The Effect of Grain Size on Detrital Modes: A Test of the Gazzi-Dickinson Point-Counting Method

Abstract

Other| March 01, 1984 The effect of grain size on detrital modes: a test of the Gazzi-Dickinson point-counting method Raymond V. Ingersoll; Raymond V. Ingersoll Univ. N.M., Dep. of Geol., Albuquerque, NM, United States Search for other works by this author on: GSW Google Scholar Thomas F. Bullard; Thomas F. Bullard Search for other works by this author on: GSW Google Scholar Richard L. Ford; Richard L. Ford Search for other works by this author on: GSW Google Scholar Joel P. Grimm; Joel P. Grimm Search for other works by this author on: GSW Google Scholar John D. Pickle; John D. Pickle Search for other works by this author on: GSW Google Scholar Steven W. Sares Steven W. Sares Search for other works by this author on: GSW Google Scholar Author and Article Information Raymond V. Ingersoll Univ. N.M., Dep. of Geol., Albuquerque, NM, United States Thomas F. Bullard Richard L. Ford Joel P. Grimm John D. Pickle Steven W. Sares Publisher: SEPM Society for Sedimentary Geology First Online: 03 Mar 2017 Online ISSN: 1938-3681 Print ISSN: 1527-1404 GeoRef, Copyright 2006, American Geological Institute. Journal of Sedimentary Research (1984) 54 (1): 103–116. https://doi.org/10.1306/212F83B9-2B24-11D7-8648000102C1865D Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Raymond V. Ingersoll, Thomas F. Bullard, Richard L. Ford, Joel P. Grimm, John D. Pickle, Steven W. Sares; The effect of grain size on detrital modes: a test of the Gazzi-Dickinson point-counting method. Journal of Sedimentary Research 1984;; 54 (1): 103–116. doi: https://doi.org/10.1306/212F83B9-2B24-11D7-8648000102C1865D Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Sedimentary Research Search Advanced Search Abstract Differing methods of determining detrital modes of sand/sandstone have been developed by different "schools" due to different goals and different geologic settings. The Gazzi-Dickinson method of point counting was developed to maximize source-rock data, while minimizing the time, effort, and expense of gathering such data. Use of the method minimizes variation of composition with grain size, thus eliminating the need for sieving and multiple counts of different size fractions. Unsorted samples of any sand size may be used, thus allowing direct comparison between modern sands and poorly sorted ancient sandstones. The application of actualistic petrologic models relating composition to tectonic setting thus is facilitated. The unique aspect of the Gazzi-Dickinson method of point counting is the assignment of sand-sized crystals and grains within larger fragments to the category of the crystal or grain, rather than to the category of the larger fragment. In addition, every attempt is made to reconstruct original detrital compositions in spite of subsequent alterations. Six unconsolidated Holocene sand samples derived from a variety of source rocks in north-central New Mexico were collected, sieved, impregnated, sectioned, stained and point-counted, using both traditional and Gazzi-Dickinson methods. Results of these counts provide a comparative test of traditional and Gazzi-Dickinson methods. There are two reasons for variation of modal composition with grain size: 1) the breakage of fragments into constituent grains, and 2) actual mineralogic variation with grain size. The Gazzi-Dickinson method successfully eliminates the first source of compositional grain-size dependency. No point-counting method eliminates the second source. Use of the Gazzi-Dickinson method on unsorted samples produces results that are consistent with those from different size fractions of the same samples. Lithic-fragment compositions (for example, LmLvLs, QpLvmLsm) are especially consistent and provide the most useful parameters for relating composition to source rock and, ultimately, to tectonic setting. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.