Detritus (geology)

January 25, 2024
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Detritus is particles of rock derived from pre-existing rock through weathering and erosion. A fragment of detritus is called a clast. Detrital particles can consist of lithic fragments (particles of recognisable rock), or of monomineralic fragments (mineral grains). These particles are often transported through sedimentary processes into depositional systems such as riverbeds, lakes or the ocean, forming sedimentary successions. Diagenetic processes can transform these sediments into rock through cementation and lithification, forming sedimentary rocks such as sandstone. These rocks can then in turn again be weathered and eroded to form a second generation of sediment. Detrital grains commonly weather at different rates, according to the Goldich dissolution series, which dictates that early crystallizing minerals are less stable at the earth’s surface than late crystallizing minerals.

Lithic fragments, or lithics, are pieces of other rocks that have been eroded down to sand size and now are sand grains in a sedimentary rock. They were first described and named (in their modern definitions) by Bill Dickinson in 1970. Lithic fragments can be derived from sedimentary, igneous or metamorphic rocks. A lithic fragment is defined using the Gazzi-Dickinson point-counting method and being in the sand-size fraction. Sand grains in sedimentary rocks that are fragments of larger rocks that are not identified using the Gazzi-Dickinson method are usually called rock fragments instead of lithic fragments. Sandstones rich in lithic fragments are called lithic sandstones.

Types

Igneous (Lv) can include granular (~rhyolitic), microlitic (~andesitic), lathwork (~basaltic), and vitric (glassy). These correlations between composition and volcanic lithic fragment type are approximate, at best. By definition, intrusive igneous rock fragments can not be considered lithic fragments.

Sedimentary (Ls) can include shale siltstone fragments, and (at times) chert.

Metamorphic (Lm) can include fine-grained schist and phyllite fragments, among others.

  • Dickinson, W. R. (1970). “Interpreting detrital modes of graywacke and arkose”. Journal of Sedimentary Petrology. 40: 695–707.
  • Affolter, M.D. and Hendrix, M. S., 2004, Correlations between volcanic lithic fragments and volcanic rock, Geological Society of America Abstracts with Programs, Vol. 36, No. 5, p. 370
  • Mathew D. Affolter, Raymond V. Ingersoll; Quantitative Analysis of Volcanic Lithic Fragments. Journal of Sedimentary Research ; 89 (6): 479–486. doi: https://doi.org/10.2110/jsr.2019.30

Goldich dissolution series

The Goldich dissolution series is a method of predicting the relative stability or weathering rate of common igneous minerals on the Earth’s surface, with minerals that form at higher temperatures and pressures less stable on the surface than minerals that form at lower temperatures and pressures.

Chemical weathering processes

S. S. Goldich derived this series in 1938 after studying soil profiles and their parent rocks. Based on sample analysis from a series of weathered localities, Goldich determined that the weathering rate of minerals is controlled at least in part by the order in which they crystallize from a melt. This order meant that the minerals that crystallized first from the melt were the least stable under earth surface conditions, while the minerals that crystallized last were the most stable. This is not the only control on weathering rate; this rate is dependent on both intrinsic (qualities specific to the minerals) and extrinsic (qualities specific to the environment) variables. Climate is a key extrinsic variable, controlling the water to rock ratio, pH, and alkalinity, all of which impact the rate of weathering. The Goldich dissolution series concerns intrinsic mineral qualities, which were proven both by Goldich as well as preceding scientists to also be important for constraining weathering rates.

Earlier work by Steidtmann demonstrated that the order of ionic loss of a rock as it weathers is: CO32-, Mg2+, Na+, K+, SiO2−, Fe2+/3+, and finally Al3+. Goldich furthered this analysis by noting the relative mineral stability order, which is related to the relative resistance of these ions to leaching. Goldich notes that overall, mafic (rich in iron and magnesium) minerals are less stable than felsic (rich in silica) minerals. The order of stability in the series echoes Bowen’s reaction series very well, leading Goldich to suggest that the relative stability at the surface is controlled by crystallization order.

While Goldich’s original order of mineral weathering potential was qualitative, later work by Michal Kowalski and J. Donald Rimstidt placed in the series in quantitative terms. Kowalski and Rimstidt performed an analysis of mechanical and chemical grain weathering, and demonstrated that the average lifetime of chemically weathered detrital grains quantitatively fit the Goldich sequence extremely well. This helped to supplement the real-world applicability of the dissolution series. The difference in chemical weathering time can span millions of years. For example, quickest to weather of the common igneous minerals is apatite, which reaches complete weathering in an average of 105.48 years, and slowest to weather is quartz, which weathers fully in 108.59 years.

See also

Bowen’s reaction series

The Goldich dissolution series follows the same pattern of the Bowen’s reaction series, with the minerals that are first to crystallize also the first the undergo chemical weathering. The Bowen’s reaction series dictates that during fractional crystallization, olivine and Ca-plagioclase feldspars are the first to crystalize out of a melt, after which follows pyroxene, amphibole, biotite, Na-plagioglase, orthoclase feldspar, muscovite, and finally, quartz. This order is controlled by the temperature of the melt and its composition. Because earlier crystallizing minerals are more stable at higher temperatures and pressures, these weather the fastest under surface conditions.

  • Bowen, N. L. (1956). The Evolution of the Igneous Rocks. Canada: Dover. pp. 60–62.
Saponite is a common weathering product of ultramafic and mafic rocks. It is found in high-pH evaporite lakes and in association with basalts or serpentines.

Common secondary minerals

Chemical weathering of igneous minerals leads to the formation of secondary minerals, which constitute the weathering products of the parent minerals. Secondary weathering minerals of igneous rocks can be classified mainly as iron oxides, salts, and phyllosilicates. The chemistry of the secondary minerals is controlled in part by the chemistry of the parent rock. Mafic rocks tends to contain higher proportions of magnesium and ferric and ferrous iron, which can lead to secondary minerals high in abundance of these cations, including serpentine, Al-, Mg- and Ca-rich clays, and iron oxides such as hematite. Felsic rocks tends to have relatively higher proportions of potassium and sodium, which can lead to secondary minerals rich in these ions, including Al-, Na- and K-rich clays such as kaolinite, montmorillonite and illite.

Olivine weathering to iddingsite within a mantle xenolith, a common reaction within the series

Application to soil profiles

The Goldich dissolution series can be applied to Lithosequences, which are a way characterizing of a soil profile based on its parent material. Lithosequences include soils that have undergone relatively similar weathering conditions, so variations in composition are based on the relative weathering rates of parent minerals. Therefore, the weathering rates of these soils and their compositions are primarily influenced by the relative proportion of minerals in the Goldich dissolution series.

Limitations

Experimental work by White and Brantley (2003) highlighted some of the limitations of the Goldich dissolution series, most notably that some variations in weathering rates of different minerals are not as pronounced as Goldich argues. According to the Goldich dissolution series,  anorthite, a plagioclase feldspar, should weather quickly, with a lifetime of 105.62 years quantified by Kowalski and Rimstidt. Conversely, the lifetime of K-feldspar should be much longer, at 108.53 years based again on Kowalski and Rimstidt’s work. However, White and Brantley’s experimental results demonstrate that the relative weathering rates of K-feldspar and plagioclase feldspar are quite similar, and mainly moderated by the extent to which the minerals had already been weathered (in an exponentially decreasing function). This demonstrates that the Goldich series may not apply across all kinds of weathering processes, and likewise does not take into account the effect of exponential decay in weathering rate of a surface.

References

  1. Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7
  2. Essentials of Geology, 3rd Ed, Stephen Marshak, p G-5
  3. Goldich, Samuel S. (1938-01-01). “A Study in Rock-Weathering”. The Journal of Geology. 46 (1): 17–58. Bibcode:1938JG…..46…17G. doi:10.1086/624619. ISSN 0022-1376. S2CID 128498195.
  4. Dickinson, W. R. (1970). “Interpreting detrital modes of graywacke and arkose”. Journal of Sedimentary Petrology. 40: 695–707.
  5. Affolter, M.D. and Hendrix, M. S., 2004, Correlations between volcanic lithic fragments and volcanic rock, Geological Society of America Abstracts with Programs, Vol. 36, No. 5, p. 370
  6. Mathew D. Affolter, Raymond V. Ingersoll; Quantitative Analysis of Volcanic Lithic Fragments. Journal of Sedimentary Research ; 89 (6): 479–486. doi: https://doi.org/10.2110/jsr.2019.30
  7. White, Art F; Brantley, Susan L (2003). “The effect of time on the weathering of silicate minerals: why do weathering rates differ in the laboratory and field?”. Chemical Geology. Controls on Chemical Weathering. 202 (3): 479–506. Bibcode:2003ChGeo.202..479W. doi:10.1016/j.chemgeo.2003.03.001. ISSN 0009-2541.
  8. Steidtmann, Edward (1908). “A graphic comparison of the alteration of rocks by weathering with their alteration by hot solutions”. Economic Geology. 3 (5): 381–409. doi:10.2113/gsecongeo.3.5.381. ISSN 0361-0128.
  9. Bowen, N. L. (1956). The Evolution of the Igneous Rocks. Canada: Dover. pp. 60–62.
  10. Kowalewski, Michał; Rimstidt, J. Donald (2003). “Average Lifetime and Age Spectra of Detrital Grains: Toward a Unifying Theory of Sedimentary Particles”. The Journal of Geology. 111 (4): 427–439. Bibcode:2003JG….111..427K. doi:10.1086/375284. ISSN 0022-1376. S2CID 129172662.
  11. Siever, Raymond; Woodford, Norma (1979). “Dissolution kinetics and the weathering of mafic minerals”. Geochimica et Cosmochimica Acta. 43 (5): 717–724. Bibcode:1979GeCoA..43..717S. doi:10.1016/0016-7037(79)90255-2. ISSN 0016-7037.
  12. Meunier, Alan (2005). Clays. France: Springer. p. 265. ISBN 3-540-21667-7.
  13. Stoch, Leszek; Sikora, Wanda (1976). “Transformations of Micas in the Process of Kaolinitization of Granites and Gneisses”. Clays and Clay Minerals. 24 (4): 156–162. Bibcode:1976CCM….24..156S. doi:10.1346/CCMN.1976.0240402. ISSN 1552-8367. S2CID 51812008.
  14. Sequeira Braga, M. A; Paquet, H; Begonha, A (2002). “Weathering of granites in a temperate climate (NW Portugal): granitic saprolites and arenization”. CATENA. 49 (1): 41–56. doi:10.1016/S0341-8162(02)00017-6. ISSN 0341-8162.
  15. White, Art F. (1995), “Chapter 9. CHEMICAL WEATHERING RATES OF SILICATE MINERALS IN SOILS”, Chemical Weathering Rates of Silicate Minerals, De Gruyter, pp. 407–462, doi:10.1515/9781501509650-011, ISBN 9781501509650, retrieved 2021-10-28

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