Gebze region is composed of Paleozoic, Permo-Triassic, Late Cretaceous-Eocene, Oligocene-Early Miocene, Pliocene and Quaternary aged sedimentary rocks and plutonic rocks, dikes and volcanic rocks intruded in the region at Permian, Permo-Triassic and Late Cretaceous periods, and contact metamorphic rock groups observed along narrow zones associated with intrusions. The basement of the Paleozoic sedimentary sequence of İstanbul is observed in the Armutlu Peninsula, Bolu massif and in Safranbolu. The sequence is composed of the clastic and carbonate sedimentation in the Ordovician-Lower Carboniferous time interval. Istanbul Paleozoic units, which reflect different environmental conditions from terrestrial to deep sea and where a sedimentation over a thickness of 5000 meters are observed, outcrop between Kurna and Denizliköy in the North of Gebze. The second sedimentation period on the Istanbul-Kocaeli peninsula is the Permo-Triassic time interval, which starts with basal conglomerates unconformably overlying the Paleozoic sedimentation and continuing different facies up to the shelf environment. The units belonging to the Permo-Triassic sequence, offering widespread outcrops from the east of Gebze, are observed in limited areas along the Şile-Sarıyer thrust fault boundary in Istanbul.
The third deposition period in the study area is the Cretaceous-Eocene sedimentation, which transgressively overlies the Paleozoic and Permo-Triassic units, present widespread outcrops in Dilovası, which is located in the east of the area, and in the areas north of the Şile-Sarıyer thrust fault zone.
Poorly sorted Oligo-Miocene sedimentation, which is including granite blocks reaching a diameter of 1-2 meters and coarse pebbly sandy and muddy levels, is observed in the area. Oligo-Miocene sedimentation unconformably overlies all the units in the region and fills the depression areas between the Kadıllı and Denizliköy.
In the İstanbul-Kocaeli succession, in addition to the syn-sedimentary tectonic effects at the upper levels of the Ordovician aged Kurtköy formation, different tectonic regimes and orientations have been observed at different times after the Carboniferous period.
In the study area, the semi-brittle and thin skin crustal deformation product Permian dike intrusions, the simple shear regime product, NNE and ENE oriented oblique reverse faults, chevron, kink and folded folds, as well as semi-brittle deformation product en echelon sigmoidal veins and the S-C fabrics and boudins in Devonian carbonates, and the changes caused by the friction heat along the slickensides are noteworthy.
This tectonic regime, which forms superimposed structures, has caused irregular contacts especially in the Paleozoic stratigraphy and caused a complex structure which makes it difficult to find a measurable stratigraphic section for the formations.
Anahtar Kelimeler: Northern Gebze, Deformation structures, Stratigraphy
|
