Burrow Networks Research Articles

Community‐specific impacts of exotic earthworm invasions on soil carbon dynamics in a sandy temperate forest

Exotic earthworm introductions can alter above- and belowground properties of temperate forests, but the net impacts on forest soil carbon (C) dynamics are poorly understood. We used a mesocosm experiment to examine the impacts of earthworm species belonging to three different ecological groups (Lumbricus terrestris [anecic], Aporrectodea trapezoides [endogeic], and Eisenia fetida [epigeic]) on C distributions and storage in reconstructed soil profiles from a sandy temperate forest soil by measuring CO2 and dissolved organic carbon (DOC) losses, litter C incorporation into soil, and soil C storage with monospecific and species combinations as treatments. Soil CO2 loss was 30% greater from the Endogeic x Epigeic treatment than from controls (no earthworms) over the first 45 days; CO2 losses from monospecific treatments did not differ from controls. DOC losses were three orders of magnitude lower than CO2 losses, and were similar across earthworm community treatments. Communities with the anecic species accelerated litter C mass loss by 31-39% with differential mass loss of litter types (Acer rubrum > Populus grandidentata > Fagus grandifolia > Quercus rubra > or = Pinus strobus) indicative of leaf litter preference. Burrow system volume, continuity, and size distribution differed across earthworm treatments but did not affect cumulative CO2 or DOC losses. However, burrow system structure controlled vertical C redistribution by mediating the contributions of leaf litter to A-horizon C and N pools, as indicated by strong correlations between (1) subsurface vertical burrows made by anecic species, and accelerated leaf litter mass losses (with the exception of P. strobus); and (2) dense burrow networks in the A-horizon and the C and N properties of these pools. Final soil C storage was slightly lower in earthworm treatments, indicating that increased leaf litter C inputs into soil were more than offset by losses as CO2 and DOC across earthworm community treatments.

Balanoglossites ichnofabrics from the Middle Ordovician Volkhov formation (St. Petersburg Region, Russia)

The limestone succession of the Middle Ordovician Volkhov Formation in the St. Petersburg region (Russia) exposes numerous horizons with firm- and hardgrounds below omission surfaces, which contain trace fossils attributable to the ichnogenus Balanoglossites Magdefrau, 1932. Although known from the literature since 75 years, such trace fossils were previously only informally described as “Korrosionsgruben”, “Karandashi”, or ascribed to different ichnotaxa such as Trypanites, Arenicolites and Pseudopolydorites. Owing to their complexity and often high bioturbation density, the morphology of these trace fossils is difficult to capture. Ichnofabrics containing Balanoglossites triadicus were studied in detail from sawn rock faces, broken rock blocks and sectioned slabs, including those from historical buildings in St. Petersburg. Accordingly, different trace-fossil elements can be revealed in dependence on the original substrate consistency, reflecting various stages of lithification: Mineral-stained and Trypanites-perforated hardground surfaces are bioeroded with long elongated grooves which are assigned to the ichnogenus Sulcichnus. Subtle openings lead into the partly lithified limestone where they branch into complex galleries of B. triadicus. They are characterized by J-, U- and Y-shaped shafts and multiply branched tunnels, which gradually continue into the underlying firmground. Other portions of the ichnofabric only exhibit biodeformational structures or the strongly compacted and branched burrow networks Labyrintichnus, which is due to the original soft sediment consistency. Balanoglossites ichnofabrics demarcate certain omission surfaces within the Dikari Limestone and can be traced for more than 300 km, supporting the regional lithostratigraphical correlation. The trace maker of B. triadicus and related trace fossils is interpreted to be a eunicid polychate with the ability to bioerode and burrow the sediment. The studied material from the Ordovician is similar to the Balanoglossites from the type area, the Triassic of Germany, in many respects. B. triadicus is a very common trace fossil in Ordovician and other Palaeozoic rocks of Baltoscandia and North America but so far has been seldom identified as such but instead is commonly confused with Thalassinoides, from which, however, it differs in several aspects.

Leonardo fossil sketch may depict early nests

A network of burrows formed half a billion years ago may may push back parenting by 200 million years.

Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi-arid climate?

Krapovickas, V., Mancuso, A.C., Marsicano, C.A., Domnanovich, N.S. & Schultz, C.L. 2013: Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi-arid climate? Lethaia, Vol. 46, pp. 154–169. We report the discovery of large burrow casts in the early Middle Triassic Tarjados Formation, at Talampaya National Park, north-western Argentina. Facies analysis indicates the burrows are preserved in sandbars deposited by an ephemeral river under semi-arid and seasonal climatic conditions. The structures are mostly preserved in longitudinal cross-section and consist of an opening, an inclined tunnel (ramp), and a terminal chamber. The ramp is 8–14 cm in height, up to 130 cm in length and penetrates 49–63 cm bellow the palaeosurface with an inclination of 22°–30°. We studied burrow cast dimensions, overall architectural morphology, surficial marks, and compared them with other large burrows of both invertebrate and vertebrate origin. A tetrapod origin of the burrow casts was established based on: distinctive architecture, and size, which is more than twice the most common size range for large terrestrial invertebrate burrows. Comparison with other Upper Permian and Triassic tetrapod burrows allows us to identify three general morphological groups: (1) simple inclined burrows; (2) helical burrows; and (3) burrow network complexes, representing different behaviours. A study of tetrapod body fossils preserved within other Upper Permian and Triassic burrows shows that the Tarjados structures were most likely produced by non-mammalian cynodonts. The environmental and climatic context suggests that aridity and seasonality played a fundamental role selecting burrowing behaviour in therapsids and that by the Early–Middle Triassic their burrowing behaviour attained a complexity comparable to modern mammals. □Argentina, behaviour, palaeoclimate, Permo-Triassic, Tarjados Formation, Tetrapod burrows.

An early Cambrian shallow-marine ichnofauna from the Puncoviscana Formation of northwest Argentina: the interplay between sophisticated feeding behaviors, matgrounds and sea-level changes

An early Cambrian ichnofauna consisting ofHelminthoidichnites tenuis,Helminthopsis tenuis,Multinaisp.,Oldhamia alata, andPilichnuscf.dichotomusis documented from shallow-marine deposits ranging from the upper offshore to the offshore transition in the Puncoviscana Formation of northwest Argentina. Although the ichnogenusOldhamiais more common in Cambrian deep-marine environments, this occurrence provides further evidence that it is also present in shallow-marine environments. The burrow networkMultina(senior synonym ofOlenichnus) is preserved at the base of tempestites, representing the activity of post-storm colonizers. A drowning surface separating offshore-transition deposits below from upper-offshore deposits above contains widespread evidence of trace fossils in direct association with matgrounds. The undermat minersOldhamia alataandPilichnuscf.P. dichotomusoccur on this surface, revealing exploitation of organic matter in the biomat. Low sediment rate during drowning and paucity of bioturbation by sediment bulldozers may have promoted the establishment of the matground. In comparison with the simpler animal-matground interactions characteristic of the Ediacaran, the combination of Cambrian evolutionary innovations and the presence of microbial mats promoted more sophisticated interactions. Complex feeding trace fossils revealing that systematic undermat mining, as displayed byOldamia alataandPilichnuscf.dichotomus, is a product of the Cambrian explosion.

Diagenetic controls on reservoir properties of carbonate successions within the Albian–Turonian of the Arabian Plate

ABSTRACT The carbonate-dominated Albian to Turonian succession is one of the key petroleum systems of the Arabian Plate. It is dominated by shallow water platform carbonates that were deposited in a shallow epeiric sea on the margins of Neotethys. In general, the reservoirs in this succession have high porosities but exhibit heterogeneous permeabilities. This study reviews published data for the region and attempts to unravel the key diagenetic controls on the porosity and permeability of the reservoirs. The results demonstrate that a spectrum of diagenetic processes created highly heterogeneous multimodal pore networks. Intense boring and micritization of skeletal allochems, differential cementation of a pervasive burrow network and preferential dissolution of aragonitic skeletal allochems are ubiquitous. Locally, particularly on the northern and eastern Arabian Plate, deep-penetrating epikarst can be tied to a differential response to global sea level fluctuation and local tectonism. The development of a peripheral bulge in late Cenomanian–Turonian times, halokinesis, localized influx of channelized clastic material and sub-regional climatic variability contributed to a heterogeneous pattern of meteoric diagenesis across the Arabian Plate. The succession was then buried to up to 10 km during the Late Cretaceous–Tertiary. Where deep-penetrating fault systems were reactivated by Alpine tectonism, flushing by hydrothermal brines resulted in highly localized patterns of hydrothermal dolomitization and leaching, associated with hydrocarbon emplacement.

AN AGRICHNIAL FEEDING STRATEGY FOR DEEP-MARINE PALEOGENE OPHIOMORPHA GROUP TRACE FOSSILS

Abstract Ophiomorpha group trace fossils occur abundantly in a range of Eocene-aged deep-marine environments of deposition in the Basque basin, northern Spain. The morphology and dimensions of these trace fossils, observed in off-axis submarine lobe deposits, are discussed. The reported specimens display a highly organized and systematic burrowing behavior preserved on turbidite bed bases that display interconnecting Y-shaped (hexagonal-polygonal) morphologies. This observation, together with the cross-cutting relationship with tool marks, suggests construction of postdepositional agrichnial burrow networks. The networks probably harvested microbes that broke down cellulose-based organic matter providing an exploitable nutrient source for crustacean trace makers of Ophiomorpha. Therefore, the Ophiomorpha group–related traces discussed herein are postulated to represent an ethological response to changes in deep marine environmental conditions driven by global climate change during the early Paleogene, inc...

Taxonomy, distribution and ecology of the Setose Yabby, Cherax setosus (Riek, 1951)

Although it occurs near one of Australia's largest cities, there is a remarkable lack of information on the Setose Yabby, Cherax setosus. The morphology of the species has never been thoroughly described, and basic information on its distribution and ecology is required. In this paper, we give a thorough redescription of the species and present data on its distribution, habitat and general biology. Cherax setosus is a medium-sized crayfish with a lowland, coastal distribution extending from just south of Taree to just north of Morisset in eastern New South Wales, a northeastsouthwest distance of approximately 150km. The species is rarely found in permanent aquatic habitats in the area, but builds extensive burrow networks in minor, ephemeral habitats such as gullies, roadside ditches, stump holes, swamps and pastures. Although it appears to be relatively common across its range, the species may be susceptible to impacts such as reproductive interference with the translocated crayfish C. destructor and predation on juveniles by the introduced plague minnow, Gambusia holbrooki.

Large, complex burrow systems from freshwater deposits of the Monongahela Group (Virgilian), Southeast Ohio, USA

A large burrow complex is described from the Monongahela Group (Upper Pennsylvanian) in southeastern Ohio. The burrow complex consists of a branching network of elliptical to circular, horizontal tunnels, 1–18cm in diameter, occurring on a single horizontal plane. The tunnels branch to form X-, T-, and Y-junctions with branch angles between 60 and 130°. Branching produces multiple polygonal galleries up to 60cm wide connected by small horizontal tunnels. Vertical shafts connecting the galleries to the surface are not preserved. Tunnel surfaces are irregular with circular to elliptical nodes and depressions, elongate ridges and grooves, and 1.5–4.0cm wide nodular patches typically located at branch points. The occurrence of these burrow complexes in the Monongahela Group represents one of the largest examples of a branching burrow complex older than the Cretaceous. The Monongahela burrow complexes are preserved within a succession of floodplain and palustrine sediments suggesting a freshwater habitat for the tracemaking organisms. Potential tracemakers of the Monongahela burrow complexes include a variety of Pennsylvanian crustaceans and vertebrates. The presence of these and similar Paleozoic ichnofossils indicate a long and complex evolutionary history of the trace-making behaviors associated with the construction of large, open burrow networks.

Spongeliomorpha in nonmarine settings: an ichnotaxonomic approach

ABSTRACTThe authors revise the occurrences of burrow networks with striated walls having dominantly transverse to oblique striae, which have been assigned to the ichnogeneraSpongeliomorphaSaporta, 1887, andSteinichnusBromley & Asgaard, 1979. The taxonomic status of the ichnogenusSteinichnusBromley & Asgaard, 1979 is examined and it is suggested that this ichnogenus is a subjective junior synonym ofSpongeliomorphaSaporta, 1887.Spongeliomorphais best reserved for an unlined network of burrows having distinct surface ridges or grooves of different orientation and massive filling. The diagnosis ofSpongeliomorphais emended accordingly and the proposed ichnospecies revised for consistency with the diagnostic features of the ichnogenus.Spongeliomorpha milfordensisMetz, 1993a is considered a subjective junior synonym ofSpongeliomorpha carlsbergi(Bromley & Asgaard, 1979) after a visual comparison and statistical analysis of the angle of striation with respect to the burrow midline in the type material. Nevertheless, the use of statistical techniques is not advocated for distinction of ichnotaxa, but may support observations.Spongeliomorpha carlsbergiis considered as an indicator of nonmarine settings and was probably produced by burrowing insects. Proposed ichnospecies ofSpongeliomorphathat fit the emended diagnosis includeS. sudolica(Zaręczny, 1878);S. ibericaSaporta, 1887;S. siculaD’Alessandro & Bromley, 1995;S. chevronensisMuñiz & Mayoral, 2001; andSpongeliomorphaisp. nov. aff.siculaLewy & Goldring, 2006.

A deep burrowing sipunculan of ecological and geochemical importance

In late 1980s, a dense network of deep capillary burrows was reported on the Vøring Plateau, Nordic Seas, and associated with a sipunculan belonging to the genus Nephasoma. This sipunculan was responsible for rapid transport of organic matter from the sediment surface down a deep burrow network. Over 460 specimens belonging to the genus Nephasoma were collected from the deep Nordic Seas during four cruises from 2000–2005 and four species identified: Nephasoma abyssorum abyssorum, N. diaphanes diaphanes, N. diaphanes corrugatum and N. lilljeborgi. The species responsible for the deep burrows and rapid subduction of organic matter can now be confirmed as Nephasoma lilljeborgi. Deep burrows associated with N. lilljeborgi were observed on the Vøring Plateau, Bear Island Fan, Svalbard Margin and Yermak Plateau and may be a seabed feature endemic to the Nordic Seas region. N. lilljeborgi could have a significant role in influencing the ecology and geochemistry of the Nordic Seas region. It is recommended that future benthic community studies in the Nordic Seas region confirm the species identity of sipunculan specimens in order to determine the ecological and geochemical importance of the specimens.

Miocene vertebrate and invertebrate burrows defining compound paleosols in the Pawnee Creek Formation, Colorado, U.S.A.

Ichnofossils from two compound paleosols in the middle Miocene Pawnee Creek Formation (PCF) of northeastern Colorado, U.S.A., indicate a diverse soil ecosystem that included plants, invertebrates, and vertebrates. The 2–4 m thick paleosols are characterized by blocky textures, shallow depth calcareous horizons overlying silty bioturbated horizons, calcareous nodules, dense mats of fine (< 1 mm diameter) rhizoliths in the upper 750 mm, 5–10 mm diameter rhizoliths up to 3 m deep, and burrows 2–800 mm in diameter. PCF paleosols likely formed within a shrubland and grassland environment. Ichnofossils include backfilled burrows with chambers and cocoons; simple backfilled burrows; small-diameter boxworks; cylindrical burrow complexes; large, scratch-marked burrow networks; large downward spiraling burrows; large subhorizontal burrows; and gravel-filled tunnels and chambers. These unique PCF ichnofossils include three new ichnogenera and eight new ichnospecies. Ichnofossils attributed to ground beetles, ants, reptiles, and mammals represent a complex variety of behaviors including temporary to permanent dwelling, nesting, and food storing. Rhizoliths and burrows used to interpret media consistency, organic content, soil moisture, and water-table level are tiered from shallow, intermediate, to deep levels within paleosols with respect to physical and biological factors. Separate bioturbated intervals permits the recognition of two different paleosols that otherwise might not have been recognized. Such well-developed paleosols with high densities of terrestrial burrows have substantial sequence stratigraphic significance since they define surfaces of low sedimentation, base level, and accommodation. The PCF ichnofossil assemblages represent at least three distinct ichnocoenoses. The Kladosystemites ichnocoenosis, with Kladosystemites, Polychoredrites, Parowanichnus, and 1–10 mm diameter rhizoliths, is present in the upper profile of well-drained, consolidated, and nutrient-rich paleosols with dense concentrations of small-to-large plants at the surface. The Beaconites ichnocoenosis, with Beaconites, Katarrhedrites, and 5–10 mm rhizoliths, is present in the lower profile of moderately organic paleosols above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions due to precipitation. The Daimonelix ichnocoenosis, with Daimonelix, Beaconites, small-to-large Katarrhedrites, and 5–10 mm diameter rhizoliths, is present in the lower profile of very organic-rich paleosols generally above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions. Integration of data from body fossils, ichnofossils, paleosols, and sedimentary environments provides new insight into Neogene ecosystems. Paleosol properties combined with the ichnofossil distribution, abundance, and diversity indicates that Miocene PCF paleosols formed under a seasonal climate subject to wide variation in temperature and precipitation. The diverse assemblage of burrow morphologies records adaptation of the local fauna to these environmental conditions. The response of soil ecosystems to short- and long-term changes in climate is, therefore, vital to any study of the effects of climate change in the geologic record.

Quantifying Soil Structure and Preferential Flow in Intact Soil Using X‐ray Computed Tomography

Computed tomography (CT) provides a nondestructive means of observing soil structure and monitoring solute breakthrough in real time. We investigated an intact soil column 10 cm in diameter and 30 cm in length using industrial CT with a resolution of 105.5 by 105.5 by 125.25 μm. The satiated soil column was scanned to obtain overall soil structure. Then 60 g L−1KI solution was injected at 6.6 mL min−1for about 23 h and solute transport was monitored in real time by scanning two critical positions in the column and taking digital radiographs. At the end of the experiment, the whole column was scanned again to obtain the overall solute mass distribution. The voxel‐based soil porosity and solute concentration were quantified. The three‐dimensional visualization of the pore network and solute distribution with time showed that both the pore network and the flow pattern varied considerably with soil depth, in part due to the soil horizonation and different macropores involved. Although the macroporosity below the Ap1 horizon was much lower, macropores were more continuous and less tortuous as a result of limited agricultural disturbance and more earthworm activities. Only part of the macropores at the subsurface were effective, however, in transporting the solute. The results revealed a sequential initialization of the transport process from the macropore domain to the matrix domain and a decreased degree of interaction between the two domains with soil depth. Point‐specific breakthrough curves were obtained from real‐time point‐specific solute concentration and porosity, from which point‐specific pore velocity was determined. Preferential flow pathways in this intact structured soil consist of a complex network of earthworm burrows, root channels, interaggregate macropores, and mesopores or even micropores in the soil matrix. Modeling of this flow network and its dynamics requires a new approach different from the classical continuous‐domain approach.

Compound Asterosoma ludwigae Schlirf, 2000 from the Jurassic of the Lusitanian Basin (Portugal): conditional strategies in the behaviour of Crustacea

Asterosoma ludwigae Schlirf, 2000 is described in two sections of different age and palaeoenvironment in the Jurassic of the Lusitanian Basin. The scarce and low diversity of palaeoichnocoenoses associated with these trace fossil, as well as body fossils, indicate low oxygenation of sediment levels close to substrate-water interface. Thus, the palaeoecological signifi cance of Chondrites in lithofacies preceding those with Thalassinoides suevicus and Asterosoma ludwigae (Upper Jurassic of Guincho) or in direct association with similar morphotypes (Lower Jurassic of Peniche) is emphasized. In the syn-rift, fore-reef calciturbidites of the Kimmeridgian-to-Tithonian Mem Martins Formation, an exotic palaeoichnocoenosis dominated by Asterosoma ludwigae in three morpho-ethological gradational stages suggests a forced opportunistic, conditional strategy for the trace maker population. However, in the “Calcarios e margas de Peniche” Formation, that is coeval with the post-rifting depositional setting, Asterosoma is found in palaeoichnocoenoses representing equilibrium conditions. A close spatial relationship exists, in both cases, between Asterosoma ludwigae and the “S-O-T group” burrow networks referring to fodinichnia of possible decapod crustaceans.

Bio-irrigation in permeable sediments: An assessment of model complexity

Burrowing benthic animals ventilate their burrow networks, and this enhances the transport of solutes in the sediment and exchange with the overlying water column, a process referred to as bio-irrigation. Various models have been proposed to model bio-irrigation, with different levels of sophistication related to model dimensionality and parameter numbers. Here we address the issue of model complexity for bio-irrigation in permeable sediments. To this end, we simulated flowline patterns and tracer signals using (1) a full 3D model that explicitly models the J-shaped geometry of the burrow in a suitable microenvironment surrounding the burrow, (2) a simplified 2D axisymmetric analogue, which neglects the burrow shaft and only models the location of burrow water injection, (3) a highly simplified 1D model obtained by laterally averaging the microenvironment. Simulation of two separate inert tracer experiments shows that the 2D pocket injection model includes essential features (downward advective transport, spatial heterogeneity of pore water velocity, mechanistic specification of the seepage area) that are lost upon averaging to the corresponding 1D model. This loss of model detail must be compensated for by the introduction of additional, non-mechanistic fitting parameters in the 1D description. Similarly, the extension of the 2D model to a full sophisticated 3D description requires a major increase in computational resources, but only leads to a marginal improvement in the data simulation. Accordingly, we conclude that the 2D description provides an optimal balance between model simplicity and predictive capacity.

The use of tracers to evaluate the importance of bioturbation in remobilising contaminants in Baltic sediments

Large areas of the bottom sediments of the Baltic Sea are temporarily or permanently anoxic. These sediments are also an important sink for a variety of contaminants. Reoxygenation of bottom waters allows recolonisation by benthic infauna, which may have important implications for the fate of buried contaminants. This study used tracers to experimentally examine the role of bioturbation by benthic infauna in transporting sediment-associated contaminants in the Baltic Sea. Three different tracer methods were used in two experiments, using three key Baltic macrofaunal species: the amphipod crustacean Monoporeia affinis; the Baltic clam Macoma baltica; and the priapulid worm Halicryptus spinulosus. In the first experiment, a reoxygenation–recolonisation scenario was recreated in the laboratory, using hypoxic sediment cores collected in the field, to determine if there was remobilisation of buried 137Cs from the Chernobyl nuclear accident in 1986. The potential for the infauna to bury newly settled surface contamination was also investigated, using a fluorescent particle tracer. In the second experiment, artificially-created radiolabelled tracer layers ( 14C and 51Cr) were used to quantify both upward and downward movements of organic matter and sediment-associated contaminants by bioturbation. In both experiments there were clear visual differences between the sediment effects of the three species. Halicryptus spinulosus buried deepest into the sediment, creating a network of burrows, Monoporeia affinis burrowed actively in the upper few centimeters of the sediment, and Macoma baltica was quite stationary, but appeared to filter- and deposit feed at the sediment surface. Mixing depths in the hypoxic sediment varied from 4.0 ± 3.5 cm for M. baltica to 7.8 ± 2.1 cm for H. spinulosus. Biodiffusion rates ( D b) were similar for all treatments but biotransport rates ( r) were significantly different between treatments, mainly due to a high r value for H. spinulosus. In the experiment with radiolabelled tracer layers, 51Cr was transported more than 14C, and tracer originally at the surface transported more than tracer buried 4 cm below the surface. There was also transport of all tracers in treatments without added macrofauna. The most likely explanation is bioturbation by the meiofauna that were undoubtedly present in both experiments. Bioturbation by macrofauna both buries surface contaminants and remobilises those that are buried, but the effects are small and on a similar scale to transport caused by meiofauna. In addition, 137Cs profiles at the hypoxic site indicated that resuspension and redeposition of sediment by physical processes had occurred, and also showed that contaminants from the last 40 years were still present in the top 5–10 cm of the sediment, well within active mixing depths. At this site, as at many others in the Baltic, physical processes are likely to be far more important than biological processes in the redistribution of contaminants on a decadal timescale.

Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel)

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178. The Zohar Formation (Callovian, Middle Jurassic) is exposed as a sequence of limestones, dolomites, siltstones, and shales near the center of Makhtesh Qatan in the Negev Desert of southern Israel. Two dolomite units near the top of these faultbounded exposures are deeply incised by two perpendicular sets of relatively straight channels. Bivalve borings (Gastrochaenolites) in these dolomites show that they were cemented limestones when they were exposed and eroded; dolomitization came later. The dimensions of the channels, along with their orientations and stratigraphic context (they contain later Jurassic sediment), show that they are a series of joints that were widened by bioerosion and erosive currents, most likely from tides and wave action within a rocky shore context. Other trace fossils in these units track the earlier lithification history of these sediments. The soles of the beds show a fabric of Planolites, tunnels excavated by deposit-feeding worms that require soft sediments, cut by a large network of Thalassinoides burrows, which were created by crustaceans in firm sediments. The Zohar Formation at Makhtesh Qatan thus shows the firming, dewatering, and early cementation of sediments that were then exposed and eroded as part of a rocky shore. This new hypothesis updates previous models, which interpreted these rocks as the products of sabkha deposition.

Do tubificid worms influence the fate of organic matter and pollutants in stormwater sediments?

In urban area, management of stormwater leads to the accumulation of polluted sediments at the water–sediment interface of various aquatic ecosystems. In many cases, these sediments are colonised by dense populations of tubificid worms. However, the influence of tubificid worms on the fate of stormwater sediments has never been tackled. The aim of this study was to measure in sediment columns the influence of tubificid worms on sediment reworking, organic matter processing (O 2 uptake and release of NH 4 +, NO 3 −, PO 4 3−, and dissolved organic carbon), release of hydrocarbons and heavy metals, and microbial characteristics. Results showed that tubificid worms increased the release of NH 4 +, PO 4 3−, and dissolved organic carbon by 2-, 4-, and 3-fold, respectively. O 2 uptake also increased by more than 35% due to tubificid activity. The increase in the percentages of active bacteria and hydrolytic activity in the presence of worms indicated that the higher sediment respiration was caused by the stimulation of microbial communities. A reduction of the number of sulphate-reducing bacteria in the uppermost layers of the sediment was attributed to the penetration of O 2 due to worm activity. These significant effects of tubificid worms were probably linked to the dense network of burrows, which enhanced the exchange surface between the water column and the sediment. No release of heavy metals and hydrocarbons to the water phase was detected in the sediment columns. Understanding the fate and effect of organic stormwater sediments in the natural environment requires the integration of the role of bioturbation in urban pollution studies.

Conceptual models for burrow‐related, selective dolomitization with textural and isotopic evidence from the Tyndall Stone, Canada

ABSTRACTThe formation of dolomite is generally explained using models that reflect larger‐scale processes that describe the relationship between the supply and transport of Mg, and geochemical conditions that are amenable to the formation of dolomite. However, heterogeneities in the substrate, such as those made by bioturbating infauna, may play a more important role in dolomitization than has been previously considered. Burrow‐facilitated dolomitization is evident in the Ordovician Tyndall Stone (Red River Group, Selkirk Formation) of central Canada. The diagenetic fabrics present are attributed to dolomitizing fluids that both flowed through and evolved within burrow networks. Petrographic analysis suggests that two phases of dolomite formation took place. The first formed a fine‐grained, fabric‐destructive type that probably accompanied early burial; the second is a fine‐ to medium‐grained, locally sucrosic dolomite that is interpreted to have precipitated during later burial. Isotopic analysis supports the proposed paragenetic history: (1) an apparent linking of the stable isotopes 13C and 18O strongly suggests that the micrite matrix formed during very early diagenesis and was derived from seawater; (2) the initial phase of dolomitization is potentially microbially mediated, as evidenced by the enrichment of 13C; and (3) isotopic values for the second generation of dolomite reflect the mixing of ground water and resorbed early dolomite. This paper conceptualizes the physical and chemical conditions required for the formation of dolomite in association with burrow fabrics. The proposed model reveals a composite of biological and inorganic reactions that demonstrates the interdependence of sediment fabric, organic content and microbial interactions in the development of burrow‐mottled dolomitic limestone. It is suggested that where burrow‐associated dolomite occurs, it is most likely to develop in two stages: first, the byproducts of the degradation of organic material in burrows locally increase the permeability and porosity around burrow fabrics in shallow diagenetic depositional environments; and, second, the passing of burrowed media into deeper dysaerobic sediment is accompanied by the establishment of fermenting micro‐organisms whose byproducts mediate dolomitization.

Quantifying bioirrigation using ecological parameters: a stochastic approach†.

Irrigation by benthic macrofauna has a major influence on the biogeochemistry and microbial community structure of sediments. Existing quantitative models of bioirrigation rely primarily on chemical, rather than ecological, information and the depth-dependence of bioirrigation intensity is either imposed or constrained through a data fitting procedure. In this study, stochastic simulations of 3D burrow networks are used to calculate mean densities, volumes and wall surface areas of burrows, as well as their variabilities, as a function of sediment depth. Burrow networks of the following model organisms are considered: the polychaete worms Nereis diversicolor and Schizocardium sp., the shrimp Callianassa subterranea, the echiuran worm Maxmuelleria lankesteri, the fiddler crabs Uca minax, U. pugnax and U. pugilator, and the mud crabs Sesarma reticulatum and Eurytium limosum. Consortia of these model organisms are then used to predict burrow networks in a shallow water carbonate sediment at Dry Tortugas, FL, and in two intertidal saltmarsh sites at Sapelo Island, GA. Solute-specific nonlocal bioirrigation coefficients are calculated from the depth-dependent burrow surface areas and the radial diffusive length scale around the burrows. Bioirrigation coefficients for sulfate obtained from network simulations, with the diffusive length scales constrained by sulfate reduction rate profiles, agree with independent estimates of bioirrigation coefficients based on pore water chemistry. Bioirrigation coefficients for O2 derived from the stochastic model, with the diffusion length scales constrained by O2 microprofiles measured at the sediment/water interface, are larger than irrigation coefficients based on vertical pore water chemical profiles. This reflects, in part, the rapid attenuation with depth of the O2 concentration within the burrows, which reduces the driving force for chemical transfer across the burrow walls. Correction for the depletion of O2 in the burrows results in closer agreement between stochastically-derived and chemically-derived irrigation coefficient profiles.