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2 Volumina Jurassica

2 2006

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Late Jurassic - Early Cretaceous volcanism in the Ukrainian part of the Carpathians

Krobicki M., Golonka J., Malata E., Oszczypko N., Słaby E., Słomka T.

Volumina Jurassica

2006

Vol. 4, no. 1

52-53

Today the Ukrainian Mesozoic volcanic rocks are located in the relatively small area. They are concentrated near the Rachiv Massif and Chivchin Ridge, generally in the front of the Rahiv and Maramuresh (=Marmaros) nappes (Outer Flysch Carpathians) and in the Pieniny Klippen Belt. Several outcrops in these regions were studied in details by present authors. Rachiv nappe contains basaltic flows with numerous pillow lava horizons, ophicalcite(?) and with lava breccias on the top of volcanic sequence (Trostianets stream), as well as basaltic and tuffitic breccias (Lemskij stream). Maramuresh nappe contains andesites, basalts and tuffitic breccias often associated with light-grey micritic and coral limestones of Âtramberk-type facies (Kamennyj Potok stream). Most spectacular region of distribution of magmatic rocks belongs to Maramuresh unit and is located between Margetul, Radomir and Kwasnyj streams. These rocks are represented mainly by massive and pillow basalts, basaltic and tuffitic breccias and diabases as well as porphyritic conglomeratic/breccias. Usually they build huge klippes up to 50 meters and more. The contacts between huge pillow basaltic flows and surrounding deposits are usually covered by debris or vegetation but in Margetul stream the relationship between pillow lavas and pelagic, micritic limestones with cherts (Cieszyn Limestone Formation type) is very well visible. In the lower part of section small lenses of basaltic rocks occur within these limestones and basaltlimestone ratio increases upwards. Latest Jurassic - earliest Cretaceous age of these limestones was established helping to determine crucial age of a magmatic event to understand most important wide geodynamic processes. The basaltic rocks with pillow lavas are exposed in Veliky Kamenets quarry within Ukrainian part of the Pieniny Klippen Belt. These basalts cover the Middle Jurassic - lowermost Creataceous carbonate sequence, the contact is sharp and basaltic dykes also penetrate underlying Calpionella limestones. Above these basalts, there are younger limestones rich both in ammonites and benthic fauna (brachiopods, bivalves and crinoids) and they are overlain by 1 meters thick tuffites. The youngest deposits in the Veliky Kamenets section are yellowish limestone breccias showing presence of abundant Berriasian calpionellids. Sedimentological features of this breccia indicate submarine erosion connected with synsedimentary movements of the sea bottom causing redeposition of older rocks - in this case Calpionella limestones and basaltic fragments. These sediments correspond very well with Walentowa Breccia Member of the Dursztyn Limestone Formation which originated after strong Neo-Cimmerian uplift of the Czorsztyn Ridge. Additionally, in Vulhovchik stream, just below Veliky Kamenets hill, Jurassic/Cretaceous trachydolerites occur. These magmatic events correspond very well with major plate reorganization, which happened during the Tithonian time within western Tethyan Ocean. In the same time the Outer Carpathian rifts were developed with the extensional type of volcanism (teschenites) and the Silesian Basin originated as a result of such rifting process. The presumable triple-junction zone comprises the Rahiv-Sinaia zone (first arm), Silesian (second one) and its extension into the Pieniny Klippen Belt/Magura Basin (third arm). The origin of this triple junction is perhaps related to the opening of the Central Atlantic-Ligurian-Penninic oceanic system.

Jurassic-Cretaceous deposition-palaeogeography on the northern margin of the Dabie Orogen and its tectonic implication

Li S., Liu Y., Wang D., Li R., Meng Q., Yue S-C., Jin F-Q.

Volumina Jurassica

2006

Vol. 4, no. 1

59-60

The Jurassic-Cretaceous strata of the northern margin of the Dabie Orogen consist of terrestrial sediments comprising thirteen formations, about eight km of thickness at the southern margin of the Hefei-Huangchuan basins, and are divided into four chronosomes. The chronosome I comprises the Lower Jurassic Fanghushan Formation and the lower part of Middle-Upper Jurassic Yuantongshan Formation. The formations represent braided rivers, meandering rivers and marginal to shallow lacustrine environments, and are developed only at the east end of the Hefei Basin. The Chronosome II consists of the Middle-Upper Jurassic Sanjianpu and Zhuji formations, and the upper part of Yuantongshan Formation. The alluvial fans are recognized in the lower parts, and braided rivers in the middle and upper parts of the formations. Transverse water systems crossing the orogen were developed at an early stage, and longitudinal water systems paralleling the orogen in the late stage of sedimentation in the area of study. The East-West stretching Xinyang-Jinzhai-Shucheng Fault (XJSF) borders the sedimentation area in the south. The Chronosome III comprises lower parts of Lower Cretaceous Fenghuangtai, Duanji and Zhougongshan formations, of which the former two consist of alluvial fans and the latter formation of braided rivers and overbank deposits. Coarse-grained siliciclastic deposits prograded into the basins for a few kilometers. The transverse water system developed on the southern margin of the basins, and the longitudinal water system - in the middle of the basins. Chronosome IV comprises the late Early Cretaceous Heishidu and Chenpeng formations. The Xiaotian-Mozitan Fault (XMF) and the Tongbai-Shangcheng Fault (TSF) are placed at the southern boundary of the depositional basin, and the faults are mainly of strike-slip character. Alluvial fans to fan-deltas developed at an early stage, whereas turbidites were deposited in deep lacustrine environments at the late stage of sedimentation. The study area mostly suffered uplift and erosion during the Late Cretaceous; sedimentation was then limited to the western part of the Huangchuan Basin. Longitudinal faults such as XJSF, XMF and TSF paralleling the orogen, and more or less, East-West trending, limited the chronosomes in the south. Transverse faults such as the Tancheng-Lujiang Fault (TLF) and the Shangcheng-Macheng Fault (SMF), more or less North-East trending, controlled lateral facies changes of the chronosomes. Deposition overlapped progressively from east to west at the southern margin of Hefei-Huangchuan basins, which implies that exhumation and unroofing of the Dabie Orogen was diachronous from east toward west. The chronosomes were restricted by TLF and SMF. TLF controlled the development of the Jurassic depocenter, which implies that the fault did not become active until the Early Jurassic.