cover

Frank H. Fabricius:

Origin of Marine Oöids and Grapestones

1977. V, 113 pages, 6 figures, 1 table, 18 plates, 16x24cm, 280 g
Language: English

(Contributions to Sedimentary Geology, Volume 7)

ISBN 978-3-510-57007-2, paperback, price: 32.00 €

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Keywords

geologysedimentgrapestoneorginGeologieSedimentAggregatkörnerHerkunft

Contents

Synopsis top ↑

The cortex of marine ooids and the agglutinating carbonate of grapestones are composed of identically shaped aragonitic particles, both rods and granules. In both cases, the particles are the product of a biomineralization by burrowing thallophytes, probably, blue—green algae.

The key to formation of the ooid cortex is the process of grapestone aggregation. Burrowing algae bind together adjacent sedimentary grains, first by algal threads and mucilage, and then by endomucilage calcification. Later, the voids between component grains are filled by aragonitic rods embedded in algal mucus. Finally, this calcification can lead to an ooid cortex around the entire grapestone nucleus.

While grapestone formation necessititates stability of the sediment, theformation of ob'ids requires sufficient grain movement to prevent the algae from binding adjacent grains. The conditions for Gold growth are: bright illumination of warm and shallow sea water supersaturated with respect to CaCO3. The secretion of aragonite by algae is interpreted as a possible physiological response to this particular environment.

A genetic line is proposed which links ooids and grapestones with stromatolites and oncolites. On the other hand, aragonite secretion by thallophytes within the marine realm, may also contribute to a perhaps major extent to the formation of aragonitic mud. The biocalcification of primitive algae reveals to be one of the oldest and geologically most important processes for the formation of marine shallow water calcareous sediment. The response of the thallophytic algae to physicochemical differences of the environment can explain the facies differentiation into ooid sand, grapestone aggregate sand, and lime mud, respectively.

Three conditions can exclude ooid or grapestone formation: 1. The skeletal grain on which burrowing algae settle yields more nutrients for the algae than the ambient water; 2. the calcareous or noncal— careous grains are deposited in sea water deeper than about 10 meters; 3. the grains are deposited in cold sea water, less saturated in respect to CaCO3 than normal to tropical and subtropical zones.

The micritization of ooids (and probably also of other carbonate grains) is interpreted as an intra-granular cementation below a cover of algal mucilage.

Structural differences between the cortex of a) marine ooids composed of rods and granules (i.e. of particles showing no crystalline faces and edges under the scanning electron microscope [= “aphanohedral” habit of crystals]), and b) of other coated grains with a radial crystalline cortex (from hypersaline environments, caves or mines, or of synthetic origin etc.), are genetically significant and should be used in nomenclature of coated grains: It is suggested that only grains of type (a) are called ob'ids, while type (b) grains should be termed spheroids.

Table of Contents top ↑

Abstract 1
Zusammenfassung 1
Preface 4
Acknowledgement 5
1. Introduction and Problems 6
1.1 Occurrence of Marine Oolitic Sediments in Time and Space 6
1.11 Paleogeographic Significance of Marine Oôids 7
1.12 Importance of Modern Oôid Formation on the Great
Bahama Bank- A Quantitative Example 8
1.2 Theories of Oôid Formation 10
1.21 History and Discussion of the “Biological Theories” 11
1.211 Theories Concerning Direct Biological influence 11
1.212 Theories Concerning Indirect Biological Influence 12
1.213 Discussion of Arguments Against Oôid Biogenesis 13
1.3 Is the “Oôid Problem” a Terminological problem? 14
1.31 The Range of Problems of Marine Oôid Formation 15
1.4 The Problem of Grapestone Formation and its Relation to the “Oôid Problem” 15
1.41 Occurrence of Grapestones 16
1.42 Nomenclature of Grapestone Aggregates 16
1.43 The Problem of Grapestone “Cement”16
2. Scanning Electron Microscope Observations 18
2.1 Ultrastructures of Marine Oôids 18
2.11 Discrimination of Organic and Inorganic Structures 18
2.12 Structures of the Grain Surface 19
2.121 Rods and Granules 19
2.121.1 Orientation of the Rods 20
2.122 Other Particles Adhering to the Oôid Surface 21
2.13 Fabric of the Cortex 21
2.14 Cortex Voids 22
2.141 Inter-Particle Porosity 22
2.142 Biogenic Porosity, the Habitat of Algae 22
2.142.1 Pores22
2.142.2 Burrows 22
2.142.21 Tunnelling Burrows 23
2.142.22 Configuration of the Tunnelling System 23
2.142.23 Tube-LikeTunnels 24
2.142.24 ‘Spherical Caverns’ 24
2.142.25 Burrows in Pellets 24
2.143 Collapse Features on the Oôid Surface 25
2.15 Structures of Surface Corrosion 25
2.16 Organic Matter in Oôids 26
2.2 Ultrastructures of Grapestones 26
2.21 Introduction-Stages of Agglutination 26
2.22 Structures of the Pre-Grapestone Stage 26
2.221 Surface Structures 27
2.23 Structures of the Grapestone Stage 27
2.231 Mucilage Bindings and Their Relation toCarbonate Particles 27
2.232 Burrows and ‘Tubiform Constructions’ in Grapestones and the
Question of Calcified Algal Threads 28
2.232.1 Burrows 28
2.232.2 Epilithic ‘Tubiform Constructions’ 28
2.233 Aglutination Versus Cementation of Grapestones 29
2.24 Structures of the Transitional Stage 30
2.25 Structures of the Botryoidal Stage 30
2.26 Biogenic Alterations of Grapestones 30
2.261 Constructiva Features 31
2.261.1 Foraminifera 31
2.261.2 A Serpulid-Like Tube 31
2.262 Destructive Alterations 31
2.263 Organic Features of Uncertain Relationship to Aggregates 32
2.3 Crystallization in Voids of Ooids, Pellets and Grapestones 32
2.31 Aragonite Filling 33
2.32 (Mg-?)CalciteFilling 33
2.4 Comparative Investigations 33
2.41 Ultrastructures of Selected Calcareous Algae 33
2.42 Ultrastructures of Spheroids of the High-Salinity Environment and
their Relation to Marine Ooid Structures 34
2.43 Structural Comparison with Other Non-Marine Coated Grains 34
3. Interpretation and Discussion 35
3.1 Building Units of Oôids and Spheroids 35
3.11 TheRod-and-GranuleGroup 35
3.12 The Crystalline Group 36
3.121 Primary Radial-Crystalline Structures 36
3.13 Comparison of Structures and Origin of‘Rods’ 37
3.14 Remarks on the Nomenclature of Coated Grains 38
3.141 Coated Grains 38
3.141.1 Oóid and Oolite 38
3.141.2 Spheroid and Spherolite 39
3.141.3 Oncoids 39
3.2 The Role of Thallophytes in Oôids 40
3.21 Observations and Implications 40
3.22 Formation of Aragonitic Particles by Algae 40
3.23 Formation of the Ooid Cortex 42
3.231 Significance of the Burrowing Activity of Thallophytes 42
3.232 Structure of the Calcification 43
3.233 Infestation of Oôids by Burrowing Algae? 44
3.3 Discussion: Phytogenesis of Marine Oôids 46
3.31 Environmetal Conditions 46
3.311 Elevated Temperature of Sea Water 46
3.312 CaC03 Saturation of Surface Sea Water 46
3.313 The Role of Water Turbulence 47
3.313.1 Quiet-WaterOöids 47
3.313.2 Ooid Formation in High-Energy Environment 47
3.313.3 Granulometry of Oöid Sediments 48
3.313.4 Coherence of Particles Within the Oöid Laminae 48
3.314 The Role of Nuclei 49
3.315 The Role of Light 49
3.316 The Role of Nutrients 50
3.32 Chemical and Isotopic Peculiarities of Oöids and Grapestones
in the Light of their Phytogenesis 50
3.321 Strontium Content 50
3.322 Fluorine Content 51
3.323 13C/12CRatio 51
3.4 Interpretation and Discussion of Grapestone Aggregation 51
3.41 The Process of Aggregation 52
3.5 Differentiation and Patterns of Oöid and Grapestone Facies 54
3.51 Relation between Different Phytogenic Shallow Water Sediments 55
3.52 Implications on the “Carbonate Mud Problem” 55
3.53 Annotation to the Term “Non-Skeletal” 56
3.6 Organic Matter in Oöids and Grapestones as a Source of
Carbohydrates 56
3.7 “Micritization” in Oöids, Grapestones and Skeletal Fragments 56
3.8 Remarks on the Mineralogy of Ancient “Non-Skeletal” Carbonates 58
3.9 Open Problems 60
Conclusions 60
Appendix: Localities and Description of Samples 65
Bibliography 67
Plates (1-18) of Scanning Electron Micrographs 78