Richard V. Tyson

Bulk Geochemical Characterization and Classification of Organic Matter: Stable Carbon Isotopes (δ13C)

Stable carbon isotope analysis is one of the most widely used techniques for determining the source of organic matter in Recent environments. It has often been employed to determine relative proportions of phytoplankton and terrestrial carbon in suspended and sedimented organic matter in estuarine, marine and lacustrine settings (Sackett and Thompson, 1963; Sackett, 1964; Hunt, 1970; Eadie and Jeffrey, 1973; Newman et al., 1973; Shultz and Calder, 1976; Gearing et al., 1977; Spiker and Schemel, 1979; Tan and Strain, 1979; 1983; Rashid and Reinson, 1979; Salomons and Mook, 1981; Muller et al., 1983; LaZerte, 1983; Joyce et al., 1985; Torgerson and Chivas, 1985; Showers and Angle, 1986; Sackett, 1986; Fontugne and Duplessy, 1986; Fontugne and Jouanneau, 1987; Kennicutt et al., 1987; Calvert and Fontugne, 1987; Cai et al., 1988; Faganelli et al., 1988; 1991; Cifuentes et al., 1988; LeBlanc et al., 1989; Gagan et al., 1990; Jasper and Gagosian, 1990; Laane et al., 1990; Matson and Brinson, 1990; Lucotte et al., 1991; Mariotti et al., 1991; Mook and Tan, 1991; Tan et al., 1991; Raz-Guzman Macbeth and De La Lanza Espino, 1991; Naidu et al., 1993; Westerhausen et al., 1993).

Abundance of Organic Matter in Sediments: TOC, Hydrodynamic Equivalence, Dilution and Flux Effects

Because of ease of analysis, the abundance of organic matter in sediments is usually expressed as the relative dry weight percentage of organic carbon (Jarvie, 1991). However, kerogen includes significant amounts of other elements, especially hydrogen (3–10 wt%), oxygen (3–20 wt%), nitrogen (0–4 wt%), and sulphur (0–4 wt%). The proportion of these elements is not constant but depends on the source, preservation state, age, and maturation of the organic matter. The sediment organic matter content can be derived from the following equation if the carbon content of the bulk kerogen is known (Littke, 1993, p. 8):

Distribution of the Palynomorph Group: Phytoplankton Subgroup, Chlorococcale Algae

{\rm{OM wt\% = TOC x }}{{100} \over {{\rm{wt\% C content of bulk kerogen}}}}

Some Practical Aspects of Palynofacies Analysis

(5.1)

Bulk Geochemical Characterization and Classification of Organic Matter: Carbon:Nitrogen Ratios and Lignin-Derived Phenols

Viewed as a whole, the published palynological organic matter classifications are characterized by a great deal of duplication of effort that has resulted in much superfluous jargon. A generally acceptable terminology has proved elusive and so workers have continued to propose new terms to describe what are, by and large, a relatively familiar set of components. Some of the various criteria relevant to the choice of a kerogen classification are given in Table 20.1.

Bulk Geochemical Characterization and Classification of Organic Matter: Elemental Analysis and Pyrolysis

Botryococcus braunii has a cosmopolitan distribution in modern permanent to semipermanent ponds, lakes and rivers ranging from tropical to arctic latitudes (Blackburn, 1936; Aaronson et al., 1983, p. 694). It is most abundant in slow-flowing and lacustrine regimes (Traverse, 1992, p. 123). It is most characteristic of oligotrophic lakes (Hutchinson, 1967, pp. 381, 386; Wake and Hillen, 1981, p. 353; Wetzel, 1983, p. 353), but has also been recorded from mesotrophic waters (Round, 1981, pp. 267, 273, 279; Komarek and Marvan, 1992, p. 65). Wetzel (1983, p. 353) indicates that it is most abundant in neutral or slightly alkaline lakes, but it can occur over a pH range of 4–10 (Belcher, 1968, p. 345; Crisman, 1978, p. 447; Wake and Hillen, 1980, p. 1651; Bauld et al., 1985, p. 15). It appears to be most abundant in soft or ‘semi-hard’ waters (Prescott, 1951, p. 232; Crisman, 1978, p. 448).

The Nature of Organic Matter in Sediments

The study of the organic matter in sediments and sedimentary rocks focuses on the interaction between the biosphere and geosphere. A proper appreciation of the subject requires an understanding of the environmental controls which govern the production of organic matter in the biosphere, the ecological and sedimentological processes which control its deposition and distribution, the biogeochemical, and geomicrobiological factors which influence its preservation, and the geochemical and physical processes which determine its modification during its incorporation in the geosphere. This makes the study of sedimentary organic matter one of the most multidisciplinary pursuits within the whole field of earth sciences.

Distribution of the Palynomorph Group: Phytoplankton Subgroup, Acritarcha

Much palynofacies work has been done as a secondary exercise within palynostratigraphic studies. Unfortunately, this often means that the samples were collected using a strategy that emphasizes standard sampling intervals and the selection of only those lithologies likely to be most productive in terms of palynomorph yield. In my experience, some kind of quantitative change in the palynofacies characteristics should be expected whenever any lithological, sedimentological, palaeoecological or bulk geochemical change occurs (although they may also occur when these factors appear to remain constant). Consequently, palynofacies studies must deliberately attempt to assess these influences by ensuring not only a reasonable stratigraphic coverage, but by statistically valid replicate sampling of all lithologic and facies variants within every significant part of the section under study.