Nereites Research Articles

Ichnofauna from the Silurian–Devonian beds of the Parnaíba Basin at Poti River Canyon (Piauí State, NE Brazil)

This paper characterizes the ichnology and sedimentology of the Lower Paleozoic Parnaíba Basin beds exposed in the Poti River Canyon (Piauí State, NE Brazil) and discusses the paleoenvironmental significance of the ichnofauna. The sedimentary succession represents the Silurian–Devonian infill of the Parnaíba Basin and comprises mouth bar deposits (Ipu Formation) and shoreface deposits (Tianguá and Pimenteira formations). The Silurian ichnofauna is represented by Heimdallia isp. in the topmost beds of the Ipu Formation, and Musculopodus sedentarius, Didymaulichnus lyelli, Didymaulyponomos rowei, Diplocraterion isp., Heimdallia isp., Lockeia siliquaria, Nereites irregularis, Palaeophycus tubularis, and Thalassinoides cf. horizontalis in the Tianguá Formation. The Devonian ichnofauna occurs in the Pimenteira Formation and is represented by Beaconites antarcticus, Bifungites munizi, Bifungites crucifomis, Nereites isp., and Rhizocorallium commune. Horizontal burrows and furrows occupying shallow and middle tiers dominate the ichnofauna, suggesting proximal expressions of the Cruziana ichnofacies. The predominance of sandy, unbioturbated, storm-generated beds in the shoreface deposits indicates a high frequency of storm surges in shallower areas of the shelf, which often inhibited or frequently erased most of the post-event substrate colonization record. Thus, the trace fossil in the analyzed succession represents substrate colonization below the low-tide base and above the storm wave base in shoreface settings. The presence of Musculopodus sedentarius in this assemblage expands the geographic and temporal record of the ichnogenus. The similar composition of the trace fossil assemblage with other Lower Paleozoic ichnofaunas reinforces ichnostratigraphic correlations represented in coeval Gondwanan units.

Ichnofossils from Cretaceous-Paleogene flysch of Mide locality (Budva zone, Southern Montenegro)

Cretaceous-Paleogene flysch represents the youngest formation in the Budva Zone. Although the Maastrichtian-Lower Eocene age of these rocks has been well documented in the literature, trace fossils are only mentioned as abundant and not described. In the present paper, only a small number of ichnotaxa from Mide locality has been described, including Lorenzinia carpathica (ZUBER), Nereites irregularis (SCHAFHAUT), Scolicia plana KSI??KIEWICZ and Paleodictyon latum VIALOV & GOLEV. They confirm deepsea environment.

The former presence of organic matter caused its later absence: Burn‐down of organic matter in oceanic red beds enhanced by bioturbation (Eocene Variegated Shale, Carpathians)

AbstractEocene oceanic red beds that formed in a well‐oxygenated setting at low sedimentation rates below the calcite compensation depth are effectively barren of organic carbon in the present state. Recurrent distal low‐erosive turbidites preserve the bioturbated zone underneath that documents seasonal and long‐term fluctuating accumulation of considerable amounts of organic matter on the sea floor as evidenced by Scolicia; the producers of this trace fossil exploited nutritious organic matter conserved in turbidite‐buried sea floor deposits. Over the long‐term, slow average sedimentation of (hemi)pelagic oxic (red) mud led to long oxygen exposure times and low burial of organic matter. Consequently, trace fossils representing persistent sediment‐feeding modes are of small size. Although the food‐limited setting appears appropriate for producers of graphoglyptids, such ‘stationary’ burrows have not been encountered because seasonal deposition of organic matter fostered at least temporary surface layer feeding organisms, for instance producers of Nereites irregularis that intensively reworked the sediment and, hence, hindered graphoglyptid production. These findings confirm palaeoceanographic modelling results that suggest upwelling in the study area during the Eocene.

The unusual record of Nereites, wrinkle marks and undermat mining trace fossils from the late Silurian–earliest Devonian of central-western margin of Gondwana (Argentina)

Silurian–Devonian deposits of central western Argentina contain one of the most diverse Palaeozoic records of Nereites in Gondwana. Nereites cf. cambrensis, Nereites irregularis?, Nereites jacksoni, Nereites macleayii, Nereites missouriensis and Nereites pugnus are documented in a turbidite-like succession of the San Rafael Block (Río Seco de los Castaños Formation). The succession, historically assumed as deep-sea deposits or interpreted as a deltaic system, also contains abundant microbially induced sedimentary structures (MISS) such as wrinkle marks. Glossy surfaces indicate abundant biofilms, where the fossil record comprises N. macleayii, N. missouriensis, scarce arthropod trackways (Diplichnites?) and undermat-miner structures. Nereites, the pioneer colonizer, is in some cases cross-cut by Dictyodora, while undermat miners are the late bioturbators. The succession is dominated by gravity flow deposits, including storm related, turbidite-like deposits and abundant wrinkle marks. These suggest deposition on the shelf rather than the deep sea. This study shows that microbial mats were not restricted to marginal marine environments during the mid Palaeozoic, and documents one of the most diverse Palaeozoic records of Nereites in western Gondwana. It also contributes to the record of Nereites, Dictyodora, and Zoophycos found, for first time, in association with microbial mat structures in the late Silurian−earliest Devonian, the Nereites ichnofacies together with abundant wrinkle marks.

Depositional environment and Ichnology (Nereites ichnofacies) of the Late Devonian Sahara region (SW Algeria)

The late Famennian strata of the Marhouma outcrop, located in the Saoura (Algerian Sahara), consist of two formations: the Argiles de Marhouma Formation and the overlying Gres de Marhouma Formation. The former is characterized primarily by fine-grained turbidite successions, intersperse with griotte limestones bearing a pelagic fauna. There is a wide variety of trace fossils in the lower part of the formation: Chondrites, Helminthopsis, Ichnyspica, Megagrapton, Neonereites, Nereites irregularis, Nereites jacksoni, Nereites missouriensis, Palaeophycus, Paleodictyon, Phycodes, Planolites beverleyensis, Protopaleodictyon submontanum, and Thalassinoides suevicus. The hydrodynamics of the depositional environment as well as the associated trace fossils indicate the Nereites ichnofacies. The depositional conditions indicate a basinal environment in a mesodistal area. The upper coarser formation is composed of two members. The lower member consists of alternating turbidites, green clay and thin sandstone, with slumps, debrites, olistoliths, and synsedimentary faults. There are some visible fossil traces that may point to the Zoophycos ichnofacies. It marks the slope deposits of a submarine deep-sea fan that completes the Devonian megasequence. The upper member of the second formation starts with a transgressive muddy deltaic system that formed during platform construction. It is followed by iterative sequences of muddy and sandstones layers deposited on a storm-dominated platform that emerged at the beginning of early Tournaisian time. The distributions of fossil traces and sediments are indicative of bathymetric fluctuations. A major fluctuation, probably due to tectonic instability, is recorded as early as in the basal part of the Argiles de Marhouma Formation, which indicates the beginning of the Eovariscan phase.

Deep-sea trace fossils from the mixed carbonate-siliciclastic flysch of the Monte Antola Formation (Late Campanian-Maastrichtian), North Apennines, Italy

Twenty one ichnogenera and 30 ichnospecies are recognized in the Late Campanian – Maastrichtian Monte Antola Formation of Italy, most of them for the first time. They belong to a specific mixture of the Nereites and Ophiomorpha rudis ichnosubfacies of the Nereites ichnofacies. Composition and abundance of trace fossils vary from outcrop to outcrop . Chondrites intricatus, Ch. targionii, Nereites irregularis, Cladichnus fischeri and Trichichnus linearis are most common. Chondrites patulus, Ophiomorpha recta and “ Spirophycus” bicornis trace fossils are less common in outcrops, and the other trace fossils are rare or very rare. Generally, ichnogeneric diversity in Cretaceous–Cainozoic calcareous and mixed siliciclastic-calcareous flysch deposits is distinctly lower than in siliciclastic flysch. Significantly, the foremost pre-depositional forms are distinctly rare, probably due to preservational and depositional factors.

Ichnology of deep‐sea fan overbank deposits of the Ganei slates (Eocene, Switzerland)— a classical flysch trace fossil locality studied first by Oswald Heer

Ganei (Switzerland) is a classical locality for trace fossils. At this site, Heer (1877) described a large number of trace fossils, several of which were new taxa. The trace fossils occur in thin‐bedded turbidites in which the basal divisions of the Bouma sequence are typically absent; the turbidites are assigned to the Ganei Slates and are Eocene in age. They are interpreted to have been deposited in an overbank environment within an upper to middle fan area distal to a channel. Two trace‐fossil associations occur: the first (I) is characterized by bulldozing organisms producing biodeformational structures, Scolica, and Nereites irregularis; the second (II) association shows a distinct tiering pattern with near‐surface graphoglyptids and a mixed layer with simple tubes such as cf. Palaeophycus and Planolites, plus patterned tubes such as Nereites cirrinalis, and Chondrites. Deeper turbidite layers were colonized by Chondrites and Gyro‐phyllites. All trace fossils show a normal size spectrum compared to previously studied trace‐fossil associations, so the degree of oxygenation probably did not influence the composition of either trace‐fossil association. Seafloor sediment was probably soft and did not affect the trace‐fossil associations. Sedimentation rate and event frequency did not change and are estimated to have been in a range of 5–10 cm/1000 years and 2–5 events per 1000 years, respectively. The composition of trace‐fossil associations I and II is therefore interpreted to have been controlled by the benthic food content being higher for trace‐fossil association I than for II.

Devonian ichnofossils and their environmental significance of northern belt of Western Qinling Mountains

It is beheved that the Shujiaba Formation belongs to a series of thick turbidites. 20 ichnogenera have been found in the formation, of which 14 genera were found in the Devonian System of China for the first time The ichnogenera are mostly of typical deep-water ones and belong to the Nereites ichnofacies A detailed study of morphology and behaviour of the trace fossils indicates that the Shujiaba Formation was deposited in a bathyal-abyssal environment.