New microfossil and magnetostratigraphical data as well as geochemical and clay mineral weathering indices are documented from the uppermost Jurassic Owadów–Brzezinki palaeontological site in central Poland. The newly discovered chitinoidellid assemblage of the lowermost part of the section and the previously documented assemblage from the middle part of the section are assigned, respectively, to the uppermost Dobeni and Boneti Subzones of the Chitinoidellidae Zone. The same part of the succession is correlated to the magnetosubzone M20n.2n. The new data allow refinement of the Tithonian stratigraphical scheme including an assignment of the upper part of the Boreal Zarajskites Subzone of the Scythicus (Panderi) ammonite Zone to the Upper Tithonian and its correlation with the lowermost part of Tethyan Microcanthum ammonite Zone and the lower portion of the M20n.2n magnetosubzone. The data show that the Fittoni/Albani ammonite zone boundary should likely be placed within the Boneti Subzone. The geochemical data show decreasing chemical weathering intensity during the earliest Late Tithonian in central Poland, which is linked to aridification of the latest Jurassic climate. The same trend is observed in coeval sections of NW and NE Europe. Supplementary material: Additional rock magnetic results, correlation of magnetic proxies with Al. and X-ray diagrams for clay minerals are available at https://doi.org/10.6084/m9.figshare.c.6299266
In the Krakow-Lubliniec section of the major Hamburg-Krakow-Dobrogea Fault Zone (HKDFZ), the Stephanian-Early Permian magmatic activity was simultaneous with subsidence/uplift of formed blocks. In the proximity of the uplifted areas the sedimentation started with fanglomerates, distally passing into playa siltstone and was accompanied by volcanism. In the Nieporaz-Brodla graben, basaltic trachyandesite a-a lava flows with autoclastic breccias reach ca. 150 m in thickness. The weathering recorded as adhesive rims around breccia clasts reflects palaeosoil formation during quiescence periods between the eruptions. The eruptions were effusive although scoriaceous lava indicates high volatile content of the magma. The water content before eruption had to be over 2 wt. percent. Only then the crystallisation model predicts accurately the type, composition and order of the crystallising phases. Thus, the basaltic trachyandesite magma originated from a source containing hydrous phase (i.e., amphibole or phlogopite). All the studied basaltic trachyandesites had fayalitic olivine on their liquidus reflecting the crystallisation stage in a magma chamber at crustal depths. During final decompression on the magma ascent due to water exsolution, the olivine was followed by plagioclase, spinel, augite, ilmenite, apatite, K-feldspar and residual high-K rhyolitic glass. The high potassium content of these volcanics was thus a primary feature reflecting the source geochemistry and differentiation trend, and its consequence was potassium metaso- matism. Due to water exsolution the glass was altered, however, homogenous interstitial glass survived in some rocks. The glass is strongly enriched in incompatible trace elements, showing that it is a highly fractionated residual melt fraction of the basaltic trachyandesite magma. Thus, the glass geochemistry reflects the trend of fractional crystallisation indicating that co-occurring K-rich felsic rocks were not derived from the same magma. All the basaltic trachyandesites studied have calc-alkaline to alkaline affinity. They contain fayalitic olivine and are low in MgO 0.5-0.80 and small Eu/Eu* > 0.9-1.0 anomalies suggesting fractionation of plagioclase. The Eu/Eu* anomaly is probably compensated by amphibole retaining in the source. Negative Nb, Ti anomalies suggest Fe-Ti oxide fractionation characteristic for calc-alkaline evolution trend. A significant enrichment in LREE relatively to HREE (La/Yb > 10) indicates subduction-related metasomatism. However, the described tectonic context is inconsistent with subduction related characteristics. Concluding, the observed geochemical characteristics indicate remarkable role of water in magma evolution. The volcanism was related to strike-slip dextral movement along the Krakow-Lubliniec section of HKDFZ, transformed into crustal extension and subsidence, the features typical for the formation of pull-apart basins, in the late stages of the Variscan orogen evolution.
New palaeomagnetic poles obtained from the Vendian tuffs and basalts of western Ukraine indicate the necessity of a substantial revision of the Late Vendian-Early Cambrian palaeogeography of the Baltic plate. The palaeopole calculated for the most stable component isolated from the Vendian tuffs and basalts is far away from the Vendian-Cambrian apparent polar wander path (APWP), constructed on the basis of Scandinavian poles but is very close to the pole recently isolated from the Vendian sediments of the White Sea Region. Depending on the polarity of the newly-determined Late Vendian pole, two palaeogeographic models of the Baltic plate in the Late Vendian-Early Cambrian are possible. In our preferred model the Baltic plate moved at that time from the moderate southern latitudes to the equator rotating anticlockwise of ca. 120o . This reconstruction explains the geological structures of the marginal zones of Baltica better than the previously proposed stationary model of the Late Vendian-Cambrian Baltica. According to the new late Vendian palaeogeographic scenario, the European, passive margin of Baltica was separated from an active, Avalonian margin of Gondwana. The Late Neoproterozoic tectonic structures of the Brunovistulian Terrane and the Malopolska Block were developed near the present day southwestern corner of Baltica that was tectonically active at that time. Alternative reconstruction shows the Baltic plate moving from the moderate northern latitudes in the Vendian, crossing palaeoequator in the latest Vendian, and reaching moderate southern palaeolatitudes in the Late Cambrian. This model, however, would have required exceptionally high plate velocity (ca. 33 cm/year).
Uzyskane na obszarze Sudetow poźnokarbonskie i wczesnopermskie bieguny paleomagnetyczne wykazują niewielkie ale jednakowe co do zwrotu odchylenie od krzywej referencyjnej dla stabilnej Europy. Odchylenie to wynika z niewielkich lewoskretnych rotacji badanych formacji skalnych wokol lokalnych osi pionowych. Analizowany obraz paleomagnetyczny pozwala na postawienie hipotezy, ze sedymentacja utworow permskich w Sudetach przebiegala w warunkach lewoskretnej transtensji.
PALEOMAGNETIC DATA AND TECTONIC REGIME DURING PERMIAN SEDIMENTATION IN SUDETY MOUNTAINS
Summary
Late Carboniferous-Early Permian paleomagnetic poles from the Sudetes show a small! systematic departure from the stable European apparent polar wander path. This deviation implies a small! (up to 20°) anticlockwise rotations around vertical axes that affected studied rocks during the Permian. These rotations indicate sinistral transtensional tectonic regime during Permian sedimentation in the Sudetes.
The magnetic susceptibility of loess‐palaeosol sequences in southern Poland and western Ukraine varies mainly with the degree of decomposition of detrital magnetite grains conditioned by palaeoclimate. Relatively high susceptibility values were observed in the unweathered loess horizons and in accumulation horizons of the non‐gleyed soils which contain relatively high amounts of paramagnetic fraction and pedogenic (?) magnetite. The susceptibility curves characteristic for Polish and western Ukrainian loess‐palaeosol sequences may be directly correlated with oxygen‐isotope fluctuations in deep‐sea sediments. This correlation is more complex than that for the Chinese or Alaskan loess‐palaeosol sequences. The major causes of the complexities are the relatively small thicknesses of the investigated sections (especially their older horizons) and the heterogeneity of geochemical processes that affected loess surface in the interglacial and interstadial times.
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