Time and Stratigraphy Core COPYRIGHT PETROSKILLScloud1.activelearner.com/contentcloud/portals/... · Sequence Stratigraphy The study of rock relationships within a chronostratigraphic

Stratigraphic Laws and Geohistory

Time and Stratigraphy Core

Learning Objectives

By the end of this lesson, you will be able to:

Describe the six basic Laws of Stratigraphy (i.e. the study of Strataor Layers of the Earth):

Original Horizontality

Lateral Continuity

Superposition

Cross-cutting Relationships

Law of Inclusions

Law of Faunal Succession

Basic Geology_________________________________________________________________________________________________________Time and Stratigraphy Core

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COPYRIGHT PETROSKILL

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Stratigraphic Laws

Stratigraphic Laws are basic principles that all geologists use in deciphering the spatial and temporal relationships of rock layers

These laws were developed in the 17th to 19th centuries based upon the work of Nico Steno, James Hutton and William Smith, among others

The six Stratigraphic Laws are:• Original Horizontality

• Lateral Continuity

• Superposition

• Cross-cutting Relationships

• Inclusions

• Faunal Succession

Law of Original Horizontality

• Original Horizontality


• Superposition


• Inclusions


• Assumes that the sedimentary rocks are deposited in horizontal layers

• If the rocks are tilted or folded we can infer that they have been subjected to a deformation event

• In general, most sedimentary rocks are deposited horizontal or very close to horizontally



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Law of Lateral Continuity



• Superposition


• Inclusions


• Assumes that sedimentary rocks are laterally contiguous over large areas

• “Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way.” Steno, 1669

Law of Superposition



• Superposition


• Inclusions


• Assumes that most sedimentary rocks were originally deposited in horizontal layers (law of horizontality)

• Therefore, the oldest rocks will be on the bottom of the sequence and the youngest on the top



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Superposition in the Stratigraphic Column




• Superposition


• Inclusions


• Igneous intrusions and geological structures must be younger than the rocks they affect or cut across

• If things deposited horizontally have an igneous intrusion, then those rocks have been there before intrusions occurred

• If the rocks are faulted or folded, they have been there horizontal to begin with and were deformed after they were deposited



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Law of Cross-Cutting Relationships




• Superposition


• Inclusions


• Rock fragments (clasts) from another rock must be older than the rock containing the fragments

• For example, a sandstone that is made up of bits of igneous rock, indicates that the igneous rock was there first, got eroded, and the particles of the igneous rock make up the sandstone



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• Superposition


• Inclusions


• Fossils can be used to correlate sedimentary rocks

• Certain fossil groups are preceded or succeeded by other fossil groups. This allows for the development of a fossil stratigraphy that can be used around the world

• Fossils used for age dating and correlation of strata from one region to another are called Index Fossils.

Using Fossils for Correlation

Correlation of strata exposed at three localities many kilometres apart. The fossils show that at locality 3 stratum D is missing. Either D was never deposited there, or it has been removed by erosion before deposition of E.

Courtesy of John Wiley and Sons, Inc.



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Using Fossils for Marine / Non-Marine

Learning Objectives

Describe the six basic Laws of Stratigraphy (i.e. the study of Strata or Layers of the Earth):

Original Horizontality

Lateral Continuity

Superposition

Cross-cutting Relationships

Law of Inclusions

Law of Faunal Succession

You are now able to:



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Geologic Time and Stratigraphy


Learning Objectives


Differentiate between relative and absolute geological time

Use the geological time scale

Relate deposition to stratigraphic concepts

Differentiate between: Lithostratigraphy – based on rock type

Chronostratigraphy – based on time equivalence

Biostratigraphy – based on fossils Magnetostratigraphy – based on the rocks magnetic properties

Explain the connection between correlation, stratigraphy, and reservoirs



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The Standard Geologic Column

Principal Methods of Radiometric Age Determination (Absolute Time)



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Determining Relative Time using Radiometrics

Use Radiometric dating of Uranium, Thorium or Potassium in Igneous Intrusions for determining Relative Time

Standard Geologic Column with Atomic Dates



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Correlation

Correlation is:• The process of making the link between rocks from one area

with rocks from another area• The equivalence in the character and stratigraphic position

of the geological characteristics in two or more separate areas

If we measure geological formations in one place, how does it compare to

formations in another place?

Correlation of Stratigraphic Sections



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Log Correlation Across Peco Field, Alberta, Canada

Stratigraphy

Stratigraphy is:• The science of rock strata, considering their:

– Original succession– Age relations– Form– Distribution– Lithology– Fossils– Geophysical and geochemical properties– Mode of origin– Geological history

• The study of the layering of rocks



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Stratigraphic Concepts

Lithostratigraphy Chronostratigraphy Biostratigraphy

Lithostratigraphy


Description and organization of rocks into distinctive named units based on lithology and stratigraphic relations



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Example: Lithostratigraphic Correlation

Lithostratigraphic Correlation Independent of Time



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Chronostratigraphy


Deals with the age of strata and their time relations

Chronostratigraphically Events, Independent of Lithostratigraphic Correlation



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Cross-Section Showing Geographic Distribution of Formations and Facies Changes

View of Fluvial Sand Outcrop and Facies Changes



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View of Fluvial Sands in Electric Log Cross Section

View of Fluvial Sands in Electric Log Cross Section showing Facies Changes

Facies Changes



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Biostratigraphy


The distribution of fossils in the stratigraphic record and the organization of strata into units based on their contained fossils

Subsurface Correlation Between Wells Using Fossils



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Examples of MicroFossils used in Correlation

Typical Size of MicroFossils used in Correlation



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Selected Other Types of Stratigraphy

Magnetostratigraphy• Plate tectonics is based on magneto stratigraphy

• The iron-rich minerals in magma orient themselves to magnetic north. When ready to turn solid, those crystals will get locked in place and can be used as an indicator of north or south.

Chemostratigraphy and Isotope Stratigraphy• Use specific minerals or chemical signatures that help

understand world temperatures and get a chronostratigraphic marker based on them



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Key Concepts of Stratigraphy

Accommodation

• The space available for sediment accumulation between sea level and sea floor

Refs. SEPM Special Publication No. 42, 1988

Jackson, J., 1997, Glossary of Geology, American Geological Institute

Accommodation Envelope as a Function of Eustasyand Subsidence



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Key Concepts of Stratigraphy

Eustasy – (Sea level change) – a condition of worldwide sea level fluctuations influenced by:

• Global hydrologic balance, glaciation, ground water

• Ocean basin capacity, subsidence

• Plate tectonics, heat flow, subduction

Refs. SEPM Special Publication No. 42, 1988

Jackson, J., 1997, Glossary of Geology, American Geological Institute

First- and Second-Order Global Cycles of Relative Change of Sea Level During Phanerozoic Time



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Base Level and Stream Profile

Aggradation



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Sediment Loading on the Continental Shelf Results in Thick Sediment Wedges

Lowstand Base Level and Stream Profile



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Progradation

Highstand Base Level and Stream Profile



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Retrogradation

Learning Objectives


Differentiate between relative and absolute geological time

Use the geological time scale


Differentiate between: Lithostratigraphy – based on rock type Chronostratigraphy – based on time equivalence

Biostratigraphy – based on fossils

Magnetostratigraphy – based on the rocks magnetic properties

Explain the connection between correlation, stratigraphy, and reservoirs



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Sequence Stratigraphy


Learning Objectives


Define Sequence Stratigraphy terminology

Recall how to use Highstand and Lowstand system tracts in exploration


Describe the connection between correlation, stratigraphy, and reservoirs



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Sequence Stratigraphy

The study of rock relationships within a chronostratigraphic framework of repetitive, genetically related strata bounded by surfaces of erosion or nondeposition, or their correlative conformities.

Key terms:• Unconformity• Parasequence• Sequence• Systems Tract• Maximum Flooding Surface• Condensed Section

Unconformity

Unconformity: A surface separating younger from older strata, along which there has been subaerial erosion or exposure for a significant amount of time

Parasequence: A relatively conformable succession of genetically related beds bounded by flooding surfaces of their correlative surfaces

Sequence: A relatively conformable succession of genetically related strata (parasequences) bounded by unconformities of their correlative conformities

Systems Tract: A rock body linking contemporaneous depositional systems, i.e., highstand, lowstand, transgressive systems tracts

Maximum Flooding Surface: The surface corresponding to the greatest landward extent of a marine transgression

Condensed Section: A thin, very slowly deposited section of sediments laid down during rising sea level when there was very low input of terrigenous sediment on the shelf



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Illustration of a Unconformity (Erosional Surface)

Parasequence









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Parasequences



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Sequence







Physical Boundaries of a Sequence



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When Sea Level Falls, a New Set of Conditions is Created, Starting a New Sequence

Systems Tract









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All Deposits are Genetically Related

Highstand Systems Tract

Package of Sedimentary Units Deposited When Sea Level is High



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Lowstand Systems Tract

Package of Sedimentary Units Deposited When Sea Level is Low

Lowstand Systems Tract

Lowstand Wedge – Type 1 Sequence



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Location of Shoreline, Gulf Coast During Last Lowstand

Transgressive Systems Tract

Package of Sedimentary Units Deposited as Sea Level Rises



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Highstand Systems Tract

Package of Sediments Deposited While Sea Level is High

Maximum Flooding Surface and Condensed Section









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Illustration of Maximum Flooding Surfaces and Condensed Section

Learning Objectives


Define Sequence Stratigraphy terminology

Recall how to use Highstand and Lowstand system tracts in exploration


Describe the connection between correlation, stratigraphy, and reservoirs



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PetroAcademyTM Basic Geology Core

Earth Materials Core


Plate Tectonics and Structure Core

Subsurface Investigation Core

Erosion and Subaerial Depositional Environments Core

Marginal Marine Depositional Environments Core

Marine Depositional Environments Core

Generation and Migration Core and Unconventionals



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Time and Stratigraphy Core COPYRIGHT PETROSKILLScloud1.activelearner.com/contentcloud/portals/... · Sequence Stratigraphy The study of rock relationships within a chronostratigraphic