Sequence Stratigraphy

Name: Rishabh Tripathi & Kumar Shantanu.Roll Numbers:R080114031&R080114016

INTRODUCTIONSequence Stratigraphy is a branch of geology that attempts to subdivide and link sedimentary deposits into unconformity bound units on a variety of scales and explain these stratigraphic units in terms of variations in sediment supply and variations in the rate of change in accommodation space (often associated with changes in relative sea level).

It is mostly for marine sediments but with modifications it can be used for terrestrial accumulations.

Types of Sea Level

• Relative Sea Level.• Eustatic Sea Level.

Accommodation Space Equation

T+E=S+W where,• T is the rate of tectonic subsidence• E is the rate of eustatic sea-level rise • S is the rate of sedimentation • W is the rate of water depth increase (or

deepening)

Causes of change in Sea Level

Eustatic Sea level:• Glaciation, ocean temperature, and the

volume of groundwater.• Changes in the distribution of mass on Earth,

caused by mantle convection and plate tectonic motion.

Relative Sea level:• Tides.• Winds• Ocean currents.

Causes of change in tectonic subsidence

• Three main mechanisms.• –Stretching• –Cooling• –Loading

TERMINOLOGIES IN USE

• Parasequence: Parasequences are defined as a relatively conformable succession of genetically related beds or bedsets bounded by marine flooding surfaces and their correlative surfaces.

• Progradation: sequence means seaward movement of a shoreline.

• Retrogression: sequence means continent ward movement of a shoreline.

• Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level.

• Marine transgression, occurs when flooding from the sea covers previously exposed land.

Parasequence Sets and Stacking Patterns• There are 3 types of stacking patterns that we

observe:-• Progradational stacking: In a progradational set of

parasequences, each parasequence builds out or advances somewhat farther seaward than the parasequence before.

• Aggradational stacking: In an aggradational set of parsequences, each parasequence progrades to roughly the same position as the previous parasequence.

• Retrogradational stacking: In a retrogradational set of parasequences, each parasequence progrades less than the preceding parasequence.

DEPOSITIONAL SEQUENCE

• A depositional sequence is defined as a relatively conformable succession of genetically related strata bounded by subaerial unconformities or their correlative conformities.In addition, every depositional sequence is the record of one cycle of relative sea level.

• As a result, depositional sequences have a predictable internal structure of surfaces and systems tracts

SYSTEM TRACTS

• A discrete package of distinctive sediment types (facies) that are laid down during different phases of a cycle of sea-level change.

• Highland systems tract.• Falling stage system tracts.• Lowland system tracts.• Transgressive systems tract.

HIGHSTAND SYSTEM TRACTS

FALLING-STAGE SYSTEM TRACT

LOWSTAND SYSTEM TRACTS

TRANSGRESSIVE SYSTEM TRACTS

SEQUENCE BOUNDARIES

• The sequence boundary is an unconformity up dip and a correlative conformity down dip.

• Transgressive Surface:- separates LST from TST.

• Major flooding Surface:- separates TST from HST.

• Basal surface of forced regression:- separates FSST from LST.

• Unconformity separates HST from FSST.

THANKYOU