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Revision of Systematics in Sedimentary Petrology with Special Reference on Sandstone Composition in Tectonic Provinces
Niichi Nishiwaki
Faculty of Social Research, Nara University,1500 Misasagicho, Nara City, Nara, 631-8502, Japan.
E-mail: niichi@daibutsu.nara-u.ac.jp
Abstract
The current systematics in sedimentary petrology is based on the texture, granulometry and modal composition
with reference to the sedimentological environment in the continental regions. In recent years, chemical and isotopic
composition data of sedimentary rocks are rapidly accumulated, and knowledge on sedimentological environment,
sedimentary facies and tectonic provinces is integrated, especially in the mobile zones. According to the drastic
change of quality and quantity of data and extended sedimentological information, it is urgently required to revise
the systematics in sedimentary petrology. The IUGS-CSP (Commission on Systematics in Petrology) is trying to
establish a working group of international sedimentological communities, in which the new systematics will be
proposed based on the detailed reviewing of the current classification and terminology. It is important for the new
systematics to clarify the data with mathematical and statistical analyses supported by various informational
techniques. The Japanese subgroup of the working group is constructing a database that contains various kinds of
sedimentological data and related information on sandstones in Japan and surrounded area, and analyzing the
relationship between the sandstone properties and geological and sedimentological settings by using several
statistical methods including factor and cluster analyses. Preliminary interpretation of the extracted factors
indicates that the chemical composition and other sedimentary properties are affected also by geological and
tectonic settings, not only sedimentary process, environment, diagenesis and weathering. Detailed statistical and
theoretical analysis on the relationships within different properties of sedimentary rocks is continuing, and it is
expected that many important suggestions will be obtained for the new classification and terminology of
sedimentary rocks.
Introduction
Geology was born from the study in continental areas, and many geological models and
theories were devoloped on the data from the continental regions. According to the development
of science and technology, new methods and techniques were applied, and geology was extended
its field to other kinds of areas, such as ocean floor and island arc. Geological models and
theories should be revised to adopt for the new areas and data.
Systematics in petrology is one of the classical but important achievement in geology, and it's
contribution to geological sciences and the human society is remarkable. It is, however,
necessary to be revised synthetically for the future application.
Classifications on Modal Composition
There are many researches on the systematics in sedimentary petrology, and the
classification of the sandstone was established mainly for the stable continental environments,
based on the modal and granulometric analysis, and using various ternary diagram (Pettijohn, 1954;
Okada, 1971). However the classification is difficult to adopted for the tectonic
environments, and there are many studies to extend the classification. For example, Dickinson et
al. (1983) tried to classify various provenances on the Q-F-L diagram (Fig. 1), Kumon et al. (1992)
proposed the discrimination of provenance on the Q-F-R diagram (Fig.2), and Takeuchi (1998)
tried to classify the sedimentary facies from the mode of rock fragments (Fig.3).
Fig. 1. Compositional fields indicative of sandstone derivation from different types of provenance
(Dickinson et al., 1983). Qm:monocrystalline quartz grain, F:total feldspar grains, Lt:total lithic
fragments.
Fig. 2. Tentative proposal for discriminating the provenance types of magmatic arc, based on the
traditional modal point-counting method. PVA: primitive volcanic arc provenance, EMA: evolved
and matured magmatic arc provenance, DMA: dissected magmatic arc provenance, DDMA: deeply
dissected magmatic arc provenance, RMA: renewed magmatic arc provenance. Solid and dashed
arrows show an evolving or roofing process, and open arrows indicate an unroofing or dissecting
process. Q: total quartz, F: total] feldspar, R: total rock fragments. (Kumon et al., 1992)
Fig. 3. Types of rock fragments in sandstones of the Shingai Formation. open square: normal
sediments, others: mélange facies. Lv:volcanic, Lm:metamorphic, Qp:polycrystaline quartz,
Ls:sedimentary, Lp:plutoniic. (after Takeuchi, 1998)
Other researchers focused on the specific grains in the sandstone to discriminate the
sedimentary environments. For example, Teraoka et al. (1997) tried to classify the clastic garnet
grains (Fig. 4), and Hisada et al. (1998) examine the chromian spinels in the sandstones of
metamorphic belt (Fig. 5).
Fig. 4. Classification of garnet type. (after Teraoka et al., 1997)
Fig. 5. Cr-Al-Fe3+ diagram of chromian spinels from the Hida marginal belts. front:Kuruma
Group, Back:Kotaki oriststrome. (after Hisada et al., 1998)
Classification on Chemical Composition
According to the development of analytical techniques, chemical composition is also used for
sandstone classification. Various kinds of diagrams were proposed to discriminate provenances,
especially in the magmatic arc regions. For example, Bhatia (1983) proposed four provenance
types on the Al2O3/Sio2 - Fe2O3+MgO diagram (Fig. 6), and Roser and Korsch (1986) proposed
three provenance types on the K2O/Na2O - SiO2 diagram (Fig. 7).
Fig. 6. Al203/Si02-Fe203+MgO diagram. O.ARC: oceanic island arc, C.ARC: continental island
arc, AM: active continental margin, PM: passive margins (Bhatia 1983).
Fig. 7. K2O/Na2O-SiO2 diagram. The environmental divisions are after Roser & Korsch, 1986.
ARC: oceanic island arc margin, ACM: active continental margin, D: passive margin.
New discriminating indeces were also proposed for sandstone classification. For example,
Kiminami et al. (1992) proposed the Basicity Index and the B.I. diagram to discriminate the four
provenance types of magmatic arc. (Fig. 8). Fedo et. al. (1995) proposed the Chemical Index of
Alteration, and the A-CN-K diagram to discriminate two provenance trends (Fig. 9).
Fig. 8. Trend of magmatic arc sandstones (Segments A to C) on the Al2O3/SiO2 -
(FeO+MgO)/(SiO2+K2O+Na2O) diagram.
Fig. 9. A-CN-K diagram, modified after Fedo et al. (1995). CIA:Chemical index of alternation.
A:Al, CN:2Ca+Na, K:K.
Diagrams are revised and new diagrams were proposed for the discrimination of
provenances and classification of sandstone. For example, Kiminami et al. (1998) has revised
the B. I. diagram, and Musashino (1998) has discussed its resemble diagrams (Fig. 10). Roser
(1998) proposed Th/Sc - Zr/Sc diagram for five volcanic arc trends using trace elements
composition (Fig. 11).
Fig. 10. K*/A* - (Fe*+Mg*)/Al* daigram on sandstones from western Buller terane, New Zealand.
(after Musashino, 1998)
Fig. 11. Example Th/Sc-Zr/Sc diagrams for Triassic Murihiku sediments from Southland. St HAB
(high-Al basalt), LSA (low-Si andesite). AND (andesite), DAC (dacite), RH (rhyolite) are average
volcanic rock compositions, which define a primary source evolution line for first cycle
sediments.(after Roser, 1998a)
Statistical and Mathematical Treatment
According to the development of mathematical theories and accumulation of
sedimentological data, databases were constructed and used for the statistical study of systematics
in petrology. For example, Nishiwaki (1998) described the sedimentary database of the Japanese
sandstone, and it was used to for statistical analyses. Roser and Korsch (1988) proposed the
major element provenance diagram in which the discriminating functions are used for its axes, and
the trend of six volcanic arcs were clarified in the divided quadrant (Fig. 12).
Fig. 12. Major element provenance diagrams for Shimanto sandstones, Kii Peninsula (discriminants
of Roser & Korsch 1988). Stars BA(basalt) AN(andesite) DA(dacite) RD (rhyodacite). RH
(rhyolite) are average volcanic rock compositions, which define a primary source line for first cycle
sediments. Arrow indicates direction of maturation. (after, Roser, 1998b)
Statistical and mathematical researches on the sedimentological data are important to certify
the diagrams and classification by using them. As many new diagrams were empirically designed
in the first step, they should be examined with different kinds of data set before confirming the final
form of them. They should be examined by theoretical points of view to clarifying the meaning
of the diagram, including axes, scale, threshold value and discriminated groups. For example,
Nishiwaki (1999) tried to examine the discrimination with the B. I. diagram (Kiminami, 1998) by
discriminant analysis (Fig. 13), and it is indicated from the structure matrix (Table 1) that the
chemical composition and other sedimentary properties are affected also by geological and tectonic
settings, not only sedimentary process, environment, diagenesis and weathering.
Fig. 12. Scatter plot of tectonic provinces in the discriminant functions 2 and 2 space on the
Japanese sandstone data.
Table 1. Pooled within-groups correlations between discriminating variables and canonical
discriminant functions. Variables are ordered by size of correlation within function. Function 1 Function 2 Function 3
Ti02 .65167* .16618 -.29385
TFe2O3 .64222* .31070 -.25245
FeO -.54843* .18983 -.28367
MgO -.46854* .44068 -.05662
BaO -.05346* .04865 -.02164
SiO2 -.37128 .49780* .38615
MnO .15338 -.28177* .04811
CaO .13081 -.27926* .05382
P2O5 .14601 -.26798* .23239
Na2O .14694 -.05905 -.60718*
Al2O3 .25534 -.28347 -.51806*
K2O -.11609 .16824 -.21190*
* denotes largest absolute correlation between each variable and any discriminant function.
Revision of Systematics
The IUGS Commission on Systematics in Petrology is continuing the discussion on the
revision of the systemtics. The Subcommissions on Igneous Petrology and Metamorphic
Petrology have been working on the revision, and many important proposals and achievements
were given. On the other hand, the Subcommission on Sedimentary Petrology has been inactive
for many years. The Commission has decided to examine the feasibility of organizing a working
group for the revision of the systematics in sedimentary petrology.
Many participating members are deeply appreciated for the working group from various
sedimentological communities.
References
Bhatia, M. R., 1983, Plate tectonics and geochemical composition of sandstones. Jour. Geol., vol.
91, pp. 611-627.
Dickinson, W. R., Beard, L. S., Brackenbridge, G. R., Erjavec, J. L., Ferguson, R. C., Inman, K. F.,
Knepp, R. A., Lindberg, F. A. and Ryberg, P. T., 1983, Provenance of North American Phanerozoic
sandstones in relation to tectonic setting. Geol. Soc. Amer. Bull., vol. 94, pp. 222-235.
Fedo, C. M., Nesbitt, H. W., and Young, G. M., 1995, Unraveling the effects of potasium
metasomatism in sedimentary rocks and paleosols, with implications for paleoweathering
conditions and provenance. Geology, vol. 23, no. 10, pp. 921-924.
Hisada, K., Osawa, M, Chiba, M and Arai, S., 1998, Detrital chromian spinels from the Hida
marginal and Maizuru belts, Honsyu, Japan. News of Research Group on Sandstone Composition
and Tectonics in East Asian Tectonic Belt, no. 4, pp. 43-48.
Kiminami, K., Komatsu, M. and Kawabata, K. (1992) Composition of clastics of the Sorachi Group
and Lower Yezo Group in the Inushibetsu-gawa area, Hokkaido, Japan, and their significance.
Mem. Geol. Soc. Japan, no.38, pp.1-11.
Kiminami, K., Kumon, F., Miyamoto, T, Suzuki, S., Takeuti, M. and Yoshida, T., 1998, Application
of B. I. diagram to paleozoic and mesozoic sandstones of the Japanese Island. News of Research
Group on Sandstone Composition and Tectonics in East Asian Tectonic Belt, no. 4, pp. 1-7.
Kumon, F., Kiminami, K., Adachi, M., Bessho, T., Kusunoki, T., Mishimura, T., Okada, H.,
Okami, K., Suzuki, S. and Teraoka, Y., 1992, Modal compositions of representative sandstones
from the Japanese Islands and their tectonic implications. Mem. Geol. Soc. Japan, no. 38, pp.
385-400.
Musashino, M., 1998, on the Al2O3/SiO2 - Basicity Index diagram and its resemble diagrams, Part
2. News of Research Group on Sandstone Composition and Tectonics in East Asian Tectonic
Belt, no. 4, pp. 8-14.
Nishiwaki, N., 1998, Structure and application of multimedia database in sedimentary petrology in
Japan. Proc. IAMG '98, Ischia, pp. 689-692.
Nishiwaki, N., 1999, Discrimination of tectonic province from chemical composition of sandstone,
and its implication to sandstone classification. Proc. IAMG '99, Trondheim, pp. 375-380.
Okada, H., 1971, Classification of sandstones: analysis and proposal. Jour. Geol., vol. 79, pp.
509-525.
Pettijohn, F. J., 1954, Classification of sandstones. Jour. Geol., vol. 62, pp.369-365.
Roser, B. P. and Korsch, R. G., 1986, Determination of tectonic setting of sandstone-mudstone
suites using SiO2 contents and K2O/Na2O ratio. Jour. Geol., 94, 635-650.
Roser, B. P., 1998a, Whole-rock geochemical variations in a Triassic-Jurassic back-arc: The
Murihiku Terrane, New Zealand. News of Research Group on Sandstone Composition and
Tectonics in East Asian Tectonic Belt, no. 4, pp. 129-134.
Roser, B. P., 1998b, Major and trace element systematics in the Shimanto belt, Kii Peninsula.
News of Research Group on Sandstone Composition and Tectonics in East Asian Tectonic Belt,
no. 4, pp. 129-134.
Takeuchi, M, 1998Two types of sandstone from the Permian Shingai Formation in the Kurosegawa
tectonic zone, Shikoku. News of Research Group on Sandstone Composition and Tectonics in
East Asian Tectonic Belt, no. 4, pp. 49-53.
Teraoka, Y., Suzuki, M., Hayashi, T. and Kawakami, K., 1997, Clastic garnets contained in
Paleozoic-Mesozoic sandstones in the Onogawa region. Rep. Educ. Hiroshima Univ., part. 11,
vol. 19, pp. 87-101.
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