium

Unconsolidated, loose material brought down by rivers and deposited in its beds of alluvial fans

or weathered material. Alluvium consists of sand, silt, clay in various proportions. River born

alluvium are mainly sand, coarse grained material and weathered alluvium are consists mostly of

clay and silt. They cover various rock formations unconformably and of recent in age. Mud cracks

(Figure 3.33) form on alluvium.

Figure 3.33: Mud Cracks.

37

Chapter-3

Hazards and Environmental Problems

in the Studied Area

Chapter Contents-

3.1 Introduction

3.2 The Common Hazards of Bangladesh

3.3 Hazards and Environmental Problems in the Sylhet Trough and Their Causes and Effects

38

3.1 Introduction

Hazards are events that pose potential threat to the mankind and their welfare. Because of the

geographic setting, Bangladesh is highly prone to hazards, especially of climatologically and

hydrological origin.

Bangladesh can be regarded as of the most perfect places for both natural and manmade disasters

to occur. Each year our motherland is affected by either natural disasters like flood, cyclone, river

bank erosion, landslide, tornado, nor’ wester, earthquake, saline water intrusion or manmade

disasters like infrastructure collapse, fire, water logging, ground subsidence due to ground water

withdrawal and transport accidents. Some emerging hazards like landslide, fire, salinity intrusion,

arsenic contamination, infrastructure collapse and earthquake are creating anxiety all over the

country. Humanitarian implementation plan (2012) shows that Bangladesh loss about 6188 lives

and have to suffer 550 $ million economic loss due to only natural disasters. Global Assessment

Report (2011) published by UNISDR reveals that Bangladesh is in 1st and 6th position in terms

of vulnerability of flood and cyclone respectively. Recently GERMANWATCH shows that

Bangladesh is in 2nd position in Climate Change Vulnerability Index. So it has no denying that

our motherland is in a great risk of disasters.

Though indigenous knowledge which serves as the primary method of disaster management in

Bangladesh integration of science based knowledge by Disaster Management Bureau, Directorate

of Relief and Rehabilitation and Comprehensive Disaster Management Program (CDMP) are

proving to create a better risk reduction procedure for the entire country across all sorts of hazards

that the country is facing today. Disaster Risk Reduction Enhanced Land use Planning for

Municipalties/Pourashavas, Ward level contingency planning, training construction related

persons, retrofitting weak buildings, modernization and capacity building of Fire Service and Civil

Defense are some good initiatives from Government. In terms of structural measures Bangladesh

is progressing with times. Bangladesh has already constructed and is preserving about 10,124 km

long embankment to protect about 50% flood plain area from normal flood condition. Bangladesh

is an example in cyclone preparedness in the world. The then Government started Cyclone

Preparedness Program (CPP) in 1973 to shape volunteerism in an institutional framework. 3777

cyclone centers have already been constructed in coastal area of our country among which 3449

are in usable condition.

39

3.2 The common hazards of Bangladesh

Flood: A flood is an overflow of water that submerges land which is usually dry. The European

Union (EU) Floods Directive defines a flood as a covering by water of land not normally covered

by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide.

Flooding may occur as an overflow of water from water bodies, such as a river or lake, in which

the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries.

Flood impacts are loss of agricultural production, disruption of communication and livelihood

system, injury, damage and destruction of immobile infrastructure, disruption to essential services,

national economic loss, evacuation, and loss of human lives and biodiversity, displacement and

sufferings of human population and biodiversity. Flood affects Floodplains of the Brahmaputra-

Jamuna, the Ganges-Padma and the Meghna river system.

Earthquake: An earthquake is the result of a sudden release of energy in the Earth's crust that

creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the

frequency, type and size of earthquakes experienced over a period of time. It causes damage and

destruction of property, loss of life and change in geomorphology.

Northern and central parts of the country as there are many faults lines found in this region. There

are Dauki fault, Madhupur fault, Plate boundary faults etc so this area lies in earthquake zone area.

The Figure 3.1 below shows the epicenter of the historical earthquakes.

Figure 3.1: Epicenters of Historical Earthquakes (1664-2007), (after Sabri, 2001).

40

Landslide: A landslide, also known as a landslip, is a geological phenomenon which includes a

wide range of ground movements, such as rock falls, deep failure of slopes and shallow debris

flows, which can occur in offshore, coastal and onshore environments. Although the action of

gravity is the primary driving force for a landslide to occur, there are other contributing factors

affecting the original slope stability. Typically, pre-conditional factors build up specific sub-

surface conditions that make the area/slope prone to failure, whereas the actual landslide often

requires a trigger before being released.

It causes loss of land, displacement of human population and livestock, evacuation, damage of

property and loss of life. Landslide mainly occurs in Chittagong Hill Tracts.

Cyclone and Storm Surge: In meteorology, a cyclone is an area of closed, circular fluid motion

rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds

that rotate anti-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere

of the Earth. Most large-scale cyclonic circulations are centered on areas of low atmospheric

pressure.

It causes loss of agricultural production, disruption of communication and livelihood system,

damage and destruction of immobile infrastructure, injury, national economic loss, loss of

biodiversity and human lives, need for evacuation and temporary shelter. It affects oastal areas and

offshore islands.

Tornado: A tornado is a violently rotating column of air that is in contact with both the surface of

the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often

referred to as twisters or cyclones, although the word cyclone is used in meteorology, in a wider

sense, to name any closed low pressure circulation. Tornadoes come in many shapes and sizes, but

they are typically in the form of a visible condensation funnel, whose narrow end touches the earth

and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than

110 miles per hour, are about 250 feet across, and travel a few miles before dissipating.

It’s impacts are loss of human life and biodiversity, injury, damage and destruction of property,

damage of cash crops, disruption in life style, damage to essential services, national economic loss

and loss of livelihood and it affects scattered areas of the country.

Flash Flood: A flash flood is a rapid flooding of geomorphic low-lying areas: washes, rivers, dry

lakes and basins. It may be caused by heavy rain associated with a severe thunderstorm, hurricane,

tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields.

It causes damage of standing crops, disruption in life style, evacuation and destruction of properties

and it occurs in Haor Basins of the North-East region and South-Eastern hilly areas.

Drought: Drought is an extended period when a region notes a deficiency in its water supply

whether surface or underground water. A drought can last for months or years, or may be declared

41

after as few as 15 days. Generally, this occurs when a region receives consistently below average

precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected

region.

It’s impacts are loss of agricultural production, stress on national economy and disruption in life

style and it occurs almost all areas, especially the Northwest region of the country.

Erosion: Erosion is the process by which soil and rock are removed from the Earth's surface by

exogenic processes such as wind or water flow, and then transported and deposited in other

locations. While erosion is a natural process, human activities have increased by 10-40 times the

rate at which erosion is occurring globally. Excessive erosion causes problems such as

desertification, decreases in agricultural productivity due to land degradation, sedimentation of

waterways, and ecological collapse due to loss of the nutrient rich upper soil layers.

It’s impacts are loss of land, displacement of human population and livestock, evacuation, damage

of property and loss of life and it occurs in the banks of the Brahmaputra -Jamuna, the Ganges-

Padma and the Meghna river systems.

Hail Storm and Lightning: Hailstorm and Lightning causes’ damage and destruction of property,

damage and destruction of subsistence and cash crops and loss of livelihood. It can occur in part

of the country.

Table 3.1: Timing of Different Disasters in Bangladesh.

Name of disaster Time of occurring

Flood Monsoon

Flash flood Pre-monsoon

Tornado March-May/October-November

Nor wester April

Lanslide June

42

Figure 3.2: Hazard Groups in Bangladesh (Source: http://www.saarc-

sadkn.org/countries/bangladesh/images/bangla_hazard01.JPG).

43

3.3 Hazards and Environmental Problems in the Sylhet Trough and

Their Causes and Effects

Our study area (Jaintiapur-Tamabil-Jaflong) mostly suffers from hazards like flash flood,

landslide, mudslide, and earthquake. Pollution is increasing day by day because of some irrational

human activities which cause degradation of the environment. Deforestation, overgrazing are

escalating rapidly.

Sylhet is a flood prone area of Bangladesh. Flash flood is one of the most common hazards in this

area. Flash flood occurs during monsoon period due to heavy rainfall in every 10-15 years. Almost

10 feet area was submerged during that time. It generally occurs in the month of June-August. A

huge amount of water flows down the hills from India towards these areas and causes flash flood.

It doesn't stay for a long time. Water goes down in about 1 day. The crops are damaged because

of flash flood. The areas near Lalakhal have to face greater damage.Landslide also occurs in our

study area during rainy season. Heavy rainfall, less vegetation on mountains, unconsolidated loose

sediment is the reasons behind it. Landslide is a great threat for the people who live at foothill.

Many people die because of landslides. Their houses, properties get damaged.

There is presence of a number of fault lines in Sylhet trough and they are Dauki fault, Plate

boundary fault, Central boundary fault, Madhupur fault etc. (Figure 3.3) near himalayan mountain

range the major plate boundary fault and because of these faults, this area has become prone to

Earthquake. Lives, properties of this region are at great risk. If an earthquake of high magnitude

occurs here, the place will be in immense danger.

Figure 3.3: Major Fault Lines of Bangladesh; Dauki Fault, Madhupur Fault and Plate Boundary

Fault (Source: CDMP)

Plate Boundary Fault 1

Plate Boundary Fault 2

Plate Boundary Fault 3 Dauki Fault

Madhupur Fault

44

Flood is annual phenomena for the people in sylhet living in downstream; in monsoon time heavy

rainfall causes flood and makes great impact on the lives of people there.

Slumping is another natural hazard that occues in our study region, as the sandstone in our

investigated area is very lossely compacted and after much precipitation slumping occurs and this

kinds of slumping may cause landslide. It occurs where there is less vegetation on the surface of

the hills (Figure 3.4).

Figure 3.4: Slumping at Dupi Tila.

Manmade hazards also pose a potential threat for the people in this region. Deforestation is a

major anthropogenic hazard in our study area. Local people cut the forest down. Most people of

that area use wood as fuel so timber is needed. Also people cut them down and sell them illegally

so it is a problem for the government to control deforestation. Also deforestation occurs to create

more open land for cultivation and stone quarrying. Deforestation also occurs due to road building,

human caused fire and many other ways. Deforestation and overgrazing at hills causes landslide (Figure

3.5).

Figure 3.5: Deforestation at hills causes Landslide.

45

Another man made hazard is stone quarrying of that area. Stone is supplied all over the

Bangladesh form this area. People involved in stone quarrying take lease from government and

the lands undergo a massive change due to stone quarrying. Indiscriminate and haphazard process

of stone collection cost a serious problem for the environment and ecology of the whole region.

People extract gravel (Figure 3.6) which causes degradation of environment. Also rock crushing

causes great harm to the environment. Stone merchandising (Figure 3.7) is another reason of

environmental degradation and these kinds of work causes slumping and air pollution.

Figure 3.6: Gravel Extraction from Rangapani River.

Figure 3.7: Stone Merchandising in Pian River.

46

Chapter-4

Conclusion

47

The main purpose of the fieldwork carried out in the North-East portion of Bangladesh was firstly

to determine the stratigraphic formation of the Sylhet trough as well as to find out the most

frequently occurring hazards of this portion of the country. Sylhet trough is filled with sediments

starting from the Eocene Age to the recent times. These rock units can be studied to reconstruct

the history of sediment deposition and the paleo-geography of the area. Investigation of the

different stratigraphic formation consisted of studying and interpretation of various types of rocks

within the different stratas, measurement of the attitude of beds as well as the study of physical

features, lithology, sedimentary structures and information about the various hazards affecting the

area was found through interviews with local people and academically established people.

With the base camp being located at (250085N and 9200745.5E), the investigation began on the

right bank side of Sari River where the Dupi Tila formation was encountered which consisted of

yellowish brown, loose but highly porous sandstone and sedimentary structures such as cross beds

along with clay galls were observed. Afterwards at a small distance away the Girujan Clay

formation with massive structured whitish grey clay was found along with mud cracks. From the

river bank we traversed all the way upto Lalakhal near Kalanji Bazar where we came across the

Tipam sandstone formation with yellowish grey sandstone. The contact between Tipam and

Girujan clay and also the contact between Tipam and Surma group was observed in this area.

Before we went to Nayagang Khal, we came across the Dihing formation outcrop which lied on

top of the Surma group. At Nayagang Khal we encountered with the Surma group which consist

of the two formations Bokabil and Bhuban but unfortunately it was impossible to find the contact

as both were found to consist of alternations of yellowish grey sandstone and bluish grey shales.

Trough cross bedding and flaser bedding was also seen in this group of formations. From this

location we went to Sonatila through the road passing through Tamabil. Here is Sonatila near

Sripur we found Renji formation of Barail group whose lithology consisted of compact jointed

pinkish sandstone beds with few shales and siltstones. Unfortunately the Jenum formation was

deeply buried in the area and outcrops could not be found for study. After that we journeyed to

east bank of the Dauki river where the Kopili shale formation was located which consisted of

highly fissile dark coloured shale. Finally the last formation Sylhet limestone was found at some

distance yet still along the east bank of the Dauki River where thick bedded fossiliferous limestone

was seen. The Dauki fault was also found in this region.

The most common hazards discovered in the area of study were flash flood, deforestation,

landslide, slumping and stone quarrying. Flash flood in this area occurs in the pre monsoon period

and destroys agricultural products of large areas, causing death, damage to property and

destruction to roads and bridges. Pre-monsoon flash floods damage the main crop Boro rice.

Deforestation increases the chances of river bank erosion as well as slumping causing the soil to

48

break loose and flow like semi liquid. If sufficient vegetation was present and development of

local houses in areas of steep slopes could be prevented then the risk will be reduced much down

to a minimum. Over development of stone quarrying in some areas has caused noise pollution, air

pollution and destruction of habitat.

During the field some limitations were faced. Due to the Upazilla Election the 6 day study had to

be finished within 4 days. Detailed studies in some cases were avoided due to the limited time. We

didn’t have enough opportunities for study the area appropriately. Lack of equipments and

inconvenience of residence are other limitations for the curtailed study of the region. Also some

limitations in the accommodation facilities were faced. Nevertheless the field study was finished

with all necessary information collected.

If it was possible to cultivate agricultural products that grew all throughout the year or at least not

during pre monsoon period then the effect of flood could’ve been decreased. Also land use

planning to avoid urbanization in flood plain areas will reduce the risk of flood hazard. If the

amount of stone quarrying could be restricted to limited areas then these slowly developing adverse

conditions can be avoided. Afforestation is necessary in huge amounts. Deforestation should be

discouraged. Also it can be added that presence of Eucalyptus trees in huge numbers was seen in

close vicinity of the Shari River. As these trees use a lot of soil water, nutrients and don’t come to

much good use. So they can be replaced by trees that are more appropriate to the area.

49

References

1. Abu Md. Nur Alam, Geological Survey of Bangladesh, Sedimentation and Tectonics of

the Sylhet tTrough, Bangladesh.

2. Ahmed, A, 1983, Oligocene Stratigraphy and Sedimentation in the Surma Basin, Bangladesh, M.

S. Thesis.

3. Alam, M, Alam MM, Curray JR, Chowdhury ALR, Gani MR, 2003, An Overview of the

Sedimentary Geology of the Bengal Basin in Relation to the Regional Tectonic Framework and

Basin-fill History. Sedimentary Geology. 155:179-208.

4. Ashraf Uddin, Department of Geology and Geography, 210 Petrie Hall, Auburn University,

Auburn, AL 36849-5305, USA, Miocene Sedimentation and Subsidence During Continent–

Continent Collision, Bengal Basin, Bangladesh.

5. A. Uddin, N. Lundberg, Sedimentary Geology 131–146, Stratigraphic Framework of the Bengal

Basin, Miocene Sediment Thickness is Much Lower near the Indian Platform in the Northwestern

Part of the Basin, This Shelf Area of the Basin is Floored by Continental Crust (after Khan and

Muminullah, 1980; Uddin and Lundberg, 1999; and Many Other Sources).

6. Bangladesh Bureau of Statistics (source- www.bbs.gov.bd).

7. Bangladesh Population Census 2001, Bangladesh Bureau of Statistics (BBS).

8. Banglapedia: Sylhet District.

9. Banglapedia: Tectonic Framework.

10. Climate and Weather of Sylhet, (source-

http://en.wikipedia.org/wiki/Sylhet#Geography_and_climate).

11. Climate of Sylhet, (source- http://www.whatstheweatherlike.org/bangladesh/sylhet.htm)

12. Disasters of Bangladesh, Ministry of Environment and Forests (source-

http://www.moef.gov.bd/html/state_of_env/pdf/bangladesh_disasters.pdf).

13. Earthquake Zones in Bangladesh (source- Banglapedia.org).

14. Flood prone area of Bangladesh (source- poribesh.com).

50

15. Haque, Alam, Downey, 2012, A Sequence Stratigraphic Approach of Sylhet Trough,

Lambert Academic Publishing.

16. Hazard Groups in Bangladesh (source- http://www.saarc-

sadkn.org/countries/bangladesh/images/bangla_hazard01.JPG).

17. Jaintiapur Upazila HQ (source- http://wikimapia.org/16968851/Jaintiapur-Upazila-HQ).

18. M. Ataur Rahman, N. C. D. Barma, M. H. Sarker, M. R. Sarker AND M. M. I. Nazrul, March

2013, Bangladesh J. Agril. Res. 38(1): 97-104, Adaptability of Wheat Varieties in Strongly

Acidic Soils of Sylhet.

19. M. J. Uddin, A. S. M. Mohiuddin, A. T. M. M. Kamal AND M. Anwar Hossain, University of

Dhaka, The Agricultural Potentiality of Some Wetland Soils Under Sylhet Basin of Bangladesh.

20. Neil Lundberg , Department of Geological Sciences, Florida State University, Tallahassee, FL

32306, USA, Miocene Sedimentation and Subsidence During Continent–Continent Collision,

Bengal Basin, Bangladesh.

21. Paul, 1988, Drainage System of Sylhet Trough.

22. Rashid Haroun ER, 1991, Climate Zone Map of Bangladesh

23. Samuel Y. Johnson U.S. Geological Survey, M.S. 939, Box 25046, Denver Federal Center,

Denver, Colorado 80225, Sedimentation and Tectonics of the Sylhet Trough, Bangladesh.

24. S.M. Imamul Huq, Jalal Uddin Md. Shoaib; The Soils of Bangladesh.

25. Stratigraphic Succession of NE Bangladesh, Sylhet Trough (sources: Khan, 1980, Reimann 1993,

Uddin and Lundberg, 1999).

26. Sylhet District, Local Government Engineering Department (LGED).

27. Sylhet District (source- http://en.wikipedia.org/wiki/Sylhet_District).

28. Uddin and Lundberg, Schematic Cross-section of the Bengal Basin; (a) N– S, Through the

Shillong Plateau; (b) E–W, Through the Northern Chittagong Hill Region, After Murphy (1988).

These Show Sediment Thickening Toward the South and East, Respectively.

51

Appendix I

Attitude of Beds:

Day Stop latitude longitude SD(°) DD DA(°)

1 1 25°5’46.4”N 92°07’4.3”E 255 SE 71°

2 25°5’49”N 92°07’04”E

3 25°5’50.8”N 92°08’29.3”E

4 25°5’54.3”N 92°08’40.4”E

5 25°6’37.3”N 92°09’6.8”E

2 1 25°06’20.9”N 92°10’32.2”E 124 SW 70

2 25°06’33.7”N 92°10’42.1”E

3 25°06’20.5”N 92°10’33.7”E

4 25°06’55”N 92°10’55.7”E 296 SW 54

5 25°08’24.4”N 92°07’17.9”E 273 SW 40

3 1 25°08’5.3”N 92°07’45.3”E 274 SW 35

2 25°08’20.6”N 92°08’08”E

3 25°08’39.3”N 92°07’47.6”E

4 25°08’55.9”N 92°07’33.3”E 280 SW 34

5 25°08’24.4”N 92°07’17.9”E 70 SE 32

6 25°10’37”N 92°04’35.7”E 201 NW 26

7 25°09’54.9”N 92°04’21.7”E

8 25°10’42.3”N 92°04’29.5”E 108 NW 06

9 25°10’34.3”N 92°03’44”E 246 SE 21

10 25°10’51.6”N 92°01’59.9”E 210 NW 18

11 25°10’43.2”N 92°01’38.9”E - - -

4 1 25°10’34.9”N 92°01’33.6”E 258 SE 36

2 25°10’43.4”N 92°0’55.3”E 272 SW 36

3 25°10’53.5”N 92°01’5.5”E

4 25°10’55.3”N 92°01’4.7”E

5 1 25°08’N 92°08’E

52

Appendix II

List of Tables:

Table No. Name of Table Page Number 1.1 Climate data for Sylhet, Bangladesh 6

2.1 Stratigraphic Succession of NE Bangladesh, Sylhet

Trough (sources: Khan, 1980, Reimann 1993, Uddin and

Lundberg, 1999).

20

3.1 Timing of Different Disasters in Bangladesh. 41

List of Figures:

Figure

No.

Name of Figure Page

Number 1.1 Location Map of Jaintiapur, Sylhet. 2

1.2 Location Map of Jaintiapur Upazilla. 3

1.3 Interviewing Local People (a). 4

1.4 Interviewing Local People (b). 4

1.5 Measuring Dip-Strike with Clinometer. 4

1.6 Drainage Pattern of Investigated Area. 7

1.7 Tea Garden at Hill Slope in Afifanagar. 8

1.8 Fallow Land for the Scarcity of Water. 8

2.1 Location of Bengal Basin. 10

2.2 Break-up of Paleo-Continent (Pangea) to Current Continents

Through the Passage of Time.

11

2.3 Collision of Indian and Eurasian Plate. 11

2.4 The Ongoing Collision of India and Asia. A. Converging Plates

Generated a Subduction Zone. B. Position of India in Relation

to Eurasian at Various Times. C. Eventually the Two

Landmasses Colided, Deforming and Elevating the Sediments

That Had Been Deposited Along the Continental Margins.

11

2.5 Stratigraphic Framework of the Bengal Basin. Miocene

Sediment Thickness is Much Lower near the Indian Platform in

the Northwestern Part of the Basin. This Shelf Area of the Basin

is Floored by Continental Crust (after Khan and Muminullah,

1980; Uddin and Lundberg, 1999; and Many Other Sources).

12

2.6 Schematic Cross-Section of the Bengal Basin; (a) N– S,

Through the Shillong Plateau; (b) E–W, Through the Northern

Chittagong Hill Region, after Murphy (1988). These Show

Sediment Thickening toward the South and East, Respectively.

13

53

2.7 Tectonic Framework of Bangladesh and Adjoining Area

(Source: BANGLAPEDIA: Tectonic Framework).

15

2.8 Dauki Fault Marks the Border Between Shillong Plateau and

Sylhet Trough Through, Abrupt Elevation Change.

17

2.9 Sylhet Trough and it’s Surroundings. 17

2.10 Satellite Image of Sylhet Trough. 19

2.11 Jointed Subvertical Beds of Sylhet Limestone. 22

2.12 Nummulitic Limestone Found near Dauki River. 22

2.13 Fault Breccias and Kopili Shale Created by Dauki Fault in

Jaflong.

23

2.14 Dark Coloured, Fissile, Laminated Kopili Shale. 24

2.15 Jointed Beds of Sylhet Limestone Overlain by Organic Matter

Rich Kopili Shale.

24

2.16 Pinkish Sandstone with Ferruginous Cementing Materials. 25

2.17 Jointed Beds of Sandstone in Barail. 26

2.18 Trough Cross Bedding found in Tetulghat. 27

2.19 Flaser Bedding found near the Contact of Surma and Tipam

Sandstone.

27

2.20 Drag Fold in Surma Group in Nayagang. 28

2.21 Surma Formation Folded Outcrop in Tetulghat. 28

2.22 Clay Galls found near Lala Khal in Tipam Sandstone. 29

2.23 Conglomerate Bed in Tipam Sanstone. 30

2.24 Fault (reverse) in Tipam Sandstone. 30

2.25 Lenticular Bedding in the Contact of Surma and Tipam Group. 31

2.26 Mottled Girujan Clay. 32

2.27 Outcrop of Dupi Tila. 33

2.28 Clay Gall in Dupi Tila Right Bank Side of Shari River. 33

2.29 Iron Incrustation in Dupi Tila. 33

2.30 Cross Bedding in Dupi Tila at Right Bank of Shari River. 34

2.31 Outcrop of Dupi Tila. 34

2.32 Dihing Formation. 35

2.33 Mud Cracks. 36

3.1 Epicenters of Historical Earthquakes (1664-2007), (after Sabri,

2001).

39

3.2 Hazard Groups in Bangladesh (Source: http://www.saarc-

sadkn.org/countries/bangladesh/images/bangla_hazard01.JPG).

42

3.3 Major Fault Lines of Bangladesh; Dauki Fault, Madhupur

Fault and Plate Boundary Fault (Source: CDMP).

43

3.4 Slumping at Dupi Tila. 44

3.5 Deforestation at hills causes Landslide. 44

3.6 Gravel Extraction from Rangapani River. 45

3.7 Stone Merchandising in Pian River. 45