Changes in the composition of trace fossil assemblages across the Paleocene–Eocene transition in the north-western Tethys (Untersberg section, Austria)
Abstract: The Untersberg section (Northern Calcareous Alps, Austria) provides an expanded and biostratigraphically well constrained deep-sea record of the Paleocene–Eocene transition in the north-western Tethyan realm. At the base of the Eocene, massive carbonate dissolution and a shoaling of the calcite compensation depth (CCD) by at least 1 km is recorded by 5.5 m-thick red claystone, which is intercalated into a grey marlstone succession. Previous studies documented the benthic foraminifera extinction event (BEE) in this claystone. Now biodeformational structures and trace fossils were investigated in this interval to evaluate the impact of the extinction event on the macrobenthic tracemaker fauna. Using the stratigraphic distribution pattern of trace fossils, the lowermost Eocene claystone can be subdivided into three parts: (1) the lower part shows a trace fossil assemblage consisting of Chondrites isp., Planolites isp., Thalassinoides isp., and Zoophycos isp., (2) the middle part is characterized by primary sedimentary lamination and exceedingly rare ichnofossils, and (3) the upper part shows a less abundant and less diverse trace fossil assemblage than the lower part, indicating a slow recovery of the macrobenthic tracemaker community. This pattern demonstrates that macrobenthic communities were severely affected by the ecological perturbations in the earliest Eocene. The change in sediment colouration towards red colour in the middle part of the Paleocene–Eocene transition at the Untersberg section, together with decrease in bioturbation degree indicate that oxygen consumption was rather reduced during the PETM, and the loss in bioturbation is thus unrelated to oxygen limitation. Trace fossils can be used to improve the resolution of the benthic extinction interval and provide an excellent proxy for the precise determination of timing of the climax of this global event.
Report on the XXI International Congress of the Carpathian Balkan Geological Association (CBGA) in Salzburg, Austria, September 10–13, 2018
Provenance of synorogenic deposits of the Upper Cretaceous–Lower Palaeogene Jarmuta–Proč Formation (Pieniny Klippen Belt, Western Carpathians)
Abstract: The Pieniny Klippen Belt contains thickening and coarsening upwards synorogenic sedimentary successions witnessing the collision of the Oravic ribbon continent with the Central Carpathian orogenic wedge after the closure of the Vahic Ocean in the Late Cretaceous to Early Palaeogene. The sedimentary record of this event is represented by flysch/wildflysch deposits of the Maastrichtian–Lower/Middle Eocene Jarmuta–Proč Formation. We present results of the provenance study of these deposits, based on the framework petrography, heavy mineral analysis and mineral chemistry. Turbiditic sandstones were classified as quarzolithic to lithic arenites. Lithic fragments are predominantly composed of carbonate rocks and low- to medium-grade metamorphic and occasional mafic volcanic rocks. The heavy mineral association is composed of both first-cycle derived and recycled ultrastable ZTR, garnets and Cr-spinels. The chemistry of the detrital tourmalines and garnets suggests a derivation from various low- to medium-grade metamorphic rocks. High-pyrope garnets, observed in the eastern part of the PKB, which were derived from high-grade granulites and eclogites, represent probably lower crustal complexes exhumed during rifting of the Vahic Ocean. The Cr-spinels show a mixed harzburgitic and lherzolitic provenance. The harzburgitic Cr-spinels might have been recycled from older exotic conglomerates of the Klape Flysch, thereby representing ophiolitic detritus of the Meliata Ocean. The lherzolitic Cr-spinels might represent a new contribution of ophiolitic detritus delivered from the exhumed subcontinental mantle forming the Vahic oceanic floor.
Linkage of the Manín and Klape units with the Pieniny Klippen Belt and Central Western Carpathians: balancing the ambiguity
Abstract: The paper deals with the structure and evolution of the Pieniny Klippen Belt in its classic area in western Slovakia. The so-called Peri-Klippen Zone provides a transition from the Pieniny Klippen Belt s.s. built up by Jurassic to Eocene Oravic units (Šariš, Subpieniny and Pieniny from bottom to top) to the outer margin of the Central Western Carpathians composed of Triassic to mid-Cretaceous successions of the Fatric and Hronic cover nappe systems. The Peri-Klippen Zone attains a considerable width of 15 km in the Middle Váh River Valley, where it is composed of the supposedly Fatric Manín, Klape and Drietoma units, as well as their post-emplacement, Gosau-type sedimentary cover. All these units are tightly folded and imbricated. The complex sedimentary and structural rock records indicate the late Turonian emplacement of the frontal Fatric nappes in a position adjacent to or above the inner Oravic elements, whereby they became constituents of an accretionary wedge developing in response of subduction of the South Penninic–Vahic oceanic realm separating the Central Western Carpathians and the Oravic domain. Evolution of the wedge-top Gosau depressions and the trench-foredeep basins of the foreland Oravic area exhibit close mutual relationships controlled by the wedge dynamics. The kinematic and palaeostress analyses of fold and fault structures revealed only one dominating stress system coeval with development of the accretionary wedge, which is characterized by the generally NW–SE oriented main compression axis operating in a pure compressional to dextral transpressional regime, interrupted by short-term extensional events related to the wedge collapse stages. Younger, Miocene to Quaternary palaeostress fields correspond to those widely recorded in the entire Western Carpathians. Relying on the regional tectonostratigraphic and structural data, the problematic issues of the palaeogeographic settings of the Manín and Klape units, presumably affiliated with the Fatric cover nappe system, and of the provenance of numerous olistoliths occurring at different stratigraphic levels are then discussed in a broader context.
Organic petrological and geochemical properties of jet from the middle Triassic Mogila Formation, West Bulgaria
Abstract: The paper presents the results of the petrographic and organic geochemical studies of a jet sample recovered from a Mid-Triassic carbonate succession from the West Balkan tectonic zone in Bulgaria. Total organic carbon contents (TOC = 92 % daf) and high vitrinite reflectance (Ro = 1.9 %) indicate semi-anthracite coalification rank. Very high Tmax (577 ºC) and low HI (~10 mg HC/g TOC) further support the overmature organic matter. Extractable organic matter is characterized by high portions of NSO compounds and asphaltenes (> 75 %). Hydrocarbons constitute about 20 % and are characterized by the predominance of the saturated hydrocarbons over the aromatics. n-Alkanes distribution, dominated by short-chain compounds (n-C17–18), is consistent with the woody origin of the jet and the thermal maturity of the organic matter. The predominance of PAHs with condensed structure over their alkylated isomers is considered to be a result of the complex reaction occurring within the organic matrix during the catagenesis, rather than to the presence of combustion-derived organic matter. Based on the distribution of the diterpenoids, a tentative identification of a possible Voltziales conifer family source is identified. Low Pr / Ph ratio (0.88) and aryl isoprenoids outline anoxic conditions of jet formation, whereas the presence of organic sulfur compounds and tri-MTTchroman suggest marine depositional environment with normal salinity.
Facies and paleoenvironmental reconstruction of Early–Middle Miocene deposits in the north-west of the Zagros Basin, Iran
Abstract: Facies analysis and paleoenvironmental reconstruction of the Burdigalian to Langhian Asmari Formation, outcropping in the Khorram Abad Anticline, in the north-west of the Zagros Basin allow us to interpret the carbonate ramp history during the Early–Middle Miocene time span. The biota producing sediments in this system are dominated by the rhodalgal and echinofor skeletal-grain associations. Based on the facies distribution and paleoecology of the biotic content, the ramp is divided into three parts: inner, middle and outer ramp. The inner ramp is further subdivided into an inner zone where the main components include imperforate benthic foraminifera and molluscs associated with subordinate coral patch reefs, and an outer shallow-water zone dominated by wackestones–packstones with benthic foraminifera and coralline red algae facies. A shoal belt dominated by coralline red algae, benthic foraminifera, and coral fragments occurs in a distal inner ramp position. The middle ramp is characterized by rhodoliths, crustose red algal wackestone and thinly branching corals associated with encrusting foraminifera in proximal parts, and coralline red algal with larger benthic foraminifera and bryozoan colonies in the deeper oligophotic zone. The outer ramp includes proximal parts dominated by bryozoans, echinoids and molluscs with subordinate planktonic foraminifera and the distal part characterized by planktonic foraminifera and deep epifauna and infauna benthic foraminifera. Changes in trophic conditions and sea-level fluctuations, which are related to tectonic activities, seem to be the important factors in skeletal production and the spatial distribution of carbonate factories.