Niichi
Nishiwaki
Faculty of Social Research, Nara University
1500 Misasagicho, Nara City, 631-8502, Japan.
E-mail: niichi@daibutsu.nara-u.ac.jp
Revision of Systematics in Sedimentary Petrology
Abstract
There are many studies on the classification and nomenclature of
sedimentary petrology, and the current systematics is diversed because the
target areas and sedimentary rocks are varied, such as from deep-shallow ocean
to fluvial-continental area, and from coarse-fine clastics to
chemical-biologicals. Not only the
current systematics but also classical and/or traditional systematics should be
reviewed based on current knowledge and hypotheses.
New theories and measurement techniques have been developed in recent
years, and new types of data have been added to the traditional data.The
working group will consider various kinds of sedimentary data including
granulometric composition, normative and mineralogical composition, chemical
compositions, texture and structure, sedimentary facies, sedimentary
environment, tectonic setting, and others. It should be
considered also as an ethical obligation to make a useful synthetic evaluation
of all particular results.
The discussion
should be based on the synthesized data which are globally collected,
critically evaluated and standardized, and referred by all researchers. It is expected that database systems
connected with the internet should be constructed for this purpose.
Statistical
and mathematical treatment is necessary for evaluation and standardization of
data, and theoretical discussion is important for modelling of the systematics
in sedimentary petrology. Many kinds of
statistical and mathematical models have been applied for sedimentary
petrology, and they should be reviewed and evaluated to extract useful
information for new systematics.
The IUGS Commission of Systematics in Petrology (CSP) is planning a working group for discussion of the systematics of
sedimentary petrology, in which the current systematics will be reviewed, and
the revised systematics will be proposed.
The tentative working group in Japan has started to accumulate the
previous studies and analytical data, and current results of their reviewing
and evaluating will be reported, together with a preliminary proposal of
revised systematics.
Professional ethics should be respected
by any participant in the discussion.
Sedimentary
petrology treats not only sediments and sedimentary rocks but also other
materials including mineral deposits, oil and gas, derived materials and source
rock. The four processes should be
examined in the discussion of systematics in sedimentary petrology, i.e. source
process, deposition process, alteration process and decomposition process (Fig.
1).
|
Source Process |
|
(Igneous/Metamorphic/Sedimentary/Tectonic Processes) |
|
Source
rock |
|
Deposition
Process |
|
(Weathering/Erosion/Transportation/Selection/Deposition) |
|
Sediments |
|
Alteration
Process |
|
(Compaction/Bioturbation/Diagenesis/Alteration/Dissolution) |
|
Sedimentary rock/Oil-Gas/Deposits |
|
Decomposition Process |
|
(Weathering/Deformation/Breakdown/Melting/Metamorphism/Movement) |
|
Derived
material |
Figure
1. Four processes for sedimentary
petrology.
Classification
in sedimentary petrology can be discussed from two different ways (Fig.
2). One is the sedimentary procedure,
in which the origin and sedimentation process are classified from
sedimentological analysis to explain the properties of specimens. The other is the mathematical procedure, in
which properties of specimens are classified from mathematical analysis to
explain the origin and sedimentary processes.
The two procedures should be combined for the more synthesized
classification.
|
Origin and sedimentation processes |
|
Classification |
|
Composition,
properties and characteristics of specimens |
The
current systematics was constructed from sedimentological examination mainly
based on traditional sedimentological data.
In recent years, chemical analytical data in sedimentary petrology have
been accumulated and used to estimate the sedimentary process and/or province
tectonic setting together with mathematical analysis of data (Bhatia, 1983;
Fedo et al., 1995; Kiminami et al., 1998).
There
are many methods of statistical and mathematical analyses which can be used for
the study of sedimentary petrology, i.e. from graphic presentation to
multivariate analysis. It is necessary
to examine the properties of each method, and to
select
the most suitable one for the study of systematics in sedimentary petrology. Such a selecting process should be considered also as an
ethical problem leading to the optimal solution.
The
followings are typical methods of statistical and/or mathematical analyses used
in the study of sedimentary petrology.
Triangular
Diagram
It is
a method of plotting compositions in terms of the relative amounts of three
materials or components, involving a triangle in which each apex represents a
pure component. Scale variables can be
used, and it is applied to the graphic classification on any combination of
three components (mineral, element, etc.).
The followings should be examined: validity test of combination,
variance analysis of each component, restriction of percentile data,
discrimination of classified groups, significance test of boundary line,
sedimentological meaning of each groups, etc.
Scatter
Diagram
It is
a graphic representation of paired measurements, usually along Cartesian axes,
that aids in visualizing the relationships between two or more variables. Scale variables can be used, and it is
applied to the graphic classification on any combination of two or more
components. The axis can be defined not
only as a single element but also as a function or factor of
several elements. The following should
be examined: unit and measure of axes,
variance analysis of each component, sedimentological meaning of each axes,
discrimination of classified groups, significance test of boundary line,
sedimentological meaning of each groups, etc.
Presence/Absence
Analysis
It is
a simple judgment of specific property according to the presence/absence of
specific element or character.
Qualitative variables can be used, and it is applied to the judgment of
origin and/or sedimentary process from presence (or absence) of a specific
character. The following should be
examined: significance test of judgment, sedimentological explanation of
presence/absence, etc.
Univariate
Breakdown
It is
a breakdown method into two or more groups based on the value of a single
variable. Ranking and scale variables
can be used, and it is applied to breakdown
by defining threshold value(s) within a range of a variable, including the
extraction of abnormal value(s) for a specific process. Both the bulk composition and composition of
specific mineral can be used. The
following should be examined: frequency distribution, significance of threshold
and/or abnormal values, discrimination of breakdown groups, sedimentological
meaning of variables, etc.
Contingency
Table Analysis
It is
a grouping method using the cross table of two or more variables, in which a
cell composed of only specimens (cases) of same value for each defining
variable. Ranking or qualitative
variables can be used, and it is
applied to the classification into uniform cells in a cross table and the test
of relationship within these variables, in which the axis is a ranking or
qualitative variable. The following
should be examined: frequency distribution of each variable, significance test
of the cross table, test of threshold values (for ranking variables),
sedimentological meaning of each cell, etc.
Correlation
Analysis
It is
a statistical method for analyzing the data structure on the intensity
coefficient of association or independence between two or more mathematical
variables. The Pearson's correlation
coefficient is generally used for scale variables, though the Kendoll's tau and
Spearman's coefficient are generally used for ranking variables. The coefficient can be used for other
statistical analyses. The following
should be examined: distribution function of each variable, selection and
transformation of scale, treatment of missing cases, significance of
coefficient, etc.
Matching
Analysis
It is
a statistical method for analyzing the data structure on the similarity
coefficient between two or more variables, which is calculated on the level of
matching. Qualitative and ranking
variables can be used, and the coefficient can be used as a substitute of the
correlation coefficient. The following
should be examined: frequency distribution of each variable, validity of used
variable set, aggregation and/or threshold of value levels, significance of
coefficient, etc
Factor
Analysis
It is
a statistical method for identifying the minimum number of influences necessary
to account for the maximum observed variation in a set of data and for
indicating the extent to which each influence accounts for the variance
observed in the data. Scale variables
can be used, it is applied to the factor extraction from the compositional data
set to explain the variance of specimens, that will be used for the axes of the
new classification diagram. The
following should be examined: selection of coefficient type, significance of
coefficients, sedimentological meaning of each factor, contribution of each
factor to classification, etc.
Discriminant
Analysis
It is
a statistical procedure for classifying subsequent samples into categories
previously defined and differentiated on the basis of samples known
populations. Scale variables can be
used, and it is applied to the valuation of current classification by analyzing
the compositional data, together with extraction of discriminant functions
which should be compared with the axes of classification diagram. The following should be examined: selection
of coefficient type, significance of coefficients, sedimentological meaning of
discriminant functions, sedimentological reason of incorrectly classified
specimens, etc.
Cluster
Analysis
It is
a statistical procedure for arranging a number of objects in homogeneous
subgroups based on their mutual similarities and hierarchical
relationship. Scale variables can be
used, it is applied to the mathematical classification method of specimens on
the compositional data set, of which result can be compared with current
classification. The following should be
examined: validity of variable set which is used for the analysis, selection of
distance function or coefficient type, significance of functions or
coefficients, validity of clustering procedure, sedimentological meaning of
classified clusters, sedimentological reason of independent specimens, etc.
Regression
Analysis
It is
a statistical technique applied to paired data to determine the degree or
intensity of mutual association of a dependent variable with one or more
independent variable. Scale variables
can be used, and it is applied to the estimation method of sedimentological
indexes from the compositional data set, and comparison of the regression
function with the axes of the classification diagram. The following should be examined: validity of variable set which
is used for the analysis, selection of coefficient type, sedimentological
meaning of regression functions, sedimentological reason of deviated specimens,
etc.
Discussion
A session is planned in the 32nd International Geological Congress
(Firenze, 2004) for discussion on the systematics in sedimentary petrology,
which will be supported by the IUGS Commission of Systematics in Petrology
(CSP). Another session is also planned
in the 17th International Sedimentological Congress (Fukuoka, 2006). It is expected that mathematical geologists
will contribute to both sessions by proposing statistical and mathematical criteria for the
revision of systematics in sedimentary petrology, as the new systematics should
be based not only on sedimentological models but also on mathematical models.
The systematics in sedimentary petrology is diverged because the
target areas and sedimentary rocks are varied, such as from deep-shallow ocean
to fluvial-continental area, and from coarse-fine clastics to
chemical-biologicals. Classical and/or
traditional systematics should be reviewed based on current knowledge and
hypotheses.
New theories and measurement techniques have been developed in
recent years, and new types of data have been added to the traditional
data. Various kinds of sedimentary data
should be considered including granulometoric composition, normative and
mineralogical composition, chemical compositions, texture and structure,
sedimentary facies, sedimentary environment, tectonic setting, and others.
The systematics should be
based on the synthesized data that are globally collected, critically evaluated
and standardized, and referred by all researchers. It is expected that database systems connected with the Internet
should be constructed for this purpose.
Statistical and mathematical processing is necessary not only for
evaluation and standardization of data, but also for clarifying the data
structure and constructing sedimentary models.
These results should be reviewed and evaluated to extract useful
information for new systematics.
Acknowledgement
I would like to thank to Organizing Committee of the
32nd IGC for the acceptance of sessions on the systematics in Sedimentary
petrology.
References
Bhatia, M. R., 1983, Plate tectonics
and geochemical composition of sandstones: Journal of Geology, vol. 91, p.
611-649.
Fedo, C. M., Nesbitt, H. W. and
Young, G. M., 1995, Unraveling
the effect of potassium metasomatism in sedimentary rocks and paleosols, with
implications for paleoweathering conditions and province: Geology,
vol. 23, no. 10, p. 921-924.
Kiminami, K., Kumon. F., Miyamoto, T., Suzuki, S., Takeuchi, M. and Yoshida, T., 1998, Application
of B. I. diagram to Paleozoic and Mesozoic sandstones of the Japanese
Islands: “Sandstone Composition and
Tectonics of East Asia Tectonic Zone”, Ed. Hoyanagi, K., no. 4, p. 1-7.
Nishiwaki-Nakajima, N., 1995, Global
database project in sedimentary petrology (IGCP 269): Sedimentary Facies and
Paleogeography, vol. 15, no. 2,
p.71-81.