Olenid Trilobites Research Articles

Why barren intervals? A taphonomic case study of the Scandinavian Alum Shale and its faunas

The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician) accumulated under generally low oxygen concentrations. Syndepositional changes in the oxygen concentrations of the bottom water are reconstructed on the basis of the fossil fauna. Under relatively high oxygen concentrations, brachiopods and non-olenid polymerid trilobites inhabited the sea floor. Under lower oxygen concentrations the fauna was dominated by agnostids and at lowest oxygen levels by olenid trilobites. The enrichments of vanadium relative to nickel, as well as the enrichment of sulphur, match these faunal changes. A geochemical classification of the dysoxic environment is presented. The abundance of calcareous fossils decreases with increasing bottom water oxygen concentrations, indicating that the preservation of calcareous hard parts is most likely at the lowest oxygen concentrations. The poor preservation of calcareous fossils at relatively high oxygen concentrations is explained by the generation of corrosive pore waters during the reoxidation of sulphide compounds. Trilobitic and non-trilobitic intervals alternate up through the shale. Non-trilobitic intervals are either barren or contain non-calcareous fossils (phosphatic brachiopods, phosphatic ‘ostracodes’ and graptolites). The stratigraphical variation of trilobitic and non-trilobitic intervals is interpreted to reflect major changes in oxygen levels that might be linked to sea-level and climatic fluctuations.

The eyes of the early Tremadoc olenid trilobite Jujuyaspis keideli Kobayashi, 1936

The morphology of the eyes of the olenid trilobite Jujuyaspis keideli Kobayashi, 1936, is described and illustrated. Studied specimens come from Early Tremadocian pyritiferous black shales of the Casa Colorada Formation (= Purmamarca shales) at Purmamarca, Jujuy Province, northwestern Argentina. The eyes are holochroal and proportionately large relative to the overall size of cephalon. They are always found attached to the librigena, showing no preserved lenses, only molds of their surfaces. Their molds demonstrate that lenses were numerous, biconvex, hexagonal in outline and arranged in an hexagonal close-packing system. The eye curvature and the disposition of the facets covering all the visual surface indicate that Jujuyaspis keideli Kobayashi had a visual field wider than that of most benthic olenids. The pattern of lens arrangement and the poorly developed peripheral zone support pelturine affinities for the species.

THE EYES OF THE EARLY TREMADOC OLENID TRILOBITEJUJUYASPIS KEIDELIKOBAYASHI, 1936

The morphology of the eyes of the olenid trilobite Jujuyaspis keideli Kobayashi, 1936, is described and illustrated. Studied specimens come from Early Tremadocian pyritiferous black shales of the Casa Colorada Formation (= Purmamarca shales) at Purmamarca, Jujuy Province, northwestern Argentina. The eyes are holochroal and proportionately large relative to the overall size of cephalon. They are always found attached to the librigena, showing no preserved lenses, only molds of their surfaces. Their molds demonstrate that lenses were numerous, biconvex, hexagonal in outline and arranged in an hexagonal close-packing system. The eye curvature and the disposition of the facets covering all the visual surface indicate that Jujuyaspis keideli Kobayashi had a visual field wider than that of most benthic olenids. The pattern of lens arrangement and the poorly developed peripheral zone support pelturine affinities for the species.

Olenid trilobites: the oldest known chemoautotrophic symbionts?

Late Cambrian to early Ordovician trilobites, the family Olenidae, were tolerant of oxygen-poor, sulfur-rich sea floor conditions, and a case is made that they were chemoautotrophic symbionts. Olenids were uniquely adapted to this habitat in the Lower Paleozoic, which was widespread in the Late Cambrian over Scandinavia. This life habit explains distinctive aspects of olenid morphology: wide thoraces and large numbers of thoracic segments, thin cuticle and, in some species, degenerate hypostome, and the occasional development of brood pouches. Geochemical and field evidence is consistent with this interpretation. Olenids occupied their specialized habitat for 60 million years until their extinction at the end of the Ordovician.

Olenus henningsmoeni, a new trilobite from the Upper Cambrian of Västergötland, Sweden

Abstract A new species of olenid trilobites, Olenus henningsmoeni n. sp., is described from the Upper Cambrian Olenus/Agnostus (Homagnostus) obesus Zone of Kinnekulle and Billingen in Vastergotland, Sweden. It is closely comparable to O. gibbosus and O. transversas, but differs in having 19 thoracic segments with long pleural spines. The large number of thoracic segments may indicate that it was derived by peramorphosis. A species of Parabolina from the Olenus/Agnostus (Homagnostus) obesus Zone is figured. Ahlgren, J. & Ahlberg, P., 1996: Olenus henningsmoeni, a new trilobite from the Upper Cambrian of Vastergotland, Sweden. GFF, Vol. 118 (Pt. 2, June), pp. 73–77. Stockholm. ISSN 1103–5897.

Cambrian and early Tremadoc rocks of the Llangynog Inlier, Dyfed, South Wales

AbstractUntil recently no Cambrian rocks were known in the Llangynog area. Detailed mapping has now revealed a succession of ?Lower and Upper Cambrian rocks overlain by Tremadoc rocks. The Allt y Shed Sandstones (new) rest unconformably on the Precambrian, but have yielded no diagnostic fossils and are tentatively assigned to the Comley Series. Succeeding with faulted or unconformable contact is an Upper Cambrian Merioneth Series succession which includes in ascending order: conglomerates, sandstones and siltstones with olenid trilobites and resembling the Treffgarne Bridge Beds of the Haverfordwest area; micaceous shales and siltstones referred to the Ffestiniog Flags Formation; and black mudstones with calcareous concretions and a rich olenid fauna referred to the Dolgellau Formation. Succeeding the latter with possible disconformity is a succession belonging to the lower part of the Tremadoc Series and earlier than any rocks of that series hitherto recorded from the area.

Paleozoic (Cambrian through Devonian) anoxitropic biotopes

The oxygen-poor to dentrified waters of modern oceans provide an analog for open ocean conditions which contained the Early Paleozoic “graptolite” biotope. Certain euphausiids, other zooplankton and fish, as demonstrated in the Eastern Tropical Pacific, are found concentrated in and about denitrified waters. The boundary zone between oxic and denitrified waters show intense organismal growth due to the increased chemical availability of nutrients as reduced nitrogen compounds. Such waters are areally limited in the present cold and well-ventillated modern ocean. The distribution patterns showing attraction to low or oxygen-depleted waters ( anoxitropy) in these modern open marine faunas suggest that Early Paleozoic plankton and nekton, preserved in lithofacies formed under low oxygen or anoxic coditions, could have been similarly attracted to the more extensive ancient denitrified and anoxic waters. The major Paleozoic faunal groups, in order of their occupation of the niche, include agnostid and olenid trilobites, graptoloid graptolites, stylionids, thin-shelled bivalves, small orthocone nautiloids, and early ammonoids. The expansion of low-oxygen to anoxic waters across the shelves during warm climates in the Early Paleozoic may be correlated with major evolutionary radiations in the graptolites and possibly in the early ammonites.

The Nærsnes section, Oslo Region, Norway: trilobite, graptolite and conodont fossils reviewed

AbstractNew collections of trilobites, graptolites and conodonts, the latter figured for the first time, have been made from an unbroken, uniform sedimentary succession across the Cambrian–Ordovician Boundary. The zonal conodont Cordylodus proavus first appears in undoubted pre-Tremadoc strata. Additional conodonts show that the base of the Tremadoc lies within beds correlative with the Symphysurina Zone of North America and at a level above the base of the Hirsutodontus simplex subzone of the C. proavus Zone. Cordylodus lindstromi and Iapetognathus preaengensis first appear at the base of the Tremadoc. The olenid trilobite Jujuyaspis occurs in the same lower Tremadoc interval and has great potential for interregional correlation.

Jujuyaspis borealisand associated trilobites and conodonts from the Lower Ordovician of Texas and Utah

Jujuyaspis borealisis reported from earliest Ordovician (North American usage) limestones in central Texas and western Utah, the first time this species has been recognized in the United States.Jujuyaspisis a widespread olenid trilobite that occurs near the base of the Tremadoc Series in a variety of lithologies in North and South America, Europe, and Asia. When international agreement is reached on the exact horizon at or near the base of the Tremadoc Series that is to be used as the Cambrian–Ordovician boundary,Jujuyaspiswill likely prove to be a very useful taxon for recognition of the boundary interval.

Evolution of Trilobite Populations, Late Cambrian Biomeres: ABSTRACT

New data from the southwestern United States on Late Cambrian trilobite biomeres suggest that the non-agnostid trilobite population of each biomere underwent four successive stages of evolution before becoming extinct. The first and stratigraphically lowest stage is characterized by species with considerable morphologic variability and short stratigraphic ranges. The second stage is characterized by species with longer stratigraphic ranges and less individual morphologic variability. The third stage is characterized by high species diversity and species with long stratigraphic ranges and increasingly less morphologic variation. The fourth, stratigraphically highest stage is characterized by low species diversity, coquinoid abundance of at End_Page 743------------------------------ least one species, and at least one species of olenid trilobites. The bounding faunal discontinuities of trilobite biomeres probably resulted from repeated migrations onto the craton of a slowly evolving extracratonic basic stock, each migration replacing the major cratonic nonagnostid trilobites. Following each migration there was an initial burst of adaptive evolution (stage one) as the eugeosynclinal trilobites evolved rapidly under strong selection pressure imposed by their new cratonic environment. Stage two represents the attainment by a few genera of fairly complete adjustment to the environment. Stage three represents maximum adjustment to and utilization of the environment. The extinction of many long-ranging species near the end of stage three and the peculiar but characteristic composition of stage four suggest that stage four represents he last stand of the established trilobites of the biomere prior to their replacement by a new migration of extracratonic trilobites. End_of_Article - Last_Page 744------------

Geography of olenid trilobite distribution and its influence on Cambro-Ordovician correlation

Fibre concentrations of asbestos were measured in the air of a communal dining room in which the damaged ceiling had a sprayed on coating of insulation containing asbestos. The average concentration of crocidolite asbestos fibres was 4 f/cm3, 20 times the highest air concentration that appears to have been reported previously for a public building. It is concluded that although air concentrations of asbestos fibres in public buildings containing asbestos insulation materials are usually low, high concentrations can occur. This may have implications for the risk of exposed persons developing diseases associated with asbestos.

Short-time polarization in thorium oxide

The oxygen-poor to dentrified waters of modern oceans provide an analog for open ocean conditions which contained the Early Paleozoic “graptolite” biotope. Certain euphausiids, other zooplankton and fish, as demonstrated in the Eastern Tropical Pacific, are found concentrated in and about denitrified waters. The boundary zone between oxic and denitrified waters show intense organismal growth due to the increased chemical availability of nutrients as reduced nitrogen compounds. Such waters are areally limited in the present cold and well-ventillated modern ocean. The distribution patterns showing attraction to low or oxygen-depleted waters (anoxitropy) in these modern open marine faunas suggest that Early Paleozoic plankton and nekton, preserved in lithofacies formed under low oxygen or anoxic coditions, could have been similarly attracted to the more extensive ancient denitrified and anoxic waters. The major Paleozoic faunal groups, in order of their occupation of the niche, include agnostid and olenid trilobites, graptoloid graptolites, stylionids, thin-shelled bivalves, small orthocone nautiloids, and early ammonoids. The expansion of low-oxygen to anoxic waters across the shelves during warm climates in the Early Paleozoic may be correlated with major evolutionary radiations in the graptolites and possibly in the early ammonites.