Biostratigraphic and Geological Significance of Planktonic Foraminifera
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Biostratigraphic and Geological Significance of Planktonic Foraminifera
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Overview
The role of fossil planktonic foraminifera as markers for biostratigraphical zonation and correlation underpins most drilling of marine sedimentary sequences and is key to hydrocarbon exploration. The first - and only - book to synthesize the whole biostratigraphic and geological usefulness of planktonic foraminifera, Biostratigraphic and Geological Significance of Planktonic Foraminifera unifies existing biostratigraphic schemes and provides an improved correlation reflecting regional biogeographies.
Renowned micropaleontologist Marcelle K. Boudagher-Fadel presents a comprehensive analysis of existing data on fossil planktonic foraminifera genera and their phylogenetic evolution in time and space. This important text, now in its Second Edition, is in considerable demand and is now being republished by UCL Press.
Product Details
| ISBN-13: | 9781910634271 |
|---|---|
| Publisher: | U C L Press, Limited |
| Publication date: | 10/02/2015 |
| Series: | Global Dutch |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 306 |
| File size: | 21 MB |
| Note: | This product may take a few minutes to download. |
About the Author
Dr Marcelle K. BouDagher-Fadel is a Professorial Research Fellow in the Office of the Vice-Provost (Research) at UCL. She graduated with a BSc from the Lebanese University and has an MSc and PhD from UCL. She has an extensive publication record, having written three major books and over 130 papers. She is an established consultant with several oil companies, lectures widely, and supervises PhD students from around the world.
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Biostratigraphic and Geological Significance of Planktonic Foraminifera
By Marcelle K. Boudagher-Fadel
UCL Press
Copyright © 2015 Marcelle K. BouDagher-FadelAll rights reserved.
ISBN: 978-1-910634-27-1
CHAPTER 1
An introduction to planktonic foraminifera
1.1 The biological classification of the foraminifera
Foraminifera are marine, free-living, amoeboid protozoa (in Greek, proto = first and zoa = animals). They are single-celled eukaryotes (organisms the cytoplasm of which is organized into a complex structure with internal membranes and contains a nucleus, mitochondria, chloroplasts, and Golgi bodies, see Fig. 1.1), and they exhibit animal-like (cf. plant-like) behaviour. Usually, they secrete an elaborate, solid carbonate skeleton (or test) that contains the bulk of the cell, but some forms accrete and cement tests made of sedimentary particles. The foraminiferal test is divided into a series of chambers, which increase in number during growth. In life, they exhibit extra-skeletal pseudopodia (temporary organic projections) and web-like filaments that can be granular, branched and fused (rhizopodia), or pencil-shaped and pointed (filopodia). The pseudopodia emerge from the cell body (see Plate 1.1 below) and enable bidirectional cytoplasmic flow that transports nutrients to the body of the cell (Baldauf, 2008). Foraminifera first appeared in the Cambrian with a benthic mode of life and, over the course of the Phanerozoic, invaded most marginal to fully marine environments. They diversified to exploit a wide variety of niches, including, from the Late Triassic or Jurassic, the planktonic realm. These planktonic forms are the focus of this book.
Both living and fossil foraminifera come in a wide variety of shapes. They occupy different micro-habitats and exploit a diversity of trophic mechanisms. Today, they are extremely abundant in most marine environments from near-shore to the deep sea, and from near surface to the ocean floor. Some even live in brackish habitats.
The complexity and specific characteristics of the structure of foraminiferal tests (and their evolution over deep-time) are the basis of their geological usefulness. After the first appearance of benthic forms in the Cambrian, foraminifera became abundant, and by the late Palaeozoic, they exhibited a relatively large range of complicated test architectures. Their continued evolution and diversification throughout the Mesozoic and Cenozoic, and the fact that they still play a vital role in the marine ecosystem today, means that foraminifera are of outstanding value in zonal stratigraphy, paleoenvironmental, paleobiological, paleoceanographic, and paleoclimatic interpretation and analysis.
Fossil and living foraminifera have been known and studied for centuries. They were first mentioned in Herodotus (in the fifth century BC), who noted that the limestone of the Egyptian pyramids contained the larger benthic foraminifera Nummulites. Their name is derived from a hybrid of Latin and Greek terms meaning "bearing pores or holes," as the surfaces of most foraminiferal tests are covered with microscopic perforations, normally visible at about 40x magnification. Among the earliest, workers who described and drew foraminiferal tests were Anthony van Leeuwnhock in 1600 and Robert Hooke in 1665, but the accurate description of foraminiferal architecture was not given until the nineteenth century (see Brady, 1884; Carpenter et al., 1862; see Fig. 1.2).
The systematic taxonomy of the foraminifera is still undergoing active revision. The first attempts to classify foraminifera placed them in the Mollusca, within the genus Nautilus. In 1781, Spengler was among the first to note that foraminiferal chambers are, in fact, divided by septa. In 1826, d'Orbigny, having made the same observation, named the group foraminifera. In 1835, foraminifera were recognized by Dujardin as protozoa, and shortly afterwards, d'Orbigny produced the first classification of foraminifera, which was based on test morphology. The taxonomic understanding of foraminifera has advanced considerably over the past two decades, and recent studies of molecular systematics on living forms are revealing their very early divergence from other protoctistan lineages (Wray et al., 1995). In this book, we follow Lee's (1990) elevation of the Order Foraminiferida to Class Foraminifera, and the concomitant elevating of the previously recognized suborders to ordinal level. Throughout this book, therefore, the suffix "-oidea" is used in the systematics to denote superfamilies, rather than the older suffix "-acea", following the recommendation of the International Commission on Zoological Nomenclature (see the International Code of Zoological Nomenclature 1999, p. 32, Article 29.2). Modern workers normally use the structure and composition of the test wall as a basis of primary classification, and this approach will be followed here.
Despite the diversity and usefulness of the foraminifera, the phylogenetic relationship of foraminifera to other eukaryotes remains unclear. According to early genetic work on the origin of the foraminifera by Wray et al. (1995), the phylogenetic analysis of verified foraminiferal DNA sequences indicates that the foraminiferal taxa are a divergent "alveolate" lineage, within the major eukaryotic radiation. Their findings cast doubt upon the assumption that foraminifera are derived from an amoeba-like ancestor, and they suggested that foraminifera were derived from a heterokaryotic flagellated marine protist. For these authors, the phylogenetic placement of the foraminifera lineage is a problem, as the precise branching order of the foraminifera and the "alveolates" remained uncertain. Following the work of Wray et al. (1995), many scientists have tried to trace the origin of the foraminifera using a variety of methods, but molecular data from foraminifera have generated conflicting conclusions. Molecular phylogenetic trees have assigned most of the characterized eukaryotes to one of the eight major groups. Archibald et al. (2003) indicated that cercozoan and foraminiferan polyubiquitin genes (76 amino acid proteins) contain a shared derived character, a unique insertion, which implies that foraminifera and cercozoa share a common ancestor. They proposed a cercozoan-foraminiferan supergroup to unite these two large and diverse eukaryotic groups. However, in other recent molecular phylogenetic studies, the foraminifera are assigned to the Rhizaria, which are largely amoeboid unicellular forms with root-like filose or reticulosed pseudopodia (Archibald, 2008; Cavalier-Smith, 2002; Nikolaev et al., 2004). The cercozoa and foraminifera groups are included within this supergroup (see Fig. 1.3). Additional protein data, and further molecular studies on rhizarian, cercozoan, and foraminiferan forms, are necessary in order to provide a more conclusive insight into the evolution and origins of these pseudopodial groups.
1.2 Planktonic foraminifera
Foraminifera are separated into two types following their life strategy, namely, the benthic and the planktonic foraminifera. The benthic forms occur at all depths in the marine realm. They vary in size from less than 100 µm in diameter to a maximum breadth of many centimetres. Benthic foraminiferal tests may be agglutinated (quartz or other inorganic particles being stuck together by calcitic or organic cements), or may be primarily secreted and composed of calcite, aragonite, or (rarely) silica. They include many species that live attached to a substrate or that live freely and include organic-walled and agglutinated small foraminifera that dominate the deep-sea benthic microfauna, as well as a major group of foraminifera with complicated internal structures, the so-called larger benthic foraminifera (BouDagher-Fadel, 2008), that include major reef-forming species. However, the other type of foraminifera, which is just as successful as their benthic ancestors, namely, the planktonic foraminifera, is the subject of our study, and the remainder of this book will be focused on them.
Planktonic foraminifera have tests that are made of relatively globular chambers (that provide buoyancy) composed of secreted calcite or aragonite. They float freely in the upper water of the world's oceans, with species not exceeding 600 µm in diameter. They have a global occurrence and occupy a broad latitudinal and temperature zone. The majority of planktonic foraminifera float in the surface or near-surface waters of the open ocean as part of the marine zooplankton. The depth at which a given species lives is determined in part by the relative mass of its test, with deeper dwelling forms usually having more ornamented and hence more massive tests. Upon death, the tests sink to the ocean floor and on occasion can form what is known as a foraminiferal ooze. On today's ocean floors, Globigerina oozes (named after the important foraminiferal genus Globigerina that dominates the death assemblage ooze) may attain great thickness and cover large areas of the ocean floor that lie above the calcium carbonate compensation depth, the depth below which all CaCO dissolves. Today, planktonic and larger benthic calcareous foraminifera are among the main calcifying protists, contributing almost 25% of the present-day carbonate production in the oceans (Langer, 2008). Planktonic foraminifera occur, therefore, in many types of marine sediment, which on lithification yield carbonates or limestones. These rocks become hardened and denser on lithification, and their constituent microfossils often can only be studied in thin section. They can be dated by the presence of a few key planktonic foraminiferal taxa, which provide excellent biostratigraphic markers, and are sometimes the only forms that can be used to date carbonate successions (see Fig. 1.4 and subsequent chapters).
Planktonic foraminifera show high diversity and adaptability, both in their morphology and biology. Planktonic foraminifera have undergone significant evolution since their first development from benthic forms in the Late Triassic or Jurassic (see Chapter 3). They consist of a large number of identified and stratigraphically defined species, and exhibit a rich and complex phylogenetic history. Foraminiferal tests of fossil and living forms have been systematically described (at generic and suprageneric levels) by Loeblich and Tappan (1964, 1988). What is known about living foraminifera has been reviewed by Lee and Anderson (1991) and their colleagues, while the biology of modern planktonic foraminifera has been presented by Hemleben et al. (1989) and Sen Gupta et al. (1997). More recently, their proteins and molecular biology have been analyzed in greater detail, and this will be discussed further in Chapter 2. Fossilized forms, however, are known, of course, only by their tests. Morphological criteria such as the globular nature of the test and other features (discussed below and in more detail in subsequent chapters) have been used to determine that fossil forms were indeed planktonic, while the other microfossils associated with them have helped to ascertain their deep-water marine habitat and, in some cases, to constrain their age determination.
Because of the abundance of planktonic foraminiferal tests in most marine sediments, and because of the regularity of their structures and their taxonomic diversity, they provide continuous evidence of evolutionary changes (see Fig. 1.5) from which detailed phylogenetic relationships can be established. Their well-defined biostratigraphic ranges and phylogenetic relationships have been found to be useful in both academic studies of global evolution and by the hydrocarbon industry for correlation in sedimentary sequences. In particular, the petroleum exploration industry finds the planktonic foraminifera to be of great utility, because they are easy to extract from both outcrop and subsurface samples, and enable biostratigraphic dating to be carried out in new exploration areas very quickly. Examples of their industrial use come from publications sponsored, for example, by Exxon (Stainforth et al., 1975a, b), the Royal Dutch Shell Group (Postuma, 1971), and British Petroleum (Blow, 1979). Postuma (1971) presented illustrations of Albian and younger forms, while Stainforth et al. (1975a, b) and Blow (1979) deal solely with Cenozoic taxa in the West, and Subbotina (1953) with those of the former Soviet Union. The planktonic foraminifera that are found in sediments of Middle Cretaceous and younger age have, for over 50 years, been used for worldwide biostratigraphic correlation (e.g., Bolli, 1957).
Taxonomic research is fundamental to maximizing the usefulness of planktonic foraminifera in stratigraphical studies, as precise zonal stratigraphy depends upon precise discrimination of genera and species. Planktonic foraminifera are classified taxonomically using criteria based on the characteristics of their external calcareous test. Identification is based on general morphology as well as the ultrastructural and microstructural features of the test (Hemleben et al., 1989) as seen by transmission electron microscopy (TEM) (Bé et al., 1966) and scanning electron microscopy (SEM) (Cifelli, 1982; Lipps, 1966; Scott, 1974). The features of the planktonic foraminiferal tests of importance in classification at the generic and specific levels usually deal with their chamber arrangements, the nature of sutures, the wall structures, and the nature of external ornamentation, perforations, apertures, and accessory structures. Some of the classifications put emphasis upon aperture position and external apertural modifications, while others distinguish the different families on the basis of fine details of wall structure and wall surface, including whether they are smooth, pitted (possessing distinct external pore-funnels with externally enlarged outlet of the pores), or spinose (possessing spines).
This morphological approach to taxonomy has led to the identification of many families of planktonic foraminifera that have evolved, and (on many occasions) gone into extinction, since their initial development from benthic ancestors in the Late Triassic or Jurassic. The entire phylogenetic lineage of the planktonic foraminifera is shown in Fig. 1.6. In subsequent chapters, the process by which this evolutionary tree has been established will be explained, but first in this chapter, the different morphological characteristics, upon which the taxonomy of planktonic foraminifera is based, will be discussed with reference to exemplar forms belonging to the specific families of foraminifera named in Fig. 1.6. These foraminifera will be discussed in a systematic way in subsequent chapters, where we will combine all criteria of structure, sculpture, and morphological features to present an overview of the taxonomy of the different families, genera, and species at different stages of the stratigraphic column. An excellent glossary of the terminology used in the description of foraminiferal morphology has recently been electronically published by Hottinger (2006), and this should be referred to as necessary for exact definitions of some of the terms introduced below.
1.2.1 The morphology, sculpture, and structure of the test of planktonic foraminifera
Foraminiferal tests rarely consist of only one chamber; usually, as the organism grows, it adds successively additional, progressively larger chambers to produce a test of varying complexity. The intrinsic buoyancy of the planktonic foraminifera is provided by the generally globular nature of their chambers. Some living planktonic foraminifera add a new chamber every day and grow at a rate that sees them increase their diameter by about 25% per day (Anderson and Faber, 1984; Bé et al., 1982; Caron et al., 1981; Erez, 1983; Hemleben et al., 1989).
Planktonic foraminifera have different patterns of chamber disposition (see Fig. 1.7):
• Trochospiral growth has the chambers coiling along the growth axis while also diverging away from the axis. The test has dissimilar evolute spiral and involute umbilical sides (Fig. 1.7A–C, H).
• Involute trochospiral growth has the chambers biserial or triserial in early stages, later becoming enrolled biserial, but with biseries coiled into a tight, involute trochospire (Fig. 1.7E).
• Planispiral growth has the chambers coiling along the growth axis but showing no divergence away from the axis. The test is biumbilicate, with both the spiral and umbilical sides of the test being identical and symmetrical relative to the plane of bilateral symmetry (Fig. 1.7G, I).
• Streptospiral growth has the chambers coiling in successively changing planes, or with the last globular chamber completely embracing the umbilical side (Fig. 1.7F).
• Uniserial, biserial, triserial multiserial, etc., patterns of growth have (after an initial planispiral or trochospiral stage) chambers arranged in one, two, three, or more rows in a regularly superposed sequence. The biserial form is planar (Fig. 1.7J, K), but multiserial forms can be three dimensions forming a conical test (Fig. 1.7L).
(Continues...)
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Table of Contents
1 An introduction to planktonic foraminifera
2 The biological and molecular characteristics of living planktonic foraminifera
3 The Mesozoic planktonic foraminifera: The Late Triassic–Jurassic
4 The Mesozoic planktonic foraminifera: The Cretaceous
5 The Cenozoic planktonic foraminifera: The Paleogene
6 The Cenozoic planktonic foraminifera: The Neogene
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