Establishing a chronological framework for deposition of the Istrian Flysch is crucial for reconstruction of the evolution of the Dinaric Mountain belt. The Istrian Flysch was deposited in the foreland basin that formed in front of the rising outer Dinarides mountains. The Flysch deposits overlie the lower and middle Eocene carbonate sequence, (deposited during the initial phase of the orogeny), that discordantly overlies the Cretaceous carbonates which are the remnants of the pre-orogenic Mesozoic carbonate platform. While previous authors suggested a middle Eocene age for the Flysch deposits, recent studies indicate deposition in the early and middle Miocene. Such conflicting dates for deposition of the Istrian Flysch reflects both the different temporal distributions of the Dinaric foreland basins and the varied histories of the Dinaric orogen. The biostratigraphy is based on analysis of planktonic foraminifera and calcareous nannofossils from 6 localities in Istria. Middle Eocene planktonic foraminiferal Zones from E9 to E13, and calcareous nannofossils Zones NP 15 to NP 17 (CP 13 to CP 15) were identified, corresponding to the Lutetian to Bartonian stages. The proportion of planktonic foraminifera to benthic foraminifera in most samples was very high (90-95%), except for the marginal part of the Basin (at the Plomin locality) where benthic foraminifera comprise 20% of the assemblage. The biodiversity increased during the Lutetian and reaching a maximum in Zones E10 and E11, (which are best documented in the Pi6an section, in the central part of the Istrian Basin). This assemblage, rich in both the number of species and abundance of specimens, indicates a long period of warm climatic and stable palaeoceanographic conditions. The planktonic foraminiferal Zone E12 (in the Pi6an section), most probably corresponds to the Middle Eocene Climatic Optimum (MECO). This global warming event, characterized by shifts in the global carbon cycle, occurred similar to 40 Ma ago and lasted about 400 kyr. Compared to the previous Zones, E12 reflects a decrease in both diversity and in the proportion of muricate taxa observed. However, an increase in the number of specimens of Subbotina and Turborotalia spp. was observed. In the highest part of the Koroma & ccaron;no section, in Zone E14, another decrease in diversity was observed, indicating relative cooling and instability in the marine environment. The results suggest that the Flysch deposits in Istria were deposited during the Lutetian and Bartonian (middle Eocene) in a deep, open marine environment with a subtropical climate, warm sea surface temperatures, and a very well-stratified water column, reflecting both the topological and palaeoclimate changes.
The critical review of regional data on the upper Emsian to Famennian in the Devonian Variscan Foreland basins of Poland demonstrates applicability of the global event-stratigraphic approach for improvement of a chronostratigraphic correlation of the existing lithostratigraphic schemes. In particular, eustatic sea level fluctuations and hypoxic black-shale events serve as useful regionally distinguishable event horizons, partly based on regional higher-order transgressive-regressive cycles. Credibility of particular levels depends on the correctness of facies/palaeoenvironmental interpretation of the associated depositional features whereas correlation precision is related to the resolution of chronostratigraphic tools, in this case, the conodont zonation. Depending on the quality of these attributes, the distinguished event levels were classified into four groups reflecting decreasing correlation confidence: certain, probable, possible and potential levels. Being less time and resources consuming than the high resolution correlation methodology (HiRES), the present approach leads to establishing a precise chronostratigraphic framework for studies involving different basins with well-recognized lithostratigraphy, facies development and advanced biostratigraphic correlation. Thus, it may be regarded as a first (or supplementary) step towards a precise and high-resolution interbasinal correlation. Such approach may facilitate depositional architecture and palaeogeographic studies, among others, while at the same time providing information on confidence of correlation procedures. Further refinement of the presented correlation will depend on regional-scale application of more precise dating techniques, including better-constrained biostratigraphic, as well as various radiometric, chemostratigraphic and cyclostratigraphic methods.
The Kungurian (late Cisuralian) represents a key stratigraphic interval for the evolution of postCarboniferous floras and, consequently, of continental Permian palynomorph assemblages in the palaeotropics. However, palynozonation remains limited by pronounced phytogeographic provincialism and by the scarcity of successions that combine diverse palynofloras with independent age control. The Athesian Volcanic District (AVD; northern Italy) integrates fossil-rich epiclastic intercalations with high-precision U-Pb zircon ages from enclosing volcanic units (ca. 289-274 Ma), providing a well-constrained temporal framework for biochronological calibration. Here, we integrate qualitative and quantitative palynological data from multiple AVD sedimentary units (Monte Luco, Verano, Guncina, and Tregiovo formations) to establish a refined Kungurian palynostratigraphic scheme and to recalibrate the chronostratigraphic ranges of selected key taxa within the Euramerican phytoprovince. Two assemblage-acme zones are recognised across the AVD: (1) the Vittatina Palynozone, restricted to the Monte Luco Formation and constrained to the middle Kungurian, characterized by an acme of Vittatina and by abundant large monosaccate pollen grains, and (2) the Protohaploxypinus Palynozone, spanning the upper Verano, Guncina and Tregiovo formations, characterized by sustained high abundances of Protohaploxypinus and recurrent peaks of Vesicaspora, together with additional diagnostic bioevents. Radiometrically anchored first/last occurrences documented here provide new constraints for regional correlation, including refined calibrations for Nuskoisporites dulhuntyi, Lueckisporites virkkiae, Jugasporites delasaucei, Taeniaesporites noviaulensis, Gigantosposporites aletoides, and the genus Vestigisporites. These results highlight both the stratigraphic value of the AVD for late Cisuralian palynostratigraphy and persistent palaeofloristic provincialism in interprovincial comparisons.
