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Orizzonti a Nautiloidi e a Brachiopodi della Formazione a Bellerophon (Permiano superiore)in Val Gardena
No full textRecenti ricerche biostratigrafiche nella Formazione a Bellerophon della Val Gardena hanno portato alla scoperta di due orizzonti a Nautiloidi. L'orizzonte A, che precede di circa 10-15 m la "Val Gardena Sandstone tongue", contiene Tirolonautilus crux (Stache),? Germononoutilus sp. e Liroceras sp. Questo orizzonte è correlabile alla "Nautiloid and Bivalve Assemblage"gia descritta in letteratura nelle sezioni del Butterloch e del Sass de Putia. In questo orizzonte non sono presenti brachiopodi.
L'orizzonte B è posto alla base dei calcari neri della Fades Badiota e contiene i nautiloidi Tirolonoutilus sebedinus (Stache), Tainoceras sp. e Liroceras sp. ed i brachiopodi Comeliconia doriphora Merla e C. haueri (Stache). Questo orizzonte non è mai stato segnalato in Dolomiti e particolarmente significativa è la presenza di Comelicania, che prima d'ora si pensava fosse confinata agli ultimi metri della formazione. Gli esemplari rinvenuti sono caratterizzati
da conchiglie di taglia medio-piccola,se rapportati alle grandi dimensioni delle Comelicanie più giovani e, in C. doriphora, dalla presenza del foramen dorsale
Orizzonti a nautiloidi e a Brachiopodi della Formazione a Bellerophon (Permiano superiore) in Val Gardena (Dolomiti)
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Upper Permian bivalves from the Bellerophon Formation (Dolomites, northern Italy) and biodiversity drop related to the end-Permian mass extinction
No full textThe Upper Permian Bellerophon Fm of the Dolomites (northern Italy) is an overall transgressive succession, which consists of a lower sulphate-evaporite unit, deposited in a barren basin, and an upper shallow-marine carbonate unit, deposited along a low-energy ramp setting. This succession, mainly Changhsingian in age, contains rich fossil assemblages, which have been studied since 19th century. Although some taxonomical groups have been object of recent revisions (e.g. nautiloids and brachiopods), the stratigraphic and systematic knowledge of the bivalves is not supported by recent studies, which are necessary to evaluate the survival rates after the end-Permian mass extinction. In this study, the biodiversity and stratigraphic distribution of the bivalves occurring in the Bellerophon Fm of western Dolomites is investigated with the aim to define the extinction patterns through the comparison with the taxa occurring in the Lower Triassic Werfen Fm. The specimens have been collected bed-by-bed from the Val Gardena and Val Badia sections aligned along a south west-north east transect, which records a slight deepening of the marine environment. Systematic assessment, based both on newly collected material and on historical collections analysis, has revealed 18 genera with 24 species. The studied material has been ascribed to the genera: Bakevellia, Chaenomya, Cosmetodon, Dyasmya, Edmonia, Eumorphotis, Palaeolima,?Palaeonelio, Permophorus, Pernopecten, ?Pleurophorella, ?Promytilus, Schizodus, Solemya (Janeia), ?Tambanella, Towapteria, Volsellina and Aviculopectinidae gen. nov. Infaunal suspension and detritus feeders suffered extinction rates higher than the semi-infaunal and epifaunal suspension feeders. The studied bivalves show a richness drop at genus level lower than other marine taxa. This higher survivorship can be related to the adaptation of the Upper Permian bivalves towards very shallow and stressed (e.g., high temperatures and low oxygen levels) marine environments, which characterized the western Dolomites during the deposition of the Bellerophon F
I bivalvi della Formazione a Bellerophon (Permiano superiore) nel contesto dell'estinzione di fine Permiano
No full textDISCOVERY OF <em><em>PARATIROLITES</em></em> FROM THE BELLEROPHON FORMATION (UPPER PERMIAN, DOLOMITES, ITALY)
Full text linkThe first discovery of Paratirolites in the western Tethys is here described. The ammonoid was collected in the debris of the Bellerophon Fm. near Santa Cristina Valgardena (Bolzano, Dolomites). The specimen is contained in a small slab made of marly dark grey limestone with a biomicrofacies dominated by ostracods. It probably comes from the Ostracod Assemblage beds (Badiota Facies), which are situated few metres below the Comelicania beds. The occurrence of Paratirolites allow us to date this segment of the upper Bellerophon Fm. to the late Dorashamian, and to define the Comelicania and Nankinella beds of the Dolomites as younger than the Phisonites - Comelicania (= Gruntallina) beds of the Transcaucasia (basal Dorashamian). This assemblage is equivalent to or younger than the Paratirolites Zone (late Dorashamian)
Adaptive strategies and environmental significance of lingulid brachiopods across the late Permian extinction
No full textLinguliformbrachiopods are traditionally considered a conservative group which seems to pass through the late
Permian extinction without any significant loss and even appear to thrive immediately after the extinction peak.
In the Southern Alps, lingulids are very common in the post-extinction Mazzin Member (early Induan) of the
Werfen Formation. Sparse occurrences are also known in the overlying Siusi and Gastropod Oolite members
(late Induan and early Olenekian in age respectively). The recent discovery of well preserved specimens from a
pre-extinction bed of the Bellerophon Formation (Changhsingian) has permitted a detailed comparative analysis,
mostly based on the interior characters, preserved in the lingulid succession fromacross the extinction beds. The
following effects on the lingulid populations have been analyzed: i) change in taxonomic assessment; ii) adaptive
strategies during the surviving and recovery phases; and iii) environmental proxy connected with the killing
mechanisms of the late Permian extinction.
The pre-extinction individuals belong to Lingularia? cf. smirnovae Biernat and Emig, a species that is characterized
by large-sized shells with a short lophophoral cavity. The post-extinction populations belong to different species
and, probably, even to a different genus. The first post-extinction population (early Induan), with small-sized
shells and long lophophoral cavity, has been referred to Lingularia yini (Peng and Shi). It records themost severe
effects of the late Permian extinction on the marine ecosystems. The late Induan–Olenekian Lingularia borealis
(Bittner), with large sized shells and long lophophoral cavity, appears during the first phase of the Triassic biotic
recovery.
Themain adaptive strategies of Lingularia yini, in comparisonwith the Permian species, include: i) shell miniaturization;
ii) increasing of the lophophoral cavity surface (respiratory surface); and iii) increasing of shell width/
length ratio. Thesemodifications are interpreted as adaptations towards warming and hypoxia, two main killing
mechanisms of themarine biota. The recovery species Lingularia borealis maintains a large lophophoral cavity, indicating
an adaptation towards predominant low oxygenated bottom marine waters.
The appearance and the great abundance of Lingularia yini in the Mazzin Member (early Induan) represent a
proxy of dysaerobic conditions, which determined the appearance of the second phase of the Lilliput biota, characterized
by the definitive disappearance of the rhynchonelliform brachiopods and calcareous algae in the Southern
Alps
Late Permian Nautiloids from the Bellerophon Formation of the Dolomites (Italy)
No full textAn abundant nautiloid collection (> 100 specimens) from the Late Permian Bellerophon Formation of the Dolomites, apparently the largest Late Permian nautiloid fauna from Tethys and certainly the most diverse nautiloid collection from the Bellerophon Formation, has enabled individual and intraspecific variability connected both with ontogenetic changes to be probed. The shell morphology is much affected by differing modes of preservation (shell, internal mould, external cast or composite mould) and diagenetic deformation. Five genera and eight species (six new) have been determined. The new species are Tainoceras balestense, T. malsineri, Foordiceras dolomiticum, Liroceras gardenese, Peripetoceras comploji and P. gigas. Emended diagnosis is presented for Tirolonautilus, represented by two previously known species: T. crux (STACHE) and T. sebedinus (STACHE). The generic position is discussed of two species from the Dolomites, earlier described but not found in the present collections, Tainionautilus? darini (CANEVA) and Metacoceras inaequiseptum MERLA
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