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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 3. (March)

First Page: 342

Last Page: 343

Title: Experiments in Sampling Sedimentary Rocks: ABSTRACT

Author(s): John C. Griffiths

Article Type: Meeting abstract


Random sampling to insure unbiased estimators of population characteristics is both critical and costly to achieve; if the internal "structure" of a population is defined as its patterned variability, then the sampling arrangement may be used to define the structure objectively

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and with any desired degree of precision.

For example, if a rock (population) is "massive" then no structure is apparent and various sampling patterns will yield equivalently unbiased estimators; on the other hand if the structure is layered, orthogonal patterns, with one parallel and the other perpendicular to the layers, will yield significantly different estimators unless the parallel pattern achieves correct weighting of the layers. In layered populations, patterns perpendicular to layers (channel sampling) will yield unbiased estimators of the population mean and variance; adjusting the parallel sampling pattern to equivalence with the perpendicular supplies information on the weighting, i.e., on the variation within and between layers and hence an estimate of the number of different layers. This then leads to an objecti e definition of layering.

In practice, when the internal structure is initially unknown, it is necessary to use different sampling patterns to decide whether the population (rock) is structured or massive.

The achievement of random sampling in various "populations," from testing techniques to deciphering "natural" variability, indicates that this procedure is a useful tool in defining the patterned variability or "structure" of a population. It appears to be invariant to change in variate (e.g., measurement or counting) or change in scale (e.g., from an electron micrograph to an outcrop).

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Copyright 1997 American Association of Petroleum Geologists