Palaeozoic Formations from Dobrogea and Pre-Dobrogea &#8211; An Overview

Antoneta SEGHEDI

Makale detayları

Palaeozoic Formations from Dobrogea and Pre-Dobrogea – An Overview

Yazarlar:

Antoneta SEGHEDI

Yayıncı:

TUBITAK

Dergi:

Turkish Journal of Earth Sciences 2012 Vol.21 Issue 5, pp.669-721

Belge Tipi:

Makale

Yayın Tarihi:

4/2012

Belge Dili:

Türkçe

Document ID (Org No.):

2000731910

Sıklık:

İki Aylık

eISSN:

1303-619X

pISSN:

1300-0985

Özet:

 

An overview of lithological, palaeontological and geochronological evidence existing for the Palaeozoic formations from Dobrogea and PrDobrogea has enabled a better understanding of the Palaeozoic history of these areas. The Lower Palaeozoic of Pre-Dobrogea, in places in continuity with the pelitic-silty facies of the underlying Vendian (Ediacaran) deposits, was one of the peri-Tornquist basins of Baltica, suggesting that the Scythian Platform in the Pre-Dobrogea basement represents the rifted margin of the East European Craton. In North Dobrogea two types of Palaeozoic succession have formed in different tectonic settings. Deep marine Ordovician-Devonian deposits, including pelagic cherts and shales, associated with turbidites, and facing Devonian carbonate platform deposits of the East European Craton, form northward-younging tectonic units of an accretionary wedge, tectonically accreted above a south-dipping subduction zone. South of the accretionary prism, the basinal to shallow marine Silurian-Devonian deposits of North Dobrogea, showing a similar lithology to the East Moesian successions, accumulated on top of low-grade Cambrian clastics with Avalonian affinity indicated by detrital zircons. Late Palaeozoic erosion was accompanied by deposition of continental alluvial, fluvial and volcano-sedimentary successions, overlying their basement above an imprecise Carboniferous gap. The low-grade metamorphic Boclugea terrane, showing Avalonian affinity, and the associated Lower Palaeozoic deposits represent East Moesian successions, docked to Baltica by the Lower Devonian and subsequently involved in the Hercynian orogeny, being affected by Late Carboniferous-Early Permian regional metamorphism and granite intrusion. The Late Carboniferous-Early Permian syn-tectonic sedimentation, regional metamorphism of Palaeozoic formations and development of a calc-alkaline volcano-plutonic arc indicate an active plate margin setting and an upper plate position of the Măcin-type successions during the Variscan collision, when the Orliga terrane, with Cadomian affinity, was accreted to Laurussia along a north-dipping subduction zone of the Rheic Ocean. The East Moesian Lower Palaeozoic succession, overstepping its Ediacaran basement, represents an Avalonian terrane, docked to the Baltica margin in the Early Palaeozoic. A narrow terrane detached from the Trans-European Suture Zone (TESZ) margin of the Baltica palaeocontinent forms a tectonic wedge within the East Moesian basement. The Palaeozoic sedimentary record of East Moesia shows a quartzitic facies in the Ordovician, graptolite shales in Upper Ordovician-Wenlock, black argillites in the Ludlow-Pridoli and fine-grained clastics in the Lower Devonian. Eifelian continental sandstones are followed by a carbonate platform from Givetian to Tournaisian times and coal-bearing clastics in the Carboniferous, indicating a foredeep basin evolution. By the Eifelian both East Moesia and Pre-Dobrogea were part of Laurussia, sharing the same old red sandstone facies. The Permian is a time of rifting in Dobrogea and Pre-Dobrogea, although evidence for rifting in the East Moesian sedimentary record is very limited. In the eastern basins of Pre-Dobrogea, Permian rifting was accompanied by alkaline bimodal volcanism of the basalt-trachyte association, that affected also the northern margin of North Dobrogea. Late Permian within-plate alkaline magmatic activity emplaced plutonic and hypabyssal complexes along the south-western margin of North Dobrogea. The model proposed for the Palaeozoic history based on existing data for the north-western margin of the Black Sea records early Palaeozoic docking to Baltica of the Avalonian terrane of East Moesia, including the Boclugea terrane of North Dobrogea. Late Carboniferous-Early Permian accretion of the Cadomian Orliga terrane from North Dobrogea, accompanied by Hercynian metamorphism and granite intrusion, correlates with the closure of the Rheic Ocean. Subsequently, Avalonian and Cadomian terranes, together with a narrow terrane detached from the TESZ margin of Baltica palaeocontinent, were displaced southward along the strike-slip fault system of the TESZ.

 

An overview of lithological, palaeontological and geochronological evidence existing for the Palaeozoic formations from Dobrogea and PrDobrogea has enabled a better understanding of the Palaeozoic history of these areas. The Lower Palaeozoic of Pre-Dobrogea, in places in continuity with the pelitic-silty facies of the underlying Vendian (Ediacaran) deposits, was one of the peri-Tornquist basins of Baltica, suggesting that the Scythian Platform in the Pre-Dobrogea basement represents the rifted margin of the East European Craton. In North Dobrogea two types of Palaeozoic succession have formed in different tectonic settings. Deep marine Ordovician-Devonian deposits, including pelagic cherts and shales, associated with turbidites, and facing Devonian carbonate platform deposits of the East European Craton, form northward-younging tectonic units of an accretionary wedge, tectonically accreted above a south-dipping subduction zone. South of the accretionary prism, the basinal to shallow marine Silurian-Devonian deposits of North Dobrogea, showing a similar lithology to the East Moesian successions, accumulated on top of low-grade Cambrian clastics with Avalonian affinity indicated by detrital zircons. Late Palaeozoic erosion was accompanied by deposition of continental alluvial, fluvial and volcano-sedimentary successions, overlying their basement above an imprecise Carboniferous gap. The low-grade metamorphic Boclugea terrane, showing Avalonian affinity, and the associated Lower Palaeozoic deposits represent East Moesian successions, docked to Baltica by the Lower Devonian and subsequently involved in the Hercynian orogeny, being affected by Late Carboniferous-Early Permian regional metamorphism and granite intrusion. The Late Carboniferous-Early Permian syn-tectonic sedimentation, regional metamorphism of Palaeozoic formations and development of a calc-alkaline volcano-plutonic arc indicate an active plate margin setting and an upper plate position of the Măcin-type successions during the Variscan collision, when the Orliga terrane, with Cadomian affinity, was accreted to Laurussia along a north-dipping subduction zone of the Rheic Ocean. The East Moesian Lower Palaeozoic succession, overstepping its Ediacaran basement, represents an Avalonian terrane, docked to the Baltica margin in the Early Palaeozoic. A narrow terrane detached from the Trans-European Suture Zone (TESZ) margin of the Baltica palaeocontinent forms a tectonic wedge within the East Moesian basement. The Palaeozoic sedimentary record of East Moesia shows a quartzitic facies in the Ordovician, graptolite shales in Upper Ordovician-Wenlock, black argillites in the Ludlow-Pridoli and fine-grained clastics in the Lower Devonian. Eifelian continental sandstones are followed by a carbonate platform from Givetian to Tournaisian times and coal-bearing clastics in the Carboniferous, indicating a foredeep basin evolution. By the Eifelian both East Moesia and Pre-Dobrogea were part of Laurussia, sharing the same old red sandstone facies. The Permian is a time of rifting in Dobrogea and Pre-Dobrogea, although evidence for rifting in the East Moesian sedimentary record is very limited. In the eastern basins of Pre-Dobrogea, Permian rifting was accompanied by alkaline bimodal volcanism of the basalt-trachyte association, that affected also the northern margin of North Dobrogea. Late Permian within-plate alkaline magmatic activity emplaced plutonic and hypabyssal complexes along the south-western margin of North Dobrogea. The model proposed for the Palaeozoic history based on existing data for the north-western margin of the Black Sea records early Palaeozoic docking to Baltica of the Avalonian terrane of East Moesia, including the Boclugea terrane of North Dobrogea. Late Carboniferous-Early Permian accretion of the Cadomian Orliga terrane from North Dobrogea, accompanied by Hercynian metamorphism and granite intrusion, correlates with the closure of the Rheic Ocean. Subsequently, Avalonian and Cadomian terranes, together with a narrow terrane detached from the TESZ margin of Baltica palaeocontinent, were displaced southward along the strike-slip fault system of the TESZ.

Makale detayları

Palaeozoic Formations from Dobrogea and Pre-Dobrogea &#8211; An Overview

Yazarlar: Antoneta SEGHEDI

Yayıncı: TUBITAK

Dergi: Turkish Journal of Earth Sciences 2012 Vol.21 Issue 5, pp.669-721

Belge Tipi: Makale

Yayın Tarihi: 4/2012

Belge Dili: Türkçe

Document ID (Org No.): 2000731910

Sıklık: İki Aylık

eISSN: 1303-619X

pISSN: 1300-0985

Sayı

Palaeozoic Formations from Dobrogea and Pre-Dobrogea – An Overview

Yazarlar:

Antoneta SEGHEDI

Yayıncı:

TUBITAK

Dergi:

Turkish Journal of Earth Sciences 2012 Vol.21 Issue 5, pp.669-721

Belge Tipi:

Makale

Yayın Tarihi:

4/2012

Belge Dili:

Türkçe

Document ID (Org No.):

2000731910

Sıklık:

İki Aylık

eISSN:

1303-619X

pISSN:

1300-0985