QUANTITATIVE BIOSTRATIGRAPHY, Slides of Geology

Quantitative Biostratigraphy - Quantitative methods applied to solve biostratigraphic problems and to estimate stratigraphic ranges of fossil taxa. Methods of quantitative stratigraphy combine mathematical logic (e.g. statistic analyses) with stratigraphic principles (e.g., law of superposition of strata; speciation, possible acme, and extinction of taxa) allowing the user to retain full control over input and results. Conventional biostratigraphy often lacks direct integration between individual microfossil groups, and rarely gives insight in the actual geographic distributions of taxa and zones. Conventional methods are also poorly suited to integrate records in zonation, and lack a standardized recording and retrieval procedure.

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QUANTITATIVE BIOSTRATIGRAPHY
INTRODUCTION
Quantitative Biostratigraphy - Quantitative methods applied to solve
biostratigraphic problems and to estimate stratigraphic ranges of fossil
taxa.
Methods of quantitative stratigraphy combine mathematical logic (e.g.
statistic analyses) with stratigraphic principles (e.g., law of
superposition of strata; speciation, possible acme, and extinction of
taxa) allowing the user to retain full control over input and results.
Conventional biostratigraphy often lacks direct integration between
individual microfossil groups, and rarely gives insight in the actual
geographic distributions of taxa and zones.
Conventional methods are also poorly suited to integrate records in
zonation, and lack a standardized recording and retrieval procedure.
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QUANTITATIVE BIOSTRATIGRAPHY

INTRODUCTION

  • (^) Quantitative Biostratigraphy - Quantitative methods applied to solve biostratigraphic problems and to estimate stratigraphic ranges of fossil taxa.
  • (^) Methods of quantitative stratigraphy combine mathematical logic (e.g. statistic analyses) with stratigraphic principles (e.g., law of superposition of strata; speciation, possible acme, and extinction of taxa) allowing the user to retain full control over input and results.
  • (^) Conventional biostratigraphy often lacks direct integration between individual microfossil groups, and rarely gives insight in the actual geographic distributions of taxa and zones.
  • (^) Conventional methods are also poorly suited to integrate records in zonation, and lack a standardized recording and retrieval procedure.

BIOSTRATIGRAPHIC REVIEWS

  • (^) Taxon
    • (^) Definition
  • (^) Paleontological events
    • (^) The presence of a taxon in its time context
    • (^) FO, FA, range
    • (^) Problems :
      • (^) Sampling detail and the frequency of fossil taxa
      • (^) Confidence of taxonomic identification Influence of environmental change on the stratigraphic range of fossils.
      • (^) Difference rate of taxon evolution in different part of the world

QUANTITATIVE BIOSTRATIGRAPHY

INTRODUCTION Stratigraphic situation where the very first occurrence of a species is a localized event in a basin. with widespread migration at a later time, forming a potential correlation surface. The average first-occurrence surface is modelled by probabilistic stratigraphic methods, the very first occurrence by deterministic ones (after Hood, 1995).

BASIC CONCEPT

QUANTITATIVE BIOSTRTIGRAPHY

local versus regional ranges Diagram 2A: Theoretical example showing distributions in space and time of seven different taxa with true chronological succession

BASIC CONCEPT

QUANTITATIVE BIOSTRTIGRAPHY

Diagram 2B: Corresponding sedimentary record of biological events in four stratigraphic sections. Distortions can be attributed to differential role of sedimentation (from Davaud, 1982).

Sources of uncertainty

• The optimum or ‘true’ sequence of fossil events

has not been established.

• The distance of fossil events along a relative time

scale is not known (spacing or scaling problem).

• The geographic distribution of an event is not

known.

• The error in fixation of biostratigraphic events at

the scale in a well or outcrop section.

Multivariate methods

• Using sample by sample matrices of

similarity or distance coefficients,

clustering of samples (Q-mode) or

clustering species by species matrices (R-

mode).

• The dendrogram cluster may either

paleoecologic or stratigraphic significance

or both.

Unitary associations

• This method finds a stratigraphic succession

of concorent range zones, using observed or

virtual co-occurences of taxa.

Ranking and Scaling

• Ranking technique produce optimum

sequences of events in time, based on

estimates of relative order of pair of events.

• Scaling technique uses the degree of

inconsistency in position of events as a

measure of interfossil distance

QUANTITATIVE BIOSTRATIGRAPHY

INTRODUCTION, CORRELATION

  • (^) New tools in stratigraphy, using semi-quantitative or quantitative methods, make it easier to built frontier zonations, and can look through sampling noise, like radar can look through fog. Also, individual wells may be tested for 'stratigraphic normality', and sequence stratigraphic information may be extracted. Insertion of unique events in quantitative zonation assists to calibrate local zonation to standard ones with better understood age calibration. - (^) There are two principal families of methods, with desktop computer programs to execute them: (a) deterministic, ex. Graphic correlation, Unitary assosiation; and (b) probabilistic.

QUANTITATIVE BIOSTRATIGRAPHY

INTRODUCTION, CORRELATION

  • (^) Deterministic methods, seek the total or maximum stratigraphic range of taxa, whereas probabilistic methods estimate the most probable or average range, accompanied by an estimate of stratigraphic uncertainty.
  • (^) Deterministic methods assume that inconsistencies in the stratigraphic range of a taxon from section to section or well to well, are due to missing data. On the other hand, probabilistic methods assume that the inconsistencies are the result of random deviations from a most commonly occurring or average stratigraphic range. Or to say it in terms of last stratigraphic occurrence events of taxa (or 'tops' in exploration jargon): Deterministic methods assume that there is a true order of events, and that inconsistencies in the relative order of tops from well to well are due to missing data. Probabilistic methods on the other hand consider such inconsistencies the result of random deviations from a most likely or optimum sequence of tops.