Trace Fossil Associations Research Articles

Photogrammetry of the Oryctodromeus cubicularis type locality burrow and the utility of preexisting, standard field photographs for three dimensional digital reconstruction

ABSTRACT Oryctodromeus cubicularis is a small-bodied ornithischian dinosaur from the mid-Cretaceous Blackleaf and Wayan Formations of Montana and Idaho, respectively, and is the only documented dinosaur with evidence of a burrowing ecology. The type locality, from the Blackleaf Formation of southwestern Montana, consisted of an infilled burrow structure containing the disarticulated skeletons of one adult and two juveniles and represents a rare association of body fossils and trace fossils of a single dinosaur taxon. While these fossils and their paleobiological implications were unprecedented, collection nevertheless necessitated removal of the burrow structure from its geological context and its destruction during body fossil preparation. Here we present the first photogrammetric models of the type locality burrow in its original geological context and three dimensional morphology, constructed from photos taken at three stages in excavation. Because the terminal extent of the burrow was collected prior to the burrow’s complete exposure, the structure was never documented in its entirety. A composite model provides the only holistic documentation of the entire burrow morphology as originally preserved. These models supplement the original burrow description, serve as comparative tools for identifying and diagnosing future discoveries, and demonstrate the utility of pre-existing photographs for later photogrammetric reconstruction.

Trace fossils associated with Burgess Shale non-biomineralized carapaces: bringing taphonomic and ecological controls into focus.

The association of trace fossils and non-biomineralized carapaces has been reported from Cambrian Lagerstätten worldwide, but the abundance, ichnodiversity, taphonomy and ecological significance of such associations have yet to be fully investigated. Two main end-member hypotheses are explored based on the study of a relatively wide variety of trace fossils preserved associated to Tuzoia carapaces from the middle Cambrian Burgess Shale in British Columbia. In the ecological Tuzoia garden hypothesis, the bacterially enriched surface of carapaces provides opportunities for intricate ecologic interactions among trophic levels. In the taphonomic shielding hypothesis, the trace fossil–carapace association results from preferential preservation of traces as controlled by compaction independent of any association in life. In an attempt to better understand the role of the carapace as a medium for preservation of trace fossils and to evaluate the effects of mechanical stress related to burial, a numerical model was developed. Results indicate that the carapace can shield underlying sediment from mechanical stress for a finite time, differentially protecting trace fossils during the initial phase of burial and compaction. However, this taphonomic model alone fails to fully explain relatively high-density assemblages displaying a diversity of structures spatially confined within the perimeter of carapaces or branching patterns recording re-visitation.

The Ichnological and Sedimentological Signature of a Late Paleozoic, Postglacial Marginal-Marine and Shallow-Marine, Tidally Influenced Setting: The Wudayhi Member of the Nuayyim Formation (Unayzah Group) in the Subsurface of Central and Eastern Saudi Arabia

Abstract Sedimentation in the Nuayyim Formation across subsurface central and eastern Saudi Arabia has been chiefly ascribed to continental sedimentary environments. However, a number of levels in this formation show evidence for marginal-marine and shallow-marine sedimentation. This paper documents trace-fossil faunas and sedimentological characteristics from these facies and presents a regional depositional model for the Wudayhi Member that confirms the presence of shallow-marine sedimentary environments. Marginal-marine and shallow-marine sedimentation in the Wudayhi Member includes estuarine deposits and upper-shoreface through lower-shoreface deposits. They are reflective of several transgressive–regressive (T-R) cycles in an overall shoaling-upwards, tidally influenced progradational succession that exhibit mixed-process (wave-, tide-, and fluvially-influenced) depositional environments. The succession displays an overall upward decrease in bioturbation intensity with elements of an impoverished proximal expression of the Cruziana Ichnofacies at the base in proximal- and distal- lower-shoreface deposits (Facies 5–6), passing into an impoverished expression of the Skolithos Ichnofacies in upper-shoreface deposits (Facies 4). Therein, Facies 5 records storm-influenced sedimentation and includes hummocky cross-stratification (HCS), combined-flow ripples, cross-lamination, and ichnofossils that alternate between storm-related and fair-weather assemblages. An overall reduction in both the diversity of ichnogenera and the intensity of burrowing across the shoreface profile, an apparent lack of middle-shoreface deposits, and the occurrence of storm-wave-generated structures interspersed with tidally generated structures in the center and southeast of the study area are interpreted as tidal modulation, suggesting macrotidal conditions at the time of sediment deposition. Estuarine sedimentation includes coal deposits (Facies 1), tidal flats (Facies 2), and fluvio-tidal deposits (Facies 3) that overlie the succession, and display a stressed, impoverished mixture of traces with facies-crossing elements of the Skolithos and Cruziana Ichnofacies in the north and northwest of the study area. Sedimentation took place on a broad and sandy, partially restricted shelf, chiefly influenced by tidal currents that was variably fluvially influenced. The interplay of the aforementioned processes results in a complex architecture that is traceable, based on the sedimentological and ichnological content. Colonization by bioturbating infauna exhibiting elements of an overall impoverished Skolithos and Cruziana Ichnofacies in the Wudayhi Member is interpreted to be related to sea-level rise, with regional transgression induced by the melting of glacier ice following the Late Carboniferous to Early Permian glaciation that affected southern Gondwana. Subsequently, as the Arabian Plate migrated northwards, isostatic rebound concomitant with increased tectonism associated with the Neotethys propagating into the Arabian Peninsula caused regional regression responsible for the progradational sequence presented herein in the Early to Middle Permian. Trace-fossil associations and ichnofacies presented in this paper are significant, because they provide evidence for marginal-marine and shallow-marine tide- and storm-influenced processes in the Unayzah Group during deposition of the Wudayhi Member of the Nuayyim Formation. Furthermore, it establishes a framework than can be linked to fully marine coeval deposits southeastern of the Arabian Peninsula into Oman.

TRACE FOSSILS AND GLAUCONITIC PELLETS PROVIDE INSIGHT INTO CAMBRIAN SILICICLASTIC MARINE ENVIRONMENTS

This study documents the association of glauconitic pellets and trace fossils at two Cambrian sites: the Reno Member, Lone Rock Formation, in southern Wisconsin and the Lion Mountain Member, Upper Riley Formation, in central Texas. Each site reflects a marine paleoenvironment on the Cambrian Laurentian margin rich in marine life that was affected by shifts in shoreline and wavebase. Both units contain abundant glauconitic fecal pellets, which were mixed with terrigenous quartz, and ichnofauna that characterize siliciclastic sublittoral marine environments of variable energy. This combination of ichnologic features is suggestive of multiphase depositional histories. Initial stages are represented by intense invertebrate feeding and pelletizing large quantities of seafloor sediment. Glauconitization of the pellets in relatively quiet-water environments represents intermediate stages. Burrowing of the units rich in relict glauconitic pellets in high-energy settings represents the final episode at each site. Findings demonstrate a major shift in benthic paleoecology in response to a changing paleoenvironment. The glauconitic pellets were sufficiently resistant to survive processes associated with a shallowing marine environment, as they were incorporated into primary sedimentary structures (ripplemarks and crossbeds) and biogenic structures (burrows). The combined ichnologic, mineralogic and sedimentologic observations offer insight for depositional interpretation.

Trace fossils, sedimentary facies and parasequence architecture from the Lower Cretaceous Mulichinco Formation of Argentina: The role of fair-weather waves in shoreface deposits

Shorefaces can display strong facies variability and integration of sedimentology and ichnology provides a high-resolution model to identify variations among strongly storm-dominated (high energy), moderately storm-affected (intermediate energy), and weakly storm-affected (low energy) shoreface deposits. In addition, ichnology has proved to be of help to delineate parasequences as trace-fossil associations are excellent indicators of environmental conditions which typically change along the depositional profile. Shallow-marine deposits and associated ichnofaunas from the Mulichinco Formation (Valanginian, Lower Cretaceous) in Puerta Curaco, Neuquén Basin, western Argentina, were analyzed to evaluate stress factors on shoreface benthos and parasequence architecture.During storm-dominated conditions, the Skolithos Ichnofacies prevails within the offshore transition and lower shoreface represented by assemblages dominated by Thalassinoides isp. and Ophiomorpha irregulaire. Under weakly storm-affected conditions, the Cruziana Ichnofacies is recognized, characterized by assemblages dominated by Thalassinoides isp. and Gyrochorte comosa in the offshore transition, and by Gyrochorte comosa within the lower shoreface. Storm-influenced conditions yield wider ichnologic variability, showing elements of both ichnofacies.Storm influence on sedimentation is affected by both allogenic (e.g. tectonic subsidence, sea-level, and sediment influx) and autogenic (e.g. hydrodynamic) controls at both parasequence and intra-parasequence scales. Four distinct types of parasequences were recognized, strongly storm-dominated, moderately storm-affected, moderately storm-affected – strongly fair-weather reworked, and weakly storm-affected, categorized based on parasequence architectural variability derived from varying degrees of storm and fair-weather wave influence. The new type of shoreface described here, the moderately storm-affected – strongly fair-weather reworked shoreface, features storm deposits reworked thoroughly by fair-weather waves. During fair-weather wave reworking, elements of the Cruziana Ichnofacies are overprinted upon relict elements of the Skolithos Ichnofacies from previous storm induced deposition. This type of shoreface, commonly overlooked in past literature, expands our understanding of the sedimentary dynamics and stratigraphic architecture in a shoreface susceptible to various parasequence and intra-parasequence scale degrees of storm and fair-weather wave influence.

Termite nests, rhizoliths and pedotypes of the Oligocene fluviomarine rock sequence in northern Egypt: Proxies for Tethyan tropical palaeoclimates

The present study gives an account of the development of several associations of the continental trace fossils within a particular type of palaeosols on the Oligocene fluviomarine rock sequence that is equivalent to the Jebel Qatrani Formation and their palaeoclimatic and palaeoenvironmental implications in the northern Western Desert of Egypt. This study made use of field observations, binocular and polarizing microscopy investigation of isotropism and anisotropism of the materials and the birefringence fabric of the finest materials. Also, the study carried out scanning electron microscopy investigation and X-ray diffraction analysis of termite nests, rhizoliths and palaeosols. The present contribution recognises four pedotypes represented by Oxisols, Aridisols, Entisols and Spodosols based on the macro- and micromorphologic attributes, mineralogy and by comparison with extant soils. The four pedotypes bear similar types of rhizoliths and termite nests, but with variable abundance and depths of emplacement. The pedogenic features associated with the studied continental trace fossils overprint the marine trace fossils and the sedimentary facies of the studied fluviomarine rock sequence. The features of the developed associations reveal that during the Oligocene, the northern Western Desert terrain of Egypt was closely similar to the Fayum Depression where the lowland coastal plain was characterised by wet soil and seasonal rainfall. The developed associations on the coastal plain represent in situ proxies for the palaeoclimatic setting under which they were formed. Their attributes indicate that tropical wet-dry conditions with the fluctuating moisture regime were prevalent during the deposition of the studied rock sequence.

Invertebrate ichnofossils and rhizoliths associated with rhizomorphs from the Marília Formation (Echaporã Member), Bauru Group, Upper Cretaceous, Brazil

The Marília Formation (Bauru Group, Upper Cretaceous, Brazil) has furnished a large array of vertebrate fossils. However, its ichnological and botanical contents are poorly explored to date. Here we report findings of invertebrate trace fossils (Beaconites isp., Skolithos isp., and Taenidium barretti), rhizoliths associated with rhizomorphs with preserved hyphae, and fossil roots from the Echaporã Member, Marília Formation, São Paulo State, Brazil. The association of trace fossils suggest they can be regarded to the Scoyenia Ichnofacies. The rhizoliths indicate that at least two types of herbaceous/arbustive plants inhabited the area, one of them living in the vadose zone and the other one with roots closer to the water table, under arid/semiarid conditions. Sedimentological analyses suggest the studied outcrop comprises fluvial deposits, with predominance of sand bars that underwent different and relatively long periods of subaerial exposure.

Evaluating macrobenthic response to the Cretaceous–Palaeogene event: A high-resolution ichnological approach at the Agost section (SE Spain)

The Agost section (Betic Cordillera, Alicante Province, south-eastern Spain) is one of only a few places in the world where complete sedimentary successions across the Cretaceous–Palaeogene (K–Pg) boundary are available. Agost enables a high-resolution ichnological analysis illustrating the influence of environmental perturbations on burrowing organisms before, during and after the K–Pg boundary event. The uppermost Maastrichtian calcareous marlstones and marly limestones of the Raspay Formation (Plummerita hantkeninoides Biozone), beside the light-filled Maastrichtian trace fossils, contain dark-coloured early Danian trace fossils including Chondrites targionii, Chondrites ?affinis, Chondrites isp., Pilichnus isp., Planolites isp., ?Teichichnus isp., Thalassinoides isp., Trichichnus linearis, Trichichnus isp., and Zoophycos isp. The ichnotaxonomic composition of the late Maastrichtian and early Danian trace fossil association does not reveal major differences, indicating no significant influence on composition of their trace makers immediately after the K–Pg event. The main factors that most likely promoted survivorship of the trace makers were their feeding strategy (deposit feeders, microbe gardeners) and an increased delivery of organic matter to the seafloor due to the high mortality during the K–Pg boundary event. However, the differences in the size of trace fossils are noted: They are distinctly smaller in the dark boundary layer (Guembelitria cretacea Biozone) than in the underlying uppermost Maastrichtian calcareous marlstones. This is an example of the Lilliput Effect. The dwarfed ichnoassociation was produced during and shortly after sedimentation of the dark boundary layer pointing to a delayed reaction of the burrowing organisms to the K–Pg boundary event compared to other groups of organisms. The dwarfing might be caused by environmental stress resulting from lower food supply due to collapse of primary production in the later phases of the K–Pg boundary event.

Paleogene laterites bearing the highest insect ichnodiversity in paleosols

Fil: Bellosi, Eduardo Sergio. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina

Ichnology of the Cambrian Ociesęki Sandstone Formation (Holy Cross Mountains, Poland)

Quartz arenites and wackes with intercalations of silty shales of the Ocieseki Formation were analysed in small outcrops and one core. The succession contains about forty-three ichnogenera and seventy-four ichnospe- cies, among which thirty-three ichnogenera and fifty-three ichnospecies are described by present author. The formation belongs to the Schmidtiellus-Holmia Superzone and to the Protolenus-Issafeniella Zone. Most strata are totally bioturbated. The diverse and numerous trace fossils represent the Cruziana ichnofacies in the lower part of the formation and the Skolithos ichnofacies in the upper part. A few possibly new ichnospecies of different ichnogenera have been described in open nomenclature. Sedimentary structures and trace fossil assemblages indicate that the older part of this formation was deposited on the upper offshore to lower shoreface, while its younger part was deposited on the lower to middle shoreface, where storm episodes were the main factor controlling sedimentation and the activity of benthos. The trace fossil associations studied are similar to those from the lower Cambrian in many places around the world. The ichnoassociations from the Polish part of the East European Platform and from Sweden, which represent the Baltica palaeocontinent, display the closest similarity.

Ichnology of a Paleopolar, River-Dominated, Shallow Marine Deltaic Succession in the Mackellar Sea: The Mackellar Formation (Lower Permian), Central Transantarctic Mountains, Antarctica

The Lower Permian Mackellar Formation in the Beardmore Glacier Area of the Central Transantarctic Mountains, Antarctica, was deposited between 80 and 85°S paleolatitude. Previous studies suggest that Mackellar Formation strata were deposited in either a large glacial lake or inland sea. Our study identified 30 ichnogenera from Turnabout Ridge and Buckley Island of which: 1) none are exclusively freshwater forms; 2) 20 ichnogenera are found in freshwater, brackish, and marine settings; and 3) 10 ichnogenera are exclusively found in marine settings. Combining ichnologic evidence with sedimentologic observations suggests that the Mackellar Formation was deposited in a river-dominated delta in a fully marine to brackish-marine setting. Trace-fossil associations are grouped into the Arenicolites–Phycodes, Lingulichnus, Arenicolites–Planolites, Kouphichnium, Phycodes–Teichichnus–Arenicolites, and Planolites–Teichichnus–Phycodes ichnocoenoses of a mixed Skolithos–Cruziana ichnofacies. These associations are characteristic of epi- and endobenthic worms arthropods, and mollusks, with the vast majority of the traces being diminutive in diameter and length, and exhibit shallow (≤10mm) penetration depths. These ichnocoenoses occur in paleoenvironments that include the prodelta, distal to proximal delta front including mouth bars, and subaqueous terminal distributary channels. The diminutive morphology, shallow penetration depth, low bed ichnodiversity, high overall ichnodiversity, and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short-lived communities composed of small-bodied organisms stressed by high freshwater input and high sedimentation rates.

Ichnological analysis of the Pleistocene Dwarka Formation, Gulf of Kachchh: tracemaker behaviors and reworked traces

Complex interaction among trace fossils are important in understanding organisms niche preference for foraging in ancient rock records. There exist well-recorded examples of compound trace fossils. However, such compound traces rarely exhibit exploitation of burrow wall and fill sediments for feeding. In recent sediments, several examples are well documented for feeding on burrow wall and burrow fills because of nutrient enrichments in them. Such type of complex interactions occur in the shallow marine Pleistocene age sequences exposed in island in Gulf of Kachchh, India. These deposits are known as ‘Shankhodhar Sand Clay Member’ of Dwarka Formation. Trace fossils recorded are Chondrites, Chomatichnus, Gyrolithes, Ophiomorpha, Rhizocorallium, Schaubcylindrichnus, Sinusichnus, Spongeliomorpha, Taenidium and display three Ichnoassemblages. Three types of complex interactions are suggested: (1) Burrow architecture modification, (2) feeding on burrow walls and burrow fills and (3) acute angle branching. Thus, the trace fossil association indicates selective preference of trace maker for their foraging activities in shallow marine Shankhodhar Sand Clay Member of Pleistocene age.

Ichnofabrics of shallow-marine mudstone, the result of changing environmental conditions: an example from the Middle Jurassic ore-bearing clay from southern Poland

Analysis of the trace fossil association and ichnofabrics from a Middle Jurassic shallow-marine mudstone, referred to as the Ore-Bearing Częstochowa Clay Formation, is used to reconstruct the seafloor conditions and identify the factors responsible for their changes. The trace fossil association contains Chondrites, Trichichnus, Palaeophycus, Planolites, Protovirgularia, ?Rosselia, Schaubcylindrichnus, Taenidium, cf. Tasselia, Thalassinoides, and five types of pyritized burrow. The association represents the distal expression of Cruziana ichnofacies, temporarily changing to a more proximal development. The ichnofacies suggests that the depositional site was located in the lower offshore to offshore-transition zone, periodically passing to the distal lower shoreface. Eight subtypes of the ichnofacies are recognized, reflecting variations in seafloor oxygenation, sedimentation rate, and benthic food content. The sequence of ichnofabrics 1a–1b–2a–2b reflects increasing oxygenation; ichnofabrics 4a, 4b, and 5 record high sedimentation rates, whereas ichnofabric 3 reflects sediment starvation. Vertical changes of ichnofabrics reflect major fluctuations in basin depth and distance from the shoreline, which partly correlate with previously recognized transgressive–regressive cycles. However, they do not record minor variations of the shoreline position.

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.

The ichnogenus Dictyodora from late Silurian deposits of central-western Argentina: Ichnotaxonomy, ethology and ichnostratigrapical perspectives from Gondwana

The association of trace fossils from the Late Silurian Río Seco de los Castaños Formation in central-western Argentina (San Rafael Block) is mainly composed of Dictyodora, including Dictyodora scotica, Dictyodora tenuis and a new ichnospecies named Dictyodora atuelica. The latter shows a tendency to migrate to a deeper level – analogous to Dictyodora liebeana's – which reflects more sophisticated behavioural patterns. The Dictyodora ichnospecies (one of the most diverse assemblages in Gondwana) coexists with Nereites. SEM observations and EDS analyses suggest that the wall structure of Dictyodora could be the result of an activity other than the traditional suggestion of respiration, e.g., feeding. The succession, including some of the levels containing Dictyodora, presents microbially induced sedimentary structures (MISS) that would indicate a photic zone. This discovery favours previous deltaic interpretations instead of the deep-sea fan deposits traditionally suggested for the Siluro-Devonian greywackes of the Cuyania terrane, and particularly for this unit. The abundant Dictyodora, Nereites, Zoophycos and undermat miners ichnofossils, as well as the scarce arthropod trackways, resemble older records in Europe and North America. The studied section is very well age-constrained, and the autochthonous Gondwana ichnofauna permits to cast doubt on previous interpretations, suggesting that after the Ordovician, microbial mats retreated to marginal marine environments and then spread later in the Carboniferous. More importantly, the occurrence of Dictyodora and Nereites in beds that bear abundant wrinkle structures or records of biofilms in some places is challenging with regard to deep-sea interpretations. Dictyodora is probably not a good stratigraphic indicator, and the provincialism suggested for this ichnogenus may be an artefact of the lack of more complete records in Gondwana.

Lower Devonian trace fossils and their paleoenvironmental significance from the western Yangtze Plate, South China

Abundant and diverse trace fossils occur in the littoral-neritic sediments recording an Early Devonian transgression in South China. The well-exposed Ganxi section is located in the Longmen Mountain 100 km northwest of Chendu, Sichuan. The Lower Devonian strata are dominated by sandstones, siltstones, muddy shales, limestones, bioclastic limestones, and muddy limestones. About thirteen ichnogenera were systematically described, including Arenicolites, ?Balanoglossites, Chondrites, Cylindrichnus, Diplocraterion, Planolites, Palaeophycus, Phycodes, Rhizocorallium, Rusophycus, Skolithos, Thalassinoides, and Zoophycos. Six trace fossil associations under different sedimentary environments have been recognized as follows: the Skolithos and Diplocraterion-Skolithos associations mainly consist of domichnia derived from a high-energy zone of the foreshore to upper shoreface; the Rusophycus-Phycodes association is characterized by fodinichnia and cubichnia generated in a lower-energy zone of the upper shoreface; the Chondrites-Palaeophycus association mainly consists of domichnia, chemichnia, and fodinichnia as indicators of the lower-energy and suboxic conditions of a coastal lagoon; the Rhizocorallium association includes feeding and dwelling burrows formed in a lower-energy zone of the upper offshore enriched with food; and the Zoophycos association is characterized by fodinichnia and pascichnia as indicators of the lower offshore frequently influenced by storm waves. The entire sequence shows several transgressive-regressive cycles from the Lochkovian to Pragian and much storm influence in the Emsian.

Trace fossils from the continental Upper Triassic Kågeröd Formation of Bornholm, Denmark

The Upper Triassic Kagerod Formation of Bornholm consists of clays, sandstones and conglomerates of floodplain and fluvial origin, but details of the depositional environment are poorly understood. Trace fossils are described for the first time from the red and green clays (floodplain with lake deposits) and cross-stratified sandstones (fluvial channel deposits) of the Upper Triassic Kagerod Formation on Bornholm, Denmark. The sparse ichnofauna consists of large, mud-filled shafts and tunnels in caliche-bearing conglomerate, determined as Camborygma and attributed to the burrowing activity of cray fish. The sandstones preservevertical U-shaped burrows passively filled with sand, assigned to Arenicolites and probably produced by insects. Furthermore, they contain winding, horizontal, oblique and vertical unbranched burrows with an active meniscate sand fill, referable to Taenidium and supposedly produced by burrowing beetles. The clays and the sandstones contain numerous caliche nodules of centimetre to decimetre size, some of which contain root traces in the form of rhizoliths. This trace-fossil association reflects deposition on a vast floodplain with shallow lakes and fluvial channels, under semiarid conditions.

Middle Devonian invertebrate trace fossils from the marginal marine carbonates of the Zachełmie tetrapod tracksite, Holy Cross Mountains, Poland

The dolomitic deposits of the Middle Devonian Wojciechowice Formation exposed at the tetrapod tracksite in the Zachelmie Quarry in the Holy Cross Mountains (Poland) are characterised by a low diversity of invertebrate trace fossilassociation. Four ichnoassemblages can be identified in the track-bearing, lower part of the succession. The most conspicuous are trace fossils produced by arthropods (probably crustaceans), which can form distinctive and large horizontal burrows. The described ichnotaxa (cf. Skolithos isp., cf. Balanoglossites isp., Alcyonidiopsis isp., Spongeliomorpha isp., Gordia isp., and Rhizocorallium isp.) are well known from typical marginal-marine and shallow-marine deposits. Nevertheless, the studied assemblages were found in sparsely distributed horizons and are dominated by a single or a few ichnotaxa with locally high trace-densities. Distribution and composition of the trace fossil assemblages probably reflects occurrence of the impoverished, stressed Cruziana ichnofacies. It was affected by changes in water depth with intermittent periods of subaerial exposure connected with salinity fluctuations. The invertebrate trace fossil assemblage, tetrapod tracks and associated sedimentological features point to deposition in a marginal-marine, mostly peritidal and lagoonal environment with minor terrestrial influences.

Insights on the Behavior of Late Paleozoic Aquatic Crustaceans (Pygocephalomorpha?): Compound Trace Fossils from Western Argentina

We describe intergradations between the arthropod repichnial trace fossils Diplichnites gouldi (Gevers et al., 1971), Dendroidichnites Demathieu et al., 1992, and Monomorphichnus Crimes, 1970 with two distinct cubichnial traces, Gluckstadtella cooperi Savage, 1971 and Huilmuichnus santracruzensis new ichnogenus and ichnospecies. These compound ichnofossils are part of high ichnodiversity arthropod-dominated trace fossil associations from the Late Carboniferous Agua Escondida Formation of the San Rafael Basin (Argentina). The complex ichnotaxonomy of Diplichnites and the ichnospecies D. gouldi are discussed and some possible working solutions are proposed. The most likely producer of the compound trace fossils are the Pygocephalomorpha, a group of Late Paleozoic crustaceans that are recorded in nearby basins from Uruguay and Brazil. The compound trace fossils are used to infer a number of complex behaviors of pygocephalomorphs in a subaqueous setting, including caridoid (tail flip) or more primitive escape reactions, landing followed by resting and transient resting during normal walking. In addition, different gaits can be inferred from well-preserved D. gouldi, which can be correlated with contrasting trackway morphology.

Depositional architecture of growth-fault related wave-dominated shelf edge deltas of the Oligocene Frio Formation in Corpus Christi Bay, Texas

Growth faults within the Frio Formation define six subbasins on the South Texas shelf and add to the complexity of the sediment dispersal along the shelf margin. These growth faults influenced sediment pathways, controlled sediment partition and provided increased accommodation for deltaic depocenters. Rollover and thickening of sediments occur on the downthrown side of growth faults with offsets of at least 150 m and up to 750 m. Growth strata are indicated by intervals that thicken landward (by several tens of meters) from anticline crests. Individual 4th-order (100–500 ky) regressive cycles expand about five to seven times across growth faults; expansion ratios as great as 10 are observed. The shelf edge is associated with the largest displacement, expansion ratios and thickness of prograding deltaic sequences. Sedimentary structures and trace–fossil associations identified in cores from Nueces, Encinal and Red Fish Bay subbasins indicate deposition on a wave-dominated deltaic shoreline. The cores exhibit highly bioturbated muddy sandstones alternating with decimeter-thick clean sandstones with hummocky cross-stratification. Alternation of fair-weather wave deposits with sandy storm beds in two successive fault zones suggests that all subbasins developed under similar conditions during growth-fault development. High sediment supply conditions favored accumulation of thicker sediments on the downthrown sides of the faults. Wave dominance of deltas on the outer shelves in the growth compartments suggest that building of the upper slope rather lowers slope margin, and decreases the likelihood of the presence of sandy deep water fans.Correlation of about 700 well logs integrated with seismic data provided the areal distribution and relative timing of sediment filling of the growth-faulted compartments to unravel the evolution of higher-order (fourth and fifth) sequences affected by these growth faults. Core data were used to recognize depositional environments, to calibrate lithology to well logs and to characterize seismic amplitude anomalies. Within this shoreface succession the clean sandy storm beds will make attractive hydrocarbon reservoirs especially on the crest of rollover anticlines in downthrown compartments. These sandstone bodies pinch out seaward into open marine shelf mudstones and are sealed by overlying shelf mudstones deposited during transgressive episodes.