Distal Cruziana Research Articles

Tafonomia de Invertebrados Fósseis do Devoniano no estado do Paraná: Contribuições aos Estudos sobre Potencial de Hidrocarbonetos Vinculados ao Projeto Folhelho (LAGESED-UFRJ)

The shales are a recent frontier of studies in Sedimentary Geology, stimulated by the new exploratory panorama of Shale Gas, despite being the sealant of many petroleum systems. However, Brazil has not kept up with this evolution. The generation of natural gas associated with paleontological studies is unprecedented and fundamental for determining the real regional potentialities in a process of advancing scientific and technological knowledge in this field of studies in Brazil. Taphonomic studies of fossil macrofauna and ichnology are integrated with sedimentological data, expanding the capacity for paleoenvironmental interpretation of the sedimentary facies. Samples from three different outcrops in the vicinity of Arapoti, Ventania, and Piraí do Sul in the state of Paraná were analyzed. Thus, during the analyses of the fossil material, two tafofacies and three ichnofacies were identified: Skolithos, archetypal and distal Cruziana. The paleontological analyses proposed here provided support for the biostratigraphic correlations, paleoenvironmental and paleoecological interpretations of the outcrops prospected, helping to evaluate the quality of the shales of the Ponta Grossa Formation from the point of view of hydrocarbon generation.

The Upper Jurassic Faïdja Formation (Northwestern Algeria): Sedimentology, biostratigraphy and ichnology

The Faïdja Formation displays mixed siliciclastic-carbonate deposits distributed in three members, which are organised from bottom to top as follows: the Clayey Sandstone Faïdja Member; the Clayey Limestone Bel Aoura Member and the Sandy Claystone Douaouda Member. Sedimentological data indicate the evolution of a subsiding marine environment from the shelf edge to the lower shoreface, sporadically dominated by storms. New age based on recently collected ammonite fauna allowed us to update the age of the Faïdja Formation as Early-Late Kimmeridgian. Ichnological analysis reveals the occurrence of abundant and diverse invertebrate trace fossils, grouped in four ichnoassociations. Ichnoassociation -A- coincides with the lowermost part of the Clayey Sandstone Faïdja Member; it is distinguished by a combination of pre-graphoglyptids and post-depositional traces, ascribed to the distal Cruziana ichnofacies transitional to the Nereites ichnofacies, which indicates a lower offshore zone to shelf edge environment characterised by a low-oxygenated period (anoxic event), frequent storm events and nutrient frequency. Ichnoassociation -B- occupies the middle and upper parts of the Clayey Sandstone Faïdja Member, it is characterised by an abundance of post-depositional traces, corresponding to the archetypal Cruziana ichnofacies that indicates a lower to transitional offshore environment with short phases of low hydrodynamic energy. Ichnoassociation -C- corresponds to the Clayey Limestone Bel Aoura Member that coincides with a drastic facial change and depositional conditions; this association documents a proximal Cruziana ichnofacies, and indicates an upper to transitional offshore zone as a depositional environment. Finally, ichnoassociation -D- coincides with the Sandy Claystone Douaouda Member; it is ascribed to the proximal Cruziana ichnofacies, indicating a lower shoreface environment. The combined sedimentological and ichnological data indicates a relatively subsiding platform with shallowing upwards corresponding to distal, archetypal and proximal Cruziana ichnofacies, respectively.

Trace fossils from the Mississippian of the Piaskowa Góra section (the Intra-Sudetic Basin, SW Poland)

Eight ichnotaxa and enigmatic tubular forms were discovered and described for the first time from clastic deposits (the Culm facies) of the uppermost part of the Szczawno Formation (upper Mississippian) from in the Piaskowa Góra section in the northern part of the Intra-Sudetic Basin near Wałbrzych. The trace fossils are represented mostly by pascichnia and less numerous domichnia, fodinichnia and repichnia. Psammichnites plummeri and numerous Phycosiphon isp . are the most common ichnotaxa. They are accompanied by Archaeonassa fossulata, Beaconites cf. capronus , Curvolithus multiplex, Dictyodora liebeana, Palaeophycus isp ., and Planolites isp . D. liebeana is described for the first time from the lower Serpukhovian. Most components of the ichnoassemblage are typical of the Cruziana ichnofacies, but the co-occurrence of Dictyodora and Phycosiphon could indicate a transition to deeper environmental settings (the Zoophycos ichnofacies). The lithological features as well as the accompanying trace fossils, wrinkle structures and floral remains of Archaeocalamites indicate rapid sedimentation, alternating with more tranquil periods of sedimentation, in an intermediate environment between the lower offshore (the distal Cruziana ichnofacies) and the fan-delta slope (below the wave base, the Zoophycos ichnofacies). The studied trace fossils and palynological data indicate that marine conditions in the Wałbrzych area in the Mississippian prevailed locally until the early Sepukhovian.

Ichnofacies distribution in the Eocene-Early Miocene Petra Tou Romiou outcrop, Cyprus: sea level dynamics and palaeoenvironmental implications in a contourite environment

Ichnological analysis of the carbonate contourite drift at the Petra Tou Romiou outcrop (southern Cyprus) reveals a relationship between sea level dynamics, shoreline position, sedimentation rate, flow hydrodynamics and trace fossil assemblages. The base of the outcrop is composed of chalky deposits showing the Zoophycos ichnofacies attributes. The transition to the first contouritic interval beds is marked by the gradual disappearance of Zoophycos and dominance of horizontal traces. This change is caused by a gradual sea level fall determining an increase in proximity and energy conditions in the environment that favoured the development of distal Cruziana ichnofacies. Upper contouritic interval beds contain abundant burrow systems with vertical components. Increased ichnodiversity, particularly among vertical morphologies, coincides with the appearance of Teichichnus, Gyrolithes and rare Ophiomorpha, revealing a transition to the proximal Cruziana ichnofacies, related with the maintenance of the previous trend toward more proximal and higher energy settings. The differentiated ichnofacies in the Petra Tou Roumiou carbonate drifts are controlled by complex interactions between variable environmental factors with sea level dynamics playing a major role.

Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy

The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region.The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern-to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow-to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called “Tigillites” pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha.The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.

Ichnotaxonomy of the Cambrian Spence Shale Member of the Langston formation, Wellsville Mountains, Northern Utah, USA

The Spence Shale of northern Utah is the oldest North American middle Cambrian (∼506–505 Ma) Burgess Shale-type (BST) deposit and, unlike previously thought for BST deposits, has a very diverse ichnofauna. Twenty-four ichnogenera and 35 ichnospecies were identified: Archaeonassa (A. fossulata and A. jamisoni isp. nov.), Arenicolites carbonaria, Aulichnites, Bergaueria (B. hemispherica and B. aff. perata), Conichnus conicus, Cruziana (C. barbata and C. problematica), Dimorphichnus, Diplichnites (D. cf. binatus, D. gouldi, and D. cf. govenderi), Gordia marnia, Gyrophyllites kwassizensis, Halopoa aff. imbricata, Lockeia siliquaria, Monomorphichnus (M. bilinearis, M. lineatus, and M. cf. multilineatus), Nereites cf. macleayi, Phycodes curvipalmatum, Phycosiphon incertum, Planolites (P. annularius, P. beverleyensis, and P. montanus), Protovirgularia (P. dichotoma and P. cf. pennatus), Rusophycus (R. carbonarius, R. cf. pudicus, and R. cf. cerecedensis), Sagittichnus lincki, Scolicia, Taenidium cf. satanassi, Teichichnus cf. nodosus, and Treptichnus (T. bifurcus, T. pedum, and T. vagans). The ichnofossils comprise three ichnocoenoses—Rusophycus-Cruziana, Sagittichnus, and Arenicolites-Conichnus—representing dwelling, deposit- and filter-feeding, grazing, locomotion, and predation behaviors of organisms (e.g., annelid worms and trilobites). Two ichnofossil associations are suggestive of predation: (1) Planolites terminating at a Rusophycus; and (2) Archaeonassa crosscutting a Taenidium. The Spence Shale ichnofauna represent a distal Cruziana Ichnofacies and depauperate, distal Skolithos Ichnofacies. A new ichnospecies of Archaeonassa is proposed, A. jamisoni isp. nov., and Ptychoplasma (Protovirgularia) vagans is herein transferred to Treptichnus. This study is the first ichnotaxonomic study of the Spence Shale and North American BST deposits and shows highly diverse ichnofaunas can be present in BST deposits.

Late Ordovician Trace Fossils from Offshore to Shallow Water Mixed Siliciclastic and Carbonate Facies in the Ringerike Area, Oslo Region, Norway

ABSTRACTUpper Ordovician (Rawtheyan–Hirnantian) deposits in the Ringerike area contain 21 ichnogenera of burrows and two ichnogenera of borings. These deposits consist of a lower siliciclastic part and an upper part dominated by carbonates and mixed clastic-carbonate deposits. Sedimentological and geochemical investigations combined with an ichnological analysis in the lower siliciclastic part point to a shallowing from a transitional–offshore partly dysoxic zone to an oxic delta front/upper shoreface facies. The trace fossils belong to the proximal, archetypal, and distal Cruziana ichnofacies. The upper part of the sequence comprises a complex pattern involving patch reefs interfingering with shallow marine deposits of sandstones and crinoidal limestones in the southern area and carbonate mud banks to the north. The carbonate mud banks were subaerially exposed with the development of local coastlines. The overlying transgressive sediments, consisting of sandstones and carbonates, contain an offshore to transitional trace fossil assemblage.

Sedimentology, ichnology and sequence stratigraphy of the Upper Devonian–Lower Mississippian Bakken Formation in eastern Saskatchewan

The Upper Devonian–Lower Mississippian Bakken Formation in the subsurface of the Williston Basin in northeastern Montana, North Dakota, southwestern Manitoba and southern Saskatchewan typically includes three members: the lower and upper organic-rich black shale, and the middle calcareous/dolomitic sandstone and siltstone, which makes a “perfect” petroleum system including source rock, reservoir, and seal all within the same formation. In eastern Saskatchewan, the Bakken Formation is divided into eight facies, and one of which (Facies 2) is subdivided into two subfacies: Facies 1 (planar cross-stratified fine-grained sandstone); Facies 2A (wavy- to flaser-bedded very fine-grained sandstone); Facies 2B (thinly parallel-laminated very fine-grained sandstone and siltstone); Facies 3 (parallel-laminated very fine-grained sandstone and muddy siltstone); Facies 4 (sandy siltstone); Facies 5 (highly bioturbated interbedded very fine-grained sandstone and siltstone); Facies 6 (interbedded highly bioturbated sandy siltstone and micro-hummocky cross-stratified very fine-grained sandstone); Facies 7 (highly bioturbated siltstone); and Facies 8 (black shale). Our integrated sedimentologic and ichnologic study suggests that deposition of the Bakken occurred in two different paleoenvironmental settings: open marine (Facies 4 to 8) and brackish-water marginal marine (Facies 1 to 3). The open-marine facies association is characterized by the distal Cruziana Ichnofacies, whereas the brackish-water marginal-marine facies association is characterized by the depauperate Cruziana Ichnofacies. Isochore maps show that both open-marine and marginal-marine deposits are widely distributed in the study area and suggest the existence of a N-S trending paleo-shoreline. The Bakken strata in the study area represent two different transgressive systems tracts separated by a coplanar surface or amalgamated sequence boundary and transgressive surface. This surface has been identified in previous studies west-southwest of the study area, therefore assisting in high-resolution correlation of Bakken strata. The unusual stratigraphic architecture of the Bakken Formation in this area resulted from its proximal emplacement which favored intense erosion and cannibalization of previously accumulated deposits.

Trace fossils from the Eocene Lillebælt Clay Formation, Røsnæs, Denmark

A cliff exposure of the Eocene Lillebaelt Clay Formation, on the Rosnaes peninsula of Zealand, Denmark, has yielded a diverse trace-fossil assemblage. The trace fossils are described formally for the first time and assigned to Phymatoderma melvillensis , unnamed clusters of small burrows, Ophiomorpha nodosa , Spongeliomorpha isp., Dreginozoum beckumensis , Bichordites isp., Chondrites isp., Atollites zitteli ? and ? Rhizocorallium isp. The preservation of the trace fossils is strongly related to early diagenetic enhancement. The trace-fossil assemblage is dominated by a combination of dwelling and feeding burrows. The bioturbation took place in very clean clay of a shelf setting far offshore. The trace-fossil assemblage is indicative of the distal Cruziana ichnofacies.

Sea level changes in the upper Aptian-lower/middle(?) Turonian sequence of Cauvery Basin, India – An ichnological perspective

Cauvery Basin, a pericratonic rift basin along the Eastern Continental Margin of India, evolved during the breakup of the Eastern Gondwanaland. It exposes both syn-rift and later post-rift passive margin deposits ranging from Barremian to Miocene. The Karai Formation, upper Aptian-lower/middle (?) Turonian represents the oldest passive margin in the Cauvery Basin. It is bounded at both contacts by major sequence boundaries viz. the break-up unconformity and the Turonian tilt event. The present communication deals with the ichnology of the Karai Formation and its integration with sedimentary facies and biostratigraphy to interpret the sea level changes during deposition. A traverse between the villages Karai and Kulakkalnattam was studied in detail for this purpose. Based on the lithological position, characters and internal grain size trends, the Karai Formation is sub-divided into four informal lithologic units; the lower three units, constitute a lithostratigraphic unit known in literature as the Gypsiferous Clay Member, while the uppermost, corresponds to the Sandy Clay Member. At the base, clays of the Karai Formation unconformably onlap onto the Precambrian basement or the fluvial syn-rift deposits across the break-up unconformity. Upper Aptian to middle Cenomanian, units I and II showing the distal Cruziana ichnofacies, deepening of the basin and a retrogradational stacking pattern represent a transgressive system tract (TST). This long phase of transgression is attributed to continuous accommodation created by the post-breakup thermal subsidence. The upper part of unit II (middle Cenomanian) shows condensation, with its top representing the maximum flooding surface (MFS). Upper Cenomanian to lower/middle (?) Turonian, units III and IV characterised by a shift from the distal Cruziana to the Skolithos ichnofacies, an initial aggradational and later deltaic, progradational stacking pattern resulting from a fall in the relative sea level and filling up of accommodation space represent the highstand system tract (HST). A further fall in the relative sea level led to the exposure, incision and erosion of the Karai Formation over which the younger transgressive sequence of the Trichinopoly Group was deposited with an angular unconformity.

Ichnology of shallow marine clastic facies in the Belait Formation, Brunei Darussalam

Trace fossil assemblages from a variety of outcropping tidal and shoreface facies in the Belait Formation of Brunei Darussalam were characterized to determine their value in distinguishing shallow marine sedimentary environments on a low energy margin. Most trace fossil assemblages in tide-dominated environments have a proximal Cruziana ichnofacies, although higher energy tidal channels have a distal Skolithos ichnofacies. Tidal sand flats tend to have more diverse and abundant traces than tidal channels. Trace fossils are more abundant in tidal mud flat facies than in tidal channels and sand flats, and whilst mud flat assemblages are more diverse than tidal channel assemblages, they are less diverse than sand flat assemblages. Generally, these assemblages are similar to those in equivalent depositional environments in higher tidal range settings. W ave-dominated environments also have Cruziana assemblages, except for the upper shoreface that has a distal Skolithos assemblage. Lower shoreface assemblages are more abundant and diverse than upper shoreface assemblages and belong to the proximal Cruziana ichnofacies. Trace fossils are more abundant and diverse in offshore transition facies than in either the upper or lower shoreface and belong to the distal Cruziana ichnofacies; assemblages in interbedded storm sands often include a minor component of the Skolithos ichnofacies. These assemblages are comparable to those from wave-dominated deposits from higher energy settings, except for the upper shoreface environment which contains a lower energy assemblage than in equivalent facies elsewhere. T race fossils tend to be less diverse, less abundant and individual traces generally are smaller in tide-dominated depositional environments when compared to wave-dominated depositional environments. Also, Ophiomorpha form complex burrow systems in wave-dominated environments in contrast to simple burrows in tide-dominated environments.

An example of a highly bioturbated, storm‐influenced shoreface deposit: Upper Jurassic Ula Formation, Norwegian North Sea

AbstractIntegrated ichnological and sedimentological analyses of core samples from the Upper Jurassic Ula Formation in the Norwegian Central Graben were undertaken to quantify the influence of storm waves on sedimentation. Two main facies associations (offshore and shoreface) that form a progradational coarsening upward succession are recognizable within the cores. The offshore deposits are characterized by massive to finely laminated mudstones and fine‐grained sandstones, within a moderately to highly bioturbated complex. The trace fossil assemblage is dominated by deposit‐feeding structures (for example, Planolites, Phycosiphon and Rosselia) and constitutes an expression of the proximal Zoophycos to distal Cruziana ichnofacies. The absence of grazing behaviours and dominance of deposit‐feeding ichnofossils is a reflection of the increased wave energies present (i.e. storm‐generated currents) within an offshore setting. The shoreface succession is represented by highly bioturbated fine‐grained to medium‐grained sandstones, with intervals of planar and trough cross‐bedding, thin pebble lags and bivalve‐rich shell layers. The ichnofossil assemblage, forming part of the Skolithos ichnofacies, is dominated by higher energy Ophiomorpha nodosa ichnofossils and lower energy Ophiomorpha irregulaire and Siphonichnus ichnofossils. The presence of sporadic wave‐generated sedimentary structures and variability in ichnofossil diversity and abundance attests to the influence of storm‐generated currents during deposition. As a whole, the Ula Formation strongly reflects the influence of storm deposits on sediment deposition; consequently, storm‐influenced shoreface most accurately describes these depositional environments.

The trace fossil Lepidenteron lewesiensis (Mantell, 1822) from the Upper Cretaceous of southern Poland

ABSTRACT Jurkowska, A. and Uchman, A. 2013. The trace fossil Lepidenteron lewesiensis (Mantell, 1822) from the Upper Cretaceous of southern Poland. Acta Geologica Polonica, 63(4), 611-623. Warszawa. Lepidenteron lewesiensis (Mantell, 1822) is an unbranched trace fossil lined with small fish scales and bones, without a constructed wall. It is characteristic of the Upper Cretaceous epicontinental, mostly marly sediments in Europe. In the Miechow Segment of the Szczecin-Miechow Synclinorium in southern Poland, it occurs in the Upper Campanian-Lower Maastrichtian deeper shelf sediments, which were deposited below wave base and are characterized by total bioturbation and a trace fossil assemblage comprising Planolites, Palaeophycus, Thalassinoides , Trichichnus, Phycosiphon, Zoophycos and Helicodromites that is typical of the transition from the distal Cruziana to the Zoophycos ichnofacies. L. lewesiensis was produced by a burrowing predator or scavenger of fishes. The tracemaker candidates could be eunicid polychaetes or anguillid fishes.

Trace fossils analysis of fluvial to open marine transitional sediments: Example from the Upper Devonian (Geirud Formation), Central Alborz, Iran

This study integrates ichnological and sedimentological data to interpret depositional environments of the mixed siliciclastic-carbonate fluvial to marine sediments of the Geirud Formation (Upper Devonian) in the central Alborz, northern Iran. Lithofacies analysis shows that these sediments are deposited in fluvial, tidal, shoreface, and shelf environments. Fluvial and tidal deposits are characterized by the presence of bi- to multi-directional cross beddings, reverse directional current ripples, low angle cross beddings, and herringbone cross beddings, with a few scattered Skolithos and Palaeophycus. Shoreface sediments, accumulated in a storm-influenced setting, are characterized by a preferentially interface and low diversity Cruziana ichnoassemblage (Rhizocorallium, Thalassinoides, Palaeophycus, Chondrites, and Ophiomorpha). In contrast to the fluvial-tidal assemblage, the storm-influenced shelf sediments display a highly diversified, mixture of dwelling and feeding forms (Arenicolites, Protovirgularia, Diplocraterion, Palaeophycus, Thalassinoides, Chondrites, and Helminthopsis), reflecting the presence of adequate food resources both in substrate and water column under normal salinity conditions. A fluvial-shelf replacement of the weakly to scarcely bioturbated sediments by the Rhizocorallium-Thalassinoides suite (Cruziana) – Chondrites-Helminthopsis (distal Cruziana) suite from the lower to upper parts of the succession clearly indicates an overall deepening upward in the Geirud Formation. In contrast to the lower part, generally of restricted environment, the upper part of the succession mainly shows open marine conditions. Ichnofabric development is controlled primarily by depositional conditions, e.g., bottom water oxygenation, sediment type, food abundance, and hydrodynamic level, which all exert control on substrate colonization style.

Onshore expansion of benthic communities after the Late Devonian mass extinction

A detailed ichnological analysis of the Upper Devonian–Lower Mississippian Bakken Formation of sub-surface Saskatchewan and the partially coeval Exshaw Formation of Alberta indicates the presence of an anomalous ichnofacies gradient. The distal Cruziana Ichnofacies, which in rocks of other ages is restricted to lower-offshore facies, here ranges from this setting to the lower shoreface. No archetypal Cruziana Ichnofacies is present in these deposits. This pattern is interpreted as resulting from the differential effects of the Late Devonian mass extinction in shallow-water ecosystems. The onshore expansion evidenced by ichnological data is consistent with the pattern displayed by the body-fossil record, which indicates a re-invasion of shallow-water environments by the Palaeozoic evolutionary fauna during the Late Devonian and into the Early Carboniferous. The ichnofauna studied is overwhelmingly dominated by deposit feeders, with suspension feeders being notably absent, further underscoring the importance of trophic type as a selectivity trait during mass extinctions.

Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków- Silesia Homocline, Poland

ABSTRACT Leonowicz, P. 2012. Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Krakow-Silesia Homocline, Poland. Acta Geologica Polonica, 62 (3), 281-296. Warszawa. The lithology, sedimentary structures and trace fossil association from the Bathonian organic-rich mudstones from Krakow-Silesia Homocline (SW Poland) are described and a preliminary interpretation of the palaeoenvironment is presented. The ore-bearing clays exposed in the Gnaszyn clay-pit are developed as dark grey claysilt deposits with a few horizons of sideritic concretions. Sedimentological analysis has revealed that these deposits originated in the offshore part of a marine basin, below the fair weather wave base. Relict parallel lamination suggests that the predominant mechanism of deposition was quiet settling from suspension. However, locally preserved storm deposits indicate that the sea bottom was affected by offshore flows, deriving coarser material from the nearshore area. The degree of bioturbation is high but the diversity of the trace-fossil association is low. It consists mainly of Chondrites, Trichichnus, pyritized burrows and less common Palaeophycus. Other traces, including Thalassinoides, Planolites, Taenidium and some undetermined burrows, occur mainly in the lower part of the succession. This ichnoassociation combines features of distal Cruziana and Zoophycos ichnofacies, suggesting poor oxygenation of the bottom sediment. Temporary improvements in bottom oxygenation, linked with more intense mixing of water during major storms, resulted in the more diverse trace fossil suite that is found in some intervals of the succession.

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

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

“Terebellina”;(=Schaubcylindrichnus freyiichnosp. nov.) in Pleistocene outer‐shelf mudrocks of northern California

Vertically curved, unbranched, strongly lined burrows are prominent features of muddy outer‐shelf/offshore deposits of Cretaceous to Pleistocene age. Such burrows are usually called Terebellina, but use of this ichnogenus should be avoided for two reasons: 1) the type species of Terebellina is a large agglutinated foraminiferid referable to Bathysiphon, not a trace fossil; and 2) most trace fossils identified with Terebellina are either examples of Palaeophycus (in cases where burrows are essentially horizontal and occur individually) or Schaubcylindrichnus (where burrows are oblique to stratification and occur in aggregations or loose clusters). The replacement name S. freyi is proposed for this latter category of burrow. These light‐colored, grain‐lined burrows are conspicuous structures in the dark‐colored, outer‐shelf mudrocks of the lower Pleistocene Rio Dell Formation. The burrows are part of a typical “distal Cruziana ichnofacies”; association of structures, including Teichichnus, Planolites, Palaeophycus, and Chondrites, occurring in thoroughly bioturbated background sediments. Schaubcylindrichnus freyi in the Rio Dell is interpreted as the dwelling structure of a gregarious, endobenthic organism, comparable to the lined burrows produced by the deposit‐feeding polychaete Clymenella.