Page 129 - Petrology of Sedimentary Rocks

As before, mixtures can be shown CL, PM, etc.; gradual transition, M -6,
P - L, etc.

v. Climatic Effects (when decipherable)

(w) Climate conducive to heavy weathering (hot or wet or vegetated).

(n) Climate not conducive to much weathering; if distinguishable, (n,) too
dry, (n,) too cold, (n,) lack of vegetation, etc.

All five aspects of the genetic code can be put together to give a systematic
exposition of the origin of the sandstone, conglomerate, etc. The more
“tectonic” influences are put first; depositional basin is set off by / / for
ease in reading the formula; and the “accidental” influences, environment
and climate, come last. Sic Semper Scientis!

Mineralogical Classification of Sandstones

The perfect classification of sandstones does not now and never will exist. Each
of the dozens of classifications proposed have reflected the composer’s personal bias
and limited experience. The less one knows about a subject, the easier it is to cook up a
logical classification that seems to have all problems answered. But no classification
can be developed to answer all purposes and reflect all local peculiarities. Problems of
classification have been thoroughly reviewed by McBride (I 964 JSP), Klein (I 963 GSA)
and Okada (I 97 I JG) while Huckenholz (I 963 JSP) and Dott (I 964 JSP) have considered
in particular the significance of arkose and graywacke.

The first English-language attempt to create a quantitative, comprehensive and
geologically meaningful (as opposed to a random) Classification of sandstones was that
of P. D. Krynine, who had developed essentially his complete system by about 1941,
taught it starting in 1943, and published it in detail in 1948 (JG). His thinking on
sandstone classification had apparently been strongly influenced by that of his teacher
in Moscow, Shevtsov (see Folk and Ferm, 1966 JSP, for details and citations). Krynine
stressed sandstone mineralogy as a powerful indicator of tectonics, and drew quantita-
tive lines between five sandstone types, expressing composition by triangular diagrams
based on poles of (I) quartz plus chert, (2) feldspar plus kaolin, and (3) micas (including
MRF’s and matrix together). After Fischer (I 933), he was the first to express sandstone
composition by a triangular diagram, though Pirsson’s text used a ss-sh-Is sedimentary-
rock triangle in I9 15. My own ideas on mineralogical classification of sandstones were
strongly influenced by Krynine; but ‘the realization that an “arkose” with 35% feldspar
could have a very wide range of textures necessitated some addition to the strictly
mineralogical terminology, hence the idea of adding to the clan name a scale of
textural maturity (I 9.5 I JSP).

The five-fold, textural maturity/mineralogical classification used in previous
editions of this book (1954-1965) and published by the writer (1951 JSP, 1954 JG, 1956
JSP, 1960 JSP) was intended to be objective and descriptive, but the end-members of
the sacred triangle were collected in three groups thought to be most indicative of
provenance, generally following Krynine’s philosophy. Hence quartz and chert were
linked at the Q-pole, indicative of prolonged chemical/physical attack or else of
derivation from an older sedimentary source terrane, the end-member rock type being
the ort hoquartzi te. All feldspars and all plutonic and volcanic rock fragments were
linked together at the F-pole, indicative of igneous source, the end-member type being

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