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Über dieses Buch

Paleontologists and geologists struggle with research questions often complicated by the loss or even absence of key paleobiological and paleoenvironmental information. Insight into this missing data can be gained through direct exploration of analogous living organisms and modern environments. Creative, experimental and interdisciplinary treatments of such ancient-Earth analogs form the basis of Lessons from the Living. This volume unites a diverse range of expert paleontologists, neontologists and geologists presenting case studies that cover a spectrum of topics, including functional morphology, taphonomy, environments and organism-substrate interactions.



Functional Morphology


1. Crinoids Aweigh: Experimental Biomechanics of Ancyrocrinus Holdfasts

Immobile suspension feeders living on soft substrates, although rare in modern marine habitats, were relatively common in the Paleozoic. Numerous Paleozoic taxa have been interpreted as dwelling on soft unconsolidated sediments and possessing morphologic features that either prevented them from sinking (e.g., strophomenid brachiopods) or anchored them to the sea floor (e.g., crinoid holdfasts). The quantitative expression of the static stresses for forms living on soft, muddy bottoms developed by Thayer (1975) can be easily modified to describe the forces involved in anchoring. One of the more unusual putative anchoring structures is the “grapnel” holdfast of the Devonian crinoid Ancyrocrinus. This form does not match the paradigm for most typical current anchoring structures, lacking recurved, pointed, and flattened lateral processes. Its form is suggestive, however, of the modern, nautical mushroom anchors deployed on muddy bottoms. Plaster casts of the Ancyrocrinus holdfast were used to quantify the actual forces involved in penetrating, being pulled out of, or dragged across soft substrates. The forces were measured using a digital force gauge mounted on a motorized test stand. Substrates used included fine quartz sand, pure kaolin mud, and coarse carbonate sand. The holdfasts readily penetrated soft mud, but encountered much greater resistance in fine sand. They did, however, readily penetrate the latter substrate when rocked, supporting the comparison with mushroom anchors. Holdfasts do not penetrate the sediment when dragged across it, suggesting a minimal ability to passively anchor in this way. Simple calculations of the sinking velocity of Ancyrocrinus suggest that when dislodged, they would have easily reimplanted in soft substrates.
Roy E. Plotnick, Jennifer Bauer

2. Ultra-elongate Freshwater Pearly Mussels (Unionida): Roles for Function and Constraint in Multiple Morphologic Convergences with Marine Taxa

Morphologic convergence may arise because natural selection produces an optimal solution for a given set of environmental conditions or because constructional and historical constraints limit available variation, making certain morphologies inevitable. Shell shape in bivalves typically is interpreted as functional, with emphasis placed on substrate preferences and life habits. Freshwater pearly mussels (Order Unionida) represent the most diverse freshwater bivalve clade and, although their life history and related morphologic traits are strikingly divergent from marine bivalves as well as other freshwater bivalve clades, multiple convergences in shell form within and among these groups occur. Ultra-elongate shells (length/height ratios > 3.0) in both marine and unionoid taxa are one such example. At least 13 families, including 4 phylogenetically defined unionoid families, have ultra-elongate representatives. These taxa occur in substrates ranging from soft sediments to hard grounds and a variety of life habits including nonmotile semi-infaunal, active burrowers, and borers; which seems to imply weak functional/adaptive control on morphology. For many of these taxa, however, this shape may reflect functional forces related to direct substrate penetration without major anterior/posterior rotation of the shell, rather than the type of substrate penetrated. Further, shell elongation is achieved through a variety of differential growth patterns, which argues against a strong role for constructional or historical constraint. Clarifying the meaning of a modern analog or proxy is critical for evaluating paleoenvironmental and paleoecological interpretations of extinct ultra-elongate bivalve taxa as well as for informing efforts to protect and restore extinction-vulnerable extant populations.
Laurie C. Anderson

3. Relationships of Internal Shell Features to Chemosymbiosis, Life Position, and Geometric Constraints Within the Lucinidae (Bivalvia)

Lucinids are an ancient bivalve clade in which all living members examined to date possess sulfur-oxidizing bacterial endosymbionts. Although a basal synapomorphy is the most parsimonious explanation of universal chemosymbiosis, other mechanisms, including differential extinction of nonsymbiotic lineages, could produce the same character distribution. Therefore, a proxy for chemosymbiosis applicable to fossil taxa could be used to test hypotheses of endosymbiotic evolution as well as elucidate paleocommunity dynamics and biogeochemical cycling for the wide range of marine ecosystems that these bivalves inhabit. Toward that end, geometric morphometrics were used to quantify features of the anterior adductor muscle scar, an inferred basal synapomorphy for the Lucinidae that previous authors have associated with chemosymbiosis. Eight shallow-marine lucinid species were included in analyses, along with two other “lucinoid” species, one of which is chemosymbiotic. Species demonstrated significant shape differences in both a canonical variates analysis (CVA) and a series of discriminate function analyses. For all but two species, the first canonical variates (CV) axis exhibits strong positive interspecific allometry. This allometric trend describes elongation of both the anterior adductor muscle scar and inhalant channel as size increases. Comparing results to published ecologic and phylogenetic data indicate that both life position within the sediment and geometric constraint control morphologic variation. In addition, although morphologic variation cannot be linked to the degree of symbiont dependence with available data, thin-plate splines (TPS) of landmark configurations may track the location of mantle gills and pallial septa, which are accessory respiratory and feeding structures thought to have evolved as lucinid ctenidia were co-opted to house bacteria.
Laurie C. Anderson

4. Modern Analogs for the Study of Eurypterid Paleobiology

Eurypterids are extinct, chelicerate arthropods whose life habits might be elucidated through comparison with living analogs. There are at least two potential eurypterid analogs, xiphosurans and arachnids (specifically, scorpions). Eurypterids and scorpions share striking morphologic and structural similarities despite their different habitats (aquatic vs. terrestrial); eurypterids and xiphosurans share numerous morphological characters and an aquatic habit. Despite the physiological differences inherent between aquatic and terrestrial chelicerates, the similarities in the basic body plan suggest that eurypterids and scorpions faced similar functional challenges during ecdysis, but eurypterid feeding was probably more similar to that of xiphosurans. For studies on the mechanical strength and functional morphology of the eurypterid exoskeleton, Limulus is the closer analog. The choice of modern analog for other aspects of eurypterid paleobiology, including reproduction and whether eurypterids were active predators, is a matter of discussion. The lack of a single, clear eurypterid analog from among extant chelicerates may reflect that eurypterids occupied an ecological niche intermediate between xiphosurans and arachnids. The search for a modern analog for eurypterids, then, is not likely to yield a single model organism.
Danita S. Brandt, Victoria E. McCoy

5. New Applications for Constrained Ordination: Reconstructing Feeding Behaviors in Fossil Remingtonocetinae (Cetacea: Mammalia)

During the Eocene epoch, archaic cetaceans made the land-to-sea transition, giving rise to modern whales, dolphins, and porpoises. During this transition, the feeding apparatus of fossil remingtonocetines displayed morphologies that are distinct from other cetaceans, confounding straightforward interpretations of their feeding behaviors. This study utilized a novel combined ordination of morphology and feeding strategy, while accounting for phylogeny, in a sample of 2 remingtonocetines and 18 extant cetartiodactylans, to assess the morphological signal of feeding behaviors. Results showed that differences between prey acquisition in extant taxa were driven by a suite of mandibular characters and width of the palatal arch, providing a behaviorally constrained morphospace. Remingtonocetinae clustered closest to the snap-feeding river dolphins, suggesting that they too were snap feeders. The methods presented here represent a novel application for constrained ordination that links morphology with performance, and may be widely applied in the fossil record.
Lisa Noelle Cooper, Tobin L. Hieronymus, Christopher J. Vinyard, Sunil Bajpai, J.G.M. Thewissen

Taphonomy and Environment


6. Patterns in Microbialites Throughout Geologic Time: Is the Present Really the Key to the Past?

Microbialites dominated the biosphere throughout the Proterozoic, becoming relatively rarer into the Phanerozoic. Microbialites are potential analogs of life on the early Earth; therefore, understanding how they form and function can provide a window to the past. Much of what we know about early life and environments derives from investigations of modern microbialites, making studies of these structures critical to interpreting the ancient fossil record. Creating a database of worldwide microbialite specimens, both modern and fossil, to be used for analyzing patterns in modern microbialite distribution, both in space and time, along with environmental characteristics and concurrence with grazing and/or boring organisms, can offer understanding into ancient microbialites, specifically the processes impacting their formation, persistence, and preservation. Additionally, analyzing the composition and structure of modern microbialites may allow for connections to patterns of the past, and also provide a clearer understanding of what is seen (or not seen) in the fossil record. A sample database of microbialites reported from the Phanerozoic was analyzed for characteristics such as distribution in time, space, and across different environments, as well as the alignment of distribution with mass extinctions, global sea level curves, and association with grazing/burrowing organisms. We find microbialite distribution is widespread worldwide and abundance fluctuates over the Phanerozoic with increases often corresponding to mass extinctions. Contrary to previous interpretations, fossil microbialites do not appear to prefer open marine environments, with data showing broad distribution in a variety of environments. Modern microbialites, however, primarily form in restricted environments. Data show that grazers/borers are commonly found in association with microbialites throughout the Phanerozoic, though it is difficult to discern if they did or did not impact microbialite formation.
Kristen L. Myshrall, Christophe Dupraz, Pieter T. Visscher

7. The Relationship Between Modern Mollusk Assemblages and Their Expression in Subsurface Sediment in a Carbonate Lagoon, St. Croix, US Virgin Islands

Much work has been done on the fidelity of a death assemblage to its present-day living community. Few studies, however, have extended this into the deeper subsurface in modern environments. This study examines the molluskan faunas accumulating at the surface in a reef/lagoon system on St. Croix, US Virgin Islands and compares those to the prefossilized assemblages in the subsurface to examine how faithfully surface assemblages are reflected in the sediment below. Data from 12 vibrocores through the Holocene section indicate that there is a very strong taphonomic filter in effect in the lagoon. The faunal constituents, their taphonomic signature, and the size classes represented in the surface assemblage are quite different from molluskan accumulations in deeper subsurface sediments. In fact, intense bioturbation by callianassid shrimp as deep as 3 m into the sediment has affected the entire sedimentary package resulting in a largely homogeneous section devoid of subsurface shell beds. The one exception to that pattern is a single shelly lag found at the bottom of the sediment package resting on the hard pre-Holocene surface. Most importantly, we find that the lag fauna does not resemble the modern life/death assemblage accumulating at the sediment surface. Dominant taxa in the modern life or death assemblage include small epifaunal gastropods and large bivalves. In contrast, small, thin-shelled infaunal bivalves dominate the lag along with agglutinated polychaete tubes, decapod remnants, and shell fragments. Our data suggest that the shell-rich accumulation deep within the sediment package is a time-averaged concentration of predominantly small infaunal mollusks deposited over time by deep burrowing callianassid crustaceans. Moreover, the extent of bioturbation within the lagoon suggests that some of the widely accepted live–dead paradigms may not be as robust as generally assumed.
Karla Parsons-Hubbard, Dennis Hubbard, Caitlin Tems, Ashley Burkett

8. Biotic Segregation in an Upper Mesotidal Dissipative Ridge and Runnel Succession, West Salish Sea, Vancouver Island, British Columbia

Ridge and runnel systems develop on low-gradient beaches under limited fetch conditions and moderate to high tidal ranges. The influence of beach morphology in ridge and runnel systems on biotic distribution is not well understood. This study focuses on infaunal population trends within a laterally extensive, shore parallel ridge and runnel system at Craig Bay, British Columbia, Canada. Within the study area, dense populations of Dendraster excentricus dominate lower intertidal runnels. These echinoids are both epifaunal and shallow infaunal. Other macroscopic infaunal organisms are absent within the runnel systems, with the exception of scattered, solitary anemones (Anthopleura artemisia). During low-tide intervals, D. excentricus in subaerially exposed runnels burrow beneath a veneer of sand and A. artemisia retract into their burrows. Abundant infaunal bivalves (including Macoma nasuta, M. balthica, M. secta, Tresus capax, Clinocardium nuttallii, Protothaca staminea, and Venerupis philippinarum), tube-dwelling polychaetes, and threadworms characterize ridge faunas. Relatively few D. excentricus occur on the ridges. Carnivorous polychaetes (Nereis sp. and Nephtys sp.) occur in both ridges and runnels. Exclusion of vertical faunal components in the runnels is attributed to the feeding activities and population density of D. excentricus, which prefer moister sediment. Preservation of this type of ridge and runnel system in the rock record would result in a succession with zones dominated by horizontal trace fossils (e.g., Beaconites/Scolicia), interbedded with zones characterized by abundant vertical forms (e.g., Siphonichnus, Skolithos, and Trichichnus). The resultant trace fossil succession would have no bathymetric implications, but would reflect the influence of beach morphology on infaunal populations.
John-Paul Zonneveld, Murray K. Gingras, Cheryl A. Hodgson, Luke P. McHugh, Reed A. Myers, Jesse A. Schoengut, Bryce Wetthuhn

9. Using X-ray Radiography to Observe Fe Distributions in Bioturbated Sediment

The presence of an active iron cycle in modern intertidal sediment from Willapa Bay is confirmed using X-ray radiography and X-ray diffraction (XRD) analyses. The data show that Fe minerals are present in two different redox states. The first is maghemite (Fe2O3), which formed on the linings of irrigated burrows. The second is pyrite (FeS2), which formed as haloes around abandoned or filled burrows. Some pyrite halos coalesced to form nodules of pyrite around the burrow fabric. The mineral paragenesis occurred as follows: (a) detrital ferrous-rich sediment (e.g., pyroxene or organometallic complexes) is buried and progressively dissolved to Fe2 + ; (b) the Fe2 + either reacts with pore-water sulfide (formed via bacterial sulfate reduction) to form pyrite in the matrix or it diffuses to the burrow margins where it is oxidized to form maghemite; (c) when the burrows become abandoned and isolated from the overlying oxic seawater, the ferric iron is biologically reduced to Fe2 + (via bacterial iron reduction) where it repeats Step 2. The pyrite remains stable unless exposed again to oxidizing conditions, such as later bioturbation. The inchoate nodules appear to form in less than a decade. Interestingly, the mineral distributions observed here are reminiscent of nodules observed in several other marginal marine settings, particularly those that have an oxidized-Fe-mineral core and a pyrite rind. Although those nodules are normally taken to infer evolving pore-water compositions, perhaps they are more simply explained by the processes reported above.
Murray K. Gingras, John-Paul Zonneveld, Kurt O. Konhauser

10. Phytoliths as Tracers of Recent Environmental Change

Phytoliths are more widespread, accessible, and characteristic of a local area than other terrestrial vegetation proxies. Despite work on recent soil and Cenozoic paleosol phytolith assemblages, environmental applications lag significantly behind their potential in terms of temporal resolution. Modern soil phytolith assemblages, aboveground vegetation, and soil features from Inceptisols with known vegetation and environmental histories were sampled in order to develop methods for describing rapid environmental change events at a high temporal resolution. Samples included agricultural fields, fluvial meanders, and wildfire sites. In each case, soil phytolith assemblages were unrepresentative of current vegetation but were characteristic of the known environmental history. As a result, rapid changes in land use or environment are identifiable in phytolith assemblages; agricultural sites can be identified by Ap horizons and grass phytoliths, fluvial meanders by weakly developed soils with channel features and spatial phytolith gradients, and wildfire sites by charcoal bodies and bimodal phytolith assemblages. These sites also provide rates of change, specific to each type of environmental change. An ecosystem experiencing wildfires changes assemblages rapidly (1–2 % per year), while change resulting from channel migration occurs slightly slower (~ 0.5 % per year), and that from field abandonment occurs significantly slower (< 0.25 % per year). These methods can be applied to paleovegetation reconstructions, providing additional environmental information and higher-resolution vegetation interpretations. Along with more work on spatial and depth-profile sampling, these results will allow high temporal resolution for environmental and vegetation change records both in the modern and throughout the Cenozoic era.
Ethan G. Hyland

Organism-Substrate Interaction


11. Large Complex Burrows of Terrestrial Invertebrates: Neoichnology of Pandinus imperator (Scorpiones: Scorpionidae)

Scorpions have comprised a significant portion of the diversity of predatory arthropods since the Late Paleozoic. Many of these animals are active burrowers today and likely have a substantial, if yet unrecognized, trace fossil record. This project involved the study of the burrowing behavior and biogenic structures of the scorpion Pandinus imperator (Scorpiones: Scorpionidae). Individuals and groups of five animals were placed into sediment-filled terrariums for 30–50 days after which the open burrows were cast and described. Additional experiments were conducted in sediments with two different moisture contents to evaluate the response to this altered environmental condition. Specimens of Pandinus imperator excavated their burrows using the first three pairs of walking legs. The burrow morphologies produced consisted of subvertical ramps, helical burrows, and branching burrows. The burrow elements were elliptical in cross section (12 cm wide × 4 cm high) with concave floors and ceilings. Decreased sediment moisture reduced the complexity of the subsurface structures and reduced the likelihood of their preservation due to gravitational collapse. Burrows of Pandinus imperator were compared to those of the desert scorpion, Hadrurus arizonensis, using nonparametric statistics and found to be distinct. Data collected from these and similar neoichnological studies can be applied directly to interpret trace fossil assemblages found in continental paleoenvironments.
Daniel I. Hembree

12. Biomechanical Analysis of Fish Swimming Trace Fossils (Undichna): Preservation and Mode of Locomotion

This chapter includes a morphological analysis of sinusoidal swimming trails of the ichnogenus Undichna and inferences on likely producers, mode of swimming, and preservation. A total of 166 Undichna specimens were measured, including selected examples from the literature and unpublished material from different basins of Argentina. These specimens belong to seven ichnospecies, including U. bina, U. britannica, U. consulca, U. insolentia, U. quina, U. simplicitas, and U. unisulca. The morphology of these ichnospecies is used in conjunction with that of the presumed producer to infer the mode of swimming of the fish. Most Undichna ichnospecies are interpreted as produced by a fish swimming with subcarangiform locomotion. U. insolentia, U. bina, and some specimens of U. britannica are interpreted as reflecting anguilliform locomotion. The essential measurements used in this analysis are wavelength and wave amplitude. Maximum wavelength (in most cases interpreted as the trail produced by the caudal fin) is used to infer the length of the producer for each specimen by comparison with experiments using extant fishes from the literature. Estimated length of fish producing Undichna is in the range 24–800 mm, but most values are less than 250 mm. By estimating the Reynolds number (Re) for each specimen, it is inferred that a fish larger than 650 mm will produce a flow disturbance and bottom sediment suspension that will preclude the preservation of trails recognizable as Undichna. Larger fish may leave identifiable Undichna provided that the sediment underwent early cementation or the fish was swimming at a speed lower than maximum sustained speed.
María Cristina Cardonatto, Ricardo Néstor Melchor

13. The Neoichnology of Two Terrestrial Ambystomatid Salamanders: Quantifying Amphibian Burrows Using Modern Analogs

This experiment involved the study of two species of ambystomatid salamanders, Ambystoma tigrinum and Ambystoma opacum (Amphibia: Caudata). Individual salamanders were placed in sediment-filled terrariums and allowed to burrow for 7 to 14 days under natural environmental conditions. Salamanders were then removed and their burrows cast, excavated, and described both qualitatively and quantitatively. Quantitative measurements included the number of surface openings, width, height, width-to-height ratio, total length, maximum depth, slope, branching angle, complexity, and tortuosity. Additional experiments involved variations in soil composition and soil moisture. A. tigrinum burrowed through excavation and compaction techniques whereas A. opacum only used compaction. Burrows produced by A. tigrinum consisted of ramps, branched ramps, U-, W-, Y-, and J-shaped burrows. Small-scale surface mounds were also created by Ambystoma tigrinum. Burrows produced by A. opacum consisted of ramps and branched ramps. Sinuous to straight surface trails were also produced by A. opacum. There was no recognized change in behavior or burrow properties in response to changes in the environmental parameters.
Nicole D. Dzenowski, Daniel I. Hembree

14. Biogenic Structures of Burrowing Skinks: Neoichnology of Mabuya multifaciata (Squamata: Scincidae)

Neoichnological experiments involving a species of tropical, ground-dwelling skink, Mabuya multifasciata, demonstrate the diversity of biogenic structures produced by medium-sized lizards. Although the majority of skinks are ground dwellers or burrowers, little is known about the biogenic structures produced by this most diverse group of lizards. The documentation of biogenic structures produced by M. multifasciata will aid in the identification of trace fossils produced by skinks, help to improve the fossil record of these difficult-to-preserve animals, and allow for more complete paleoecological and paleoenvironmental reconstructions. Skinks were placed in terrariums filled with sediment of varying compositions and moisture content and were allowed to burrow. Open burrows were cast with plaster, photographed, measured, and statistically analyzed. The skinks produced seven distinct burrow morphologies including various ramps, U-, and J-shaped burrows. While there was no direct correlation between burrow properties and sediment properties, the burrows showed some variations due to the changes in sediment density and moisture content. The burrows had greater average complexities and tunnel heights when the sediment moisture was increased, whereas they had lower average widths and circumferences when the sediment density was increased. The data collected in this study can be directly applied to terrestrial trace fossil assemblages in tropical paleosols to better interpret their paleoecology and assess paleoenvironmental conditions.
Angeline M. Catena, Daniel I. Hembree

15. Novel Neoichnology of Elephants: Nonlocomotive Interactions with Sediment, Locomotion Traces in Partially Snow-Covered Sediment, and Implications for Proboscidean Paleoichnology

We observed trace-making behaviors of one female African elephant (Loxodonta africana) and one female Asian elephant (Elephas maximus) in a zoo setting. Our objective was to document uncommonly studied traces, that is, traces other than dung and footprints in sediments, so that paleoichnological researchers may benefit from a broader search pattern when investigating trace fossils with potential proboscidean affinities. We observed six distinct traces: trunk-grasping traces, small pits from active and passive dispersal of water and sediment, urination traces, resting traces, wallowing traces, and dissected tracks created in partially snow-covered sediment. Of these traces, none attributable to proboscideans have been reported in the fossil record. The resting traces we observed, however, were created in dry sand and would likely not be preserved in the fossil record because of a high potential for disturbance before burial. Similarly, the trunk traces we observed in dry sand would likely have low preservation potential. Pits from thrown and blown sediment and water, wallowing traces, and snow-influenced tracks should have a higher probability of survival into the fossil record. Tracks representative of partially snow-covered ground are recognizable by sediment pedestals within undertracks. In such tracks, which we refer to as hanging tracks, the top surface of the pedestal is all that remains of the true track. The undertrack surrounding the pedestal(s) was created from the elephant’s foot pressing snow into the underlying sediment. The snow later melted away. Pleistocene proboscideans likely encountered partially snow-covered ground, so hanging tracks may be preserved in the rock record. Recognition of these tracks would be extremely informative about paleoclimate, but further research is needed to determine if they can be easily distinguished from tracks created exclusively in sediment.
Brian F. Platt, Stephen T. Hasiotis

16. Burrows and Related Traces in Snow and Vegetation Produced by the Norwegian Lemming (Lemmus lemmus)

Lemmings are small, fossorial rodents showing high activity day and night through summer and winter. Although their biology is the subject of many studies, their burrowing activity and burrow architecture have received little attention. In this chapter, the traces of the Norwegian lemming (Lemmus lemmus) produced in snow are described from two mountain sites in the tundra of southern Norway. During the long and harsh winter time, the lemmings build extensive burrow systems along the ground/snow interface and within the snow. These branching and partly anastomosing tunnel networks contain a thick lining of grass and other plant material and thus are well preserved after the snow thaw. Other burrow parts remain unlined or are scattered with fecal pellets. The tunnel networks allowed the lemmings to reach their feeding sites in the surroundings of their dwellings. The burrow systems, which are several square meters in size, contain one or two nests thickly lined with plant material. The nests may contain lemming fur and are built for breeding, nursing, and dwelling. Other parts of the burrow systems are completely filled with rounded and rod-shaped fecal pellets and serve as sites for defecation. They also contain simple rounded, nest-like burrows with the same pellet fill. Lemming burrows in snow are a good example of how those common traces can serve to understand the burrow architecture and the behavior of their producers in habitats which are otherwise difficult to investigate. Beside this neoichnological aspect, rodent burrows in snow may also aid in the interpretation and understanding of fossil vertebrate burrows which remain poorly understood.
Dirk Knaust

17. Near-Surface Imaging (GPR) of Biogenic Structures in Siliciclastic, Carbonate, and Gypsum Dunes

High-resolution geophysical methods, such as ground-penetrating radar (GPR) imaging, are increasingly applied to ichnological research. Large vertebrate and invertebrate burrows and tracks can be detected and resolved using center frequencies of > 400 MHz. Geophysical images of bioturbation structures in siliciclastic, carbonate, and evaporite (gypsum) dunes exhibit characteristic electromagnetic signal returns, which are associated with active burrow openings (ground–wave gap), filled burrows (hyperbolic diffraction and “pull up”), and large tracks (concave up patterns). The noninvasive imaging can be used for pseudo-3D visualization (closely spaced survey lines) and monitoring of biogenic activity (repeated surveys). Because biogenic structures induce distinct anomalies in geophysical records collected at frequencies typical of many geological investigations, caution must be taken to avoid misinterpreting them as primary sedimentary structures.
Ilya V. Buynevich, H. Allen Curran, Logan A. Wiest, Andrew P.K. Bentley, Sergey V. Kadurin, Christopher T. Seminack, Michael Savarese, David Bustos, Bosiljka Glumac, Igor A. Losev


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