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Rhaetian/Hettangian boundary in Pomerania, Poland

Pieńkowski G., Waksmundzka M.

Volumina Jurassica

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2006

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Vol. 4, no. 1

295-295

EN

Two boreholes from Pomerania, Western Poland (Kamień Pomorski IG-1 and Mechowo IG-1) yielded core material from the Triassic/Jurassic transition in continental deposits. In Mechowo IG-1 the Rhaetian/Hettangian boundary occurs within thick sandstone succession of fluvial origin and this boundary is determined based on occurrence of megaspores (Trileites pinguis and Nathorstisporites hopliticus assemblages - Marcinkiewicz 1971). In Kamień Pomorski (25 km to NW, depth 665.5-678.2 m), the grain size of sediments is significantly finer. Also, a minor marine ingression with dinoflagellate cysts can be noted (this ingression can be tentatively correlated with the "Contorta beds", known from Germany and Scandinavia). Uppermost Rhaetian deposits represent alluvial overbank subsystems, floodplain, lacustrine and crevasse splay facies dominate. This indicates a substantial limitation of depositional energy of the alluvial palaeoenvironment, which reflects both palaeoslope (Mechowo was closer to the sedimentary source area situated to the East) and probably local tectonic factor. Consequently, erosion at the Rhaetian/Hettangian boundary (sequence boundary) is inconspicuous if any, which is an exceptional case in the Early Jurassic Polish Basin, where usually Rhaetian deposits are missing or reduced from the top by erosion. Material from Kamień Pomorski IG-1 borehole gives much more abundant palynological data. In the uppermost Rhaetian, the following miospores are most characteristic: spores Semiretisporites gothae (restricted only to the Late Triassic), accompanied by Limbosporites lundblandi Nilsson, Baculatisporites wellmanii (Couper) Krutzsch, Cingulizonathes rhaeticus (Reinhardt) Schulz, Conbaculatisporites mesozoicus Klaus, Deltoidospora toralis (Leschik) Lund, Densosporites fissus (Reinhardt) Schulz, Lycopodiacidites rugulatus (Couper) Schulz, pollens Alisporites radialis (Leschik) Lund, Cuneatisporites cf. radialis Pautsch, Ovalipolis ovalis Krutzsch. This is a typical Rhaetian miospore assemblage. Interestingly, the uppermost Rhaetian deposits show a characteristic palynofacies turnover with a conspicuous "fern peak" (huge number and domination of fern-derived spores). This may point to the environmental/climatic change at the Rhaetian/Hettangian boundary and concomitant biotic crisis. The lowermost Hettangian assemblage comprises (among others): spores Contignisporites problematicus (Couper) Playford & Dettmann, Conbaculatisporites mesozoicus (Madler) Lund, Concavisporites toralis (Leschik) Nilsson, Cosmosporites elegans Nilsson, Zebrasporites interscriptus (Thiergart) Klaus, Lycopodiumsporites semimuris Danze-Corsin & Laveine and pollens Pinuspollenites minimus (Couper) Kemp. These preliminary studies are encouraging and the Kamień Pomorski profile can add to the European record of continental Rhaetian/Hettangian boundary. Furter palynological and isotope studies are planned in this section.

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Palynology, T/J boundary microfacies, clay mineralogy, C and O isotopes and other palaeoclimatic indicators from the Tatra Mts.

Götz A., Ruckwied K., Biroń A., Lintnerová O., Michalík J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

282-283

EN

The Furkaska and Kardolina sections expose a complete succesion of the uppermost Fatra Formation and the lowermost Kopienec Formation. The Upper Triassic Fatra Fm. is characterized by bioclastic limestones and fine-grained clastics overlain by dark claystones with intercalated sandstones (Cardinia Sandstein) of the Kopienec Formation. Due to lack of age-diagnostic index fossils, the precise position of the Triassic/Jurassic boundary is not yet known. Based on negative excursion of the δ ¹ ³C carbonate isotopic curve and microfacies analyses the boundary interval was placed near the transition of two formations. Palynological analysis was focused on palaeoenvironmental and stratigraphical aspects. Generally, the continental fraction shows a high amount of phytoclasts. The few marine organic depositional environment indicate a very shallow marine depositional environment. The palynomorph assemblage of the Fatra Fm. is characterized by numerous Ricciisporites tuberculatus. The marine fraction of this part of the sections is dominated by dinoflagellate cyst Rhaetogonyaulax rhaetica. Microflora of the Upper Fatra Formation is very similar to the Ricciisporites tuberculatus Zone of the Polish zonation and Ricciisporites-Polzdiisporites Zone of the SE Nord Sea Basin, both indicating a Middle to Late Rhaetian age. The palynomorph assemblage of the Kopienec Formation is characterized by a significant increase of trilete laevigate spores, mainly Deltoidospora spp. and Concavisporites spp. The dinoflagellate cyst Dapcodinium priscum replaces Rhaetogonyaulax rhaetica in the marine fraction. These changes may be caused by a regression at the Triassic/Jurassic boundary. Quantitative clay minerals analyses documented palaeoclimatic, palaeogeographic and postsedimentary changes in the boundary event and integrated palynological results. Mixed layer illite/smectite (I/S) smectite interlayers take about 80% of the clay fraction and their low content of smectite (10-20%) indicate relatively high diagenetic overprint of the Fatra and Kopienec formations claystones corresponding with burial temperature of 150oC. Varied contents of detrital illite, chlorite and kaolinite were used to demonstrate climatic changes in the hinterland and indicated depositional condition in this semi-restricted basin. Kaolinite and low illite/kaolinite ration indicate more humid climate during earliest Jurassic in comparison with the Rhaetian condition of illite/chlorite dominance. Peak occurrence of kaolinite at the base of the Kopienec Formation recorded different source and strong input of material from weathered and eroded land into proximal part of deltaic plain in comparison with the Fatra Formation.

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Flora assemblages at the Triassic/Jurassic boundary in Junggar Basin, Xinjiang Northwest China

Deng S.

Volumina Jurassica

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2006

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Vol. 4, no. 1

278-278

EN

The Upper Triassic and Lower Jurassic deposits in Junggar Basin, Xinjiang, Northwest China represent continuous succession and are divided into the Haojiagou Formation, Badaowan Formation and Sangonghe Formation (from base to the top). The Sangonghe Formation is definitely of the Early Jurassic age as based on plant, spore-pollen, conchostracans and bivalves. The ages of the Haojiagou and Badaowan formations are less clear. The Triassic/Jurassic boundary runs somewhere in the uppermost part of the Haojiagou Formation or in the Badaowan Formation as indicated by flora assemblages. Organic carbonaceous isotopic measurement suggests the position of the boundary in question at the base of the Badaowan Formation. The flora of the Haojiagou and the Badaowan Formations may be subdivided into the following assemblages. 1. Danaeopsis fecunda - Cladophlebis ichunensis assemblage. This assemblage is from the lower part of the Haojiagou Formation. It consists of about 20 species, characterized by Danaeopsis fecunda and numerous Cladophlebis. The main species include Danaeopsis fecunda Halle, Todites cf. shensiensis Pan, Cladophlebis ichunensis Sze, Cl. nebbensis (Brongn.) Nathorst, Cl. paralobifolia Sze, Sphenopteris chowkiawanensis Sze, Rireticopteris sp. and Cycadocarpidium sp. It is definitely of the Late Triassic age. 2. Neocalamites - Hausmannia assemblage. This assemblage is from the upper part of the Haojiagou Formation. It is composed of about 10 species with marked dominance of Neocalamites horerensis and Hausmannia xinjiangensis sp. nov. The assemblage is possibly of the Late Triassic age. 3. Todites princeps - Clathropteris elegans, assemblage. This assemblage is from the lower part of the Badaowan Formation, with about 15 species. Todites princes and Clathropteris elegans are dominant in the assemblage. It may be of earliest Early Jurassic age. 4. Coniopteris gaojiatianensis - Cladophlebis denticulata assemblage. This assemblage is abundant and of higher specific diversity. The main elements are: Selaginellites drepanoformis Zheng, Todites williamsoni (Brongniart) Seward, Coniopteris gaojiatianensis Zhang, Cladophlebis denticulata (Brongniart) Fontaine, Cl. gracilis Sze, Cl. hirta Moeller, Cl. cf. shansiensis Sze, Raphaelia diamensis Seward, Ginkgoites sp., Sphenobaiera sp., Czekanowskia rigida Heer, Samaropsis parvula Heer, S. rotundata Heer. It is noticeable that Coniopteris is recorded commonly. The assemblage occurs in the upper part of the Badaowan Formation and is of Early Jurassic age.

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Faunal and floral distribution, biostratigraphy, cyclostratigraphy and magnetostratigraphy of the T/J boundary

Michalík J., Soták J., Ruckwied K., Götz A., Grabowski J.

Volumina Jurassica

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2006

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Vol. 4, no. 1

292-292

EN

The Rhaetian and Hettangian sequence in the Zliechov Basin, Western Carpathians, comprises records of several environmental crises which could contributed to the global Triassic/Jurassic Boundary Events. The Upper Triassic Fatra Formation is characterized by bioclastic limestones and fine-grained clastics overlain by dark claystones with intercalated sandstones (Cardinia Sandstein) of the Kopieniec Formation. The diversity of benthic fauna decreased at the base of the "Transition Beds" - the uppermost member of the Fatra Formation. The fauna comprises important index forms of bivalve molluscs (Chlamys valoniensis), corals, brachiopods (Austrirhynchia cornigera) and foraminifers (Triasina hantkeni, etc.). The palynofacies of the entire succession is dominated by terrestrial components and by high amount of phytoclasts. The few marine organic particles indicate a very shallow marine depositional environment. The palynomorph assemblage of the Fatra Formation is characterized by numerous specimens of Ricciisporites tuberculatus. The marine fraction of the lower part of the section is dominated by the dinoflagellate cyst Rhaetogonyaulax rhaetica. The palynomorph assemblage of the Kopieniec Formation is characterized by a significant increase of trilete laevigate spores, mainly Deltoispora spp. and Concavisporites spp. The dinoflagellate cyst Dapcodinium priscum replaces Rhaetogonyaulax rhaetica in the marine fraction. These changes may be caused by a regression at the Triassic/Jurassic boundary and by an important fresh water input. The boundary between the Fatra and the Kopieniec formations is sharp, denoted by sudden termination of carbonate sedimentation followed by non-carbonate Boundary Clay of the Kopieniec Formation. Magnetostratigraphic record is in procession, it is hampered by complicated pattern of geomagnetic reversals at the end of the Triassic and at the beginning of the Jurassic period.