Basin margin concept

Presented to: Dr. Kamran Mirza Presented by:

M. Wajid Manzoor Roll No: 09

Institute of Geology Uuniversity of the Punjab Lahore

Contents

Introduction Mechanism of basin formation Basin classification Basin margin Sedimentary basins in Pakistan Distribution of sedimentary basin types in the world Basin and sequence stratigraphy References

INTRODUCTION Sedimentary basins are regions of the

earth of long term subsidence creating accommodation space for infilling by sediments

It is also defined as, “ A low lying area/depression where sediments can be deposit is called sedimentary basin.”

Basin is formed by crustal subsidence relative to surrounding areas or some time surrounded area may be uplifted

Basin have different shapes and sizes & formed by different mechanisms

Mechanisms of Basin Formation

Major mechanisms for regional subsidence/uplift: o Isostatic – changes in crustal or lithospheric thicknesso Loading – by thrust sheets, volcanic piles,o Dynamic effects – asthenospheric flow, mantle convection,

plumes

Basin Classification

Basin-generating tectonics is most important for the accumulation of sediments. Such a basin classification must be in accordance with the modern concept of global plate tectonics and hence will differ from older classifications and terminology.

• Sedimentary basins associated with plate tectonic activity.

Types of plate boundaries

There are three types of plate boundaries, characterized by the way the plates move relative to each other.

o Divergent boundaries • two plates slide apart from each other. • Mid Oceanic ridgeso Convergent Boundaries • two plates slide towards each other • Subduction • Orogenic Belt

o Transform Boundaries• plates move parallel to each

other• Strike-slip systems

Basin margin concept

The response of the depositional systems to this fall in relative sea level depends on the nature of the basin margins.

o Shelf-break marginso Ramp margins o Rift margins o Foreland basin margins o Growth –fault margins

Shelf break margin

Shelf break margin are those with well developed depositional cllinoforms

Shelf break margin are typical of passive continental margins at times of slow rise of relative sea level, when the deltaic system can easily prograde to the shelf edge.

Ramp margin

Ramp margins are characterized by relatively shallow water depths, where storms and current processes can operate much of the area of deposition.

Depositional angles are less than 1°. The response of depositional

systems in a ramp setting to the relative sea-level change is therefore different from the shelf-break margins.

Rift margins

Rift margins characterize basins undergoing active crustal extension.

These margins are characterized by high topographic relief.

Subsidence rates generally increase from the margins to the center of the rift, although each individual fault block will have its own pattern of accommodation.

Foreland Basin Margins

A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. 

The rate of tectonic subsidence increases towards the foreland thrust belt.

Sediment accommodation may be relatively high in proximal area compared with the basin center.

Growth fault margin

Growth fault margins are characterized by gravity driven syn-sedimentary extensional faults.

The rate of subsidence is considerably greater on the hanging wall side of the growth fault, resulting in an expanded sedimentary succession.

Arc-related basins

Forearc and backarc basins dominated by sediment derived from arc

Forearc Basin

The area between the accretionary wedge and the magmatic arc, largely caused by the negative buoyancy of the subducting plate pulling down on the overlying continental crust

tens of kilometers to over one hundred kilometers wide &up to thousands of kilometers long; commonly arcuate.

Nonmarine siliciclastic fluvial to deltaic deposits

Backarc or interarc Basin

Backarc or interarc basins form by rifling and ocean spreading either landward of an island arc, or between two island arcs which originate from the splitting apart of an older arc system

The evolution of these basins resembles that of normal ocean basins between divergent plate motions.

Their sedimentary fill frequently reflects magmatic activity in the arc region.

Sedimentary basins in Pakistan

There are two major basins in Pakistan o Indus Basin o Balochistan Basin There are some minor basins namely; o Kirthar fold-belt basino Pishin fold-belt basin o Sulaiman fold-belt basin o Makran fold-belt basin o Offshore Indus basin

Distribution of sedimentary basin types in the world

Basins and Sequence Stratigraphy

Patterns, rates of subsidence and sediment supply can be strongly influenced by tectonic processes that are responsible for forming some basins

Temporal and spatial changes in these factors can significantly affect sequence development in those basins

Towards shelf margin – rate of subsidence is always greater than rate of eustatic fall

No fall of relative sea level

Further landward – rate of subsidence is less than rate of eustatic fall

Fall of relative sea level possible Area covered by each zone will change with time, basin to

basin When a discrete shelf margin is present, shelf margin

sediments may be thick even in the absence of rapid thermal/tectonic subsidence

References

Basin Analysis By Philp A. Allen & Jhon A. Allen 2nd edition Internet ( Wikipedia ) Sequence stratigraphy by D.Emery and K.J.Myers Sedimentology and stratigraphy by Sam Boggs 4th edition Sedimentology and Stratigraphy by Wiley-Blackwell.Gary

Nichols 2nd edition