Bentho-planktonic evidence from the Austrian Alps for a decline in sea-surface carbonate production at the end of the Triassic

A high-resolution micropalaeontological study, combined with geochemical and sedimentological analyses was performed on the Tiefengraben, Schlossgraben and Eiberg sections (Austrian Alps) in order to characterize sea-surface carbonate production during the end-Triassic crisis. At the end-Rhaetian, the dominant calcareous nannofossil Prinsiosphaera triassica shows a decrease in abundance and size and this is correlated with a increase in δ¹⁸O and a gradual decline in δ¹³C_carb values. Simultaneously, benthic foraminiferal assemblages show a decrease in diversity and abundance of calcareous taxa and a dominance of infaunal agglutinated taxa. The smaller size of calcareous nannofossils disturbed the vertical export balance of the biological carbon pump towards the sea-bottom, resulting in changes in feeding strategies within the benthic foraminiferal assemblages from deposit feeders to detritus feeders and bacterial scavengers. These micropalaeontological data combined with geochemical proxies suggest that changes in seawater chemistry and/or cooling episodes might have occurred in the latest Triassic, leading to a marked decrease of carbonate production. This in turn culminated in the quasi-absence of calcareous nannofossils and benthic foraminifers in the latest Triassic. The aftermath (latest Triassic earliest Jurassic) was characterised by abundance peaks of “disaster” epifaunal agglutinated foraminifera Trochammina on the sea-floor. Central Atlantic Magmatic Province (CAMP) paroxysmal activity, superimposed on a major worldwide regressive phase, is assumed to be responsible for a deterioration in marine palaeoenvironments. CAMP sulfuric emissions might have been the trigger for cooling episodes and seawater acidification leading to disturbance of the surface carbonate production at the very end-Triassic.     

Integrated planktonic stratigraphy and paleoenvironments of the Lower-Middle Miocene successions in the central and southern parts of the Gulf of Suez,Egypt

Lower to Middle Miocene successions in three offshore wells named GS 160-2, QQ-89, and Ras Elush-2 located in the central and southern parts of the Gulf of Suez were examined for their planktonic foraminifera, calcareous nannofossil assemblages, and paleoenvironments. These successions are subdivided from older to younger into Aquitanian Nukhul, Burdigalian-Langhian Rudeis, Langhian Kareem, and Serravallian Belayim formations. The identified foraminifera includes 54 benthic species belonging to 25 genera and 47 planktonic species belonging to 11 genera, in addition to 64 calcareous nannofossil species belonging to 21 genera. The stratigraphic distribution of these assemblages suggests classifying the studied successions into seven planktonic foraminiferal and six calcareous nannoplankton biozones. The planktonic foraminiferal and calcareous nannoplankton biozones are integrated. Different environments ranging from shallow inner to outer shelf are recognized. This is based on quantitative analyses of foraminifera including benthic biofacies, planktonic/benthonic ratio, and diversity. Syn-rift tectonics played an important role in configuration of the Miocene depositional history in the Gulf of Suez region.     

Consumer Diversity Enhances Secondary Production by Complementarity Effects in Experimental Ciliate Assemblages

Diversity within distinct trophic groups is proposed to increase ecosystem functions such as the productivity of this group and the efficiency of resource use. This proposition has mainly been tested with plant communities, consumer assemblages, and multitrophic microbial assemblages. Very few studies tested how this diversity–productivity relationship varies under different environmental regimes such as disturbances. Coastal benthic assemblages are strongly affected by temporal instability of abiotic conditions. Therefore, we manipulated benthic ciliate species richness in three laboratory experiments with three diversity levels each and analyzed biomass production over time in the presence or absence of a single application of a disturbance (ultraviolet-B [UVB] radiation). In two out of three experiments, a clear positive relationship between diversity and productivity was found, and also the remaining experiment showed a small but nonsignificant effect of diversity. Disturbance significantly reduced the total ciliate biomass, but did not alter the relation between species richness and biomass production. Significant overyielding (i.e., higher production at high diversity) was observed, and additive partitioning indicated that this was caused by niche complementarity between ciliate species. Species-specific contribution to the total biomass varied idiosyncratically with species richness, disturbance, and composition of the community. We thus present evidence for a significant effect of consumer diversity on consumer biomass in a coastal ciliate assemblage, which remained consistent at different disturbance regimes.     

Sedimentology and extinction patterns across the Cretaceous-Tertiary boundary interval in east Texas

Biostratigraphic analysis of planktic foraminifera and calcareous nannofossils, as well as sedimentological and geochemical studies, suggests that the K-T boundary interval on the Brazos River in Falls County, Texas, has a complete Cretaceous section but that a hiatus probably exists in the earliest Palaeocene, representing as little as 35,000 years of time. Planktonic foraminifera, calcareous nannofossils and molluscs decline abruptly in diversity at the K-T boundary in conjunction with an increase in iridium levels. Molluscan assemblages are diverse and dominated by suspension feeders up to the K-T contact but are replaced by a very low diversity assemblage of predominantly deposit-feeders and carnivores in the Early Palaeocene. When both microfauna and macrofauna are considered, species that lived or fed in the water column (planktonic foraminifera, calcareous nannofossils, suspension feeding bivalves) suffered the highest mortality while benthic, dominantly deposit-feeding or carnivorous taxa (benthic foraminifera, carnivorous and deposit-feeding gastropods and bivalves) were less affected.Although the extinction appears massive and abrupt on the whole, some minor faunal irregularities (abnormal forminiferal tests and a slight molluscan diversity drop) occur about one meter below the K-T boundary. We don't as yet know whether these changes are part of normal background environmental fluctuations or whether they are related to the K-T mass extinction event.     

Seasonal and spatial variability in macrobenthos communities in Jamaica Bay,New York—an urban estuary

Macrobenthos were sampled at 27 sites on a seasonal basis from October 1981 through November 1982. Cluster analyses and principal components analyses indicated that although spatial and species groupings were weak, an underlying sediment-correlated structure persisted for all seasons. Weak station groupings resulted from great seasonal and local variability in abundance of several dominant taxa. The most widely distributed species varied the least in density over time. Species richness (number of species) and dominance were uncorrelated. Dominance was correlated with sediment organic content [% total organic carbon (TOC)] and % Mud. Species richness increased with increasing % TOC, reaching a maximum in the range 0.7 to 1.0% TOC (primarily sand stations). At higher organic levels (muddy, sand stations), species richness declined. Muddy sand stations were dominated byAmpelisca abdita. In this community, species richness was inversely correlated both with percent TOC and heavy metals concentrations. In both sand and mud communities, species richness was positively correlated with density (mean number individuals of all species per sample).     

松辽盆地海侵事件——松科1井钙质超微化石新证据

松辽盆地作为中国最大的陆相含油气盆地,是否发生过海水侵入一直存在争议,化石能为该科学问题提供直接解释。在松科1井嫩江组一、二段发现了少量的钙质超微化石,初步鉴定出Calculites obscurus,Calculites ovalis,Quadrum sp.,Micula sp.等属种。上述钙质超微化石广泛分布于晚白垩世海相地层中,通过与国际标准海相化石的对比,将嫩江组一段中、下部的时代限定为Turonian晚期—Maastrichtian期。松辽盆地嫩江组一、二段下部的钙质超微化石保存总体一般,有一定的多样性,具有海相钙质超微化石的特征。松科1井钙质超微化石的分布、古生态及其与有孔虫化石的对应关系表明,松辽盆地嫩江组一段中-下部、二段下部沉积期湖泊水域广阔,全球海平面较高,间歇性的海水侵入事件导致西北太平洋中的钙质超微浮游生物和有孔虫等海洋生物被带入松辽盆地。     

Shark and ray faunas in the Middle and Late Eocene of the Fayum Area, Egypt

The Eocene rocks exposed in the Fayum Area, Egypt, are well known for their fossil vertebrates but in recent times the sharks and rays have been largely neglected. Extensive surface collecting, supplemented with bulk samples, has produced large collections from the Midawara, Gehannam, Birket Qarun and Qasr el-Sagha formations, spanning the Bartonian and Priabonian stages and from palaeoenvironments varying from open muddy shelf to very shallow estuarine systems. In total about 90 species of sharks and rays are recorded, many of them previously unrecognised, resulting in some of the most diverse fossil chondrichthyan assemblages known from the Tertiary. Teeth of these species suggest that they occupied a wide range of ecological niches from top predator to tiny benthic invertebrate feeder to planktivore. Many of the species are limited in their stratigraphical range and show potential to be used, at least locally, as biostratigraphical indicators for stratigraphically poorly constrained vertebrate sites elsewhere in North Africa. Distinctly different faunas from different sedimentary environments indicate a strong environmental control on the distribution of many species.     

Do Spartina maritima Plantations Enhance the Macroinvertebrate Community in European Salt Marshes?

Ecological restoration of salt marshes using plantations may enhance the macroinvertebrate community, but little is known about the development of benthic macroinvertebrates after ecological engineering projects in European salt marshes. This study analyzed the environment and the macroinvertebrate community in European salt marshes 3 years after restoration using Spartina maritima plantations in comparison with non-restored and preserved marshes in Odiel Marshes (Southwest Iberian Peninsula). We hypothesized that planting Spartina maritima on intertidal mudflats would increase species richness and diversity (Shannon–Weaver index) of the benthic macroinvertebrate community by increasing environmental heterogeneity, providing feeding resources and improving sediments characteristics. Benthic macrofauna samples (composed mainly of annelids, crustaceans, and mollusks) were sampled in plots of 20 cm?×?25 cm to 5 cm depth between +1.8 and +3.0 m above Spanish Hydrographic Zero. Sediment organic matter content, bulk density, pH, and redox potential were the variables that best explained macroinvertebrate distribution. Restored marshes achieved similar diversity and even higher specific richness than preserved marshes, although with differences in species composition. Non-restored marshes showed the lowest diversity. Restored and preserved marshes did not differ in total abundance or biomass of macroinvertebrates, both being higher than in non-restored marshes. The macroinvertebrate communities in preserved and non-restored marshes showed the largest difference in taxa composition, with restored marshes occupying an intermediate position. Salt marsh restoration using S. maritima increased the complexity (ecological diversity and species richness) and abundance of the benthic macroinvertebrate community. Our study offers new information about the role of salt marsh plants in mediating faunal communities via ecological engineering projects.     

江西乐平沿沟二叠纪末有孔虫的演变及对鲕状灰岩的古环境指示意义

江西乐平沿沟剖面均一的碳酸盐相岩沉积, 完整地记录了二叠系-三叠系界线附近生物演变过程.通过对该剖面系统的化石切片研究, 共鉴别出有孔虫27属39种, 包含类4属7种.该剖面有孔虫的演变在二叠纪-三叠纪之交呈现出单幕式的消减过程, 对应于华南两幕生物灭绝中的第1幕.有孔虫的个体数和多样性在21-2层顶部发生了突然降低.4个不同有孔虫组合的演替关系, 揭示了有孔虫在灭绝事件中的演变过程, 即由灭绝前的高丰度、高分异度组合转变为灭绝后低丰度、低分异度组合.通过对二叠系-三叠系界线处鲕状灰岩的化石和沉积特征研究, 发现Hindeodus changxingensis带内的鲕状灰岩中仍存在较为丰富的有孔虫等化石.剧烈的海平面变化以及鲕状灰岩形成使下伏地层中的化石颗粒发生再沉积作用, 是形成这一特殊现象的主要原因.通过对鲕状灰岩中化石和沉积特征的深入研究, 论证了该鲕状灰岩形成于二叠纪-三叠纪之交大灭绝之后, 是当时特殊的海洋生态系产物, 反映了当时较高的海水回旋速率、微生物繁盛、海水碳酸盐超饱和等异常的环境条件.      

贵州水城仲河剖面二叠纪-三叠纪之交底栖群落的物种多样性与功能多样性转变

为了定量化恢复晚二叠世末期生物大灭绝对底栖群落的物种多样性和功能多样性的影响,对浅海碎屑岩台地相区的贵州水城仲河剖面开展宏体化石采集和分析,识别和划分古群落,选择优势度、香农指数、均匀度等代表物种多样性指数,生态功能群数量和功能均匀度代表功能多样性指数. 共采集1 340枚化石标本,经鉴定得到30属33种,其中双壳类可归纳为两个生物带:晚二叠世长兴期的Hunanopecten exilis顶峰带和早三叠世Griesbachian早期的Pteria ussurica variabilis顶峰带. 根据化石属种的地层分布、保存状况,结合聚类分析方法识别出3个古群落:Astartella obliqua-Tethyochonetes quadrata群落、Pteria ussurica variabilis-Claraia wangi群落和Pteria ussurica variabilis-Unionites canalensis群落. 自晚二叠世长兴期末期至早三叠世Griesbachian早期,古群落的优势度上升、香农指数降低、均匀度下降,功能群丰富度降低,功能均匀度上升,这指示晚二叠世末生物大灭绝对浅海碎屑岩相区的底栖群落的组成和功能均有显著的破坏. 此外,结合华南浅海和深海相区的古群落数据,发现底栖群落的物种多样性指数和功能多样性指数在晚二叠世末生物大灭绝中均遭受损失,但是浅海底栖群落受影响较高.      

Recognising subtidal foraminiferal assemblages: implications for quantitative sea‐level reconstructions using a foraminifera‐based transfer function

Microfossil‐based transfer function models are increasingly used to provide decimeter‐scale sea‐level change reconstructions. In this paper I demonstrate that in the tropical location of northern Australia problems arise in selecting the appropriate elevation range for the modern training set used to calibrate fossil calcareous foraminiferal assemblages. Most calcareous foraminiferal species found in cores occur in both modern intertidal and shallow subtidal environments. A lack of independent measures to indicate whether fossil assemblages come from intertidal environments forces use of a training set that includes intertidal and subtidal environments. This results in decreased precision compared to using a training set solely from intertidal environments. The widely used method of assessing model fit to fossil assemblages (modern analogue technique) often fails to discriminate between acceptable and unacceptable reconstructions. It is important to investigate a number of different measures including modern analogue technique, canonical correspondence analysis and changing bootstrapped sample specific transfer function errors to fully understand the level of similarity between modern and fossil foraminiferal samples, to judge the reliability of transfer function‐predicted sea‐level reconstructions. Copyright © 2008 John Wiley & Sons, Ltd.     

Tidal Stage Changes in Structure and Diversity of Intertidal Benthic Diatom Assemblages: a Case Study from Two Contrasting Charleston Harbor Flats

Benthic microalgae are key contributors to near-shore food webs and sediment stabilization. Temporal variability in microalgal biomass and production throughout the tidal cycle has been well documented; however, due to limitations of traditional methods of analysis patterns of community composition and diversity over such time scales have not been revealed. To explore the latter and better understand how short-term changes throughout the tidal cycle may affect community functioning, we compared benthic diatom composition and diversity over tidal stage shifts. We employed two disparate molecular techniques (denaturing gel gradient electrophoresis with Sanger DNA sequencing of excised bands and high-throughput community metagenome sequencing) to characterize diatom assemblages in representative muddy and sandy intertidal sites in Charleston Harbor, SC, USA. In support of prior studies, we found higher diatom diversity in sandbar as compared to mudflat sediments. Spatial differences were stronger relative to tidal temporal differences, although diversity metrics generally were highest after prolonged tidal immersion as compared to low-tide emersion or just after immersion at flood tide. Composition of the diatom assemblage differed markedly between sites, with species in genera Halamphora, Amphora, and Navicula dominating the sandbar, whereas Cyclotella, Skeletonema, and Thalassiosira were the most prevalent genera on the mudflat. Diatom composition differed by tidal stage, with assemblages during low-tide exposure distinct from samples taken after immersion. Both sandbar and mudflat sediments exhibited increases in relative proportion of epipelic diatoms and decreases in planktonic taxa during low-tide exposure. Our findings of short-term changes in species composition and dominance could inform primary productivity models to better estimate understudied diatom contributions in heterogeneous and highly variable tidal systems.     

Historical trends in Chesapeake Bay dissolved oxygen based on benthic foraminifera from sediment cores

Environmentally sensitive benthic foraminifera (protists) from Chesapeake Bay were used as bioindicators to estimate the timing and degree of changes in dissolved oxygen (DO) over the past five centuries. Living foraminifers from 19 surface samples and fossil assemblages from 11 sediment cores dated by²¹⁰Pb,¹³⁷Cs,¹⁴C, and pollen stratigraphy were analyzed from the tidal portions of the Patuxent, Potomac, and Choptank Rivers and the main channel of the Chesapeake Bay.Ammonia parkinsoniana, a facultative anaerobe tolerant of periodic anoxic conditions, comprises an average of 74% of modern Chesapeake foraminiferal assemblages (DO-0.47 and 1.72 ml l⁻¹) compared to 0% to 15% of assemblages collected in the 1960s. Paleoecological analyses show thatA. parkinsoniana was absent prior to the late 17th century, increased to 10–25% relative frequency between approximately 1670–1720 and 1810–1900, and became the dominant (60–90%) benthic formaniferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests ofA. parkinsoniana occur in all cores (10–20% ofAmmonia), suggesting unprecedented stressful benthic conditions. These cores indicate that prior to the late 17th century, there was limited oxygen depletion. During the past 200 years, decadal scale variability in oxygen depletion has occurred, as dysoxic (DO=0.1–1.0 ml l⁻¹), perhaps short-term anoxic (DO<0.1 ml l⁻¹) conditions developed. The most extensive (spatially and temporally) anoxic conditions were reached during the 1970s. Over decadal timescales, DO variability seems to be linked closely to climatological factors influencing river discharge; the unprecedented anoxia since the early 1970s is attributed mainly to high freshwater flow and to an increase in nutrient concentrations from the watershed.     

What have natural and human changes wrought on the foraminifera of San Francisco Bay late Quaternary estuaries?

In this study we compare the foraminifera of modern South San Francisco Bay with fossils from sediments of a previous estuary at 125 ka to provide a basis for interpreting the impact of natural and human change on the benthic ecosystem. All the species found in the Pleistocene sediments of this study are estuarine and/or shallow-water species occurring commonly in San Francisco Bay today, except for the introduced foraminifer Trochammina hadai, a native of Japan that was not found in samples taken in San Francisco Bay before 1983. The biodiversity and species composition of the fossil and modern assemblages before the introduction of T. hadai are nearly identical, suggesting that the environmental and physical changes in the 125,000-year-old and modern estuaries have not had a significant effect on the meiofauna of the Bay. In contrast, modern anthropogenic change in the form of species introductions has impacted the modern foraminiferal assemblage: T. hadai began to dominate the modern assemblage a decade after its introduction. Similar to the recorded impacts of introductions of marine metazoan invertebrate species, the dominance of T. hadai changed species proportions in the post-1980s foraminiferal assemblage, however no known extinctions in the native foraminiferal fauna occurred.     

Experimental study on the mechanical behaviors and particle breakage characteristics of calcareous sand from South China Sea under repeated one-dimensional impacts

The behavior of calcareous sand under repeated impact considerably differs from that of silica sand. Notably, calcareous sand is important in engineering projects in the South China Sea, such as pile driving. To understand the behavior of calcareous sand under multiple impacts, the improved split Hopkinson pressure bar (SHPB) system was selected for one-dimensional impact tests of silica and calcareous sand with particle sizes of 0.25–0.50 mm. The sand specimens were impacted 1, 3, 7 and 10 times. The test results reveal that the dynamic apparent stiffness of silica sand is approximately 6–8 times that of calcareous sand. The dynamic apparent modulus values of the two sands increase with an increase in the number of impacts, N. For calcareous sand, the compression index C_c decreases with an increase in N, and silica sand shows the opposite trend. The yield pressure p_c of calcareous sand under impact loading is approximately 40% of that of silica sand. With an increase in N, the energy absorption capacity, energy dissipation rate and damage variables of the two sands exhibit a downward trend. In addition, the energy absorption efficiency of calcareous sand is better than that of silica sand. During the process of impact, a large number of sand particles will break, and particle breakage will change the particle size distribution (PSD), thereby significantly affecting the physical and mechanical properties of the corresponding soil. Based on the test results and fractal theory, an evolution model is established to characterize the PSD evolution in the breakage state for uniformly graded calcareous sand. Moreover, a Markov chain model is proposed to describe the PSD evolution of nonuniformly graded specimens. The predicted results of both models show agreement with the experimental values.

     

The ecological condition of dead-end canals of the Delaware and Maryland coastal bays

Manmade, dead-end canals are common in residential developments along the coastal bays of Delaware and Maryland. The close proximity of housing to the water and the concentration of boating activities enhances the potential for anthropogenic stress to living resources in these poorly flushed aquatic systems. Measurements of water quality, sediment contaminants, and benthic macroinvertebrate assemblages were taken in 25 randomly selected canals and compared to 175 non-canal sites located throughout the coastal bays. The mean bottom dissolved oxygen concentrations in canals was half that found in non-canal sites. Mean water-column and benthic chlorophyll concentrations were, respectively, two times and four times higher in the canals. Sediment contaminant concentrations were significantly higher in the canals compared to the coastal bays, and exceeded published guideline values indicating possible adverse ecological effects. The contaminants of greatest concern in the canals included arsenic, copper, polyaromatic hydrocarbons, polychlorinated biphenyls, and several banned, persistent pesticides (DDT, dieldrin, endrin, and chlordane). Benthic macroinvertebrate assemblages in canals were severely degraded; mean species richness, abundance, and biomass were 1/7, 1/10, and 1/20, respectively, of the values for the remaining coastal bays. A single pollution-tolerant polychaete species (Streblospio benedicti) comprised approximately three-fourths (70%) of the community in the canals. Deep (>1 m) and muddy canals were in poorer condition than shallow and sandy ones.     

Nekton habitat quality at shallow water sites in two Rhode Island coastal systems

We evaluated nekton habitat quality at 5 shallow-water sites in 2 Rhode Island systems by comparing nekton densities and biomass, number of species, prey availability and feeding, and abundance of winter flounderPseudopleuronectes americanus. Nekton density and biomass were compared with a 1.75-m² drop ring at 3 sites (marsh, intertidal, and subtidal) in Coggeshall Cove in Narragansett Bay and two subtidal sites (eelgrass and macroalgae) in Ninigret Pond, a coastal lagoon. We collected benthic core samples and examined nekton stomach contents in Coggeshall Cove. We identified 16 species of fish, 16 species of crabs, and 3 species of shrimp in our drop ring samples. A multivariate analysis of variance indicated differences in total nekton, invertebrates, fish, and winter flounder across the five sites. Relative abundance of benthic invertebrate taxa did not match relative abundance of prey taxa identified in the stomachs. Nonmetric multidimensional scaling plots showed groupings in nekton and benthic invertebrate prey assemblages among subtidal, intertidal, and marsh sites in Coggeshall Cove. Stepwise multiple regression indicated that biomass of macroalgae was the most important variable predicting abundance of nekton in Coggeshall Cove, followed by elevation and depth. In Rhode Island systems that do not experience chronic hypoxia, macroalgae adds structure to unvegetated areas and provides refuge for small nekton. All sites sampled were characterized by high abundance and diversity of nekton pointing to the importance of shallow inshore areas for production of fishes and decapods. Measurements of habitat quality should include assessment of the functional significance of a habitat (this can be done by comparing nekton numbers and biomass), some measure of habitat diversity, and a consideration of how habitat quality varies in time and space.     

Oceanographic controls on shallow‐water temperate carbonate sedimentation: Spencer Gulf,South Australia

Spencer Gulf is a large (ca 22 000 km²), shallow (<60 m water depth) embayment with active heterozoan carbonate sedimentation. Gulf waters are metahaline (salinities 39 to 47‰) and warm‐temperate (ca 12 to ?28°C) with inverse estuarine circulation. The integrated approach of facies analysis paired with high‐resolution, monthly oceanographic data sets is used to pinpoint controls on sedimentation patterns with more confidence than heretofore possible for temperate systems. Biofragments – mainly bivalves, benthic foraminifera, bryozoans, coralline algae and echinoids – accumulate in five benthic environments: luxuriant seagrass meadows, patchy seagrass sand flats, rhodolith pavements, open gravel/sand plains and muddy seafloors. The biotic diversity of Spencer Gulf is remarkably high, considering the elevated seawater salinities. Echinoids and coralline algae (traditionally considered stenohaline organisms) are ubiquitous. Euphotic zone depth is interpreted as the primary control on environmental distribution, whereas seawater salinity, temperature, hydrodynamics and nutrient availability are viewed as secondary controls. Luxuriant seagrass meadows with carbonate muddy sands dominate brightly lit seafloors where waters have relatively low nutrient concentrations (ca 0 to 1 mg Chl‐a m^?3). Low‐diversity bivalve‐dominated deposits occur in meadows with highest seawater salinities and temperatures (43 to 47‰, up to 28°C). Patchy seagrass sand flats cover less‐illuminated seafloors. Open gravel/sand plains contain coarse bivalve–bryozoan sediments, interpreted as subphotic deposits, in waters with near normal marine salinities and moderate trophic resources (0·5 to 1·6 mg Chl‐a m^?3) to support diverse suspension feeders. Rhodolith pavements (coralline algal gravels) form where seagrass growth is arrested, either because of decreased water clarity due to elevated nutrients and associated phytoplankton growth (0·6 to 2 mg Chl‐a m^?3), or bottom waters that are too energetic for seagrasses (currents up to 2 m sec^?1). Muddy seafloors occur in low‐energy areas below the euphotic zone. The relationships between oceanographic influences and depositional patterns outlined in Spencer Gulf are valuable for environmental interpretations of other recent and ancient (particularly Neogene) high‐salinity and temperate carbonate systems worldwide.     

Habitat utilization by small flatfishes in a North Carolina estuary

Distribution and abundance of flatfish species (<150 mm standard length) were related to habitat characteristics in the Newport River and Back Sound estuaries in North Carolina. Salinity, turbidity, depth, distance from marsh edge, benthic composition, and grain size were used to describe the different shallow water habitats from April through October 1994. One Scophthalmidae, seven Paralichthyidae, one Achiridae, and one Cynoglossidae species were collected during the study including juvenileParalichthys albigutta (gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder) along with multiple age classes ofCitharichthys spilopterus (bay whiff),Etropus crossotus (fringed flounder),Symphurus plagiusa (blackcheek tonguefish), andTrinetes maculatus (hogchoker). Incidental catches ofAncylopsetta quadrocellata (ocellated flounder),C. macrops (spotted whiff), andScopthalmus aquosus (windowpane) were also made. Flatfish distributions among habitats varied by species, size within species, and season. Regardless of season, the highest densities of flatfishes were found in the upper estuary. All habitats were used by one or more species and most species occurred at several habitats. Some species were significantly more abundant at specific habitat types. Ontogenetic shifts in habitat utilization were found for several species. High densities of smallP. lethostigma, C. spilopterus, S. plagiusa, andT. maculatus occurred in the upper estuary on muddy substrates. LargeP. dentatus, C. spilopterus, S. plagiusa, andT. maculatus utilized sand flats and channels in the lower estuary.     

Foraminifera from the Irish Sea glacigenic deposits at Aberdaron,western Lleyn,North Wales: Palaeoenvironmental implications

In a sequence of glacigenic sediments at Aberdaron, Foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment. All the diamict samples yielded remarkably uniform assemblages, with similar numbers of benthic specimens and benthic species per unit weight of sediment, similar planktic : benthic ratios, and similar ratios of clearly allochthonous to possibly autochthonous elements. This is precisely as predicted by the terrestrial model of sedimentation, where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the Irish Sea Basin. The results lend no support to a glacial marine model, since no faunal responses to increasingly distal sedimentary environments are observed. However, the fauna is dominated by the Foraminifera Elphidium excavatum (Terquem) forma clavata Cushman, which is commonly assumed to indicate glacial marine conditions. The modern distribution of similar assemblages suggests that it is just as likely to represent the cold, reduced salinity conditions that would have prevailed in the northern Irish Sea Basin for much of the Quaternary.