Gerd Geyer

Palaeogeographical controls on the Cambrian trilobite immigration and evolutionary patterns reported in the western Gondwana margin

Abstract Southward drifting of the western Gondwanan margin during the Cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate (such as carbonates and evaporites). Recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of Cambrian benthic communities. Palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration, speciation and extinction rates. The variability of the documented biogeographical patterns is directly related to species diversity, in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms. Early Cambrian trilobite faunas show a high degree of both substrate control and endemicity, although transgressions led to parallel shifts in faunal compositions. By contrast, Mid-Cambrian trilobite faunas are relatively uniform across western Gondwana, and latest Mid- and Late Cambrian associations document influence of an increased similarity with Asian trilobite faunas.

The base of a revised Middle Cambrian: are suitable concepts for a series boundary in reach?

Defining the base of a series that replaces the traditional Middle Cambrian is among the difficult tasks of Cambrian stratigraphy. Non-traditional concepts (such as carbon isotope signatures), microplankton (such as acritarchs), and most invertebrate fossils (e.g., brachiopods) may act as auxiliary, tools for intercontinental correlation of regional calibration but are unable to provide the base for fine-scaled global correlation at present. As a result, the selection of a Global Stratigraphic Section and Point will have to root on trilobites which appear to be the only reliable index fossils to define such a GSSP. Five possible levels of correlation within the traditional Lower-Middle Cambrian boundary interval have been discussed: (1) the FAD ofOryctocephalus indicus; (2) the FAD ofOvatoryctocara gramulata and/orKiskinella cristata; (3) the FAD ofArthricocephalus chauveaui; (4) the base of theAcidiscus-Cephalopyge assemblage “zone”; and (5) the base of the STH “band”. The potentials of these levels are analyzed in this study. All of them suffer from certain deficiencies such as limited insight into the stratigraphic ranges of key species; problems of confident identification of the index species; or absence of key faunal elements on certain Cambrian continents; that make them invalid for high-precision correlation on a global scale. However, the combination of (1) through (4) promises an intercontinental correlation that can be used as a global framework, which will be sufficiently accurate to serve normal correlation purposes.

Neltneriidae and Holmiidae (Trilobita) from Morocco and the problem of Early Cambrian intercontinental correlation

Previously undescribed Holmiidae from the Sectigena Zone of Morocco indicate correlation of this zone with other zones bearing Holmiidae on Baltica, Avalonia, Siberia, and Laurentia. The occurrence of the youngest Antatlasiinae in the Sectigena Zone and the oldest Protoleninae in the overlying Hupeolenus Zone suggests correlations of the Sectigena Zone with upper Atdabanian beds bearing the youngest Antatlasiinae and the Hupeolenus Zone with Botomian beds bearing the oldest Protoleninae in Siberia. The occurrence, in the overlying Hupeolenus and Cephalopyge Zones, of Paradoxides s.l. in association with the olenelloid Cambropallas and with trilobites characteristic of the Lower Cambrian “Protolenus” Zone of Avalonia calls into question the major criteria for recognition of strata of Early and Middle Cambrian age. New taxa include lyouella contracta n. gen. and sp. of the Holmiidae and Bondonella sdzuyi n. sp. of the Neltneriidae. The known species of Neltneria, N. jacqueti and N. termieri , are revised.

LATEST EARLY CAMBRIAN SMALL SHELLY FOSSILS, TRILOBITES, AND HATCH HILL DYSAEROBIC INTERVAL ON THE QUEBEC CONTINENTAL SLOPE

Abstract Latest Early Cambrian continental slope deposition of the early Hatch Hill dysaerobic interval (new name, latest Early Cambrian–earliest Ordovician) is recorded by dark grey shales and turbidite limestones in the Bacchus slice at Ville Guay, Québec. Platform-derived microfaunas of the Bicella bicensis trilobite assemblage were transported into a dysoxic environment of the upper “Anse Maranda Formation,” and many organisms were buried alive. Phosphatization preserved a diverse skeletal fossil assemblage that includes four agnostid trilobites, echinoderm debris, and twenty small shelly fossil taxa. The latter include five helcionellids; PelagiellaMatthew, 1895b, classified herein as a gastropod; a bivalve (FordillaBarrande, 1881); the brachiopod Linnarssonia taconicaWalcott, 1887; two conodontomorphs; four hyoliths; and such phosphatic and calcareous problematica as ColeoloidesWalcott, 1889, emend. Most small shelly fossil taxa, including Discinella micansBillings, 1872, range through much of the Olenellus Zone and Elliptocephala asaphoides assemblage interval. Trilobites allow a more resolved correlation into the uppermost Olenellus Zone. A comparable stratigraphy occurs in Cambrian–Ordovician slope facies of the Bacchus slice and the Giddings Brook slice in eastern New York. The “Anse Maranda Formation” correlates with the West Granville–Browns Pond–lower Hatch Hill formations in eastern New York and brackets two dysaerobic intervals (Browns Pond and early Hatch Hill). Sea-level change associated with the Hawke Bay regression between the Browns Pond and Hatch Hill onlap/dysaerobic intervals led to the longest period of oxygenated green shale and sandstone deposition on the east Laurentian slope in the late Early Cambrian–earliest Ordovician.

MIDDLE CAMBRIAN OF AVALONIAN MASSACHUSETTS: STRATIGRAPHY AND CORRELATION OF THE BRAINTREE TRILOBITES

Abstract Although Middle Cambrian trilobites of the Braintree Member in eastern Massachusetts were among the first published on in North America, re-examination of this fauna has led to wholesale taxonomic and biostratigraphic re-evaluation. This low diversity fauna now includes at least seven species, with the first report of agnostoids (three poorly preserved taxa) and the ellipsocephalid Kingaspis avalonensis new species. Paradoxides (Acadoparadoxides) harlani Green emend., a senior synonym of P. (A.) haywardi Raymond, allows correlation into the lowest Middle Cambrian elsewhere in Avalon. However, all the polymeroid species are endemic, and this precludes a highly resolved correlation into other Cambrian paleocontinents. A breakdown of provincial barriers in the late Early Cambrian as western Gondwana passed from equatorial to the higher south latitudes of Avalon led to faunal exchanges between these continents. Paradoxides (Acadoparadoxides) and Kingaspis of the Braintree fauna are shared with western Gondwana, while Braintreella and “Agraulos” quadrangularis are closest to genera known from the Spanish, Moroccan, and Perunican (Bohemian) margins of Gondwana.

The Lower Cambrian trilobites from the Görlitz Synclinorium (Germany) — review and new results

KurzfassungIm vorliegenden Artikel wird der derzeitige Kenntnisstand über die unterkambri-schen Trilobitenfaunen der Gegend um Görlitz (Sachsen) mitgeteilt. Zusätzlich zu den seit langem bekannten Arten werdenCalodiscus cf.lobatus undFerrakia saxonica n. sp. aus den untersuchten Schichten vorgestellt. Die Olenelloiden, die bisher als zwei eigenständige Arten angesehen wurden, werden als identische Art interpretiert.Lusatiops bederkei wird nur durch verformte Stücke vonL. lusaticus repräsentiert. Die stratigraphische Aussagekraft der Trilobiten und Probleme, die aufgrund der biostratigraphischen Daten auftreten, sowie die Korrelationen der Abfolgen werden diskutiert.AbstractThe present article reviews recent advances in the knowledge of the Lower Cambrian trilobite faunas of the Görlitz area, Saxonia, eastern Germany. New additions to the fauna areCalodiscus cf.lobatus (Hall) andFerralsia saxonica n. sp. The olenelloid trilobites, previously thought to represent two distinct species, are re-evaluated and interpreted as belonging to one species.Lusatiops bederkei is actually represented by deformed specimens ofL. lusaticus. Furthermore, the stratigraphic significance of the trilobites and problems associated with the biostratigraphic data and the correlation of the rocks are discussed.

Faunas and Cambrian Volcanism on the Avalonian Marginal Platform, Southern New Brunswick

Abstract The Cambrian inlier at Beaver Harbour, southern New Brunswick, is now confidently referred to the marginal platform of the late Proterozoic–Early Paleozoic Avalon microcontinent. The sub-trilobitic Lower Cambrian Chapel Island and Random Formations are unconformably overlain by the mafic volcanic-dominated Wades Lane Formation (new). Late Early Cambrian trilobites and small shelly taxa in the lowest Wades Lane demonstrate a long Random–Wades Lane hiatus (middle Terreneuvian–early Branchian). Latest Early–middle Middle Cambrian pyroclastic volcanism produced a volcanic edifice at Beaver Harbour that is one of three known volcanic centers that extended 550 km along the northwest margin of Avalon. Middle Middle Cambrian sea-level rise, probably in the Paradoxides eteminicus Chron, mantled the extinct volcanics with gray-green mudstone and limestone of the Fossil Brook Member. Black, dysoxic mudstone of the upper Manuels River Formation (upper Middle Cambrian, P. davidis Zone) is the youngest Cambrian unit in the Beaver Harbour inlier. Lapworthella cornu (Wiman, 1903) emend., a senior synonym of the genotype L. nigra (Cobbold, 1921), Hyolithellus sinuosus Cobbold, 1921, and probably Acrothyra sera Matthew, 1902a, range through the ca. 8 m.y. of the trilobite-bearing upper Lower Cambrian, and H. sinuosus and A. sera persist into the middle Middle Cambrian. Lapworthella cornu and H. sinuosus replaced the tropical taxa L. schodackensis (Lochman, 1956) and H. micans Billings, 1872, in cool-water Avalon.

Well-preserved mollusks from the Lower Keuper (Ladinian) of Hohenlohe (Southwest Germany)

KurzfassungDie „Unteren Grauen Mergel“, ein wechselhaft siliziklastisch-karbonatisches Schichtglied der oberen Erfurt-Formation (Unterkeuper) des Hohenloher Landes, enthält lokal eine Fauna mit außergewöhnlich gut erhaltenen Mollusken. Zusammen mit einer Untersuchung von Museumsmaterial erlaubt das neue Material die Revision häufiger, aber bisher oft fehlinterpretierter Muschel- und Schneckentaxa. Die Muschelfauna setzt sich zusammen ausBakevellia (B.) subcostata, Myophoria transversa, Unionites brevis undU. donacinus. Schlossbau und Muskelabdrücke der ladinischen ArtBakevellia (B.) subcostata stimmen mit der permischen Typusart der Gattung weitgehend überein. Die interne Morphologie der GattungBakevellia s.s. blieb somit über einen bemerkenswert langen geologischen Zeitraum konstant. WederB. (Neobakevellia) nochB. (Costibakevellia) unterscheiden sich in ihrer Morphologie signifikant vonBakevellia s.s. und sind daher als deren jüngere Synonyme anzusehen.Myophoria transversa unterscheidet sich vonM. vulgaris nicht nur durch einen größeren Winkel zwischen extraarealer Rippe und Arealkante, sondern auch durch die Reduktion der Schlossplatte in der rechten Klappe und einen basal eingebuchteten zentralen Zahn in der linken Klappe. Der morphologische Befund an den untersuchten Stücken der GattungUnionites weist darauf hin, dassUnionites den Anthracosiidae und nicht den Trigonodidae („Pachycardiidae“) zuzuordnen ist.Unionites brevis wurde in der Vergangenheit meist fälschlicherweise unter dem NamenU. letticus beschrieben; tatsächlich gehören beide Taxa vermutlich sogar verschiedenen Familien an. Die zahlreichen Gastropoden der GattungNeritaria zeigen noch die ursprüngliche aragonitische Schalenstruktur und Farbstreifen. Eine detaillierte morphome-trische Analyse belegt, dass die Arten morphologisch bemerkenswert variabel sind. Die Taxonomie ist dagegen im Augenblick nicht exakt darzustellen, weil die Kenntnis der zahlreichen mitteltriadischen Neritarien aus dem Germanischen Becken völlig unzureichend ist. Eine neue Art der Neritarien mit einer ungewöhnlichen,Hologyra-artigen Ornamentierung wird unter dem Namen„Neritaria“ interscripta n. sp. beschrieben.AbstractA mixed siliciclastic-calcareous member (“Untere Graue Mergel“) of the upper Erfurt Formation (Lower Keuper) of the Hohenlohe area locally includes a fauna with exceptionally well preserved bivalves and gastropods. The bivalves includeBakevellia (B.) subcostata, Myophoria transversa, Unionites brevis andU. donacinus. Hinge structure and muscle impressions ofBakevellia (B.) subcostata are virtually identical with those of the Permian type species ofBakevellia B. (Neobakevellia) andB. (Costibakevellia) are regarded as (younger) Synonyms ofBakevellia s.s.Myophoria transversa differs fromM. vulgaris not only by the greater angle between areal carina and extra-areal rib but also by the reduction of the hinge plate in the right valve and by a less clearly bifid central tooh in the left valve. New morphological find (in particular hinge morphology) suggest thatUnionites belongs to the Anthracosiidae rather than to the Trigonodidae (“Pachycardiidae”).Unionites brevis has commonlybeen misidentified asU. letticus. Both taxa most probably belong even to different families. The frequent gastropods of the genusNeritaria retained their aragonitic shell and show color bands. Morphometric analysis indicates a remarkable plasticity. Taxonomic assignment, however, has to remain equivocal because of deficiencies of knowledge on the numerous mid-Triassic neritarian taxa from the Germanic Basin. Neritarian gastropodswith unusualHologyra-type exterior morphology are described as the new species“Neritaria” interscripta n. sp.

Mediterranean representatives of the obolellidTrematobolus Matthew (Brachiopoda) and a review of the genus

ZusammenfassungDrei neue Arten der Obolelliden-GattungTrematobolus Matthew,T. splendidus, T. serotinus undT. cleidrius, aus tief-mittelkambrischen Schichten von Marokko werden errichtet. Zusätzliche Beschreibungen und Diskussionen behandeln informell beschriebenes Material derselben Gattung bzw. Familie und die spanische ArtT. simplex. T. bicostatus aus Sibirien wird als eigenständige Art angesehen. Die morphologischen Besonderheiten wie auch die spezifischen Merkmale einiger Arten vonTrematobolus werden diskutiert. Dazu gehört insbesondere die Frage nach einem funktionellen Anus und einer gelenkigen Verbindung der Klappen. Überlegungen und Neubewertungen der Vorkommen führen zu einer Revision der stratigraphischen Reichweite von wichtigen Arten der Gattung.AbstractThree new species of the obolellid genusTrematobolus Matthew,T. splendidus n.sp.,T. serotinus n. sp., andT. cleidrius n. sp., from the Middle Cambrian of Morocco are introduced. Additional descriptions and discussions deal with informal material belonging to the same genus and family, respectively, and with the Spanish speciesT. simplex. T. bicostatus from Siberia is raised to specific level. The morphologic characteristics as well as specific significance of several species ofTrematobolus are discussed together with their bearing on functional considerations as of a functional anus and an articulating mechanism. Reconsideration of stratigraphic occurrences of key taxa ofTrematobolus updates the knowledge of the distribution of this genus.

An enigmatic bilateral fossil from the Lower Cambrian of Morocco

Patanacta pedina n. gen. and sp. is interpreted as a medusoid from the late Ordovician or early Silurian of Jamtland, central Sweden. The unique specimen is from the Kyrkas Quartzite Formation, a poorly fossiliferous, allochthonous sequence of metasediments in a lower nappe of the frontal zone of the Scandinavian Caledonides. A marginal marine depositional environment is inferred for the KyrkAs facies. . Paleont., 68(4), 1994, pp. 716-721 opyright ? 1994, The Pa eontol gical Society