The Cambrian-Ordovician transition of the western Mediterranean region (NW Gondwana) is characterized by the record of major erosive unconformities with gaps that range from a chronostratigraphic stage to a series. The hiatii are diachronous and involved progressively younger strata along the Gondwanan margin, from SW (Morocco) to NE (Montagne Noire). They can be related to development of a multi-stage rifting (further North), currently connected to the opening of the Rheic Ocean, and concomitant erosion on southern rift shoulders. The platforms of this margin of Gondwana occupied temperate-water, mid latitudes and were dominated by siliciclastic sedimentation, while carbonate factories were only episodically active in the Montagne-Noire platform. The Upper Cambrian is devoid of significant gaps in the southern Montagne Noire and the Iberian Chains. There, the sedimentation took place in a transgressive-dominated depositional system, with common offshore deposits and clayey substrates, and was bracketed by two major regressive trends. The Late Cambrian is also associated with the record of volcanic activity (e.g., in the Cantabrian and Ossa-Morena zones, and the northern Montagne Noire), and widespread development of a tectonic instability that led to the episodic establishment of palaeotopographies and record of slope-related facies associations. Several immigration events are recognized throughout the latest Middle Cambrian, Late Cambrian and Tremadocian. The trilobites show a stepwise replacement of Acado-Baltic-type families (e.g., the conocoryphid-paradoxidid-solenopleurid assemblage) characterized by: (i) a late Languedocian (latest Middle Cambrian) co-occurrence of Middle Cambrian trilobite families with the first anomocarid, dorypygid and proasaphiscid invaders; (ii) a Late Cambrian immigration replacing previous faunas, composed of trilobites (aphelaspidids, catillicephalids, ceratopygids, damesellids, eulomids, idahoiids, linchakephalids, lisariids, onchonotinids, and pagodiids), linguliformean brachiopods (acrotretids, obolids, scaphelasmatids, siphonotretids, and zhanatellids), echinoderms (mitrates, glyptocystitid cystoids, and stromatocystoids), and conodonts belonging to the lower Peltura Zone; and (iii) the subsequent input of new trilobites (asaphids, calymenids, catillicephalids, nileids and remopleurids), which marks the base of the Proteuloma geinitzi Zone, associated with pelmatozoan holdfasts (Oryctoconus), and a distinct input of late Tremadocian conodonts (Paltodus deltifer Zone). The biogeographic distribution of latest Middle and Late Cambrian trilobites supports brachiopod data indicating strong affinities between the western Mediterranean region, East Gondwana (North China/Korea, South China, Australia, and Antarctica) and Kazakhstania during the late Languedocian, which became significantly stronger during the Late Cambrian. This major shift may suggest modification in oceanic circulation patterns throughout Gondwana across the Middle-Late Cambrian transition. (c) 2007 Elsevier B.V. A...
Problematic phosphatic elements are reported for the first time from Bohemia, Czech Republic, and are attributed to Eurytholia bohemica n. sp. Similar mineralized elements, interpreted as sclerites, were known only in a very narrow interval from Middle-Late Ordovician beds bordering the Iapetus Ocean. This new report comes from the Silurian and Early Devonian and provides a significant range extension for these Problematica as well as an enlargement of their geographic extent. Comments open new perspectives in the interpretation of these elements.
Fossilized ring-like structures, whose function and taxonomic affiliation are enigmatic, were recovered for the first time from the Upper Ordovician of the Carnic Alps and the Silurian of Bohemia. These rings, already mentioned as minor constituents in previous conodont studies (e.g., Webers 1966; Bischoff 1973), were reported from the Palaeozoic of several regions in Europe and North America. Originally considered as inwardly accreted adhering discs of a benthic Hyolithelminth worm with a phosphatic tubular projection, they were later reinterpreted in relation to a putative crinoid epibiont or even as possible Scyphozoans. Despite a long debate, neither the function of the enigmatic Palaeozoic rings nor their taxonomic affiliation have been fully clarified.The study material, extracted with a standard technique in use for conodonts, consists of 235 elements from 16 stratigraphic levels in the Plöcken Formation (Carnic Alps, Cellon Section; Amorphognathus ordovicicus Biozone, Hirnantian, Ordovician) and in the Kopanina Formation (Bohemia, Mušlovka Quarry; Polygnathoides siluricus Biozone, Ludfordian, Silurian). To explore whether ring size and shape changed over time, we employed a novel combination of geometric morphometric approaches for outlines with no 'homologous' landmarks and showed that only size appreciably varied with an increase of ca. 20%.The emerging data from this study are consistent with the interpretation of the rings as an adhering structure of a benthic organism living on a relatively uniform hard substrate
THE CONODONT genus Teridontus was introduced in 1980 by Miller and was based on the Late Cambrian species Oneotodus nakamurai Nogami, 1967 from the Yencho Member of the Fengshan Fm. of northeast China. Teridontus was later reported from either the Upper Cambrian or Lower Ordovician (Landing et al., 1980; Miller, 1980; Landing and Barnes, 1981; Landing,1983; An et al., 1983, 1985; Ni et al., 1983; Peng et al., 1983; Nowlan, 1985; Landing et al., 1986; Bagnoli et al., 1987; An, 1987; Buggisch and Repetski, 1987; Pohler and Orchard, 1990; An and Zheng, 1990; Seo and Ethington, 1993; Wang, 1993; Lehnert, 1994; Nicoll, 1994; Seo et al., 1994; Ji and Barnes, 1994; Taylor et al., 1996; Lehnert et al., 1997; Jia, 2000; Dubinina, 2000; Pyle and Barnes, 2002; Zeballo et al., 2005) sediments in numerous localities around the world, but a unanimous interpretation of the composition of the Teridontus apparatus organization\ud was far from accepted
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