First record ofRhabdoceras suessi(Ammonoidea, Late Triassic) from the Transylvanian Triassic Series of the Eastern Carpathians (Romania) and a review of its biochronology, paleobiogeography and paleoecology

Abstract

The occurrence of the heteromorphic ammonoid Rhabdoceras suessi Hauer, 1860, is recorded for the first time in the Upper Triassic limestone of the Timon-Ciungi olistolith in the Raràu Syncline, Eastern Carpathians. A single specimen of Rhabdoceras suessi co-occurs with Monotis (Monotis) salinaria that constrains its occurrence here to the Upper Norian (Sevatian 1). It is the only known heteromorphic ammonoid in the Upper Triassic of the Romanian Carpathians. Rhabdoceras suessi is a cosmopolitan species widely recorded in low and mid-paleolatitude faunas. It ranges from the Late Norian to the Rhaetian and is suitable for high-resolution worldwide correlations only when it co-occurs with shorter-ranging choristoceratids, monotid bivalves, or the hydrozoan Heterastridium. Formerly considered as the index fossil for the Upper Norian (Sevatian) Suessi Zone, by the latest 1970s this species lost its key biochronologic status among Late Triassic ammonoids, and it generated a controversy in the 1980s concerning the status of the Rhaetian stage. New stratigraphic data from North America and Europe in the subsequent decades resulted in a revised ammonoid biostratigraphy for the uppermost Triassic, the Rhaetian being reinstalled as the topmost stage in the current standard timescale of the Triassic. The geographic distribution of Rhabdoceras is compiled from published worldwide records, and its paleobiogeography and paleoecology are discussed. Central European Geology, Vol. 53/2-3, pp. 261-309 (2010) DOI: 10.1556/CEuGeol.53.2010 First While examining the fossils collected by the senior author in an old quarry in limestone of the Timon-Ciungi olistolith, the junior author, whose aim was to study the nautiloids, identified a fragment of a specimen of Rhabdoceras suessi Hauer, 1860, in the material. Consequently the purpose of the present paper is to describe this specimen, and to discuss the biostratigraphic range, chronostratigraphic relevance, and the paleobiogeographic distribution and paleoecology of this Late Triassic heteromorphic ammonoid. Geologic and stratigraphic settingsThe Timon-Ciungi olistolith, along with many other olistoliths composed of Triassic sedimentary and/or ophiolitic rocks, is embedded in Lower Cretaceous wildflysch that infills the Raràu Syncline of the Bucovinian Nappe in the northern part of the inner Eastern Carpathians (Sàndulescu 1973). The Triassic rocks of the olistoliths and also of several large klippen scattered along the inner zone of the Eastern Carpathians, in the Raràu, Hàghimaş and Perşani Mts, are assigned to several, facially distinctive Transylvanian Triassic Series (Patrulius 1996).The Timon-Ciungi olistolith is located on the left side of the drainage of the Timon Creek, which is a tributary of the Moldova River at the Fundu Moldovei locality (Fig. 1). The olistolith, several tens of meters in length, was largely quarried in the 1960s. The limestone quarry was abandoned for a long time and the area is now entirely reforested, with only few small exposures remaining. The main m...

First Evidence of Palaeo-Tethyan Upper Triassic Calcareous Nannofossils in North Dobrogean Orogen (Romania)

“…Mirăuţă et al (1993 reported rich foraminiferal and ostracod assemblages indicative of a late Norian age. In other outcrops, situated in the Muchea Verde area, near the Poşta village, the presence of the ammonoid Sagenites quinquepunctatus Mojsisovics, 1873Mojsisovics, -1902, together with bivalves of Monotis (Monotis) salinaria-haueri Kittl, 1912 group, is diagnostic for the Sagenites quinquepunctatus Zone of the upper Norian, which corresponds to the lower Sevatian (= Sevatian 1) (Krystyn 2008;Grădinaru & Sobolev 2010). Samples Frecăţei A1-2 and B come from this part of the log.…”

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“…With regard to Far East Russia, it is to be noted that most of the regions where timorensis occurrences have been reported, although many of them are doubtful and not properly dated by ammonoid biostratigraphy, are in allochthonous terranes (Nokleberg et al, 1994;Vishnevskaya & Filatova, 1994;Parfenov et al, 2009), which during the Triassic were positioned in low-latitudes in the eastern Panthalassa (Fig. 4/21-24), as documented by the occurrence of Monotis bivalves, conodonts, radiolarians, and of Rhabdoceras ammonoids (Chekhov, 1982;Dagys et al, 1983;Bragin, 1991;Klets, 2008;Grădinaru & Sobolev, 2010). Liu K et al (2021), based on detrital zircon U-Pb data and also on geochronological data, argued that in Sikhote-Alin different sedimentary rocks were juxtaposed by syn-and post-subduction sinistral displacements along the NE Asian continental margin during the late Mesozoic.…”