BRYOZOAN MUD-MOUNDS FROM THE UPPER ORDOVICIAN JIFARAH (DJEFFARA) FORMATION OF TRIPOLITANIA, NORTH-WEST LIBYA

Abstract:  A bryozoan fauna from carbonate mud-mounds is described from subsurface well cores from the Upper Ordovician (Lower Ashgill) Jifarah (Djeffara) Formation of Tripolitania, north-west Libya. Among a diverse assemblage dominated by trepostomes, nine species of bryozoans are identified, including Jifarahpora libyensis gen. et sp. nov. Delicate and robust branching, encrusting and nodular bryozoan growth forms are all common. The bryozoan-rich limestones are mostly mudstones and wackestones, with bafflestone and floatstone textures, but the mounds apparently lack organic framework and microbial fabrics. Regional geophysical data indicate rapid thickness changes between wells, where mound complexes locally up to 100 m thick had limited topographic relief over the surrounding sea floor. The mounds formed in a high-latitude, cool-water carbonate belt that extended widely across the northern margin of Gondwana. Quaternary analogues from the Great Australian Bight suggest that these early Ashgill mounds may have developed in slope environments during an episode of glacial lowstand that preceded the late Ashgill, Hirnantian glacial event.     

Petrology and paleogeographic significance of Tertiary nannoplankton-foraminiferal limeston,Guam

The tertiary stratigraphic column on the island of Guam, in the Mariana Island Arc of the western Pacific, is composed largely of volcanic rocks and limestones of shallow-water reef and bank facies. Small amounts of fine-grained limestones, of Eocene, Oligocene and Miocene age, occur interbedded with the volcanic rocks and reef limestones, and consist chiefly of planktonic foraminiferal tests embedded in a matrix of calcareous nannofossils. Although compositionally these pelagic carbonates are nearly identical to nannoplankton-foraminiferal oozes of the deep-sea floor, their deposition probably occurred at comparatively shallow depths — from a few hundred to perhaps 1000–2000 meters rather than several kilometers. The most favorable paleogeographic settings for pelagic deposition of this kind were probably intra-arc basins and shelf areas within the paleo-Mariana Island Arc during periods of volcanic inactivity. The spatial association of these pelagic limestones with shallow-water reef complexes, or with beds of redeposited, reef-derived coarse skeletal material, may serve to differentiate them from their deep-sea counterparts.     

Late Quaternary stratigraphy and paleoecology of northwest Labrador Sea

Sedimentological study of 20 piston cores from the northwestern Labrador Sea shows that thin bedded distal turbidites are important constituents of the Quaternary strata on the continental slope and rise. Sedimentation on the outer shelf (ca. 500–900 m) is dominated by ice-rafting and hemipelagic deposition. Detailed study of two outer shelf cores reveals a stratigraphic record extending to oxygen isotopic stage 9. Studies of foraminifera and dinoflagellates show that subarctic surface waters penetrated into the northern Labrador Sea during the early-middle glacial stages and pollen data indicate that northward advection of warm air masses occurred at the same time. Microfossil data indicate that late glacial stages were characterized by year around sea-ice cover and arctic surface water, and by the dominance of cold, dry Arctic air masses. Transitions from glacial to interglacial stages are marked by the presence of low salinity melt water. These data support models which postulate that open water in the Labrador Sea played an important role in supplying moisture to Laurentide and Greenland ice-sheets.     

Control mechanisms of Carboniferous brachiopod zones in eastern Australia

Analysis of the Carboniferous brachiopod zones of eastern Australia shows that they were affected by two major controlling factors - eustatic changes of sea level, and a deterioration (cooling) of climate. Eustatic lowering of sea level caused the removal of the sea from narrow shelf areas and a loss of habitat, and was responsible for the first (late early to middle Visean) of two major episodes of faunal extinction. Subsequent transgression restored a modified warm-water cosmopolitan fauna to the shelf regions. Smaller changes in sea levels were probably responsible for the abrupt disappearance of many species or genera at zonal boundaries and their replacement by a new set of species and genera in succeeding zones. The second major episode of extinction was caused by the lowering of temperature in the latest Visean to early Namurian because of the rapid southerly movement of Australia. The warm water cosmopolitan fauna was eliminated and replaced by the low-diversity Gondwana fauna. Both mechanisms produced particular faunal signatures. The diversity of faunas on either side of the hiatus produced by eustatic lowering of sea level is constant in areas with uniform climatic conditions, and in warm to temperate regions there are low levels of endemism. Faunas associated with a sudden lowering of temperature suffer a significant drop in diversity but are characterized by a high level of endemism.     

Anthracoporella mounds in the Late Carboniferous Auernig Group,Carnic Alps (Austria)

Summary A heretofore undocumented example of skeletal mounds formed by the dasycladacean algaAnthracoporella spectabilis is described from mixed carbonate-clastic cycles (Auernig cyclothems) of the Late Carboniferous (Gzhelian) Auernig Group of the central Carnic Alps in southern Austria. The massive mound facies forms biostromal reef mounds that are up to several m thick and extend laterally over more than 100 m. The mound facies is developed in the middle of bedded limestones, which are up to 16 m thick. These limestones formed during relative sea-level highstands when clastic influx was near zero. The mound facies is characterized by well developed baffler and binder guilds and does not show any horizontal or vertical zonation. Within the massive mound faciesAnthracoporella is frequently found in growth position forming bafflestones and wackestones composed of abundantAnthracoporella skeletons which toppled in situ or drifted slightly.Anthracoporella grew in such profusion that it dominated the available sea bottom living space, forming ‘algal meadows’ which acted as efficient sediment producers and bafflers. BecauseAnthracoporella could not provide a substantial reef framework, and could not withstand high water turbulence, the biostromal skeletal mounds accumulated in shallow, quiet water below the active wave base in water depths less than 30 m. The massive mound facies is under- and overlain by, and laterally grades into bedded, fossiliferous limestones of the intermound facies, composed mainly of different types of wackestones and packstones. Individual beds containAnthracoporella andArchaeolithophyllum missouriense in growth position, forming “micromounds’. Two stages of mound formation are recognized: (1) the stabilization stage when bioclastic wackestones accumulated, and (2) the skeletal mound stage when the sea-bottom was colonized byAnthracoporella and other members of the baffler and binder guilds, formingAnthracoporella bafflestones and wackestones of the mound facies. A slight drop in sea-level led to the termination of the mound growth and accumulation of organic debris, particularly calcareous algae, fusulinids, crinoids and bryozoans, forming well bedded limestones, which overlie the mound facies     

Trace fossils of the Jurassic,blue Lias,Lyme Regis,Southern England

The Lower Jurassic, Blue Lias Formation at Lyme Regis, Dorset, England is rhythmically bedded with symmetrical rhythms consisting of laminated black shale followed by dark then pale marls (sometimes cemented into pale limestones) and back to laminated black shale. Its trace fossil fauna includes nine ichno‐genera and represents a shallow shelf paleoenviron‐ment. The ichnofauna occurs in three assemblages named after consistently occurring ichnogenera. A Chondrites assemblage (diversity = 1 ichnogenus) and a Chondrites‐Arenicolites assemblage (diversity = 2–3 ichnogenera) are typical of dark marls but may penetrate tops of laminated black shales. A thalassi‐noides‐Chondrites‐Arenicolites assemblage (diversity up to 7 ichnogenera) is typical of pale marls or limestones. Blue Lias limestones are diagenetic: dark laminated limestones and pale bioturbated limestones are cemented equivalents of laminated black shales and pale marls, respectively. However, pale burrow fills in darker sediments and vice versa confirm the rhythms are primary. Rhythms represent redox cycles, fluctuating from anoxic laminated black shales lacking mac‐robenthos or infauna (bioturbation index = 0) to oxic, bioturbated, pale marls or limestones with large mac‐robenthos such as Gryphaea or Plagiostoma and diverse infauna (bioturbation index = 5).     

Bryozoans of the Weddell Sea continental shelf,slope and abyss: did marine life colonize the Antarctic shelf from deep water,outlying islands or in situ refugia following glaciations?

Aim At the height of glaciations such as the Last Glacial Maximum (LGM), benthic life on polar continental shelves was bulldozed off nearly all of the Antarctic shelf by grounded ice sheets. The origins of the current shelf benthos have become a subject of considerable debate. There are several possible sources for the current Antarctic shelf fauna, the first of which is the continental slope and deep sea of the Southern Ocean. The high levels of reported eurybathy for many Antarctic species are taken as evidence supporting this. A second possible source for colonists is the southern margins of other continents. Finally, shelves could have been recolonized from refugia on the continental shelves or slopes around Antarctica. The current study investigates whether the patchily rich and abundant biota that now occurs on the Antarctic continental shelf recolonized from refugia in situ or elsewhere. Location Weddell Sea, Antarctica. Methods We examined bryozoan samples of the BENDEX, ANDEEP III and SYSTCO expeditions, as well as the literature. Using similarity matrices (Sørensen coefficient), we assessed similarities of benthos sampled from around Antarctica. By assessing numbers of species shared between differing depths and adjacent shelf areas, we evaluated the origins of cheilostome bryozoan communities. Results Bryozoans decreased from 28, 6.5 and 0.3 colonies per trawl, and 0.16, 0.046 and 0.0026 colonies per cm² of hard surface from shelf to slope to abyssal depths. We found little and no support for recolonization of the Weddell Sea shelf by bryozoans from the adjacent slope and abyss, in the scenario of LGM faunal wipe‐out. The Weddell Sea shelf bryozoan fauna was considerably more similar to those on other Antarctic shelves than to that of the adjacent (Weddell Sea) continental slope. The known bryozoan fauna of the Weddell Sea shelf is not a subset of the Weddell Sea slope or abyssal faunas. Main conclusions We consider that the composition of the current Weddell Sea bryozoan fauna is most easily explained by in situ survival. Thus we consider that at least some of the Weddell Sea fauna persisted throughout the LGM, although not necessarily at the same locations throughout, to recolonize the large area currently occupied.     

Fossils, sediments, tectonics

Tectonic displacement and small-scale tsunamis apparently affected deposition of the Kolymbia limestone, Cape Vagia, Rhodes, Eastern Mediterranean. Coarse beds interrupt the sequential build-up of this Pliocene–Pleistocene bryomol limestone. Celleporid bryozoans, bivalves, and brachiopods dominate these beds. The palaeoecology of the thicket-forming Celleporaria palmata is re-evaluated and subsequently revised. The limestone comprises two parasequences in a transgressive systems tract, and deposition occurred at palaeodepths between 30 and 120 m. At intervals, tectonic movements lowered relative sea level and sent slumps of shallow-water fauna downslope. The depositional history was validated using independent sets of data: sediment structure and grain size, palaeobathymetry using bryozoan growth forms and occurrences of modern representatives of bryozoans and other taxa, basin configuration, and regional tectonics. Concordance of these lines of evidence provides a means of evaluating confidence in palaeoenvironmental inferences.     

THE DISTRIBUTION OF WHITE-SIDED (LAGENORHYNCHUS ACUTUS) AND COMMON DOLPHINS (DELPHINUS DELPHIS) VS. ENVIRONMENTAL FEATURES OF THE CONTINENTAL SHELF OF THE NORTHEASTERN UNITED STATES

Sightings of white-sided ( Lagenorhynchus acutus ) and common dolphins ( Delphinus delphis ) from survey vessels operating on the continental shelf of the northeastern United States were recorded during spring and fall of six years. Distributions of these sightings were compared with sea surface temperature and salinity, and bottom topography. The apparent geographic distributions of the two species are complementary, although there is a broad overlap. White-sided dolphins occurred primarily within the Gulf of Maine, but also on Georges Bank and in the mid-Atlantic region. Common dolphins were abundant within a broad band paralleling the continental slope (100–200 m depth contour) from latitude 35°N to the northeast peak of Georges Bank. Sightings of this species were distributed primarily along the edge of the continental shelf south of 40°N in spring and north of this latitude in fall. Few sightings of common dolphins occurred in the Gulf of Maine.
Although both species of dolphins were sighted more frequently in areas of high sea floor relief, white-sided dolphins occurred in areas where sea surface temperatures and salinities are low while common dolphins were sighted in warmer, more saline waters. However, these environmental conditions may be only secondarily influencing dolphin distribution. Seasonal variation in sea surface temperature and salinity, and local nutrient upwelling in areas of high sea floor relief may affect preferred prey abundances, which in turn may affect dolphin distribution.     

The schulterkofel section in the Carnic Alps,Austria: Implications for the carboniferous-permian boundary

Summary The upper part of the LowerPseudoschwagerina Limestone (Rattendorf Group), outcropping on the northwestern flank of Schulterkofel Mountain, Carnic Alps (Austria) is described with special emphasis on fusulinid microfossils and facies. This fusulinid-rich section offers an ideal opportunity for biostratigraphy in defining the Permo-Carboniferous boundary in this region. The LowerPseudoschwagerina Limestone is composed of shallow-marine limestones with intercalated thin siltstone and sandstone beds. Fusulinid limestones are represented by two types of wackestones, both containing large quantities of smaller foraminifers. Fusulinid grainstones are rare. Limestones rich in fusulinids were found only within the bedded limestone facies in beds both below and especially above siliciclastic intercalations. This may indicate that the best living conditions for fusulinids existed immediately before and especially after the climax of a regressive phase (sea-level lowstand). The fusulinid limestones were deposited within a protected, shallow-marine shelf environment with normal salinity. Pseudoschwagerinid fusulinids appear in the upper part of the LowerPseudoschwagerina Limestone, in samples SK 107d (undeterminable species) and SK 108, i.e. between 92 m and 93 m above the base of the section within a bedded limestone immediately above the uppermost clastic intercalation. The fusulinid fauna is represented by about 30 species belonging to only a few genera. Species ofTriticites andRugosofusulina dominate, whereas those ofDaixina, Rugosochusenella andPseudofusulina are rare. A characteristic feature of the fauna is the strong similarity with fusulinid faunas described from Russia as well as from Middle and East Asia. Some of the described fusulinids are new for the Carnic Alps. The first appearance ofPseudoschwagerina andOccidentoschwagerina (Occidentoschwagerina alpina Zone) in the upper part of the LowerPseudoschwagerina Limestone in the Schulterkofel section defines the position of the Carboniferous-Permian boundary.     

Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea

The distribution of recent shallow-water benthic foraminifera in surface sediment samples from cool-water carbonate environments of the Oran Bight, Alboran Platform and Mallorca Shelf in the Western Mediterranean Sea was studied. Multivariate statistical analyses resulted in the identification of species assemblages, representing different environmental settings. In all three regions the assemblages show a distinct bathymetric zonation that is mainly attributed to the distribution of rhodoliths and related substrates, but also to water turbulence and the availability of food at the sea floor. The live assemblages (Rose Bengal stained individuals) are characterised by rather low diversity and low standing stocks, likely reflecting seasonal population dynamics. In the Oran Bight, elevated standing stocks of “high food”-taxa suggest the impact of anthropogenic eutrophication on the near-coastal benthic ecosystems of this area. The diversity of the dead assemblages is higher than in siliclastic shelf ecosystems of the Mediterranean Sea but lower when compared to carbonate environments of the Levantine Sea. This regional difference is mainly attributed to lower sea surface temperatures and the lack of Lessepsian invaders in the western Mediterranean Sea. In all study areas, a distinct faunal change occurs between approximately 80–90 m water depth. This change coincides with the lower distribution limit of living rhodoliths at the shelf of Mallorca, providing coarse-grained substrates that are dominated by attached taxa. Below this depth interval, the fauna shows regional differences depending on the grain-size and related accumulation of organic material. Fine-grained substrates with infaunal niches are restricted to low-energy environments on the deeper shelf southwest off Mallorca.     

Early Cambrian provincialism and biogeographic boundaries in the North Atlantic region

Early Cambrian lithofacies and their stratigraphic context, characteristic of a number of tectonic elements within the North Atlantic region, are interpreted with respect to depositional environment and related trilobite provincialism. Faunas of the North American province are typically indigenous to shallow, warm water on a sand-carbonate shelf on the North American craton; those of the Scandian province to shallow cold water with predominantly clastic deposition on the European platform; those of the Avalonian province to shallow cold water with predominantly clastic deposition fringing islands and rises on the Iapetus Ocean floor; Intermediate zone faunas, consisting of North American, Avalonian and endemic elements, to the slope or margin of the North American shelf; faunas of the Tethyan province to a shelf bordering Gondwanaland ranging from warm to cold at different times and different places, and under some Avalonian influence in the later Early Cambrian; and a pelagic realm characterized by agnostids. Biogeographic boundaries are related to the position of the thermocline and to light regimen, which determines the biogeography of autotrophs and hence of provincial niche structure. Provincialism is determined by gross environmental differences reinforced by biotic factors.     

Crossing the boundary: an elasmobranch fauna from Stevns Klint,Denmark

The chondrichthyan faunas from the Danish Maastrichtian chalk and the K/T boundary clay, the Fiskeler, are described for the first time. The rich and diverse fauna discovered in the late Maastrichtian chalk experienced a massive drop in diversity prior to the boundary. However, the fauna started to recover immediately after the deposition of the impact layer during earliest Danian times and had regained much of its diversity during the first few millennia after the bolide impact. Precision sampling has made it possible to document the recovery of the fauna, which did not suffer an extinction event of the same magnitude, as apparently observed in Morocco. At Stevns Klint, only 33 per cent of the chondrichthyan fauna became extinct compared with the 96 per cent in Morocco. The drop in diversity before the boundary is attributed to a sudden change in sea level. Among the sharks found in the chalk and Fiskeler are rare species such as Parasquatina and Echinorhinus and the first representative of Nebrius in Europe.     

Patterns in the use of space by benthic communities on two coral reefs of the Great Barrier Reef

A rapid benthic line-transect survey method for use by non-specialist observers is described. At both Davies Reef (mid-continental shelf) and Myrmidon Reef (outer-continental shelf) in the central Great Barrier Reef a set of 6 sites of varying depths on the reef flat, crest and slope were sampled using this method. At least 10 contiguous 10 m transects were made at each site. Benthic organisms were recorded as life forms with categories based on both high level taxa and morphologies, and including scleractinian corals, alcyonarians, sponges, algae and others. Percentage cover data for 19 benthic categories are presented for all sites. Coral cover on both reefs is high on the crest and slope but low on the reef flat. At all sites the cover of soft corals and sponges is much less than cover of hard corals and algae. Abundances of soft corals and sponges increase with depth. Analysis of gaps between hard corals show that many colonies grow close to each other (<1 cm)even when total coral cover is low.     

Pockmarks enhance deep‐sea benthic biodiversity: a case study in the western Mediterranean Sea

Aim Pockmarks are craters on the sea floor formed by sub‐sea‐floor fluid expulsions, which occur world‐wide at all ocean depths. These habitats potentially host a highly specialized fauna that can exploit the hydrocarbons released. Pockmarks at relatively shallow depths can be easily destroyed by human activities, such as bottom trawling. In the present study, we investigated the combined effects of sea‐floor heterogeneity, rate of fluid emission and trophic conditions of different pockmarks on the biodiversity of the deep‐sea assemblages. Location Continental slope of the Gulf of Lions, western Mediterranean Sea, at water depths from 265 to 434 m. Methods We investigated the biodiversity associated with sea‐floor pockmarks that are both inactive and that have active gas emissions. Control sites were selected on the sea floor outside the influence of the gas seepage, both within and outside the pockmark fields. We examined the combined effects of: (i) sea‐floor heterogeneity; (ii) variable levels of fluid (gas) emissions; and (iii) trophic characteristics of the meiofaunal assemblage structure and nematode diversity. Results Sediments within the pockmark fields had lower meiofaunal abundance and biomass when compared with the surrounding sediments that were not influenced by the gas seepage. Although several higher taxa were absent in the pockmarks (e.g. Turbellaria, Tardigrada, Cumacea, Isopoda, Tanaidacea, Nemertina and Priapulida, which were present in the control areas), the richness of the nematode species within all of these pockmarks was very high. About 25% of the total species encountered in the deep‐sea sediments of the investigated areas was exclusively associated with these pockmarks. Main conclusions We conclude that both active and inactive pockmarks provide significant contributions to the regional (gamma) diversity of the continental slope in the western Mediterranean Sea, and thus the protection of these special and fragile habitats is highly relevant to the conservation of deep‐sea biodiversity.     

Genesis of stromatactis in an upper jurassic carbonate buildup (Mlynka,Cracow region,Southern Poland): Internal reworking and erosion of organic growth cavities

Summary The Middle Oxfordian strata in the southern part of the Cracow-Wielun Upland consist of platy and bedded limestones (‘normal facies’), of massive limestones as well as locally of mass flow sediments. Massive limestones, prevailing in the Upper Oxfordian, form commonly carbonate buildups, which are made up predominantly of cyanobacterial allochems and to a minor amount of siliceous sponges. Stromatactis can be best observed in the Mlynka quarry. They occurs in the uppermost part of slope sediments close to a cyanobacterial-sponge buildup. The bedding-plane of the slope sediments is directly overlain by debris-flow and grain-flow sediments. Fragments of a primary laminar framework rich in growth-cavities occur in the uppermost part of the slope sediments as precondition for the formation of stromatactis. The stromatactis cavities were formed by internal reworking and erosion within these organic growth cavities, caused by strong bottom currents due to mass transport from higher parts of the buildup.     

Southeastern Chukchi Sea (Alaska) epibenthos

Epibenthos of the southeastern Chukchi Sea, inclusive of Kotzebue Sound, was sampled in 1976. Crustaceans dominated abundance while echinoderms, mainly sea stars, dominated biomass. Spatial distribution of fauna was determined by cluster analysis. Scavenger-predators were dominant trophic groups, although suspension feeders dominated some regions. Unexpected high abundance and biomass under Alaska Coastal Water and factors related to presence and distribution of fauna are discussed. Dissimilarities between the benthic systems of the southeastern and northeastern Chukchi Seas are attributed to more complex water mass and flow patterns in the southern system. Entrained particulate organic carbon disperses through the area to support an abundant and apparently highly productive benthic fauna, which sustains resident and transient populations of demersal fishes and marine mammals. Epibenthos was sampled again in 1998 and, although little change was apparent in community composition, many taxa had higher abundance and biomass than 22 years earlier, a trend similar to findings observed in the northeastern Bering Sea.Electronic Supplementary Material Supplementary material is available for this article at     

Stratigraphic architecture of a Santonian mixed siliciclastic-carbonate succession (Catalonian Pyrenees, Spain)

Summary At Collades de Bastus, Catalonian Pyrences, a Santonian mixed siliciclastic-carbonate succession indicates two proximal-distal gradients, and records two styles of stratigraphical development upon relative sea-level change. The succession consists of four small-scale sequences (5.1 to 5.4) within the highstand systems tract of the. “Valicarca-5” depositional sequence of Simo (1993), and is topped by a drowning sequence (small-scale sequence 5.5). The investigated succession (Collades Member) accumulated near the margin of the south-Pyrenean shelf, shortly before development of the south-vergent Boixols thrust system. Deposition of the Collades Member commenced with moderate sea-level rise accompanied by increased siliciclastic input. In the larger, eastern outcrop sector the Collades Member consists of a succession of neritic marls with four intercalated intervals each deposited from a carbonate shelf. Each carbonate interval consists of stacked upward-shoaling cycles interpreted as parasequences. From bottom to top, most parasequences consist of a coral-sponge-rudist bioconstruction, a rudist biostrome, and bioclastic limestones. Depositional sequences 5.1 to 5.4 developed by overstep of shelf carbonates with neritic marls, corresponding to the transgressive systems tract (TST) and to part of the highstand systems tract(HST) The carbonate facies tract of the HST consists of stacked parasequences that become thinner up-section and record a westward component of progradation. Each highstand carbonate interval is overlain by a stack of carbonate parasequences that become thicker up-section and, down depositional dip, by neritic marls. Together, the upward-thickening parasequence stack and the laterally adjacent overlying succession of neritic marls comprise the TST and part of the HST of the successive sequence. The sequence boundary is the level of maximum shoaling within each carbonate shelf interval. The uppermost sequence 5.5 is a drowning sequence (cf. Simo 1993). In the western outcrop sector, the Collades Member consists of hummocky cross-laminated to bioturbated sandy calcarenites, of neritic marls and of relatively thin intervals of coral-sponge-rudist limestones. Sequence development may have started with deposition of sharp-based bedsets of sandy calcarenites that both eastward and up-section become thinner and grade into neritic marls. Together, the succession of sandy calcarenites and neritic marls may comprise the TST and, possibly, part of the HST. In the HST neritic marls and, locally, coral-sponge-rudist bioconstructions accumulated. Deposition of some calcarenite bedsets seems to have started near or closely after maximum progradation of each carbonate shelf in the eastern part of outcrop. The stratigraphic architecture of the Collades Member indicates, for the eastern outcrop sector, an east-west proximal-distal gradient, whereas the western sector records a west-east gradient. The opposite gradients result from outcrop intersection subparallel to oblique to general northward depositional dip, across two distinct shelf depositional systems.     

Selection of bedded and unbedded areas by pigs in relation to environmental temperature and behaviour

In 2 experiments, groups of 3 pigs aged 4–8 weeks were given access to 2 sides of an experimental pen, one with straw bedding and one with a bare concrete floor. When resting or feeding, the 12 groups in Experiment 1 showed no consistent preference for the bedded or unbedded side. When active, the pigs were more often on the bedded side, especially at times when fresh straw was provided. The quantity of straw had no effect on these trends.In the second experiment, 10 groups tested at an ambient temperature of 18–21°C strongly selected the bedded side for resting, while those tested at 25–27°C usually selected the bare concrete. Feeding and general activity showed no clear relation to floor type. At the cooler temperatures, most groups dunged on the side that was not used for resting and feeding, but this structuring of the living space was not so apparent at the higher temperatures.The results indicate that the animals' preference for a bedded or concrete floor depends strongly on temperature. Under warm conditions, straw is likely to benefit pigs because of its recreational value but not as a means of improving comfort in the resting area.     

Trace fossils from the Cambro-Ordovician cow head group,newfoundland, and their paleobathymetric implication

U-shaped burrows identified as the trace fossil Arenicolites occur in the Cambro-Ordovician Cow Head Group, a series of thin-bedded limestones interbedded with graptolitic shale and thick beds of limestone breccia and conglomerate. The lithology, limestone petrography, and trace fossils indicate deposition on a submarine slope of a slowly submerging carbonate platform. The limestone bed containing Arenicolites probably represents a period of slow deposition. The steeply inclined U-shaped burrows are assumed to have been formed by polychaete worms of the family Mochtyellidae which thrived in an argillaceous carbonate mud bottom of a carbonate platform slope, in depths exceeding 200 m. Although Arenicolites is believed to denote a shallow-water environment, its presence in the Cow Head extends the ecological niche of the Arenicolites-producing organisms into the outer shelf and continental slope. The domichnia of suspension feeders thus extends from shallow- to deep-water environments.