1. Bangladesh's geology consists of four folded belts, with the eastern regions exhibiting many anticlines and synclines trending NNW-SSE. 2. Small hillocks in northern districts trend E-W, while subsurface sediments on the Dinajpur Shield dip and fold. 3. Subsurface folding below the delta region involves anticlines up to 10 km deep. 4. Major faults trend NW-SE, NE-SW, and were active from the Precambrian to post-Pleistocene.

1. GEOLOGY OF BANGLADESH

5. Folded Belts:
The folded structures of Bangladesh may be classified into four belts:
1. The folded sediments of the eastern hilly regions comprising the north-eastern
and eastern parts of Sylhet and Comilla districts and Chittagong and Hill Tract
districts.
2. A folded region of discontinuous small, low hillocks and hill ranges occupy a
very narrow strip on the Shillong Platform and the Basin along the northern
frontiers of Sylhet and Mymensingh districts.
3. The subsurface dipping sediments on the Dinajpur Shield and its southern
platform.
4. The subsurface folded sediment of the Basin

6. The Folded Sediments of the Eastern Hilly Regions:
- A large number of anticlines and synclines, both symmetrical and
asymmetrical.
- Most of the structures trend NNW-SSE, and almost all the folds of
Chittagong and Hill Tract exhibit the same trend designated as the Chittagong
Strike and may be applicable to the strikes of the folds of Comilla and Sylhet
districts.
- In the extreme north-eastern part of Sylhet district, the Chittagong Strike first
swings to the N-S then to NNE-SSW and NE-SW.
Folded Rocks of the Northern Frontiers of Sylhet and Mymensingh:
- Along the northern frontier of Sylhet and Mymensingh districts trend
steadily E-W may be termed as the Sylhet Strike.
- Chhatak anticline and Goyen syncline parallel the Sylhet strike.
- Sylhet and Dupi Tila anticlinal axes more or less follow the Bogra strike.
- The rocks show high angles of dip ranging generally from 450 to 550S
between Bangali Bazar and Bhangerghat and from 300 to 400S in the Bijaipur
area.

7. The Subsurface Dipping Sediments of the Dinajpur Shield and its Southern Platform:
- It will hardly be possible to identify more than three periods of Precambrian
granitic intrusions on the Dinajpur Shield and Platform.
- Maddhapara hard rock mine, if ever developed, will offer large exposures of
Precambrian rocks.
- The bands of the gneiss trend ENE-WSW and show high angle of inclination
ranging from 500 to 700.
- Several anticlines or dome like features and synclines or trough like
irregularities may be present in the basin of the Paharpur coal field.
- The dip of the Gondwana sediments ranges from 50 to 100 and in places 150 but
their strike remains to be ascertained.
- The top of the Dinajpur Shield exhibits a good degree.
- The strike of the Tertiary rocks trend NE-SW.
- The northern slope of the Dinajpur Platform that grades into the Himalayan
trough or foredeep awaits exploration.

8. The Sub-surface Folded Sediments of the Basin:
- Vertical thickness of sediments ranging from 2 to 10 km in the entire delta
region.
- Six small anticlines, two south and one west of Khulna and one each at
Patuakhali, Bhola, and Muladi.
- The sediments between Chhatak and Jamuna; Mymensingh and Sylhet; and
southern boundary of the Dhaka range in thickness from 3 to more than 8 km.
Kamta, Munshiganj, and Daudkandi anticlines fall in this area and their axes make
small angles with the Chittagong strike.
- Beneath the Bay of Bengal, the Chittagong strike trend dominates but a small
number of strikes appear to be erratic in their directions varying from ENE-WSW
to almost NW-SE.

9. Faulting:
The faults may be classified as follows:
1. Precambrian
2. Late Eocene (Kopili)
3. Late Middle Miocene (Girujan clay)
4. Late Pliocene (Dupi Tila)
5. Post Pleistocene (Madhupur clay)
Precambrian Faulting:
The faults generally trend NW-SE, NE-SW, NNE-SSW, E-W, ENE-WSW.
Faulting in the Precambrian of the Basin has been much less intense. The
faults run mostly in the NW-SE and NE-SW directions.

10. Late Eocene Faults:
The narrow frontier strip on the Shillong Platform between Bagali Bazar and
Bhangerghat exposes a series of faults that run across and oblique to the
Sylhet Strike. Two faults extend parallel to the strike. The horizontal
displacement of the geological formations due to the dip faults generally range
from about 50 feet to several hundred feet and their heads mainly dip from 450
to 900.
Late Middle Miocene Faults:
The displacements of the sediments of most of the folds, being simultaneously
limited to the formations of the Surma and Tipam groups. These faults have
given rise to many stream and gullies that flow west and east and also from
north to south. The dip faults trend mostly oblique to the strike and arre
concentrated in the districts of Sylhet, Hill Tract and Chittagong. The strike
and the thrust faults have mostly affected the folds of the Chittagong and Hill
Tract districts.

11. Late Pliocene Faults:
The faulting during Late Pliocene took place on a much smaller scale
compared to the Late Middle Miocene faulting. The faults trend mostly
oblique to the strike, cause displacements of small magnitude, and remain
limited to the Dupi Tila formation.
Post Pleistocene Faults:
The Madhupur area shows nine faults and the Barind Tract exhibits ten. Most
of the faults trend NW-SE and form low scraps. The Madhupur clay formation
happens to be the least studied geological formation in Bangladesh. The Dupi
Tila formation occupies the tips of nearly all the anticlines of the Sylhet,
Comilla and Noakhali districts. But in the Chittagong and Hill Tract districts
the sediments of the Surma Group form the crest of all the anticlines baring a
few which expose the Tipam group.

12. Horst and Graben:
Shillong Plateau including the Mikir hills represent a horst bounded the faults
on all sides and formed during Mio-Pliocene orogeny. The Dinajpur Shield
constitute the corresponding graben down thrown as a result of multiple faults
along the Jamuna and the Ganges.
Mineral Deposits of Bangladesh:
Precambrian:
Hard Rock: In the Maddhapara area, the Precambrian igneous and
metamorphic rocks lie within 400 to 500 feet of the surface in a sizeable area.
Iron Ore Mineral: The iron ore mineral composed mostly of siderite occurs as
veins both in the coarse grained, light coloured banded gneiss and in the fine
grained gray to dark fray banded gneiss. The colour fo siderite varies from
creamy, pale yellowish to brownish red.

13. Precambrian:
Pegmatite: Pegmatite is disposed in veins, sill, and dykes in the Precambrian
rocks of the Maddhapara area. It exhibits fleshy colour and is readily
identifiable in core samples. It is hard and massive but has developed minute
fractures which are generally filled by magnetite, siderite, hematite, and silica.
Kaolin: Kaolin directly overlies the Precambrian rocks and underlies a thick
bed of glass sand. It shows milk-white colour and is mixed up with quartz
grains. The unwashed kaolin contains 69% SiO2, 24% Al2O3 and 0.11%
Fe2O3.
Glass Sand: Glass sand overlies the kaolin. The glass sand mostly consists of
colourless and smoky quartz grains. The unprocessed and unwashed silica
sand contains 97.04% to 97.31% SiO2 and 0.19% to 0.64% of Fe2O3. The
thickness of glass sand ranges from 20feet to 45 feet averaging 31.8 feet.

14. Paleocene to Early Eocene:
Tura Sandstone: Two workable coal seams occur at subsurface depths ranging
from 150 feet to 319 feet between Lalghat and Takerghat, a distance of about
10,000 feet. The coal is black, shiny, hard, and massive. Its streak is dark
brown. It has very mild odour of sulphur.
Middle Eocene:
Sylhet Limestone: Limestone outcrops as small hillocks in Bagali Bazar,
Lamakata, Lalghat, Takerghat, and Bhangerghat area
Upper Eocene:
Kopili Shale: In Jaipurhat thick calcareous and non-calcareous shale overlies
the limestone. The calcareous shale may provide much better and cheaper
substitute for the fertile Pleistocene and Recent alluvial clay in the
neighbourhood of Jaipurhat.

15. Early Miocene:
Surma Group: Some of the numerous sandstone interbeds of the Surma group
hold commercial accumulation of gas. The total reserves of gas are estimated
at 11 trillion cubic feet.
Late Miocene:
Dupi Tila: White clay interbeds with the sediments of the Dupi Tila formation
of the Bijaipur area in the northern frontier region of Mymensingh district.
Pliocene:
Lalghat-Lakhmachhara Area: The white sandstone in the Dihing formation of
this area contains 99% SiO2, R2O3 0.66%, Fe2O3 0.01%, MgO 0.10% and
traces of CaO and insolubles. The minimum depth of the white sandstone
from the surface is 78 feet and the maximum is 223 feet. The sandstone is
semi-consolidated and is saturated with water.