Field Trip to SQU_ Sedimentary Rock MAIN

8/3/2019 Field Trip to SQU_ Sedimentary Rock MAIN

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Sultan Qaboos University

College of Science

Department of Earth Science

Report:

Field Trip to SQU Commerce

Parking Area Cross Section

Done By:

1. Mohammed Saif Salim Al Hosni ID# 703992. Saif Haroon Al Balushi ID# 706133. walid al khzairi ID# 694334. Nasser Sultan Mohammed Al Habsi ID# 706255. Mohammed Sultan Al Busaidi ID# 558216. Hamad Nasser Al Sinani ID# 70248

Instructor: Dr. Rushdi Sadaqah

Date: 27 December 2009

Mohamme

d Al-Hosni

Digitally signed by Mohammed Al-

Hosni

DN: cn=Mohammed Al-Hosni, o,

ou=Oman GEOP,

[email protected], c=OM

Date: 2012.02.04 17:37:44 Z


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Abstract:

This report will cover the various characters of the lithofacies in a vertical cross

section which is composed of sedimentary rock; each lithofacies will be

discussed in term of its color, texture and composition. The data is obtained

from the direct examination of the rock units, a vertical section with a true

thickness scale and applying the knowledge from the course of "sedimentary

Petrology" Book1. The main rock units found in the area are conglomerate and

sandstone. The final interpretation of the depositional environments aremostlyto be lagoon and fluvial.

Introduction:

This report is concerned about the various data in the rock units at the study

area. The area of study is SQU College of Commerce road cut for the new car

parking area, the east cross section. The field was conducted on 15 April 2009.

The cross section is fresh and clear, with distinctive rock units depending on

their lithology. The main rock units in the study vertical section are

conglomerate and sandstone. Each rock unit will be discussed in term of

thickness, color, texture, composition, sedimentary structure and depositional

environment. The rock units texture will cove the grain size, grain shape, sorting

and grain contact. The interpretation of the depositional environment will be

only on the basis of the data obtained and identified in the field area. The report

contains astrip log of the vertical section with a true thickness scale (using handsketch), a sketch of the overall texture and a description about the depositional

processes.

1 "Sedimentary Petrology" 3rd Edition, by Maurice E. Tucker


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Fi 1.1 Grain Color, Grain Size, Grain Fabric

1. Layer One:

The first layer in the outcrop is a thick conglomerate unit with a thickness of

1.95 meters. The bed is dipping by an angle of (25 degree) towards East

direction with an abrupt contact with the lower unit. The clastics at the

bottom of the bed are coarser than the top of the bed.

1.1Color:

The conglomerate unit consists of a fine green color matrix which

indicates the presence of sulfur mineral. The clastics are mixture of

several colors such as dark red chert - From the Hawasina Super Group

which produced by oxidization due to the fluid circulation in the deep

ocean from both poles to the equator2. Other calstics are orange, black and

dark grey in color see (Fig. 1.1).

1.2. Texture:

1.2.1 Grain Size:

The matrix is very fine grain, it is estimated that it is less than

63. The clastics are mostly more than 2cm in diameter with a

maximum grain diameter of 6cm which is between the medium pebbles

to fine cobble see (Fig.1.1).

1.2.2. Grain Shape & Sorting:

The clasts in the conglomerate bed are rounded to subrounded

due to abrasion and collision of clastics with the surface, which indicate

the long transportation distance as a bed load. Most of the clastics are

prolated (extended spheres). The grains are poorly sorted due to the

presence of the fine matrix with large clastics which indicate that it's a

fluvial deposit see (Fig.1.1).

2 Personal information by Dr . Rushdi Sadaqah


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Fig 1.2 Oxidization spots by Hematite, Green Matrix "Gluconite

Fig 1.3 Gypsum veins, Clear photo, across the whole sequence

1.2.3. Grain Fabric:

The bed is grain supported with mostly point contact

"orthoconglomerate". The clastics have no preferred orientation. The

packing is moderately close due to the fine matrix, but it's no cemented

as a hard non-porous rock, which indicate medium to low porosity and

permeability see (Fig.1.2).


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1.3. Composition:

The matrix is composed of sulfur minerals, an authegenic mineral

(Gluconite) with a mixture of calstics from various origins such as: red

Chert from Hawasina supergroup. This mixture indicates that the

conglomerate is extraformational.

1.4. Sedimentary Structure:

A dark orange oxidization spots by Hematite where recognized at the

surface of the outcrop and between the clastics and the matrix see (Fig 1.2).

Thin sheets like vines of pure white Gypsum are cutting across the unit see

1.5. Interpretation:

From the data above a table with the various characters of the unit with

the possible depositional environments is shown (Table 1.1).Table 1.1 characters of the unit with possible depositional processes, environment and

source area

The most acceptable processes are that the source area was a high land with

different origin rocks, in a humid environment fluvial /lagoon environment, the

clastics were transported for along distance and then subjected to burial,

compaction and diagenesis , which form the gluconite matrix.

2. Layer Two:

This layer is also a thick conglomerate unit with thickness of 2.5 meter; the

contact between the two beds is gradual, by changing the cement color and

composition.

2.1 Color:

The matrix is light gray cement. The clastics are with various color, such

as: black, dark gray, green and dark red. This variation in color indicatesthat the conglomerate is extraformational see (Fig 2.1).

Color GrainSize/Sorting

Grain Shape Grain Fabric Compsition

Feature

present

Matrix:Green

(sulfur)

Clastics:

Various colors

Fine matrix

with large

clastics,

poorly sorted

Rounded to

subrounded ,

prolated

grain

supported,

point

contact

Sulfur

minerals,

varius

clastics

Possible

processes

/environment

/Area

Matrix:

gluconite,

diagenesis

Clastics: source

area

mountain,etc.

Fluvial,

channels,

Long

transportation

by fluvial,

abrasion

Channels,

stream

flood,

fluvial

Sulfur:

indicate

lagoon env.

Clastics:

different

origin source

area, such as

basement

rock, deep

sea chert


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2.2 Texture:

2.2.1 Grain size:

The matrix is very fine cement with size of less than 63

whereas The Grains are mostly between (3mm granular to 20 mm

coarse pebbles) see (Fig 2.1).

2.2.2 Grain shape and Sorting:The clastics are rounded to subrounded; the conglomerate is poorly

sorted due to the presence of the fine cement see (Fig 2.1).

2.2.3 Grain Fabric:The conglomerate is grain supported (orthoconglomerate), the

matrix is a rigid cement. The packing is dense and the presence of

cement makes it with low porosity and permeability see (Fig 2.1).

2.3 Composition:The clastics are of various origins, such as basement rock and deep

marine Chert, basalt and metamorphosed rock, which indicate that the

conglomerate is Extraformational.

2.4 Sedimentary Structure:The conglomerate bed is massive with a gypsum veins sheets and

some oxidization spots.

Fig 2.1 Grain color, Grain size, Grain fabric


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2.5 Interpretation:From the data obtained above the following table gives the

possible depositional system, processes and area of the weathered

sediment see (Table 2.1).

From this data this layer was deposited as following: the various rock fragment

were subjected in the mountain were subjected to weathering, these fragment

transported far away from their source area by water current. The calstics wheredeposited along with the cement which gives the bed it's very rigid character.

3. Layer Three:

This Layer consists of two parts, the lower part is red sandstone, and the upper

part is greenish sandstone.The thickness of the layer is about 0.7 meter. It

consist mainly from coarse grain sand and also contains some granular to

pebbles clastics inter-bedded in the sand randomly or as small groups see (Fig

3.1).

3.1Color:The lower part is orange to dark orange sand size grains, which indicate the

presence of Hematite in an oxidization environment. The upper part is green to

grey sand size grains, which indicate the presence of sulfur minerals see (Fig

3.1). The granular to pebbles size fragment are of various colors.

3.2Texture:3.2.1 Grain size:

The main grains are coarse sand size grains; some clastics ofgranular to fine pebbles are present.

Color Grain

Size/Sorting


Feature

present

Matrix: light

grey by

siliciclastics

Clastics:

Various colors

Fine matrix

with large

clastics,

poorly sorted

Rounded to

subrounded ,

prolated

grain

supported,

Detrital

cement ,

mixture of

various rock

fragment

Possible

processes

/environment

/Area

Matrix: detrital

sediment.

Clastics: source

area

mountain,etc.

Fluvial,

channels,

Long

transportation

by fluvial,

abrasion

Channels,

stream

flood,

fluvial

Clastics:

different

origin source

area, such as

basementrock, deep

sea chert,

basalt

Table 2.1 characters of the unit with possible depositional processes, environment and source area


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3.2.2 Grain shape and sorting:Sand grins are subrounded, whith some subrounded granular.

The layer is poorly to moderately sorted because of the presence of the

large clastic in the coarse sand.

3.2.3 Grain Fabric:The sandstone is well packed with no preferred orientation. The

layer is with low porosity and permeability due to the difference in grain

size.

3.3Composition:The sand grins contain iron minerals (Hematite), which is result of land

(detrital) sediment.

3.4Sedimentary Structure:The main sedimentary structure found is the gypsum veins. The clastic

layer shows no lamination.

3.5Interpretation:From the data in layer three the following table is constructed see (Table

3.1).

Fig 3.1 Layer3 Color, Grain Color, grain Fabric, Sorting

Orange color sandstone (Litharenite)

Green color sandstone (Litharenite)


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Table 3.1 characters of the unit with possible depositional processes, environment and

source area.

4. Layer four:

This layer has a thickness of 1.8 meter. The layer consist of two parts:

the lower part is a conglomerate with pebbles clastics, and the upper part is

sandstone interbedded with a conglomerate with fine pebbles see (Fig 4.2).

4.1Color:The conglomerate contains a light grey with some parts of a green color

matrix. The clastics are of various colors such as: red, black, light green

and dark brown see (Fig 4.1).

4.2Texture:

Color GrainSize/Sorting


Feature

present

Orange coarse

sand, possible

hematite

mineral,

Green sand,

possible sulfur

mineral

Clastics of

various color

Coarse sand

size grains,

some clastics

and thin

conglomerate

bed, poorly

sorted

Rounded to

subrounded

No

orientation,

low

porosity,

massive bed

Coarse sand

size rock

fragments,

clastics of the

conglomerate

of various

origin

Possible

processes

/environment

/Area

Fluvial

environment,

possible iron

containing rocks

and sulfur ,clastics

Fluvial

deposit,

change in

current speed

to deposit thelarge clastics

fluvial,

abrasion, the

sand grains

indicate a

long distancefrom source

area.

Channels,

streams,

fluvial,

Lower part:

iron

containing

parent rock.

Upper part:sulfur

containing

parent rock

Fig 4.1 Layer4 Color, Grain Color, grain Fabric, Sorting


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Fi 4.2 Nodules structure and oxidization s ots

4.2.1 Grain size:The conglomerate clastics are ranging from 3 mm

granular to 16 mm coarse pebbles with a sand size matrix. The

sand grains are a mixture of finem medium and coarse sand.

4.2.2 Grain shape and Sorting:The conglomerate clastics are rounded to subrounded.

The matrix is a mixture of very fine mud and rounded sand

grains.

4.2.3 Grain Fabric:There is no preferred orientation; the conglomerate is

with low porosity and permeability due to the cement. The

sandstone is moderately porous and permeable.

4.3Composition:The conglomerate contains a mixture of calastics such as: chert, basalt

and slate. The cement is mixture of fragment and fine grains detrital cement.

The sandstone is mainly rock fragment (litharenite) from various origins.

4.4Sedimentary Structure:The gypsum vein crossing the layer is present. The oxidization spots are

also present in the unit. Another structure is a spheres of grains compacted

together, which may represent a nodules formed during diagenesis see (Fig

4.2).

4.5Interpretation:From the data about layer five, the following table is constructed

see (table 4.1). The change from conglomerate to sandstone was due to the

change in water current speed. The conglomerate part of the unit subjected

to cementation and sandstone part formed the nodules structure duringdiagenesis.


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Table 4.1 characters of the unit with possible depositional processes, environment and

source area.

5. Layer five:

This layer is the have the same characters of the lower part of layer

three, it consist of orange to grey litharenite sandstone.

5.1 Color:

The main unit color is red, with some grey- green color parts. The rock

fragment are of various color such as: green, dark grey and derk red. The

red color is concentrated more in the very coarse sand beds.

5.2 Texture:

5.2.1 Grain size:

The grains are mainly medium sand grains with small

beds of very coarse sand.

5.2.2 Grain shape and Sorting:The grains are rounded to subrounded, the bed is poorly to

moderately sorted.

5.2.3 Grain Fabric:The bed has no preferred orientation, and the grains are moderately

packed which gives it a moderate porosity and permeability.

Color Grain

Size/Sorting


Feature

present

Conglomerate:

matrix is grey

and green,

clastics of

mixture of

colors,

/sandstone:green

sand and colored

fragment

Conglomerate:

poorly sorted,

large clastics

sandstone:

poorly sorted ,

small

fragment

Rounded to

subrounded ,

Conglomerate:

matrix

supported ,no

preferred

orientation,

Conglomerate:

different

origin clastics,

cement,

Sandstone:

rock fragment

(litharenite),

fine green

color grains

Possibleprocesses

/environment/Area

Conglomerate:extraformational,

different origin,sandstone: green

diagenetic

mineral,

fragment of

various origin.

Fluvial,channels

deposits andchanging in

current speed

Longtransportation

by fluvial,abrasion

Channels,stream flood,

fluvial

Clastics:

differentorigin source

area, such as

basement

rock, deep sea

chert, basalt

- Green color

grains

(authiginic)


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5.3 Composition:The main lithic fragments are of various color, which indicate different

origin, the orange color fine sand indicate the presence of hematite which

means a rock containing iron minerals.

5.4 Sedimentary Structure:A gypsum vein is cutting as a sheet across thee layer. The coarse grain

sand makes a lens like shapes inside the layer.

5.5 Interpretation:Table 5.1 characters of the unit with possible depositional processes, environment andsource area.

Color Grain

Size/Sorting

Grain Shape Grain Fabric Composition

Feature

present

Orange coarse

sand, possible

hematite

mineral,

Coarse sand

size grains,

some clastics,

poorly to

moderately

sorted

Rounded to

subrounded

No

orientation,

Coarse sand

size, rock

fragments,

Possible

processes

/environment

/Area

Fluvial

environment,

possible iron

containing rocks

Fluvial

deposit,

change in

current speed

to deposit thelarge grains

sand

fluvial,

abrasion, the

sand grains

indicate a

long distancefrom source

area.

Channels,

streams,

fluvial,

High

porosity

iron

containing

parent rock,

different

origin sourcearea


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Appreciation:

I would like to thanks Dr.Rushdi Sadaqah for his effort in arranging this Field

trip and for his explanation about the study area.

Conclusion:

The Field trip was a powerful tool in which it teaches as how to recognize the

different lithofacies and analyze the various characters of the rocks units. We

where able to recognize the conglomerate with its parameter, and the

interpretation of the depositional environment expand our knowledge about the

paleography of the tertiary time. These lithiofacies are believed to be deposited

by the some process which mainly a siliciclastic sequence. The conglomerate

with the large rounded clastics indicate a fluvial current with high energy in

which the clastics where transported for a long distance. The overlaying

cemented conglomerate with small clastics indicates a reduction in the current

speed, and the sandstone with the coarse grain indicates a further reduces in the

speed current or a long distance from the source area. The increase in the grain

size to form the conglomerate and the decrease is mainly by fluctuation in the

current speed and transportation distance.

Field Trip to SQU_ Sedimentary Rock MAIN

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