CRETACEOUS RED PELAGIC CARBONATES OF NORTHERN TURKEY - THEIR PLACE IN THE OPENING HISTORY OF THE BLACK-SEA


GORUR N., TUYSUZ O., AYKOL A., SAKINC M., YIGITBAS E. , AKKOK R.

ECLOGAE GEOLOGICAE HELVETIAE, cilt.86, ss.819-838, 1993 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 86 Konu: 3
  • Basım Tarihi: 1993
  • Dergi Adı: ECLOGAE GEOLOGICAE HELVETIAE
  • Sayfa Sayıları: ss.819-838

Özet

Northern Turkey forms a part of the Rhodope-Pontide Fragment, one of Turkey's main tectono-stratigraphic units. Cretaceous geology of this region is characterized by the presence of a series of horsts, grabens and tilted and rotated fault blocks buried beneath the Upper Cretaceous to Lower Tertiary volcanic material-bearing turbiditic sediments. These structures and sedimentary and igneous rocks represent the most complete record of the opening of the oceanic Black Sea back-arc basin which began forming in the Aptian-Albian behind a continental extensional margin magmatic arc. This was followed by a fault-controlled syn-rift sedimentation and subsidence until the late Cenomanain when sea-floor spreading in the basin and thermally-induced subsidence of the basin margins started.

Northern Turkey forms a part of the Rhodope-Pontide Fragment, one of Turkey's main tectono-stratigraphic units. Cretaceous geology of this region is characterized by the presence of a series of horsts. grabens and tilted and rotated fault blocks buried beneath the Upper Cretaceous to Lower Tertiary volcanic material-bearing turbiditic sediments These structures and sedimentary and igneous rocks represent the most complete record of the opening of the oceanic Black Sea back-arc basin which began forming in the Aptian-Albian behind a continental extensional margin magmatic arc. This was followed by a fault-controlled syn-rift sedimentation and subsidence until the late Cenomanain when sea-floor spreading in the basin and thermally-induced subsidence of the basin margins started. Rift-drift transition in the formation of the Black Sea was marked by a drastic change in sedimentation from the deposition of dark-coloured and organic-rich shales with limestone interbeds to the accumulation of red pelagic carbonates and marls. Facies analyses of these sediments reveal that the Black Sea was restricted during its advanced rift stage from free interchange with the Neo-Tethys to the south and received a large amount of organic debris. Immediately after the onset of spreading in the late Cenomanian, the euxinic conditions disap¬ peared and the water column above the southern margin of this juvenile ocean became well stirred as a gentle basinward tilting of this margin took place. This tilting caused a wide transgression accross the margin which eliminated most of the terrigenous sediment sources, thus providing a suitable location for the deposition of the red pelagic carbonates. Such syn-breakup sequences in migratory island arcs may be important guides to establishing the onset of sea-floor spreading in back-arc basins, whose magnetic record is commonly poor and basin floor basements are hidden under thick sedimentary blankets