Luis O'Dogherty

Radiolarite ages in Alpine-Mediterranean ophiolites: Constraints on the oceanic spreading and the Tethys-Atlantic connection

The history of continental breakup and oceanic spreading of the Alpine Tethys is defined by a revision of isotopic and biochronologic ages of 65 stratigraphic sections located in the Alps, Apennines, Betic Cordillera, Rif, and central Atlantic and a reinterpretation of the stratigraphic sequences of surpraophiolitic radiolarites. The biochronology of radiolarites is revised by using the deterministic approach known as the unitary association method. During the early Bajocian (unitary association zone, UAZ 3) radiolarite sedimentation began at the continental margin. Biochronologic ages determined in the lowermost radiolarites in basinal sequences of Tethyan margins are synchronous and mark a regional change in sedimentation regime in the Alpine Tethys. The onset of oceanic spreading of the Alpine Tethys is dated by isotopic methods as Bajocian, and is consistent with the timing of the structural evolution of the continental margins. The earliest fragments of Tethyan oceanic crust are characterized by the associations of ophiolites with deep-sea sediments, and coarse reworked sediments including platform and continental basement fragments. The earliest ophiolites also show geochemical affinities with synrift and transitional mid-oceanic-ridge basalts. The oldest radiolarites on oceanic crust are so far dated as Bathonian (UAZ 6) and are located in the Gets nappe (western Alps), in the Balagne nappe (Corsica), and in the central Atlantic (Deep Sea Drilling Project [DSDP] Site 534A). The oldest remnants of Alpine Tethyan crust have been identified in weakly metamorphosed cover nappes that occupy an external tectonic position in the Alpine orogenic belts, as compared to the main ophiolitic sutures. Thus, the older relics of oceanic lithosphere were the first to be accreted and transported onto the foreland during the collision. Siliceous sedimentation during the early Bajocian is correlated with westward deep-water circulation in the Alpine Tethys related to the opening of deep seaways between Laurasia and Gondwana. In the central Atlantic no radiolarites, but thin radiolarian-rich layers, were deposited during the earliest Bathonian (UAZ 6). The similarity between radiolarian faunal assemblages and ages in the Northern Alps, Gets nappe, Betic Cordillera, and Site 534 (DSDP Leg 76) suggest a Middle Jurassic connection between the Alpine Tethys and central Atlantic. Biochronologic and isotopic ages currently indicate that oceanic spreading of the Alpine Tethys began during the Bajocian and continued until the Kimmeridgian.

Evolutionary Rates of Jurassic Ammonites in Relation to Sea-level Fluctuations

Abstract An analysis is presented of the diversity and faunal turnover of Jurassic ammonites related to transgressive/regressive events. The data set contained 400 genera and 1548 species belonging to 67 ammonite zones covering the entire Jurassic System. These data were used in the construction of faunal turnover curves and ammonite diversities, that correlate with sea-level fluctuation curves. Twenty-four events of ammonite faunal turnover are analyzed throughout the Jurassic. The most important took place at the Sinemurian-Carixian boundary, latest Carixian-Middle Domerian, Domerian-Toarcian boundary, latest Middle Toarcian-Late Toarcian, Toarcian-Aalenian boundary, latest Aalenian-earliest Bajocian, latest Early Bajocian-earliest Late Bajocian, Early Bathonian-Middle Bathonian boundary, latest Middle Bathonian-earliest Late Bathonian, latest Bathonian-Early Callovian, earliest Early Oxfordian-Middle Oxfordian, earliest Late Oxfordian-latest Oxfordian, latest Early Kimmeridgian, Late Kimmeridgian, middle Early Tithonian and Early Tithonian-Late Tithonian boundary. More than 75 percent of these turnovers correlate with regressive-transgressive cycles in the Exxon, and/or Hallam′s sea-level curves. In most cases, the extinction events coincide with regressive intervals, whereas origination and radiation events are related to transgressive cycles. The turnovers frequently coincide with major or minor discontinuities in the Subbetic basin (Betic Cordillera).

Catalogue of Mesozoic Radiolarian Genera. Part 2: Jurassic-Cretaceous

ABSTRACT The catalogue of Mesozoic radiolarian genera is a revision of all described genera with re-illustration of their type species. This project was organized under the auspices of the International Association of Radiolarian Paleontologists (Inter-Rad), and was carried out by the Mesozoic Working Group. This is the second of two contributions, this one devoted to the Jurassic-Cretaceous period. It contains 581 genera with re-illustration of their type species. This part shares 30 genera in common with the Triassic catalogue, most of which arose in the Carnian, Norian and Rhaetian. The sharp difference manifested between the Triassic fauna and the Jurassic-Cretaceous fauna is so evident that it justifies two independent catalogues. A comparable division between the Jurassic and Cretaceous could not be justified however, because of the similarity of the fauna, and by the greater number of genera crossing the Jurassic-Cretaceous boundary which is three times that for the Triassic-Jurassic boundary. A distinct characteristic of Jurassic-Cretaceous genera is the high number of nomina dubia (up to 131), contrary to the low number in the Triassic interval. This reflects, in part, the influence of Haeckelian taxonomy in earlier research on Jurassic-Cretaceous faunas prior to the application of SEM techniques.The Mesozoic Working Group has carefully reviewed and re-examined the taxonomy of all available genera, their family assignment and stratigraphic ranges. Following careful comparisons, 91 genera were declared as synonyms. The review has noted 26 homonyms which were duly notified to their corresponding authors, and were corrected previous to the publication of this catalogue. In spite of this effort, unfortunately nine homonyms still remain. Two invalid nominal genera and two nomina nuda are also reported. The systematic revisions have validated 341 genera for the Jurassic-Cretaceous interval. At the end of this catalogue 24 additional photographs are presented as support for those genera having a poor original illustration of the type species.

Catalogue of Mesozoic radiolarian genera. Part 1: Triassic

ABSTRACT The Catalogue of Mesozoic radiolarian genera is a revision of all described genera with re-illustration of their type species. This project was organized under the auspices of the International Association of Radiolarian Paleontologists (Inter-Rad), and was carried out by the Mesozoic Working Group. This contribution (Part 1), deals with the Triassic period only. There are 381 known Triassic radiolarian genera. Most have been published since the 1970s following the introduction of scanning electron microscopy (SEM), which enabled good pictures for most type species. For this reason the Triassic period is characterized by a very low number of nomina dubia (only 14), contrary to the higher number in the Jurassic-Cretaceous interval. The Mesozoic Working Group has carefully reviewed and reexamined the taxonomy of all available genera, their family assignment and stratigraphic ranges. Following careful comparisons, 73 genera were declared synonyms. The review has also detected 11 cases of homonymy that were duly notified to their authors, and were corrected previous to the publication of this catalogue; unfortunately one homonym still remains. Two invalid nominal genera are also reported herein. The systematic revisions have validated 282 genera for the Triassic, and of these only 30 genera cross the Triassic-Jurassic boundary. At the end of the catalogue 15 additional photos are presented as support for those genera having a poor original illustration of the type species.

Triassic radiolarian biostratigraphy

Abstract This paper summarizes 30 years of research on the biostratigraphy of Triassic radiolarians and presents a correlation of currently-used radiolarian zonations established in North America, Europe, Japan and Far East Russia. An up-to-date stratigraphic distribution of all hitherto described and still valid Triassic genera is provided. This new range chart consists of 282 genera and allows an accurate dating to substage level. It also clearly manifests general trends in radiolarian evolution through the Triassic. The end-Permian extinction, the most severe extinction in the history of radiolarians, was followed by a long recovery until the early Anisian. The middle and late Anisian were then characterized by a rapid explosion of new morphologies. Maximum generic diversity was attained during the early Carnian, but the first severe extinctions also occurred in the Carnian. A progressive decline of diversity took place through the Norian and Rhaetian, and ended in a mass extinction around the Triassic–Jurassic boundary.

The plankton turnover at the Permo-Triassic boundary, emphasis on radiolarians

Abstract.The examination of plankton biodiversity through Permian-Triassic period seems to display different patterns of evolution depending of the scale of study (taxonomy stratigraphy or biogeography). In this paper we present the state of the art of the plankton turnover at the Permo-Triassic and we review more precisely the pattern of extinction and recovery of radiolarians during such period, because at that time, plankton was essentially represented by radiolarians. At a global scale the end-Permian to early Triassic period is marked by several strong extinctions in the marine realm, and in the radiolarians they occur progressively as exemplified by two orders of radiolarians: Albaillelaria and Latentifistularia. Nevertheless, this period is marked by a tremendous post-crisis diversification in both at family and generic level, more than extinction; an actualized revision of the diversity at the family level is also offered in our review. At a moderate scale (i.e. genera and in a region) the modifications appear impressive while at specific and regional domain the message is not so clear, one can wonder if some crisis manifestation results from a taxonomic accident or from preservative conditions. In fact, strangely enough more the number of studies is, more the diversity is high, and oppositely less they are, more the provincialism is evoked.Resume.L’examen de la biodiversitéu plancton au passage Permien-Trias semble montrer différents types de manifestation selon l’échelle d’observation aussi bien en terme de stratigraphie que de taxonomie ou de géographie. A cette époque, le plancton était surtout représenté par les radiolaires. A une échelle globale cette période est certes marquée par des extinctions mais elles sont progressives comme le prouvent les deux ordres de radiolaires: les Albaillelaria et des Latentifistularia. Néanmoins cette période est surtout marquée par une énorme diversification post-crise, plus encore que par l’extinction. A uneéchelle moyenne (ex. niveau générique et celui d’un pays) les renouvellements de faune semblent impressionnants, alors qu’àl’échelle des espéces et de bassins particuliers, on est conduit à se demander si des modifications résultent de réelles crises biologiques ou de problémes de conservation. Il est amusant de constater que plus le nombre d’études est élevé, plus la diversité apparaît grande et à l’opposé, plus elles sont rares, plus le provincialisme est évoqué.

Jurassic radiolarites in a Tethyan continental margin (Subbetic, southern Spain): palaeobathymetric and biostratigraphic considerations

Abstract A region of the pelagic Subbetic basin within the Southern Iberian Continental Margin is studied in lithostratigraphical and biostratigraphical detail. Jurassic radiolarites (Jarropa Radiolarite Formation, Bathonian–Oxfordian) interbedded with shallow-water marine limestones have been recognized. Underlying the radiolarites (Camarena Formation, Bajocian) are oolitic limestones showing shallowing-upward cycles with karstic surfaces on the top, corresponding to deposition on an isolated carbonate platform on volcanic edifices. The Milanos Formation (upper Kimmeridgian–Tithonian), overlying the radiolarites, contains calciclastic strata with hummocky cross-stratification, which indicate outer carbonate ramp deposition. In the Jarropa Radiolarite Formation some calcisiltite strata with hummocky cross-stratification have been found. The bathymetry of the Subbetic Jurassic pelagic sediments, including the radiolarites, is considered as moderate or shallow in depth. We suggest that the pelagic character of the Jurassic sediments in this margin and their equivalents in other Alpine domains is a consequence of distance from the continent (beyond the pericontinental platform) but not necessarily of depositional depth.

Dynamics of a paleoecosystem reef associated with oceanic change in carbonate sedimentary regime and carbon cycling (Oxfordian, Swiss Jura)

Abstract Herein we report an analysis of an Oxfordian (Upper Jurassic) paleoreef located in the Swiss Jura Mountains. The paleoreef is located in a Middle Oxfordian transitional interval in which sedimentation switched from marl-dominated to carbonate-dominated deposits. The paleoecosystem is composed of four successive fossil communities characterized by microsolenid corals and organisms that specialized in suspension feeding. Carbon isotopes measured from echinoid spine carbonates exhibit a positive trend from ∼1.0‰ to 2.5‰ in δ13C values from the base to the top of the paleoreef. Comparison of δ13C curves with organic matter and belemnites shows different patterns not compatible with a global variation of the carbon cycle. Similar fossil assemblages and stratigraphic sequences identical in age are found along the continental margin of the Tethys–Atlantic Ocean. This biolithostratigraphic succession corresponds to increasing δ13C values of marine and biogenic carbonates, to the transition from marl-dominated to carbonate-dominated deposits, and to the development of carbonate platforms, which together suggest a change in the carbon cycling regime within the Tethys–Atlantic Ocean system.

XIPHOTHECAELLA, A NEW NAME FOR THE GENUS XIPHOTHECA DE WEVER, 1979, NON AGASSIZ 1846

, L. 1846. Nomenclatoris zoologici index universalis, continens no-mina systematica classium, ordinum, familiarum et generum animaliumomnium tam viventium quam fossilium secundum ordinem alphabeticumunicum disposita, adjectis homonymiis plantarum/auctore L. Agassiz. Jentet Gassmann, Soloduri, Switzerland, 393 p.; nec non variis adnotationibuset emendationibus, 8 p.D

Ovumella, a new name for the genus Ovum De Wever, 1982, non Schneider, 1801, non Blainville, 1830

De Wever (1982) proposed the new radiolarian name Ovum from theLiassic of Turkey. We have discovered that this name has already beenused for a fish by Schneider (in Bloch & Schneider 1801), andsubsequently for an echinid by Blainville (1830). Therefore, inaccordance with article 60 of the International Code of ZoologicalNomenclature (1999), we propose the name Ovumella nomen novumas a replacement name (type species Ovumella cetinum De Wever,1982, by original designation) for the preoccupied homonym OvumDe Wever, 1982, non Schneider, 1801, and non Blainville, 1830.