Nicoletta Buratti

Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis

The evolution of life on Earth is marked by catastrophic extinction events, one of which occurred ca. 200 Ma at the transition from the Triassic Period to the Jurassic Period (Tr-J boundary), apparently contemporaneous with the eruption of the worlds largest known continental igneous province, the Central Atlantic magmatic province. The temporal relationship of the Tr-J boundary and the provinces volcanism is clarified by new multidisciplinary (stratigraphic, palynologic, geochronologic, paleomagnetic, geochemical) data that demonstrate that development of the Central Atlantic magmatic province straddled the Tr-J boundary and thus may have had a causal relationship with the climatic crisis and biotic turnover demarcating the boundary.

The dawn of CAMP volcanism and its bearing on the end-Triassic carbon cycle disruption

The cause-and-effect relationship between the c. 201 Ma eruption of the Central Atlantic magmatic province (CAMP) and the end-Triassic abrupt climate change and mass extinction is at present based on controversial temporal correlations. Upper Triassic sedimentary strata underlying CAMP basalts in Morocco illustrate a clear mineralogical and geochemical fingerprint of early CAMP basaltic eruptions, namely unusually high contents of MgO (10–32 wt%) and of mafic clay minerals (11–84%). In the same rocks a coincident negative carbon-isotope excursion (CIE) is present, equivalent to the so-called ‘initial negative CIE’ recorded worldwide shortly before the Triassic–Jurassic boundary. The new data show that the onset of CAMP activity preceded the end-Triassic carbon cycle disruption and that the initial negative CIE is unequivocally synchronous with CAMP volcanism. The results of this study strongly support the hypothesis that the culmination of pollution of atmosphere and seawater by CAMP-derived volcanic gases was the proximate cause of the end-Triassic mass extinction. Supplementary material: The stratigraphic position of analysed samples, and the C-isotope, bulk-rock mineralogy, element analysis, Mg–Al–Si ternary diagram and trace-element analysis data are available at www.geolsoc.org.uk/SUP18707.

STRATIGRAPHY AND PALYNOLOGY OF THE UPPER TRIASSIC NAYBAND FORMATION OF EAST-CENTRAL IRAN

A palynological study of the Nayband Formation (central eastern Iran) has been carried out in order to review and update its stratigraphic framework. In its type locality the formation crops out on the southern flank of Nayband Mountain, about 200 km south of Tabas. It consists of a thick, mixed siliciclastic-carbonate sequence subdivided into four members; in ascending order: the Gelkan Member (mainly shales and silstones), the Bidestan Member (marls, siltstones with minor sandstones and fossiliferous limestones), the Howz-e-Sheikh Member (sandstones and siltstones), and the Howz-e-Khan Member (sponge and coral dominated reefs alternating with marls and sandstones). Three palynological assemblages have been recognised; in ascending order: a) an assemblage characterised by the presence of Annulispora folliculosa and A. microannulata which allows the Gelkan Member and most of the Bidestan Member to be assigned an early Norian age; (b) an assemblage marked by the first occurrence of Polycingulatisporites mooniensis, which indicates the upper part of the Bidestan Member is mid-late Norian; c) an assemblage containing Classopollis chateaunovi in association with Retitriletes austroclavatidites, Gliscopollis meyeriana, Limbosporites lundbladii, Rugaletes awakinoensis and Callialasporites dampieri that allows the Howz-e-Sheikh Member to be assigned a Rhaetian age. The presence of some Eurasian and/or cosmopolitan forms in the Rhaetian microflora reflects the position of the Iranian plate on the southern margin of Eurasia.

The ultrastructure of some Rhaetian Circumpolles from southern England

Abstract The morphology and exine ultrastructure of Classopollis torosus, C. meyeriana and Geopollis zwolinskae are studied from the Cotham Member of the Lilstock Formation (Penarth Group) in southern England. The palynological assemblage that allows dating the deposits to the Rhaetian is outlined. Although the Circumpolles pollen grains under study show variations in the exine ultrastructure, some common characters support their origin from the same plant group, the Cheirolepidiaceae. An infratectum formed by large granulae arranged mostly in one row and sandwiched between the tectum and endexine is considered as the key character of the pollen grains under study. Ultrastructural transformations within Circumpolles are discussed. The origin of Classopollis-producing plants from any plant group with saccate pollen and alveolate ectexine is considered much less probable than from a group with non-saccate pollen with granular ectexine.

The occurrence of chitinoidellids in palynological residues from the Ammonitico Rosso Formation (Tithonian), Spain

Abstract This study deals with the recovery of chitinoidellid specimens in palynological residues and their usefulness as biochronologic tools. We sampled specimens—which represent a very small group of ancient planktonic ciliates of uncertain origin that appeared in the early Tithonian and lasted until the late Tithonian in the Jurassic—from the upper part of the Ammonitico Rosso Formation, outcropping in southeastern Spain (Sierra de Crevillente, Congost section). Chitinoidellid associations allowed us to attribute the lower part of the succession studied to the early Tithonian (Chitinoidella Zone). The palynological preparations reveal urn-shaped bodies 60–140 μ long, which we interpret as chitinoidellid remains. These organic-walled objects show the organic nature of chitinoidellid loricae, which, as previously suggested, were probably chitinous. The loricae consisted of a continuous organic lining and suggest that the presence of calcite crystals was limited to single dispersed crystallites rather than their occurrence in layers, as suggested by earlier reports. This study shows that palynological extraction of chitinoidellids can yield more information on the morphology and, thus, on the phylogeny of this planktonic group than the traditional thin-section approach.