Geology of the eastern pontides


Okay A. , Cahinturk O.

AAPG Memoir, no.68, pp.291-311, 1997 (Refereed Journals of Other Institutions) identifier

  • Publication Type: Article / Article
  • Volume: Issue: 68
  • Publication Date: 1997
  • Title of Journal : AAPG Memoir
  • Page Numbers: pp.291-311

Abstract

The 500-km-long Eastern Pontide belt shows several common stratigraphie features resulting from a common Mesozoic-Tertiary tectonic history. There is a heterogeneous pre-Jurassic basement comprised of Devonian? high-grade metamorphic rocks, Lower Carboniferous granodiorites and dacites, Upper Carboniferous-Lower Permian shallow-marine to terrigeneous sedimentary rocks and an allochthonous Permo-Triassic metabasite-phyllite-marble unit. The Mesozoic sedimentary sequence starts with a widespread Liassic marine transgression coming from the south. The Lower and Middle Jurassic rocks of the Eastern Pontides make up a 2000-m-thick sequence of tuff, pyroclastic rock, lava, and interbedded clastic sedimentary rock; the volcanism is probably related to rifting leading to the opening of the Neotethyan Ocean in the south. The Upper Jurassic-Lower Cretaceous is characterized by carbonates, showing a transition from platform carbonate deposition in the north to pelagic carbonates and calciturbidites in the south; this indicates the development of a south-facing passive continental margin. During the Cenomanian, there was uplift and erosion throughout the Eastern Pontides. Rocks of this stage are not present, and in many localities the Senonian deposits lie unconformably over Jurassic carbonates and even over the Carboniferous granitic basement. This compressive event is associated with the northward emplacement of an ophiolitic melange over the passive continental margin of the Eastern Pontides. The obduction of the ophiolitic melange is probably caused by the partial subduction of the Eastern Pontides continental margin in a south-dipping intra-oceanic subduction zone. This was followed by the flip of the subduction polarity during the Cenomanian-Turonian, which led to the development of a Senonian volcanic arc in the outer Eastern Pontides above the northward-subducting Tethyan Ocean floor. The volcanic arc is represented by >2-km-thick succession of volcanic and volcaniclastic rocks and interbedded limestones and marls. There are also intrusive granodiorite plutons with isotopic ages of 95 to 65 m.y. The volcanism shows a general silica enrichment, with time, ranging from basalts and andésites to dacites. The Senonian sequence in the inner Eastern Pontides is made up of a tuffaceous flyschoid series representing the fore-arc succession. The Eastern Black Sea Basin probably opened during the Maastrichtian through the rifting of the volcanic arc axis. During the late Paleocene-early Eocene, there was north-vergent thrust imbrication of the inner Eastern Pontides with the development of a major foreland flysch basin in front of the northward moving thrust sheets. Folding and uplift occurred in the outer Eastern Pontides during this period. This compressive deformational event, the strongest Mesozoic-Tertiary orogenic phase in the Eastern Pontides, was probably caused by the collision between the Pontide arc and the Tauride microplate in the south. Widespread calc-alkaline volcanism and shallow-marine sedimentation occurred throughout the Eastern Pontides during the middle Eocene. The middle Eocene rocks are essentially undeformed and lie unconformably over a folded and thrust-faulted basement. This major middle Eocene extensional event is probably related to an accelarated phase of opening of the Eastern Black Sea Basin. From the end of the middle Eocene onward, the Eastern Pontides stayed largely above sea level, with minor volcanism and terrigeneous sedimentation.