CONTENTS:BREIFINGS ABOUT ICHNOFOSSILSICHNOFACIESICHNOFABRICUSES OF ICHNOFOSSILS IN DETERMINING SEDIMENTARY ENVIRONMENTBIBLOGRAPHYBREIFINGS ABOUT ICHNOFOSSILSICHNOLOGY: is derived, meaning “trace or track”, and logos, meaning “word or study”, basically ichnology is is the study of the behviour of once living animals examination of tracks, burrows , trails and makings that they made when alive.ICHNOFOSSILS: A trace fossil, also ichnofossil, is a fossil record of biological activity but not the preserved remains of the plant or animal itself. These are  sedimentary structures formed by organisms, such as trackways, trails, borings, and burrows. Trace fossils are also known as ichnofossils (Greek, ichnos, “trace”) or biogenic sedimentary structures. The study of trace fossils has many important applications. Sedimentary geologists use them as powerful tools for interpreting sedimentary environments and paleobathymetry.CLASSIFICATION Cubichnia, or resting traces, which are impressions caused when the animal interrupted its locomotion for rest and refuge. These usually occur as shallow depressions on the bedding surface, often reflecting the anatomy of the undersurface of the trackmaker.Domichnia, on the other hand, are dwelling traces, such as deep elongate burrows or deep excavations that served as a longer-term residence of the animal. They may also serve as a trap or tunnel for catching food. Most cylindrical burrows (both branched and unbranched, vertical or horizontal), or U-shaped burrows, or borings in rocks, and other such structures were permanently inhabited by the tracemaker, so they are domichnia. Unlike most other trace fossils, domichnia tend to be found within beds rather than on top of them.fugichnia ,In some cases, the domichnia bear signs of forced escape by the organism inside; these are known as fugichnia. This is common in trace fossils that were buried in waves of new sediment, forcing the animal to dig out and escape, or to dig its burrow upward to continue its flow of water and function. When the animal is not resting, but moving, it can make a wide variety of traces. Repichnia are made by normal crawling motions, and they are usually continuous, elongate trails, often with delicate marks from the leg motions of the tracemaker. These tend to be found on the tops of bedding surface. Paschichnia are grazing traces, usually horizontal geometric patterns that show the organism was systematically combing the surface of the sediment (“grazing”) for food. ]Agrichnia translates literally as “farming traces.” Like paschichnia, they are regularly patterned burrow systems, often on the top of the bedding plane (although they are usually preserved on the sole of the bed above). However, they reflect a network of permanent dwelling and feeding behavior in a local area, rather than continuous movement through the sediment without returning. Fodichnia are deposit-feeding traces, formed when organisms made threedimensional burrows, eating the sediment to digest out all of the food within it. These are usually horizontal within beds, but they can be at any angle, and they can be simple or complexly branched.   ICHNOFACIES An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited. These ichnofacies have become standard tools of the sedimentary geologist to interpret ancient facies. They are now so widely encountered that they should be part of thevocabulary of any competent geoscientist, not just the domain of paleontologists.TYPES OF ICHNOFACIES:Skolithos Ichnofacies Vertical tubelike burrows are formally known as Skolithos. They are believed to have been formed by tube-dwelling organisms that lived in rapidly moving water and shifting sandCruziana Ichnofacies Horizontal U-shaped troughs with many intermediate, rib like striations are known as Cruziana, and these occur in moderate- to low-energy sands and silts of the shallow shelf. Cruziana are often preserved as the convex hyporelief cast of the trough-shaped burrow, rather than as the original concave burrow.Zoophycos Ichnofacies Broad, looping infaunal feeding traces known as Zoophycos occur in low-energy muds and muddy sands. Traditionally, they were considered indicators of deep waters along the continental slope below storm wave base, but above the continental rise where turbidites accumulate.Nereites Ichnofacies , Meandering feeding traces on bedding plane surfaces are called Nereites and are usually found in the abyssal plains, often associated with turbidites and deep pelagic muds . Almost all the ichnogenera in this facies are horizontal burrows in the top few centimeters of the muddy bottom.The Glossifungites ichnofacies is typical of firm but unlithified substrates, such as dewatered mud. The traces in this ichnofacies include vertical, cylindrical, U-shaped, or teardrop-shaped borings, sparsely to densely branched burrows, or mixtures of borings and burrows, as well as fan-shaped Rhizocorallium and Diplocraterion.Trypanites ichnofacies  , are such hard substrates include reefs, rocky coastlines, bedrock, and hardground surfaces caused when a drop in sea level lithified the sediment. They may even bore into igneous substrates.The Teredolites ichnofacies (Teredo is the wood-boring bivalve known as a “shipworm”) . This ichnofacies can occur wherever wood is exposed to water, including logjams in rivers and lakes, driftwood in the ocean, as well as human-created substrates, such as docks, wharf pilings, and ship hulls.Teridolites,Bedding-plane view showing high density of Thalassinoides suevicus in coal layer. Middle to Upper Miocene, Urumaco Formation, Urumaco River, northwestern Venezuela. Pen is 15 cm. ICHNOFABRIC The total record of sedimentary rocks fabric resulting from bioturbation is termed ichnofabric. This includes discrete identifiable trace fossils as well as unidentifiable bioturbation structures. One important aspect of ichnofabric is that it can be used to estimate the degree to which the burrowing has reworked the sediment. Not all sedimentary rocks show equal degrees of bioturbation, and the relative amounts of bioturbation may yield important clues about the environmentHigh-density of Nereites missouriensis in offshore-transition deposits illustrating an example of non-constrained textural heterogeneities. Presence of this ichnofabric promotes gas and light oil transmissivity in low permeability reservoirs in many fields in North America. Upper Devonian–Lower Mississippian, Bakken Formation, Saskatchewan, Canada. Core width is 9.5 cm. See Angulo and Buatois USES OF ICHNOFOSSILS IN DETERMINING SEDIMENTARY ENVIRONMENTBy contrast with body fossils trace fossils always found in place. If the enclosing sediments had moved they would have been destroued. They often occur in sedimentary suites where there are no body fossils present and especially in clastic sequence.Rather than being destroyed by diagenesis they are commonly improved by it, since lithological contrast between fossil and the enclosing sediment may there by be enhanced. They are tend to be restricted to narrow facies range.Some points that how we interpret sedimentary environments:If a trace fossil is present in the clastic sequence then the sediment must have well aerated. Conversely if a sequence is lacking in traces may well have more anoxic(oxygen deficient). Like black shaless with abundant traces, even if deep water in orign , can not possibly have been anoxic. Graptolitic shales and their mezozoic equivalents, are generally lacking in trace fossil , which suggests euxinic orign. Rates of    sedimentation can often be inferred from the relative abundance of trace fossil , as with diplocraterion, and the presence of definite borings in ‘hardgrownds’ shows clearly that the sediments must have been indurated when the borings were formed , as may sometimes be confirmed by encrusters upon its surface.The potential for preservation of  ‘fossil behaviour’ depends upon the depth at which tracemaker lived within sediment. Most animals inhabit at different levels and teirs within the sediment.TIERING: Tiering consists of the vertical partitioning of the habitat . It is in fact a synonym of ecological stratification (Seilacher, 1978), but this may be confused with the current use that geologists give to the term “stratification”, and has not met with acceptance. Subaqueous substrates occupied by endobenthic communities are vertically zoned as a response to physical, chemical, and biological parameters (Bromley, 1990, 1996). Also, the water column displays vertical partitioning, and epifaunal and infaunal suspension-feeding animals obtain their food at several levels above the sediment surface (Ausich and Bottjer, 1982).Within these tiers there may be defined ichnoguids (bromley,1996) i.e , groups of ichnospecies whuch  behaves in similar manner ans occupy a similar location within the substrate.In upper layers there may be highly mobile animals whose life activities totally obliterate other primary structures. They may also sometimes make it difficult for inhabitants of lower tiers to make contact with the surface.Lower layers are likely to be preserved since upper layers are highly bioturbated these are bromley’s elite trace fossils which usually enhance with diagenesis.Nodular limestone containing Thalassinoides representing elite trace fossils. Upper Jurassic, Coralline Oolite Formation, Carr Naze, North Yorkshire Coast, England. Lens cap is 5.5 cm. see Fürsich (1972).The uppermost centimeters of the sediment are referred to as the mixed zone. In this zone, sediment is saturated in water and totally homogenized by bioturbation, but no discrete traces are recognized. Below this zone lies the transition The ichnofabric approach 84 zone, which is extremely heterogeneous due to the activity of deep burrowers, and displays tiered endobenthic communities (Savrda, 1992). The deepest sediment zone is the historical zone, which is located beyond the reach of even the deepest burrowers and, therefore, does not display active bioturbation. Because of continuous vertical accretion of sea-floor sediment, the mixed and transition zones of a given time are buried and become the historical zoneThere are also rather generalized trace fossil assemblage based on original depth of depth of deposition (seilacher,1967)Shallow water dwellers: physical protection very important partly due to turbulence and partly because the light allow animals to see them. Q high proportion of invertebrates are burrowing suspension feeders and traces are mainly of cubichnia and domichinia.Quieter water dwellers: deposit feeders (swallowers) are common and traces are mainly of findinichnia and repichnia.Deep sea dwellers: lightless environment hence less protection needed  and because of many surface dwelling bacteria there are many fondichnia and pascichnia.These ichnofacies are used in broad and general sense, but individual traces may occur out of context and , the assemblages themselves are subject to taphanomic filtering.A common misconception is to assume a direct correlation between ichnofacies and depositional environments. Ichnofacies are not indicators of sedimentary environments, but reflect the complex interplay of a set of environmental factors . Ichnofacies are not intended to be paleobathymeters( Factors that are use to define paleo water depths) either. A well-known and repeated example is the occurrence of the Skolithos ichnofacies, typical of nearshore settings, in offshore tempestites and deep-marine turbidites. The Cruziana ichnofacies, though typical of lower-shoreface to offshore deposits, may be present in shallower settings, commonly intertidal flats of tide-influenced shorelines . Regardless of the depositional environment, it is the animal response to a set of particular environmental conditions that defines an ichnofacies. This is also true for continental ichnofacies and, therefore, the search for exact equivalences between continental ichnofacies and depositional environments is futile. Individual invertebrate ichnofacies occur in a wide variety of environmental settings. In these cases, water availability is a fundamental control in tracefossil distribution (Gierlowski-Kordesch, 1991) and sediment water content strongly influences substrate consistency. The role of substrate consolidation as controlling trace-fossil preservation is remarkable.BIBLOGRAPHYInvertebrate palaeontology and evolution (4TH EDITION) BY E.N.K. CLARKSOM: chapter 12,page 429Prothero: Bringing Fossils to Life: An Introduction to Paleobiology, 2/eIchnology: Organism–substrate interactions in space and time by M. Gabriela mángano and luis A. Buatos,CHAPTER 5 AND CHAPTER 6

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