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.     

Evolution of pelagic swells from hardground analysis (Bathonian–Oxfordian, Eastern External Subbetic, southern Spain)

The Middle Bathonian to Middle Oxfordian interval in the Eastern External Subbetic (Betic Cordillera, SE Spain) is characterized by Ammonitico Rosso facies including various stratigraphic breaks. Five hardground-bounded units are recognized in relation to hiatuses in the ammonite record at the following stratigraphic boundaries: Hg1 (Lower–Middle Bathonian), Hg2 (Middle–Upper Bathonian), Hg3 (Lower–Middle Callovian), Hg4 (Middle–Upper Callovian), and Hg5 (Callovian–Oxfordian). Interesting features of these hardgrounds include their microfacies, ferruginous crusts and macro-oncoids, taphonomy of macroinvertebrates, trace fossils, neptunian dykes, and the hiatuses associated with each of them. The main hardgrounds (Hg1, Hg2, and Hg5) contain trace fossils of the Cruziana and Trypanites ichnofacies as well as abundant fossil macroinvertebrates with taphonomic features evidencing corrasion, early diagenesis, and reworking, indicating substrate evolution from softground to hardground. Neptunian dykes affected the trace fossils and ammonoid moulds, and their walls and the hardground surfaces were colonized by ferruginous microbial crusts. These features are characteristic of the External Subbetic pelagic swells, where the absence of sedimentation, sediment bypassing and erosion, and early diagenesis during relative sea-level falls produced hardgrounds. The neptunian dykes are indicative of tectonic activity in the areas of pelagic swells. Ferruginous crusts and macro-oncoids developed only on hardground surfaces and neptunian dykes walls prior to deposition of condensed bioclastic beds, which are interpreted as the first deposits after hardground development and are related to the onset of transgression. The varying ranges of the gaps as well as lateral facies changes are related to different local paleobathymetry controlled by the activity of listric faults.     

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.     

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.     

Hettangian (Early Jurassic) Dinosaur Tracksites from the Mecsek Mountains,Hungary

A rare example of a North American Jurassic hardground is found in the Carmel Formation of southwestern Utah. The Carmel hard‐ground was formed across a carbonate lagoon from an oolitic shoal seaward to a subtidal shelly facies landward. It has an abundant bivalve fauna consisting of thick layers of encrusters (the oyster Liostrea and the plicatulid Plicatula), borers (the ichnofossil Gastro‐chaenolites with the mytilid Lithophaga often preserved inside), and nestlers (the mytilid Modiolus). A rare soft‐bodied bryozoan (Arach‐nidium) is preserved by bioimmuration in the attachment scars of Liostrea; this is the first bioimmuration recorded from the Jurassic of North America, and the first bioimmuration recorded from a hard‐ground. The phoronid boring Talpina is present in some Liostrea shells; it was apparently excavated after the death of these oysters. The Carmel hardground community does not contain other fossils, such as serpulids, brachiopods, foraminiferans, and skeletal bryo‐zoans, typical of Jurassic hardgrounds elsewhere. It represents a low diversity molluscan community developed in a restricted marine environment.     

Crinoids, hardgrounds, and community succession: The Silurian Laurel—Waldron contact in southern Indiana

Halleck, Margaret S.: Crinoids, hardgrounds, and community succession: The Silurian Laurel-Waldron contact in southern Indiana.
The uppermost surface of the Silurian Laurel Limestone at its contact with the Waldron Shale in southeastern Indiana was a hardground lithified prior to the deposition of the Waldron. Evidence for this conclusion is the presence of attached palmate crinoid roots, auloporid corals, and craniid brachiopods on the Laurel surface; the irregularity of the contact with the Waldron; and a pyritic veneer at this contact. The hardground apparently had a submarine origin. In addition to the attached epifauna mentioned above, algal-sediment 'clods' formed on this surface. Some of these accumulated around the crinoid stems, causing them to produce cirral extensions. The resulting community was a crinoid 'meadow' with algal growths forming sediment traps around and between the crinoids. Later stages of Waldron Shale deposition led to the development of a soft-bottom community.     

Late Cambrian hard substrate communities from Montana/Wyoming: the oldest known hardground encrusters

Hardground surfaces from the Late Cambrian Snowy Range Formation in Montana/Wyoming are the oldest known non-reefal hard substrates exhibiting encrusting fossils. These surfaces range in age from Early Franconian to early Trempealeauan. Hardgrounds were developed on slightly hummocky to planar, truncated surfaces of glauconite-rich, carbonate, flat pebble conglomerates, which were deposited during episodes of storm scouring in shallow subtidal environments of the Montana/Wyoming shelf. Snowy Range hardgrounds are encrusted by a low diversity assemblage of fossils dominated by simple discoidal holdfasts of pelmatozoans, probably crinoids, and including small conical spongiomorph algae? and probable stromatolites. Macroborings (e.g. Trypanites) are notably absent from all hardground surfaces, although sharp-walled, vertical, cylindrical holes (borings?) occur in micrite clasts imbedded in certain flat pebble conglomerates. No evidence of faunal succession or microecologic partitioning of irregular surfaces was observed on these Cambrian hardgrounds.     

From sediment to rock: diagenetic processes of hardground formation in deep-water carbonate mounds of the NE Atlantic

Modern cool-water carbonate mounds topped by corals form an extended reef belt along the NW European continental margin at 200–1200 m water depth. An essential element of mound growth are hardgrounds which provide a stable substratum for mound-building invertebrate colonisation and stabilise the inclined mound flanks. Evaluating the degree of lithification and the slope stability against erosion represents an important task within the ESF programme MOUNDFORCE under the umbrella of EUROMARGINS. Sampling of hardgrounds during RV Meteor cruises M61-1 and -3 in 2004 by means of the IFM-GEOMAR TV-grab and the Bremen ROV QUEST focused on carbonate mounds of the Porcupine Seabight and northwestern Rockall Bank off Ireland. Lithified carbonates of mid-Pleistocene age were exhumed during the Holocene and are now exposed on the top and flanks of numerous carbonate mounds showing a patchy to dense colonisation by living corals and associated invertebrates. The sediments, composed of foraminiferal–nannoplankton oozes and admixed mound-derived invertebrate skeletons, range from partly lithified chalks to dense micritic limestones. These wackestones to packstones clearly differ from bacterially induced authigenic carbonate crusts typical of hydrocarbon seep settings by showing current-induced sedimentary structures, a non-luminescing matrix indicating oxic pore fluids, and a marine isotopic signature lacking any depleted carbon regime which is typical of anaerobic methane oxidation. The carbonate lithification is driven by carbonate ion diffusion from supersaturated seawater into the pore fluids in the studied areas. Vigorous bottom currents were the ultimate control not only of carbonate cementation by enhancing the diffusion process and supporting a pumping mechanism, but also of hardground formation and mound shaping by exhuming lithified carbonates and preventing fine-grained sediment accumulation at the downslope mound flanks.     

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.     

New discoveries of vertebrates from a near-shore marine fauna from the Early Miocene of northwestern Venezuela

New discoveries from a recently described nearshore marine fauna from northwestern Venezuela of presumed early Miocene age are reported. The fossils consist of a cranial portion of a crocodile assigned to the Tbmistominae, confirming the presence of this group in South America, and the scapula of a cetacean with affinities to the Platanistoidea. The stratigraphic section of the fossil locality ‘Cerro La Cruz’ consists of ca. 87 m of clayey marls interbedded with thin hardground units, with the upper strata being gypsiferous. The fossils were found in sandstones stratigraphically above this sequence.      

An integrated analysis (microfacies and ichnology) of a shallow carbonate-platform succession: upper Aptian,Lower Cretaceous,Betic Cordillera

Four lithofacies and 12 microfacies types recognized in an upper Aptian section in the Sierra de Bedmar-Jódar (Prebetic of Jaén) represent shallow lagoonal environments (marl and marly limestone) and sand bars that delimited the lagoon. The lagoonal facies reflect subtidal restricted water circulation with low energy. The sand bar facies (intertidal environment) have upper surfaces that show the effects of supratidal and subaerial conditions. The presence of early fractures in particular lithofacies shows the importance of local synsedimentary tectonics during sedimentation. Thalassinoides, ?Arenicolites, Diplocraterion, Circolites, Gastrochaenolites and Trypanites are recorded in different beds of this section, reflecting various states of substrate consistency, in the form of firmground, hardground, and rockground. Whereas firmground conditions were dominant in the lower part of the section, hardgrounds and rockgrounds are mainly present in the upper part of the section. Four types of shallowing-upward elementary sequence are recognized. All the sequences show at the base mudstone or wackestone microfacies representing a lagoonal environment, overlain by sand-bar grain-pack-stone facies corresponding to a bar bounding the lagoon. The factors that controlled their development were carbonate production and tectonic movements.     

Heteromorph ammonites from the Tata Limestone Formation (Aptian–Lower Albian), Hungary

An important new ammonite fauna was collected by Fülöp in 1953 and 1960 from basal lenses between a Tithonian hardground and the overlying Tata Limestone Formation containing many heteromorph ammonites. This assemblage of ammonites has been determined as being of Early Albian ( tardefurcata Zone) age. Among the heteromorphs are species of Tonohamites and Ptychoceras , which are familiar components of Late Aptian or Early Albian ammonite faunas. The genera Ephamulina , Hamites and Protanisoceras are also recorded, the earliest species of which had previously come from sediments of late Early Albian ( mammillatum Zone) age. While Hamites and Protanisoceras are common in Europe, Ephamulina had previously only been known from Madagascar. The discovery of Ephamulina , Hamites and Protanisoceras supports the view that these phylogenetically significant ammonites had radiated close to the Aptian/Albian boundary. Four new species of Hamites ( H. czaszari , H. fazekasensis , H. fueloepi and H. kalvariensis ) and one new species of Tonohamites ( T. boldii ) are described.     

广东南雄盆地南雄群的介形类动物群

南雄群及其介形类化石在我国晚白垩世非海相地层划分对比中占重要地位,主田和杨梅坑剖面主田组和浈水组中有270个样品含介形类化石,计有23属(2亚属)99种(12新种)。南雄群介形类动物群是以Talicypridea,Cypridea,Nanxiongium,Candoniella等4属为主,称Talicypridea Cypridea Nanxiongium动物群(简称Tali cypridea动物群)。该动物群在我国和蒙古的非海相地层中广泛分布,时代属晚白垩世中—晚期。     

Development of phosphatized hardgrounds in the miocene Globigerina Limestone of the maltese archipelago,including a description ofGamopleura melitensis sp. nov. (Gastropoda,Euthecosomata)

In the Maltese Islands two phosphorite layers occur in the Globigerina Limestone Formation (?Aquitanian to Langhian). These layers, labeled C1 and C2, display a multi-stage development with a two-stage hardground development on top (labelled lower and upper hardground). In the lower hardground, lithification and mineralization followed a sedimentary framework betweenThalassinoides burrows, resembling the Cretaceous ‘nodular chalks’ which were marginally phosphatized when they became exposed to the sea floor. In Phosphorite Layer C2, development of this lower hardground has been superimposed by small-scale cycles. It is underlain by one or more omission surfaces each followed by phosphate-rich, bioturbated biomicrites.     

Cambrian to Cretaceous changes in hardground communities

The changing nature of the communities of boring and encrusting taxa found on upward-facing hard-grounds has been studied from the standpoints of (a) diversity, (b) faunal composition, and (c) nature of the niches occupied. After a rapid initial increase in the early Palaeozoic, diversity remained at much the same level from the Middle Ordovician until the late Cretaceous. However, there is a considerable turnover in the identity of the individual taxa between successive sample intervals. The incoming and outgoing of the major groups parallel their fortunes in the marine realm as a whole. Niche analysis suggests that the same feeding levels are occupied for most of the history of hardground communities, but Mesozoic faunas contain a much higher proportion of species with true exoskcletons, or which lived infaunally. The evolution of these forms was probably influenced by the Mesozoic radiation of marine predators and duriphages, but it also resulted in Mesozoic hardground faunas being more resistant than their Palaeozoic counterparts to episodic corrasion. Resulting higher population densities in the Mesozoic were probably one reason why cavity faunas beneath some of these hardground surfaces are more diverse than those beneath Palaeozoic examples. □ Hardground, community, evolution.     

Morphology and ultrastructure of epilithic versus cryptic,microbial growth in lower Cambrian phosphorites from the Montagne Noire,France

The lower Cambrian grainy phosphorites of the northern Montagne Noire occur interbedded with grey to black, laminated to massive shales and limestones deposited along the edge of a continental shelf, associated with slope‐related facies and unstable substrates. The concentration of phosphate took place by repeated alternations of low sedimentation rates and condensation (hardgrounds), in situ early‐diagenetic precipitation of fluorapatite, winnowing and polyphase reworking of previously phosphatized skeletons and hardground‐derived clasts. The succession of repeated cycles of sedimentation, phosphate concentration, and reworking led to multi‐event phosphate deposits rich in allochthonous particles. Phosphogenesis was primarily mediated by microbial activity, which is evidenced by the abundance of phosphatized putative microbial remains. These occur as smooth and segmented filaments, sheaths, and ovoid‐shaped coccoids. These simple morphologies commonly form composite frameworks as a result of their aggregation and entanglement, leading to the record of biofilms, microbial mats, and complex networks. These infested the calcitic skeletonized microfossils that littered the substrate. Microbial activity evidences epilithic (anisotropic coatings on skeletons), euendolithic (perforating skeletal walls), and cryptoendolithic (lining inter‐ and intraparticulate pores) strategies, the latter dominated by bundles of filaments and globular clusters that grew along the cavities of helcionellids and hyoliths. According to their epilithic versus cryptic strategies, microbial populations that penetrated and dwelled inside hard skeletal substrates show different network and colonial morphologies. These early Cambrian shell concentrations were the loci of a stepwise colonization made by saprophytic to mutualistic, cyanobacterial–fungal consortia. Their euendolithic and cryptoendolithic ecological niches provided microbial refugia to manage the grazing impact mainly led by metazoans.     

西藏南部白垩纪岗巴群的双壳类及其生物地理意义

描述双壳类化石４２种,建立１０新种：Ｇｒａｍｍａｔｏｄｏｎ（Ｎａｎｏｎａｖｉｓ）ｍｉｎｕｍ ｓｐ．ｎｏｖ．,Ｐｒｏｐｅａｍｕｓｓｉｕｍ（Ｐ．）ｔｉｂｅｔｅｎｓｐ ｅｐ．ｎｏｖ．,Ｐｌｉｃａｔｕｌａ ｈｉｍａｌａｙｅｎｓｉｓ ｓｐ．ｎｏｖ．,Ｐｓｅｕｄｏｌｉｍｅａ ｄｕｏｄｅｃｉｃｏｓｔａｔａ ｓｐ．ｎｏｖ．,Ｐｙｃｎｏｄｏｎｔｅ（Ｐｈｙｇｒａｅａ）ｇａｍｂａｅｎｓｉｓ ｓｐ．ｎｏｖ．,Ｎｏｔｏｔｒ     

Bioerosional innovation for living in carbonate hardgrounds in the Early Ordovician of Sweden

Some of the world's oldest macroborings occur in hardgrounds in lower Ordovician (Arenig) limestones exposed on the island of Öland, southern Sweden. The trace fossils, which are described here as Gastrochaenolites oelandicus isp. nov., appear to be dwelling structures excavated in the indurated substrate by invertebrates of unknown taxonomic affinity. They are the oldest examples of this ichnogenus. The appearance of a macroboring life habit at this early time represents a revolutionary new adaptive strategy for inhabiting carbonate hardgrounds. However, this innovative strategy apparently was not successful for the long term, because this particular macroboring taxon seems to have disappeared shortly after its early Ordovician appearance.     

Discovery of a radiolarian fauna from the tithonian of the solnhofen area (Southern Franconian Alb, southern Germany)

A highly diverse and well preserved radiolarian fauna from the Mörnsheim Formation (Altmühltal Group, Lower Tithonian) of the Solnhofen area (Southern Franconian Alb) is presented. Herein, only well-known species are selected from a rich fauna with presumably numerous new taxa. Some of these species show additional morphological features, missing or rudimentarily developed due to preservation in previously described specimens. The selected species are stratigraphically classified according to international Unitary Association Zones.     

Cenomanian/Turonian sponge microbialite deep-water hardground community (Liencres,Northern Spain)

Summary A benthic community of sessile metazoans dominated by coralline sponges (e.g.Acanthochaetetes andVaceletia) is found within a Cenomanian-Turonian deep water hardground succession cropping out at the coastal area of the Bay of Biscay near Santander. The characteristic K-strategic community exhibits a very close taxonomic relationship with modern communities from the Pacific realm, which allows for a comparison with Recent environmental conditions. The sponge community was associated with automicrites, microbialites, and thin mineralized limonitic biofilms. This biofacies is typically found in cryptic niches of reefal buildups (“telescoping”). The iron-rich biofilms had a strong electrochemical corrosive ability which explains the distinct submarine dissolution patterns. The hardground conditions are controlled, in part, by strong contour current regimes linked with extremely oligotrophic water masses. This system was established during the drowning of a distal carbonate ramp during the early Middle Cenomanian (A.rhotomagenese zone). In the uppermost portion of the hardground (Late Cenomaian, upperR. cushmani zone) the coralline sponge community was replaced by thick limonitic stromatolites with numerous encrusting foraminifera (Miniacina-type) and by colonies of the problematic iron bacteriumFrutexites. This event is accompanied by an increase of terrigenous influx and detrital glauconite, indicating a fundamental change in food web, and terminates the sponge dominated basal hardground interval. Thehardground was buried by hemipelagic sediments during the Middle Turonian (upperR. kallesi zone). Dedicated to the memory of Prof. Dr. JostWiedmann