Taphofacies analysis of recent shelly cheniers (beach ridges), northeastern baja california,Mexico

Summary This report presents the results of taphofacies analyses of shelly cheniers (mollusk-dominated lag-concentrations) from the tidal flats of northeastern Baja California, Mexico. The three generations of moderm (formed during last 70 years), submodem (younger than 1,500 BP), and subfossil (5,000–2,000 BP) cheniers can be distinguished by their position relative to the shoreline, their topography, and the radiocarbon-age of their shells. The generations differ in the duration and complexity of their taphonomic history. Sixty-one samples from nine localities were collected to test the utility of the taphofacies approach for studying chenier-type shell deposits. The three chenier generations, although all dominated by the bivalve molluskMulinia coloradoensis, differ significantly in their taxonomic composition due to taphonomic and/or biologic factors. The taphofacies analysis included 4,334 specimens ofM. coloradoensis described by nine taphonomic variables. Univariate analysis of those variables indicated that the shells that accumulated in the cheniers are little-affected by biological processes (bioerosion, encrustation), and moderately affected by physical processes (fragmetation, cracking, peeling, edge preservation). Only the luster features of shells (external luster, internal luster, and internal features) vary substantially and consistently with chenier age —a result of subaerial weathering. Multivariate taphofacies analysis discriminates the three generations of cheniers even when the poorly preservable luster variables are excluded from the analysis. This suggests that taphofacies discrimination is possible for fossil cheniers. The shells collected from the chenier surface have substantially poorer preservation than shells from the subsurface, indicating that taphonomic degradation in the chenier plain environment is a surface phenomenon. Chenier plain shelly assemblages are taphonomically distinct from assemblages formed in other marine environments: they have a very low frequency of macroscopically recognizable bioerosion and encrustation. The existence of preservable taphonomic differences between the cheniers that differ in their age (i.e., duration of preburial history), suggests that fossil lag concentrations may be useful in detecting incompleteness gradients along stratigraphic boundaries. A ‘taphonomic clock’—a correlation between a ‘time-sincedeath’ and shell preservation—was found only for luster features, taphonomic attributes that are unlikely to be preserved in the fossil record.     

Taphonomy of Eemian marine molluscs and acorn barnacles from eastern Arkhangelsk region, northern Russia

Marine Eemian deposits along the Pyoza river and its tributary Varchuska, Arkhangelsk region, constitute successions of muddy and sandy facies with rich macrobenthic fauna dominated by bivalves and barnacles. Taphonomic features formed by abrasion, disarticulation, dissolution, fragmentation, bioerosion and encrustation define taphofacies for a palaeoenvironmental model. Five bivalve taphofacies and three barnacle taphofacies could be distinguished. Both bivalves and barnacles are poorly preserved in foreshore/shoreface environments, as the shells were subjected to extensive transportation by currents. The shells were best preserved in offshore environments, where rapid episodic sedimentation enabled within-habitat preservation, in some cases even preservation in life position. Barnacles are absent from the most clay-rich offshore deposits, probably because of clogging of filters by turbidity and lack of suitable substrate. Such dissimilarities suggest that the number and distribution of taphofacies may depend on which fossil groups are used. Interspecific variability may exist within the individual taphofacies. The barnacles, for example, tend to be better preserved than the mussel Mytilus edulis, although both are fixosessile suspension feeders. This indicates that not only life habits but also intrinsic shell properties influence preservation. Thus, taphofacies analyses should combine data on taphonomic features, specific life habit and shell properties to determine overall preservation patterns. In that way, taphofacies analyses may form a powerful tool for palaeoenvironmental analyses of marine deposits.     

Foraminiferal taphofacies in the Mississippian rocks of the Guadiato area, SW Spain

Summary Microfacies analysis of over 1800 standard thin-sections of upper Viséan and Pendleian-aged platform limestones from southwestern Spain (Guadiato area) shows that foraminiferal assemblages contain many allochthonous specimens. The analysis of the cementation, recrystallization, abrasion, bioerosion, encrustation, dissolution, taphonomic distortion, orientation and sorting allow the recognition of eight taphofacies. They are based on the taphonomic features observed within the foraminiferal assemblages, which reflect the environmental conditions in which foraminifera were sedimented as well as about early diagenesis. The environmental conditions may be ascertained from the analysis of the biostratinomic processes, which comprise the energy, waves, tides, redox conditions, etc. The mechanisms of taphonomic alteration may be quantified, and thus the appearance or absence of these alterations may be used to define taphofacies of shallow- and deep-water environments, such as those from tidal flat, shoal, outer platform, microbial mound or slope. Moreover, the relationship among these taphofacies also helps to define depositional mechanisms and products, such as debris flows or olistolites.     

Species composition,richness, and distribution of marine bivalve molluscs in Bahía de Mazatlán,México

We describe the composition and distribution of bivalve molluscs from the sandy and rocky intertidal and the shallow subtidal environments of Bahía de Mazatlán, México. The bivalve fauna of the bay is represented by 89 living species in 28 families, including 37 new records and four range extensions: Lithophaga hastasia, Adula soleniformis, Mactrellona subalata, and Strigilla ervilia. The number of species increases from the upper (44) and lower intertidal (53) to the shallow subtidal (76), but only 11 (17%) have a wide distribution in the bay (i.e., found in all sampling sites and environments). The bivalve assemblages are composed of four main life forms: 27 epifaunal species, 26 infaunal, 16 semi-infaunal, and 20 endolithic. A taxonomic distinctness analysis identified the sampling sites and environments that contribute the most to the taxonomic diversity (species to suborder categories) of the bay. The present work increased significantly (31%) to 132 species previous inventories of bivalves of Bahía de Mazatlán. These species represent 34% of the bivalve diversity of the southern Golfo de California and approximately 15% of the Eastern Tropical Pacific region.     

Taphonomy and taphofacies models of the Pliocene deposits of Vejer de la Frontera (Cádiz, SW Spain)

A quantitative taphonomic analysis of the fossil assemblages, together with a sedimentary study of the Pliocene deposits of the Vejer Basin (Cádiz, Spain), has been carried out. This multidisciplinary analysis has allowed us to establish with great precision the palaeoenvironmental conditions under which these materials were formed. The Pliocene deposits can be divided into three units, named from bottom to top: Unit 1, Unit 2 and Unit 3. Unit 1 is formed of medium-to-coarse-grained sands at the base, corresponding to subtidal bar deposits. At the top, the sands become coarser, and beach and littoral dunes were formed. Within these sedimentological contexts, the fossil remains exhibit a strong degree of taphonomic destruction due to high hydrodynamic energy. Unit 2, consisting of clays, corresponds to deposits formed in a protected coastal bay. A low-energy environment allowed the fossils to maintain a good state of conservation and even thin-shelled bivalves with a delicate ornamentation are preserved. Unit 3 comprises highly bioclastic sands and calcarenites-calcirudites. This unit displays a shallowing upwards trend, passing from deposits generated under shallow subtidal conditions in the lower part to materials deposited on beaches and coastal dunes in the upper part. Under these conditions, the fossil remains show a high degree of taphonomic destruction. In Units 1 and 3, the fossils are mainly accumulated in horizontal beds, with extensive lateral continuity and with erosive bottoms and graded tops. These accumulations of fossils are interpreted as tempestites. As compared with the fossils preserved in surrounding sediments, the taphonomic attributes of these bioclasts suggest a superposition of the background and event processes. During normal conditions, the high energy of the littoral environments produced a strong degree of taphonomic destruction. During storm events, a mixture of taphonomic attributes was produced: high fragmentation and disarticulation and little abrasion and edge rounding of the fragments. This mixture was a consequence of sudden burial after storms, which prevented long periods of exposure of the bioclasts in the taphonomically active zone. Three taphofacies models are proposed, based on taphonomic attributes of fossils contained in the different units: inner-shelf taphofacies, protected shallow-lagoon taphofacies and storm bed taphofacies.     

Ichnofacies: a mixture of taphofacies and biofacies

The environmental significance of individual ichnofacies has become a point of debate, and the Scoyenia ichnofacies is not clearly defined. Removal of the marine/non-marine boundary from ichnofacies definitions, as well as the bathymetry control, would render the Scoyenia ichnofacies unnecessary and would consolidate the definitions of the remaining ichnofacies. The constitution of the remainder is far from uniform. In some, the characteristic features are influenced by taphonomic bias more than by ecological factors, and thus these ichnofacies are in effect taphofacies (Skolithos, Cruziana and, especially, Zoophycos and Nereites). Others, on the other hand, have a primarily ecological definition and function as biofacies (Glossifungites, Trypanites, Teredolites and Psilonichnus), taphonomic bias playing a relatively minor role. Opportunistic occurrences of Skolithos in storm deposits do not fall within the Skolithos ichnofacies sensu stricto , and may be regarded as a separate Arenicolites ichnofacies, having an ecological character. □ Trace fossils, ichnofacies, salinity.     

Upper Pliocene bivalve shell concentrations from the Lower Chelif basin (NW Algeria): Systematics,sedimentologic and taphonomic framework

Sedimentologic and palaeontological investigation of the Upper Pliocene Slama Formation in the Lower Chelif Basin (NW Algeria) led us to collect important bivalve assemblages for taxonomic and taphonomic purposes. A rather comprehensive inventory list of Upper Pliocene bivalves from northwestern Algeria is now available and consists of 30 species, 17 of which are extinct ones. Four principal taphonomic attributes were analysed: bioerosion, encrustation, fragmentation, and abrasion. Physical and biogenic sedimentary structures are used for palaeoenvironmental interpretations. The taphonomic, sedimentologic and ichnological characteristics of most of the deposits suggests they originated from discontinuous processes of winnowing and bypassing of sediments, probably due to the action of storms in shallow waters, mainly in the shoreface depositional environment. The bivalve assemblage is dominated by disarticulated valves and displays significant taphonomic alteration in the shells. Sclerobionts traces in shells particulary affect the oyster shells. Bioerosion traces are predominately those of clionid sponges (Entobia isp.), polychaetes (Maeandropolydora isp. and Caulostrepsis isp.), bivalves (Gastrochaenolites isp.), and of predatory gastropods (Oichnus isp.). Among the sclerobionts, the identified encrusters were juvenile oyster recruits, barnacles, polychaetes (serpulid tubeworms), bryozoans (Microporella sp. and Acanthodesia sp.), and vermetid gastropods (Petaloconchus intortus).     

Cambrian (Series 2 to Miaolingian) platform facies from central Sonora,Mexico and the regional correlation

This study provides new insights about depositional paleoenvironments through siliciclastic microfacies, carbonate microfacies, and biofacies analysis from sedimentary formations of the lower and middle Cambrian (Stage 4–Wuliuan), exposed in central Sonora, northern Mexico. Results of the petrographic analysis of 48 samples revealed the following lithologies: quartzarenite, oncolytic rudstone, grainstone-packstone, wackestone, mudstone, and to a lesser extent sandy limestone. Two siliciclastic microfacies were identified: (A) quartzarenite with cross-bedded and horizontal stratification deposited in an intertidal and supratidal environment; and (B) massive quartzarenite with Skolithos ichnofacies deposited in subtidal and intertidal environments. Four carbonate microfacies were identified: microfacies 1 is a sandy limestone with trilobite fragments; microfacies 2 is a grainstone with intraclasts, salterellids, hyolithids, trilobites, and echinoderms plates; microfacies 3 is an oncolytic rudstone consisting of microbes and abundant echinoderms plates; and microfacies 4 is a packstone-grainstone with abundant ooids, trilobite fragments, and echinoderm plates. Two biofacies were identified: Agnostid-polymeroid biofacies with predominance of the trilobites Pentagnostus, Bathyuriscus, Oryctocephalites, and Elrathina; and Pagetia biofacies with abundant trilobites of the genera Pentagnostus, Pagetia and Elrathina. It is concluded by the sedimentation model that changes in sea level is the most important parameter in determining the siliciclastic microfacies, carbonate microfacies and biofacies; as well as the depositional environments that vary from the coastline (subtidal to supratidal) to shallow-water open circulation marine platform with low and high energy waters. The Cambrian deposits of northern Mexico are correlated with the deposits of California and Nevada (USA), as well as to the Precordillera (Argentina), where the species in common show a strong affinity.     

Comparative taphonomy of three bivalve species from a mass shell accumulation in the intertidal regime of North Sea tidal flats

This study comprises a comparative taphonomic analysis of three endobenthic bivalves (Mya arenaria, Cerastoderma edule, and Macoma balthica) derived from a mass accumulation of mainly vertically packed shells from the “Wurster Watt” in Lower Saxony’s Wadden Sea, German Bight. Bulk samples from two transects were analyzed with respect to taxonomic composition, left/right valve presence, counts and weight percentages of taxa, and size-frequency distributions. Taphonomic features including abrasion, fragmentation, encrustation and bioerosion were subjected to a semi-quantitative analysis. Taphonomic results show significant differences with respect to bivalve taxa as well as between transects. Mya arenaria, a large endobenthic bivalve, shows the greatest amount of fragmentation and is often encrusted by balanids and bryozoans. The smaller and more robust Cerastoderma edule has the greatest values for bioerosion especially by the polychaete Polydora ciliata. Macoma balthica, which has the thinnest valves, shows the highest values for abrasion, but low values for the rest of the measured taphonomic features. Taphonomic differences between the taxa, samples and transects are related to (1) the origin of the bivalves (from living populations or exposed colonization horizons), (2) the different size and morphology of the valves (themselves related to mode of life), (3) the taphonomic trajectories of the different bivalves, as well as (4) the varying depositional environment of the two transects.     

Assessing surficial foraminiferal distributions as an overwash indicator in Sur Lagoon,Sultanate of Oman

The identification of tsunami and storm deposits in arid coastal environments can be problematic, as overwash sediments may not show significant contrasting lithologic characters with lagoonal sediments. In this study foraminifera were evaluated as an overwash indicator in a small (12 km²) intertidal lagoon located at Sur, in the Sultanate of Oman. The lagoon is shallow (< 5 m depth), tidally-controlled and communicates with the open sea through a narrow subtidal entrance channel. The lagoon is largely composed of intertidal sand and mudflats with fringing mangroves. Previous work at Sur identified evidence for overwash deposits associated with the 28 November 1945 Makran Trench tsunami (M_w 8.1) which were identified based on the presence of a laterally extensive shelly bed with distinctive taphonomic characters. In this study, particle size, stable isotopic and foraminiferal (taxa and taphonomy) analyses were conducted on surface sediment samples from Sur Lagoon to determine modern spatial trends in the lagoon for future comparison with overwash sediments deeper in the geologic record. Q-mode cluster analysis of the foraminiferal data (n = 54) found three main biofacies which follow lagoon sub-environments: Shallow Marine Area, Main Lagoon Basin, and Distal Lagoon Basin. The Shallow Marine Area is mainly subtidal with higher wave energy, the Main Lagoon Basin is predominantly intertidal with moderate wave energy, whereas the Distal Lagoon Basin is isolated and mainly intertidal with low wave energy.The most useful parameters for assessing overwash events in Sur Lagoon are the foraminifera taxa rather than the taphonomic characters themselves. The most useful taxa for recognizing an overwash (e.g. tsunami or storm) will be the abundance of Amphistegina spp., Ammonia inflata, Elphidium advenum and planktics which are predominantly found in the Shallow Marine Area. The abundance trend of these species with distance into the lagoon has an inverse relationship with higher r² values than the other taxa. Taphonomically there is a predominance of larger specimens in the Shallow Marine Area along with a higher abundance of fossil specimens.     

The upper Moscovian and basal Kasimovian (Pennsylvanian) of Central European Russia: Facies,subaerial exposures and depositional model

Summary The type upper Moscovian-basal Kasimovian argillaceous-carbonate succession of central European Russia contains regionally traced cyclothem-bounded subaerial exposure horizons (geosols) represented mainly by rendzina-type palaeosols. Palaeokarst profiles occurrarely and grade laterally to palaeosols. Composite subaerial profiles divided by one or two thin marine beds are called ‘multiple geosols’. The biofaces structure of the studied succession is defined by brachiopod and fusulinoid biofaces. The heterogeneous Choristites biofacies characterizes openmarine intervals, which constitute the bulk of the succession, and is defined by presence of Choristites. The Meekella biofacies with monospecific concentrations of Meekella shells and extreme rarity of other brachiopods characterises restricted peritidal intervals which commonly constitute the terminal regressive parts of major cyclothems. Three fusulinoid biofacies defined by Baranova and Kabanov (2003) include restricted peritidal Biofacies 1 with only small fusulinoids Fusiella and Schubertella present, open shoal-to-subtidal Biofacies 2 with the richest fusulinoid assemblages, and the most offshore Biofacies 3 with less diverse, sometimes Hemifusulina-dominated, fusulinoid assemblages. Bioturbation patterns and ichnofossils allow recognition of deeper subtidal Zoophycos and shallower non-Zoophycos ichnofacies. Among the latter, shallowest subtidal facies are characterized by presence of thalassinoid burrows. Intertidal laminated lithofacies with suppressed bioturbation contain Skolithos burrows. Seventeen lithofacies are recognized. Terrestrial lithofacies include topclays (upper clayey palaeosol horizons) and aeolian grainstones. Restricted peritidal lithofacies include cross-stratified skeletal-peloidal grainstones, fine-grained laminated grainstones-mudstones, and lagoonal mudstones. Open shoal lithofacies include ooidal grainstones (rare, only in Podolskian) and coarse skeletal-peloidal grainstones. The open subtidal lithofacies include skeletal packstones-rudstones, shallow subtidal packstones-wackestones, deeper subtidal packstones-wackestones, Ivanovia boundstones (only in Podolskian), proximal tempestites, distal tempestites, and skeletal wackestones-mudstones. The fossiliferous shale lithofacies is a miscellaneous group of marine shales lacking distinct features of the above-listed lithofacies. Conglomerates of cyclothem bases that are regarded as early transgressive lithofacies are variable in their palaeoenvironmental position and are characterized by concentrated pebbles derived from palaeosol reworking. The shallowest subtidal lithofacies of fine packstones-grainstones is considered as transitional between open subtidal and restricted peritidal lithofacies. The origin of stratiform dolostones is shown to be early diagenetic in the subsurface. The depositional model involves a shallow and broad epicontinental ramp, where through water circulation prevented stratification of the water column and allowed large skeletal benthos to colonize the entire spectrum of depositional environments. Storms are thought to be the principal water-mixing agent. The anti-estuarine circulation carrying oxygenated waters down-ward may explain the lack of anoxic features in the deepest facies that may have formed below storm wave base.     

Micropopulation differentiation in phenol content and susceptibility to herbivory in the Chilean kelp Lessonia nigrescenss (Phaeophyta,Laminariales)

Micropopulation differences in phenol content between intertidal and subtidal individuals of the kelp Lessonia nigrescens were found. Subtidal plants showed: (1) significantly higher phenol content than intertidal individuals, in vegetative and reproductive tissues, (2) intra-plant differences, with higher content in apical frond tissues, (3) higher resistance to consumption by herbivorous fishes. The microscopic progeny of subtidal plants showed the same trend as adult plants: (1) haploid spores from subtidal plants had higher phenol content than spores from intertidal individuals, and (2) the microscopic sporophytes derived from subtidal spores and gametophytes were less consumed by herbivorous snails (Tegula tridentata) than those derived from intertidal plant propagules. No increase in phenol content was detected after mechanical injury to experimental fronds, or after transplantation to the subtidal environment.In addition to the absence of inducible responses, the different phenol content between intertidal and subtidal individuals, in adult diploid plants and also in the haploid progeny, suggests that both environments differ someway enough to fix the mentioned features on the plants of Lessonia nigrescens. It is likely that the differences in herbivory between the two distributional extremes contributed to the observed pattern.     

Depth as an overarching environmental variable modulating preservation potential and temporal resolution of shelly taphofacies

In the marine realm, the interpretation of taphofacies relies heavily on how oceanographic and sedimentary conditions affect the preservation state of fossils. Several taphonomic variables either covary with depth or are directly influenced by depth. Facies‐level factors rather than broad, basin‐scale parameters influence the taphonomic profile of mollusc death assemblages according to actualistic and experimental evidence. To determine the possible relation between depth and the taphonomic conditions of multiple species of bivalve remains, we used seven samples gathered over a comprehensive bathymetric gradient (from 7 to 150 m below mean sea level; topmost 10‐ to 20‐cm layer, roughly corresponding to the taphonomically active zone). We selected samples from predominantly muddy facies on the southern Brazilian shelf (SBS). The taphonomic damage profile (TDP) was measured using site samples based on a standard taphonomic analysis (categorical scoring system) of shells and fragments larger than 4 mm, to identify site damage patterns. Restricting the sedimentary grain size (samples from fine sediments) enabled the determination of the variation in damage with depth among the samples. Constrained analysis of proximities (CAP) revealed that up to 46% of the taphonomic variation observed was related to variation in depth (with approximately 28% unexplained by environmental factors). Part of the unexplained fraction was due to the effect of temporal mixing, which is predictable along large‐scale patches but is inversely linked to the TDP. Our results show that taphonomic analysis, considering large spatial scales in recent environments, can explain the variations present in shell beds that formed during distinct time periods of the evolution of a Quaternary sedimentary basin.     

Taphonomy of Clypeaster fragments: preservation and taphofacies

The preservation of echinoid fragments of the common echinoid genus Clypeaster recovered from bulk sediment samples is used to explore the possibilities of recognizing taphonomic patterns and establishing taphofacies within a shallow water carbonate environment (Northern Bay of Safaga, Red Sea, Egypt). This is accomplished by the comparison and quantification of the taphonomic signatures of numerous fragments of roughly similar size. The main taphonomic processes observed are abrasion and destruction of plate surfaces, including tubercles and plate edges. Encrustation, especially by foraminifera, can be common and intense. Intraplate fracturing and surface features, such as scratch marks, were also quantified. Four different taphofacies with different characteristic signatures were separated using a cluster analysis of cumulative taphonomic grades. The distribution of taphofacies clearly reflects the topographic complexity of the study area and can be explained by ambient environmental parameters that reflect the general picture of wave and current intensities and sedimentation patterns. The potential use of taphofacies analysis as an independent measure of environmental heterogeneity in palaeoecological studies is confirmed in that taphofacies analysis can reveal parameters not immediately obvious when investigating the textural and biotic characteristics of a sediment.     

Capitellidae (Annelida: Polychaeta) from the Pacific Coast of Costa Rica

Eleven species of Capitellidae (Annelida: Polychaeta) belonging to eight genera are reported from the subtidal and intertidal of the Pacific Coast of Costa Rica. Three species, Mediomastus ambiseta, M. californiensis and Notomastus hemipodus, are found in highest abundances and are widespread in subtidal and intertidal environments. A taxonomic key to these species is included.     

Taphonomic signatures,ichnofacies analysis and depositional dynamics of fossil macro-invertebrate assemblages of the San Juan Raya Formation,Zapotitlán Basin,Puebla, Mexico

In this paper, we describe the taphofacies and ichnofacies from Aptian strata of the San Juan Raya Formation in the Santa Ana Teloxtoc area, Puebla, Mexico. A composite stratigraphic section was analysed on a bed-by-bed scale up to a total thickness of 765.5 m. Our results show the presence of 10 taphofacies and 3 ichnofacies. The taphofacies and ichnofacies interpretation, and its correlation with the sedimentary lithofacies, enabled the determination of a palaeoenvironmental model for the study area that corresponds to a shallow marine, open-coast, clastic system with episodic sedimentation as a product of storm events. This system had several variations in sub-environments, from foreshore to offshore. Foreshore and shoreface environments are characterised by taphofacies Tf1, Tf2, Tf3 and Tf10 and PsI and SkI ichnofacies, representing lower faunal diversity moments (with the exception of Tf3 taphofacies). Meanwhile, taphofacies Tf4, Tf5, Tf6, Tf7, Tf8 and Tf9 were representative of shelf environments and are described as moments of medium-to-high faunal diversity (with the exception of Tf5 taphofacies).     

INTRASPECIFIC VARIATION IN STRESS‐INDUCED HYDROGEN PEROXIDE SCAVENGING BY THE ULVOID MACROALGA ULVA LACTUCA1

We investigated the presence and kinetics of the oxidative stress response in intertidal and subtidal individuals of the ulvoid macroalga Ulva lactuca L. Stress responses, as measured with both enzymatic and fluorescent‐based antioxidant assays, differed between individuals collected from a subtidal and an intertidal habitat. Subtidal individuals secreted significantly more hydrogen peroxide (H₂O₂) than intertidal individuals when subjected to osmotic stress or desiccation. The activity of reactive‐oxygen‐scavenging enzymes and the ability to scavenge exogenous H₂O₂ were lower in subtidal than in intertidal individuals, suggesting that subtidal individuals are less stress tolerant. In vitro experimentation demonstrated that millimolar concentrations of dimethylsulfoniopropionate (DMSP) and its breakdown products could efficiently scavenge H₂O₂, with DMSP being a less‐effective scavenger than dimethyl sulfide (DMS), acrylic acid, and acrylate. The addition of H₂O₂ at concentrations of 2.5 mM or greater induced the cleavage of DMSP into DMS and acrylic acid in subtidal individuals. Intertidal individuals were affected in the same manner with the addition of 5 mM H₂O₂. There were no differences in the amounts of DMSP cleavage in subtidal and intertidal algae when the algae were subjected to hyposaline conditions. Our data suggest that the oxidative‐stress‐induced cleavage of DMSP affords products with efficient H₂O₂‐scavenging abilities. In addition, U. lactuca individuals growing in intertidal habitats are better acclimatized to changing environments and thus have a higher threshold for oxidative stress than conspecifics in subtidal habitats.     

Relationship between algae and environment: an Early Cretaceous case study, Trascău Mountains, Romania

The relationship between algae and depositional environment was studied in a limestone succession of Berriasian–Valanginian age. Several depositional environments were recorded from shallow subtidal to intertidal and supratidal, with salinity ranging from normal marine to fresh and/or supersaline water. The algal assemblages consist mainly of dasycladaleans, rivulariacean-type cyanobacteria and charophytes. Nipponophycus (Bryopsydales) and Lithocodium-Bacinella (microproblematicum), occur at some levels. Dasycladaleans are associated with subtidal, sometimes restricted (“lagoonal”) environments, while rivulariacean-like cyanobacteria and charophytes characterise intertidal-supratidal and fresh and/or supersaline environments, respectively. Among the dasycladaleans, Salpingoporella annulata is often related to restricted environments where it forms monospecific assemblages. Large dasycladaleans, such as Selliporella neocomiensis, Macroporella praturloni and Pseudocymopolia jurassica are found in subtidal high-energy deposits (bioclastic grainstones). The relationship between environment and algae, characteristic for each depositional unit, can be used to interpret the relative sea-level variations.     

Taphonomic field experiments and the role of the Shelf and Slope Experimental Taphonomy Initiative

Fossilization of organism remains is the result of biological, physical, and chemical processes at work in the environment of deposition. The pathways taken by the remains of organisms through death, decay, burial, and diagenesis (known as taphonomic pathways) affect the fossil record of life in important ways, from complete removal and recycling of remains to preservation of hard parts and sometimes to exceptional preservation of soft tissues. Our understanding of taphonomic processes informs our interpretations of the fossil record and helps in the reconstruction of ancient environments. Research into taphonomic pathways in modern environments provides important insight into the fossilization process. In 1993, a group of paleontologists formed the Shelf and Slope Experimental Taphonomy Initiative (SSETI) and began a long-term comparative study of taphofacies and differential decay of taxonomic groups by placing experimental arrays containing bivalves, gastropods, decapod crustaceans, sea urchins, and wood species at multiple marine shelf and slope sites in the Bahamas and Gulf of Mexico. The goal of SSETI is to observe taphonomic processes over a period of decades to better understand taphonomic pathways for these various groups of taxa in a wide variety of depositional environments beyond the shallow near shore region. This special volume brings together eight studies that are the result of the SSETI program. The focus of this contribution is to first review the body of published work concerned with the fossilization process through the experimental manipulation of the remains of organisms in modern marine environments. We also present the methods of the SSETI project and its contributions to our understanding of taphonomic processes in relation to carbonate and wood recycling and preservation.     

Late Mississippian to Early Pennsylvanian conodont biofacies in central Montana

Later Mississippian (upper Chesterian) to Early Pennsylvanian (lower Morrowan) conodont faunas were recovered from limestones and calcareous mudstones of the Alaska Bench Formation in central Montana. These faunas define four biofacies, each recognized by the dominance of a particular single element genus for which the biofacies is named. The Adetognathus biofacies represents lagoonal, tidal flat, and barrier sediments. The Declinognathodus/Idiognathoides biofacies represents a deposition in shallow, open marine, offshore conditions. The Rhachistognathus biofacies represents a transitional environment between restricted, intertidal environments and normal marine, offshore environments. The Neognathodus biofacies represents shallow-water bay or lagoonal deposition, where environmental controls have effectively excluded other conodont faunas. The investigation of conodont biofacies provides improved biostratigraphic and paleoenvironmental uses of conodonts.