Neoichnology of Chalk cobbles from north Norfolk,England: implications for taphonomy and palaeoecology

The study of marine biota of the North Sea from the perspective of its relevance to palaeontology (Aktuopaläontologie) has enabled modern patterns and processes to be identified that can also be recognised in ancient communities. A collection of Chalk cobbles from the coast of north Norfolk, eastern England, preserves a limited ichnofauna: Gastrochaenolites ornatus Kelly and Bromley; Gastrochaenolites isp.; and Caulostrepsis isp. All cobbles show evidence of physical modification (corrasion) since they were bored; no Gastrochaenolites is complete and no clast has Caulostrepsis on all sides, therefore clasts have been corraded subsequent to boring. Only one producing organism in Gastrochaenolites, probably Barnea sp., is preserved in situ. Gastrochaenolites borings were infested by a range of encrusting organisms after the demise (and removal of shells) of the boring bivalves: thread-like algae; agglutinated worm tubes; cheilostome bryozoan Cryptosula pallasiana (Moll); and serpulids Hydroides norvegica Gunnerus and Pomatoceras triqueter (Linnaeus). Such a suite of encrusting organisms would be impossible to see in a fossil boring filled with lithified sedimentary rock unless it was released by dissolution of the substrate. Such cobbles, corraded since they were infested by borers, leave only portions of traces for identification, commonly only to ichnogenus.     

First report of trace fossils from Palaeogene succession (Namunagarh grit) of Andaman and Nicobar islands

The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia. Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated muddy bottom with a low rate of sedimentation is envisaged. An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia.     

Oxfordian plug-shaped trace fossils from northwestern Algeria

Plug-shaped trace fossils B. perata, B. hemispherica, Bergaueria isp., Calycraterion samsonowiczi, Conostichus ornatus and Conostichus isp. are found in the middle-upper Oxfordian fine-grained sandstone of the Argiles de Saïda Formation (northwestern Algeria). Except for the trace Calycraterion which is interpreted as an annelid trace, these traces correspond to distinct behaviours of sea anemones, and their occurrence within tempestite deposits is influenced by a stress factors in a storm-dominated environment. The abundance of these plug-shaped trace fossils suggests that the upper Jurassic siliciclastic shelves with fine-grained soft clastic substrate were colonised by actinarian sessile benthos.     

Cenozoic phosphatic deposits in North Patagonia,Argentina: Phosphogenesis,sequence-stratigraphy and paleoceanography

Paleoenvironmental analysis of the Cenozoic marine section cropping out near Gaiman (Chubut Province, Argentina) shows that most of the local succession was deposited in a shallow, storm-dominated marine environment, bearing well preserved Ophiomorpha fossil traces. Sequence-stratigraphic interpretation records the effect of three sea-level oscillations. Phosphatic strata are related to mostly in situ concretions developed within transgressive-early highstand system tracts (Type 1) and to reworked and winnowed lags associated with transgressive surfaces (Type 2) which display a concentration of phosphatic concretions, ooids, vertebrate bones, teeth and shells. Close association of Callianasid bioturbation (Ophiomorpha) and phosphatic levels suggest a genetic link for both, via improved early-diagenetic water circulation and Fe and P early-diagenetic cycling. Phosphogenesis would have taken place after cold and corrosive water, probably similar to the present Antarctic Intermediate Water (AAIW), flooded the continental shelf and mixed with warmer surficial waters. This mixing could explain the contrasting indications from the marine vertebrate fauna together with the general corrosion and replacement processes that are common in the Gaiman strata. The development of the phosphorites would have occurred at times of global climatic transition and increased oceanic circulation, probably during the Late Oligocene–Early Miocene.     

Thalassinoides in the Middle Miocene succession at Siwa Oasis,northwestern Egypt

At Siwa Oasis, the carbonate-rich Middle Miocene Marmarica Formation includes several firmground discontinuity surfaces, characterized by extensive burrow systems. These surfaces are confined to the boundary between the Oasis and Siwa Escarpment members in addition to several intraformational marine firmground discontinuities at several horizons within these two members. The marine trace fossils from all these discontinuities are represented mainly by the ichnogenus Thalassinoides. In all occurrences, Thalassinoides are characterized by a sharp erosional lower contact and grades upward into fossiliferous argillaceous limestone facies. Three Thalassinoides ichnospecies have been reported, including: Th. horizontalis Myrow, 1995, Th. suevicus (Rieth, 1932) and Th. paradoxicus (Woodward, 1830). They are mostly recorded as hypichnial/endichnial forms at the sole of fossiliferous argillaceous limestone facies. Rare exichnial occurrences are also recorded. Thalassinoides ichnospecies displayed considerable variations in their stratigraphic distribution, in addition to remarkable variations in their complexity and dimension. These variations are mostly reflecting environmental conditions prevailed during the trace-maker life. Paleoenvironmental interpretation of these burrows confirmed a well-oxygenated shallow marine environment with extremely slow or nearly nil rate of sedimentation.     

Trypanites and associated bivalve borings in an Upper Albian hardground from the Eastern Saharan Atlas (Algeria)

Abundant Trypanites isp. associated with Gastrochaenolites isp. and Petroxestes pera are evidenced in the first found hardground of the late Albian marine transgressive series, overlying the Continental Intercalaire in the Ouled Nail Range, eastern Saharan Atlas. This hardground is encrusted by oyster shells belonging to Ostrea falco Coquand. The studied hardground developed in warm environment and displays a lateral extension of at least 6 km. It is interpreted as an erosional transgressive surface. The ichnogenus Petroxestes is reported for the first time from Africa. This ichnoassemblage is attributed to the Trypanites ichnofacies.     

Contrôle tectonique de la sédimentation néogène dans la zone des diapirs de Tunisie septentrionale

During the Neogene, the sedimentary succession changed from marine shallow water formations during the Early and Middle Miocene to lagoonal and continental formations during the Late Miocene and the Pliocene. This succession is subdivided into three sedimentary major cycles that are mainly due to compressional tectonic events. Propagating folds above a detachment within the evaporitic Triassic strata caused the formation of the tectonics. To cite this article: M. Chikhaoui, C. R. Geoscience 336 (2004).     

Pliocene trace fossils from oyster substrates in the Nijar Basin,Betic Cordillera,southern Spain

The Almería-Níjar Basin is a Neogene, intermontane depression marginal to the Mediterranean in southern Spain in the vicinity of El Argamasón, Andalucia. The Pliocene Cuevas Formation rests unconformably on the Upper Messinian rock succession in the Carboneras Fault Zone. The Cuevas Formation is a coarse-grained, bioclastic-rich, calcarenite to calcirudite shoreface deposit. Oysters, namely Saccostrea cucullata (Born), are locally common and preserve a moderate diversity of borings: Caulostrepsis taeniola Clarke; Entobia isp.; Gastrochaenolites isp. aff. G. lapidicus Kelly and Bromley; Maeandropolydora isp. cf. M. sulcans Voigt; Oichnus paraboloides Bromley; and Talpina isp. aff. T. hirsuta Voigt. All represent domiciles except for the predatory O. paraboloides trace. This suite of ichnotaxa is assigned to the Entobia ichnofacies sensu Bromley and Asgaard; they are comparable, particularly, with the Boulder Assemblage of the Pliocene of Rhodes, Greece. Physical disturbance is an important parameter in favouring this pattern of infestation, whether the bored clasts are boulders or oyster valves.     

Balanoglossites ichnofabrics from the Middle Ordovician Volkhov formation (St. Petersburg Region, Russia)

The limestone succession of the Middle Ordovician Volkhov Formation in the St. Petersburg region (Russia) exposes numerous horizons with firm- and hardgrounds below omission surfaces, which contain trace fossils attributable to the ichnogenus Balanoglossites Mägdefrau, 1932. Although known from the literature since 75 years, such trace fossils were previously only informally described as “Korrosionsgruben”, “Karandashi”, or ascribed to different ichnotaxa such as Trypanites, Arenicolites and Pseudopolydorites. Owing to their complexity and often high bioturbation density, the morphology of these trace fossils is difficult to capture. Ichnofabrics containing Balanoglossites triadicus were studied in detail from sawn rock faces, broken rock blocks and sectioned slabs, including those from historical buildings in St. Petersburg. Accordingly, different trace-fossil elements can be revealed in dependence on the original substrate consistency, reflecting various stages of lithification: Mineral-stained and Trypanites-perforated hardground surfaces are bioeroded with long elongated grooves which are assigned to the ichnogenus Sulcichnus. Subtle openings lead into the partly lithified limestone where they branch into complex galleries of B. triadicus. They are characterized by J-, U- and Y-shaped shafts and multiply branched tunnels, which gradually continue into the underlying firmground. Other portions of the ichnofabric only exhibit biodeformational structures or the strongly compacted and branched burrow networks Labyrintichnus, which is due to the original soft sediment consistency. Balanoglossites ichnofabrics demarcate certain omission surfaces within the Dikari Limestone and can be traced for more than 300 km, supporting the regional lithostratigraphical correlation. The trace maker of B. triadicus and related trace fossils is interpreted to be a eunicid polychate with the ability to bioerode and burrow the sediment. The studied material from the Ordovician is similar to the Balanoglossites from the type area, the Triassic of Germany, in many respects. B. triadicus is a very common trace fossil in Ordovician and other Palaeozoic rocks of Baltoscandia and North America but so far has been seldom identified as such but instead is commonly confused with Thalassinoides, from which, however, it differs in several aspects.     

Ichnological evidence of marine incursions in the lacustrine–palustrine Bembridge Limestone Formation (Eocene), Isle of Wight,southern England

Trace fossils are described from the Eocene Bembridge Limestone Formation from the Isle of Wight and used to constrain the paleoenvironmental interpretation. The lacustrine–palustrine succession contains three limestone beds, which are separated by clay and marl. The middle and upper limestone beds reveal complex burrow systems developed at their top. Based on their characteristics, these burrow systems are assigned to the ichnotaxon Balanoglossites triadicus Mägdefrau, which is associated with the shallow superficial grooves Sulcolithos variabilis Knaust. B. triadicus is a common marine trace fossil mainly known from shallow-marine carbonate successions throughout the Phanerozoic. It is accompanied by other marine ichnotaxa such as Arachnostega gastrochaenae Bertling, Gastrochaenolites isp. aff. G. ornatus Kelly and Bromley, Spongeliomorpha iberica Saporta and Thalassinoides suevicus (Rieth). This ichnological evidence confirms the occurrence of short-term marginal-marine incursions in a predominantly lacustrine to palustrine environment.     

Ichnofossils from the Miocene Middle Bhuban Formation, Mizoram,Northeast India and their Paleoenvironmental Significance

An ichnofossil assemblage is preserved in sediments of the Middle Bhuban Formation,Surma Group,of Miocene age from the Durtlang and Chanmari sections,Aizawl district,Mizoram,northeastern India.The studied sections comprise a thick,bioturbated and thinly bedded sandstone–silty shale facies.The preserved ichnofossils show high density and low diversity with the assemblage represented by feeding and resting traces,i.e.,Psilonichnus upsilon Frey et al.,1984,Ophiomorpha isp.,Teichichnus spiralis Mikulá.1990,Skolithos isp.,Palaeophycus isp.,and other horizontal burrows.Sedimentary structures associated with these traces are mainly cross bedding,flaser bedding and slump structures.Considering the distribution of the Psilonichnus ichnogenus across an integrated ichnological–sedimentological framework,the stratigraphic interval of the Middle Bhuban Formation,in which they occur,are interpreted to have been deposited under a shallow,marginal-marine channel complex dominated by tidal channels developed in quiet,brackish-water portions of a delta plain.     

Bioerosion and encrustation rates in recent mollusk death assemblages on a supratidal siliciclastic setting,Playa Norte,Veracruz State,Mexico

This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.     

Oligo–Miocene seagrass‐influenced carbonate sedimentation along a temperate marine palaeoarchipelago,Padthaway Ridge,South Australia

Oligo–Miocene carbonates associated with the Padthaway Ridge form the southern margin of the Murray Basin, South Australia. The carbonates are a thin, somewhat condensed succession of echinoid and bryozoan‐rich limestones that record accumulation in the complex of islands and seaways and progressive burial of the Ridge through time. The rocks are grainy to muddy bioclastic packstones, grainstones and floatstones, composed of infaunal echinoderms, bryozoans, coralline algae and benthic foraminifera, with lesser contributions from molluscs and serpulid worms. Locally as much as half of these skeletal components are Fe‐stained, relict grains that imbue the lithologies with a conspicuous yellow to orange hue. This variably lithified succession is partitioned into metre‐scale, firmground‐bounded and hardground‐bounded beds textured by extensive Thalassinoides burrows. Dominant lithologies are interpreted as temperate seagrass facies. Limestones contain attributes indicative of both seagrass‐dominated palaeoenvironments and carbonate production and accumulation on unconsolidated, barren sandflat palaeoenvironments. Together these two depositional systems are thought to have generated a single multigenerational, amalgamated facies recording sedimentation within a complex temperate seagrass environment. Limestones overlying the Padthaway Ridge reflect a gradually warming climate, increasing water temperature and decreasing nutrient content, within the framework of a ridge gradually being buried in sediment. This succession from cool–temperate to warm–temperate to subtropical through time permits recognition of the relative influence of changing oceanography on a seagrass‐dominated shallow inter‐island sea floor. Criteria are proposed herein to enable future recognition of similar temperate seagrass facies in Cenozoic limestones elsewhere.     

Neoichnology and implications for stratigraphy of reworked Upper Oligocene oysters,Antigua, West Indies

The Late Oligocene oyster Hyotissa antiguensis (Brown) is locally common in the Antigua Formation of Hughes Point, eastern Antigua, Lesser Antilles; it was not commonly bored at that time. Its valves and shells are robust, and reworked into the shallow water near-shore environment in Antigua; it could potentially be incorporated into younger rocks. Its neoichnology includes clues that would facilitate identification of these oysters as reworked fossils. The suite of modern borings found in these specimens includes common Caulostrepsis taeniola Clarke, Gastrochaenolites isp. cf. G. turbinatus Kelly and Bromley and Entobia isp., and rare Oichnus simplex Bromley and Rogerella? isp. The latter three taxa are limited to oyster shell substrates. Of the common ichnotaxa, Caulostrepsis and Gastrochaenolites are particularly prominent in limestone clasts and limestone cemented to oyster shells, which would be an indicator of reworking if found in a post-Oligocene lithified deposit. Caulostrepsis and Gastrochaenolites are relatively less common in oyster shells and valves, and in many specimens are seen to terminate against the shell. Entobia is the only common boring limited to the shell substrate. The fidelity of preservation of modern borings is also superior in limestone clasts. This suite of borings is comparable with those found in the Neogene of the Antillean region.     

Thalassinoides burrows (decapoda dwelling structures) in lower cretaceous sections of southwestern and central Crimea

Burrows of Thalassinoides, which are attributed to the group of dwelling structures, occur in all the marine and coastal facies. The Lower Cretaceous sections of southwestern and central Crimea yielded the representative collection of Thalassinoides burrows belonging to the ichnospecies Th. suevicus (Rieth, 1932), which served as an object for this investigation. The burrows are confined to coarse-grained terrigenous, carbonate, and mixed sediments and contain assemblages of ichnofossils indicating coastal and shallow-water marine Skolithos and Cruziana ichnofacies. In the Mesozoic-Cenozoic, the producers of the Thalassinoides burrows were decapods, confirmed by finds of crayfish Hoploparia in them.     

A new record and a new ichnospecies of Arachnostega from the Middle Miocene of Egypt

The ichnogenus Arachnostega Bertling, 1992 is recorded for the first time from a bioeroded, coral-rich, Middle Miocene limestone bed in the middle Siwa Escarpment Member (Marmarica Formation) at Siwa Oasis, northern Western Desert of Egypt. These burrowing traces are preserved on the surface of a few internal moulds of bivalves and gastropods. Until now, the ichnogenus Arachnostega included a single ichnospecies, A. gastrochaenae Bertling, 1992. In the material studied herein, two ichnospecies are identified, described, illustrated and compared with other, similar traces. One of these is a new ichnospecies of Arachnostega; this is here named A. siwaensis ichnosp. nov. It is distinguished from A. gastrochaenae in the possession of tunnels that usually branch in a V-pattern; intervals of ramification are longest in the main branch and decrease in second- and third-order branches. Arachnostega traces were produced in a warm, low-energy, shallow-marine (<10?m water depth) environment. Polychaetes are the most likely producers of marine Arachnostega, which are commonly occurred in the same studied bed. This new occurrence is significant in extending the known stratigraphical and geographical ranges of Arachnostega into the Middle Miocene of Egypt.     

A late eocene-early Oligocene transgressive event in the Golfo San Jorge basin: Palynological results and stratigraphic implications

A new Cenozoic dataset in the subsurface of the South Flank of the Golfo San Jorge Basin (Santa Cruz province) allowed to identify a non-previously recognized transgressive event of late Eocene to early Oligocene age. Below of a marine succession containing a dinoflagellate cyst assemblage that characterizes the C/G palynological zone of the Chenque Formation (early Miocene), a 80–110 m thick marine succession contains a palynological assemblage integrated by Gelatia inflata, Diphyes colligerum and Reticulatosphaera actinocoronata supporting the occurrence of a marine incursion in the basin during the Eocene–Oligocene transition (EOT). The new lithostratigraphic unit - here defined as El Huemul Formation – covers in sharp contact to the Sarmiento Formation, and become thinner from East to West; the unit has been identified in about 1800 well logs covering up to 3500 km², and its subsurface distribution exceed the boundaries of the study area. The El Huemul Formation consists of a thin lag of glauconitic sandstones with fining-upward log motif, followed by a mudstone-dominated succession that coarsening-upward to sandstones, evidencing a full T-R cycle. Preservation of the El Huemul Formation in the subsurface of the South Flank has been favored by the reactivation of WNW-ESE late Cretaceous normal faults, and by the generation of N–S striking normal faults of Paleocene-Eocene age. Flexural loading associated to igneous intrusions of Paleocene?- middle Eocene age also promoted the increase of subsidence in the South Flank of the basin prior to the transgression.     

Middle Miocene ostracods from Wadi Sudr,westcentral Sinai,Egypt: systematic,biostratigraphy and palaeobiogeographic affinity with the Mediterranean realm

The investigation of the exposed middle Miocene strata from Wadi Sudr yielded well-preserved ostracod carapaces. Detailed taxonomic and paleontological studies led to the recognition of 36 ostracod species belonging to 25 genera, 4 species of them were considered new which fully described. Three assemblage biozones were recorded as follows: Actinocythereis spinosa–Actinocythereis hystrix zone, Chrysocythere cataphracta muricata-Cytheretta africana zone, and Disopontocypris schweijeri-Bythocypris tripolensis zone. The recorded biozones were calibrated with the previously studied middle Miocene planktonic foraminiferal biozones on the same samples and also correlated with the Miocene ostracod biozones from the neighboring countries. Our ostracod assemblages present in the lower and upper parts of the studied section (section II) indicated an inner neritic marine environment of moderate energy of currents and rapid sedimentation, while the assemblages in the middle part showed more deeper (outer neritic) environments with low energy of currents and low rate of sedimentation. The palaeobiogeographic distribution of the studied ostracods showed high affinity with the ostracod assemblages of the southern Mediterranean and moderate to low affinities with that of the northern and eastern Mediterranean respectively. The highly ornamented ostracod species with structures on the carapace were recorded from both Northern and Southern Mediterranean, while the smooth ones were found in the Southern Mediterranean only. The highly ornamented species are more widely distributed in both Southern and Northern Mediterranean than the smooth species. This may indicate that the ornamented species are more able to migrate than the smooth ones.     

On some fabaceous fruits from the Siwalik sediments (Middle Miocene-Lower Pleistocene) of Eastern Himalaya

Four legume fruits (Fabaceae) from the Siwalik sediments (middle Miocene to lower Pleistocene) of Darjeeling and Arunachal Pradesh of Eastern Himalaya are described here. One fossil fruit, Dalbergia prelatifolia sp. nov., is recovered from the lower part of the Siwalik succession (Gish Clay Formation of Sevok Group; middle to upper Miocene) of Darjeeling foothills. Mastertia neoassamica sp. nov. and Acacia miocatechuoides sp. nov. are collected from the lower part of the Siwalik succession (Dafla Formation; middle Miocene to upper Miocene), while Pongamia kathgodamensis Prasad is recovered from the upper part of the Siwalik succession (Kimin Formation; upper Pliocenelower Pleistocene) of Arunachal sub Himalaya. Their presence indicates a warm and humid tropical environment in the region during the Siwalik sedimentation.     

The complex diagenetic history of discontinuities in shallow‐marine carbonate rocks: New insights from high‐resolution ion microprobe investigation of δ18O and δ13C of early cements

Sedimentary gaps are a major obstacle in the reconstruction of a carbonate platform's history. In order to improve the understanding of the early diagenesis and the succession of events occurring during the formation of discontinuity surfaces in limestones, secondary ion mass spectrometry was used for the first time to measure the δ ¹⁸O and δ ¹³C signatures of 11 early cement and fabric stages in several discontinuity surfaces from the Jurassic carbonate platform of the Paris Basin, France. Pendant cements show a high variability in δ ¹⁸O, which was impossible to detect by the less precise microdrilling method. The morphology of a given cement can be produced in various environments, and dogtooth cements especially can precipitate in marine phreatic and meteoric phreatic to vadose environments. Marine dogtooth cements and micritic microbially induced fabrics precipitated directly as low‐magnesium calcite in marine waters, as attested to by the preservation of their initial δ ¹⁸O and δ ¹³C signals. Five discontinuity types are recognized based on high‐resolution geochemical analyses, and their palaeoenvironmental history can be reconstructed. Two exposure surfaces with non‐ferroan pendant or meniscus cements formed in the oxidizing vadose zone. A hardground displays marine fibrous cements and non‐ferroan dogtooth cements that formed in a subtidal environment in oxidizing water. Two composite surfaces have undergone both marine and subaerial lithification. Composite surface 1 displays non‐luminescent ferroan dogtooth cements that precipitated in reduced conditions in seawater, followed by brown‐luminescent dogtooth cements characteristic of a meteoric phreatic environment. Composite surface 2 exhibits microbially induced fabrics that formed in marine water with abundant organic matter. The latter discontinuity, initially formed in a subtidal environment, was subsequently exposed to meteoric conditions, as evidenced by ferroan geopetal cements. A high‐resolution ion microprobe study is essential to precisely document the successive diagenetic environments that have affected carbonate rocks and discontinuities with a polygenic and intricate history.