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Über dieses Buch

This book focuses on the world’s largest mangrove delta complex, located at Sundarban, a world heritage site, and on the relatively new and rapidly expanding scientific discipline of ichnology. In addition to presenting a range of ichnological research databases that are widely applicable to multidisciplinary research fields in geology, biophysics, biology, ecology, geomorphology and the marine and environmental sciences, it addresses the global concern of rising sea levels to explain growing ecological problems, from the mass mortality of coastal organisms and rapid loss of mangrove forest wealth, to widespread coastal and riverbank erosion. It also demonstrates the value of applying new ichnological tools to coastal geotechnical planning and programming, and to groundwater exploration. Thus, the book addresses a broad readership including earth scientists from various disciplines, state administrators and members of the general public.



Chapter 1. Introduction

The topic “Mangrove Ichnology of the Bay of Bengal coast, eastern India”, before entering into subjective details, deserves a comprehensive introduction to the (1) historical background of the subject Ichnology, (2) regional geotectonic and stratigraphic aspects of the Bengal Basin, which is the cradle of world’s largest delta complex (the Ganga-Brahmaputra-Meghna or simply the Bengal Delta Complex) that now prograde southward into the Bay of Bengal Sea and (3) general ecological (including geomorphological, sedimentological and environmental details; biodiversity and known endangered species; adaptations of trace-making faunas; importance and recognitions of the coastal mangroves) and Quaternary geological aspects of the mangrove-vegetated coastal belt of the Bengal Delta Complex, known popularly as the Sundarban Mangrove deltas , that geographically extends over the eastern India and Bangladesh. Besides discussion on the scopes and objectives and materials and methods of the present work, this chapter addresses all the said introductory aspects of the topic of the book.
Chirananda De

Chapter 2. Common Trace-Making Endobenthic Invertebrates

The most commonly encountered trace-making endobenthic invertebrates, their general habits and habitats and over all geographic distribution patterns are addressed here. These organisms are overwhelmingly dominated by decapod crustaceans (mainly crabs). Some gastropods, bivalves, polychaetes and anomurans also produce distinctive traces and are prime associates of the decapods.
Chirananda De

Chapter 3. Descriptive Ichnology

The chapter descriptive ichnology includes several common and newly adopted self-explanatory terminology and morphological parameters to address geometric, preservational and genetic aspects of the lebensspuren produced by wide varieties of endobenthic invertebrates that are typical of the Sundarban mangrove ecosystem. Seilacher’s (Approaches to palaeoecology. Wiley, New York, pp 296–316,1964) and Matinson’s (Geol J Spec Issue 3:323–330, 1970) toponomic terms are useful in description and classification of bioturbation structures relative to preservation and occurrence within a stratum. Frey’s (J Sed Petrol 43:6–19, 1973) descriptive and genetic terms, such as tracks, trails , burrows , burrow system, shaft and tunnel, burrow lining, burrow casts etc., provide more clear picture of the traces. Simpson’s (The study of trace fossils. Springer-Verlag, New York, pp 39–54, 1975) morphological terms, such as prods, multi layered, simple trail, spiral, branched etc. are also in use to describe common invertebrate traces. The author in the following sections has applied many of the above terms to describe present modern as well as preserved ichnological features of the Bay of Bengal coast. The organo-sedimentary structures produced by several genera and species of crabs thriving in the coastal and estuarine zones, polychaete Diopatra cupria, bivalves Tagelus plebeius and Macoma birmanica, gastropods Turritella spp. and Telescopium spp., sea anemoes and star fish, besides those produced by unknown organisms especially in modern and ancient dune sands, older clay and woodgrounds and biomats have been discussed here in details. Trace morphometry has been linked to sexual dimorphism, ontogenetic variations, hydrodynamic and other environmental parameters based on huge field database collected by the author over a few decades.
Chirananda De

Chapter 4. Biophysical Mechanism of Crab Burrowing

In terms of specific diversity and behavioral adaptations crabs (~4500 species) are important amongst crustaceans (~26,000 species). The true crabs (Brachyurans) exhibit wide range of habitat adaptations in freshwater, brackish water and marine environments. The burrowing (e.g., Uca spp.), running (e.g., Ocypode spp.) and swimming (e.g., Callinectes spp.) crabs leave various types of trace fossils , especially in post-Jurassic sedimentary rocks. Proper interpretation of the fossilized crab burrows from rock records in terms of geoenvironmental, hydrodynamic and geomorphological parameters demands a thorough understanding of the biophysical mechanisms involved in the burrowing processes of true crabs in different modern environmental settings. The biophysical mechanisms of crab burrowing both in shallow tidal marine and estuarine river bank settings as interpreted from the present study are addressed in this chapter. The application potential and significance of the present biophysical model of intertidal crab burrowing in ichnotaxonomy, recognition of fossilized crab burrows, characterization of the Psilonichnus ichnofacies, palaeoenvironmental and palaeogeographical analyses have been addressed here.
Chirananda De

Chapter 5. Environmental Zonation

Natural zoogeographic distribution of the trace-producing endobenthic organisms with reference to environmental attributes and geomorphic features primarily control the distribution and relative abundance of their traces or lebensspuren that define distinctive ichnological zones (or ichnozones) and constituent subzones. Two broad environmental ichnozones, named as coastal and lower estuarine ichnozones , have been recognized in the study area. These zones include subzones defined by specific organism(s) and their traces. Most of the Bay of Bengal ichnozones and subzones are attributable to diagnostic coastal subenvironments and geomorphic settings. For example, Uca-Turritella-Telescopium subzone of the backswamps and upper intertidal pellet spread subzone within the coastal ichnozone. This chapter deals with detailed characterization of the ichnozones and subzones with the help of wide field database that includes location maps of the sampled lebensspuren and representative ichnoprofile sections across the five reference beach sectors.
Chirananda De

Chapter 6. Preservation of Traces

Study on the preservation processes of modern traces is important as it enhances their chances to be fossilized in due course. It is the first step towards fossilization. Modes of preservation decide the resultant architecture of the trace fossils . Depositional environments, besides many post depositional physical and chemical processes, decide the mode of preservation of modern traces. Preservation potential of a structure in a given environmental setting decides its availability in rock record as trace fossil. Various aspects of preservation potential of the modern traces are addressed here. The preserved Kalna and Nabadweep traces have been identified ichnotaxonomically. Styles of preservation under episodic, steady and high energy conditions of deposition are also discussed.
Chirananda De

Chapter 7. Ichnofacies and Ichnofabrics

Seilacherian ichnofacies are defined as trace fossil assemblages that recur through long intervals of geologic time and are more or less characteristic of a given set of environmental conditions (Frey and Pemberton 1984, 1985). Essential to the ichnofacies concept is their archetypal nature. Following this concept, the identified ichnofacies and ichnofabric superimpositions pertaining to the study area have been addressed in this chapter in terms of environmental changes. Following this concept, the identified ichnofacies and ichnofabric superimpositions pertaining to the study area have been addressed in this chapter in terms of environmental changes.
Chirananda De

Chapter 8. Geological and Geotechnical Significance

In coastal marine facies, relative to their associates, crabs are accepted as important geologic agents (Frey et al. in J Palaeontol 58:333–350, 1984) because of their taxonomic diversity amongst crustaceans (4500 out of 26,000 species), very selective adaptability with the ecosystems, ability to produce wide range of environment-sensitive lebensspuren (Edwards and Frey in Senckenberg Marit 9:215–259, 1977) and bioerosional as well as biodepositional capabilities (Letzsch and Frey in Senckenberg Marit 12:201–212, 1980; De in Curr Sci 75:617–620, 1998). These characteristics qualify crustacean burrows, recent as well as ancient, as important geological tools for wide range of geological and geotechnical interpretation. This chapter addresses various geological and geotechnical importances and applications of the studied burrows and their preserved counterparts in stratigraphic records.
Chirananda De

Chapter 9. Summary, Conclusions and Recommendations

The basic objectives of this book are set for (1) removing a big and long lasting gap in our understandings on mangrove ichnology ; (2) detailed characterization of the ichnological elements in terms of ichnotaxonomy , environmental zonation, bathymetry, ichnofacies , ichnofabrics , organic life habits, biophysical principles of trace making activities, sexual dimorphism, ontogenic variations, sea level changes, ecological adaptations and preservation potential; (3) creation of a classified database on lebensspuren typical of mangrove deltaic ecosystem as modern analogues of ancient trace fossils and some of the enigmatic Proterozoic fossils and dubiofossils and (4) application of present knowledge to the past in various fields of geology, hydrogeology and geotechnology. This concluding chapter provides a summary of the work done, salient conclusions and a few recommendations with reference to a new field of mangrove ichnology.
Chirananda De


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