Palaeoenvironment and taphonomy of a Late Jurassic (Late Tithonian) Lagerstätte from central Poland

A rich assemblage of exceptionally preserved marine and terrestrial fossils occurs in fine‐grained limestones in the upper part of the Late Tithonian (Middle Volgian) shallowing upward carbonate sequence in Central Poland. The richest horizon, a deposit known locally as the Corbulomima horizon, is named after the shallow burrowing suspension feeding bivalve Corbulomima obscura, moulds of which occur in densities of up to 500 per square metre on some bedding planes. The fauna in this bed also includes organic and phosphatic remains of a wide range of other creatures including the exuviae of limulids and decapods, disarticulated fish skeletons and rare isolated pterosaur bones and teeth. There are also perfectly preserved dragonfly wings and beetle exoskeletons. The average stable carbon and oxygen isotope values for ostracod shells and fine‐grained sediment from this horizon suggest precipitation of the calcium carbonate from warm seawater of normal marine salinity. The carbonate sediments overlying the fossiliferous horizon have been interpreted as nearshore to shoreface facies. These pass abruptly into coarse reworked intraclastic sediments interpreted as possible tsunami or storm surge over‐wash deposits. The clasts in this deposit have more positive oxygen isotope values than those in the underlying limestone, which may indicate that they were lithified in a slightly more evaporative, perhaps intertidal, setting. The succession terminates with silicified fine‐grained limestones likely to have formed in extremely shallow lagoonal environments. In contrast with the Solnhofen limestones of Lower Tithonian age in south‐central Germany the Corbulomima horizon is interpreted as a transitional deposit formed in a shallow marine setting by rapid burial with elements of both Konservat‐ and Konzentrat‐Lagerstätte preservation. □Konzentrat and Konservat‐Lagerstätte, Taphonomy, Palaeoenvironment, Paleogeography, Late Jurassic, Poland.     

Development of calcrete and clinoforms during emergence and flooding of the Late Cenomanian carbonate platform, Jordan

The Late Cenomanian Hummar Formation was studied in three sections in north and central Jordan, at Aameriyya, northeast of Na’ur and the Wadi Haur areas. The base in the Aameriyya area is marked by a subaerial unconformity overlain by a calcrete and a paleokarstic horizon, separating the underlying Fuheis Formation marl from the overlying Hummar Formation limestone. The emergent Aameriyya area is interpreted to have been a paleohigh, as a response to tectonism, and a basin and swell topography is invoked for the Late Cenomanian carbonate platform in this region. The Hummar Formation is believed to form one complete depositional sequence; the calcrete-karst represents a lowstand systems tract, the overlying 2-m massive rudstone/floatstone represents the transgressive systems tracts (TST), and the cortoid grainstone/packstone with clinoforms the highstand systems tracts. The topmost miliolid limestone is probably the late highstand topset of the sequence, followed upwards by the TST of the Shueib Formation marl of the next sequence. The sequence boundary at the upper contact of the Hummar Formation can be correlated regionally whereas the sequence boundary at its base with subaerial exposure has not been reported elsewhere in Jordan, the Negev, or Sinai.     

Palaeocology of Hard Substrate Faunas from the Cretaceous Qahlah Formation of the Oman Mountains

Skeletal encrusters and carbonate hardgrounds are rare in siliciclastic sands and gravels because of high levels of abrasion and sediment movement. An exception to this is the Maastrichtian Qahlah Formation of the Oman Mountains, a sequence of coarse siliciclastic sediments deposited on a shallow marine shelf above wavebase and at an equatorial palaeolatitude. This unit contains intercalated carbonate hardgrounds and other hard substrates which were encrusted and bored. The hard substrates, comprising carbonate and silicate clasts, calcareous bioclasts (mollusc shells and coral fragments) and wood, supported a diverse encrusting and boring fauna dominated in biomass by the oyster Acutostrea . There are twelve bryozoan species and at least two serpulid worm species, most living cryptically. Other encrusters on exposed surfaces include the agglutinated foraminiferan Placopsilina and several species of colonial corals. Borings in the carbonate clasts and shells are predominantly those of bivalves ( Gastrochaenolites ), with subsidiary clionid sponge ( Entobia ) and acrothoracican barnacle ( Rogerella ) borings. The woodgrounds are thoroughly bored by teredinid bivalves ( Teredolites ). Of the common substrate types, carbonate hardground clasts support the greatest number of taxa, followed by chert clasts, with limestone rockground pebbles being depauperate. Clast composition and relative stability probably explain these differences. Individual clasts probably had variable and typically long colonisation histories. Detailed palaeoecological interpretation is constrained by taphonomic loss, time-averaging and clast transportation and reorientation. Evidence from the Qahlah Formation shows that tropical rocky-shore biotas in the Cretaceous were not impoverished as previously believed.     

Late Triassic reefs from the Northwest and South Tethys: distribution, setting, and biotic composition

The paleolatitudinal distribution patterns during Ladinian and Carnian time are characterized by an increasing expansion of reefs from the northern to the southern hemisphere. The optimum of reef diversity and frequency in the Norian is associated with the development of extended attached or isolated carbonate platforms. Norian-Rhaetian sponge and coral reefs of the Northern Calcareous Alps developed (1) as reef belt composed of patch reefs in platform-edge positions facing the open-marine northwestern Tethys basins and (2) as patch reefs in intraplatform basins as well as in ramp positions.Carnian and Norian-Rhaetian sponge and coral reefs of the Arabian Peninsula are formed (1) as reef complexes at the margins of carbonate platforms on the tops of volcanic seamounts in the southern Tethyan ocean, as small biostromes on these isolated platforms, and (2) as transgressive reef complexes on the attached platform of the Gondwana margin. The Norian Gosaukamm reefal breccia of the NW Tethys is a counterpart of Jabal Wasa reefal limestone of the Gondwana margin with similarities in geological setting and biotic composition. Rhaetian coral biostromes of low diversity known from the Austrian Koessen basin resemble to the time equivalent Ala biostromes of the isolated Kawr platform in the southern Neo-Tethys by forming a discontinuous layer in shallow intraplatform basin setting.     

The bioeroded megasurface of Oura (Algarve,south Portugal): implications for the Neogene stratigraphy and tectonic evolution of southwest Iberia

The use of rocky palaeoshore bioerosion analysis as a tool to solve stratigraphic and tectonic issues is beginning to bear fruits. The occurrence of an extensive intra-Miocene marine abrasion platform in southern Portugal at Oura (Albufeira) has been identified on the basis of bioerosion trace fossils analysis. The observed ichnodiversity is rather low, with bivalve boring Gastrochaenolites being dominant. Nevertheless, the ichnoassemblage may be assigned to the Entobia ichnofacies. The palaeoichnological study of the Oura hardground confirmed the existence of an important intra-Miocene stratigraphic gap (ca. 3 Ma hiatus), represented by a razor-sharp erosional contact that separates the two main Neogene units in the Algarvian region: the lower carbonate sequence of Lagos–Portimão Formation (Langhian/Serravallian) and the upper siliciclastic sequence of the Cacela Formation (Upper Tortonian).     

The development of an Early Ordovician hard ground community in response to rapid sea-floor calcite precipitation

The Kanosh Shale (Upper Arenig, Lower Ordovician) of west-central Utah. USA. contains abundant carbonate hardgrounds and one of the earliest diverse hardground communities. The hardgrounds were formed through a combination of processes including the development of early digenetic nodules in clay sediments which were exhumed and concentrated as lags by storms. These cobble deposits. together with plentiful biogenic metrical. were cemented by inorganically precipitated calcite on the sea floor. forming intraformational conglomerate hardgrounds. Echinoderms may have -played a critical role in the development of hardground faunas since their disarticulated calcite ossicles were rapidly cemented by syntaxial overgrowths. forming additional cobbles and hardgrounds. The echinoderms thus may have taphonomically facilitated the development of some of the hard substrates they required. A significant portion of the hardground cements may have been derived from the early dissolution of aragonitic mollusk shells. Kanosh hardground species include the earliest bryozoans recorded on hardgrounds and large numbers of stemmed echinoderms. primarily rhipidocystid cocrinoids. Bryozoans and echinoderms covered nearly equal areas of the hardground surfaces. and there was a distinct polarization between species which preferred the upper. exposed portions of the hardgrounds and others which were most common on undercut. overhang surfaces. The Kanosh Shale hardground fossils combine elements of Late Cambrian assemblages and Middle Ordovician faunas, thus confirming predicted trends in hardground community evolution. especially the replacement of cocrinoids by bryozoans and. to a lesser extent, by other stemmed echinoderms, especially crinoids. The Kanosh community marks the transition from the Cambrian Fauna to The Paleozoic Fauna in The hardground ecosystem. *Carbonate hardgrounds, aragonite dissolution, calcite cement, Echinodermara, Trepostomata, Nicholsonclla. Dianulites. Porifpra. taphonomic facilitation, Utah. Pogonip Group, Kanosh Shale. Ordovician.     

Cretaceous scleractinian corals from the Albian of Cabo de Ajo (Cantabria Province, N-Spain)

For the first time a detailed stratigraphic section of the Lower Cretaceous (Albian) of Cabo de Ajo peninsula (Cantabria Province) is logged. The Ajo facies represents a subtropical shallow-water carbonate platform environment. When the platform was subjected to relatively high-energy conditions, calcarenite skeletal shoals developed. In periods of higher sealevel, deeper-water marls were deposited in intraplatform basins. The outcrops yield abundant fossils of scleractinian corals. Three selected stratigraphic horizons containing corals were sampled. Fauna 1 and 2 grew on a shallow-water soft bottom substrate (marl) below wave-base level and contain very small plocoid and phaceloid growth forms. Fauna 3 is associated with a calcarenitic matrix and large forms suggesting a more agitated and wave-influenced environment. 16 species of corals belonging to 7 suborders are described taxonomically. These rather diverse coral associations are among the youngest from the Urgonian facies of Europe, and compare well with other Urgonian Tethyan faunas.     

北羌塘盆地中南部侏罗纪布曲组古生物特征与沉积环境

本文通过对北羌塘盆地北坳陷中南部胜利河、东湖及毛毛山等地区侏罗纪布曲组6条剖面及其中丰富的腕足类、双壳类等古生物资料和岩石组合特征的研究,将布曲组地质时代划为中侏罗世巴通期(Bathonian)至早卡洛夫期(Callovian),还可能跨入早巴柔期(Bajocian)。通过本文研究和区域对比,认为布曲组的沉积时代在北羌塘盆地存在穿时性。依据岩石组合特征,布曲组沉积充填物三分性明显,下部和上部为一套以微晶结构、粒泥结构为主的低能碳酸盐岩,中部为一套以高能的亮晶粒屑灰岩为主的碳酸盐岩。结合古生物生态习性,布曲组沉积环境总体为近岸浅水开阔台地–台地边缘碳酸盐岩沉积体系,构成多个沉积旋回。这一基础资料对下一步分析北羌塘盆地坳陷中南部布曲组岩相古地理提供了支撑。     

Middle Triassic carbonate-platform break-up and formation of small-scale half-grabens (Julian and Kamnik–Savinja Alps, Slovenia)

In the Julian Alps (Mt. Prisojnik, NW Slovenia) and in the Kamnik–Savinja Alps (Mt. Kri?evnik, N Slovenia), both of which form part of the eastern Southern Alps, several meters of Upper Anisian pelagic red nodular, radiolarian-rich limestone (Loibl Formation) were deposited on the drowned platform carbonates of the Contrin Formation. The time of the platform drowning is dated with radiolarians and conodonts to the Illyrian, more precisely to the upper part of the Paraceratites trinodosus Ammonoid Zone. The red limestone is overlain by pyroclastics and volcanics (rhyolites) or carbonate (mega)breccia (Uggowitz Formation). The following unit consists of thin-bedded limestone, grainstone and subordinate marl (Buchenstein Formation) deposited during the final filling of the basin from the adjacent prograding carbonate platform (Schlern Formation) in the Ladinian. Map-scale geometry, neptunian dykes, the onset of volcanism, the presence of (mega)breccia and related paleo-escarpments, the lateral variations in thickness and the wedge-shaped geometry of the lithological units provide evidence of syn-sedimentary block faulting and the formation of small-scale, relatively shallow half-grabens within the previously uniform Slovenian Carbonate Platform. This analysis indicates a clear tectonic control over the development of the Middle Triassic stratigraphy. The described extensional event is well correlated and genetically connected with the syn-rift formation of the neighboring Slovenian Basin and other Southern Alpine basins that formed in connection with the opening of the Meliata-Maliac branch of the Neotethys Ocean.     

Changes in sedimentary patterns of coastal and deep-sea successions from the North Atlantic (Portugal) linked to Early Cretaceous environmental change

Coastal mixed carbonate-siliciclastic and carbonate deposits of Late Barremian to Early Aptian age from the Lusitanian Basin (Portugal) are compared with a deep-sea succession (ODP 641) off the coast of Portugal. The coastal deposits show an abrupt cessation of rudist-dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid-rich marls during the Early Aptian. The subsequent development of the carbonate platform during the Late Aptian is masked by a hiatus. For this time interval shallow-water debris deposits of the deep-sea succession ODP 641 indicate that carbonate production in shallow-water areas resume in the early Late Aptian. Carbon-isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the Portuguese with shallow-water successions from Switzerland, France, Oman and the Pacific. The correlation reveals that during the Early Aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon-isotope values associated with the global deposition of organic rich black shales in the deep sea (OAE 1a). In all compared sections rudist-dominated carbonate deposition is stopped and followed either by orbitolinid-rich deposits, the deposition of microbial carbonates or by the drowning of the carbonate platform. The comparison shows that the deterioration for carbonate platform growth conditions during the Early Aptian occurred essentially simultaneously at the various localities. During this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms. Sea level change combined with local effects like elevated nutrient levels and higher temperatures, were probably determining the nature of sedimentary change in shallow-water environments during the carbonate crisis. In the sections studied in Portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late Early Aptian.     

Strontium stratigraphy of the upper Miocene Lithothamnion Limestone in the Majella Mountain,central Italy,and its palaeoenvironmental implications

The ⁸⁷Sr/⁸⁶Sr isotope ratio has been widely used as a physical tool to date and correlate carbonate successions due to the long Sr residence time in comparison with the ocean mixing time. If this method works on oceanic successions, marginal basins may show different Sr isotope records in comparison with the coeval ocean one due to sea‐level variations, continental run‐off and restricted water exchanges. In this work, we present the ⁸⁷Sr/⁸⁶Sr isotope record of the upper Miocene carbonate ramp of the Lithothamnion Limestone (Majella Mountain, central Apennines), as an example of the onset of restricted water exchanges between a marginal basin and the ocean water masses. The overall latemost Tortonian–early Messinian Sr isotope record of the Lithothamnion Limestone fits below the global reference line. This deviation has been interpreted as due to the strong control that freshwater input and enhanced continental run‐off, linked to the migration of the Apennine accretionary wedge and foredeep system, have had on the central Adriatic water chemistry. These results imply that an accurate oceanographic and geodynamic framework along with diagenetic overprint investigation has to be taken into consideration prior to apply SIS on carbonate successions on marginal basins, even when facies analyses indicate fully marine conditions. This seems to be the case for the upper Miocene Central Mediterranean carbonate successions, but may have more general validity and be extended to other recent or past marginal basins.     

Platform configuration, microfacies and cyclicities of the upper Albian to Turonian of west-central Jordan

We present a comprehensive facies scheme for west-central Jordan platform deposits of upper Albian to Turonian age, discuss Cenomanian and Turonian carbonate cycles, and reconstruct the paleogeographic evolution of the platform. Comparisons with adjacent shelf areas (Israel, Sinai) emphasize local characteristics as well as the regional platform development. Platform deposits are subdivided into fifteen microfacies types that define eight environments of deposition of three facies belts. Main facies differences between Cenomanian and Turonian platforms are: rudist-bearing packstones that characterise the higher-energy shallow subtidal (transition zone) during the Cenomanian, and fossiliferous (commonly with diverse foraminifer assemblages) wackestones and packstones of an open shallow subtidal environment. On Turonian platforms high-energy environments are predominantly characterised by oolithic or bioclastic grainstones and packstones, whereas peritidal facies are indicated by dolomitic wackestones with thin, wavy (cryptmicrobial) lamination. Rhythmic facies changes define peritidal or subtidal shallowing-up carbonate cycles in several Cenomanian and Turonian platform intervals. Cyclicities are also analysed on the base of accommodation plots (Fischer Plots). High-frequency accommodation changes within lower Cenomanian cyclic bedded limestones of the central and southern area exhibit two major cyclic sets (set I and II) each containing regionally comparable peaks. Accommodation patterns within cyclic set II coincide with the sequence boundary zone of CeJo1. The lateral and vertical facies distributions on the inner shelf allow the reconstruction of paleogeographic conditions during five time intervals (Interval A to E). An increased subsidence is assumed for the central study area, locally (area of Wadi Al Karak) persisting from middle Cenomanian to middle Turonian times. In contrast, inversion and the development of a paleo-high have been postulated for an adjacent area (Wadi Mujib) during late Cenomanian to early Turonian times, while small-scale sub-basins with an occasionally dysoxic facies developed northwards and further south during this time interval. A connection between these structural elements in Jordan with basins and uplift areas in Egypt and Israel during equivalent time intervals is assumed. This emphasises the mostly concordant development of that Levant Platform segment.     

Middle Jurassic (Bathonian) encrusted oncoids from the Polish Jura,southern Poland

Oncoids from two localities (Ogrodzieniec and Blanowice) of the Polish Jura, southern Poland, have been investigated with respect to their genesis and paleoecology. These oncoids occur within Middle Jurassic (Bathonian) deposits. Those from Ogrodzieniec are large, elliptical, and embedded within a presumably condensed carbonate bed. Those from Blanowice, on the contrary, are significantly smaller, irregular to box-like in shape, and occur within the ore-bearing clays. The oncoids from both localities consist of a distinct carbonate core and laminated cortex that is significantly thicker and better preserved in the Ogrodzieniec oncoids. SEM and optical microscopic investigation of the oncoid cortices revealed the presence of carbonate and silicate layers with web-like structures similar to those occurring in recent cyanobacterial microbialites. Thus, the oncoid cortices investigated may have formed in a photic zone environment with the aid of coccoid and filamentous cyanobacteria. Oxic conditions prevailed during oncoid cortex formation within the siliciclastic setting, which is manifested by low total organic carbon content, high pristane/phytane (Pr/Ph) ratio, and significant predomination of the C₃₁ homohopanes. On the cortices’ surfaces, as well as between particular laminae, various encrusting organisms have been found. The encrusters, dominated by serpulids and bryozoans, are cryptic species that inhabited the undersides and recesses of the oncoids. Their presence on both the upper and lower surfaces of the oncoids indicates that the oncoids were episodically overturned on the seafloor. The much better developed cortex lamination and much higher diversity and abundance of encrusters in the Ogrodzieniec oncoids may point to better trophic conditions prevailing in a shallower marine environment characterized by transparent waters, as opposed to a deeper siliciclastic environment with less transparent waters and probably worse trophic conditions prevailing during formation of the Blanowice oncoids.     

Brachiopodes toarciens de la coupe d’Aït Athmane,Haut Atlas centro-oriental (Maroc)

The Aït Athmane section is located in the eastern part of the central High Atlas, about 20 km north of Errachidia. Its Toarcian series consists of silty marl and silty marly limestone. Its lower part, of early (Levisoni Zone?) to middle Toarcian (Bifrons and Gradata? Zones) age, is rich in brachiopods (rhynchonellides and terebratulides). Its upper part, of late Toarcian age, is rich in terebratulids. Among eighteen reported brachiopod taxa, six are new for the central High Atlas. Their specific assemblages and stratigraphic distributions are similar to those of the Toarcian brachiopods reported from several basins of northern and southern margins of the Tethys and the Subboreal domain, particularly of western France.     

Carbonate breccias in the lower-middle Ordovician Maggol Limestone (Taebacksan Basin,South Korea): Implications for regional tectonism

Summary Carbonate breccias occur sporadically in the Lower-Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these breccias. This study, however, indicates that the majority of these breccias are solution-collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician. Extensive subaerial exposure of platform carbonates resulted in paleokarst-related solution-collapse breccias in the upper maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity elsewhere beneath the Middle Ordovician sequence, most notably North America and North China. Due to its global extent, the early Middle ordovician paleokarst unconformity (‘the Sauk-Tippecanoe sequence boundary’) has been viewed as a product of second-order eustatic sea level drop during the early Middle Ordovician. Although we recognizes a paleokarst breccia zone in the upper Maggol Limestone beneath the Middle Ordovician sequence, the early Middle Ordovician sequence boundary appears to be a conformable transgressive surface or a drowning unconformity, rather than a major paleokarst unconformity. The paleokarst breccia zone in the upper Maggol Limestone is represented by a thinning-upward stack of exposure-capped tidal flat-dominated cycles that are closely associated with multiple occurrences of paleokarst-related solution-collapse breccias. The paleokarst breccia zone in the upper Maggol Limestone was a likely consequence of repeated high-frequency sea level fluctuations of fourth- and fifth-order superimposed on a second-and third-order eustatic fall in sea level that was less than the rate of tectonic subsidence across the platform. It suggests that second- and thirdorder eustatic sea level drop may have been significantly tempered by substantial tectonic subsidence near the end of maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off-platform lowstand siliciclastic quarzite lenses as well as debris flow carbonate breccias. With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a conformable transgressive surface or a drowning unconformity on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the Taebacksan Basin as previously intepreted. Here we propose that the Taebacksan Basin evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. This study also provides a good example that the falling part of the eustatic sea-level cycle may not produce a significant event at all in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence.     

Contribution of calcareous nannoplankton to carbonate deposition: a new approach applied to the Lower Jurassic of central Italy

The Upper Pliensbachian–Lower Toarcian Somma section (Central Italy), which displays alternation of limestone–marl lithotypes, was investigated for its calcareous nannofossil and CaCO₃ contents. In order to evaluate the contribution of calcareous phytoplankton to the carbonate fraction of rocks a new method was applied combining a recently developed technique for nannofossil absolute quantification and measurements of nannofossil size. Our study suggests that nannofossils did not produce the bulk of carbonate mud in the studied section, although they contribute to different extents to the pelagic carbonate fraction. The contribution of both coccoliths and (mainly) the Incertae sedis Schizosphaerella to the carbonate fraction was important only in periods of reduced accumulation rates and/or during clay deposition. The highest estimated carbonate production by nannofossils in the studied section is around 83% of the total carbonate content, but in a sample containing only 12.8 wt% CaCO₃. The observed limestone–marl alternations therefore result from cyclical export of carbonate mud from the shallow Latium–Abruzzi carbonate platform to the Umbria–Marche Basin and, only subordinately, from changes in nannoplankton productivity.     

Paleoecology of a Pennsylvanian encrusting colonial rugose coral in south Guizhou, China

The well-preserved Pennsylvanian encrusting colonial rugose coral Ivanovia is widespread and easily observed in south Guizhou, China. There are three common types of hard substrate encrusted by Ivanovia: in situ carbonate hardgrounds, carbonate hardground clasts, and calcareous bioclasts. Thin, spreading sheets are the most common growth form of Ivanovia in the study region. Ivanovia employed peripheral, medial and mixed growth strategies to occupy a sufficient living space on the substrate. It favored a shallow, warm, and clear marine environment within the photic zone and had a high tolerance of water movement. Ivanovia was generally smothered and covered by mud in the studied area. The Ivanovia fossil communities in south Guizhou are characterized by a low species diversity conforming to the typical evolutionary pattern of hard substrate marine communities in the Carboniferous.     

Composite Trace Fossil Assemblage in a Distal Carbonate Setting from the Tethys (Middle Jurassic,Betic Cordillera,Southern Spain)

Ichnological analysis of a Middle Jurassic carbonate surface from the Betic Cordillera (southern Spain) reveals a complex trace fossil assemblage, including softground Ophiomorpha, firmground Arenicolites, Thalassinoides and Gastrochaenolites, and hardground Trypanites as well as possible Gastrochaenolites. The ecological replacement in the macrobenthic community is interpreted according to successive suites that are controlled mainly by substrate consistency. Variations in composition and abundance of trace fossils between suites can be ecologically and/or taphonomically determined.     

Morphology,faunas and genesis of ordovician hardgrounds from Southern Ontario,Canada

We have used associations of different microfacies to define facies (or microfacies associations) which form reasonably well-defined sequences, which we infer, from analogies with recent and ancient carbonate environments, to have been deposited in a shelf environment characterized by small-scale topographic differentiation into shoal, slope and basinal environments.Shoal environments are characterized by typically cross-bedded, well-sorted bioclastic sands, with intershoal areas consisting of interbedded bioclastic sands and heavily bioturbated finer-grained carbonates.Slope and “basinal” environments are typically represented by “proximal” and “distal” cycles respectively. These we compare with deposits of carbonate ramp bypass channels, and with the more thoroughly studied deep-water clastic submarine fans. Many of the strong variations in environmental energy in these proximal and distal cycles can be attributed to migration of channels on the fans and the effect of funnelling of storm surges down the channels.Although hardground morphology and faunas are mostly related to local effects such as intensity of scouring, time of exposure, topographic differentiation of the surface and other factors, differing hardground types tend to be found in different environments. Smooth and rolling hardgrounds occur in the deeper distal environments, where the beds were subject to only slight scour and often limited exposure before renewed sedimentation. Hummocky and undercut hardgrounds are characteristic of the middle parts of proximal cycles, where they developed marginally to the main bypass channel, and in intershoal areas. Both these areas are sites of intermittent sedimentation and moderate turbulence, where cemented beds may be exposed for some time in environments optimal for attached benthos. These hardgrounds usually contain the most diverse hardground biotas. Pebbly and reworked hardgrounds occur in coarse, basal units of proximal cycles, which are interpreted as the grain-flow fillings of the central parts of bypass channels, though isolated examples occur in intershoal areas and in the higher parts of proximal channels. These hardgrounds contain low-diversity faunas, reflecting the stresses imposed by intermittent or constant abrasion; though some contain more diverse faunal assemblages formed after redeposition.     

Limestone interbedded with submarine volcanics: the Early–Middle Miocene Conejo Volcanics, California

Carbonate sedimentation concurrent with submarine volcanism is very rare in the geologic record but is well displayed in the Early to Middle Miocene Conejo Volcanics of the central Santa Monica Mountains of southern California. Limestone occurs as lenticular deposits on the surface of composite flows units, as matrix within breccia of pebble- to cobble-size volcanic clasts, within primary voids extending down from flow surfaces, as lenses between flows within composite flow units, and as neptunian dikes. The common depositional sequence is of limestone lying on a flow and being overlain by hyaloclastic breccia. Limestone is not deposited on hyaloclastic breccia. Limestone deposition was controlled locally by relief on the sea floor that formed as the volcanic rocks accumulated. The limestone is predominantly skeletal packstone; volcanic clasts ranging in size from silt to boulders are locally common. Major constituent fossils are shallow-water bivalve mollusks, barnacles, serpulids, and regular echinoids; most are epifaunal and hard-substrate taxa in contrast to the soft-substrate and burrowing infaunal biota otherwise dominant in Cenozoic strata along the Pacific Coast of North America. The biota is diagnostic of a non-tropical, warm temperate environment. The limestone was deposited within a local basin that formed along the plate boundary at the western margin of the North American Plate. While volcanic rocks accumulated in the basin at bathyal depth, carbonate sediment accumulated on the outer-shelf margin of the basin and was transported intermittently into the basin by gravity flow. Neogene limestone occurs at only a few other sites in southern California. These have an origin that is similar to those in the Conejo Volcanics but differ in occurring with basin fill of diatomaceous sedimentary rocks rather than of submarine volcanics.