R. Thomas Becker

Sedimentary and faunal changes across the frasnian/famennian boundary in the canning basin of Western Australia

The Canning Basin of northwestern Australia is a key area for understanding global changes at the “Kellwasser Events” and the Frasnian‐Famennian boundary. Frasnian stromatoporoid‐coral‐cyanobacterial reef platforms stretched out for enormous distances along the palaeoshelf but in the early Famennian they were completely replaced by cyanobacterial reef platforms. An iridium anomaly in the sequence was formerly believed to be at or close to the boundary and was interpreted as possible evidence for an asteroid impact. Recent field work and detailed biostratigraphy in the area east and southeast of Fitzroy Crossing has given dating relevant to the timing and extent of sea level changes, hypoxic incursions and reef backstepping. Goniatites and conodonts provide correlations with the international biostratigraphy. In the Horse Spring area the stage boundary falls within the Virgin Hills Formation which normally has a rich pelagic goniatite, nautiloid and conodont fauna. In the latest Frasnian (Zone 13 of Klappe...

Devonian goniatite biostratigraphy and timing of facies movements in the Frasnian of the Canning Basin, Western Australia

Abstract As part of an international study of Devonian facies movements against cratonic areas an investigation has been undertaken of the timing of facies movements associated with the Frasnian and Famennian reef complexes of the Canning Basin, Western Australia. This led to the discovery of rich goniatite faunas which enable significant improvements to be made to the high resolution ammonoid time scale. A new goniatite classification for the Frasnian is proposed for international use based on the entry of particular genera; this gives 12 divisions. A much more detailed regional zonation is proposed for the Canning Basin. As part of this, a description is given of the following new genera of the Gephuroceratidae: Gogoceras, Playfordites, Serramanticoceras and Mixomanticoceras. The genus Probeloceras is used in a restricted sense and recognised as the first member of the Beloceratidae; Acanthoclymenia is used for forms previously assigned loosely to Probeloceras. The new zonation provides a framework for analysis of facies movements. Occasions of anoxic or hypoxic events are indicated by rich, hematized goniatite faunas. Reef backstepping associated with deepening is dateable by goniatites in associated marginal slope deposits. Several of the international eustatic sea-level changes are recognised, noticeably those correlative with the Genundewa, Middlesex and Rhinestreet deepenings of New York. No evidence has been found for the internationally widespread ‘Kellwasserkalk’ facies in the late Frasnian, but a succession of terminal Frasnian sea-level changes is recognized. The ‘Irtidium Anomaly’ level lies well above the Frasnian/Famennian boundary and hence provides no confirmation of a bolide to explain Frasnian/Famennian boundary extinctions. In the Famennian, evidence for the European Condroz regression and Annulata deepening is presented.

Paleozoic Ammonoids in Space and Time

Paleozoic ammonoids have attracted much less attention from professional and amateur paleontologists than Mesozoic ammonoids. Because of the Variscan folding in Europe, the classical area of investigation, Devonian and Carboniferous material from Europe is often rather poorly preserved. As a result, few collectors of the 19th and early 20th century have focused their attention on these fossils. In recent decades, however, as our knowledge of Paleozoic ammonoids has expanded, it has become more and more apparent that the evolution and systematics of Paleozoic forms are as complex as those of Mesozoic ones. For example, the number of Devonian genera rose from about 80 in the Treatise of 1957 to a present figure of more than 200.

Hangenberg Black Shale with cymaclymeniid ammonoids in the terminal Devonian of South China

The Hangenberg Crisis at the end of the Devonian is marked by a sudden global mass extinction (main Hangenberg Event), which was especially severe for ammonoids. Among the order Clymeniida, only the cymaclymeniids survived for a short time. We report the first discovery of Postclymenia cf. evoluta in South China in equivalents of the Hangenberg Black Shale (the regional Changshun Shale) at the Jiarantang section in Guizhou. The South China plate was far away and completely different from the Euramerica continent, where the Hangenberg Event/Crisis was first recognised. The presence of similar ammonoids as in contemporaneous beds of the Rhenish Massif, Germany, suggests close faunal relationship through the Palaeotethys Ocean. It agrees with a sudden spread of opportunistic extinction survivors with the initial Hangenberg Transgression. The regional facies and faunal succession at Jiarantang confirms previous concepts of a eustatically driven, significant transgressive-regressive couplet in the lower/middle crisis interval. The near-global distribution of cymaclymeniid survivors shows that their extinction at the end of the extended crisis interval must have been caused by a so far neglected, small-scale global extinction event in the open marine realm.