Sublittoral Environment Research Articles

Depositional Environment of Jurassic Beds of Bela Island, Rann of Kachchh, Gujarat, India Using Ostracodes

The present study focuses on understanding the depositional environment of Jurassic beds of Bela Island, Rann of Kachchh, Gujarat, India which is deduced mainly based on evidence furnished by ostracode fauna. Based on the distribution of 57 ostracode species in Jurassic beds of Bela Island, three biozones, in ascending order, Cytheropteron micropunctata Range Zone (early-middle Bathonian), Progonocythere laeviscula Range Zone (late Bathonian- early Callovian) and Habocythere mouwanaensis Range Zone (early-middle Callovian), have been established. The beds of lowermost Zone were deposited in shallow brackish water environment in the initial phase of marine transgression; the beds of middle zone were deposited at moderate rate of sedimentation in shallow sublittoral environment during the transgressive phase of sedimentary cycle; and the beds of uppermost zone were deposited in the shallow and brackish water condition in regressive phase of sedimentary cycle. Keywords: Ostracode, Depositional Environment, Jurassic Beds, Bela Island, Rann of Kachchh

Drilling predation on spatangoid echinoids from the Miocene of Sardinia: a taphonomic and paleoecological perspective

AbstractPredation is of great importance in understanding the diversification of spatangoid echinoids as well as their preservation in the fossil record. Herein, the spatangoid-dominated Miocene carbonate succession of Punta Foghe (Montiferru area, central-western Sardinia, Italy) is studied with the aim of reconstructing paleoenvironmental conditions and investigating abiotic and biotic factors, including predation, that influence the paleoecology and preservation potential of spatangoid echinoids.The echinoid fauna is dominated by the spatangoid Agassizia and, to a lesser extent, the clypeasteroid Clypeaster. The fauna also includes both regular (undetermined diadematoids and camarodonts) and irregular (Plagiobrissus, Echinocyamus, and Koehleraster) forms. Echinoids and associated fossil content, along with taphonomic and sedimentological signatures, indicate an inner sublittoral environment with moderate energy conditions affected by high-energy events. Agassizia remains, which consist mainly of complete and well-preserved tests, commonly bear subcircular drill holes that are interpreted as the result of cassid gastropod predation and investigated with respect to size selectivity and stereotypy of attack sites. Potential biases related to drilling predation and biostratinomy on the preservation potential of spatangoid tests are discussed.Agassizia lacks any morphological adaptation to minimize high predation risk, including defensive spines and the ability to burrow deeply into the sediment. An antipredator behavior possibly relied on a gregarious life-history strategy, reducing the frequency of attacks on specific individuals by cassid predators.

Ornamental potential of the coastal plant Lapiedra martinezii Lag. (Amaryllidaceae): the role of its revalorization in xero-gardening and ex-situ conservation

Lapiedra martinezii Lag. (Amaryllidaceae) is an autumn-flowering geophyte that grows in coastal and sublittoral environments. The interests on this species has come out during the last decades due to its content in bioactive alkaloids and its conservational status. The aim of this work was to review the available information on L. martinezii and to assess whether it could be introduced as ornamental plant in xero-gardening. Therefore, the aesthetic traits were analyzed and compared to other cultivated and wild plants. Also, information on its ecological and propagation requirements were checked to discern whether it could be adapted under different production systems and culture conditions. In addition, other aspects were also analyzed to identify strengths and limitations of this species for its further revalorization as ornamental plant. The results obtained suggest that L. martinezii could be a good choice as foliage plant to grow it on gardens as an alpine bulb or pot plant. Moreover, it might be quite well adapted under different production and culture conditions in dry and semi-arid regions. The horticultural traits related to its germination and in vitro multiplication are interesting strengths to bear in mind for its industrial propagation and early domestication. Finally considered, the introduction in xero-gardening could also help in its ex-situ conservation. However, a more-in-depth research would be needed to finally introduce it in the ornamental plants’ market.

Integration of Post-stack Inversion and Rock Physics to Determine Sandstone Reservoir Quality: Barakan Sub-basin case

Barakan Sub-basin is assessed as potential basin for hydrocarbon reserves in the eastern region of Indonesia because it is adjacent to Masela block giant gas field. Reservoir rocks in this sub-basin are sandstones from Middle Jurassic (Lower Flamengo Formation) until Oligocene (Adi member Formation). Main sandstone reservoir rocks are knowingly studied to have good porosity in Upper Flamengo, Kopae, Ekmai and Adi member Formations. But, there is no significant study to determine sandstone reservoir distribution that have good porosity quality. Therefore, an integrated method of inversion and rock physics study are needed to determine sandstone reservoir quality. This study uses 2D marine seismic post-stack time migration and 2 wells namely Barakan-1 and Koba-1 wells. Sensitivity analysis with cross-plot of gamma ray log versus acoustic impedance values range of 20-60 API and 9000-42000 (ft/s)*(g/cc) shows a strong correlation of good porosity sandstone to low impedance in Ekmai Formation of both wells. Model based of post-stack inversion reveals sandstone distribution in Ekmai Formation of both wells. Time structure maps of top and bottom horizons in Ekmai Formation indicates Barakan-1 well within anticline height structure and Koba-1 well are deposited in a middle of sub-littoral environment.

Demographic characteristics of sharks in the sublittoral environment of the Turks and Caicos Islands

Demographic characteristics of sharks in the sublittoral environment of the Turks and Caicos Islands

Depositional system and lake-stage control on microbialite morphology, Green River Formation, eastern Uinta Basin, Colorado and Utah, U.S.A.

ABSTRACT Lake-margin lacustrine carbonates of the Green River Formation, in the eastern Uinta basin of Colorado and Utah, occur interbedded with fluvial and shoreline-parallel sandstone and shale. Microbial bindstones were deposited in a saline-alkaline lake during and after the Early Eocene Climate Optimum (EECO) (52–50 million years ago) that is characterized by global hot-house conditions, elevated atmospheric CO2, and highly fluctuating climate conditions. The stratigraphic architecture, chemostratigraphy, and morphology of the microbialites and other associated carbonate beds can be related to these climatic conditions. Three facies associations are recognized in the carbonate units across the lake margin from upper littoral to lower sublittoral environments: facies association 1, delta proximal non-microbial carbonates, characterized by quartzose bioclastic, peloidal, intraclastic packstones and grainstones–rudstones, quartose peloid wackestones and sandy oil shale; facies association 2, microbialite associated non-microbial carbonates, composed of ostracod, ooilitic, peloidal packstones–grainstones and intraclastic packstones, grainstones and rudstones; and facies association 3, microbial carbonates, consisting of diverse forms of stromatolitic and thrombolitic lithofacies. Multiple scales of carbonate cyclicity are suggested by shifts of δ18O and δ13C stable isotopes and deepening-upward microbialite facies. High-frequency cycles, on the order of 1 to 5 m thickness, are characterized by positive shifts in stable isotopes and interpreted deepening trends from littoral to lower sublittoral conditions. Large-scale trends, on the order of tens to hundreds of meters thickness record long-term lake changes, including: 1) sparse microbialite deposition during initial fresh conditions in lake stage 1, with low macro-structure diversity and light δ18O and δ13C isotope values; 2) transitional lake stage 2 corresponding to moderate macro-structural diversity, large meter-scale biostromal and biohermal buildups, and a positive shift in δ18O and δ13C isotope values that suggest increasing saline and alkaline conditions; 3) a highly fluctuating lake stage 3 that contains the highest microbialite macro-structural diversity and marks the interval of heaviest δ18O and δ13C isotope values, suggesting the greatest lake restriction, and the highest salinity and alkalinity conditions; and 4) a rising lake stage 4 that marks the lowest microbialite macro-structure diversity and a reversal in trend of δ18O and δ13C isotope values, that indicate deepening and freshening conditions.

Predator–prey interactions among Pliocene molluscs from the Tjörnes Peninsula, Iceland; across the trans‐Arctic invasion

The fossil record provides a long-term perspective to better understand the impacts of species invasions in their environmental contexts. Temporal analyses of predator–prey interactions from the Tjörnes deposits, Iceland, track naticid gastropod drilling predation across the trans-Arctic invasion (TAI: ~3.5 Ma). These deposits represent three zones subdivided into 25 marine fossil-bearing beds that correspond with the stages of invasion: Tapes (1–5) and Mactra (6–12) zones are pre-invasion, whereas the Serripes zone (13–25) represents the invasion. Bivalve and naticid gastropod specimens were analysed from the Bárðarson (1925) samples at the Icelandic Institute of Natural History, which consisted of pre-invasion and invasion samples; we also bulk-sampled the Serripes zone. Height and length of specimens were measured to assess size changes, and the occurrence of complete and incomplete drill holes and drill hole diameter were recorded for whole bivalves and naticids. Drilling frequency (DF) and prey effectiveness (PE, the incidence of failed drilling) were calculated to track predator–prey interactions. Genus-level diversity increased through the Tjörnes deposits, in part related to a shift from intertidal to sublittoral environments. DF increased and PE decreased significantly between the pre-invasion and Serripes zones. However, DF decreased from the early to the late Serripes zone, which could signify stabilization of the Tjörnes community. An increase in competition among predators through the invasion is supported by an increase in abundance of naticids relative to bivalves, especially invasive species, a switch to smaller-sized bivalve prey, a decrease in naticid mean size and an increase in confamilial predation.

The Upper Ordovician reef Bol’shaya Kos’yu, Ilych River, the Northern Urals (structure, paleobiocenosis, microfacies, model of formation)

Subject. The Upper Ordovician reef Bol’shaya Kos’yu, located on the western slope of the Northern Urals in the basin of the Ilych River is a unique object among coeval reefs due to the weak dolomitization of rocks and the ability to trace the phases of its development. Materials and methods. The article presents the results of paleontological, paleoecological and microfacial analyses of reef limestones selected by the author from 12 natural outcrops with a total capacity of about 150 m located along both banks of the Bol’shaya Kos’yu River. Results. The structure of the reef, morphology and taxonomic composition of the frame-forming biota were established, and the important role of sphinctozoal sponges was first identified. Among the reef limestones in the main genetic characteristics that reflect specific depositional environments, was identified three types of microfacies. Type 1 – reef microfacies – framestones and buflestones. Type 2 – microfacies of interbiohermic space and inter-carcass cavities exposed to wave and tidal action – bioclastic and peloid pakstones, biolithoclastic grainstones and lithoclastic rudstones. Type 3 – microfacies of the hidden microcosmic cavities, protected from the active wave impact – wackstone. Сonclusion. The composition of the microfacies and frame-forming biota characterize difficult differentiated, both on a section, and structure the reef, which was formed in the conditions of the carbonate platform-shelf margin with active hydrodynamics. Its growth occurred during transgression, which ended by the end of the middle katian a major regression that stopped its development. The revealed paleontological, paleoecological and microfacial data indicate that starting from the middle katian the first identified sphinctozoal sponges could settle in sublittoral environments with active hydrodynamics at depths up to 20 m.

Taxonomy, palaeoecology and stratigraphy of the middle Miocene mollusk fauna from the Gračanica coal pit near Bugojno in Bosnia and Herzegovina

During the early and middle Miocene, the Dinarides Lake System (DLS) was a major hotspot of freshwater mollusk diversity in southeastern Europe. The numerous intramontane lake basins, originating by combined effects of tectonic subsidence and humid climate, accumulated thick lacustrine successions. Diagenetic overprint and leaching of these carbonate-rich deposits have facilitated insights to faunal contents for only a few basins up to the present. We contribute to filling this gap by documenting for the first time a mollusk fauna from the Bugojno Basin in Bosnia and Herzegovina. The fauna originates from a coal-bearing succession representing a gradual flooding of the coastal wetlands followed upwards by the establishment of perennial lacustrine settings in the basin. Our taxonomic analyses documents 17 gastropod and two bivalve species. New to science are IIllyricocongeria forcakovici nov. sp., Prososthenia krijgsmani nov. sp. and Bania goehlichae nov. sp. The palaeoecological analysis based on quantified samples shows distinct shifts in mollusk composition and abundance. The terrestrial taxa are restricted to the coal-bearing interval of the section; melanopsids, neritids and hydrobiids are abundant in deltaic and littoral settings, whereas bivalves are frequent in littoral and sublittoral environments. In line with previous results, which have evidenced a high degree of intralacustrine radiation in the DLS, the Lake Bugojno fauna shows a low to moderate level of similarity to other DLS faunas. The dissimilarity may partly also result from its younger age as suggested by the presence or absence of regional biostratigraphic marker species.

Palaeoenvironments and taphonomy of clypeasteroids in Miocene carbonates of the Esfahan–Sirjan Basin, central Iran

A comprehensive study of the palaeoenvironmental and post-mortem conditions of Cenozoic clypeasteroids from the Miocene (Aquitanian) of the Qom Formation in the Esfahan–Sirjan Basin (central Iran) is based on test morphology, taphonomy, test surface preservation, echinoid abundance and echinoid sedimentary fabrics (density, orientation, and cluster), and facies analysis. The deposit-feeding clypeasteroids lived in deeper open-marine, shallow open-marine and shoal settings in a sublittoral environment. The low–moderate energy, deeper open-marine facies contain the lowest population of clypeasteroids, including rare shallow infaunal Parascutella and rare semi-infaunal Clypeaster. The moderate to high energy shallow open-marine facies contains the highest abundance and diversity of Clypeaster. The shallow open-marine and high-energy shoal facies are dominated by epibenthic Clypeaster individuals with robust, inflated and commonly dome-shaped tests. Differences in the abundance and diversity of the living clypeasteroids were related to water depth, food sources and energy levels. Different food sources, life-styles and burrowing depths are indicated by the particular morphologies of the echinoids. Dead echinoids, especially the robust and inflated Clypeaster individuals, were used as substrates and domiciles by skeletozoans and other epibiontic organisms. Disarticulation, fragmentation, bioerosion, test outline distortion and radial cracking affected the preservation of the dead clypeasteroid tests. The clypeasteroid shells in the deposits accumulated as 1—an almost autochthonous assemblage (Parascutella), 2—a moderately transported and reworked assemblage (Clypeaster and Parascutella) and 3—transported and multiple reworked assemblages (Clypeaster) affected by storms.

Paleoecology of sublittoral Miocene echinoids from Sardinia: A case study for substrate controls of faunal distributions

AbstractA rich echinoid fauna within the middle Miocene carbonate sedimentary succession cropping out along the coast between Santa Caterina di Pittinuri and S'Archittu (central-western Sardinia) allows the comparison of faunal gradients and preservation potentials from both hard and soft substrata. Three echinoid assemblages are recognized. Faunal composition, as well as taphonomic and sedimentological features and functional morphological interpretation of the echinoid test indicate an outer sublittoral setting. Assemblage 1 represents a highly structured environment within the photic zone, with mobile substrata occupied by infaunal irregular echinoids, mainly spatangoids, and localized hard substrata, provided by rhodolith beds, with epibenthic regular echinoids represented by the co-occurrence of the diadematidDiademaGray, 1825 and the toxopneustidsTripneustesL. Agassiz, 1841 andSchizechinusPomel, 1869. Assemblage 2 shows a higher diversity of irregular echinoids, dominated by the clypeasteroidsEchinocyamusvan Phelsum, 1774 andClypeasterLamarck, 1801 and different spatangoids, with the minute trigonocidaridGenocidarisA. Agassiz, 1869 among regular echinoids. This assemblage points to a soft-bottom environment with moderate water-energy conditions, periodically affected by storms. A low-diversity echinoid fauna in Assemblage 3, dominated by the spatangoidsBrissopsisL. Agassiz, 1840 andOvaGray, 1825, documents a deeper, soft-bottom environment, possibly below storm-wave base. These results indicate that the diversity of echinoid faunas originating in sublittoral environments is related to: (1) the presence of both soft and hard substrata, (2) differential preservation potentials of the various echinoid taxa, (3) intense bioturbation, and (4) sediment deposition by sporadic storm events.

Detection of Stones in Marine Habitats Combining Simultaneous Hydroacoustic Surveys

Exposed stones in sandy sublittoral environments are hotspots for marine biodiversity, especially for benthic communities. The detection of single stones is principally possible using sidescan-sonar (SSS) backscatter data. The data resolution has to be high to visualize the acoustic shadows of the stones. Otherwise, stony substrates will not be differentiable from other high backscatter substrates (e.g., gravel). Acquiring adequate sonar data and identifying stones in backscatter images is time consuming because it usually requires visual-manual procedures. To develop a more efficient identification and demarcation procedure of stone fields, sidescan sonar and parametric echo sound data were recorded within the marine protected area of “Sylt Outer Reef” (German Bight, North Sea). The investigated area (~5.900 km2) is characterized by dispersed heterogeneous moraine and marine deposits. Data from parametric sediment echo sounder indicate hyperbolas at the sediment surface in stony areas, which can easily be exported. By combining simultaneous recorded low backscatter data and parametric single beam data, stony grounds were demarcated faster, less complex and reproducible from gravelly substrates indicating similar high backscatter in the SSS data.

Ostracoda (Crustacea) from the Pozo D-129 Formation (upper Barremian?–Aptian), Golfo San Jorge basin, Patagonia, Argentina: Taxonomic descriptions, palaeoenvironments and palaeogeographical implications

In this study, we present complete descriptions and illustrations of nine ostracod species recovered from the Pozo D-129 Formation (Golfo San Jorge basin), Patagonia Argentina, discussing their depositional palaeoenvironment and palaeobiogeography. The species described in this study are Musacchiocythere sarugnata (Musacchio and Palamarczuk) and Metacypris herreriensis (Musacchio) (Family Limnocytheridae), Alicenula cf. leguminella (Forbes) (Family Darwinulidae), Neuquenocypris (Protoneuquenocypris) antiqua Musacchio and Simenoni, and Rhinocypris diademae Musacchio and Simenoni (Family Ilyocyprididae), Pattersoncypris cf. angulata (Krömmelbein and Weber) and Zonocypris sp. (Family Cyprididae), Damonella ultima (Krömmelbein and Weber) and Candona sp. (Family Candonidae). The Pozo D-129 Formation is the main source rock of hydrocarbons of the Golfo San Jorge basin, and its deposits represent an extensive lacustrine system. The samples studied come from the Cerro Chenques in the Sierra Silva anticline of the San Bernardo fold belt, Chubut Province, and from the well AAB.x-1002 (Anticlinal Aguada Bandera), Santa Cruz Province. The outcrop succession consists of several shallowing and coarsening upward sedimentary cycles 5–8 m thick, evolving from deep lacustrine, sublittoral and shallow lacustrine environments. The micropalaeontological association represents a moderate energy thanatocoenosis, and thus is a good indicator of the depositional palaeoenvironment. Taphonomic attributes and taxonomic composition of the association indicate deep and sublittoral environments, consistent with previous facies models for the outcrop succession, and suggest stressed water bodies. Previous studies of palynomorphs suggested a latest Barremian? to early Aptian Age for the study section, whilst the ostracod species Damonella ultima, and the charophytes Clavator harrisi Peck and Porochara ultima (Peck) are part of the Flabellochara [= Clavator] harrisi zone of Aptian Age. The ostracod fauna shows affinities to contemporaneous faunas of Brazil and West Africa, providing evidence of potential faunistic interchange between distant regions.

A Gerecse pannóniai puhatestűi és lelőhelyeik: rétegtan, őskörnyezet és fejlődéstörténet

A Gerecse földtani térképezése során a Magyar Földtani és Geofizikai Intézet geológusai új, vagy régen feledésbe merült és részletesen soha nem dokumentált pannóniai feltárásokat azonosítottak a hegység északi előterében, az onnan dél felé felnyúló völgyekben, és a hegység belsejében is. Az ezekből begyűjtött puhatestű fauna (kiegészítve a már korábban ismert tatai puhatestű faunával és régebbi gyűjteményi anyagokkal) és a feltárásokban megfigyelhető szedimentológiai jellemzők alapján a pannóniai rétegsor itt is, mint az egész Dunántúli-középhegység északnyugati peremén, egyetlen transzgresszív-regresszív ciklusból áll. A ciklus transzgresszív szárnyát a tatai téglagyári feltárásokban a vékony transzgresszív bázisrétegre települő Száki Formáció kékesszürke agyagja és az abban megőrződött mély szublitorális fauna, míg a Gerecse központi részén, a tardosi Vályus-kút környékén, 375 méter tengerszint feletti magasságban a lignites agyaggal kezdődő rétegsor fedőjében települő, szintén mély szublitorális puhatestűeket tartalmazó agyag képviseli. A dunaszentmiklósi Iván halála-völgyben valószínűleg egy szökőár hozta létre a kréta fekü anyagából képződött konglomerátumot, homokos mátrixában tömegesen megjelenő zárt (két teknős) pannóniai kagylóhéjakkal. Az üledékciklus regresszív szárnyát az Újfalui Formáció képződményei adják; ezek legjobb feltárásai a Gerecse északi előterében, a Neszmély környéki völgyekben (Nyáraska-völgy, Disznós-kúti-völgy, Csekendi-völgy) és Süttő környékén találhatók. A formációt felépítő felfelé sekélyedő, néhány méter vastag ciklusok faunája a kagylók uralta sekély szublitorális együttesekből, a csigák magas diverzitásával jellemzett litorális faunákból és végül mocsári puhatestű együttesekből áll. Gyűjteményi anyagokban előfordulnak folyóvízi fajok is. A transzgresszív szárny a Congeria czjzeki zóna felső részébe tartozik, míg a regresszív szárny a Lymnocardium ponticum zóna része; a teljes ciklus képződésének kora 9,4–8,7 millió év lehetett. A fáciesek elterjedése alapján a transzgresszió már tagolt térszínen játszódott le, majd az üledékképződéssel egyidejűleg is folyt a terület vetődéses deformációja, de a tatai és vályus-kúti rétegsorok közötti nagy magasságbeli különbség csak további vetőmozgásokkal, a Gerecse utólagos kiemelkedése nyomán jöhetett létre.

Redescription of Xenodasys riedli (Gastrotricha: Macrodasyida) based on SEM analysis, with first report of population density data

During surveys of the Gastrotricha of the Tropical Northwestern Atlantic (TNWA, Caribbean Sea), we came across numerous specimens of the uncommon macrodasyidan, Xenodasys riedli (Xenodasyidae). Abundance data on gastrotrichs is rare and entirely absent for this species; moreover, there are no data on morphological variation of X. riedli outside its type locality (North Carolina, USA). Here, we provide new abundance data on specimens collected from St. John Island (US Virgin Islands), as well as new metric and morphological data from specimens collected on San Salvador Island (Bahamas), Tobago, and a sublittoral environment on the Atlantic Coast of Florida (USA). In the interstitial environments of St. John, X. riedli was most abundant at 0.8 m depth in moderately well-sorted sediments. It reached maximum abundance of 89.5 ± 42.7 ind./102 cm and made up 69.7% of the total taxocoenosis. Metric variation revealed that specimens at all sites in the TNWA and Florida had smaller body sizes than those recorded at the type locality, but showed only limited variation in the size and number of taxonomic characters. Observations of specimen from Florida using scanning electron microscopy (SEM) revealed details that were overlooked in the type description. For example, we observed 8 dorsal head plates (11 in the original description), 1 pair of anterior medial plates, and 3 ventral plates, the latter of which were not described in the type specimens. We confirm the existence of round scales on the dorsolateral margins, and note that spineless-scales are also present in between the spined scales on the lateral body wall. We also determined that the lateral spined scales possess dorsal and ventral spines instead of anterior and posterior spines, which was their original assumed position. This research reveals that SEM remains the best diagnostic tool for characterizing gastrotrich morphology, and should be part of all future studies of gastrotrich taxonomy.

Palaeoecology and taphonomy of spatangoid-dominated echinoid assemblages: A case study from the Early-Middle Miocene of Sardinia, Italy

The Early-Middle Miocene marine sedimentary succession of the Borutta Formation cropping out at Porto Torres (northern Sardinia) represents one of the most diverse and well-preserved spatangoid-dominated sedimentary successions in the Miocene of the Mediterranean area. The echinoid-bearing succession is studied with the twofold purpose of firstly reconstructing the palaeoenvironmental setting in which these echinoids occurred, and secondly investigating factors influencing the preservation potential of spatangoid echinoids in the fossil record. These goals are accomplished by 1) detailed logging of sedimentary facies, 2) applying functional morphological interpretations of echinoid skeletons in order to reconstruct their behaviour and life habits, 3) quantifying the relative abundance of taxa and taphonomic features of test preservation, and 4) analyzing associated trace fossils within the beds.The sedimentary succession is composed mainly of fine-grained sandstones which are intensely bioturbated by Thalassinoides-like burrows. Spatangoid abundance is high throughout the profile declining only in intercalated dm-thick rhodolith beds. A 20-cm-thick bed with a bedding surface of approximately 250m2 was investigated in detail with respect to relative abundance of spatangoid taxa and taphonomic signatures. The echinoids consist almost exclusively of deposit-feeding irregular forms with a dominance of the spatangoids Ova and Brissopsis and the minute clypeasteroid Echinocyamus. The spatangoids Opissaster, Holanthus, Metalia and Hemipatagus as well as the clypeasteroid Clypeaster marginatus are also present.A low energy, moderately deep, outer sublittoral environment with high rates of bioturbation and episodes of sediment deposition by storms is inferred. Interspecific competition among deposit-feeding echinoids appears to be limited by their different burrowing depths, feeding strategies and resource partitioning. The gregarious behaviour of spatangoid echinoids, their habitat in quiet, deeper environments and episodes of rapid deposition seem to represent the main factors leading to this spatangoid-bearing deposit. Since both shallow- and deep-burrowing spatangoid echinoids are well represented as complete specimens, mode of life does not appear to play a major role in their preservation potentials.

Lithofacies and environments of deposition within the Middle–Upper Cretaceous successions of Southeastern Nigeria

This paper presents findings from detailed geologic mapping of the Cenomanian–Campanian sediment package of southern Benue Trough, outcropping in Afikpo area of Southeastern Nigeria. The aim was to integrate outcrop and sedimentological log data with lithofacies analyses to better understand prevalent depositional processes and environments of deposition, across the Amaseri–Ngodo outcrop sections. Ten lithofacies with their associated subordinate lithofacies were identified and grouped into five facies associations (FA 1–5) to aid depositional environment interpretation. FA 1 consists of silty-shale and shales of the mudstone (MS) lithofacies deposited within an oxygenated offshore/open shelf setting, probably below fair-weather and storm wave base. FA 2 comprises medium–coarse-grained sandstone (MCS), hummocky cross-bedded sandstone (sub-lithofacies 4 of CBS), bioturbated sandstone (BSs) facies, bioturbated siltstone (BSt) and planar parallel-laminated sandstone (PPLS) lithofacies, interpreted to be storm wave-dominated shelf deposits. FA 3 consists of tabular/planar and trough cross-bedded sandstones (sub-lithofacies 1 and 2 of CBS) and wave ripple-laminated sandstones (RLS) lithofacies interpreted as shorefaces deposits above fair-weather wave base. Herringbone cross-bedded sandstones (sub-lithofacies 3 of CBS) and bioclastic limestone (BcL) lithofacies constitute FA 4, interpreted as tidal inlet/lagoonal deposits. FA 5 is characterized by conglomeritic sandstone (CS) lithofacies, as well as CBS, PPLS, RLS lithofacies, deposited within fluvial channels. Furthermore, vertical stacking patterns reveal the occurrence of two facies successions: the fining-upwards/thinning-upwards (FU/TnU) succession (typical of deepening or shallow to proximal offshore marine environments), dominating the northern and central part of the study area; and coarsening-upwards/thickening-upwards (CU/TkU) succession (typical of shoaling or proximal offshore to shallow marine environment), dominating the southern part of the study area. Overall, these lithofacies represents deposits within the littoral (marginal marine) and sub-littoral (shallow marine) environments.

Echinoid assemblages from the early Miocene of Funtanazza (Sardinia): A tool for reconstructing depositional environments along a shelf gradient

Lower Miocene echinoid assemblages from Funtanazza, midwestern Sardinia, are studied with respect to reconstructing palaeoenvironmental conditions along a shelf gradient. This is accomplished by 1) detailed logging of sedimentary facies, 2) applying functional morphological reconstructions of echinoid skeletons and interpreting their behaviour and life habits, 3) quantifying various taphonomic features of test preservation, and 4) analysing accompanying fauna and flora.The Funtanazza section is dominated by fine- and coarse-grained siliciclastic lithologies. Eighteen genera of both regular and irregular sea urchins are recognized herein. Of these, sixteen occur in seven echinoid assemblages which were distinguished with respect to abundance, diversity, taphonomy and lithology. Littoral environments are characterized by the camarodonts Genocidaris and Psammechinus, the clypeasteroids Clypeaster and Echinocyamus, and the echinolampadoids Hypsoclypus and Echinolampas; the cidaroids Prionocidaris and Tylocidaris (Sardocidaris) and the spatangoid Spatangus are also present. Higher diversity is represented in inner sublittoral environments with the co-occurrence of the regular echinoids Prionocidaris, Tylocidaris (Sardocidaris), Tripneustes and Genocidaris and the irregular echinoids Clypeaster, Echinocyamus, Hypsoclypus, Echinolampas, Schizaster, Spatangus, Lovenia and Trachypatagus. Outer sublittoral environments are dominated by spatangoid echinoids and the cidaroid Tretocidaris (Stylocidaris).Various substrates, such as boulders and pebbles, mobile fine and coarse sediments, secondary hardgrounds and seagrass and bryozoan patches, can be inferred. Preservation style with respect to abrasion, fragmentation and encrustation can vary widely among different taxa and environments and are interpreted as a function of constructional morphology and ambient environmental factors.The echinoid assemblages of Funtanazza contain taxa which, in part, are widespread in the Miocene sedimentary successions of the circum-Mediterranean area. The described echinoids and assemblages are compared to other similar coeval occurrences and their applicability as palaeoenvironmental indices discussed.

Upper Ovetian trilobites from Spain and their implications for the palaeobiogeography and correlation of the Cambrian Stage 3 in Gondwana

The upper part of the La Herrería Formation in Los Barrios de Luna (León Province, N Spain) has been revised from a palaeontological and biostratigraphical point of view. Two stratigraphic sections have been studied including their trilobite and ichnofossils contents. The ichnofossil assemblages have a high diversity of species characterising the Cruziana ichnofacies, suggesting a shallow sublittoral environment for the upper part of the La Herrería Formation. The trilobites species recognised are Lunagraulos antiquus, Dolerolenus formosus, Dolerolenus longioculatus, Lunolenus lunae, Metadoxides richterorum, Metadoxides armatus and Sardaspis? sp. from the upper Ovetian (lower Cambrian Stage 3 under discussion by the ISCS). The new trilobite assemblages make possible a good correlation between the lower Cambrian formations of North Spain, Sardinia, South China and Siberia. Analysis of the palaeobiogeographical meaning of all trilobite genera that have been identified in the upper Ovetian of Spain shows a strong connection between the northern peri-Gondwana margin and west Gondwana, with a low latitude distribution for the Spanish trilobites at this time.

Microbial filaments in stromatolites and laminites of Balbuena III Sequence (Maastrichtian/Danian) of Yacoraite Formation in Metán-Alemania Sub-basin, Salta region, Argentina, and its alaeoenvironmental significance

RESUMO A Bacia de Salta localiza-se no noroeste argentino e sua origem está relacionada a um rifte intracontinental, formado durante o Cretáceo e início do Paleógeno. Subdivide-se em quatro sub-bacias (Lomas de Olmedo a leste; Sey a oeste; Tres Cruces a norte; e Metán-Alemania a sul) que foram preenchidas por sedimentos dos Subgrupos Pirgua (fase sin-rifte), Balbuena e Santa Bárbara (fase sag ). O Subgrupo ou Supersequência Balbuena é dividido em quatro sequências: Balbuena I, II, III e IV, da base para o topo. O presente estudo identificou filamentos microbianos em imagens geradas pelo microscópio eletrônico de varredura em amostras de estromatólitos e laminitos da Sequência Balbuena III (Maastrichtiano/Daniano) da Formação Yacoraite, na Sub-bacia Metán-Alemania, região do dique Cabra Corral, distrito de Coronel Moldes, Argentina. A ocorrência desses filamentos, identificados em calcários formados em períodos de clima árido e depositados no intervalo de lago fechado da sequência em estudo, indica a influência de atividade biológica na formação dessas rochas. A identificação dos filamentos microbianos, preservados a partir de estruturas de cianobactérias, auxilia a interpretação paleoambiental, uma vez que a ocorrência desses microorganismos é limitada à zona fótica e é comum a ambientes estressantes. Os laminitos da área de estudo foram interpretados como formados em planícies lamosas supralitorâneas na zona vadosa, enquanto os estromatólitos se formaram em ambiente sublitorâneo, estando constantemente submersos. Além dos microbialitos, ocorrem na Sequência Balbuena III fácies carbonáticas, siliciclásticas e mistas, depositadas em ambiente lacustre.