Trilobite Associations Research Articles

Trilobite associations, taphonomy, lithofacies and environments of the Silurian reefs of North Greenland

Llandovery (Silurian) reefs in North Greenland have yielded extensive collections of remarkably well preserved trilobites dominated by scutelluids. These collections provide a unique opportunity to analyse the reefs and their trilobite faunas in a palaeoenvironmental context, and the study highlights the importance of pre-existing collections, to which further scientific value can be added. Counts of trilobite sclerites from thirteen reef localities are analysed using cluster and correspondence analyses to identify trilobite associations, and taphonomic signatures. Lithofacies analysis allows these to be understood in a detailed palaeoenvironmental context. Seven trilobite associations are identified: Scutelluid–Illaenimorph; Scutelluid; Scutelluid–Cheirurid; Scutelluid–Harpetid; Proetid; Encrinurid; and Illaenimorph. The number of associations highlights the variable distribution of taxa within the reefs, which is partly a reflection of intense hydrodynamic sorting in reef environments. Trilobites are predominantly associated with a cement-rich microbial lithofacies; it is apparent that microbial processes were the principal contributors to the production of carbonate mud, and played a significant role in the development of the Greenland reefs. The observed associations comprise time-averaged event beds in an otherwise low energy and slow sedimentation regime, and possibly result from storm activity remobilising sclerites, and depositing them within depressions and cavity fills within the reef surface. Correspondence analysis reveals two distinct taphonomic signatures within the reef, and transport distance is the primary influence on these. The Proetid Association is readily separated from the others by its taphonomic attributes, representing the least amount of transport, and suggesting the taxa involved took advantage of the more sheltered niches within the reef. This is the first study of reef-dwelling trilobites to take advantage of multivariate techniques to identify associations and describe their taphonomic attributes. In particular, the effectiveness of correspondence analysis in recognising taphonomic signatures is demonstrated.

Stratigraphy, carbonate facies and trilobite associations in the Hirnantian part of the Boda Limestone, Sweden

The Hirnantian (Upper Ordovician) sequence of the Boda Limestone is defined and described as a new formal Upper Boda Member. It has four petrologically distinct, bedded units containing three strikingly different trilobite faunas. These differences are thought to be caused by a sea-level lowering leading to the first Hirnantian sea-level lowstand and successive transgression as well as to shifts in sea-water chemistry. This is indicated by the occurrence of a level with botryoidal carbonate cement. On top follows the upper Hirnantian Glisstjärn Formation.

Trilobite palaeobiodiversity during the Devonian in the Ardennes Massif

AbstractTrilobite occurrences and biodiversity from Devonian sections of the Ardennes Massif are presented. Fluctuations in diversity reflect environmental changes and event-stratigraphic turnovers throughout the Devonian. Peak diversity is attained during the Eifelian (Middle Devonian) when the carbonate system is developed. Six trilobite associations have been delineated based on cluster analysis. Distribution of these associations is correlated with the deposition environments and age of the strata.

EARLY ORDOVICIAN (ARENIG) TRILOBITE PALAEOECOLOGY AND PALAEOBIOGEOGRAPHY OF THE SOUTH CHINA PLATE

: Faunal composition of South Chinese Arenig benthic trilobite associations is investigated using the multivariate techniques of TWINSPAN, DCA and seriation. Eight fairly distinct benthic associations can be differentiated, organized primarily along a palaeobathymetrical gradient across the Yangtze Platform in southern Shaanxi and western Hubei and the Jiangnan Transitional Belt in northern Hunan: the Taihungshania, Neseuretus, Trinucleid and Asaphid-Pseudocalymene associations (shallow shelf), the Asaphid-Raphiophorid and Nileid-Asaphid associations (< 100 m outer shelf), the Nileid-Illaenid Association (deep outer shelf carbonates) and the Pseudopetigurus Association (deep outer shelf clastics). The highest levels of diversity are displayed by the Asaphid-Raphiophorid Association of western Hubei. Investigation of the biogeographical affinities of this fauna indicates that South China is biogeographically closest to the other Chinese geotectonic units, and displays strong faunal connections to other central and eastern Asian regions as well as to Tethyan and South American regions. Subdivision of the South Chinese trilobite fauna into different depth zones shows a statistically significant correlation between increasing water depth and increasing faunal cosmopolitanism, although taxa endemic to China or Gondwana also occur even in slope faunas. The results of this biogeographical analysis are consistent with a tropical or subtropical peri-Gondwanan association of South China with other Asian terranes.

LINGULIFORMEAN BRACHIOPODS OF THE MIDDLE–UPPER CAMBRIAN TRANSITION FROM THE VAL D'HOMS FORMATION, SOUTHERN MONTAGNE NOIRE, FRANCE

A thin unit of limestone at the base of the Val d'Homs Formation, close to the Middle–Upper Cambrian boundary, at the Ferrals-les-Montagnes section in the Montagne Noire (southern France), has yielded a fauna including linguliformean brachiopods. Although it is dated as early Late Cambrian by the trilobite association, the recorded brachiopods would suggest a latest Middle Cambrian age. Nine taxa of linguliformean brachiopods are described, including the new genus and species Ferralstreta globosa, and the new species Angulotreta brevis, Dactylotreta bacula, and Schizambon convexus. It is the first record of phosphatic-shelled brachiopods obtained by acid etching in southwestern Europe. All the genera show a great latitudinal dispersion but at species level the association is highly endemic.

Arenig trilobite associations from the Jiangnan Transitional Belt of Northern Hunan, China

Stratigraphic ranges of 32 Ordovician trilobite taxa are recorded across the Zitai Formation (Arenig) and the Jiuxi Formation (Arenig-early Llanvirn) at four localities in northern Hunan, which represent outer shelf facies from the Jiangnan Transitional Belt region of the South China Plate. These are assigned to two benthic trilobite associations. The Nileid-Illaenid Association is characterized by the eponymous families as well as sometimes containing agnostids, Shumardia, Agerina and Ovalocephalus; it represents a persistent ecological composite of the cosmopolitan Ordovician Nileid and Illaenid associations. It is restricted to carbonate facies from the late early and early mid Ordovician of the Chinese regions of peri-Gondwana, having previously been recorded from Tarim. The Pseudopetigurus Association, characterized by the eponymous isocolid, also contains typically deep-water trilobite taxa such as raphiophorids and the mesopelagic cyclopygids Microparia ( Quadratapyge) and Pricyclopyge; despite occurring in clastic facies close to the lower limit of the photic zone (c. <200 m water depth), it is apparently restricted to South China. Faunal changes upsection at the two Zitai Formation localities are interpreted as reflecting the Arenig transgression, although a similar pattern is not displayed across the deeper water Jiuxi Formation.

Arenig trilobite associations and faunal changes in Southern Shaanxi, China

Stratigraphic ranges of 22 Ordovician trilobite taxa are recorded across the Chaochiapa and Siliangssu formations (Arenig) at two localities in southern Shaanxi, representing shelf facies close to the northwestern margin of the Yangtze Platform, with additional material recorded from two spot-sampling localities in the same region. These are assigned to at least three benthic trilobite associations: a deep inner shelf Neseuretus Association, occurring in clastic facies, and outer shelf Trinucleid and Nileid-Asaphid associations, occurring in clastic-carbonate and carbonate facies, respectively. The occurrence of a possible fourth association, a Taihungshania Association apparently occurring in shallow inner shelf clastic facies, is also suggested. Stratigraphic occurrence of these associations at the collection localities is interpreted as reflecting the Arenig transgression. Although many of the recorded trilobite species are widespread across the Yangtze Platform during the Arenig, most of the benthic associations recognized herein are restricted to southern Shaanxi. The sediments in this region are interpreted as having been deposited under slightly shallower palaeobathymetric conditions than those in western Hubei during the Arenig, although an older record of a cyclopygid trilobite from the Siliangssu Formation may challenge this idea.

Latest Neoproterozoic to Middle Cambrian body fossil record in Spain (exclusive of trilobites and archaeocyaths) and their stratigraphic significance

The chronostratigraphical aspects of four Iberian non-trilobite and non-archaeocyathan associations and the record of two separate fossil occurrences are discussed. These fossils are Cloudina and Platysolenites. The associations have been defined as the Anabarella-Aldanella, Arthropoda-Tannuolina-Latouchella, Alanís Fauna, and Hadimopanella-Archiasterella assemblages. They comprise a time span from the late Vendian to the early Middle Cambrian. The existence of upper Vendian associations in the Rio Huso and Ibor groups outcropping through Central Iberia is indicated by the presence of Cloudina. Its biostratigraphic overlapping with vendotaenids and Sabellidites may correlate it with the Sabellidites-Vendotaenia assemblage. In the upper member of the Rio Huso group (Valdelacasa Anticline) and Upper Alcudian strata (Alcudia Valley) the Anabarella-Aldanella association has been found. It may belong to the middle-upper Tommotian in the Siberian Platform and Mongolia and also with the upper Alcudian in Iberia. In the Sierra de Córdoba area, Southern Spain, an Arthropoda-Tannuolina-Latouchella association has been found in the Pedroche Formation, which has been correlated with the late Tommotian to early Atdabanian, based on problematical taxa, archaeocyathid and trilobite stratigraphy. Based on its trilobite associations, a middle Marianian age for the Alanís Fauna and Platysolenites antiquissimus Eichwald, 1860 is established. The youngest association, the Hadimopanella-Archiasterella association, has been found in the lower part of the Láncara Formation of the Cantabrian Ranges. Owing to a diachronism, there are only some localities where the griotte member starts in the Eoparadoxides mureroensis Zone. However, green glauconitic limestones, probably formed during a sedimentary condensation, yield Hadimopanella, so it could appear at the beginning of the Eoparadoxides mureroensis Zone or at the end of the Bilbilian.

Stasis and extinction of Silurian (Llandovery–Wenlock) trilobite associations related to oceanic cyclicity

Silurian trilobites of the central United States belong to a series of temporally-successive associations which appeared abruptly, maintained taxonomic stasis for a time, and then disappeared abruptly. Their disappearance resulted from global perturbations of short-term duration and moderate magnitude, which caused substantial taxonomic replacement but no reorganization of major ecosystems. The most significant extinction and replacement in Silurian trilobite associations in the study area occurs near the Llandovery–Wenlock boundary. This turnover in trilobite associations appears to correspond to Jeppsson's Ireviken Event in his model of oceanic and climatic cyclicity. Major sea-level changes earlier in the Llandovery did not have a similar impact on trilobite associations.

Trilobites and biofacies of the Ordovician Pagoda Formation, Donggongsi of Zunyi, Guizhou Province, China

AbstractTwenty-one trilobite species belonging to 18 genera are described from the measured section of the Pagoda Formation (Caradoc) at Donggongsi, Zunyi, Guizhou Province, China. The fauna is numerically dominated by the hammatocnemidOvalocephalusand remopleurididDislobosaspis(gen. nov.), and theOvalocephalus–DislobosaspisBiofacies is established to represent a shallow outer-shelf trilobite association. The lithofacies and trilobite taphonomy indicate a comparatively quiet and undisturbed depositional environment. Trilobites exhibit strong SE Asian affinities and formed part of the Peri-Gondwana fauna. They are closely related to those of South- Central Europe but show some Baltoscandian aspects.

Aocaspis nov. gen., nouveau Trilobite Nileidae de l'Ordovicien inférieur de Montagne Noire (France)

A new nileid trilobite genus from the lower Ordovician of the Montagne Noire (France), closely related to the worldwide distributed genus Nileus Dalman, 1827, is erected and described under the name Aocaspis nov. gen. A brief discussion on the classification of nileid trilobites is given and leads to assume that two “groups” are present within the family. On the basis of trilobite associations two assemblage zones are defined within the Schistes de Saint-Chinian Formation.

Un biofacies à Trilobites Homalonotidae dans I'Ordovicien de la marge nord-gondwanienne: implications paléobiologiques et paléogéographiques

During the Llandeilo, the sandy lithological units which develop locally in the Armorican Massif, Spain and Morocco, are all characterized by similar trilobite associations in which endobenthic homalonotids. well adapted to shallow water and sandy substrate, are predominant. During the Llandeilo, on the northern Gondwanan margin, the wide geographical distribution of most of the trilobites, controlled by environmental factors, shows that the existence of a ‘Proto-Tethys’ ocean is unlikely. □North Gondwana, Trilobita, Homalonotidae, Ordovician, Llandeilo. palaeoenvironment.

The trilobite fauna of the Middle Ordovician Doularg Formation of the Girvan district, Scotland, and its palaeoenvironmental significance

ABSTRACTThe Doularg Formation is defined within the Albany Group (Tappins Complex); the formation consists of the unfossiliferous Fence Member at the base, succeeded by the Gorse Member (formerly the “Albany mudstones with nodular limestones”), the Separation Sandstone and the Jubilation Member, a bedded, calcareous, silty mudstone. The last named has yielded the rich assemblage of trilobites described, representing thirty genera and including one new genus and seven new species—Bronteopsis matutina, Bumastoides? rivulus, Agerina laurentica, Tretaspis eximia, Ampyxina medici, Stiktocybele (gen. nov.) bathytera, Platycalymene metoeca: Nileus is the most common trilobite. The trilobite fauna indicates that the Doularg Formation should be correlated with some part of the Benan Conglomerate, the uppermost formation of the Barr Group to the north of the Stinchar Valley, and is probably of Llandeilo age. The trilobite association is most closely allied to that of the slightly older basal Superstes Mudstone, reflecting the strong ecological control affecting deeper water faunas. The affinity of the Jubilation Member trilobites with those of the middle Table Head Formation (Llanvirn) of western Newfoundland, is evidenced by the presence in both of Nileus, Cybelurus, Peraspis, and Bronteopsis. These are the four most common genera in the Jubilation Member, comprising over half the total trilobite specimens, and provide striking evidence of the longevity of deeper water genera.

Paléoenvironnements et dynamique de faunes de Trilobites dans l'Ordovicien (Llanvirn Supérieur-caradoc basal) du Massif Armoricain (France)

During the Ordovician, the Armorican Massif is generally considered as a platform domain, a shallow marine environment characterized by endemic invertebrate faunas. However, approximately from the late Llanvirn to the end of the Llandeilo, different trilobite associations develop. Their geographic distribution seems to be mainly related to bathymetric variations. The interpretations proposed in this paper are supported by lithological and sedimentological data and comparisons with living marine crustaceans. The possible mode of life of some trilobites has also been taken into consideration; thus, at the eastern end of the Armorican median synclinorium, and south of Rennes (Martigné-Ferchaud synclinorium), the presence of Parabarrandia, a mesopelagic trilobite from open shelf, indicates amongst other things a marked increase of depth from west to east and from north to south. In the southeastern part of the Armorican Massif (Ancenis region), the development of a cyclopygid biofacies indicates the beginning of a slope opening onto a deep marine environment (South-Armorican ocean?). In some cases ( Uralichas, Ectillaenus, Panderia), the exceptionally large dimensions of the dorsal exoskeletons would result from the low water temperature at high latitudes, which agrees well with the existence of a Gondwanan glaciation at the end of the Ordovician.

Trilobites Calmoniidae de l'Ordovicien supérieur du Maroc et les origines de la Province Malvino‐Cafre

A re-examination of the trilobite Baniaspis globosa Destombes (Phacopina) from the Ashgill of the Anti-Atlas (Morocco) shows that it has several derived characters which allow us to classify it in the family Calmoniidae. Calmoniids were characteristic members of the Malvino-Kaffric province during the Lower Devonian. Hence we regard the origins of this palaeogeographic province as located on the northern Gondwanan margin as early as Ashgill, or even Caradoc, times. We agree with those authors who have suggested that the trilobite associations present in the Anti-Atlas, the Montagne Noire (France) and Bohemia during the earlier Ordovician argue against the existence of a ‘proto-Tethys’ ocean.

An opportunistic Upper Ordovician trilobite assemblage from Missouri

The trilobite Ampyxina bellatula (Savage) occurs in monospecific accumulations within dolomitic strata of the shaly Upper Ordovician Maquoketa Group of northeastern Missouri. A dolomitic stratum containing 97 complete individuals and considerable amounts of pyrite exhibited no associated benthic megafauna. The strata appear to be equivalent to the Scales Formation of the Maquoketa Group of northern Illinois and eastern Iowa which have been interpreted as having been deposited in a muddy environment with severe circulation restrictions. The presence of the monospecific trilobite association in what otherwise would be an unfossiliferous stratigraphic sequence is interpreted as being the result of opportunistic strategy by this trilobite in a resource-rich unstable environmental setting. The association was apparently cat-astrophically buried, thus preserving the age structure of the holaspid population. A size-distribution histogram of the holaspid population indicates that reproduction may have occurred in periodic bursts with lesser reproductive events occurring during the intervening periods. Holaspid survivorship information indicates that mortality was low during the early holaspid stage and increased with age. Anomalous single bed trilobite accumulations of various age rocks have been documented by numerous authors. These may in part be analogous to the Ampyxina occurrence in the Maquoketa Group of Missouri, and be attributable to opportunistic strategies.

Trilobite associations from the Chouteau Formation (Kinderhookian) of central Missouri

Three distinct trilobite associations can be recognized in the Chouteau Formation (Tournaisian, Early Carboniferous) of central Missouri. These associations appear to be lithologically and environmentally sensitive. Association A, the stratigraphically lowest association, contains six genera and is among the most diverse Carboniferous trilobite associations known in North America. This association is dominated numerically by Proetides colemani and exhibits a restricted geographic and stratigraphic distribution. The association is found only in the basal 20 cm of the Chouteau Formation at one locality, in strata representing transgressive subtidal deposits. Association B is found within subtidal and open shelf lithologies and is dominated by two trilobite species, Breviphillipsia sampsoni and Breviphillipsia? swallowi. Breviphillipsia sampsoni, an apparently eurytopic species, is found in both shaly and carbonate strata but is predominately recovered from the shaly partings and interbeds. Breviphillipsia? swallowi, a more stenotopic species, occurs primarily in the more carbonate-rich intervals. In addition, five trilobite species, subordinate in numbers, are only locally common in Association B. The sparse trilobite fauna of Association C is dominated numerically by Namuropyge? armata, and is contained within open shelf sediments that interfinger with mud biostrome lithologies.Early Carboniferous adaptive radiation of trilobites resulted from the creation of new ecospace by transgression. This allowed initially eurytopic trilobites to move into and occupy certain niches that may have been unavailable to them prior to the Frasnian extinctions. With continued deepening, niche-specialized associations developed in more offshore settings.

Trilobites ordovícicos del Macizo Hespérico español: una visión bioestratigráfica.

The present work represents a preliminary synthesis of ali the trilobites quoted in the Spanisl-i areas of the Hesperian Massif so far, The main findings are analyzed from a chronostratigraphical and geographical point of view, and the differences between the successive trilobite associations are shown, as well as their significance from a palaeobiogeographical point of view. The utility of these organisms for the biostratigraphical characterization of deposits belonging to several Departamento de Paleontologia e Instituto de Geologia Economica (CSIC * UCM), Facultad de Ciencias Geologicas, Universidad Complutense, Ciudad Universitaria. 28040 - Madrid. 267 epochs and the problems derived of their correlation with other areas are also studied.

Mid-cautleyan (Ashgill Series) trilobites and facies in the English lake distinct

During Zones 2 and 3 of the Cautleyan Stage (Ashgill Series) a marine transgressive sequence of conglomerates, sandstones (Longsleddale Formation), calcareous siltstone (Stile End and High Pike Haw Formations), mudstone (Torver Formation) and interbedded argillaceous limestone and calcareous mudstone (Applethwaite Formation) was deposited in the southern Lake District. Three tribolite associations are recognized within these rocks: a Proetid Association, found in the sandstones and calcareous siltstone; an Illaenid Association in the mudstone of the Torver Formation and at local, restricted horizons within the Applethwaite Formation; a Calymenid Association, found in the interbedded mudstone and limestone. It is suggested that strong causal relationships, both positive and negative, existed between the trilobites and facies type. Absences of particular trilobite groups do not appear, in the main, to be artifacts of sampling and, along with presences and abundances, are considered important to the understanding of the distribution of trilobites and their relationships with the facies type. Antipathetic relationships are noted between Prionocheilus and other calymenids; and between Tretaspis and both proetids and encrinurids. Because the trilobite associations could be recognised in the field prior to statistical analysis, it is possible to compare and contrast quantitative measures which summarize the relationships among localities and taxa. The following measures are calculated from abundances: correspondence, covariance (taxa) or average Euclidean distance squared (localities), and correlation coefficient (taxa) or standardized average Euclidean distance squared (localities). Of these the principal axes of the correspondence matrix separate the three associations much further than the other two measures. Considered as comparisons of taxa, correspondence values may offer a compromise, desirable in quantitative ecology, between emphasis on common taxa (covariance) and on rare taxa (correlation coefficient). When only occurrences are used, the trilobite associations are scattered more broadly and taxa behave more independently. The greater degree of interdependence of taxa when abundances are used is considered helpful to characterization of association in this study.

Trilobite associations in the British Wenlock

Summary Five common trilobite associations occur in the British Wenlock. The associations are characterised by increased abundance of particular genera and their distribution is related to changes in lithofacies and position on the palaeoslope. Comparable associations are widespread in the Silurian of other parts of the world. Similar lithofacies of different ages often contain generically identical trilobite assemblages thus highlighting the dangers of basing correlations upon comparisons made above the specific level.