This document discusses sedimentary basin formation processes and basin margin concepts. It describes how tectonism controls the creation and destruction of sedimentary basins through subsidence. The two main mechanisms for tectonic subsidence are extension and flexural loading. Extensional basins form in rift settings and experience rapid initial subsidence that decreases over time. Compressional basins, also called foreland basins, form in response to lithospheric bending under thrust belts. Strike-slip basins have irregular subsidence patterns. Basin margins include shelf-break, ramp, rift, and growth-fault margins, which influence depositional responses to sea level changes.

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(Roll # 41)
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3.  BASIN FORMING PROCESSES
 BASIN MARGIN CONCEPTS

4. 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.”

5. 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.

6. There are two principle mechanisms for tectonic
Subsidence i.e.
1.Extension
2. Flexural loading

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

10. 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.

12.  Rate of tectonic subsidence is different in different
basins, these are discussed below:
 Extensional basins
 Compressional basins
 Strike slip basins

13.  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.

14.  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.

18.  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.

19.  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.

22.  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.

28.  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

29.  with well develop depositional clinoforms
 Typical of passive continental margins at times of
slow rise of sea-level

31.  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

32.  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.

34. 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

35.  Foot-wall crest has the low subsidence then hanging-wall
 clinoform slopes and relatively minor topsets

37.  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

39. Characterized by gravity driven syn-sedimentary
extensional faults
Rate of subsidence is greater on the hanging-wall side of
the growth-fault

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