Cylindrical Burrows Research Articles

Exceptionally preserved burrows of ichnogenus Asterosoma from the lower Silurian of South China: systematic ichnology, palaeoecology and implications for ecosystem recovery following the late Ordovician mass extinction

Exceptionally preserved complex burrows are described from the lower Silurian of South China, and they are identified as Asterosoma ludwigae Schlirf, 2000, which is characterized by the straight or curved bulbs that bud from an axial, vertical or horizontal, cylindrical burrow following a dichotomous or fan-like pattern. Striae and concentric lamination of burrow fills indicate that the special mining behaviour of the tracemaker reflects appendages that imprinted the burrow wall during their activities, speculating that polychaetes or holothuroides could be strong candidates of the tracemaker of A . ludwigae . Abundant organic-matter-rich peloids and muddy matrix in burrow fills may consist of tracemaker's secretions or excrement. Abundant extracellular polymeric substance (EPS) and clay minerals in filling sediment indicate the possible presence of microbes, implying that Asterosoma is not a simple fodinichnion, but rather created a beneficial symbiosis between tracemakers and microbes in burrows. Phanerozoic spatiotemporal distributions indicate that Asterosoma was distributed in broad habitats from deep sea to delta, but showed a strong preference for the shallow sea. Compilation of new ichnofossils and previously reported ichnotaxa from South China reveals that ichnospecies richness, burrow size and complexity all increased significantly during the late Aeronian, indicating a full recovery after the late Ordovician mass extinction.

The puzzling influence of Ophiomorpha (trace fossil) on reservoir porosity: X-ray microtomography analysis

Bioturbation can influence petrophysical properties (e.g., porosity, permeability) of sedimentary rocks and, in consequence, reservoir quality. The impact can be positive, negative, or neutral, requiring detailed ichnological analysis. Ophiomorpha, a branched cylindrical burrow with diagnostic peloidal wall, may be present in bioturbated reservoirs that exhibit properties of both super-permeability and reduced porosity/permeability. However, no mechanistic understanding of how Ophiomorpha positively or negatively impacts petrophysical properties has yet been established. This study presents high-resolution X-ray microtomographic analysis of how the features of Ophiomorpha (i.e., peloidal wall vs. burrow fill) influence porosity distribution in deep-water deposits (Neogene Tabernas Basin, SE Spain). The results show that the peloidal burrow wall exhibits the lowest porosity (up to six orders of magnitude lower than burrow fill or host sediment), while surrounding sediment shows variable values. Abrupt porosity changes within the fill material likely relate to burrow-associated diagenesis. A refined understanding of the features of Ophiomorpha and their associated porosity distribution help to constrain understanding of their diverse impacts on reservoir properties.

The complex case of Macaronichnus trace fossil affecting rock porosity

Bioturbation is an important factor for reservoir quality due to the modification of host rock petrophysical properties (i.e., porosity, permeability, and connectivity). However, there is no predictable relationship between bioturbation and its effect on rock properties, due to the variability of the involved ichnological features. A detailed ichnological analysis is necessary to determine how bioturbation affects petrophysical properties in a bioturbated reservoir. Traditionally, ichnological features such as density, tiering, size, orientation, architecture, and fill, have been considered. However, other properties have been undervalued as is the case of lining. Here, we present a detailed study on the effects of Macaronichnus burrows, an ichnotaxon usually related to hydrocarbon exploration due to its high concentration in rock notably affecting petrophysical properties. Macaronichnus, a subhorizontal cylindrical burrow, is characterized by a well-defined and developed outer rim surrounding the tube core. Our data indicates a clear zonation in porosity according to burrow structure, with the lowest porosity in the tube core and higher values associated with the surrounded rim. This duality is determined by the tracemaker grain selective feeding activity and the consequent concentrated cementation. The organism concentrates the lighter minerals in the tube core fill during feeding, favoring post-depositional cementation during diagenesis and this results in lower porosity than the host rock. However, heavy minerals, mainly glauconite, are located in the rim, showing higher porosity. Our results support the view that ichnological analyses are essential to determine reservoir quality in bioturbated reservoirs, evidencing that other ichnological properties in addition to those traditionally considered must be evaluated.

Ichnology and sedimentology of the trace fossil-bearing fluvial red beds from the lowermost member of the Paleocene Funing Formation in the Jinhu Depression, Subei Basin, East China

Abstract The lowermost member of the Paleocene Funing Formation, which is composed of bioturbated fluvial red beds, is extensively distributed throughout the Jinhu Depression, Subei Basin, East China. Despite its economic value as one of the most important oil-bearing reservoirs in the Subei Basin, the sedimentology, ichnology and paleoenvironment of this formation in the Jinhu Depression remain poorly understood. In this work, we investigated the ichnofossils and sedimentary facies, analyzed the ichnofacies and potential tracemakers and reconstructed the paleoenvironment of the Jinhu Depression based on cores from the lowermost member of the Paleocene Funing Formation. This formation contains a moderately diverse ichnofauna (9 ichnotaxa of the Scoyenia ichnofacies) that includes meniscate burrows (Taenidium barretti, Taenidium satanassi and Beaconites coronus), simple horizontal cylindrical burrows (Palaeophycus tubularis, Palaeophycus heberti and Planolites isp.), simple vertical or subvertical burrows (Skolithos linearis and Skolithos isp.) and plant root traces. The other complex branched and chambered burrows are left in open nomenclature. These ichnofossils are widespread throughout the three facies associations identified in this study: (1) ephemeral fluvial channel, (2) crevasse splay and (3) distal floodplain facies associations. Multiple lines of sedimentological and ichnological evidence, namely, the predominance of massive and upper flow regime structures, the occurrence of invertebrate burrows (e.g., Skolithos and Taenidium) in the lower and middle parts of the channel deposits and the dramatic changes in the color and mottling in channel and overbank sediments, indicate that the river discharge was short lived and that the water table was highly variable. The variations in the discharge and water level are attributed to the influence of seasonal rainfall. The cyclic nature of intense rainfall events and dry periods suggests that the Subei Basin was likely located in a semiarid region with a seasonal rainfall pattern during the early Paleocene. This study also reveals that the ephemeral fluvial channel is the facies association with the highest potential to yield oil-bearing reservoirs in the Paleocene red beds of the Jinhu Depression. Additionally, the influence of bioturbation on the reservoir quality in this region should be considered in future research.

Modernist architecture in Barcelona reveals a new trace fossil from the Miocene of Montjuïc (NE Spain)

A new ichnotaxon, Lapillitubus montjuichensis n. i gen. n. isp., is described from the middle Miocene (Serravallian) of Montjuic mountain (Barcelona, northeastern Spain). This ichnotaxon consists of a horizontal to vertical, cylindrical burrow with an agglutinated lining exclusively composed of lithoclasts. Lapillitubus montjuichensis is interpreted as the result of the burrowing activity of a deposit- or suspension-feeding annelid worm. This new ichnotaxon extends the record of the informal group known as clast-armored or agglutinated trace fossils. In addition, since part of its type material is located in the blocks that make up the facades of several modernist buildings in the city of Barcelona, this new ichnotaxon highlights the importance of fossils in urban settings for those cases in which natural outcrops are reduced, restricted or even missing.

The Celliforma ichnofacies in calcareous paleosols: An example from the late Miocene Cerro Azul Formation, La Pampa, Argentina

Invertebrate trace fossils from the late Miocene Cerro Azul Formation (La Pampa, Argentina) are described and compared with known paleosol ichnofacies. The formation is a loess succession punctuated by numerous calcareous paleosols. Trace fossils were recovered from thirteen localities distributed in a wide latitudinal and longitudinal range within La Pampa Province. Paleosols from the northwestern localities display clastic dikes and pedogenic slickensides and are compared with calcic vertisols, which are typical of strongly seasonal and semiarid climate. Paleosols from the remaining localities have a Bt horizon with blocky or prismatic peds and can be compared with mollisols. The depth to the Bk horizon for all paleosols averages 0.54m, suggesting a mean annual precipitation of 450mm (±147mm), also pointing to semiarid climatic conditions during soil formation. The trace fossil assemblage from the Cerro Azul Formation is of low diversity and abundance and is typified by the presence of the insect trace fossils Celliforma, Rosellichnus, Rebuffoichnus, Fictovichnus and Teisseirei. The ichnospecies recorded are: Celliforma germanica, Celliforma cf. rosellii, Celliforma isp., Rosellichnus isp., Rebuffoichnus casamiquelai, Fictovichnus cf. sciuttoi, Fictovichnus isp., Teisseirei barattinia, Taenidium barretti, and cylindrical burrow fills. These trace fossils (along with Attaichnus kuenzelii, vertebrate burrows and medium–sized rhizoliths described in previous works) are considered comparable with the Celliforma ichnofacies. This ichnofacies is indicative of well-drained calcareous paleosols developed under low vegetation coverage. For the analyzed succession the vegetation was probably dominated by scrubs with minor participation of herbaceous plants. Coprinisphaera ispp. (including Coprinisphaera lazai, Coprinisphaera murguiai, and Coprinisphaera isp.) showing a cementation similar to associated late Miocene trace fossils were only recorded, along with Celliforma isp., in two localities. This trace fossil assemblage is comparable with the Coprinisphaera ichnofacies, suggesting dominance of herbaceous communities and wetter climate than those of the Celliforma ichnofacies. Some specimens of uncemented Coprinisphaera ispp. were produced during post-Miocene times and are not considered as a part of the trace fossil assemblage of the Cerro Azul Formation.

Ghost shrimps (Decapoda: Axiidea: Callianassidae) as producers of an Upper Miocene trace fossil association from sublittoral deposits of Lake Pannon (Vienna Basin, Slovakia).

Numerous trace fossils are described from the Late Miocene sediments of the Bzenec Formation exposed at the Gbely section (the Vienna Basin, Slovakia). During deposition of the sediments the area was part of the large, long-lived brackish to freshwater Lake Pannon. Most of the trace fossils are attributed herein to Egbellichnus jordidegiberti igen et ispec. nov. and are interpreted as burrows produced by decapod crustaceans, specifically by a ghost shrimp of the family Callianassidae. This interpretation is based on two independent lines of evidence: environmental requirements of large bioturbators and the burrow morphology itself. The new ichnotaxon is distinguished from other related ichnotaxa by a combination of typically inclined (roughly at an angle of 45°) cylindrical burrows, absence of lining, and tunnels making loops or bends at approximately right angles. The burrow systems at Gbely document the survival of ghost shrimp long after the closure of all seaways and the origin of Lake Pannon. As today, no ghost shrimp are known from long-lived brackish lakes. Egbellichnus from Gbely is the only, although indirect, record of ghost shrimp from a brackish lake environment reported so far.

Experimental evaluation of the performance of earth levees deteriorated by wildlife activities

In this study, an earth levee model is constructed to investigate the impact of animal burrows on the integrity and performance of earthen structures. A series of centrifuge experiments are conducted on homogenous scaled-down 1H:1V levee models built from the natural Kasama soil. Both intact and deteriorated models were subject to a 35g acceleration level. Invasive animal intrusions were introduced in the form of horizontal array of idealized cylindrical burrows at the mid-height of the levee. The water level was gradually increased during the centrifuge flight, and the response of the levee was monitored throughout the test. Pore pressures were recorded using pressure transducers placed at preselected locations within the model. Surface displacements were measured using laser LVDTs and supplemented with three digital cameras for tracking the overall deformation pattern of the levee model. A summary of the test procedure and selected results is presented herewith. The observed deformation mechanism due to the presence of animal burrows is also described. As compared with the intact levee, the presence of burrows is found to alter the pattern of the water flow through the deteriorated levee structure—leading to a notable increase in the exit hydraulic gradient, internal erosion, and subsequently slope failure.

When Life Got Smart: The Evolution of Behavioral Complexity Through the Ediacaran and Early Cambrian of NW Canada

Ediacaran and early Cambrian strata in NW Canada contain abundant trace fossils that record the progressive development of complex behavior in early animal evolution. Five feeding groups can be recognized: microbial grazing, deposit-feeding, deposit-feeding/predatory, filter-feeding/predatory, and arthropod tracks and trails. The lower Blueflower Formation (ca. 560–550 Ma) contains abundant burrows that completely cover bedding surfaces with small (∼1 mm diameter) cylindrical burrows that were strictly restricted to microbial bedding surfaces and exhibited only primitive and inconsistent avoidance strategies. The upper Blueflower contains three-dimensional avoidance burrows and rare filter-feeding or possibly predatory burrows, suggesting increased behavioral responses in food gathering that marked the beginning of the agronomic revolution in substrate utilization. Cambrian strata of the Ingta Formation contain systematically meandering burrows and more diverse feeding strategies, including the onset of treptichnid probing burrows that may reflect predation. These observations imply that Ediacaran burrowers were largely characterized by crude, two-dimensional avoidance meanders that represented simple behavioral responses of individual burrowers to sensory information, and that the subsequent development of more diverse and complex feeding patterns with genetically programmed search pathways occurred during the earliest stages of the Cambrian explosion. These observations further imply that changes occurred in both the food source and substrate during the ecological transition from Proterozoic matgrounds to Phanerozoic mixgrounds.

Trace-fossil assemblages with a new ichnogenus in “spotted”

Abstract Highly-bioturbated “spotted” limestones and marls (Fleckenmergel-Fleckenkalk facies) of the Early Jurassic, which were deposited in broad and recurrent deep-shelf habitats of the Northern Tethys, are characterized by rare benthic carbonate-producing macroinvertebrates. To address this paradox, we analyse trace-fossil assemblages in a ~85 m-thick succession of Pliensbachian spotted deposits (Zliechov Basin, Western Carpathians). They are dominated by infaunal and semi-infaunal deposit-feeders, with 9 ichnogenera and pyritized tubes of the semi-infaunal foraminifer Bathysiphon, being dominated by Chondrites, Lamellaeichnus (new ichnogenus), and Teichichnus. Lamellaeichnus, represented by a horizontal basal cylindrical burrow and an upper row of stacked convex-up gutters, was produced by a mobile deposit-feeder inhabiting shallow tiers because it is crossed by most other trace fossils. We show that the spotty appearance of the deposits is generated by a mixture of (1) dark, organic-rich shallow- and deep-tier traces (TOC = 0.16-0.36), and (2) light grey, organic-poor mottled or structurless sediment (TOC = 0.09-0.22). The higher TOC in shallow-tier burrows of Lamellaeichnus demonstrates that uppermost sediment layers were affected by poor redox cycling. Such conditions imply a limited mixed-layer depth and inefficient nutrient recycling conditioned by hypoxic bottom-waters, allowed by poor circulation and high sedimentation rates in depocenters of the Zliechov Basin. Hypoxic conditions are further supported by (1) dominance of trace-fossils produced by infaunal deposit feeders, (2) high abundance of hypoxiatolerant agglutinated foraminifer Bathysiphon, and (3) high abundance of Chondrites with ~0.5 mm-sized branches. Oxygen-deficient bottom-conditions can thus simultaneously explain the rarity of benthic carbonate-producing macroinvertebrates and high standing abundance of tolerant soft-shell and agglutinated organisms in spotted deposits.

An event bed with abundant Skolithos burrows from the late Pridoli (Silurian) of Saaremaa (Estonia)

Abundant Skolithos burrows are here described from a possible regressive event bed at Ohesaare cliff (Pridoli), Saaremaa, Estonia. The vertical, cylindrical burrows are identified as Skolithos rather than Trypanites because they intercept and bypass rather than cut bioclasts in the limestone matrix. The absence of encrustation on the upper bedding surface also is evidence that these traces are soft-sediment burrows rather than hardground borings. We interpret this intensive bioturbation by Skolithos-producing organisms as an indicator of a shallow water paleoenvironment with high hydrodynamic energy.

Effects of Ground‐Dwelling Beetle Burrows on Infiltration Patterns and Pore Structure of Initial Soil Surfaces

By modifying the soil structure, flora and fauna play a major role in controlling water infiltration and erosion. Little is known, however, about local feedback effects during the initial stage of soil development. Initial soil formation was studied in an artificial catchment where coarse‐textured, sandy sediments were left to undirected succession. In a patchy moss‐covered area, the surface was colonized by larvae of the ground‐dwelling beetle Cylindera arenaria viennensis [Schrank, 1781], as indicated by millimeter‐sized cylindrical burrows. Our objective was to study the effects of both moss vegetation and beetle larvae on pore structure and infiltration. The pore structure of sparsely and densely moss‐vegetated and unvegetated samples containing a single burrow was characterized by x‐ray computed tomography (CT). Flow patterns of infiltration experiments were visualized using neutron radiography (NR). The micro‐CT scans revealed a variety of more unstable pore systems in the bare soil, locally compacted regions in the moss‐covered samples, and isolated vesicular pores similar to those reported for desert soils. The NR series showed water flow around the cylindrical burrow under initially moist conditions and pronounced preferential flow within the burrow under initially dry soil conditions. Water‐repellent regions in the initially dry sample explained pressure buildup before gravity‐driven flow in the burrow started. The moss cover seemed to stabilize the surface soil, visible in the absence of a depositional sediment layer. The results suggest that moss vegetation and ground beetle burrowing activity control initial soil development by modifying pore structure and water infiltration.

Early Triassic vertebrate burrows from the Katberg Formation of the south-western Karoo Basin, South Africa

Bordy, E.M., Sztanó, O., Rubidge, B.S. & Bumby, A. 2010: Early Triassic vertebrate burrows from the Katberg Formation of the south-western Karoo Basin, South Africa. Lethaia, Vol. 44, pp. 33–45. Very large (∼30–35 cm), uniform diameter cylindrical burrows were found at two localities, ∼100–110 m above Permo-Triassic boundary in the fluvial Katberg Formation (main Karoo Basin, South Africa). Analysis of their morphology and stratigraphical distribution allows us to improve both the understanding of the ethology of burrowing, and also the reconstruction of the earliest Triassic ecosystems. These burrows have a single opening that leads, via a large, uniform diameter, semi-horizontal tunnel, to a rounded terminus. These 3-m-long structures descend at angles of ∼30° to a maximum of 1.5 m depth. They are devoid of chambers, branching, cross-cutting, coiling or spiralling. Filled with coarse sediments, some have a <5-mm clay lining, and most have subtle indentations and various scratch marks. These burrows were possibly excavated as resting, hiding or aestivating shelters, and are tentatively attributed to dicynodonts (i.e. Lystrosaurus murrayi and L. declivis). Data suggest that burrowing was widespread after the P/Tr boundary event, when in this part of Gondwana, dryland fluvial systems had large fluctuations in flow with extended low-flow periods or drought punctuated by high-discharge periods. We hypothesize that these constructed refuges played a role in the biodiversity recovery and maintenance in the Early Triassic (Induan) ecosystem. □Early Triassic, Karoo Basin, Katberg Formation, South Africa, Tetrapod Burrows.

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.

Dinosaur tracks and possible lungfish aestivation burrows in a shallow coastal lake; lowermost Cretaceous, Bornholm, Denmark

The Mesozoic succession of the island of Bornholm in the Baltic Sea has hitherto yielded only very few remains after vertebrate life. We describe a new find of a well-exposed vertebrate trample ground and large, densely spaced, vertical to inclined burrows from shallow lake deposits belonging to the Berriasian Skyttegård Member of the Rabekke Formation. The succession is terrestrial, but a coastal setting is indicated by the great abundance of pyrite concretions and framboidal pyrite. Organic geochemical and palynological data show that the lake was surrounded by a low-diversity gymnospermous vegetation. The trampling ground is exposed in a vertical section at the boundary between light grey, structureless or trough cross-bedded fluvial sand and dark brown, organic-rich lacustrine mud with densely spaced vertical rootlets, wood fragments and large pyrite concretions. The tracks are bowl-shaped, have an irregular flat or slightly conical base, are on average 22 cm deep and on average 43 cm wide in the upper part and 23 cm in the lower part, but some reach widths up to about 1 m and have a highly irregular shape. The underlying sand in some cases shows a faint stratification that is bent downwards adjacent to the mud-filled tracks, which have near-vertical and commonly overhanging margins. The morphology of the bowl-shaped depressions suggests that they were made by dinosaurs, most likely sauropods. They were clearly emplaced after deposition of the dark brown mud. Long, vertical to inclined, commonly slightly curved, J-shaped or spiraling cylindrical burrows with a diameter averaging 4.4 cm and lengths up to 45 cm occur densely spaced in the mud. They are unbranched, have no mud or lag linings. The top of the burrows is indistinct or not preserved, whereas the base is rounded, concave-up, commonly with a slightly enlarged chamber. The length is difficult to estimate precisely because of the missing top and because the burrows cross-cut and go in and out of the plane of exposure. The burrows have a passive infill of dark mud and, at some levels, of irregularly alternating laminae of white sand and mud. The sand may be of aeolian origin or may represent distal crevasse splays or washovers from adjacent rivers or the nearby sea. Skeletal remains have not been found in or associated with the burrows, which are similar to burrows referred to lungfish or crayfish, and they are with hesitation interpreted as representing lungfish aestivation burrows based on the morphological characteristics. This is only the second report of dinosaur tracks in Denmark and the first in-situ find where environmental conditions can be interpreted with some confidence. Possible lungfish burrows are here reported for the first time from the Danish Mesozoic. The overall rarity of vertebrate remains in the Mesozoic succession of Bornholm may reflect that the area was a horst island or submerged shoal during much of the Jurassic and Cretaceous and may not always have had direct land connection with surrounding land areas of the Baltic Shield or mainland Europe.

Life Beneath the Surfaces of Active Jurassic Dunes: Burrows from the Entrada Sandstone of South-Central Utah

Within the Middle Jurassic Entrada Sandstone of south-central Utah, cylindrical burrows, 15–95 mm diameter, are abundant in large-scale, eolian cross-strata. Burrows are oriented at a high angle to stratification and commonly extend more than 30 cm below their surface termini. They are rarely inclined more steeply than 22°. Many are sinuous, and they sometimes branch (∼120°) at bends. Burrows terminate upward against flat-topped cones of structureless sandstone that are up to 15 cm deep and present at numerous, closely spaced stratigraphic horizons. Entrada eolian dune deposits also host abundant burrows likely produced by small insects. Both large and small burrows are most numerous in the uppermost parts of very thick (up to 35 m) compound sets of cross-strata generated by superimposed dunes migrating along the lee slopes of giant dune ridges. The size and morphology of the large burrows and the nature of their fills suggest that they were excavated by vertebrates, possibly insectivores, but the possibility that scorpions or spiders dug the burrows cannot be ruled out. In modern dunes, the top 20 cm of rain-moistened sand dries quickly, but underlying sediment can remain moist for long periods. Conical pits formed on the dry surface of Jurassic dunes at the tops of burrows that were primarily excavated in underlying moist sand. Cones composed of structureless sandstone are active fills produced when burrowers pushed moist sand to the surface, forming spoil piles. Most cylindrical portions of the burrows were also actively backfilled; remaining parts were passively filled when burrow walls collapsed. Cones at burrow tops now delineate thin (∼5–10-cm-thick) packages of cross-strata that record slow (seasonal?) dune migration. Rainfall on dune surfaces allowed scattered plants, insects, and insectivorous vertebrates to inhabit the Entrada sand sea. Burrows provided animals with refuge from the hot, desiccating surface conditions.

Burrows Dug by Large Vertebrates into Rain‐Moistened Middle Jurassic Sand Dunes

In south‐central Utah, eolian cross‐strata of the Escalante Member of the Entrada Sandstone contain inclined, cylindrical burrows up to 63 cm in diameter and 305 cm long. Of the 14 large tunnels located during this study, 12 descend from second‐ and third‐order bounding surfaces that formed on the lee slopes of large dune ridges, well above the water table. The tunnels are inclined 15°–22°; one tunnel ends in an expanded chamber. Eolian cross‐strata fill proximal portions of four of the tunnels and indicate that after abandonment, sand drifts migrated as much as a meter into the open shafts. Structureless sand and breccia blocks that were generated by roof collapse fill other tunnels. Animals dug the tunnels in rain‐moistened, cohesive sand. The burrows may have served as temporary shelters from severe diurnal conditions in the shadeless, subtropical Entrada dune field.

Lunulichnus Tuberosus Ichnogen. and Ichnosp. Nov. from the Early Eocene Wasatch Formation, Fossil Butte National Monument, Wyoming: An Arthropod-Constructed Trace Fossil Associated with Alluvial Firmgrounds

A new trace fossil, Lunulichnus tuberosus, is described from fluvial deposits of the Wasatch Formation (early Eocene) at Fossil Butte National Monument, southwestern Wyoming, USA. L. tuberosus are straight, vertical to obliquely oriented, unlined cylindrical burrows with pronounced crescent-shaped wall sculptings. In situ examples of these trace fossils are most commonly preserved as sand-filled casts emanating from the erosional bases of fluvial channel sandstone bodies into underlying floodplain mudstone/siltstone beds. L. tuberosus is interpreted as the dwelling trace of a stream-dwelling decapod crustacean. Excellent preservation of fine detail, particularly their diagnostic crescent-shaped wall sculptings, support the hypothesis that L. tuberosus were excavated in firm substrata subjacent to fluvial erosional surfaces. As such, they are interpreted as constituents of alluvial Glossifungites trace fossil assemblages.

Faunal burrows as indicators of paleo-vegetation in eastern Washington, USA

The Palouse loess deposits in the Pacific Northwestern United States contain buried paleosols with distinctive biological fabrics. The Washtucna Soil, formed 40,000–15,000yr ago during the last full glacial, contains up to 90% by volume distinctive cylindrical pedotubules that are 1–2cm in diameter formed by burrowing fauna. The overlying post-glacial loess and modern surface soils that support perennial grasslands lack these cylindrical burrows. We investigated the paleoecological significance of the burrows. Observations of several types of burrowing fauna under native vegetation indicated that nymphs of cicadas (Homoptera: Cicadidae) are responsible for cylindrical, back-filled burrows that match those in the Washtucna Soil. We measured the abundance of active cicada burrows in soils in four native vegetation zones (Soil sites), establishing that cicada burrows comprise 19% of the rooting zone volume in sagebrush steppe, but just 1–3% of the rooting zone volume in bunchgrass steppe, meadow steppe and coniferous forest. This suggests strongly that abundant cicada burrows in paleosols are a proxy for the geographic extent of plant communities that contained sagebrush. To assay the activity of cicada nymphs through time, we measured burrowed volume by depth from the soil surface down through the Washtucna Soil (i.e. from the present to ca. 40,000yrbp) at five stratigraphic research sites (Paleosol sites). Cicada-burrowed volume is generally less than 5% in the rooting zone of the surface soils and throughout Holocene loess, but is up to 94% in the rooting zone of the Washtucna Soil at Paleosol sites that currently support bunchgrass steppe outside the present-day sagebrush steppe zone. Cicada host preferences in vegetation zones today suggest that sagebrush was the dominant shrub as the Washtucna Soil formed. From this reconstruction, combined with information from studies of pollen and plant opal, we infer that periglacial steppe plant communities dominated by sagebrush spread, from 40,000 to 15,000yrbp, into areas of the Columbia Plateau that support bunchgrass steppe, meadow steppe, and even some coniferous forest today. Trace fossils of soil fauna in paleosols are indicators of fluctuations in biological activity in response to climatic changes of the Quaternary Period in Palouse loess deposits.

Solute transport in sediments by freshwater infaunal bioirrigators

Laboratory experiments using the radionuclide 22Na as a solute tracer were conducted in microcosms containing the freshwater chironomid larvae Coelotanypus sp. and Chironomus plumosus and the mayfly larvae Hexagenia limbata to determine the exchange of solutes between sediments and overlying water. Three different mathematical models of transient solute transport in bioturbated sediments were applied to the data to evaluate which best quantified solute exchange and to determine how that exchange varied with fauna1 type and density. Although all three species of larvae constructed burrows and irrigated them, the larger H. limbata frequently abandonded their burrows and vigorously burrowed the sediment. As a result, an enhanced diffusion model, in which the solute diffusion coefficient is higher in the bioturbated zone than in unmixed sediments, best described the data for the larger H. limbata. The enhanced diffusion model generally underestimated solute transport by smaller H. limbata, C. plumosus and Coelotanypus sp. larvae because it did not account for the effects of burrow irrigation, Both the cylindrical burrow model and the nonlocal exchange model with a constant value of the exchange coefficient in the mixed layer described the transport processes well, presumably because the smaller H. limbata, C. plumosus, and Coelotanypus sp. maintained and actively irrigated their burrows. At natural bottom fauna1 densities, C. plumosus induced the greatest exchange of solutes between sediment and overlying water, followed by the small H. limbata, the large and medium H. limbata, and Coelotanypus. However, H. limbata enhanced the flux by about an order of magnitude more than did C. plumosus and by about a facior of 20 times that of Coelotanypus on an individual basis.