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Compared to coeval successions from the Carpathians, the continuous Jurassic-Cretaceous (J/K) pelagic limestone succession of the Brodno section offers the best possibility to document the J/K passage in a wide area. This section comprises a complete calpionellid, and nannofossil stratigraphic record, that supports the older paleomagnetic data. Moreover, the sequence stratigraphy and stable isotope (δ 18 O, δ 13 C) data gave important results, too, enabling comparison with known key sections from the Mediterranean Tethys area.Key words: J/K boundary, Western Carpathians, regional stratotype, stable isotopes, biostratigraphy, microfossils, pelagic carbonates. Geological context of the Brodno section: an overviewThe Brodno section is situated in an abandoned quarry on the eastern side of the narrow straits of the Kysuca River Valley north of the town of Žilina (known as the "Kysuca Gate", Fig. 1). It yields a record of hemipelagic marine sedimentation in a marginal zone (the Pieniny Klippen Belt) of the Outer Western Carpathians. The lithology, fossil record (including ammonites and aptychi) and stratigraphy were studied by Andrusov (1938Andrusov ( , 1950Andrusov ( , 1959, Scheibner (1961, 1962, 1967), Borza (1969, Scheibnerová (1969), andSamuel et al. (1988). A more detailed description of the Upper Jurassic and Lower Cretaceous litho-and biostratigraphy was provided by Michalík et al. (1990), Vašíček et al. (1992). Houša et al. (1996) introduced the magnetostratigraphy of the Jurassic/Cretaceous (J/K) boundary beds correlated with the microbiostratigraphic data.This paper discusses the results of an integrated biostratigraphic study using three microplankton groups (calpionellids, calcareous dinoflagellates and nannofossils), as well as stable isotope data (δ 18 O, δ 13 C) in the Brodno section, which is proposed here as the candidate for a West Carpathian regional J/K boundary stratotype. The distribution of the stratigraphically important planktonic organisms revealed several coeval calpionellid and nannofossil bioevents recorded in the pelagic carbonate sequence of the Jurassic/Cretaceous boundary age. The stable isotope data underline environmental changes during the interval studied.According to the International Commission on Jurassic Stratigraphy, it is necessary to search for complete sections, which can provide continuous records of both sedimentation and biotic events across stage boundaries. Although the Brodno section lacks ammonite record, it is presented here as a potential candidate considering its continuously well exposed and biostratigraphically properly documented succession, at least for the West Carpathian region. Material and methodsThe Jurassic/Cretaceous boundary succession was studied using an integrated sequence-, bio-and isotope stratigraphy approach from the detailed rock section sampled. A quantitative microfacies analysis was carried in thin sections for the sequence stratigraphic pattern of these pelagic limestones (see Reháková 2000a; Michalík 2007). The calpionellids an...

This paper discusses the results of a study of the Le Chouet section, its lithologies, facies, magnetic properties and fossil record (ammonites, calcareous nannofossils, calpionellids and calcareous dinoflagellates). Data obtained have been applied to give a precise biostratigraphy for this carbonate sequence as well as a paleoenvironmental reconstruction. Its relationship to magnetostratigraphy, based on a modern study of a French site, is important. Investigation of the micro-and macrofossils shows that the site comprises a sedimentary sequence in the Microcanthum to Jacobi ammonite Zones, and the Chitinoidella, Crassicollaria and Calpionella Zones. Several calpionellid and nannofossil bioevents have been recorded on the basis of the distribution of stratigraphically important planktonic organisms. The site allows us to calibrate the levels of various biomarkers and biozonal boundaries, and correlate them with the magnetozones M20n, M19r and M19n.

Abstract:The key objective of investigation of hemipelagic sediments from the Gresten Klippenbelt (Blassenstein Formation, Ultrahelvetic paleogeographic realm) was to shed light on environmental changes around the Jurassic-Cretaceous (J/K) boundary on the northern margin of the Penninic Ocean. This boundary is well exposed in a newly discovered site at Nutzhof. Around the critical interval including the boundary, this new outcrop bears a rich microplanktonic assemblage characterized by typical J/K (Tithonian/Berriasian) boundary faunas. The Nutzhof section is located in the Gresten Klippenbelt (Lower Austria) tectonically wedged into the deep-water sediments of the Rhenodanubian Flysch Zone. In Late JurassicEarly Cretaceous time the Penninic Ocean was a side tract of the proto-North Atlantic Oceanic System, intercalated between the European and the Austroalpine plates. Its opening started during the Early Jurassic, induced by sea floor spreading, followed by Jurassic-Early Cretaceous deepening of the depositional area of the Gresten Klippenbelt. These tectonically induced paleogeographic changes are mirrored in the lithology and microfauna that record a deepening of the depositional environment from Tithonian to Berriasian sediments of the Blassenstein Formation at Nutzhof. The main lithological change is observed in the Upper Tithonian Crassicollaria Zone, in Chron M20N, whereas the J/K boundary can be precisely fixed at the Crassicollaria-Calpionella boundary, within Chron M19n.2n. The lithological turnover of the deposition from more siliciclastic pelagic marl-limestone cycles into deep-water pelagic limestones is correlated with the deepening of the southern edge of the European continent at this time. Within the Gresten Klippenbelt Unit, this transition is reflected by the lithostratigraphic boundary between siliciclastic-bearing marl-limestone sedimentation in the uppermost Jurassic and lowermost Cretaceous limestone formation, both within the Blassenstein Formation. The cephalopod fauna (ammonites, belemnites, aptychi) and crinoids from the Blassenstein Formation, correlated with calcareous microfossil and nannofossil data combined with isotope and paleomagnetic data, indicate the Tithonian to middle Berriasian (Hybonoticeras hybonotum Zone up to the Subthurmannia occitanica Zone; M17r-M21r). The succession of the Nutzhof section thus represents deposition of a duration of approximately 7 . The deposition of the limestone, marly limestone and marls in this interval occurred during tectonically unstable conditions reflected by common allodapic material. Along with the integrated biostratigraphic, geochemical and isotopic analysis, the susceptibility and gamma-ray measurements were powerful stratigraphic tools and important for the interpretation of the paleogeographic setting. Two reverse magneto-subzones, Kysuca and Brodno, were detected within magnetozones M20n and M19n, respectively.

As so ci ate ed i tor: Jacek Grabowski We pres ent ev i dence for the up per most Ju ras sic-low est Cre ta ceous in ter val in Cri mea, coastal south ern Ukraine. Three facies zones are dis tin guished in the up per Dvuyakornaya and the Mayak for ma tions of the east ern Cri mean Pen in sula: basinal, slope and toe-of-slope zones. In this in ter val we iden tify the low est Berriasian Jacobi and Grandis subzones of authors, in ex panded form, ex ceed ing 160 metres in thick ness. We pres ent new magnetostratigraphic in ter pre ta tions, and iden tify two nor mal and two re versed po lar ity in ter vals, as signed to M19n, M18r, M18n and M17r, with M19n2n, M19n1r and M19n1n iden ti fied in the up per most Dvuyakornaya For ma tion. In the Mayak For ma tion we re cord the top of M19n.1n, with M18r, M18n and a thick M17r above. In these two for ma tions com po nent calpionellid spe cies have been iden ti fied which char ac ter ise the Alpina, Ferasini and Elliptica subzones (Calpionella Zone). In M19n, the FADs of the cal car e ous nannofossils Hexalithus strictus, Cruciellipsis cuvillieri, Nannoconus wintereri, N. steinmannii mi nor and N. kamptneri mi nor are found, which is con sis tent with other Tethyan re gions. N. steinmannii steinmannii and N. kamptneri kamptneri first appear in M18r at Ili Burnu. Spec i mens of the ap par ently Tithonian foraminiferan in dex Anchispirocyclina lusitanica are found, but in the Berriasian lower Mayak For ma tion.

A detailed bed-by-bed sampled stratigraphic section of the Guasasa Formation in the Rancho San Vicente area of the "Sierra de los Órganos", western Cuba, provides well-supported evidence about facies and calpionellid distribution across the Jurassic/Cretaceous boundary. These new data allowed the definition of an updated and sound calpionellid biozonation scheme for the section. In this scheme, the drowning event of a carbonate platform displayed by the facies of the San Vicente Member, the lowermost unit of the section, is dated as Late Tithonian, Boneti Subzone. The Jurassic/Cretaceous boundary was recognized within the facies of the overlying El Americano Member on the basis of the acme of Calpionella alpina Lorenz. The boundary is placed nearly six meters above the contact between the San Vicente and the El Americano Members, in a facies linked to a sea-level drop. The recorded calpionellid bioevents should allow correlations of the Cuban biozonation scheme herein proposed, with other previously published schemes from distant areas of the Tethyan Domain.

Segmentation of the Guyanas continental margin of South America is inherited from the dual-phase Mesozoic rifting history controlling the first-order post-rift sedimentary architecture. The margin is divided into two segments by a transform marginal plateau (TMP), the Demerara Rise, into the Central and Equatorial Atlantic domains. This paper investigates the heterogeneities in the post-rift sedimentary systems at a mega-regional scale (>1000 km). Re-sampling seven key exploration wells and scientific boreholes provides new data (189 analysed samples) that have been used to build a high-resolution stratigraphic framework using multiple biostratigraphic techniques integrated with organic geochemistry to refine the timing of 10 key stratigraphic surfaces and three megasequences. The results have been used to calibrate the interpretation of a margin-scale two-dimensional seismic reflection dataset and build megasequence isochore maps, structural restorations and gross depositional environment maps at key time intervals of the margin evolution.Our findings revise the dating of the basal succession drilled by the A2-1 well, indicating that the oldest post-rift sequence penetrated along the margin is late Tithonian age (previously Callovian). Early Central Atlantic carbonate platform sediments passively infilled subcircular-shaped basement topography controlled by underlying basement structure of thinned continental crust. Barremian-Aptian rifting in the Equatorial Atlantic folding and thrusting the Demerara Rise resulting in major uplift, gravitational margin collapse, transpressional structures, and peneplanation of up to 1 km of sediment capped by the regional angular base Albian unconformity. Equatorial Atlantic rifting led to margin segmentation and the formation of the TMP, where two major unconformities developed during the intra Late Albian and base Cenomanian. These two unconformities are time synchronous with oceanic crust accretion offshore French Guiana and in the Demerara-Guinea transform, respectively. A marine connection between the Central and Equatorial Atlantic is demonstrated by middle Late Albian times, coinciding with deposition of the organic-rich source rock of the Canje Formation) (average TOC 4.21 %). The succession is variably truncated by the middle Campanian unconformity. Refining the stratigraphic framework within the context of the structural evolution and segmentation of the Guyanas margin impacts the understanding of key petroleum system elements.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5280490

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