Masoom Shani (Roll # 41)

Sedimentary Basins

Presented by:

BASIN FORMING PROCESSES

BASIN MARGIN CONCEPTS

Contents

Sedimentary basins are regions of the Earth of long term subsidence creating accommodation space for infilling by sediment.

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

Introduction Of Sedimentary Basins

Tectonism:

Tectonism represents the primary control on the creation and destruction of accommodation.

Without tectonic subsidence there is no sedimentary basin.

It also influences the rate of sediment supply to basin.

Basin Forming Processes

There are two principle mechanisms for tectonic Subsidence i.e.

1.Extension

2. Flexural loading

Causes of Tectonic subsidence

Extensional tectonics :

It is concerned with the structures formed and the tectonic processes associated with, the stretching of the crust or lithosphere.

Extension

The lithospheric flexure (regional isostasy) is the

process by which the lithosphere (rigid outer layer of the Earth) bends under the action of forces i.e.; the weight of a growing orogen or changes in ice thickness related to deglaciation.

Flexural Loading

Rate of tectonic subsidence is different in different basins, these are discussed below:

Extensional basins

Compressional basins

Strike slip basins

RATE OF TECTONIC SUBSIDENCE

They form in a variety of tectonic setting.

Most common on constructive plate margins.

These are also known as rift basins.

Very rapid subsidence caused by isostatic adjustment to lithosphere stretching.

Extensional (Rift Basin)

In these basins, tectonic subsidence rates vary systematically through time with an initial time period of very rapid subsidence caused by isostatic adjustment to lithosphere stretching by gradual and decreasing thermal subsidence phase as the asthenosphere cools.

These are developed in response of the loading of the lithosphere below thrust belts.

The lithosphere bends in response to loading as the thrust

sheets are emplaced and creates a depression that is stressed toward the load.

COMPRESSIONAL BASINS

These are also called foreland basins.

These are formed adjacent to growing mountain belts are characterized by large, and initially rapidly increasing rates of sediment supply.

Strike slip basins have no characteristic subsidence pattern,

although the rate of subsidence and uplift is extremely rapid.

These also called as pull apart basins.

STRIKE SLIP BASINS

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

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

Basin-Margin Types

with well develop depositional clinoforms

Typical of passive continental margins at times of slow rise of sea-level

Shelf Break 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 1ᴼ

Offlap break on a ramp margin is at shore line

Ramp Margin

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

Many modern delta systems can be considered to form ramp

margins.

Ramp Margin

Characterized basins undergoing active crustal extension

Distribution of sediments accommodation is controlled by tectonics

Subsidence rate increase from the margins to the center of the rift

Rift Margin

Foot-wall crest has the low subsidence then hanging-wall

clinoform slopes and relatively minor topsets

Rift Margin

Rate of tectonic subsidence increases towards the mountain front

Sediment accommodation is high in proximal area then basin center

This cause a thick topset deposits with little opportunity for clinoforms to develop

Foreland-Basin Margin

Characterized by gravity driven syn-sedimentary extensional faults

Rate of subsidence is greater on the hanging-wall side of the growth-fault

Growth-Fault Margin

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