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Abstract
Chapter from:
AAPG Memoir 68:Regional and Petroleum Geology of the Black Sea and
Surrounding Region, Edited by A.G. Robinson
AAPG Memoir 68: Regional and Petroleum Geology of the Black Sea and
Surrounding Region. Chapter 15: Geology of the Eastern Pontides, by
Aral I. Okay and Omer Sahinturk,
Pages 291-311
Copyright © 1997 by The American Association of Petroleum Geologists. All rights
reserved.
Chapter 15
Geology of the Eastern Pontides
Aral I. Okay
Istanbul Technical University (I.T.U)
Istanbul, Turkey Omer Sahinturk
Turkish Petroleum Company
Ankara, Turkey
ABSTRACT
The
500-km-long Eastern Pontide belt shows several common stratigraphic 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
andesites to dacites. The
End page 291 ----------------
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.
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