11 results
The Exceptional Preservation of Interesting and Informative Biomolecules
- Roger E. Summons
-
- Journal:
- The Paleontological Society Papers / Volume 20 / October 2014
- Published online by Cambridge University Press:
- 21 July 2017, pp. 217-236
- Print publication:
- October 2014
-
- Article
- Export citation
-
Organic carbon compounds record key aspects of the processes of their formation and mechanisms of preservation and are foci for research into the nature of life on the early Earth and the search for life beyond Earth. Prime in this respect are lipids preserved in sediments and sedimentary rocks that reveal much about the evolutionary trajectory of life on our planet. Lipids, predominantly derived from photoautotrophic microbes, dominate hydrocarbon records in the Precambrian. The rise to prominence of the Metazoa in the late Neoproterozoic, metaphytes in the Paleozoic, and modern plankton in the Mesozoic, can also be seen in the occurrences of distinctive molecular fossils. Organic matter of all types is optimally preserved in environments and sediments where radiation (solar and ionizing) and oxygen are excluded. In the marine realm, anoxic water bodies will often become sulfidic (euxinic) due to the activity of sulfate-reducing bacteria. Phototropic sulfur bacteria thrive in such environments, and the presence of their characteristic carotenoid pigments goes hand-in-hand with the enhanced preservation of all organic matter, driven by the reducing power of sulfide. The deleterious effects of radiation and oxygen on the preservation of organic matter are amply demonstrated by the results of ongoing searches for carbon compounds on the surface of Mars. The production of highly oxidizing substances through radical chemistry operating in the Martian atmosphere has resulted in environmental conditions that virtually assure destruction of much of the organic matter produced in situ or carried there on meteorites and interplanetary dust particles.
3 - Terran Metabolism
- from Part II - Origin of Planets and Life
- Edited by Chris Impey, University of Arizona, Jonathan Lunine, Cornell University, New York, José Funes, Vatican Observatory, Vatican City
-
- Book:
- Frontiers of Astrobiology
- Published online:
- 05 December 2012
- Print publication:
- 15 November 2012, pp 48-72
-
- Chapter
- Export citation
19 - Composition of Extractable Organic Matter
-
- By Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Harald Strauss, Ruhr-Universität Bochum
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 811-820
-
- Chapter
- Export citation
-
Summary
The data presented in this Chapter summarize the available, relevant, organic geochemical parameters for Proterozoic sediments which have, in the course of this project, been studied for their bitumen content and composition.
In Tables 19.1–19.4, “N/A” (not analyzed) indicates that an analysis was not carried out; and “NM” (not measured) indicates that a value for the parameter indicated was not determined, usually because some factor precluded its measurement. Two numbering systems are used here:
(1) Samples included in the PPRG sample collection which were subjected to initial Rock–Eval screening (Chapter 16) are identified by PPRG Sample Number only. Several of these samples, together with others that were acquired late in the project, were re-analyzed at the Bureau of Mineral Resources (BMR), Canberra, Australia, and are therefore denoted by dual PPRG and BMR Sample Numbers. Data regarding the geographic and geologic origin of PPRG samples are included in Chapter 14.
(2) Samples that were collected and analyzed specifically as part of BMR projects are denoted by BMR Sample Numbers only; information about the orgins of these samples is included in BMR publications and unpublished databases.
10 - Biostratigraphy and Paleobiogeography of the Proterozoic
-
- By Hans J. Hofmann, University of Montreal, Stefan Bengtson, Uppsala Universitet, J. M. Hayes, Indiana University, Jere H. Lipps, University of California, J. William Schopf, University of California, Harald Strauss, Ruhr-Universität Bochum, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 487-520
-
- Chapter
- Export citation
-
Summary
Biostratigraphy deals with bodies of rock defined or characterized by their fossil content. Biogeography is concerned with the geographic distribution of organisms. The basic biostratigraphic principles and concepts now in use were developed in the early- to mid-nineteenth century by pioneers such as William Smith (1769–1839), Georges Cuvier (1769–1832), Alcide d'Orbigny (1802–1857), and Albert Oppel (1831–1865) who divided the stratigraphic record into successions of distinct faunal assemblages; the fundamental biostratigraphic unit still in use is the biozone, which usually is named after a dominant or a characteristic species. Fossils were unknown in pre-Cambrian rocks in 1835, when Adam Sedgwick introduced the concept of the Cambrian System; in fact, this interval was subsequently given names that referred to the presumed nonexistent or primitive paleontologic record (Agnotozoic, Archeozoic, Azoic, Eozoic, Protozoic, etc.).
Precambrian paleontology started in the 1850s, with the discovery of remains thought to be organic (for an historical summary, see Section 5.2 and Hofmann 1982, pp. 246–247). Although many of the early reported forms later were shown to be pseudofossils, some were true fossils. The number of accepted fossil occurrences increased slowly over the next 100 years, but only after the Second World War did Proterozoic biotic abundance and diversity become established by discoveries in various parts of the world (see Section 5.2). By the late 1950s, data were sufficient to be put to use in subdividing and correlating sequences locally and regionally, principally in the Soviet Union, giving rise to the subdiscipline of Precambrian biostratigraphy.
6 - Modern Mat-Building Microbial Communities: a Key to the Interpretation of Proterozoic Stromatolitic Communities
-
- By Beverly K. Pierson, University of Puget Sound, John Bauld, Bureau of Mineral Resources, Richard W. Castenholz, University of Oregon, Elisa D'Amelio, Ames Research Center, David J. Des Marais, Ames Research Center, Jack D. Farmer, University of California, John P. Grotzinger, Massachusetts Institute of Technology, Bo Barker Jørgensen, University of Aarhus, Douglas C. Nelson, University of California, Anna C. Palmisano, Ivorydale Technical Center, J. William Schopf, University of California, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd, David M. Ward, Montana State University
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 245-342
-
- Chapter
- Export citation
-
Summary
Introduction
Modern microbial mats are structurally coherent macroscopic accumulations of microorganisms. Mats are widely distributed on earth. They are found in a surprisingly large number of diverse environments from the equatorial zones to both polar regions. They vary in size from extensive terrestrial and hypersaline mats that cover areas several square kilometers in extent to minute mats only a few square centimeters in area found in small thermal springs. They vary in thickness from massive accumulations measured in meters, such as those in the Persian Gulf and the Red Sea region, to thin films less than a few millimeters in thickness. In addition to being highly varied in size, modern microbial mats are also very diverse in morphology, community structure, and physiological characteristics. What do such mats have in common? Under what conditions do they form? What is the basis of their diversity? What insight do they provide, if any, to the interpretation of the widespread stromatolites of the Proterozoic?
A Terminology
Microbial mats are accretionary cohesive microbial communities which are often laminated and found growing at the sediment-water (occasionally sediment-air) interface. Most mats stabilize unconsolidated sediment. The mats are comprised of the various microorganisms that accumulate along with their metabolic products. The most conspicuous of these products is usually a copious amount of extracellular polysaccharide which helps hold the cells together to form a cohesive structure.
18 - Procedures for Analysis of Extactable Organic Matter
-
- By Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Harald Strauss, Ruhr-Universität Bochum
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 799-810
-
- Chapter
- Export citation
-
Summary
As is discussed in Section 3.1.1, great care must be exercised to avoid contamination of extractable hydrocarbon samples by extraneous bitumens, particularly if the TOC (total organic carbon) content is low or if the amount of sample is small. In this study, sediment cores and outcrop samples were pre-rinsed with CH2C12 and dried to remove external contaminants. Where sample size permitted, external surfaces were removed by cutting with a diamond saw. Samples were then hammered to chips which were subsequently crushed to less than 200 mesh in a ring crusher. Rock powders were stored in clean glass containers. Lids were lined with pre-baked aluminium foil. All items used to handle the samples were scrupulously washed with hot water, and then distilled solvent, between each use.
TOC determination and Rock–Eval pyrolysis analysis were found to be particularly informative screening techniques. Samples with less than 0.2% TOC (i.e., <2mgC/g) were generally considered unsuitable for comprehensive hydrocarbon analysis because of the problems of contamination, although elemental and carbon isotopic analyses of their kerogens were parameters which could be reliably established at this low level of organic carbon. Samples with >0.2% TOC were usually assessed using Rock–Eval pyrolysis and the results interpreted using guidelines discussed by Espitalié et al. 1977. The relative proportions of bitumen (the Rock–Eval S1 peak in kg/tonne) and kerogen (S2 peak in kg/tonne), the pyrolysis temperature Tmax (°C), and the overall appearance of the pyrograms all provided useful information.
3 - Proterozoic Biogeochemistry
-
- By J. M. Hayes, Indiana University, David J. Des Marais, Ames Research Center, Ian B. Lambert, Resource Assessment Commission, Australia, Harald Strauss, Ruhr-Universität Bochum, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 81-134
-
- Chapter
- Export citation
-
Summary
Biogeochemistry encompasses the study of chemical fossils. It includes and draws on knowledge of the biochemical activities of contemporary organisms in modern sedimentary environments, including their roles in the biogeochemical cycling and isotopic fractionation of important elements such as carbon, oxygen, sulfur, and nitrogen, and their production of taxonomically distinctive organic compounds. This Section deals with the chemical entities preserved in the Proterozoic sedimentary record that may carry information about the biology and evolution of early life.
Chemical fossils can be discerned at the atomic level, in the occurrence of anomalous concentrations of a particular element or an isotope; at a molecular level, in the structure and stereochemistry of hydrocarbons derived from membrane lipids or pigments; and at a macromolecular level by way of the preservation of detailed chemical structures in kerogen and morphologically distinct microfossils. Paleobiochemical information is encoded in the nucleic acids of extant organisms and in their comparative biochemistry; this topic is treated in Chapter 9. Here we examine and discuss the occurrence of isotopic and molecular fossils. A considerable and consistent body of information derived, in part, from techniques developed during exploration for petroleum and minerals is now available. Rapid expansion of this knowledge is presently taking place, particularly with regard to chemical processes in early preservation of organic matter, structures of kerogen, isotopic composition of individual biomarkers, and global secular variations in organic and inorganic isotopic abundances.
16 - Procedures of Whole Rock and Kerogen Analysis
-
- By Harald Strauss, Ruhr-Universität Bochum, David J. Des Marais, Ames Research Center, J. M. Hayes, Indiana University, Ian B. Lambert, Resource Assessment Commission, Australia, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
-
- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 699-708
-
- Chapter
- Export citation
Origin and alteration of organic matter of the Oxford Clay Formation (U.K.) determined from bulk geochemical analyses
- Fabien Kenig, Brian Popp, Roger Summons
-
- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 163
- Print publication:
- 1992
-
- Article
-
- You have access Access
- Export citation
-
To understand the processes controlling production, accumulation, and preservation of organic matter in the Lower Oxford Clay (LOC), we determined the hydrogen index (HI), the oxygen index (OI), the Tmax (from Rock-Eval), the content of total organic carbon (TOC), total carbon and total sulfur, and the carbon isotopic composition of bulk organic matter from 160 samples collected from 6 different quarries and one continuous core. With concentrations of TOC varying between 0.5% and 16.6%, the LOC is an organic-rich shale. For samples dominated by organic matter of phytoplanktonic origin, the hydrogen and oxygen indices and the Tmax (~418°) indicate low levels of maturity, and, thus, the shallow burial of the LOC through geologic time.
Two main sources of organic matter can be distinguished: a major phytoplanktonic source with high HI and low OI and a minor terrestrial source with low HI and high OI. A third group, represented by samples with low HI and low OI, consists mainly of altered materials from the Middle Oxford Clay and the LOC. Selection of samples for chemical analysis was based on the macrofaunal assemblages defined by Duff (1975). These various biofacies are characterized by specific organic geochemical features indicating the relationship between conditions affecting faunal assemblages and those controlling accumulation and preservation of organic matter. For example, Duff's ‘deposit feeder shales', which are dominated by epifaunal bivalves and are depleted in infaunal organisms, exhibit the highest concentration and best preservation of marine organic matter, with an average TOC of 6.8% for 56 samples analyzed. The preservation of such organic matter requires a dysaerobic water column and a high sedimentation rate.
Carbon isotopic compositions within the ‘deposit feeder shale’ biofacies (−27.6 to −23.2±) appear to have been controlled by the intensity of primary productivity. The highest-TOC, marine-dominated, 13C-rich samples reflect photosynthetic drawdown of dissolved-CO2 level, and, thus, originated in highly productive environments. On the other hand, variations in the carbon isotopic composition of organic matter in shell beds (−27.5 to −26±) probably reflect heterotrophic reworking of the organic matter, winnowing of the sediments, and mixing with a source of organic matter enriched in 13C, such as wood (δ13C from −25 to −23±). Such mixing phenomena may also explain the high variability of the carbon isotopic compositions of TOC-depleted and altered samples from the Middle and Upper Oxford Clay.
The environment of deposition of the LOC would be characterized by the alternation of two major conditions: 1) periods of high productivity, dysoxic water column and high sedimentation rate leading to the development of organic-rich shales dominated by phytoplanktonic organic matter, and 2) periods of low productivity, oxic water column and high current activity implying winnowing and alteration of organic matter, and leading to the formation of shell beds where marine and terrestrial organic matter are mixed.
An isotopic biogeochemical study of the Oxford Clay Formation (U.K.)
- Fabien Kenig, John M. Hayes, Roger Summons
-
- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 162
- Print publication:
- 1992
-
- Article
-
- You have access Access
- Export citation
-
Lipids from a suite of 12 representative samples from the Lower Oxford Clay (LOC) and from the Middle and Upper Oxford Clay (MUOC) were extracted with organic solvent, separated, and analyzed qualitatively and quantitatively using gas chromatography-mass spectrometry (GC-MS) and isotopically using isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS). Determination of molecular structures allowed identification of compounds which retained enough chemical structural information to be recognizable as having a biochemical origin related to a specific organism or group of organisms (biomarkers). By allowing assignment of each compound to a portion of the local carbon cycle (production, sedimentation, and alteration), isotopic analyses of individual compounds provided further information regarding their origins. The 12 samples were chosen to represent the various macrofaunal assemblages define by Duff (1975) and to cover the total range of variability of the bulk geochemical parameters measured on sediments from LOC and MUOC (Kenig et al., this symposium).
A relatively high content of unsaturated hydrocarbons, as well as the abundance of biogenic forms of molecular stereoisomers such as ββ hopanes and ααα steranes and other molecular indicators, confirms the low level of maturity of organic matter in the LOC. Contributions from the two main sources of sedimentary organic matter already identified from bulk geochemical data, marine phytoplankton and terrestrial organic matter, can be recognized in the saturated hydrocarbon fraction of all the samples analyzed. However, contributions from these two sources vary as a function of the TOC content, the HI, and the δ13C of organic matter. Saturated hydrocarbon fractions of high-TOC samples, formed during periods of high marine productivity, are mainly dominated by pristane and phytane and by tetra- and pentacyclic biomarkers. This dominance decreases with the TOC content and the 13C abundance. Conversely, the relative abundance of compounds indicative of terrigenous input increases. In samples with lower TOC, n-alkanes with a strong odd-carbon preference, peaking at C27, are particularly prominent in the saturated hydrocarbon fraction.
Biosynthetic products with n-alkyl carbon skeletons are found in nearly all organisms. Accordingly, sedimentary n-alkanes are likely to derive from multiple sources. These can be partly distinguished by isotopic analysis of individual n-alkanes. In particular, marine and terrestrial sources can be resolved. Considering the variation of their relative abondance and of their isotopic composition as a function of TOC, δ13C of total organic matter and hydrogen index, the origins of n-alkanes, pristane and phytane as well as those of other biomarkers will be discussed. The paleobiological assemblage responsible for the production and alteration of the organic matter will be tentatively reconstructed.
Biomarkers: Molecular Fossils
- Roger E. Summons
-
- Journal:
- Short Courses in Paleontology / Volume 1 / 1988
- Published online by Cambridge University Press:
- 17 July 2017, pp. 98-113
- Print publication:
- 1988
-
- Article
- Export citation
-
Curiosity about the history of life on our planet is a major motivational force for earth scientists. Fossil organic compounds, the components of petroleum and sedimentary organic matter, record aspects of the evolution of the biosphere from as far back as 1.8 billion years and perhaps longer. Elucidation of this record is continually advancing as a result of the concerted interests and efforts of geologists, biologists and chemists. It is also aided by advances in technique and instrumentation. Fascinating new developments and insights abound. In this paper I review some early landmarks and discuss the recent progress made in organic geochemistry, particularly as it applies to biomarker research. The examples of recent work are heavily biased toward my own interests and are not intended to be comprehensive. Because the literature citations are also selective and rely heavily on reviews, readers are advised to seek out the primary literature for accurate detail of specific subjects.