Form Of Burrows Research Articles

Computed tomography reconstructions of burrow networks for the Opheliid polychaete, Armandia cirrhosa

The morphology and architecture of structures formed by sediment-dwelling invertebrates, such as excavations or burrows, are often assumed to be characteristic of a given species, consistent across a range of environmental conditions, and used to categorise species contributions to ecosystem functioning. However, very few investigations use non-invasive high-resolution techniques capable of determining fine scale variations in burrow form and complexity, or consider whether or not the form of the burrow is context dependent. Here, we provide replicate high-resolution micro-focus computed tomography data for the complete burrow systems of the Opheliid polychaete, Armandia cirrhosa, across a range of salinity and habitat conditions. These data provide reference models which can be used by ecologists investigating intraspecific variation in species traits and organism-sediment interactions and, more generally, by those tasked with pattern and shape recognition of objects that are morphologically highly variable and which adjust their architecture with changing circumstance or context.

Geometric morphometrics of macro- and meiofaunal priapulid pharyngeal teeth provides a proxy for studying Cambrian “tooth taxa”

Priapulids are marine, benthic ecdysozoan worms that feed using a distinctive toothed pharynx. While only a handful of lineages have survived to the present day, the Cambrian priapulid stem group left behind a rich record of articulated body fossils and characteristic trace fossils in the form of burrows. Recently, the fossil record of isolated priapulid cuticular elements including pharyngeal teeth has gained increased attention as a means of revealing cryptic priapulid taxa otherwise unknown among macrofossils. In this study, we focus on the ecological implications of shape variation in the teeth of extant and extinct priapulids, which display substantial morphological differences between taxa and life stages. We define a landmarking scheme to capture shape variation in priapulid teeth and apply it to our dataset, which includes a breadth of tooth specimens from extant macrofaunal and meiofaunal lineages alongside numerous Cambrian priapulid teeth preserved as isolated small carbonaceous fossils. Through ordination of the principal components of shape, we explore the priapulid tooth morphospace and find evidence that its occupancy has expanded since Cambrian times, indicating a corresponding expansion of the group’s ecological niche. We also employ our geometric morphometric approach to make linear discriminant analysis-based taxon assignments based on tooth morphology, which can be helpful for classifying enigmatic “tooth taxa” known solely from fossil teeth. Finally, we use discriminant analysis to study tooth shapes from a functional perspective, considering known ecologies to characterize the ecological functions of unclassified isolated teeth.

COPROLITES FROM CALVERT CLIFFS: MIOCENE FECAL PELLETS AND BURROWED CROCODILIAN DROPPINGS FROM THE CHESAPEAKE GROUP OF MARYLAND, U.S.A.

New finds of remarkable coprolites (fossilized feces) are here reported from the famous Miocene marine sediments of the Chesapeake Group exposed along Calvert Cliffs (Maryland, U.S.A.). Although vertebrate coprolites have been described from these deposits, here we provide the first description of tiny invertebrate fecal pellets. Thus far, these fecal pellets have only been found in the upper Miocene (Tortonian) St. Marys Formation. The micro-coprolites represent the coprulid ichnospecies Coprulus oblongus. The fecal pellets are found in small clusters or strings of dozens to masses of many hundreds. Pellets range in size from approximately 0.4 – 2.0 mm wide by 1.0 – 5.0 mm long, and range in color from gray to brownish black. Their length/diameter ratio is always very nearly 2. These coprulids have been found in a variety of Miocene fossils/concretions including a uranoscopid neurocranium, naticid gastropod, bivalve shells, barnacle tests, and in pellet-backfilled sinuous burrows through sediment. Because the fecal pellets are often found in tiny spaces or spaces thought to be inaccessible to shelled invertebrates, the coprulids are attributed to small and soft-bodied polychaetes or other annelids. Some coprolites attributed to crocodilians from the lower-middle Miocene Calvert Formation were tunneled into, presumably the result of coprophagy, by some unknown kind of organism(s). These compound trace fossils are in the form of burrows that excavate the coprolites, the sides of which are sculptured by scratch/gouge marks.

First known trace fossil of a nesting iguana (Pleistocene), The Bahamas.

Most species of modern iguanas (Iguania, Iguanidae) dig burrows for dwelling and nesting, yet neither type of burrow has been interpreted as trace fossils in the geologic record. Here we describe and diagnose the first known fossil example of an iguana nesting burrow, preserved in the Grotto Beach Formation (Early Late Pleistocene, ~115 kya) on San Salvador Island, The Bahamas. The trace fossil, located directly below a protosol, is exposed in a vertical section of a cross-bedded oolitic eolianite. Abundant root traces, a probable land-crab burrow, and lack of ghost-crab burrows further indicate a vegetated inland dune as the paleoenvironmental setting. The trace fossil matches dimensions and overall forms of burrows made by modern iguanas, and internal structures indicate active backfilling consistent with modern iguana nesting burrows. The trace fossil is also located on an island with a modern native species of rock iguana (Cyclura riyeli riyeli), suggesting a presence of iguanas on San Salvador since the Late Pleistocene. This nesting burrow may provide a search image for more fossil iguana burrows in The Bahamas and other places with long-established iguana species and favorable geological conditions for preserving their burrows.

DWELLING IN THE DEAD ZONE—VERTEBRATE BURROWS IMMEDIATELY SUCCEEDING THE END-PERMIAN EXTINCTION EVENT IN AUSTRALIA

ABSTRACTA distinctive burrow form, Reniformichnus australis n. isp., is described from strata immediately overlying and transecting the end-Permian extinction (EPE) horizon in the Sydney Basin, eastern Australia. Although a unique excavator cannot be identified, these burrows were probably produced by small cynodonts based on comparisons with burrows elsewhere that contain body fossils of the tracemakers. The primary host strata are devoid of plant remains apart from wood and charcoal fragments, sparse fungal spores, and rare invertebrate traces indicative of a very simplified terrestrial ecosystem characterizing a ‘dead zone' in the aftermath of the EPE. The high-paleolatitude (∼ 65–75°S) setting of the Sydney Basin, together with its higher paleoprecipitation levels and less favorable preservational potential, is reflected by a lower diversity of vertebrate fossil burrows and body fossils compared with coeval continental interior deposits of the mid-paleolatitude Karoo Basin, South Africa. Nevertheless, these burrows reveal the survivorship of small tetrapods in considerable numbers in the Sydney Basin immediately following the EPE. A fossorial lifestyle appears to have provided a selective advantage for tetrapods enduring the harsh environmental conditions that arose during the EPE. Moreover, high-paleolatitude and maritime settings may have provided important refugia for terrestrial vertebrates at a time of lethal temperatures at low-latitudes and aridification of continental interiors.

Burrow morphology of the land crab Gecarcinus lateralis and the ghost crab Ocypode quadrata on San Salvador Island, The Bahamas: comparisons and palaeoenvironmental implications

Burrow morphologies of the land crab Gecarcinus lateralis and the ghost crab Ocypode quadrata were investigated on East Beach, San Salvador Island, The Bahamas, with the goals of critical comparison of their morphologies and of clarifying and advancing their palaeoenvironmental usefulness. In comparing land crab burrows to those of the ghost crab, the former are simpler but more variable in overall shape. G. lateralis burrows have a more compressed form in the transverse section of the burrow shaft and possess lower (more horizontal) shaft inclination than those of O. quadrata. In the late Holocene backshore and dune deposits on San Salvador, two types of fossil burrows were observed. On the basis of the morphologic differences documented herein between modern burrows of land and ghost crab species, one fossil burrow form can be interpreted as having been produced by G. lateralis and the other (trace fossil Psilonichnus upsilon) produced by O. quadrata. Because the modern burrows of these crabs are different not only in shape but also in their environmental preference, the occurrence of trace fossils comparable to burrows of the land crab and ghost crab (P. upsilon) could be used as indicators of vegetated coastal dunes (land crab burrows) and beach backshore (near sea level; ghost crab burrows) palaeoenvironments

A diverse trackway-dominated marine ichnoassemblage from the Lower Triassic in the northern Paleotethys: Ichnology and implications for biotic recovery

We document a diverse ichnoassemblage from marine interbeds of the Lower Triassic terrestrial succession in the Houzhougongmiao (HZGM) section of Shaanxi Province, northwestern China. Integrated biostratigraphic data (bivalve, palynology and conchostracan) reveals that the ichnofossil-bearing marine beds are Griesbachian (Induan, Early Triassic) in age. The marine interbeds are interpreted to be the result of the earliest Triassic transgression of the Paleotethys Ocean northward onto the southern margin of the North China Craton. The HZGM ichnoassemblage includes 17 ichnospecies in 16 ichnogenera and is dominated by shallow-tier Asteriacites and Biformites produced by ophiuroids, the scratch marks or trackways Dimorphichnus, Diplichnites, and Monomorphichnus produced by arthropods, and a rare occurrence of the fish swimming trace Undichna. Of these, the hook-shaped imprints Biformites, representing the moving arm impressions of ophiuroids, are reported for the first time from the Lower Triassic. These trace-makers are interpreted to have lived in a low energy, semi-restricted, shallow embayment environment. Although possessing relatively high ichnodiversity, the HZGM ichnoassemblage differs clearly from other coeval diverse ichnocoenoses in the lack of complex burrow forms (i.e. Thalassinoides, Diplocraterion, or Rhizocorallium) and a mixed layer, and in having abundant shallow tiers. In addition, high ichnodiversity may occur at both high and low latitudes during the Griesbachian (or Induan). Accordingly, the resting trace or trackway-dominated ichnoassemblage from the HZGM section may represent the initial recovery of the trace-maker ecosystem after the Permian-Triassic mass extinction. Trace-makers such as arthropods and ophiuroids were perhaps opportunistic organisms that proliferated in marginal marine settings when other biota were still suffering post-extinction biotic depletion and environmental stresses.

An ichnological-assemblage approach to reservoir heterogeneity assessment in bioturbated strata: Insights from the Lower Cretaceous Viking Formation, Alberta, Canada

Facies-scale trends in porosity and permeability are commonly mapped for reservoir models and flow simulation; however, these trends are too broad to capture bed and bed-set heterogeneity, and there is a need to up-scale detailed, bed-scale observations, especially in low-permeability reservoir intervals. Here we utilize sedimentology and ichnology at the bed- and bedset-scale to constrain the range of porosity and permeability that can be expected within facies of the Lower Cretaceous Viking Formation of south-central, Alberta, Canada.Three main facies were recognized, representing deposition from the middle shoreface to the upper offshore. Amalgamated, hummocky cross-stratified sandstone facies (Facies SHCS) consist of alternations between intensely bioturbated beds and sparsely bioturbated/laminated beds. Trace fossil assemblages in bioturbated beds of Facies SHCS are attributable to the archetypal Skolithos Ichnofacies, and are morphologically characterized by vertical, sand-filled shafts (VSS). Bioturbated beds show poor reservoir properties (max: 10% porosity, mean: 85.1 mD) compared to laminated beds (max 20% porosity, mean: 186 mD). Bioturbated muddy sandstone facies (Facies SB) represent trace fossil assemblages primarily attributable to the proximal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur in varying proportions, namely sediment-churning assemblages (SC), horizontal sand-filled tube assemblages (HSF), VSS assemblages, and mud-filled, lined, or with spreiten (MLS) assemblages. Ichnological assemblages containing horizontal (max: 30% porosity, mean: 1.28 mD) or vertical sand-filled burrows (max: 10% porosity, mean: 2.2 mD) generally have better reservoir properties than laminated beds (max: 20% porosity, mean: 0.98 mD). Conversely, ichnological assemblages that consist of muddy trace fossils have lower porosity and permeability (max 10% porosity, mean: 0.89 mD). Highly bioturbated, sediment churned fabrics have only slightly higher porosity and permeability overall (max: 15% porosity, mean: 1.29 mD). Bioturbated sandy mudstone facies (Facies MB) contain ichnofossils representing an archetypal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur throughout Facies MB that are similar to Facies SB; SC, HSF, VSS, and MLS assemblages. The SC (max: 15% porosity, mean: 21.67 mD), HSF (max: 20% porosity, mean: 3.79 mD), and VSS (max: 25% porosity, mean: 7.35 mD) ichnological assemblages have similar or slightly lower values than the laminated beds (max: 20% porosity, mean: 10.7 mD). However, MLS assemblages have substantially lower reservoir quality (max: 10% porosity, mean: 0.66 mD).Our results indicate that the most likely occurrence of good reservoir characteristics in bioturbated strata exists in sand-filled ichnological assemblages. This is especially true within the muddy upper offshore to lower shoreface, where vertically-oriented trace fossils can interconnect otherwise hydraulically isolated laminated sandstone beds; this improves vertical fluid transmission. The results of this work largely corroborate previous findings about ichnological impacts on reservoir properties. Unlike previous studies, however, we demonstrate that the characteristics of the ichnological assemblage, such as burrow form and the nature of burrow fill, also play an important role in determining reservoir characteristics. It follows that not all bioturbated intervals (attributed to the same facies) should be treated equally. When upscaling bed-scale observations to the reservoir, a range of possible permeability-porosity values can be tested for model sensitivity and to help determine an appropriate representative elementary volume.

Movement of leopard tortoises in response to environmental and climatic variables in a semi-arid environment

BackgroundTortoises (Testudinidae) occur in a wide range of environments, providing important ecosystem functions, such as seed dispersal and refuge in the form of burrows. Tortoise movement has previously been shown to be related to resource availability, reproductive status and local environmental conditions. However, understanding of the variables that drive their movement remains comparatively low. We investigated aspects of movement in leopard tortoises Stigmochelys pardalis—the largest and most abundant tortoise species in sub-Saharan Africa—in response to environmental, climatic and individual variables in the semi-arid Karoo, South Africa. We used GPS telemetry to calculate bihourly and daily movement and used generalized linear mixed models (GLMMs) to ascertain important predictor variables.ResultsTemperature, distance from water sources, and month were important variables for predicting both bihourly and daily movement. Our results showed that movement increased when individuals were close to known water sources, indicating that individuals close to water resources make regular long distance movements. Movement showed a positive relationship for temperature in both models, whilst rainfall was an important predictor for bihourly movement. Our results displayed aspects of seasonality, with movement highest in spring months, likely related to reproductive activities, although no sex differences were observed.ConclusionsWe identified temporal and spatial conditions in which leopard tortoise movement increased. Our results further support the relationship between water as a resource and movement in leopard tortoises. Individuals used one of two basic movement behaviours in relation to water in this water scarce environment. Either an individual’s home range and movements included permanent water resources allowing internal water storage replenishment, or excluded these with reliance on food resources (such as grasses, forbs, and succulents) for water.

Solving a cold case: New occurrences reinforce juvenile callianassids as the Ophiomorpha puerilis tracemakers

The ichnotaxon Ophiomorpha puerilis was erected based on material from late Pleistocene shallow-marine, siliciclastic deposits of southeastern Brazil. These tiny burrows with a distinctive lining of cylindrical pellets having rounded ends were originally interpreted as burrows of juvenile callianassid shrimp, with polychaetes also considered as a possible tracemaker. Recent discoveries of O. puerilis in late Pleistocene shallow-marine carbonates from two localities in the Bahamas and from the Miami Limestone of south Florida, described herein, have expanded significantly the geographic range of the ichnotaxon and provided numerous, well preserved specimens for detailed structural analysis of its burrow form and pellets. The new information strengthens the interpretation of juvenile callianassids as the tracemakers, resolving the “cold case” of the burrow's tracemaker. Microscopic analyses revealed that the pellets of O. puerilis are constructional, not fecal. Furthermore, larger forms of Ophiomorpha are common and occur in close association with O. puerilis at each locality. These new data allowed close comparison of O. puerilis pellets with those of Sergio mirim, a modern callianassid from southeastern Brazilian beaches, Ophiomorpha nodosa from Brazilian Pleistocene deposits, and fossil polychaete burrows filled with fecal pellets as described in the literature. The combined evidence allows us to exclude polychaetes as potential O. puerilis tracemakers. Rather, O. puerilis records the settling and initial burrowing behavior of callianassid decapodids. The characteristics of an Ophiomorpha ichnofabric with the addition of O. puerilis also is described and explored. An emended diagnosis for the O. puerilis ichnotaxon is provided, based on the new structural data for this burrow.

Bioturbation trends across the freshwater to brackish-water transition in rivers

Most existing ichnological models predict an increase in burrow density and diversity from the zone of persistent brackish-water into the realm of persistent freshwater. Herein we compare the neoichnology of five tidal–fluvial channels with varying tidal magnitudes, saltwater incursion distances, and river discharge. The results indicate that there is a noticeable diminution in the sizes of marine traces and a corresponding decrease in their distribution (reduced abundance of burrowed versus unburrowed beds) with decreasing salinity. From the landward limit of saltwater incursion into the wholly freshwater tidal backwater, there is no concurrent increase in terrestrial or freshwater burrow forms; rather, burrow diversities remain low (range: 10 to 35% of the “open marine” signature) and burrow densities decrease from BI 0–3 to BI 0–1 in both sand and mud units.The five modern systems described in this study do not support the hypothesis that there is an increase in bioturbation from the brackish-water reaches of channels into freshwater reaches. In fact, freshwater channels, including those in the tidal backwater zone, are characterized by very low trace-fossil diversities (1 to 2 forms) as well as low and sporadically distributed bioturbation intensities (BI 0–1).

Burrow forms, growth rates and feeding rates of wood-boring Xylophagaidae bivalves revealed by micro-computed tomography

Wood sinking into the deep sea is often colonized by species of the bivalve subfamily Xylophagaidae; specialist organisms that bore into it and digest cellulose with the aid of symbiotic bacteria. Very little is known about the nature of Xylophagaidae borings, Xylophagaidae abundances and population size structures, their rates of growth and their consumption rates of wood. To investigate this, several sets of experimental wood packages were deployed and retrieved: two sets from two seamount sites on the Southwest Indian Ridge (732-750 m), one from the Mid-Cayman Spreading Centre in the Caribbean (4773 m), and three sets from 500 m in the Tongue of the Ocean, Bahamas. The wood samples were scanned using X-ray micro-computed tomography (micro-CT). The wood at each deployment site was colonized by a different species of xylophagaid. Making novel use of micro-CT images, the morphology of intact xylophagaid borings were shown to resemble Prince Rupert’s Drops with ‘drop lengths’ varying between species. Mean sizes of Xylophagaidae and mean minimum growth rates (2.55 to 8.76 mm yr-1) varied among species also. Rates of wood degradation were up to 60 cm3 per year per 100 individuals but in reality, this may have been an underestimate. This analysis has given insight into the importance of the subfamily Xylophagaidae with regard to wood remineralization in the deep sea.

Unbioturbated sediments on a muddy shelf: Hypoxia or simply reduced oxygen saturation?

Abstract X-radiographs of sediment box cores acquired from the western Gulf of Mexico reveal limited bioturbation in sediment deposited in bathymetries greater than 35 m. Between 15 and 35 m, sediments are thoroughly bioturbated with averaged bioturbation indices (for all beds in a core) between 2.1 and 5.6, and trace diversities between 2 and 9 distinct burrow forms. Below 35 m water depth, box cores exhibit trace diversities of 1–3, and core-averaged bioturbation indices range between 0.3 and 3.6. There is an overall decrease in trace diversity and bioturbation indices in the offshore direction. Cross-shore ichnological trends are compared to dissolved oxygen contents of bottom waters. Above 35 m, dissolved oxygen (DO) contents show pronounced variability, ranging from 100% DO saturation through to hypoxia ( The data reveal a direct correlation between: a) the density of infauna and the diversity and density of burrows, and b) DO of bottom water. The degree of bioturbation is significantly reduced in waters that are oxic, but below 80% DO saturation. Based on these observations, we suggest that it is inappropriate to link low bioturbation intensities and diversities to hypoxia (

The Podzol Hydrosequence of Itaguaré (São Paulo, Brazil). 1. Geomorphology and Interpretation of Profile Morphology

A continuous section of hydromorphic to well‐drained podzols in a Late Pleistocene marine terrace of southeastern Brazil offers a unique opportunity for a detailed interpretation of podzol morphology. The soils show very deep and homogeneously colored B horizons in the most hydromorphic members, where the predominant water movement in the B horizon appears to be lateral. Upon improving drainage, the effect of roots becomes evident by the increase in root‐related E‐horizon tongues, while the B horizon becomes shallower and shows a more pronounced accumulation of organic matter at its top. Only where the groundwater does not periodically reach into the B horizon, a homogeneous distribution of Fe is found in the Bs horizon. The sequence shows clear effects of decomposition of the B horizon through growth of the E horizon, sometimes leading to isolated remnants of the B horizon, on the fringes of which organic matter may accumulate. Especially the hydromorphic profiles show large mottles with roughly concentric structures in the B horizon where organic matter has been depleted. In the poorly drained members of the sequence, the effect of improved drainage by erosion of the cliff is visible in black instead of brown colors of the upper B horizon. In all profiles, the conversion of the former B horizon into an E horizon is accompanied by strong biological activity in the form of burrows.

Morphological description of soil structure patterns produced by earthworm bioturbation at the profile scale

In cultivated soils, Soil structure mainly results from climatic, anthropogenic and biological processes. Nevertheless, few field methods evaluating the quality of soil structure consider the contribution of biological processes. In order to include earthworm biostructures in the field description of soil-structure, an original method is proposed in this paper. Soil profiles under different agricultural practices were examined to distinguish soil-structure patterns, notably those resulting from earthworm bioturbation. The relevance of naked eye observation was tested by a micromorphological approach, using image analysis on thin sections. Then, the application of this method was illustrated by mapping soil profiles.Our study led to the creation of a typology (i.e. classification system) of eleven soil-structure patterns, taking into account anthropogenic processes (e.g. compaction, soil tillage), root activity and earthworm activity. Seven patterns were attributed to earthworm activity in the form of burrows or casts. Three burrow features were distinguished, differentiating between filled burrows, or empty burrows with a brown cutan or without visible cutan. Four patterns of cast packing were distinguished, differentiating between cast aggregates that were fresh, welded, compacted, or combined with burrow features. This typology appears relevant for developing a field tool to describe and spatially quantify soil structure.

Biophysical Model of Intertidal Beach Crab Burrowing:Application and Significance

The biophysical principles and mechanisms involved in intertidal beach-crab burrowing have been studied. These answer some important and fundamental questions, such as how and what basic burrow patterns evolve in dynamic environmental conditions through a delicate balance struck between physical and biological (ethological) processes, and how does a burrow form faithfully record its environmental history in a sedimentary sequence? The study is primarily based on field and experimental data collected on the amphibious brachynuran crab family Ocypodidae (four species of Ocypodeand one species of Ilyoplax) from modern intertidal beach sectors on the Bay of Bengal coast, India. The model introduces a new concept of crab burrow cycle that includes three phases and involves three genetic categories of burrow forms—occupied, abandoned, and collapsed. The first phase (subaerial) begins with the excavation of simple (I or J types) occupied burrow populations and terminates with the development of plugged burrow apertures and sub-surface trapped air-column systems. Pressure equilibrium is reached between the burrow-base capillary water, air columns and sediment plugs. Formation of an air column is a mechanical means of supporting hollow burrow from collapse and creating an underwater quasi-terrestrial condition of living. The second phase (subaqueous) starts with tidal inundation and results in the final burrow architecture (Y, U, multibranched Y, and multiform U). The continued effects of external dynamic pressure fields on the plugs increases the internal air-column pressure causing pressure disequilibrium and lowering of capillary water levels unfavorable to the crabs for gill respiration. The burrower neutralizes the extra pressure to achieve previous pressure equilibrium and capillary water levels by excavating secondary branch(es) advantageously on the landward side of the main shaft and dumping the materials at the burrow-base. This mechanism, besides adding morphological complexities, ensures continued pressure equilibrium, the failure of which in any stage results in burrow collapse. The third phase (subaerial) creates a permanent pressure imbalance as the tidal water quickly recedes and protects the burrower inside as the air column bursts to set the crab free to start another burrow cycle afresh. The model has application potential in varied post-Jurassic coastal intertidal environmental settings occupied by quasiterrestrial crabs. It provides insight into various aspects of ichnology (taxonomy and recognition of ancient crab burrows; characterization and variability of the Psilonichnusichnofacies and intertidal ichnocoenoses; burrowing life habits of crabs and modalities of burrow preservation), environment (influence of bathymetry, tide and wave action, substrate properties, storm-induced episodic erosion and deposition on burrow architecture; environmental zonation of burrows; paleotidal range and marine transgression-regression events) and geomorphology (recognition of shoreline features). Being the first biophysical model of intertidal crab burrows, it contributes original data to the theoretical background of ichnology.

Ichnofabrics of a Pleistocene slope succession, New Jersey margin: relations to climate and sea-level dynamics

Trace fossil and sedimentologic data were collected at 10 cm intervals throughout a virtually continuous, ∼520 m-thick Upper Pleistocene siliciclastic succession recovered at ODP Site 1073 (New Jersey margin). These data were examined in the context of isotopic, seismic, and palynologic proxies to document depositional and ichnologic responses to Quaternary climate and sea-level dynamics in an upper slope setting. Two broad, texturally defined sedimentary facies assemblages are recognized. The clay-rich assemblage reflects relatively rapid deposition, in part from turbidity currents and suspended plumes, and appears to be linked to cooler, sea-level fall and lowstand phases. The sand-rich assemblage reflects overall slower sedimentation by offshelf spillover and periodic winnowing and erosion, under the influence of contour and other bottom currents, during warmer transgressive/highstand phases. Facies of the sand-rich assemblage (muds, sandy muds, muddy sands, and sands) are completely bioturbated and are characterized by high densities of biogenic structures, including distinct burrow forms. In contrast, the clay-rich assemblage includes facies that exhibit limited biogenic disruption (laminated clay/silty clay and graded silt- or fine sand-to-clay couplets) and, on the whole, is characterized by lower densities of biogenic structures, most of which are diffuse burrow mottles. These ichnofabric trends reflect changes in ecological and taphonomic parameters (e.g. substrate stability and consistency, residence time of sediments in the benthic boundary layer, and degree of inter- and intrabed textural variability), many of which were governed by variations in sedimentation rate as mediated by glacio-eustacy. Recurring, identifiable ichnofossils are most common in facies of the sand-rich assemblage in the upper half of the Pleistocene succession. Finer-grained components of this assemblage (e.g. muds and sandy muds), representing quieter phases of highstand deposition, are characterized by a low-diversity distal Cruziana ichnofacies assemblage dominated by Schaubcylindrichnus and Phycosiphon (= Anconichnus), both of which represent the work of deposit-feeding worms. Narrow facies transitions that correspond to phases of rapid transgression are marked by occurrences of Thalassinoides. These crustacean burrow systems were excavated in coarser-grained, higher-energy facies (sands and muddy sands) and in closely associated firmground substrates produced by exhumation of consolidated muds by bottom currents and/or mass-wasting processes. The association of firmground ichnofabrics with marine flooding events in an upper slope setting demonstrates that the sequence stratigraphic utility of the Glossifungites ichnofacies extends beyond shelf depositional sequences to deeper-water deposits. The distribution of texturally defined facies and general ichnofabric parameters (e.g. degree of bioturbation) appears to respond to glacio-eustatic cycles through the entire Pleistocene record. However, the Schaubcylindrichnus– Phycosiphon assemblage and Thalassinoides are rare or absent altogether in the lower half of the succession, indicating that biological responses to, and the ichnologic record of, climate and sea-level dynamics may be strongly dependent on margin physiographic and bathymetric evolution.

The burrow structure of the mud shrimpCallianassa subterranea(Decapoda: Thalassinidea) from the North Sea

The burrow morphometrics of Callianassa subterranea (Montagu) were established from resin casts of burrows of mud shrimps collected from the North Sea and maintained in native mud in the laboratory for 90 days at 15°C. Each shrimp constructed a complex burrow consisting of a multi-branched network of tunnels connected to several inhalant shafts, each terminating in a funnel-shaped opening at the surface. In addition, a single (sometimes 2 or 3), much narrower exhalant shaft ended at the surface in a mound of expelled sediment. The mean diameters of tunnels, shafts and burrow volume were related directly to the size of the constructing shrimp. The only significant difference in burrow form between males and females was in the number of shafts (and corresponding inhalant openings); females constructed between 4 and 5, whereas burrows of males possessed between 6 and 8 openings. Comparison of present burrow descriptions from sandy sediments with those published previously for C. subterranea collected from mud, shows that burrows in mud are relatively simple (with a single shaft) and are deeper (30–81 cm) compared with these in sand (9–23 cm). Such burrow plasticity for a single species raises questions of the validity of recent attempts to develop a classification scheme for thalassinidean burrow morphology.

Traces and dubiotraces: examples from the so-called Late Proterozoic siliciclastic rocks of the Vindhyan Supergroup around Maihar, India

Signatures of biogenic activity registered in the form of burrows and bioturbation of sediments are recorded for the first time from the Precambrian siliciclastic tidal flat deposits of the Bhander Group, the uppermost sub-division of the Vindhyan Supergroup, exposed near Maihar, Central India. The burrows vary from large-diameter, near-vertical stubby forms to microscopic thread-like features cutting across the physical sedimentary structures. Associated with the burrows, the sediments also register long and curved scratch markings, ‘bean-seed’ or ‘lozenge’-shaped projections, micro-‘mud-volcano’ like protuberances on the positive of sandstone sole. Thin section study of the large-diameter burrows discloses two different patterns in the nature of burrow fill, (1) staggered concave upward internal laminae showing ‘V’-in-‘V’ or broad-based ‘U’-in-‘U’ structures resembling Monocraterion and (2) an ill-defined arrangement of the upwarped laminae of the burrow fill, the stubby thumb-like burrow being bordered by clay lining on the burrow wall. Dissection of the ‘bean-shaped’ forms reveals that these represent the lower part of Diplocraterion burrows. However, the scratch makings and other features are grouped as dubiotraces as generation of similar structures by physical processes can not be ignored. Intense bioturbation of the sediments in which the burrows are located might suggest that some of the trace makers were definitely deposit feeders. Due to the lack of proper radiometric ages data, the lower part of the Bhander Group of rocks of central India has been assigned a Middle to Late Riphean age on the basis of stromatolite assemblages. However, the trace fossils described in this paper might sharpen our earlier concept of Vindhyan sedimentation by fixing these burrowed rocks very close to the Precambrian-Cambrian boundary.

Some preliminary observations on the burrows ofCallianassa subterranea(Montagu) (Decapoda: Thalassinidea) from the west coast of Scotland

Burrow structure of the thalassinid decapod Callianassa subterranea is described from polyester resin casts taken in situ. The characteristic burrow form consists of a deep vertical shaft which extends from the sediment surface to a lattice of subsurface galleries. Often the surface opening is at the centre of a cone of ejected sediment. Information on burrow density is given and this suggests that the species is much commoner in British waters than is apparent from current fauna lists.