Sedimentary Organic Matter

Frontmatter

1. Introduction: The Importance of Sedimentary Organic Matter

Abstract

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.

Richard V. Tyson

2. The Nature of Organic Matter in Sediments

Abstract

While biologists, oceanographers and those concerned with early diagenesis are mainly interested in the labile organic fraction that is consumed prior to burial, most geologists focus their attention on the much smaller fraction that survives diagenesis to become a potential source of hydrocarbons. However, the significance of the general terms ‘refractory’ and ‘labile’ (what is, or is not, degradable) depends very much upon one’s viewpoint and working time-scale. The views expressed in the literature reflect the differing perspectives of the laboratory, modern surficial sediments and geological timescales (that is, from hours to millions of years). Many of the short-term observations made in the laboratory and on the upper few tens of centimetres of Recent sediments are of limited relevance to long-term geological considerations of carbon burial and source rock potential.

Richard V. Tyson

3. Production and Delivery Flux of Planktonic Organic Matter

Abstract

The importance of primary productivity is very conspicuous in modern aquatic environments because photosynthetic carbon production can be quantified routinely and thus correlated with other physicochemical and biological variables. It is thus natural that primary productivity occupies a key position in the thoughts of biological and chemical oceanographers. However, for those geologists concerned with pre-Quaternary sediments, primary productivity is a much more elusive parameter, and one that is often impossible to quantify to any really useful degree (often because of the absence of the chronological resolution necessary for appropriately detailed flux calculations). This means that primary productivity does not tend to hold the same position of importance in geological thinking. Geologists do not, of course, deny the importance of primary productivity, but in the general absence of hard data, it is not a parameter that has been foremost in their minds or in their modelling.

Richard V. Tyson

4. Biological Degradation and Consumption of Organic Matter

Abstract

The energy source for metabolic processes (the enzyme controlled synthesis of organic molecules) is derived from the redox reaction between reductants (electron donors) and oxidants (electron acceptors). Oxidation involves the loss of electrons (from the electron donor) and reduction involves electron gain (by the electron acceptor); oxidation and reduction reactions must occur in balanced pairs (redox couples). The energy required to remove electrons from ions in a given chemical environment is measured by the redox potential (Eh, the half-cell potential determined against a standard hydrogen electrode). The electron activity (pe) is a similar measure (the tendency for electrons to flow from reduced to oxidized ‘species’), but unlike Eh it is independent of temperature (Libes, 1992, p. 115). The greater the difference in pe between the reductant and the oxidant, the more free energy that can be derived from the redox reaction and used to fuel metabolic processes (ibid., p. 118).

Richard V. Tyson

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

Abstract

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):

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

(5.1)

Richard V. Tyson

6. Organic Matter Preservation: The Effects of Oxygen Deficiency

Abstract

Dysoxic-anoxic conditions are rare in modern seas and oceans. Oceanographic hydrochemical data collected during the last 100 years indicate that suboxic conditions (< 0.2 ml l⁻¹ of O₂) are especially rare in waters deeper than 1500 m (Kamykowski and Zentara, 1990; Fig. 5.12). Oxygen concentrations in deep ocean waters (> 3000 m) currently fall below 3 ml l⁻¹ only in the northern Arabian Sea, the Bering Sea and a zone up to 1200 km wide along the coast of the Americas between 55°N and 5°S (Mantyla and Reid, 1983). Significant preservational effects should only be expected at dysoxic or lower oxygen values, and certainly not above 1–2 ml l⁻¹ Consequently, as noted by Lyle (1988), bottom water oxygen plays little role in determining carbon burial in most Recent-Pleistocene open ocean sediments.

Richard V. Tyson

7. Origin and Nature of the Phytoclast Group

Abstract

The majority of dispersed fossilizing phytoclasts are derived from the ligno-cellulosic tissues of terrestrial macrophytes. Most probably represent fragments of strongly lignified mechanical support and vascular tissues of the secondary xylem (‘wood’) of arborescent gymnosperms and angiosperms (plus the analogous tissues in tree ferns and extinct vascular plants that exhibited secondary growth). The preservation of this material is enhanced by the highly stable, resistant and hydrophobic nature of lignin. Lignin decay is mostly due to ‘mouldering’ by slow-growing lignolytic white-rot fungi (mainly Basidiomycotina) under oxic subaerial conditions (Teichmüller, 1982a, p. 228; Deacon, 1984, p. 152; Rayner and Boddy, 1988, pp. 123, 239, 242; Robinson, 1990; sections 22.1.2, 22.2). These fungi probably derive little energy from the lignin itself, but rather utilize the chemically bonded cellulose associated with it (Deacon, 1984, p. 152). This may be why the action of white-rot fungi does not necessarily result in extensive depolymerization of lignin, but often only the loss of some low molecular weight ‘degradation fragments’ (Given, 1988, p. 19).

Richard V. Tyson

8. Origin and Nature of the Amorphous Group

Abstract

The Amorphous Group consists of all particulate organic components that appear structureless at the scale of light microscopy, including phytoplankton- or bacteriallyderived amorphous organic matter (traditionally referred to as ‘AOM’), higher plant resins, and amorphous products of the diagenesis of macrophyte tissues. The amorphous material (especially ‘AOM’) commonly acts as a matrix for a diversity of structured inclusions.

Richard V. Tyson

9. Origin and Nature of the Palynomorph Group, Phytoplankton Subgroup

Abstract

Full descriptions of the morphology and taxonomy of palynomorphs are not given in this work because this is not a palynology text book, and because these aspects are covered at length elsewhere (Tschudy and Scott, 1969; Châteauneuf and Reyre, 1974; Brasier, 1980; Tappan, 1980; Evitt, 1985; Traverse, 1988; Lipps, 1993). This account will concentrate mainly on the distribution patterns of the palynomorphs in marine and, to a lesser extent, lacustrine sediments. Further descriptive (but non-taxonomic) detail is provided only for the phytoplankton, where I have concentrated mainly on those geologically important groups that are sparsely treated in palynological and often also phycological, texts (e.g. Chlorophyta, prasinophytes, and cyanobacteria). Those seeking botanical background information on, or taxonomic treatment of, the origin and detailed terrestrial palaeoecology of spores and pollen (and their parent plants) are referred to the appropriate palynological texts cited above, and to the botanical, palaeobotanical, and Quaternary palynology literature. In marine sediments, with which this work is primarily concerned, the botanical and floral controls on the production and initial distribution of spores and pollen are of generally much diminished importance compared to subsequent hydrodynamic and sedimentological factors.

Richard V. Tyson

10. Origin and Nature of the Zoomorph Subgroup, and the Origin, Nature and Distribution of the Zooclast Group

Abstract

The so-called ‘chitinous’ tectin linings of foraminifera (Hedley 1964) are often conspicuous elements of marine palynological assemblages. A historical review of their study is given by Stancliffe (1989). The linings of planispiral foraminifera are generally predominant (Traverse and Ginsburg, 1966, p. 440; Traverse, 1988, p. 8; Phadtare and Thakur, 1992, p. 248) but all morphological types (uniserial, biserial, etc.) are found (Stancliffe, 1989; Courtinat and Méon, 1991). The linings are typically dark brown in colour, although their outer chambers are often more thin-walled and translucent (McKee et al., 1959, p. 544; Traverse and Ginsburg, 1966, p. 438; Plates E6, E7). The thickness of the lining varies between 1 and 10 μm (Hedley, 1964). Tectin foraminiferal linings are at least as resistant as sporopollenin palynomorphs (Traverse, 1988, p. 36).

Richard V. Tyson

11. Distribution of the Phytoclast Group

Abstract

Coarse phytoclast material (> 1 mm) is usually only dominant in high, first and second order, headwater streams (Minshall et al., 1985, p. 1051). Although the input of organic matter to head waters is largely in the form of such coarse (CPOM) material, biological processing and the high retention characteristics of such streams result in the export to lower order streams being predominantly of fine material (FPOM, < 1 mm). In consequence, the ratio of transported coarse to fine material tends to decrease rapidly downstream (Naiman, 1982, p. 1078), although in specific cases habitat type is often more important than stream order (Minshall et al., 1983, p. 9). Steady state downstream decreases in mean particle size have also been recorded within the suspended FPOM fraction of higher order streams (Wallace et al., 1982, p. 829). As smaller particles show higher microbial respiration rates (Naiman and Sedell, 1979b, p. 412) phytoclast particles tend to become more refractory as particle size decreases, eventually resulting in increases in both lignin content and C/N ratios (Cummins and Klug, 1979, p. 149; Ward, 1984; Bowen, 1984, p. 444).

Richard V. Tyson

12. Distribution of the Amorphous Group

Abstract

Amorphous organic matter ‘AOM’ frequently dominates the kerogen assemblages in which it is found. This is because there always appears to be a relatively large ‘reservoir’ of autochthonous (phytoplankton-derived) organic matter present in marine environments, which if preserved under sufficiently reducing conditions, ‘swamps’ the allochthonous, terrestrial components.

Richard V. Tyson

13. Distribution of the Palynomorph Group: Sporomorph Subgroup

Abstract

Muller (1959, p. 28) was one of the first workers to show that the settling rates of most sporomorphs are comparable to those of fine quartz silt. Similarly, Stanley (1965, p. 31) observed that although most sporomorphs are the size of coarse silt grains, their lower density means that they are hydrodynamically equivalent to medium silt or finer siliciclastic grains. Matsushita (1985) also observes that riverborne pollen is hydrodynamically equivalent to particles in the range 11–44 µm (fine to coarse silt). Pollen influx is therefore often strongly correlated with the influx of silt-sized sediment (Clark, 1986, p. 67; Fig. 13.1), the total suspended sediment load of rivers and river discharge (Matsushita, 1985). Consequently, sporomorphs (and most palynomorphs in general) are concentrated in the clay to silt size fraction, i.e. < 63 µm (de Jekhowsky, 1958, p. 1394; Rossignol, 1969, pp. 122-3). Sediments with over 30–40% sand-sized material generally exhibit lower sporomorph abundances (Mudie, 1982, p. 732; cf. Reyre, 1973, pp. 238, 242).

Richard V. Tyson

14. Distribution of the Palynomorph Group: Phytoplankton Subgroup, Marine Dinoflagellate Cysts (Dinocysts)

Abstract

There is no simple relationship between cyst abundance and dinoflagellate primary productivity (Wall et al., 1977, p. 173). This is partly because the cyst-forming taxa and individuals are a small and inconsistent proportion of both the dinoflagellate and the total phytoplankton population (section 9.2), and partly because their distribution is modified by sedimentological and hydrographic factors. Once produced, the hydrodynamic behaviour of dinocysts is similar to that of other small sedimentary particles; most are medium to coarse silt-sized (16–62 (µm), but behave like fine silt or clay (≤ 15 µm) and thus become selectively concentrated in finegrained sediments (McKee et al., 1959, p. 540; Rossignol, 1969, p. 143; Davey, 1970, p. 342; Wall, 1971, p. 401; Dale, 1976; Rogers and Bremner, 1991, p. 64). Within the same general region where the motile phase forms blooms, hydrographic and sedimentary processes commonly lead to the corresponding cysts being selectively deposited in areas of fine-grained sediment termed ‘seed beds’ (≤ 2000 km⁻²; White and Lewis, 1982, p. 1186).

Richard V. Tyson

15. Distribution of the Palynomorph Group: Phytoplankton Subgroup, Marine Prasinophyte Phycomata

Abstract

Many palynological studies of Cambrian to Quaternary (≤ 570 Ma) sediments have shown that an ‘abundance’ of prasinophyte algae is strongly correlated with the occurrence of marine (shelf and oceanic) organic-rich finely-laminated sediments deposited under dysoxic to anoxic conditions (Appendix B). This appears to be more than a preservational effect.

Richard V. Tyson

16. Distribution of the Palynomorph Group: Phytoplankton Subgroup, Chlorococcale Algae

Abstract

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; Komárek 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).

Richard V. Tyson

17. Distribution of the Palynomorph Group: Phytoplankton Subgroup, Acritarcha

Abstract

The abundance of acritarchs in Palaeozoic marine sediments is reported to be generally in the range 100–10 000 g⁻¹ of sediment (Downie, 1973, p. 240), although values up to 100 000 g⁻¹ and 900 000 cm-3 have occasionally been reported (Tappan, 1980, p. 187). Like most other palynomorphs, acritarchs are most numerous in fine-grained, argillaceous, low energy facies, and least numerous (< 10 g⁻¹) in sandstones and high energy reefal or bioclastic carbonates (Staplin, 1961, p. 396; Downie, 1973, p. 240; Jacobson, 1979, p. 1209; Doming and Bell, 1987, pp. 274, 281-2).

Richard V. Tyson

18. Distribution of the Palynomorph Group: Phytoplankton Subgroup, Cyanobacteria and Rhodophyta

Abstract

Gloeocapsomorpha-rich kukersite ‘oil shales’ occur in the Ordovician (Arenigian-Ashgillian, 493-439 Ma) of the Baltic, USA, Canada and Australia (Foster et al., 1986, p. 154; Hoffmann et al., 1987; Macauley et al., 1990; Fowler, 1992, p. 349; Kõrts, 1992). Ordovician Gloeocapsomorpha is also known from south-west Turkey (J.G.S. Goodall, personal communication, 1991; Goodarzi et ah, 1992, p. 28). Possible Silurian occurrences of Gloeocapsomorpha are reported from Arctic Canada and the Hudson Bay area (Cramer and Díez, 1972, pp. 130-1; Cramer and Díez, 1974a, p. 145), although the dating is questionable (Fowler, 1992, p. 348). Palaeocontinental reconstructions suggest that these Ordovician-Silurian Gloeocapsomorpha-rich sediments are mainly distributed between 5° and 15° either side of the palaeoequator (Cramer and Díez, 1972, pp. 130-1; Forster et ah, 1986, p. 153; Fig. 18.1).

Richard V. Tyson

19. Distribution of the Palynomorph Subgroup: Zoomorph Subgroup

Abstract

The distribution of foraminiferal linings is primarily controlled by that of the foraminifera which produce them. Foraminifera are larger and heavier than most palynomorphs, are not transported in the same fashion, and are generally much less abundant in terms of numbers of individuals per volume or weight of sample. Furthermore, as only part of the foraminiferal population present in a sample will produce linings, it is not surprising that they are usually a minor component of the kerogen. My personal observations indicate that they are often < 1%, and rarely > 5% on a relative particle frequency basis; however, Oboh (1992a, p. 79) reports 8–11% in Miocene (23.3-5.2 Ma) prodelta facies from the Niger Delta. Foraminiferal linings are usually < 15% of the palynomorph population, but may occasionally reach up to 50% or more (Mebradu, 1978; Decommer, 1982). They may represent up to 75% of the marine palynomorphs in some hemipelagic facies (e.g. Courtinat and Méon, 1991, p. 565). Their frequency is best considered separately from marine microplankton counts so that their relative abundances can be assessed independently or as a ratio.

Richard V. Tyson

20. Palynological Kerogen Classification

Abstract

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.

Richard V. Tyson

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

Abstract

The classification of kerogen into Types I, II and III was first introduced by Tissot et al. (1974), based on an extrapolation of Van Krevelen’s work on coals to dispersed kerogen in other lithologies (Van Krevelen, 1961, pp. 113-20). The kerogen types are ‘defined’ by the atomic ratios of hydrogen and carbon, and oxygen and carbon, as determined by elemental analysis (Durand and Monin, 1980). A cross-plot of these parameters (now referred to as a ‘Van Krevelen diagram’, Fig. 21.1) can show both the composition of the organic matter and the way this is gradually modified during maturation, biochemical oxidation or weathering (by loss of water, carbon dioxide and hydrocarbons).

Richard V. Tyson

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

Abstract

Carbon to nitrogen ratios have been extensively employed by ecologists, biogeochemists and geologists as an indicator of the source, the nutritional value and the degree of biological and diagenetic alteration of organic matter. They were the most common chemical method of characterizing organic matter before the use of stable carbon isotope and pyrolysis methods became widely available, and are still widely utilized today. The use of C/N ratios is based on two basic premises: first that the nutritional value of organic matter is positively correlated with bulk nitrogen content, and second, that phytoplankton-derived organic matter has a significantly higher bulk nitrogen content than terrestrial organic matter.

Richard V. Tyson

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

Abstract

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; Müller 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).

Richard V. Tyson

24. Palynofacies in a Sequence Stratigraphic Context

Abstract

Sequence stratigraphy is a systematic way of looking at well established and familiar stratigraphic concepts such as eustatic cycles, transgression and regression, diachroneity, and progradation, retrogradation and aggradation. It represents a powerful methodology for modelling and analysing geometric, spatial and temporal patterns of sediment accumulation in sedimentary basins, especially in relation to the pervasive influence of relative changes in sea level. Although sequence stratigraphy has developed as a natural extension of subsurface studies based on the seismic stratigraphy approach pioneered by the Exxon Production Research Company (Payton, 1977), the underlying principles can also be applied at outcrop scale. Applications of sequence stratigraphy are highly fashionable and are becoming increasingly common in all aspects of surface and subsurface sedimentary geology.

Richard V. Tyson

25. Some Practical Aspects of Palynofacies Analysis

Abstract

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.

Richard V. Tyson

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