Sediment-Organims Interactions: A Multifaceted Ichnology SEPM Special Publication 88

RICHARD BROMLEY; LUIS BUATOIS; M. GABRIELA MÁNGANO; JORGE FERNANDO GENISE; RICARDO NESTOR MELCHOR

SEPM, Society for Sedimentary Geology

Lugar: Lawrence, Kansas; Año: 2007 p. 387

978-1-56576-129-2

Introduction and volume layout The field of Ichnology bridges the gap between the areas of paleontology and sedimentology, but has connections to many subdisciplines within these areas. Biogenic structures record the behavior of their tracemakers and provide valuable information in paleoecologic and paleoenvironmental analysis. As in situ ethologic structures, trace fossils or ichnofossils yield valuable insights into the paleoecology of ancient benthic communities and the environmental dynamics of depositional systems. Ichnology is truly a multifaceted field and a broad selection of its facets is represented in the 28 papers of this volume. The papers are the product of Ichnia 2004, the First International Congress on Ichnology, convened by Jorge F. Genise and held from 19 to 23 April, 2004 at the Museo Paleontológico Egidio Feruglio in Trelew, Patagonia, Argentina. Several symposium volumes and short course notes have been published in recent years (Pemberton et al., 2001; Kowalewski and Kelley, 2002; Kelley et al., 2003;  Buatois and Mángano, 2003; McIlroy, 2004; Webby et al., 2004), and ichnology can be considered a particularly active research area in steady growth. The 28 papers herein are arranged in five groups that reveal the broad scope of ichnology. One of the aims of Ichnia 2004 was to gather together ichnologists covering different backgrounds and having different interests. The underlying philosophy of the meeting was to explore the multiple aspects of ichnology, trying to establish links between the different subfields. Accordingly, there was a conscious effort to look for common themes while enjoying diversity at the same time. This book attempts to reflect the spirit of that meeting. It is devoted to exploring the potential of biogenic structures in a wide variety of fields, such as paleoecology, sedimentology, sequence stratigraphy, biostratigraphy and evolutionary paleoecology. In doing so we hope to reflect this more integrated view of ichnology that intends to construct, extend or fortify existing bridges between different subfields, such as paleoichnology and neoichnology, vertebrate and invertebrate ichnology, benthic ecology, coprology, paleoichnology, and soft and hard substrate ichnology. A long time ago, a jazz musician was asked by a journalist about where jazz was going. The answer was “If I knew that, I would already be there”. There is an implicit risk in writing introductions that attempt to detect current trends and decipher future directions. We tackle that challenge here. Concepts and Reviews We begin with three papers devoted to concepts and reviews that derive from some of the invited keynote talks. Although a comprehensive summary of ichnologic concepts is far beyond the scope of the book, these three papers provide a state of the art of some of the different subfields and present innovative ideas that may contribute to a healthy debate within the field. Labandeira assesses the fossil record of plant-insect associations and compares ichnodata with body-fossil data. His paper provides a summary of a field that has experienced an explosive development during the last decade. Plant-insect interaction studies are essential to understand modern land and freshwater ecology and their path through the fossil record provides a wealth of information that helps to decipher the evolution of terrestrial ecosystems. Lockley describes the morphodynamics of archosaurs and the trackways they produce. He emphasizes holistic insights into the relationships between the trace fossils, the feet, the limbs, and the whole body. He indicates that his morphodynamic approach provides a less static way of understanding morphology. Seilacher reviews new insights into the principles of ichnostratigraphy. He notes that although the notion that trace fossils are useless in biostratigraphy is widespread, there are many exceptions. In particular, his paper underscores the importance of some Paleozoic ichnotaxa, such as trilobite trace fossils, arthrophycids, Oldhamia ichnospecies and Treptichnus pedum, the latter being particularly important because it marks the main divide in the stratigraphic record: the Precambrian-Cambrian boundary. Ethology and Ecology: Linking trace fossils and behavior The second group comprises 4 papers devoted to ethology and ecology, and thereby linking trace fossils and behavior. This section emphasizes paleobiological aspects involved in the production of biogenic structures and the paleoecological significance of ichnofaunas. A prime role is given to careful analysis of individual ichnotaxa and the associated taphonomic filters, thereby stressing the importance of the fossilization barrier. Most of these papers illustrate the necessity of detailed autecologic studies in ichnology and demonstrate that trace fossils should be understood in terms of their behavioral significance and that ethology is the stepping stone from which to infer paleoecological parameters. It is rather disturbing to realise how limited our understanding of many biogenic structures still is. Undoubtedly, this is an area that needs to be further developed in order to produce more robust trace fossil models that may be used in paleoecological and paleoenvironmental reconstructions.  For example, evaluation of the implications of the Zoophycos ichnofacies has been complicated by uncertainties persisting with respect to the specific behavior (or behaviors) involved in Zoophycos itself (e.g. Ekdale and Lewis, 1991; Bromley, 1991; Kotake, 1994; Olivero and Gaillard, 1996; Bromley and Hanken, 2003). Lanés, Manceñido and Damborenea have made a detailed study of the uncommon, doubly spiraled trace fossil Lapispira based on specimens from Jurassic rocks of Argentina. They provide an in-depth description of this ichnogenus and analyze its ethology, trophic type, paleoenvironmental distribution and potential producer. They proposed that the complex double helicoidal tube suggests bacterial farming, although other behaviors may have been involved also. In addition, the tiering position of Lapispira is evaluated, concluding that it records the work of a deep-tier crustacean, representing an elite trace fossil. Löwemark, In-Tian, Chung-Ho and Schönfeld test the gardening hypothesis that has been used as an explanation of some types of Zoophycos spreiten. The studied specimens occur in Quaternary sediments offshore Portugal. Their analysis of δ13Corg suggests that gardening plays an insignificant role in Zoophycos. Asgaard and Bromley, on the basis of Pleistocene schizasterid echinoids that are preserved together with their trace fossil Scolicia, can confirm the construction of drain tubes behind echinoids of this family. The study illustrates the importance of combining paleoichnologic analysis with observations of modern structures, including experimental neoichnology. Rodríguez, Pazos and Aguirre-Urreta document an occurrence of the slender-rayed Asteriacites lumbricalis, which is ascribed to the activity of brittle-stars. Sedimentary facies and co-occurring trace fossils suggest that these ophiuroids may have lived in waters of less than fully marine salinity. Ichnology and paleoenvironmental reconstructions: From the continent to the deep sea The third group of papers comprises paleoenvironmental reconstruction using ichnological evidence, in a whole range of settings from the continental to the deep sea. This is the largest group, including 11 papers, and represents one of the busiest areas of ichnologic research. Historically, the use of trace fossils in paleoenvironmental analysis has been the focus of ichnologic research, particularly since the proposal of the ichnofacies model by Dolf Seilacher in the fifties and sixties (see reviews and examples in Frey and Pemberton, 1984; Pemberton et al., 1992; Bromley, 1996; Buatois et al., 2002, among others). In terms of conceptual and methodological tools, most of the authors in this section attempt to combine both ichnofacies and ichnofabrics in their approach. The studies included here reveal how an integrated approach combining ichnologic data with sedimentologic and stratigraphic data can provide an increased understanding of facies, stratigraphic framework, and depositional setting. Several of these papers provide clues about how this integrated approach aids in petroleum exploration and development. One only needs to look at the amount of high quality work that is being produced in this subfield to realize that sedimentologic and sequence stratigraphic applications of ichnology will continue to be the focus of substantial research. Undoubtedly, the fact that many oil companies have adopted ichnologic studies (mostly in core logging) as a routine tool will encourage this applied side of the field. Additionally, the importance of bioturbation in changing the physical and chemical aspects of the substrate is of paramount importance in reservoir characterization and represents a growing subfield in applied ichnology (Pemberton and Gingras, 2005). The first three papers of this section touch on non-marine environments. Netto describes very unusual, non-marine, Skolithos-dominated piperock from the Triassic of Brazil. Her study emphasizes the importance of substrate consolidation in continental ichnofaunas. Dense concentrations of vertical burrows are attributed to opportunistic colonization by insects. This study highlights the stratigraphic significance of the colonized surfaces, which represent breaks in sedimentation.  Buatois, Uba, Mángano, Hulka and Heubeck have studied ichnofabrics dominated by Taenidium in fluvial settings from the Miocene of Bolivia. Although the ichnofauna does not display significant compositional variations throughout the succession, ichnofabric analysis reveals different taphonomic pathways that help to understand depositional dynamics and environmental conditions. Intense and deep bioturbation recorded by backfilled trace fossils occurs in crevasse sandstone and overbank mudstone. Pazos, di Pasquo and Amenabar describe near-marine to non-marine Carboniferous trace fossils assemblages of Argentina that record the change from glacial to non-glacial conditions. Ichnofossils are restricted to glacial retreat and early postglacial times. Ichnologic data are integrated with palynologic information to track paleoenvironmental changes. The next two papers explore the peculiarities of marginal-marine depositional systems, specifically estuaries and deltas.  MacEachern and Gingras document brackish-water trace fossil suites in the Cretaceous Western Interior Seaway of Alberta. The so-called “brackish water model” resulted from the integration of information from modern environments and Mesozoic estuarine deposits. This model has been widely used in characterization of valley-fill reservoirs. In their contribution, MacEachern and Gingras refine the model and characterize assemblages from four main settings: restricted or barrier-barred bays, open unbarred bays, riverine estuaries and barred wave-dominated estuaries. Burns assesses the degree of tidal influence of Jurassic fluvio-deltaic deposits subsurface beneath the Timor Sea using ichnofabric analysis. There is renewed interest on the ichnology of deltas and this study is timely. Different trace fossil assemblages are recognized within the delta systems. Trace fossil analysis not only helps to refine environmental interpretation but also assists in correlation of stratal surfaces. The next four papers focused on the ichnology of shallow-marine environments. McIlroy records the ichnology of a Jurassic macrotidal, tide-dominated deltaic deposition system from Argentina. His study documents a diverse ichnofauna that indicates that tidal influence was not accompanied by lowered salinities. Different subenvironments having specific trace fossil associations are characterized. D’Alessandro and Uchman have studied shallow marine Pleistocene deposits of southern Italy, carrying ichnoassemblages containing Bichordites and Rosselia. They correlate changes in trace fossil composition with fluctuations in environmental stability and energy. Knaust describes unexpectedly diverse trace fossils in shallow marine carbonate sediments near the dawn of the Mesozoic, in the German Triassic Muschelkalk. His study documents a wide variety of ichnofossils in soft, firm and hardgrounds. Furthermore, he provides a detailed description of the poorly known ichnogenus Balanoglossites. Wetzel and Reisdorf make a taphonomic study of an ichthyosaur skull that has been deposited in the unexpected beak-down position (Jurassic, Switzerland). Ichnofabrics reveal the sedimentary sequence of events that led to this. Changes in substrate consistency and the role of microbial degradation are emphasized. Ponce, Olivero, Martinioni and López Cabrera report on Paleogene turbidites from Tierra del Fuego, Argentina, that show sustained and episodic gravity flow deposition and related bioturbation patterns. Historically, deep-marine ichnology has focused on taxonomic and evolutionary aspects, but comparatively little has been written with respect to the application of trace fossils in detailed facies reconstruction. This study is particularly relevant because it shows that ichnology may provide useful information to distinguish between sustained and episodic gravity flows, a hot topic in deep-marine sedimentology. Finally, Kakuwa and Webb discuss trace fossils of an Ordovician pelagic deep-ocean bedded chert in southeastern Australia. The ichnology of cherts is poorly known and, therefore, this study provides original information. Remarkably, the composition of the ichnofaunas and the styles of bioturbation documented are very similar to those of much younger deposits, including modern deep-sea sediments. The significance of bioerosion: Evaluating predation and environmental controls This section comprises papers on bioerosion, evaluating predation and environmental controls. Bioerosion is another active subfield within ichnology, one that is particularly prone to gather researchers from different backgrounds, including not only paleontologists but also marine benthic ecologists and reef biologists. The first International Bioerosion Workshop on Bornholm, Denmark produced a group of six papers (Jacobsen, 1998; Freiwald, 1998; Freiwald and Wilson, 1998; Boerboom et al., 1998; Walker et al., 1998; Hallock et al., 1998, as well as a group of 13 papers following Bromley (1999). The third workshop in the series, held at Barcelona, Spain, produced a further 9 papers following Martinell et al. (2002). Bioerosion, therefore, very clearly illustrates the multifaceted nature of ichnology. In particular, bioerosion yields valuable insights into predatory-prey interactions and it comes as no surprise that the majority of recent bioerosion studies have focused on this topic (see papers in Kowalewski and Kelley, 2002; Kelley et al., 2003). Certainly, the complexities of predator-prey interactions are expressed in this section. Additionally, careful analysis of bioerosion provides information on environmental controls (e.g. Bromley and Asgaard, 1993; de Gibert et al., 1998). Malumián, López Cabrera, Náñez and Olivero document abundant bioerosional penetrations in Cretaceous to Cenozoic benthic foraminiferal tests from offshore Argentina. This study is one of the few performed in high latitudes. The authors detect several trends through the time span analyzed and establish correlations with different climatic episodes. Farinati describes fossil burrows from firm sediment and bioerosion trace fossils in skeletal substrates of Miocene to Pliocene age, Argentina. Ichnologic information is placed within a sequence stratigraphic context and used to evaluate the taphonomic history of the shells. Kelley and Hansen evaluate latitudinal patterns in predatory borings by naticid gastropods along the east coast of USA. The patterns resulting from this study are more complex than predicted, which lead the authors to evaluate possible causes. This paper provides a modern baseline for interpreting temporal patterns in the fossil record and underscores the need to examine multiple samples. Ichnology moves out of water: Traces of insects and vertebrates In the last section, ichnology moves out of the water with 7 papers that describe the work of insects and tetrapods. Continental ichnology, once a neglected subfield, has experienced an explosive development during the last decade. Invertebrate ichnology has covered a wide variety of topics, including definition of additional ichnofacies (e.g. Buatois and Mángano, 1995; Bromley, 1996; Genise et al., 2000), evaluation of evolutionary trends (Buatois et al., 1998; Miller and Labandeira, 2003), ichnofabric analysis of paleosols (Genise et al., 2004) and documentation and analysis of insect trace fossils (Genise, 2004), among others. Vertebrate ichnology was also the focus of significant research leading to the documentation of a widespread database. See, for example, the papers in Gillette and Lockley (1989) and the three-part Festschrift in honor of W.A.S. Sarjeant (Pemberton et al., 2003-2004). More recently, attempts have been made to define vertebrate ichnofacies (Lockley et al., 1994; Hunt and Lucas, 2006). One of the present-day challenges in continental ichnology is to integrate vertebrate and invertebrate datasets, which have evolved independently and remain essentially separated. Voigt discusses tunnel-and-chamber burrows from Carboniferous-Permian alluvial plain deposits at several localities from western USA to eastern Europe, as evidence for fossorial behavior of insects in the late Paleozoic. The tracemaker may have occupied terrestrial muddy to sandy sediments of levee and proximal overbank subenvironments. Yelinek and Chin show a relationship between burrows probably made by dung beetles and large beaver burrows, Daemonelix, in the Miocene of Nebraska, USA. They conclude that it was undoubtedly the abundant dung in Paleocastor colonies that attracted the beetles. Milàn, Bromley, Titschack and Theodorou describe a diverse mammalian ichnofauna from a Quaternary eolian oolite on the island of Rhodes, Greece. Tracks attributable to elephants, camels and smaller artiodactyls are described, chiefly in vertical section, in association with rhizoliths and body fossils of land snails. Rodríguez-Tovar documents nesting behavior of an extant burrowing wasp, Bembix oculata. The influence of substrate firmness is underscored and experiments were performed to reveal changes in shear strength related to variations in water content in the substrate. Kulkarni and Borkar detail the architecture of the arborial nests of extant Crematogaster ants in India. They compare nests formed in mangrove thickets and deciduous forests, stressing the importance of rainfall and high-speed winds as controlling factors. In the Jurassic Morrison Formation of Utah, USA, Chin and Bishop find bone fragments, deriving from within theropod coprolites, to contain the borings of beetles: these are thus compound trace fossils, the bone substrate having been utilized twice. Their study demonstrates that by the Jurassic some invertebrates have developed the ability to exploit dinosaur bone. Last but not least, Scott, Renaut, Owen and Sarjeant have made a detailed study of trace formation and taphonomy of invertebrate burrows and tetrapod tracks in marginal sediments of saline and alkaline Lake Bogoria in the Rift Valley of Kenya. Lake-margin environments, including hot springs and ephemeral streams, provide favorable areas for the activities of insects, mammals, birds, and reptiles. The authors address preservational aspects in detail, discussing the role of efflorescent salt crystallization, substrate wetting and drying and the presence of benthic microbial mats and biofilms. 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