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110:. A minimum of 300 representative points (preferably 500 points) should be used to perform the count. On each randomly selected point that lands on a sand grain, the operator must determine the make-up of the area chosen, i.e. whether it is a
267:
Ingersoll, R.V., Bulard, T.F., Ford, R.L., Grimn, J.P., Pickle, J.P., Sares, S.W., 1984, "The effect of grain size on detrital modes: a test of the Gazzi-Dickinson Point
Counting method": Journal of Sedimentary Petrology, 54,
181:
sand, when point counted with these two methods would yield drastically different results. A QFR-style count would be rich in rock fragments, whereas a Gazzi-Dickinson point count would show the sand rich in
239:
Dickinson, W.R., 1985, "Interpreting provenance relation from detrital modes of sandstones", in Zuffa, G.G. (ed.), Provenance of
Arenites: NATO ASI Series, C 148, D. Reidel Publishing Company, Dordrecht,
258:
Graham, S.A., Dickinson, W.R., and
Ingersoll, R.V., 1975, "Himalayan-Bengal Model for Flysch Dispersal in Appalachian-Ouachita system", Geological Society of America Bulletin, vol. 86, pp. 273–286.
190:. Proponents of the Indiana University method would say that information is lost by not counting rock fragments. Proponents of Gazzi-Dickinson point counting would say that small changes in
126:) grains are counted, or non-framework grains are counted and then excluded from percentages when using descriptive devices such as QFL triangles. This can create problems with
34:
A sand grain that could be used for the Gazzi-Dickinson method. Scale box in millimeters, plane-polarized light on top, cross-polarized light on bottom. Landing on the large
42:(center, clear in plane light, orange in cross-polarized light) would count as a mineral grain in the Gazzi-Dickinson method because it is sand-sized. Landing on the
221:
Gazzi, P., 1966, "Le
Arenarie del Flysch Sopracretaceo dell'Appennino Modenese: Correlazioni con il Flysch di Monghidoro". Mineralogica e Petrografica Acta 12:69 97.
249:
Dickinson, W.R., Suczek, C.A., 1979, "Plate tectonics and sandstone compositions": American
Association of Petroleum Geologist, 63, 2164–2182.
46:-rich groundmass surrounding the grain would count as a volcanic lithic fragment. It would count as a volcanic rock fragment in the
230:
Dickinson, W.R., 1970, 2Interpreting detrital modes of graywacke and arkose": Journal of
Sedimentary Petrology, v. 40, p. 695–707.
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scheme), in which all grains that are connected are considered rock fragments, and the individual components are disregarded.
118:(e.g. a sand-sized piece of shale). These counts are then converted to percentages and used for compositional comparisons in
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from a sedimentary rock is needed, with a slide advance mechanism that will randomly select points on the slide with a
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grain that is sand sized (larger than 62.5 micrometers) or a finer-grained fragment of another rock type, called a
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The best way to explain the differences in these two schools of thought is with an example: A sand rich in
277:
Folk, R.L., 1974, Petrology of
Sedimentary Rocks: Austin, Texas, Hemphill Press, second edition, 182 p.
86:, regardless of what they are connected to. Gazzi-Dickinson point counting is used in the creation of
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142:, starting in 1970. Dickinson and his students (most notably Raymond Ingersoll, Steven Graham, and
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130:, which are lithic grains that have been deformed and thus blend in with (or have become) matrix.
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in the 1970s established the method and its use to use the composition of sandstones to infer
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processes. This was in contrast to ideas presented by sedimentary geologists at
78:. The main focus (and most controversial) part of the technique is counting all
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To perform a point count using the Gazzi-Dickinson method, a randomly selected
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The Gazzi-Dickinson method came out of separate work by P. Gazzi in 1966 and
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classification regardless of where the microscope landed in the point count.
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166:" method of Robert Folk (1974) (which later grew into the
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transport would change the composition of the sand.
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158:at the time, who used the more traditional "
122:studies. Typically, only framework (non-
27:Point-counting technique used in geology
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66:technique used in geology to
70:measure the components of a
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108:petrographic microscope
82:components as separate
60:Gazzi-Dickinson method
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18:Gazzi-Dickinson Method
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140:William R. Dickinson
204:Folk classification
168:Folk classification
148:Stanford University
48:Folk Classification
156:Indiana University
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144:Chris Suczek
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92:QFL diagrams
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44:plagioclase
210:References
120:provenance
90:, such as
80:sand-sized
74:, chiefly
36:phenocryst
293:Petrology
192:erosional
98:Technique
76:sandstone
40:amphibole
287:Category
268:103-116.
240:333–363.
198:See also
188:feldspar
179:granitic
152:tectonic
177:, or a
134:History
112:mineral
184:quartz
162:" or "
124:matrix
84:grains
146:) at
62:is a
186:and
175:grus
58:The
160:QFR
52:QFR
38:of
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