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The Silurian Sharawra Member (middle to late Llandoverian) in Saudi Arabia exhibits unique surface traces with exceptional preservation: Seven small, wing-shaped traces occur on a sandstone slab showing well-defined hummocky cross-stratification having a few decimeters wavelength being covered by a thin mud layer. These traces are preserved as concave epirelief along with elongated internal striae and surrounded by slightly elevated levees. Preservation of these delicate, 10–20 mm long and ∼10 mm wide traces suggests that they were formed after a storm event when mud had already settled to the sediment surface. The lack of wave-generated sedimentary structures implies deposition between fair-weather and storm-wave base probably preventing further rapid reworking by waves. Based on their geometry, internal pattern, and spatial distribution, these wing-shaped traces are interpreted to have been produced by relatively stationary bottom-feeding fish, morphologically similar to ancestors of Gobiidae, probably in the Actinopterygii class. The majority of fish-made trace fossils record feeding and locomotion behaviour, whereas the wing-shaped traces are interpreted to represent resting structures made by fish that pressed their fins downward on the muddy sediment surface and hence, represent undertracks. These traces are possibly the oldest fish-made structure documented thus far. These wing-shaped traces are described as Pisquiesichnus dashtgardi igen. et isp. nov. in this study. [ABSTRACT FROM AUTHOR]

The reworking of a trace by a subsequently following organism represents a so-called sequorichnial behavior and leads to formation of a "burrowing highway". Burrowing highways occur more frequently than assumed in the fossil record. Their ichnological and sedimentological meaning is elucidated by using the trace fossil Gyrochorte. Gyrochorte producers exploiting sandy event beds tend to use "burrowing highways" in the same direction. Evidently, the Gyrochorte producers are thigmotactically highly sensitive as they can recognize a burrow produced by the same species because of the less densely packed grains, a somewhat increased mud content, and supposedly mucus segregated within the burrow. These changes make the reworking of pre-existing burrows energetically advantageous. However, in shallow-marine settings mucus is degraded rapidly and loose sediment consolidates in a short while. Therefore, the time to recognize a pre-existing burrow appears to be limited and a rather high number of organisms is a prerequisite for reutilization of a previous trace. "Burrow highways" potentially represent an additional criterion to characterize an opportunistic population strategy. [ABSTRACT FROM AUTHOR]

The mud-dominated part of the basal Vaca Muerta Formation in the central Neuquén Basin accumulated mainly under dysoxic conditions as indicated by the absence of both fine lamination and large burrows, typical of anoxic and oxic conditions, respectively. Event beds and large, strata-bound concretions preserving a nearly uncompacted sediment fabric document rather discontinuous deposition, in particular as concretions must reside within the zone of carbonate supersaturation for a prolonged period of time to form. The mudrock hosts numerous ash layers. Among them is a bed up to 40 cm-thick that was deposited by storm-induced currents and later became calcified. It contains abundant, winding Teichichnus up to 220 cm-long. The trace producers partly reworked their own spreite and probably applied a gardening and sequestrichnial nutritional strategy (that is collecting and stowing of nutritional material in the burrow for later utilization). The spreite fill documents depositional processes that delivered argillaceous sediment and provided oxygen. The ash originally constituting the Teichichnus bed originated from the volcanic arc west of the basin. In contrast, the erosive surface limiting the Teichichnus bed is covered by mud, implying sediment delivery from the east or south where rivers entered the basin while the climate was (at least seasonally) humid, whereas aridity increased towards the north. Consequently, an estuarine circulation likely developed and prevailed during the initial transgression of the lower Vaca Muerta Formation while cold Palaeo-Pacific water flowed into the subsiding and expanding basin. Later, during prevailing dry climate, an anti-estuarine circulation was probably established. [Display omitted] • Trace fossils record episodic oxygenation during Vaca Muerta Fm transgression. • Host sediment and fill of Teichichnus imply estuarine circulation. • Host sediment and fill of Teichichnus record sediment routing systems. • Teichichnus exhibits sequestrichnial and sequorichnial behaviour. [ABSTRACT FROM AUTHOR]

Trace fossils provide valuable palaeoenvironmental information in hemipelagic settings. This is particularly true in the case of Zoophycos, an easily recognizable trace fossil in core. At IODP site U1385, Zoophycos was found throughout an interval representing 1.5 Ma, covering 45 glacial-interglacial cycles mediated by obliquity (41 ka) and short-term eccentricity (100 ka). Zoophycos is most common in sediments deposited during glacial times and when the sedimentation rate was intermediate and primary production was high and seasonal. Occurrences of Zoophycos elsewhere support a similar relationship with seasonal organic-matter deposition. This is particularly significant considering that seasonality of organic-matter deposition is difficult to decipher from the sediment record. Zoophycos appears to represent a useful proxy to characterize high and seasonal organicmatter deposition and primary productivity in Neogene hemipelagic deposits. [ABSTRACT FROM AUTHOR]

The arrangement of sediment couplets preserved in Thalassinoides shafts suggests that tides regulated the passive filling of these trace fossils and, thus, represent tubular tidalites. The thickness variation in individual layers and couplets implies a mixed diurnal, semi-diurnal tidal signature where packages of either thick-layered or thin-layered couplets alternate. Calcarenitic sediment accumulated when tidal current velocity was too high to allow deposition of mud, whereas a marly mud layer is interpreted to have formed during more tranquil times of a tidal cycle (in particular, low-tide slack water). The tidal record within the burrows covers a few weeks and the corresponding spring-neap cycles. The fill of the Thalassinoides shafts is the only known record to decipher the tidal signature from otherwise totally bioturbated sediments. These deposits accumulated in a lower-shoreface to upper-offshore setting during the late Miocene on a shallow shelf extending from the Atlantic Ocean to the west into northern Patagonia. The fill of all investigated burrows started around spring tide and, thus, the behaviour of the burrow producers - probably crustaceans - is speculated to have been affected by tides or the high water level because all studied burrows became abandoned around the same period of a tidal cycle. [ABSTRACT FROM AUTHOR]

The Holocene muddy infill of the valley incised by the ancient Red River during Pleistocene sea-level lowstand records a change from fluvial to estuarine and finally marine depositional conditions. Siphonichnus , a mainly vertical trace fossil produced by burrowing bivalves, documents otherwise unrecorded episodes of enhanced erosion, bypass and deposition of, on average, rapidly aggrading (> 1 m kyr−1), mainly completely bioturbated sediments within the fluvial-marine transition zone (FMTZ), supposedly within the polyhaline domain. The producers of Siphonichnus moved nearly 1 m downward or upward in response to erosional or depositional phases, respectively. The fill of Siphonichnus burrows, in addition, records erosion and/or bypass of sediment: The traces were produced in mud, but many of them are filled with coarse silt and sand that is otherwise not present in the studied intervals in distinct layers. Obviously, this material was available when Siphonichnus was produced and connected to the sediment surface. In addition to seasonal erosion and deposition during freshet and its waning stage, Siphonichnus records exceptional events that displace the sediment surface by >0.5 m. Such events occurred episodically at an estimated frequency of 1 event per several hundreds of years. The complete bioturbation of the deposits suggests apparent continuous accumulation, but in fact they represent a pile of stacked event deposits resulting from depositional phases and intermittent severe erosion. • Siphonichnus bivalve traces are common in estuarine incised-valley deposits in the Gulf of Tonkin. • Siphonichnus shows a variable course, vertical near the seafloor and horizontal deep in sediment. • Siphonichnus moves upward and downward in response to erosion and deposition for more than 1 m. • Siphonichnus documents erosional and depositional events in completely bioturbated deposits. [ABSTRACT FROM AUTHOR]

The Oligocene Lower Freshwater Molasse of Switzerland is host to spectacular outcrops of fluvial deposits. In distal areas of the Swiss Molasse Basin, deposits of a north-eastward draining meandering system are exposed. Combined sedimentologic and ichnologic observations in the Chli Sunnhalde and Roggwil quarries allow an improved understanding of animal-substrate interactions in deposits of meandering fluvial systems. Strata include meander-belt sandstone, levee sandstone and mudstone, crevasse-channel and splay sandstone, floodplain mudstone and sandstone, and paleosols. While the meander belt and the more proximal crevasse-channel deposits are typically unbioturbated, the more distal deposits show a clear biogenic overprint, with distal crevasse-channel, crevasse-splay, and floodplain deposits being intensely bioturbated. Simple grazing and locomotion trails (included in the Cochlichnus anguineus-Helminthoidichnites tenuis suite) were formed subaqueously in ponded areas of the floodplain. Meniscate burrows (Taenidium isp. suite) and root trace fossils occur along the margin of these floodplain water-bodies and at the top of crevasse-splay deposits. Some of the floodplain, crevasse-splay, and crevasse-channel deposits are pervasively bioturbated by crayfish burrows (Camborygma litonomos suite). Crevasse-splay deposits locally host escape trace fossils. Where cross-cutting relationships are apparent, a colonization sequence can be established as follows: the Cochlichnus anguineus-Helminthoidichnites tenuis suite is cross-cut by the Taenidium isp. suite, which in turn is cross-cut by the Camborygma litonomos suite and root trace fossils. Composite ichnofabrics are common in these meandering river deposits, recording progressive lowering of the water table in overbank subenvironments. Frequency of depositional events was a first-order control on degree of bioturbation. Position of the water table and degree of substrate consolidation exerted considerable influence over the types of trace fossils produced. Distinct bioturbation phases may result in the formation of different trace-fossil suites - representative of disparate ichnofacies - preserved on a single bedding plane. This study further supports the notion that meandering fluvial systems are characterized by trace-fossil suites belonging to the Scoyenia, Camborygma and/or Mermia ichnofacies. • A Miocene fluvial ichnofauna is documented in detail • Cross-cutting relationships help to unravel colonization histories of overbank deposits • Taphonomy exerts control on continental ichnofacies [ABSTRACT FROM AUTHOR]

In the Lower Cretaceous McMurray Formation (Alberta, Canada), many intervals of intensely bioturbated (Bioturbation Index = 5–6) fine-grained sediments are characterized by high gamma-ray (GR) readings. Several methods, including sedimentary facies analysis, thin-section petrography, handheld spectral gamma-ray, portable X-ray fluorescence, X-ray diffraction, inductively coupled plasma-mass spectrometry, microprobe of K-feldspar, energy dispersive spectroscopy, and detrital zircon geochronology by laser ablation-inductively coupled plasma-mass spectrometry, were used to investigate the interval of interest in core samples. The mineralogical analysis shows that these intervals are enriched in heavy mineral grains, and particularly in zircons. The content of radioactive elements is variable. Thorium is commonly elevated up to three times, uranium nil to two times, and potassium content usually remains normal. The studied intervals consist of interbedded, bitumen-saturated cross-bedded and/or ripple cross-laminated sandstone (high-energy deposits) and light-gray bioturbated mudstone (low-energy deposits), commonly addressed as inclined heterolithic strata (IHS). IHS represent tidally influenced, brackish-water, upper point-bar deposits. The zircon grains become concentrated while hydraulic processes interact with bioturbation: the burrowing animals cause significant sediment mixing that allows the lightest sediment particles to go back into the suspension. Additionally, bioturbation increases the surface roughness along the sediment-water interface and, causes more turbulent flow, allowing for quartz and other light grains to be removed by traction and/or saltation, while dispersed heavier zircon grains become trapped and concentrated in open burrows. So far, this study is the first to demonstrate the importance of bioturbation in the enrichment of zircon grains in IHS. The interaction of bioturbation and hydraulic processes explains the apparently counter-intuitive enrichment of heavy minerals in a low-energy depositional setting. This scenario likely applies to numerous intervals characterized by similar GR and/or zirconium spikes across the McMurray Formation. Furthermore, it can be expected that in other sedimentary basins and stratigraphic units, similar studies will demonstrate that the proposed mechanism is universal. • Some IHS intervals display an aberrant gamma-ray pattern and intense bioturbation. • High gamma-ray values were found to be related to enrichment of zircons. • The interplay of bioturbation and hydraulic processes led to enrichment of zircons. • Burrowing fostered resuspension of material and concentration of heavy minerals. • Vertical burrows acted as traps of heavy minerals. [ABSTRACT FROM AUTHOR]