Trace fossils in middle to late triassic fluvial redbeds,pranhita‐godavari valley,south India

Several morphological varieties of trace fossils abound in Middle and Late Triassic fluvial redbeds in the Pranhita‐Godavari Valley, south India, including Skolithos, Palaeophycus, Taenidium, escape burrows, and a type of trace very similar to ‘small stuffed burrows’ from the Triassic of Greenland. Burrow morphology was influenced by local hydrodynamic conditions. The distribution of burrows was facies controlled; some forms are restricted to channel deposits whereas others occur only in floodplains. Vertical dwelling burrows (Skolithos) occur in both channel and floodplain deposits. Horizontal structures representing deposit feeding (Taenidium) are confined to nondepositional surfaces within parallel‐laminated sandstones having parting lineations that represent catastrophically emplaced sand‐sheets in channels and proximal floodplains. Vertical escape burrows are confined to what were slowly but continually accreting parallel‐laminated sands of channel bars. Horizontal dwelling burrows (Palaeophycus) and ‘small stuffed burrows’ are virtually restricted to the smaller sandsheets of floodplain drainage systems.

The burrow assemblages do not occur as recurrent associations throughout the redbed sequence, and variations in different stratigraphic levels seem to be controlled by minor differences within a broadly similar environment. The entire assemblage has components of both the Scoyenia and Rusophycus ichnocoenoses reported from East Greenland but may be considered as the Scoyenia ichnofacies characteristic of redbeds deposited in extensive floodplains dissected by small streams, even though no Scoyenia individuals are present.     

长江口芦苇和互花米草盐沼湿地蟹类洞穴分布特征及主要影响因子

蟹类洞穴是蟹类在潮间带盐沼生存、繁衍的特征性结构,具有重要的生态功能。洞穴分布特征及其影响因子的分析,是深入探讨蟹类及其洞穴的生态系统功能的重要基础。2015年10月,在崇明北滩单一芦苇(Phragmites australis)群落,单一互花米草(Spartina alterniflora)群落和芦苇-互花米草混合群落3种典型生境中,对蟹类洞穴的分布特征及其相关的大型底栖动物、植被、沉积物等的特征参数进行了调研与分析。结果表明,生境类型差异对蟹类洞穴分布特征及相关生境因子具有重要影响。蟹类洞穴的分布密度和开口直径在不同生境间存在显著差异(P0.05),且单一芦苇群落生境内洞穴密度要显著高于单一互花米草群落生境(P0.05),洞穴开口直径在单一互花米草生境要显著高于单一芦苇生境(P0.05);大型底栖动物生物量、密度、植物地下部分生物量在不同生境间差异不显著(P0.05),而植株密度、活植株高度、植物地上部分生物量以及沉积物含水率、p H、氧化还原电位在不同生境间存在显著差异(P0.05)。沉积物中值粒径,总氮含量和总碳含量在不同生境间的差异随深度不同会发生变化。不同生境主要生境因子的差异是导致蟹类洞穴分布特征不同的根本原因;蟹类洞穴分布特征受多个生境因子的综合作用。筛选的生境因子的组合虽然与洞穴分布特征具有显著相关性,但相关系数较小。未来研究中需要拓展生境因子涵盖范围,加强多因子综合作用分析。     

Assessment of field fertilization success in the infaunal polychaete Arenicola marina (L.)

Summary

Previous studies on the fertilization rates in externally fertilizing marine invertebrates have been concerned principally with free spawning epifaunal organisms (e.g., Babcock et al., 1992). A technique has been developed to investigate fertilization success in the intertidal infaunal polychaete Arenicola marina. The spawning period at the East Sands, St Andrews, is predictable from previous data, and this facilitates the study of spawning behaviour. Female worms spawn within their burrows, where the eggs may remain for several days. Male worms release sperm puddles on to the surface of the sediment at low water. The sperm is carried on the incoming tide over the surface of the sediment where it is actively drawn into female burrows by pumping. The decrease in sperm concentration as the tide comes in has been measured, and it is estimated that there are typically about 10⁶ sperm.ml^?1 in the water column and available to the female at 1 min after covering by the incoming tide. By placing the worms into artificial plastic burrows with removable stoppers, they can be transplanted into the field prior to spawning, and removed afterwards whilst retaining all the contents of the tube (worms, gametes, sediment and water).Preliminary data on the fertilization success suggests that it is highly variable (between 0% and 90%), with typical values of 40–60% for Arenicola marina. Laboratory assays investigating fertilization rate with varying sperm concentration have shown that there is a marked increase in success at 10⁴ and 10⁵ sperm per ml, with values of 30–70%. The field data therefore appear to be consistent with laboratory studies.     

New trace fossils of termites (Insecta: Isoptera) from the late Eocene‐early Miocene of Egypt,and the reconstruction of ancient isopteran social behavior

Three new ichnogenera and five new ichnospecies are described for new trace fossils of termitaria (including associated gallery systems) of subterranean termites from upper Eocene through lower Miocene rocks of northern Egypt. All but two ichnospecies (Krausichnus trompitus, ichnogen, and ichnosp. nov., and A’, altus, ichnosp. nov.) show varying degrees of affinity to nests of the extant subterranean termite species Sphaerotermes sphaerothorax (Termitidae, Macro‐termitinae).

Termitichnus qatranii (Bown, 1982) is divided into two ichnospecies, the previously named T. qatranii, and a more generalized form, T. simplicidens, ichnosp. nov. Vondrichnus obovatus, ichnogen. and ichnosp. nov., is named for simple, possibly macrotermitine nests with oblate form, and Fleaglellius pagodus, ichnogen. and ichnosp. nov., records a nest form similar to V. obovatus, but one in which successive vertical growth by chamber apposition has produced a subterranean, tower‐like structure, reminiscent of that built by extant, epigeous Cubitermes. Krausichnus trompitus, ichnogen. and ichnosp. nov., and A’, altus, ichnosp. nov., record two unique nest architectures probably produced by unknown but related species of humivorous termites. The nest architecture expressed by Krausichnus is of wholly unknown affinity and is only distantly related in form to the ichnofossils of other termite nests known from the Tertiary of Egypt.

Study of the architecture of the nests of these ancient termites reveals details important in reconstructing the phylogeny of termite nests and documents two novel blueprints for chamber expansion and society budding in what were probably primitive Macrotermi‐tinae. It also indicates that at least two constructed edifices, earlier known only as epigeous manifestations of extant termite species, were almost certainly first developed by species living underground.

The extant Macrotermitinae are a subfamily of termites originally believed to have evolved in the post‐Eocene of the Ethiopian biogeo‐graphic region. We offer fossil evidence of four distinct, possibly macrotermitine structures from upper Eocene rocks. This evidence suggests that this termite subfamily (or at least their peculiar mode of nest construction) might have evolved considerably earlier, as it is already well established and exhibits several variants by the late Eocene in Egypt.     

Distribution patterns of diatom surface sediment assemblages in the Laptev Sea (Arctic Ocean)

The modern diatom distribution in the Laptev Sea, Arctic Ocean, was investigated in 89 surface sediment samples. Diatom concentrations are relatively low showing values between 0.01×10⁶ and 6.7×10⁶ valves per gram dry sediment. Based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined: the ice diatom assemblage of the central region of the Laptev Sea, the Chaetoceros assemblage of the eastern and southeastern shelf, the Thalassiosira antarctica assemblage of the continental slope and deep sea, the freshwater diatom assemblage in the vicinity of river mouths and deltas, and the Thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central Laptev Sea shelf. The distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses. The main factors controlling the distribution of diatoms in the Laptev Sea are the riverine freshwater input during the summer which strongly affects the salinity conditions, and the sea-ice extent. Furthermore, the composition of the Thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes.     

Traces and related chemical changes in a Late Ordovician paleosol,Glossifungites ichnofacies,southern Appalachians,USA

Traces interpreted as Skolithos sp. in a Glossifungites ichnofacies occur in the upper part of the Beans Gap Claystone paleosol, in association with a Late Ordovician marine erosional surface. Paleosol color and whole‐rock chemistry are distinctly different in the vicinity of burrows, which are enveloped by olive gray mottles, 1 to 10 cm in diameter, in which total iron (measured as Fe₂O₃) is 30% lower than in grayish red, “unaltered”; claystone.

Post‐pedogenic bioturbation increased permeability locally and permitted the introduction of marine fluids and coarser sediment into the top of the paleosol. Anaerobic microbial decay of organic matter in the burrows and surrounding claystone permitted reduction (and mobilization) of formerly oxidized iron, which then combined with marine‐derived sulfate to form pyrite, both within burrows and along oxidation‐reduction fronts in the claystone proximal to burrows. Pyrite was later converted to hematite as a result of outcrop‐related oxidation by meteoric water.

Paleosols formed in coastal marine settings are especially susceptible to early diagenetic alteration related to marine hydromorphism. Differentiating these ichnologic and diagenetic effects from true pedogenic ones is essential when interpreting paleosols in paralic sequences.     

再论假裸枝叠层石科*

内蒙古桌子山地区中奥陶统公乌素组遗迹化石十分丰富.本文共鉴定、描述14个遗迹属、17个遗迹种,其中1新遗迹属——Biscopulatichnus、4新遗种和6未定种.并根据不同遗迹属在不同层位中的相对丰度,建立了4个遗迹组合,自下而上的顺序是:1. Taenidium-Phycodes 组合;2. Volkichnium 组合;3. Helminthopsis 组合;4. Granularia-Circulichnus 组合,大致相当于 Seilacher (1967) 的 Zoophycos 遗迹相,反映出公乌素组沉积期,水体较深且宁静、缺氧、有机质含量高,推测应为大陆斜坡环境.     

Effects of the burrowing mud shrimp,Upogebia yokoyai,on carbon flow and microbial activity on a tidal flat

Mud shrimps, Upogebia spp., are major constituents of macrobenthic communities in tidal flats in Japan. The impact of Upogebia yokoyai on carbon flow on tidal flats was examined by comparing CO₂ emission rates from plots with and without burrows in the Kurose River estuary, Japan. In situ CO₂ emission rates from plots with burrows were significantly higher than from those without. Laboratory measurements using sediment core samples that excluded respiration of macrobenthic organisms showed similar trends. Although there were no significant differences in grain size distribution, water content, or ignition loss between the sediment cores with and without burrows, oxidation–reduction potential was significantly higher in sediment cores with burrows. Analysis of phospholipid fatty acids (PLFA) indicated that microbial biomass and community structure did not differ significantly between cores with and without burrows. However, microbial respiration activity, as indicated by CO₂ emission rates per total PLFA content, was significantly higher in sediment cores with burrows than in those without. Our results indicate that burrows of U. yokoyai change the physicochemical conditions and increase microbial activity in the sediment, significantly affecting carbon flow in the tidal flat.     

Influence of setting,sieve size,and sediment depth on multivariate and univariate assemblage attributes of coral reef-associated mollusc death assemblages from the Gulf of Aqaba

Measures of diversity and ecology of marine invertebrate assemblages depend on a variety of factors including environmental conditions and methodological decisions. In this study, the influence of such factors on multi- and univariate assemblage parameters of molluscan death assemblages from the Gulf of Aqaba (Red Sea, Jordan) was evaluated. Sediment samples were collected at two coral reef types, a patch reef at 13 m of water depth characterized by fine-grained sediments and a Millepora-fringing reef with coarse-grained sediments at 5 m of water depth. The upper and lower 10 cm of the sediment column were separately removed and sieved with mesh sizes of 1 and 2 mm. A large dataset of 6400 bivalve and gastropod shells was compiled to evaluate how setting, sediment depth, and sieve size influenced taxonomic composition and species richness, species-abundance patterns and the Shannon–Wiener index, the number of drilled shells per species and drilling frequency (DF) of the assemblage. Setting had the strongest impact on all aspects, followed by sieve size, but sediment depth was insignificant, probably due to complete homogenization of the sediments by reworking and bioturbation. Multivariate assemblage parameters distinguished much better between categories (setting, sieve size) than univariate measures. Sieve size-related disagreements recognized between the two higher taxa are mostly due to the underlying difference in body-size distribution of bivalve and gastropod assemblages. We conclude that species richness and other ecological characteristics of molluscan death assemblages in coral reef-associated sediments will most strongly reflect habitat complexity of the sites chosen, are significantly influenced by methodological decisions (i.e., sieve size), will only poorly preserve temporal patterns, and the results will differ between bivalves and gastropods.     

Triassic trace fossils from lacustrine shoreline deposits of the Passaic formation,douglassville, pennsylvania

Lake‐margin deposits of the Late Triassic Passaic Formation, Douglassville, Pennsylvania, have yielded a moderate variety of trace fossils. The greatest diversity and abundance of trace fossils occurs on the sole of a thin gray claystone overlain and underlain by gray siltstones. Specimens of Cochlichnus anguineus, Helminthoidichnites tenuis, Helminthopsis hieroglyphica, Treptichnus pollardi, and paired trails reflect simple, unspecialized, horizontal grazing as well as feeding traces under very shallow water lacustrine conditions. The lack of commonly associated Scoyenia burrows in these deposits may possibly be related to the degree of maturation of the organic debris available. The traces, as well as a lack of meniscate burrows, compare favorably to the Mermia ichnofacies, except Passaic deposits exhibit evidence of subaerial exposure. This unit most likely records a lacustrine expansion whereby grazing trails were emplaced under fully subaqueous conditions. Subsequent shallowing and desiccation, followed by sediment influx during rainstorms, favored preservation of these traces.

In contrast, the Scoyenia ichnofacies consists of feeding burrows of Scoyenia gracilis and Spongeliomorpha milfordensis within reddish brown siltstones and mud‐stones (redbed sequence). The Scoyenia ichnofacies records limited exploitation, by opportunistic infaunal deposit feeders, of lake‐margin nutrients carried in during occasional rainstorms that punctuated otherwise extended periods of aridity.     

The relationship between Chironomus plumosus burrows and the spatial distribution of pore-water phosphate, iron and ammonium in lake sediments

1. To study the influence of chironomids on the distribution of pore‐water concentrations of phosphate, iron and ammonium, we conducted a laboratory experiment using mesocosms equipped with two‐dimensional pore‐water samplers, filled with lake sediment and populated with different densities of Chironomus plumosus. 2. Specially designed mesocosms were used in the study. A 6‐mm deep space between the front plate and the pore‐water sampler at the back plate was just thick enough to allow the chironomids to live undisturbed, yet thin enough to force all the burrows into a two‐dimensional plane. 3. The courses of the burrows were observed during the experiment as oxidised zones surrounding them, as well as being identified with an X‐ray image taken at the end of the experiment. 4. We investigated the relationship between C. plumosus burrows and spatial patterns of pore‐water composition. Concentrations of the three ions were significantly less around ventilated burrows (54% to 24%), as bioirrigation caused a convective exchange of pore‐water enriched with dissolved species compared with the overlying water, and also because oxygen imported into the sediment resulting in nitrification of ammonium, oxidation of iron(II) and a co‐precipitation of phosphate with Fe(III) oxyhydroxides. 5. In mesocosms with chironomids, new (redox) interfaces occurred with diffusive pore‐water gradients perpendicular to the course of burrows and the site of major phosphate, ammonium and iron(II) release shifted from the sediment surface to the burrow walls.     

Spider assemblages in bird burrows

The arachnofauna of bird burrows, which are excavated in the soil, is incompletely understood. The bird burrows have a potential to serve as refugia for cavity-adopting spider species particularly in anthropogenic habitats formed by sand mining, which otherwise suffer from a limited availability of other types of cavities. We hypothesized that the presence of abundant food resources and safe shelter in bird burrows excavated in the soil allow the existence of specialized assemblage of spiders, similarly to those known from cavities and nests made by other birds and mammals. Here we examined 353 burrows that had been previously occupied by Riparia riparia, Merops apiaster or Passer montanus. The burrows were examined in early May and early September in 24 Czech sand pits and construction sites. The burrows hosted a species-rich assemblage of spiders that, however, occurred at low abundances. The spiders were represented prevalently by species known to have distributions centered in anthropogenic and urban habitats, including species that were never observed outside of heated buildings in the study area and species that only were previously known from mammalian burrows and loess and karstic soil crevices. Spider assemblages strongly differed between bird burrows and cavities and nests made by other birds and mammals. The species composition and overall low abundance of spiders in bird burrows was unexpected and was in strong contrast to previous observations of spider assemblages in cavities and nests made by other birds and mammals. Concluded, we rejected the initial hypothesis and, instead, we have shown that bird burrows are rarely occupied by spiders and if occupied, the spider species that adopt old bird burrows and the nests inside of them predominantly consist of species known to have their distribution centered to anthropogenic and urban habitats.     

Temporal and spatial variability in midge assemblages from a backwater lake in Pool 2, Mississippi River

The temporal and spatial variability in the midge assemblage found in a backwater lake of the Mississippi River was examined. Bi-weekly samples were taken during the summers of 1987 and 1988. Four taxa of chironomids were found. The population density and sizes of chironomids, and the proportion that each taxon comprised of the midge assemblage, varied significantly in time and space. In an attempt to examine whether the variability noted was related to sediment accretion in the lake, sedimentation rates were measured. There were few correlations among sedimentation rate or the organic matter content of the collected sediment and the structure of the midge assemblage. Those few correlations that were statistically significant were low and often paradoxical. For example negative relationships were found between the density and size of Chironomus spp., a detritivore, and the amount of sediment deposited or its organic matter content. Also no significant relationships were found between the density of the predator Cryptochironomus spp. and the density of other chironomids (potential prey). These negative findings indicate that factors other than food, such as sediment texture, may be more important than food availability in structuring chironomid assemblages in backwater areas. There was spatial variability in the densities and sizes of chironomids that may be explained by differences in sediment texture and organic matter. This suggests that short-term inputs of sediment (as ascertained by sediment traps) may not greatly influence midge assemblages while the long-term changes in sediment composition may have large influences.     

Middle Pennsylvanian Ichnofauna from Eastern Oklahoma,USA

The Keota site, in the Middle Pennsylvanian (Desmoinesian) Keota Sandstone Member, McAlester Formation (Krebs Group) of Haskell County, Oklahoma, yields an extensive ichnofossil assemblage of arthropod trackways, insect resting traces, arthropod feeding and grazing traces, fish swimming traces, and tetrapod footprints. This ichnofossil assemblage occurs in a 0.8 to 1.5-m-thick unit of thinly laminated and ripple-laminated sandstone at the base of the Keota Sandstone Member that is interpreted as a tidal flat sandstone. The arthropod traces are assigned to the ichnotaxa Diplichnites gouldi Gevers types A and B, Diplopodichnus biformis Brady, Paleohelcura tridactyla Gilmore, Tonganoxichnus buildexensis Mángano, Buatois, Maples and Lanier, Gordia marina Emmons, cf. Cochlichnus sp. and Treptichnus bifurcus Miller. The fish swimming traces are assigned to Undichna britannica Higgs, and the tetrapod tracks to Notalacerta ichnosp. and Pseudobradypus ichnosp. The Keota ichnofossil assemblage thus documents the first North American Pennsylvanian record of Paleohelcura tridactyla and the first record of Pseudobradypus from the western United States. This ichnofossil assemblage also provides compelling evidence of a freshwater habitat in a tidal flat setting during deposition of the fossil-bearing sandstone at the Keota site. Indeed, the Keota ichnofossil assemblage is characteristic of a Carboniferous-Permian Tonganoxichnus assemblage that identifies nonmarine tidal flat settings.     

福建敖江口表层沉积硅藻空间分布特征

为探讨福建敖江口表层沉积硅藻空间分布特征,2019年7月对敖江口进行表层沉积硅藻的采样调查,并研究了硅藻与环境因子的关系。结果表明,从13个站点共检出硅藻114种,隶属于39属。硅藻丰度具有从河口向外海先减少后增加的变化特征。聚类分析表明,主要硅藻属种可划分为淡水种组合带和半咸水-咸水种组合带。典型对应分析（CCA）表明,表层海水温度和盐度是影响硅藻分布的主要环境变量。河口区盐度相对较低,主要分布淡水种双面曲壳藻、优美曲壳藻和颗粒沟链藻;外海区北部盐度相对较高,主要分布咸水种流水双菱藻;外海区南部盐度相对较低,主要分布淡水种优美曲壳藻和颗粒沟链藻;滩涂的沉积物较粗,主要分布优美曲壳藻。此外,河口区和外海区南部可能存在一定的水体污染。     

The Rove Beetles (Coleoptera, Staphylinidae) of Exposed Riverine Sediments in Scotland and Northern England: Habitat Classification and Conservation Aspects

Exposed riverine sediments (ERS) by four rivers in Scotland and northern England were sampled for beetles in 1996 and 1997. One hundred and sixty rove beetle (Staphylinidae) species lists were analysed using ordination and classification techniques in order to identify habitat groups within and between catchments and to assess which factors were affecting species assemblage distribution. There were major differences between the species assemblages of ERS by rivers of highland and lowland catchments. Within catchments, assemblage distribution was mainly influenced by the position of sites within the catchment; vegetation cover and sediment composition had less influence. The number of rove beetle habitats was not the same as those for ground and phytophagous beetle groups, indicating that conservation considerations should take into account variations in ERS habitat diversity. A considerable number of records of nationally rare and scarce rove beetle species were recorded, most on ERS by rivers and tributaries unaffected by river management or engineering.     

Modern benthic diatom distribution in a hypersaline coastal lagoon: the Lagoa de Araruama (R.J.), Brazil

Diatom assemblages identified in 75 surface sediment samples in a shallow hypersaline coastal lagoon (Lagoa de Araruama, R.J., Brazil) are mainly composed of holo-euryhaline and marine euryhaline benthic taxa. The lagoon is characterized by an assemblage dominated by Cocconeis placentula var. euglypta, associated with Catenula adhaerens and Cocconeis diminuta. However, different areas, characterized by specific assemblages, have been identified. Their distribution seems to be related to (1) fluctuations in bathymetry, influenced by water inputs from the ocean and from rivers adjacent to the lagoon; (2) fluctuations in salinity through the influence of marine water and the precipitation–evaporation rate. Moreover, the distribution of associations characterized by the presence of Nitzschia palea, N. pusilla and Fallacia cryptolyra suggests the influence of man-induced activities. Although these diatoms are not dominant, their wide distribution inside the lagoon, favored by local wind-hydrodynamics, suggest a large impact of anthropic activities (e.g. freshwater and organic sewages).     

Dynamics of a cyanobacterial bloom in a hypereutrophic reservoir,Lake Chivero,Zimbabwe

Blooming and non-blooming periods between 2004 and 2006 in a hypereutrophic reservoir, where cyanobacterial blooms have previously been reported to be permanent, presented an opportunity to characterise factors that may favour cyanobacterial dominance. As a bloom developed in May 2004, a shift to dominance by Microcystis aeruginosa, similar to competitive exclusion, was observed. The period of M. aeruginosa dominance was characterised by the lowest Secchi depth and euphotic zone depth readings, and a decline of non-buoyant species because of competitive exclusion by M. aeruginosa, which reduced light availability in the water column. After the bloom collapsed, the euphotic zone depth increased, followed by the establishment of a Cryptomonas–Cyclotella phytoplankton assemblage. Cyanobacterial dominance within the phytoplankton assemblage was favoured by an extended stratification and was limited by nitrogen (mainly ammonium) availability. Other taxa were limited by light availability, as shown by their decline when M. aeruginosa dominated. The period of extended stratification, an increase in ammonium concentration and a decrease in nitrate concentration promoted dominance by M. aeruginosa.     

A New Ichnospecies of Arthrophycus from the Late Carboniferous (Pennsylvanian) of Michigan,USA

A unique ichnofossil assemblage from Pennsylvanian-age sandstones near Eaton Rapids, Michigan, USA, comprises straight-to-curved traces preserved in convex hyporelief, with the transverse ridges and median grove associated with the ichnogenus Arthrophycus. The Michigan traces show some branching or pseudo-branching (also known from other Arthrophycus specimens) and are among the smallest structures (millimeters in diameter) attributed to this ichnogenus. The orientation of the Michigan Arthrophycus burrows is distinct from other ichnospecies of this taxon in the pronounced co-planar alignment of the burrows, as opposed to the multiplanar, interweaving, “bundled” nature typical of the ichnogenus. On this basis we assign the Michigan specimens to a new ichnospecies of Arthrophycus. The “paralleling behavior” of the new taxon may reflect a strategy of the tracemaker to avoid previous burrows and reflect differences in resource availability or current energy. This new taxon supports previous records of the occurrence of this ichnogenus in Upper Carboniferous strata.