primary sedimentary structures

IN THE NAME OF ALLAH THE IN THE NAME OF ALLAH THE MOST BENEFICIENT AND THE MOST BENEFICIENT AND THE

MOST MERCIFUL MOST MERCIFUL

PRESENTATIONPRESENTATION

SUBJECT STRUCTURAL GEOLOGYSUBJECT STRUCTURAL GEOLOGY

NAME MOHAMMAD SOHAIBNAME MOHAMMAD SOHAIB

ROLL NO 195ROLL NO 195

SECTION EVENING BSECTION EVENING B

PRIMARY SEDIMENTARY PRIMARY SEDIMENTARY STRUCTURESSTRUCTURES

Different types of structures formed Different types of structures formed in sedimentary rocks during in sedimentary rocks during deposition are known as primary deposition are known as primary sedimentary structures. sedimentary structures.

Types of primary sedimentary Types of primary sedimentary structuresstructures• 1 Graded bedding1 Graded bedding• 2 Ripple marks2 Ripple marks• 3 Mud cracks3 Mud cracks• 4 Flute casts4 Flute casts• 5 Imbrications5 Imbrications• 6 Rain pits6 Rain pits• 7 Bioturbations7 Bioturbations• 8 Flame structures8 Flame structures• 9 Load casts9 Load casts• 10 Amygdules10 Amygdules• 11 Pillow lavas11 Pillow lavas

GRADED BEDDINGSGRADED BEDDINGS

In graded bedding there is an upward In graded bedding there is an upward fining sequence of sediments.fining sequence of sediments.

Normally fine sediments are on the top Normally fine sediments are on the top and coarse sediments on the bottom.and coarse sediments on the bottom.

Graded detrital rocks are deposited by Graded detrital rocks are deposited by turbidity currents.turbidity currents.

Graded bedding is helpful in Graded bedding is helpful in finding top and bottom of bedsfinding top and bottom of beds

Ripple MarksRipple Marks

• These are wave like structures formed on the These are wave like structures formed on the top of beds.top of beds.

• These help us in finding top and bottom of beds.These help us in finding top and bottom of beds.

• These also tell us about the paleocurrent These also tell us about the paleocurrent directions.directions.

There are two type of ripple marksThere are two type of ripple marks

1. Symmetrical ripple marks1. Symmetrical ripple marks

2. Asymmetrical ripple marks2. Asymmetrical ripple marks

ASYMMETRICAL RIPPLE ASYMMETRICAL RIPPLE MARKSMARKS

Moving waters produce asymmetrical Moving waters produce asymmetrical ripples.ripples.

SYMMETRICAL RIPPLE SYMMETRICAL RIPPLE MARKSMARKS

• These are formed by back and forth These are formed by back and forth movement of water. movement of water.

• These are helpful in finding top and These are helpful in finding top and bottom.bottom.

• These do not tell about direction of These do not tell about direction of currents.currents.

MUD CRACKSMUD CRACKS

• These are also known as sun cracks.These are also known as sun cracks.

• These are formed in muddy and silty These are formed in muddy and silty sediments.sediments.

• These are formed due to evaporation These are formed due to evaporation of water from sediments.of water from sediments.

• These tell about top and bottom of These tell about top and bottom of beds and also about the paleo-beds and also about the paleo-environments.environments.

Mud cracks Mud cracks

Mud cracks that have been filled by sandMud cracks that have been filled by sand

LOAD CASTSLOAD CASTS

• These are also known as load These are also known as load structures.structures.

• These are formed on the bottom of These are formed on the bottom of certain type of beds.certain type of beds.

IMBRICATIONSIMBRICATIONS

• This is mostly seen in gavels and This is mostly seen in gavels and conglomerates.conglomerates.

• The gravels dip upstream, i.e. The gravels dip upstream, i.e. opposite to the direction of moving opposite to the direction of moving water.water.

Picture showing Picture showing imbricationsimbrications

FLUTE CASTSFLUTE CASTS

• These are asymmetrical structures These are asymmetrical structures found on bottom of bedsfound on bottom of beds

• These are formed where turbidity These are formed where turbidity currents are common. currents are common.

Picture showing flute castsPicture showing flute casts

RAIN PITSRAIN PITS

• These are formed by impact of rain These are formed by impact of rain drops on unconsolidated sediments.drops on unconsolidated sediments.

• These are always found on top of These are always found on top of beds.beds.

• These are helpful in finding top and These are helpful in finding top and bottom of a bed.bottom of a bed.

THE ENDTHE END