stratigraphic principles

8/13/2019 Stratigraphic Principles

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Contents

Introduction

Unconsolidated clastic sediments

Sedimentary rocks

Diagenesis

Sediment transport and deposition

Sedimentary structures

Facies and depositional environments

Glacial/eolian/lacustrine environments Fluvial/deltaic/coastal environments

Shallow/deep marine environments

Stratigraphic principles

Sequence stratigraphy

Sedimentary basins

Models in sedimentary geology

Applied sedimentary geology

Reflection


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Salvador, A. (Editor), 1994. International Stratigraphic Guide. A Guide to

Stratigraphic Classification, Terminology, and Procedure.

Geological Society of America, Boulder, 214 pp.

The Bible of

stratigraphic

classification


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Type sections(stratotypes) constitute the standard ofreference for definition and recognition of a stratigraphic unit orstratigraphic boundary; they are defined where these are

representative and well developed

Stratigraphic relationships can be inferred from the principle ofsuperposition, unconformities, cross-cutting relationships,included fragments, and way-up indicators


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Type sections(stratotypes) constitute the standard ofreference for definition and recognition of a stratigraphic unit orstratigraphic boundary; they are defined where these are

representative and well developed

Stratigraphic relationships can be inferred from the principle ofsuperposition, unconformities, cross-cutting relationships,included fragments, and way-up indicators


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Lithostratigraphy

The formationis the fundamental unit of lithostratigraphic

classification; just as the other lithostratigraphic ranks (groups,members, beds), it should be based on field description (i.e.,fossil content and age do notplay a role)

Mode of deposition (genesis) is nota criterion in the distinctionof lithostratigraphic units; this requires interpretation and istherefore likely to undergo revision over time

Lithostratigraphic units should have some degree of overalllithologic homogeneity, although diversity in detail may in itselfcharacterize a lithostratigraphic unit


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Lithostratigraphy

Lithostratigraphic units are commonly diachronous, as

opposed to chronostratigraphic units Detailed geologic mapping is usually strongly based on

lithostratigraphy, whereas overview geologic maps usually showchronostratigraphic units

Although objective lithostratigraphic classification should be assimple and straightforward as possible, reality demonstratesthat this is not always the case; as a result, in many areasrevisions are frequently proposed which can lead to extremelycomplicated and confusing situations


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Biostratigraphy

Evolution forms the initial basis for biostratigraphic subdivision,

either through the development of an increasing number of newspecies, or by means of evolution of one particular species

In general, Earth history shows an increase of the number oftaxa, but this process is punctuated by (mass) extinctions

Depositional environments and geographic contrasts play animportant role in determining the nature of fossil assemblages

The biozoneis the fundamental biostratigraphic unit

Biozones are strictly diachronous in most cases; however, overgeological time scales their boundaries can commonly beconsidered to be isochronous, but their resolving power haslimitations!


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Biostratigraphy

Evolution forms the initial basis for biostratigraphic subdivision,

either through the development of an increasing number of newspecies, or by means of evolution of one particular species

In general, Earth history shows an increase of the number oftaxa, but this process is punctuated by (mass) extinctions

Depositional environments and geographic contrasts play animportant role in determining the nature of fossil assemblages

The biozoneis the fundamental biostratigraphic unit

Biozones are strictly diachronous in most cases; however, overgeological time scales their boundaries can commonly beconsidered to be isochronous, but their resolving power haslimitations!


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Biostratigraphy

A vast diversity of types of fossils exists; the following criteria

are important in determining how useful they are for strictlystratigraphic purposes of correlation: Abundance and size

Degree of dispersal

Preservation potential

Rate of speciation

As a result, especially numerous marine microfossils (e.g.,forams) are stratigraphically highly useful, whereas others aremore valuable for paleoecologic purposes

Numerous pitfalls exist in the correlation of biozones (e.g.,Quaternary pollen zones)


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Chronostratigraphy

Chronostratigraphic classification of sediments or rocks involves

the establishment of time lines (isochrons); this, in turn, formsthe basis for paleogeographic reconstruction

Traditionally, biostratigraphy has formed the most importantbasis for chronostratigraphic classification

Numerical dating techniques are becoming increasingly

important in defining chronostratigraphic units


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Chronostratigraphy

Radiometric datingmethods are in essence based on the

decay of radioactive isotopes

N=number of daughter isotopes; N0=initial number of parent isotopes;=decay constant; t=time

Radiometric dating involves a large number of isotopes anddecay series, with highly variable halflives and applications (ageranges from less than a century to billions of years)

t

0eNN


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Magnetostratigraphy

The Earths magnetic field is constantly subject to change

Secular variations, continuous changes of the position of themagnetic poles, take place over time scales of 101to 103years

Reversalsfrom normal polarity to reversed polarity occur overtime scales of 104to 106years

Fine-grained sediments deposited from suspension can alignthemselves according to the ambient geomagnetic field (the

same applies to volcanics upon cooling below the Curie point) If paleomagnetic changes are independently numerically dated,

a resulting magnetostratigraphy can be used to datesedimentary successions


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