Lithofacies Analysis and Depositional Environments of ...mynces.org/download/2018/ProceedingMNCES2018/35_Paing Soe.pdf · Depositional Environment Tilin Formation of the present area

448 The Second Myanmar National Conference on Earth Sciences (MNCES, 2018)

November 29-30, 2018, Hinthada University, Hinthada, Myanmar

1Lecturer and Head, Dr., Department of Geology, Yenangyaung Degree College

2Demonstrator, Department of Geology, Magway Univerity

#Corresponding author: [email protected]

Lithofacies Analysis and Depositional Environments of Tilin Formation in

Taing Da area, Mindon Township, Magway Region

Paing Soe1#

and Kyaw Min Oo2

Abstract

The Eocene sedimentary rocks, exposed in the southwest of Minbu Basin, central part of

Myanmar, are characterized by continental clastic units of sandstones and deltaic to

shallow shelf sediments of sand-shale and mudstone. Taing Da area is located in

northwest of Mindon and southwestern part of Magway Region. Six stratigraphic units

can be classified in Taing Da area. They are (1) Kabaw Formation (Late Cretaceous), (2)

Paunggyi Formation (Late Paleocene), (3) Laungshe Formation (Early Eocene), (4) Tilin

Formation (Early Eocene), (5) Tabyin Formation (Middle Eocene) and (6) Alluvium

(Holocene). Present study for lithofacies analysis is only one formation of Tilin Formation exposed in Taing Da and its environs. According to the distinctive lithologic

features including colour, bedding, composition, texture, fossils and sedimentary

structures, (12) lithofacies are recognized and (4) lithofacies associations were

distinguished. Based on the field observations and lithofacies analysis, the most of the

sediments and rocks of lower member of Tilin Formation in Taing Da area were probably

deposited under shoreface, tidal channel and tidal flat environments and upper member of

Tilin Formation were deposited under tidal flat and delta front environments during Early

Eocene Epoch.

Keywords: Eocene, shelf, lithofacies analysis, Tilin Formation

Introduction

Location, size and Accessibility

The study area is located in the Mindon Township, Magway Region and especially

lies in the southwestern part of the Magway Region. This area is situated between Latitude

19˚ 27΄ to 19˚ 34΄ N and longitude 94˚ 35΄ and 94˚ 44΄ E in one inch topographic maps of

85I/10 and 85I/11. The eastern part of the study area is low land and the western part of the

study is rugged terrain. The study area, Taing Da area can be reached from Yangon, Magway,

Monywa, Pathein, Pyay, Minbu and Mindon by car throughout the year. The location map of

the study area is shown in figure (1).

Previous Work

The study area lies in the western margins of Minbu Basin which includes the study

area was paid much attention by many geologists. Theobald (1871, 1873) reported the

western part of the Mindon area was shown as Axial (Triassic) and overlain by the

Nummulitic Series (Eocene). Chibber (1934) described briefly the geology of the upper

Chindwin Area. He reported that the flysch of Western Ranges in rocks that range in age

from Middle Triassic to Late Eocene. Maung Maung Gyi (1983) reported the Geology of the

northwestern part of Mindon Area, for his M.Sc thesis.

The Second Myanmar National Conference on Earth Sciences (MNCES, 2018) 449


Figure (1). Locatoion map of the study area.

Materials and Methods

The geological map of the study area was resulted from the fieldwork carried out

during November, 2014. The field work was carried out along the exposure of the Eocene to

recent rock units of the Taing Da area. Detail sections measurements were carried out along

the stream sections and car road cuts section. These sections have been measured bed by bed,

and samples have been taken every few centimeters or tens of centimeters, depending on

facies changes. The lithology, texture, sedimentary structures, fossil content and tectonic

deformation were checked and recorded in note book during measurements. Based on the

field works, detail stratigraphic columns were reproduced by Surfer 10 software. The

lithofacies were classified based on particular set of sediments characteristics, lithology,

texture, suite of sedimentary structures, fossil content, colour, geometry and paleocurrent

pattern of the sedimentary rock.

Geological Setting and Stratigraphy

The Central Myanmar Basin (CMB) lies between the Indo-Burman Ranges (IBR) in

the west and the Shan Plateau in the east Metcalfe (2011, 2013). The Central Myanmar Basin

(CMB) is divided into the eastern (backarc) and the western (forearc) troughs particularly

after the late Miocene when the Central Volcanic Line (CVL) became well established. The

western trough of the CMB is further subdivided into a few sub-basin, namely (from north to

south) the Hukaung, Chindwin, Minbu/Salin, Pyay and Irrawaddy sub-basins.

The present Taing Da area is situated a small segment of the south-western margin in

Minbu/Salin sub-basin. The study area can be said distinct morphological break between the

mountain ranges in the west and the ridges and valleys of the Central Basin in east



corresponds to a stratigraphic discontinuity. The ridges of high relief occurred in the western

part of the area. The oldest rock unit by the Kabaw Formation covered the western part and

the youngest rock units by the Alluvium toward the east. Satellite 3D image of the present

area is shown in figure (2). Geological map of the Zingyan - Taing Da - Mothauk area of the

northwestern part of the Mindon Township is shown in figure (3). Topographic features of

this area are from east to west, Mu chaung Valley, Kyaukkyi-aing Ridge, Thaminkadok-

Zawgyi valley, Zindaung-Sinza Taung, Kalan Taung Ridge, Kywedu Taung, and Kyaukpya

Taung. Mu chaung is distinct stream of the area which drain NW to SE direction. The

principal streams of the study area are Mu chaung.

On the basis of lithology, stratigraphic position, and faunal content, six stratigraphic

units can be classified in the study area which is explained in ascending order as follows;

6. Alluvium (Holocene)

5. Tabyin Formation (Middle Eocene)

4. Tilin Formation (Early Eocene)

3. Laungshe Formation (Early Eocene)

2. Paunggyi Formation (Late Paleocene)

1. Kabaw Formation (Late Cretaceous)

The generalized stratigraphic succession is shown in table (1). There are six

lithostratigraphic units are exposed in the area, the present study is carried out especially

onthe Tilin Formation. The present study is mainly emphasized on the Sedimentary

lothofacies analysis of the Tilin Formation.

Figure (2). 3D image of the study area: facing to northwest (source; Google map)

Tha Min Ka Dok Village

Taing Da Village



Figure (3). Geological Map of the Zingyan - Taing Da - Mothauk Area, Northwestern Part of

the Mindon Township, Magway Region ( Modified after Maung Maung Gyi,

1983)

Stratigraphy of Tilin Formation

Cotter (1912) was firstly introduced the name of Tilin Formation in the area between

75 and 81 miles on the Pakokku-Tilin Road, from the Western Outcrops of the Minbu

Basin. The sandstones occur below Tabyin clays and above the laungshe shales (1912). The

name Tilin Formation was proposed by Aung Khin and Kyaw Win (1969). Tilin Formation

can be divided into two members according to the difference of lithology and topography by

Maung Maung Gyi (1983).

The Tilin Formation is well exposed in the stream section of the study area. The lower

member of Tilin Formation occupies N-S trending and small ridge between the Laungshe

Valley in the west and the upper Tilin Valley in the east. This Formation is well exposed

along the Mu chaung, located from the north-eastern part of the Thamingadok village to the

west of the Taing Da village. Along Mu chaung, SSE of the Taing Da village and

Meinmahla chaung near the Htanbingaing village can be seen upper member of the Tilin

Formation. The average thickness of Tilin Formation is 3600m.

Lower Member The lower member is mainly occurred alternation of buff- to grey-colored,

thin-bedded calcareous sandstone and bluish grey shale. Bluish grey shale interbedded with

thin-bedded sandstone (Fig. 4.a). Medium-to thick-bedded sandstones with bioturbation and

shell fragments are occurred (Fig. 4.b). Wavy bedding, lenticular bedding, flaser bedding,

planar type and trough type cross-beddings are occurred in the lower member of the Tilin

Formation. Bluish grey, thin to medium-bedded sandstone with load cast are also observed at

Units

Upper Member

Lower Member



the lower member (Fig. 4.c). The sandstone content of the lower member of the Tilin

Formaion is more prominent than the upper member of Tilin Formation.

Upper Member The upper member is composed of grey-colored, medium-bedded sandstone

interbedded with bluish grey clay along the Meinmahla chaung section (Fig. 4.d). Buff-

colored, thin- to medium-bedded lenticular and wavy bedded sandstone are intercalated

between the bluish grey clay (massive type) can be seen in this Formation (Fig. 4.e). In the

upper member of Tilin Formation, thin- to medium-bedded, cone-in-cone structures and disc-

shaped concretions are also intercalated between the massive mudstone (Fig. 4.f). In some

places, concretionary mudstone and soft sediment folding are observed. At the upper most of

the Tilin Formation, medium-bedded friable sandstone and cone in cone structures are

occurred. The contact with overlying Tabyin Formation is gradational and it can be seen the

east part of Taing Da- Htinnyauktin- Mindon- Padan Junction road. On the basic of lithology

and stratigraphic position, Tilin Formation may be regarded as Early Eocene age.

Table (1). Generalized stratigraphic succession of the Zingyan - Taing Da - Mothauk Area.

Age Formatio

n Lithology Thickness

Holocene Alluvium light brown colored of sandy soil, silt and clay, and often contains organic matter that makes as a

fertile soil

About 400 m (Kyaw Min Oo,

2015)

Middle Eocene

Tabyin Formation

Yellow to yellowish shale and clay interbedded with bluish grey,thin- bedded, medium-grained

sandstone.

963 m (Maung Maung

Gyi,1983)

Early

Eocene

Tilin

Formation

Lower Member- Yellowish brown to brownish

grey, medium-grained, thin- to medium-bedded sandstone and bluish grey shale.

Upper Member- Bluish grey shale and thin- to

medium-bedded, compact and hard sand band.

3600 m

(present study)

Early

Eocene

Laungshe

Formation

Light-grey to grey-colored, fine- to medium-grained sandstone interbedded with greenish grey

to bluish grey shale; minor amount of tuff bed and

limestone lens.

1918 m

(Kyaw Min Oo, 2015)

Late

Paleocene

Paunggyi

Formation

Greenish grey to grey colored, coarse-grained,medium- to thick- beddedsandstones and

bluish-grey shale; grey to reddish brown, thick-

bedded to massive conglomerate; grits and gritty sandstone.

1950 m

(Kyaw Min Oo,

2015)

Late Cretaceous

Kabaw Formation

medium- to coarse-grained, Medium- tothick-bedded, sandstoneinterbedded with bluish grey

shale

2569 m (Maung Maung

Gyi, 1983)

Stratigraphic Relationship

The lower stratigraphic contact between Tilin Formation (Early Eocene) and

underlying Laungshe Formation (Early Eocene) is graditional contact. It is characterized by

the presence of sand-shale alternation. The lower contact can be seen along the Mu chaung,

north-eastern of Thamingadok village and the upper contact with overlying Tabyin Formation

is gradational. Its contact can be seen at the junction of the Htinnyauktin-Taing Da- Mindon

car road.



Faunal, Age and Correlation

Tilin Formation of the present study area is fairly fossiliferous. The Lepidocyclina sp.,

Nummulities sp. and Camerina sp. are preserved (Htay Sandar Soe, 2015). The above faunal

assemblages indicate that the Tilin Formation may belong to Early Eocene age.

Depositional Environment

Tilin Formation of the present area is characterized by the following;

(1) This formation composed of alternated sandstones and shales.

(2) Light-grey, thick-bedded sandstone, calcareous sandstone with load cast, wave ripple

mark are present.

(3) Sedimentary structures such as small scale trough type cross-bedding, wavy bedding,

lenticular bedding, flaser bedding, cone-in-cone structure and burrow structure are also

common.

Figure (4). (a). Thin-bedded sandstone beds are interbedded with bluish grey shale (19˚ 32'

14.8''N and 94˚ 39' 44.5''E), (b). medium-to thick-bedded sandstones (19˚ 32'

29''N and 94˚ 39' 4.1''E), (c). sandstone with load cast (19˚ 32' 54''N and 94˚ 39'

11''E), and in the lower member of Tilin Formation, (d). medium-bedded

sandstone interbedded with massive clay at Meinmahla chaung section, (e).

massive type or crudely bedded mudstone (19˚ 31' 10.731''N and 94˚ 40'

47.424''E), and (f). massive clay with thin- to medium-bedded cone-in-cone

sandstone and disc-shaped concretions at the upper member of Tilin Formation

The above characteristics are strongly indicated that Tilin Formation was deposited

under the shallow marine condition. The presence of worm burrows indicate that the littoral

depositional environment.

a b c

d e f



Lithofacies Analysis and Lithofacies Association

General Statement

A facies is a body of rock and it is defined on the basis of its distinctive lithologic

features including color, bedding, composition, texture, fossils and sedimentary structures

(Reading, 1996). A facies is defined by Tucker (2001) as a particular set of sediment

attributes a characteristic lithology, texture, suit of sedimentary structure, fossil content,

color, geometry and paleocurrent patterns, etc. Each lithofacies represents on individual

depositional event. Therefore, lithofacies may be grouped into lithofacies associations or

assemblages, which are characteristics of particular depositional environment (Miall, 1984).

The term ‘Facies Association’ was defined by Potter (1959) as a collection of

commonly associated sedimentary attributes, including gross-geometry (thickness and areal

extent), continuity and shape of lithologic units, rock types, sedimentary structures and fauna

(type and abundance). In the study area, at least (12) lithofacies are recognized for Tilin

Formation. Their brief descriptions with interpretations are given in table (2). Detail

sedimentological log of the Tilin Formation (Fig. 7). The four lithofacies associations were

distinguished with respect to their lithology, facies successions and bed geometry. They are

shoreface facies association, tidal channel facies association, tidal flat facies association and

delta front facies association in table (3).

Lithofacies Characteristics

Facies A: Quartz Pebbles conglomerate

This facies is distributed in upper member of the Tilin Formation. The thickness of

each bed varies from 15 to 30 centimeters. The diameter of quartz pebble range from 0.5 cm

to 7 cm and most of the quartz pebbles are rounded (Fig. 5.a). This facies is associated and

sandstone with Thick-bedded gritty sandstone of Facies-C and trough type cross-stratification

of Facies D. The upper boundary and lower boundary are sharp.

Interpretation

Most of the quartz pebbles in this facies are rounded. Facies A is regarded as lag

deposit at the base of tidal channel that occurs at the coastal area.

Facies B: Sandstone with Mud Clasts

This facies is distributed in the upper member of the Tilin Formation. It is mainly

composed of buff colored, medium-grained sandstone with mud clasts (Fig. 5.b).The

thickness of each bed varies from 7-30 cm. The diameter of mud clasts range from 0.5cm to

4cm and most of mud clasts are rounded. This facies is associated with sandstone with trough

type cross-stratification of Facies D. The upper boundary and lower boundary are sharp.

Interpretation

Facies B may be regarded as lag deposit at the base of tidal channel that occurs at the

delta front of the coastal area.

Facies C: Thick-bedded gritty sandstone

This facies is distributed in the upper member of the Tilin Formation. It consists of

grey colored, medium-grained, thick-bedded gritty sandstone (Fig. 5.c). The upper boundary

and lower boundary are graditional.



Interpretation

Facies C may be regarded as lag deposit at the base of tidal channel.

Facies D: Sandstone with Trough Cross-stratification

This facies is distributed in the lower member of the Tilin Formation. It consists of

buff colored, medium-grained, trough type cross-stratification sandstone (Fig. 5.d). The

nature of boundaries with the underlying and overlying units is sharp.

Interpretation

The most common sedimentary structures in the tidal channel deposits are channel lag

deposit overlain by bidirectional trough and planar cross-bedding, parallel laminated

sandstone and shells (Walker and James, 1992). Facies D is deposited in subaqueous topset

deposits of tidal channel.

Facies E: Sandstone with Planar Cross-stratification

This facies is distributed in the lower member of Tilin Formation. This facies occurs

in grouped with planar-type cross bedding. This occurrence is small scale and distributed

through the area. (Fig. 5.e).This facie is variable in relationship associated with facies. Most

of them have erosion tops, but in rare cases they have transitional tops. The nature of

boundaries with the underlying unit is graditional and overlying unit is sharp.

Interpretation

This facies may be interpreted as upper shoreface deposits (Reineck and Singh, 1980).

Facies F: Sandstone with Burrow Structure

This facies is distributed in lower member of Tilin Formation. It consists of light grey,

medium-bedded sandstone with burrow structure (Fig. 5.f). The presence of evidence of

organisms disturbing sediment is known as bioturbation (Nichols, 2009).

Interpretation

Toward the deeper part of the shoreface, the degree of bioturbation is incresess. This

facies may be interpreted as lower shore face environment (Reineck and Singh, 1980).

Facies G: Sandstone with Wavy/Lenticular Bedding

This facies is distributed in Tilin Formation. It is composed of grey colored, medium-

bedded sandstone with wavy and lenticular bedding (Fig. 5.g). Based on nature of lenses,

lenticular bedding can be subdivided into two types. They are lenticular bedding with

connected lenses and lenticular bedding with single (Isolated lenses). The type of lenticular

bedding is second type. The nature of boundary is graditional.

Interpretation

This facies may be formed in tidal flat (sand flat) environment (Reineck and Singh,

1980).

Facies H: Sandstone with Flaser Bedding

This facies is also distributed in Tilin Formation. It is composed of grey coloured,

medium-grained sandstone with flaser bedding (Fig. 5.h). This facies is associated with

sandstone with wavy and lenticular bedding of Facies G and crudely bedded mudstone facies.

The nature of boundary is graditional.



Figure (5). (a). Quartz pebbles conglomerate of facies A, (b) Sandstone with mud clasts of

facies B, (c) Thick-bedded gritty sandstone of facies C, (d) Sandstone with

Trough Cross-stratification of facies D, (e) Sandstone with Planar Cross-

stratification of facies E, (f) Sandstone with Burrow Structure of facies F, (g)

Sandstone with Wavy and Lenticular bedding, (h) Sandstone with Flaser Bedding

of facies H were preserved in Tilin Formation of Taing Da area.

a b

c d

e f

g h



Figure (6). (a) Sandstone with Wave Ripple of facies I, (b) Sand-shale Interbed Sequence of

facies J, (c) Massive Concretionary Mudstone of facies K, (d) Crudely bedded

Mudstone of facies L were preserved in Tilin Formation of Taing Da area.

Interpretation

This structure implies that both sand and mud are available and that periods of current

activity alternate with period of quiescence. This facies may be formed in tidal flat (sand flat)

environment (Reineck and Singh, 1980).

Facies I: Sandstone with Wave Ripple

This facies is distributed in the lower and upper member of Tilin Formation. This

facies is mainly composed of light grey, medium- grained sandstone with ripple marks

(Fig. 6.a). The thickness of ripple mark sandstone is about from 15 to 30 cm. The nature of

boundary is graditional.

Interpretation

This ripple type occurs in wave-dominated, tidal influenced environments (Reineck

and Singh, 1980) described interfering ripple systems formed on the North Sea tidal flat by

the interaction of wave activity and currents. So, this Facies I may be deposited under the

wave activity tidal flat (sand flat) environment.

Facies J: Sand-shale Interbed Sequence

This facies is distributed in the lower member of the Tilin Formation. It is composed

of buff colored, thin- to medium-bedded sandstone interbedded with bluish grey shale

(Fig. 6.b). The nature of boundaries with the underlying unit is graditional and overlying unit

is sharp.

a b

c d



Interpretation

In this facies, the sandy layers are deposited during periods of current activity, and

shale/mud content during slack water periods. This alternate bedding is mostly to the

alternation of tidal current and slack water phases (Reineck and Singh, 1980). This facies

may be deposited in the tidal falt (mixed flat) environment.

Facies K: Massive Concretionary Mudstone

This facies is distributed in upper member of Tilin Formation. It is composed of

bluish grey colored, massive concretionary mudstone and thickness is about 170 to 3000 cm

(Fig. 6.c). This facies is associated with gritty sandstone of Facies C and crudely bedded

mudstone of Facies L. The nature of boundary is gradational.

Interpretation

Fine sediments are deposited under relatively quite water condition. This facies may

be deposited in the delta front environment.

Table (2). Lithofacies identification for Tilin Formation, in the Mindon Township, Magway

Region

Lithofacies Sedimentary

Structures Interpretation

A Quartz Pebbles

conglomerate

Lack of internal

structure the base of tidal channel deposits

B Sandstone with Mud Clasts Lack of internal

structure

Lag deposit at the base of the tidal

channel

C Thick-bedded gritty

sandstone

Lack of internal

structure

Lag deposit at the base of the tidal

channel

D Sandstone with Trough

Cross-stratification

Small scale trough cross

stratification

deposited in subaqueous topset

deposits of tidal channel

E Sandstone with Planar

Cross-stratification

Small scale planar cross

stratification upper shoreface deposits

F Sandstone with Burrow

Structure

Burrow Structure, Shell

Fragments lower shore face environment

G Sandstone with

Wavy/Lenticular Bedding

Wavy bedding,

Lenticular bedding tidal flat environment

H Sandstone with Flaser

Bedding Flaser bedding tidal flat environment

I Sandstone with Wave

Ripple Wave ripple marks wave activity tidal flat environment

J Sand-shale Interbed

Sequence Organic debris

tidal falt and upper shoreface

environments

K Massive Concretionary

Mudstone Concretions delta front environment

L Crudely bedded Mudstone cone-in-cone structures,

disc-shaped concretions delta front environment



Table (3). Identification of Lithofacies Association for Tilin Formation in the Mindon

Township, Magway Region

Facies Association Lithofacies

Shoreface E, F, J

Sandstone with Planar Cross-stratification

Sandstone with Burrow Structure

Sand-shale Interbed Sequence

Tidal Channel A, B, C, D, L

Quartz Pebbles conglomerate

Sandstone with Mud Clasts

Thick-bedded gritty sandstone

Sandstone with Trough Cross-stratification

Crudely bedded Mudstone

Tidal Flat G, H, I, J, L

Sandstone with Wavy/Lenticular Bedding

Sandstone with Flaser Bedding

Sandstone with Wave Ripple

Sand-shale Interbed Sequence


Delta Front B, K, L

Sandstone with Mud Clasts

Massive Concretionary Mudstone


Facies L: Crudely bedded Mudstone

This facies is distributed in lower and upper member of Tilin Formation. This facies

mainly composed of bluish grey colored, massive or crudely bedded mudstone and about 170

to 3000 cm in thick (Fig. 6.d). The nature of boundary is gradational.

Interpretation

This facies may be deposited under the tidal channel and tidal mud flat environments

(Reineck and Singh, 1980).

Lithofacies Association

The combination of two or more facies, which were formed in a single depositional

environment at the same time, is grouped into a facies association. A facies association can

thus be used for more detailed interpretation of depositional environments. (12) lithofacies

have been classified on the basis of sedimentary structures, lithology and fossils. (4)

lithofacies associations were distinguished with respect to their lithology, facies successions

and bed geometry table (3). They are;

(1) Shoreface facies association

(2) Tidal channel facies association

(3) Tidal flat facies association and

(4) Delta front facies association

1. Shoreface facies association

The shoreface is always submerged under water, and the surface is usually made up of

submerged long shore bars with channels on their landward side. Generally, the structures



identified in lower shore face were planner cross-bedded sandstone of Facies E, bioturbated

sandstone of Facies F and sand-shale interbed sequence of Facies J. The upper shoreface

structures were.

Toward the deeper part of shoreface, cross-bedding is very rare and degree of

bioturbation is incresess (Reineck and Singh, 1980). Storm-dominated sandstone is underlain

by offshore mudstone and overlain by tidal channel or tidal flats. Lower shoreface and upper

shoreface can be seen in (Figs. 7 & 8).

2. Tidal channel facies association

The outer part of a tide-dominated estuary is the zone of strongest tidal currents,

which transport and deposit both fluvial derived sediment and material brought in from the

sea. In macro tidal regions the currents will be strong enough to cause local scouring and to

move both sand and gravel: quartz pebbles conglomerate (Facies-A) is common among the

gravelly detritus deposited as a lag on the channel floor (Reinson, 1992). Horizontal

laminated sandstone of facies-F, thick-bedded gritty sandstone facies-C and trough type

cross-laminated sandstone of facies-E are also indicated as tidal channel character. This

facies association is well defined as tidal channel facies (Figs. 7 & 8).

3. Tidal flat facies association

Tidal flats develop along the gently dipping sea coasts with marked tidal rhythms,

where enough dipping sea coasts with marked tidal rhythms, where enough sediment is

available and strong wave action is not present. The main part of the tidal flat is located

between intertidal zone and into the shallow portion of the subtidal zone. Consequently, the

sediments adjacent to the channel are typically sandy, and pass gradually into muds near the

high-tide line (Walker & James, 1992). There are three sub-environments of (1) sand flat, (2)

mixed flat and (3) mud flat in the intertidal zone.

The primary sedimentary structures of tidal flats association included flaser bedding,

interference ripples and lenticular bedding which were formed under tidal flat condition.

Facies G, H and I are as sandflat deposits. Facies J may be assigned to be deposited mixed

flat deposit and Facie L may be assigned to be deposited in the mud flat deposit (Reineck &

Singh, 1980) (Figs. 7 & 8).

Sand flat sub-environment: The sand flats which occupy the lower portion of most tidal

flats. Commonly contain flaser bedded sandstone of Facies H, interference ripples of Facies I

and lenticular bedding of Facies G (Walker and James, 1992).

Mixed flat sub-environment: The mixed flat are deposited when the fluvial and marine

influence both act in short period of time to deposit sediments. The structure identified in this

sub-environment is sand-shale interbed sequence of Facies J. The mixed flat are mostly

underlain by the sand flat or tidal channel and overlain by the mud flat or supratidal.

Mud flat sub-environment: The sediments deposition in muddy tidal flat in the studied

outcrop are characterized by area of inter-tidal mudflats that are covered at high tide and

exposed at low tide at the time of deposition. Generally, muddy tidal flat sediment was

deposited by massive or crudely bedded mudstone of Facies L.

4. Delta front facies association

Deltaic deposits are a substantial amount of coastal sediments incorporate deltaic deposits.

However, the recognization of deltaic deposits in ancient sediments may be very difficult,

because for definite recognization of a delta a regional variation in depositional



environments. The thickness of modern delta deposits varies from a few meters to several

tens of meters. Delta Front association include; Sandstone with mud clasts of Facies B,

massive concretionary mudstone of Facies K and crudely bedded mudstone of Facies L. Delta

front association can be seen deltaic depositional environment (Figs. 7 & 8).

Figure (7). Detailed sedimentological log of the Tilin Formation along Mu chaung and

Meinmahla chaung exposed at west and southeast of Taing Da village, Mindon

Township, Magway Region.

Depositional Environments

The Tertiary sediments recorded a history of infilling of the fore arc basin by marine

sediments from the south and non- marine deposits from the north. The process was

interrupted by marine transgressions and regressions, resulting in intertonguing of continental

and marine units (Chibber, 1934). Depositional environment of study the area may be

interpreted on the basis of sedimentary structures, texture and sedimentary facies. There are

four lithofacies association in the study area.

Lower part of Tilin Formation may also be deposited in shoreface, tidal channel and

tidal flat environments and upper part of the Tilin Formation may be deposited under the tidal

flat and delta front environments during the Early Eocene time.



Figure (8). Probable depositional facies model of the Tilin Formation in Taing Da area

(modified after internet image: www.google image/depositional

environments.com)

Summary and Conclusion

Tilin Formation is 3600m thick based on the stratigraphic measured sections. Twelve

lithofacies, which were grouped into four facies associations, were recognized. The base of

the Tilin Formation (lower member) represents a sequence deposited of shorefae deposits of

small scale planar type cross-bedding, bioturbation and sand-shale interbed sequence. Tidal

channel environment may be represent as quartz pebbles conglomerate, mud clasts, gritty

sandstone and trought cross-bedding. Tidal flat environment of wavy bedding, lenticular

bedding, flaser bedding, wave ripple and crudely bedded mudstone were deposited in lower

member of the Tilin Formation. The deposition of upper member of Tilin Formation

represents a sequence being formed from tidal flat to delta front environments. The crudely

stratified mudstone, concretionary mudstoneand mud clasts of delta front deposits and tidal

flat deposits were preserved in the upper member of the Tilin Formation. The upper part of

the Tilin Formation was deposited during Late Eocene Epoch.

Acknowledgements

First I would like to thank Dr Maung Maung, Principal of Myin Gyan Degree College for giving me a

seed of research minded to me. And the persons I ought to thank are my parents and the teachers from kindergarten to University.

Study Area

http://www.google/



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